CN105790622B

CN105790622B - Control method of five-level active neutral point clamped H-bridge inverter

Info

Publication number: CN105790622B
Application number: CN201610225059.XA
Authority: CN
Inventors: 葛琼璇; 张波; 杨博; 周志达; 崔冬冬; 于洋; 王晓新
Original assignee: Institute of Electrical Engineering of CAS
Current assignee: Institute of Electrical Engineering of CAS
Priority date: 2016-04-12
Filing date: 2016-04-12
Publication date: 2020-02-18
Anticipated expiration: 2036-04-12
Also published as: CN105790622A

Abstract

A control method of a five-level active neutral point clamped H-bridge inverter comprises the steps of firstly defining the output level and the output state of the five-level active neutral point clamped H-bridge inverter, analyzing the loss distribution condition of a switching tube, and determining the level switching mode and the proportion of reasonably using the level switching mode. The invention determines four level switching modes, and achieves the purpose of balanced distribution of the loss of each device of the five-level active neutral point clamping H-bridge inverter by adjusting the action time of the four level switching modes. The invention is suitable for a high-voltage high-power five-level active neutral point clamped H-bridge voltage source inverter.

Description

Control method of five-level active neutral point clamped H-bridge inverter

Technical Field

The invention relates to a control method of a five-level active neutral point clamped H-bridge inverter.

Background

The multi-level inverter gets more and more attention in the field of high-voltage high-power frequency conversion. Compared with a two-level inverter, the multi-level inverter has the advantages of lower output harmonic content, higher voltage output and the like.

Three-level Neutral Point Clamped (NPC) inverters have been widely used in medium-voltage driving markets with output voltages lower than 6kV, and due to the limitation of voltage withstanding of power electronic devices, frequency converters with five or more levels are required for higher voltage levels and larger-capacity output requirements. The pure five-level NPC inverter has the defect that the midpoint voltage is difficult to control, and is rarely adopted in practice. The NPC type H bridge (NPC/H) five-level inverter has the advantages of a three-level NPC type inverter and an H bridge inverter, has the advantages of simple composition, flexible control, reliable operation and low harmonic content, and has practical application in the field of medium-high voltage driving.

Compared with a three-level NPC inverter, the five-level NPC/H inverter has more output levels and switching states and certain loss balancing capability, but still has the problem of unbalanced loss of bridge arm switching devices, and the loss borne by part of the devices is large, so that the maximum output capacity of the inverter is limited.

The five-level active neutral point clamped H-bridge inverter adopts a brand new topological structure, and no existing literature about a loss balance control method of the topology is reported. The loss balance control method of the Five-Level NPC/H Inverter can be referred to, and a document of 'ANovel Five-Level Voltage Source Inverter With local Pulse width modules for Medium-Voltage Applications' is taken as a representative, the loss of devices of a bridge arm can be reduced to a certain extent by the control method, but because selectable redundant switch states are few, the loss of some switch devices is still large, the loss of some switch devices is small, the utilization rate of semiconductor switch devices is low, and the control method is not beneficial to the heat dissipation design of a system. The five-level active midpoint H-bridge inverter (ANPC/H) can enable the loss distribution of bridge arm switching devices to be more balanced by adding a switching tube at a clamping diode and by adopting a proper loss balance control strategy.

Disclosure of Invention

The invention solves the problem of poor loss distribution balance of each switching device of a five-level active neutral point clamped H-bridge inverter controlled by the conventional modulation method, provides a control method for loss balance, and more effectively utilizes the redundant state of the active neutral point clamped inverter. According to the distribution situation of the switching loss, the four level switching modes are provided according to the principle that the switching tubes of the single-phase H bridge generate the maximum switching loss in sequence, the four switching modes are operated according to a certain proportion in a certain period, the loss distribution of the four switching tubes of one bridge arm of the single-phase H bridge can be improved, the average loss of the four switching tubes is approximate, and therefore the output capacity and the power density of the five-level active neutral point clamping H bridge inverter are improved. The invention is suitable for various pulse width modulation methods.

The structure of the five-level active midpoint H-bridge inverter applying the control method of the invention is as follows:

a three-phase five-level active midpoint H-bridge inverter is a device for converting direct current into sinusoidal alternating current and comprises three direct current power supplies, six voltage division capacitors with the same parameters and a, b and c three-phase H-bridges. Each phase H bridge is composed of two bridge arms, each bridge arm is composed of 6 switching tubes, and each switching tube is reversely connected with a diode in parallel.

In the a-phase H bridge, a first switch tube, a second switch tube, a third switch tube and a fourth switch tube are connected in series to form a first bridge arm of the H bridge, the anode of the first switch tube is connected to the anode of a first direct-current power supply, the cathode of the first switch tube is connected to the anode of the second switch tube, the cathode of the second switch tube is connected to the output of a-phase alternating current and the anode of the third switch tube, the cathode of the third switch tube is connected to the anode of the fourth switch tube, the cathode of the fourth switch tube is connected to the cathode of the first direct-current power supply, the anode of the fifth switch tube is connected between the first switch tube and the second switch tube, the cathode of the fifth switch tube is connected to a midpoint potential O and the anode of the sixth switch tube, and the cathode of the sixth switch tube is connected between the third switch tube and the fourth switch tube.

The seventh switching tube, the eighth switching tube, the ninth switching tube and the tenth switching tube are connected in series to form an H-bridge second bridge arm, the anode of the seventh switching tube is connected to the anode of the first direct-current power supply, the cathode of the seventh switching tube is connected to the anode of the eighth switching tube, the cathode of the eighth switching tube is connected to the common output end n of the three-phase alternating current and the anode of the ninth switching tube, the cathode of the ninth switching tube is connected to the anode of the tenth switching tube, and the cathode of the tenth switching tube is connected to the cathode of the first direct-current power supply. The anode of the eleventh switching tube is connected between the seventh switching tube and the eighth switching tube. The cathode of the eleventh switching tube is connected to the midpoint potential O and the anode of the twelfth switching tube, and the cathode of the twelfth switching tube is connected between the ninth switching tube and the tenth switching tube.

In the b-phase H bridge, a thirteenth switching tube, a fourteenth switching tube, a fifteenth switching tube and a sixteenth switching tube are connected in series to form a first bridge arm of the H bridge. The anode of the thirteenth switching tube is connected to the anode of the second direct-current power supply, the cathode of the thirteenth switching tube is connected to the anode of the fourteenth switching tube, the cathode of the fourteenth switching tube is connected to the output of the b-phase alternating current and the anode of the fifteenth switching tube, the cathode of the fifteenth switching tube is connected to the anode of the sixteenth switching tube, the cathode of the sixteenth switching tube is connected to the cathode of the second direct-current power supply, the anode of the seventeenth switching tube is connected between the thirteenth switching tube and the fourteenth switching tube, the cathode of the seventeenth switching tube is connected to the midpoint potential O and the anode of the eighteenth switching tube, and the cathode of the eighteenth switching tube is connected between the fifteenth switching tube and the sixteenth switching tube.

A nineteenth switching tube and a twentieth switching tube, the twenty-first switching tube and the twenty-second switching tube are connected in series to form an H-bridge second bridge arm, the anode of the nineteenth switching tube is connected to the anode of the second direct-current power supply, the cathode of the nineteenth switching tube is connected to the anode of the twentieth switching tube, the cathode of the twentieth switching tube is connected to the common output end n of three-phase alternating current and the anode of the twenty-first switching tube, the cathode of the twenty-first switching tube is connected to the anode of the twenty-second switching tube, the cathode of the twenty-second switching tube is connected to the cathode of the second direct-current power supply, the anode of the twenty-third switching tube is connected between the twenty-first switching tube and the twenty-second switching tube, the cathode of the twenty-fourth switching tube is connected to the midpoint potential O and the anode of the twenty-fourth switching tube, and the cathode of the twenty-fourth switching tube is connected between.

In the c-phase H bridge, a twenty-fifth switching tube and a twenty-sixth switching tube, the twenty-seventh switching tube and the twenty-eighth switching tube are connected in series to form a first bridge arm of the H bridge, the anode of the twenty-fifth switching tube is connected to the anode of the third direct-current power supply, the cathode of the twenty-fifth switching tube is connected to the anode of the twenty-sixth switching tube, the cathode of the twenty-sixth switching tube is connected to the output of c-phase alternating current and the anode of the twenty-seventh switching tube, the cathode of the twenty-seventh switching tube is connected to the anode of the twenty-eighth switching tube, the cathode of the twenty-eighth switching tube is connected to the cathode of the third direct-current power supply, the anode of the twenty-ninth switching tube is connected between the twenty-fifth switching tube and the twenty-sixth switching tube, the cathode of the twenty-ninth switching tube is connected to the midpoint potential O and the anode of the thirtieth switching tube, and the cathode of the thirty switching tube is connected between the twenty-seventh switching tube and the.

A thirty-first switching tube, a thirty-second switching tube, the thirty-fifth switching tube and the thirty-fourth switching tube are connected in series to form an H-bridge second bridge arm, the anode of the thirty-eleventh switching tube is connected to the anode of the third direct-current power supply, the cathode of the thirty-eleventh switching tube is connected to the anode of the thirty-twelfth switching tube, the cathode of the thirty-twelfth switching tube is connected to the common output end n of three-phase alternating current and the anode of the thirty-third switching tube, the cathode of the thirty-fourth switching tube is connected to the anode of the thirty-fourth switching tube, the cathode of the thirty-fourth switching tube is connected to the cathode of the third direct-current power supply, the anode of the thirty-fifth switching tube is connected between the thirty-eleventh switching tube and the thirty-fourth switching tube, the cathode of the thirty-fifth switching tube is connected to the midpoint potential O and the anode of the thirty-sixth switching tube, and the cathode of the thirty-sixth switching tube is connected between the third switching tube.

The loss control method of the five-level active neutral point clamped H bridge inverter comprises the following steps:

1. defining output state of five-level active neutral point clamped H-bridge inverter

The five-level active neutral point clamped H-bridge inverter single-phase output voltage has five levels, namely direct current bus voltages Vdc, Vdc/2, 0, -Vdc/2 and-Vdc, and the states are defined as '2', '1', '0', '1', '2', respectively. Each output level comprises a plurality of redundant states, and the output states of the five-level active neutral point clamped H bridge inverter are respectively defined as follows:

(1) defining the state of the output voltage of a single bridge arm

And (4) taking the phase a as an example to explain the definition method of the output voltage state of a single bridge arm, and the phase b and the phase c have the same principle.

In the first bridge arm of the phase a, a fifth switching tube and a sixth switching tube are used for active clamping of voltage, and a first voltage division capacitor and a second voltage division capacitor respectively provide direct current voltage of Vdc/2 and-Vdc/2 for the inverter to form a three-level midpoint clamping bridge arm. At this time, the a-phase output terminal outputs three levels of Vdc/2, 0, and-Vdc/2 with respect to the level reference point O. The same applies to phase b and phase c. There are four ways of generating the zero level. The switching states of the switching tubes and the corresponding bridge arm output levels are described as follows:

the first switch tube, the second switch tube and the sixth switch tube are turned off, the third switch tube, the fourth switch tube and the fifth switch tube are turned off, the voltage Vao of the output end of the a-phase first bridge arm is Vdc/2, and the output level state of the bridge arm is defined to be 1.

And when the third switch tube, the fourth switch tube and the fifth switch tube are switched on, the output end voltage Vao of the a-phase first bridge arm is-Vdc/2, and the output level state of the bridge arm is defined to be '-1'.

When the second switching tube and the fifth switching tube are switched on and the first switching tube, the third switching tube, the fourth switching tube and the sixth switching tube are switched off, the output end voltage Vao of the a-phase first bridge arm is 0, and the output level state of the bridge arm is defined as 0U 2;

when the second switching tube, the fourth switching tube and the fifth switching tube are turned on and the first switching tube, the third switching tube and the sixth switching tube are turned off, the output end voltage Vao of the a-phase first bridge arm is 0, and the output level state of the bridge arm is defined as 0U 1;

when the first switching tube, the third switching tube and the sixth switching tube are turned on and the second switching tube, the fourth switching tube and the fifth switching tube are turned off, the output end voltage Vao of the a-phase first bridge arm is 0, and the output level state of the bridge arm is defined as 0L 1;

when the third switching tube and the sixth switching tube are turned on and the first switching tube, the second switching tube, the fourth switching tube and the fifth switching tube are turned off, the output end voltage Vao of the a-phase first bridge arm is 0, and the output level state of the bridge arm is defined as 0L 2;

the output state and the switch combination of the output voltage of the first bridge arm are shown in table 1, wherein "1" indicates that the switching tube is on, and "0" indicates that the switching tube is off:

TABLE 1 output State of the first leg output Voltage Vao and operating conditions of the switching tube

Similarly, in the second bridge arm of the phase a, the end n of the alternating current output can output three levels of Vdc/2, 0 and-Vdc/2 relative to the level reference point O. The generation of each level is similar to the first leg, and table 2 gives the output state and the switch combination of the output voltage of the second leg:

TABLE 2 output State of the second bridge arm output Voltage Vno and operating conditions of the switching tube

(2) Defining output states of single-phase H-bridge output voltage

The method for defining the output state of the single-phase H-bridge output voltage is described below by taking the phase a as an example, and the phases b and c have the same principle.

The a-phase H-bridge output voltage Van is a difference between the first bridge arm output voltage Vao and the second bridge arm output voltage Vno, that is, Van is Vao-Vno.

(a) When the output level is Vdc or-Vdc, the output voltage Van has no redundant output mode, and the output states at this time are defined as "2" and "-2", respectively.

(b) When the output voltage Van is Vdc/2, the single-phase H-bridge has four redundant output modes, which are respectively defined as follows:

define output state "1 _ 1": the first switching tube, the second switching tube and the sixth switching tube of the first bridge arm are switched on, the third switching tube, the fourth switching tube and the fifth switching tube are switched off, the output level of the first bridge arm is Vdc/2, and the output state is 1; the eighth switching tube and the eleventh switching tube of the second arm are turned on, the seventh switching tube, the ninth switching tube and the twelfth switching tube are turned off, the output level of the second arm is 0, when the tenth switching tube is turned on, the output state of the second arm is 0U1, and when the tenth switching tube is turned off, the output state of the second arm is 0U 2.

Define output state "1 _ 2": the first switching tube, the second switching tube and the sixth switching tube of the first bridge arm are switched on, the third switching tube, the fourth switching tube and the fifth switching tube are switched off, the output level of the first bridge arm is Vdc/2, and the output state is 1; the ninth switching tube and the twelfth switching tube of the second arm are turned on, the eighth switching tube, the tenth switching tube and the eleventh switching tube are turned off, the output level of the second arm is 0, when the seventh switching tube is turned on, the output state of the second arm is 0L1, and when the seventh switching tube is turned off, the output state of the second arm is 0L 2.

Define output state "1 _ 3": the second switching tube and the fifth switching tube of the first bridge arm are connected, the first switching tube, the third switching tube and the sixth switching tube are disconnected, the output level of the first bridge arm is 0, when the fourth switching tube is connected, the output state of the first bridge arm is 0U1, and when the fourth switching tube is disconnected, the output state of the first bridge arm is 0U 2; and the ninth switching tube, the tenth switching tube and the eleventh switching tube of the second bridge arm are switched on, the seventh switching tube, the eighth switching tube and the twelfth switching tube are switched off, the output level of the second bridge arm is-Vdc/2, and the output state is '-1'.

Define output state "1 _ 4": the third switching tube and the sixth switching tube of the first bridge arm are connected, the second switching tube, the fourth switching tube and the fifth switching tube are disconnected, the output level of the first bridge arm is 0, when the first switching tube is connected, the output state of the first bridge arm is 0L1, and when the first switching tube is disconnected, the output state of the first bridge arm is 0L 2; and the ninth switching tube, the tenth switching tube and the eleventh switching tube of the second bridge arm are switched on, the seventh switching tube, the eighth switching tube and the twelfth switching tube are switched off, the output level of the second bridge arm is-Vdc/2, and the output state is '-1'.

(c) When the output voltage Van is 0, the a-phase H-bridge output has six redundant output modes, which are defined as follows:

define output state "0 _ 1": the second switching tube and the fifth switching tube of the first bridge arm are connected, the first switching tube, the third switching tube and the sixth switching tube are disconnected, the output level of the first bridge arm is 0, when the fourth switching tube is connected, the output state of the first bridge arm is 0U1, and when the fourth switching tube is disconnected, the output state of the first bridge arm is 0U 2; the eighth switching tube and the eleventh switching tube of the second arm are turned on, the seventh switching tube, the ninth switching tube and the twelfth switching tube are turned off, the output level of the second arm is 0, when the tenth switching tube is turned on, the output state of the second arm is 0U1, and when the tenth switching tube is turned off, the output state of the second arm is 0U 2.

Define output state "0 _ 2": the third switching tube and the sixth switching tube of the first bridge arm are connected, the second switching tube, the fourth switching tube and the fifth switching tube are disconnected, the output level of the first bridge arm is 0, when the first switching tube is connected, the output state of the first bridge arm is 0L1, and when the first switching tube is disconnected, the output state of the first bridge arm is 0L 2; the ninth switching tube and the twelfth switching tube of the second arm are turned on, the eighth switching tube, the tenth switching tube and the eleventh switching tube are turned off, the output level of the second arm is 0, when the seventh switching tube is turned on, the output state of the second arm is 0L1, and when the seventh switching tube is turned off, the output state of the second arm is 0L 2.

Define output state "0 _ 3": the second switching tube and the fifth switching tube of the first bridge arm are connected, the first switching tube, the third switching tube and the sixth switching tube are disconnected, the output level of the first bridge arm is 0, when the fourth switching tube is connected, the output state of the first bridge arm is 0U1, and when the fourth switching tube is disconnected, the output state of the first bridge arm is 0U 2; the ninth switching tube and the twelfth switching tube of the second arm are turned on, the eighth switching tube, the tenth switching tube and the eleventh switching tube are turned off, the output level of the second arm is 0, when the seventh switching tube is turned on, the output state of the second arm is 0L1, and when the seventh switching tube is turned off, the output state of the second arm is 0L 2.

Define output state "0 _ 4": the third switching tube and the sixth switching tube of the first bridge arm are connected, the second switching tube, the fourth switching tube and the fifth switching tube are disconnected, the output level of the first bridge arm is 0, when the first switching tube is connected, the output state of the first bridge arm is 0L1, and when the first switching tube is disconnected, the output state of the first bridge arm is 0L 2; the eighth switching tube and the eleventh switching tube of the second arm are turned on, the seventh switching tube, the ninth switching tube and the twelfth switching tube are turned off, the output level of the second arm is 0, when the tenth switching tube is turned on, the output state of the second arm is 0U1, and when the tenth switching tube is turned off, the output state of the second arm is 0U 2.

Define output state "0 _ 5": the first switching tube, the second switching tube and the sixth switching tube of the first bridge arm are switched on, the third switching tube, the fourth switching tube and the fifth switching tube are switched off, the output level of the first bridge arm is Vdc/2, and the output state is 1; and the seventh switch tube, the eighth switch tube and the twelfth switch tube of the second bridge arm are switched on, the ninth switch tube, the tenth switch tube and the eleventh switch tube are switched off, the output level of the second bridge arm is Vdc/2, and the output state is 1.

Define output state "0 _ 6": the third switching tube, the fourth switching tube and the fifth switching tube of the first bridge arm are conducted, the first switching tube, the second switching tube and the sixth switching tube are turned off, the output level of the first bridge arm is-Vdc/2, and the output state is "-1"; and the ninth switching tube, the tenth switching tube and the eleventh switching tube of the second bridge arm are switched on, the seventh switching tube, the eighth switching tube and the twelfth switching tube are switched off, the output level of the second bridge arm is-Vdc/2, and the output state is '-1'.

(d) When the output voltage Van is-Vdc/2, the a-phase H-bridge output has four redundant output modes, which are respectively defined as follows:

define output state "-1 _ 1": the third switching tube, the fourth switching tube and the fifth switching tube of the first bridge arm are conducted, the first switching tube, the second switching tube and the sixth switching tube are turned off, the output level of the first bridge arm is-Vdc/2, and the output state is "-1"; the ninth switching tube and the twelfth switching tube of the second arm are turned on, the eighth switching tube, the tenth switching tube and the eleventh switching tube are turned off, the output level of the second arm is 0, when the seventh switching tube is turned on, the output state of the second arm is 0L1, and when the seventh switching tube is turned off, the output state of the second arm is 0L 2.

Define output state "-1 _ 2": the third switching tube, the fourth switching tube and the fifth switching tube of the first bridge arm are conducted, the first switching tube, the second switching tube and the sixth switching tube are turned off, the output level of the first bridge arm is-Vdc/2, and the output state is "-1"; the eighth switching tube and the eleventh switching tube of the second arm are turned on, the seventh switching tube, the ninth switching tube and the twelfth switching tube are turned off, the output level of the second arm is 0, when the tenth switching tube is turned on, the output state of the second arm is 0U1, and when the tenth switching tube is turned off, the output state of the second arm is 0U 2.

Define output state "-1 _ 3": the third switching tube and the sixth switching tube of the first bridge arm are connected, the second switching tube, the fourth switching tube and the fifth switching tube are disconnected, the output level of the first bridge arm is 0, when the first switching tube is connected, the output state of the first bridge arm is 0L1, and when the first switching tube is disconnected, the output state of the first bridge arm is 0L 2; and the seventh switch tube, the eighth switch tube and the twelfth switch tube of the second bridge arm are switched on, the ninth switch tube, the tenth switch tube and the eleventh switch tube are switched off, the output level of the second bridge arm is Vdc/2, and the output state is 1.

Define output state "-1 _ 4": the second switching tube and the fifth switching tube of the first bridge arm are connected, the first switching tube, the third switching tube and the sixth switching tube are disconnected, the output level of the first bridge arm is 0, when the fourth switching tube is connected, the output state of the first bridge arm is 0U1, and when the fourth switching tube is disconnected, the output state of the first bridge arm is 0U 2; and the seventh switch tube, the eighth switch tube and the twelfth switch tube of the second bridge arm are switched on, the ninth switch tube, the tenth switch tube and the eleventh switch tube are switched off, the output level of the second bridge arm is Vdc/2, and the output state is 1.

Table 3 shows the output levels and output states of the first arm and the second arm corresponding to the output states of the output voltage Van of the a-phase H-bridge:

table 3 a working states of phase H bridge output voltage Van, first bridge arm output voltage Vao and second bridge arm output voltage Vno

(3) Specifying level switching principles

Since the five-level active midpoint H-bridge inverter topology has redundant level states, and thus has multiple options for output level switching, the following principle must be satisfied for the driving signals of the multilevel inverter:

(a) in order to ensure lower voltage change rate, the level switching can be carried out only step by step;

(b) in order to meet the limit of the switch dead zone of the switching device and improve the safety and reliability of the inverter, only one semiconductor device is required to be switched on and off during level switching, and the simultaneous switching on or switching off of a plurality of switching devices is avoided as much as possible.

Based on the level switching principle, the zero level state options in table 3, such as "0U 1 or 0U 2", have only one specific state satisfying the requirement, such as "0U 1", and thus two zero level states are summarized in one switch state.

2. Analyzing switching losses of individual switching devices under individual switching modes

Four level switching situations exist in the single-phase H bridge of the five-level active midpoint H bridge inverter, namely

For the switching combination of different output states, the switching tubes generating the switching loss are different, and for different switching directions, the switching tubes generating the switching loss are also different; according to the level switching principle, screening out applied level switching modes, analyzing the commutation process of each switching mode, and obtaining that only one switching tube and one diode generate switching loss in the commutation process of each level switching and have a symmetrical relation. The switching loss generated by the switching tube and the diode under different switching conditions will be described separately below.

(1) When the level switches between Vdc and Vdc/2, according to the level switching principle, there is a

Four level switching modes.

Switching modeWhen the output state 2 is switched to the state 1_1, the ninth switching tube is firstly turned off, after a dead time, the eighth switching tube is turned on, if the direction of the output current is from a to n, the ninth switching tube and the eighth switching tube generate switching loss, and if the direction of the output current is opposite, the ninth switching tube and the eighth switching tube generate switching loss.

Switching modeWhen the output state 2 is switched to the state 1_2, the eleventh switching tube is turned off at first, and no current flows through the eleventh switching tube at this time, so that no turn-off loss is generated when the eleventh switching tube is turned off at this time, then the tenth switching tube is turned off, and after a dead time, the twelfth switching tube is turned on.

Switching mode

When the output state 2 is switched to the state 1_3, the first switching tube is turned off firstly, no current flows through the first switching tube at the moment, therefore, no turn-off loss is generated when the first switching tube is turned off at the moment, then the sixth switching tube is turned off, the fifth switching tube is turned on after a dead time, if the direction of the output current is from a to n, the sixth switching tube and the fifth diode generate a switching loss at the moment, and if the direction of the output current is opposite, the sixth diode and the fifth switching tube generate a switching loss.

Switching mode

When the output state 2 is switched to the state 1_4, the second switching tube is turned off firstly, after a dead time, the third switching tube is turned on, if the direction of the output current is from a to n, the second switching tube and the third diode generate switching loss, and if the direction of the output current is opposite, the second diode and the third switching tube generate switching loss.

(2) When the level is switched between Vdc/2 and 0, according to the level switching principle, there are only three zero level states matching each Vdc/2 level state, and there are 12 switching modes in total:

the zero level state matching the level state 1_1 has three zero levels of 0_1, 0_4, and 0_ 5. When 1_1 → 0_1, the sixth switching tube is turned off first, then the first switching tube is turned off, after a dead time, the fifth switching tube is turned on, and the first switching tube and the fifth diode bear the largest switching loss. When 1_1 → 0_4, the second switch tube is turned off first, the first switch tube is still in the on state, after a dead time, the third switch tube is turned on, and the second switch tube and the third diode generate the largest turn-off loss. When 1_1 → 0_5, the eleventh switch tube is turned off first, then the seventh switch tube is turned on, and finally the twelfth switch tube is turned on, and the seventh switch tube and the eleventh diode generate main switching loss.

The zero level state matching the level state 1_2 has three zero levels of 0_2, 0_3, and 0_ 5. When 1_2 → 0_2, the second switch tube is turned off first, the first switch tube is still in the on state, after a dead time, the third switch tube is turned on, and the second switch tube and the third diode generate the largest turn-off loss. When 1_2 → 0_3, the sixth switching tube is turned off first, then the first switching tube is turned off, after a dead time, the fifth switching tube is turned on, and the first switching tube and the fifth diode bear the largest switching loss. When 1_2 → 0_5, the ninth switching tube is turned off first, and then the eighth switching tube is turned on, and the eighth switching tube and the ninth diode generate major switching loss.

The zero level state matching the level state 1_3 has three zero levels of 0_1, 0_3, and 0_ 6. When 1_3 → 0_1, the ninth switch tube is turned off first, the tenth switch tube is still in an on state, after a dead time, the eighth switch tube is turned on, and the ninth switch tube and the eighth diode generate the largest turn-off loss. When 1_3 → 0_3, the eleventh switch tube is turned off first, then the tenth switch tube is turned off, after a dead time, the twelfth switch tube is turned on, and the tenth switch tube and the twelfth diode bear the largest switching loss. When 1_3 → 0_6, the second switch tube is turned off first, and then the third switch tube is turned on, and the second switch tube and the third diode generate main switching loss.

The zero level state matching the level state 1_4 has three zero levels of 0_2, 0_4, and 0_ 6. When 1_4 → 0_2, the eleventh switch tube is turned off first, then the tenth switch tube is turned off, after a dead time, the twelfth switch tube is turned on, and the tenth switch tube and the twelfth diode bear the largest switching loss. When 1_4 → 0_4, the ninth switching tube is turned off first, the tenth switching tube is still in an on state, after a dead time, the eighth switching tube is turned on, and the ninth switching tube and the eighth diode generate the largest turn-off loss. When the voltage is 1_4 → 0_6, the sixth switching tube is turned off first, then the fourth switching tube is turned on, and finally the fifth switching tube is turned on, and the fourth switching tube and the sixth diode generate main switching loss.

(3) When the level is switched between-Vdc/2 and 0, according to the multi-level inverter switching principle, there are only three zero level states matching each-Vdc/2 level state, and there are 12 switching patterns in total:

there are three zero level states that match the level state-1 _1, 0_2, 0_3, and 0_ 6. When the voltage is-1 _1 → 0_2, the fifth switching tube is turned off firstly, then the fourth switching tube is turned off, after a dead time, the sixth switching tube is turned on, and the fourth switching tube and the sixth diode bear the largest switching loss. When the voltage of the third switching tube is higher than the voltage of the second switching tube, the third switching tube is turned off, the fourth switching tube is still in an on state, the second switching tube is turned on after a dead time, and the third switching tube and the second diode generate the largest turn-off loss. When the voltage is-1 _1 → 0_6, the twelfth switching tube is turned off first, then the tenth switching tube is turned on, and finally the eleventh switching tube is turned on, and the tenth switching tube and the twelfth diode generate main switching loss.

There are three zero level states that match the level state-1 _2, 0_1, 0_4, and 0_ 6. When the voltage value is-1 _2 → 0_1, the third switching tube is turned off firstly, the fourth switching tube is still in an on state, after a dead time, the second switching tube is turned on, and the third switching tube and the second diode generate the largest turn-off loss. When the voltage is-1 _2 → 0_4, the fifth switching tube is turned off first, then the fourth switching tube is turned off, after a dead time, the sixth switching tube is turned on, and the fifth switching tube and the sixth diode bear the largest switching loss. When 1_2 → 0_6, the eighth switch tube is turned off first, and then the ninth switch tube is turned on, and the ninth switch tube and the eighth diode generate major switching loss.

There are three zero level states that match the level state-1 _3, 0_2, 0_4, and 0_ 5. When the voltage of the eighth switching tube is-1 _3 → 0_2, the eighth switching tube is turned off first, the seventh switching tube is still in an on state, after a dead time, the ninth switching tube is turned on, and the eighth switching tube and the ninth diode generate the largest turn-off loss. When the voltage is-1 _3 → 0_4, the twelfth switching tube is turned off firstly, then the seventh switching tube is turned off, after a dead time, the eleventh switching tube is turned on, and the seventh switching tube and the eleventh diode bear the largest switching loss. When-1 _3 → 0_5, the third switch tube is turned off first, then the second switch tube is turned on, and the third switch tube and the second diode generate main switching loss.

There are three zero level states that match the level state-1 _4, 0_1, 0_3, and 0_ 5. When the voltage is-1 _4 → 0_1, the twelfth switching tube is turned off first, then the seventh switching tube is turned off, after a dead time, the eleventh switching tube is turned on, and the seventh switching tube and the eleventh diode bear the largest switching loss. When the voltage of the eighth switching tube is-1 _4 → 0_3, the eighth switching tube is turned off first, the seventh switching tube is still in an on state, after a dead time, the ninth switching tube is turned on, and the eighth switching tube and the ninth diode generate the largest turn-off loss. When the voltage of the fifth switching tube is-1 _4 → 0_5, the fifth switching tube is turned off first, then the first switching tube is turned on, and finally the sixth switching tube is turned on, and the first switching tube and the fifth diode generate main switching loss.

(4) When the levels are switched to each other at-Vdc and-Vdc/2, there is a switching of the levels according to the level switching principle

And

there are four types of level switching:

switching modeWhen the output state-2 is switched to the state-1 _1, the eighth switching tube is turned off firstly, the ninth switching tube is turned on after a dead time, if the direction of the output current is from a to n, the eighth switching tube and the ninth diode generate switching loss, and if the direction of the output current is opposite, the eighth diode and the ninth switching tube generate switching loss.

Switching mode

When the output state-2 is switched to the state-1 _2, the twelfth switching tube is turned off at first, no current flows through the twelfth switching tube at this time, therefore, no turn-off loss is generated when the twelfth switching tube is turned off at this time, then the seventh switching tube is turned off, the eleventh switching tube is turned on after a dead time, if the output current direction is from a to n, the seventh switching tube and the eleventh diode generate a switching loss, and if the current direction is opposite, the seventh diode and the eleventh switching tube generate a switching loss.

Switching mode

When the output state-2 is switched to the state-1 _3, the fifth switching tube is firstly switched off, and no current flows at the momentAnd the fourth switching tube and the sixth diode generate switching loss at the moment if the direction of the output current is from a to n, and the fourth diode and the sixth switching tube generate switching loss if the direction of the current is opposite.

Switching mode

When the output state-2 is switched to the state-1 _4, the third switching tube is turned off firstly, after a dead time, the second switching tube is turned on, if the direction of the output current is from a to n, the third switching tube and the second diode generate switching loss, and if the direction of the output current is opposite, the third diode and the second switching tube generate switching loss.

The switching tube and the diode generating loss at the time of level switching in each of the devices conforming to the level switching principle are shown in table 4. Where "√" indicates that the device produces switching losses.

TABLE 4 loss distribution during level switching of five-level active midpoint clamping H-bridge inverter

3. Determining four level switching modes

According to the level switching manner described in step 1, when the output level of the a-phase H-bridge is switched among Vdc, Vdc/2, 0, -Vdc/2, and-Vdc, the switching tubes generating the switching loss are different for the switching combination of different output states, and only one switching tube and one diode generate the switching loss if the direction of the output current is determined. The invention takes the switching loss as a main loss source, and screens out four level switching combinations according to the sequence of the maximum loss generated by a first switching tube or a seventh switching tube, a second switching tube or an eighth switching tube, a third switching tube or a ninth switching tube, and a fourth switching tube or a tenth switching tube in turn according to the level switching principle, wherein the four level switching modes are respectively as follows:

level switching method 1:

level switching method 2:

level switching method 3:

level switching method 4:

reasonably selecting operation proportions of four level switching modes, when the level switching modes 1-4 are alternately used according to the proportion of 1:1:1:1 in a unit period with modulation voltage as a unit period, average losses of a first switching tube, a second switching tube, a third switching tube and a fourth switching tube in a first bridge arm can be represented as follows:

P_{ave_tli(i＝1,2,3or4)}＝(P_{tli_type1}+P_{tli_type2}+P_{tli_type3}+P_{tli_type4})/4

wherein, P_{ave_tli}The average loss P, which represents the average loss when the four operating modes of the arm switching tube Ta1i (i ═ 1,2,3, or 4) are used alternately, is shown_{tli_type1}、P_{tli_type2}、P_{tli_type3}、P_{tli_type4}The loss of the arm switch tube Ta1i (i is 1,2,3, or 4) in each of the level switching systems 1 to 4 is shown.

The maximum loss of each switching tube can be independently adjusted by the four selected switching modes, the loss of each switching tube can be further balanced by adjusting the action time of the four switching modes, and the minimum value which can be reached by the average value of the loss of each switching tube is as follows:

P_{min_ave}＝(P_{ave_t11}+P_{ave_t12}+P_{ave_t13}+P_{ave_t14})/4

wherein, P_{min_ave}The average value of the average losses of the arm switching tubes Ta11 to Ta14 is the minimum value.

Introducing a loss distribution adjusting coefficient k, wherein 0< k <1, and enabling four level switching modes to be according to k: (1-k): (1-k): k is used under the action of frequency, so that the average loss of four switching modes generated by a single device can reach the minimum value, and the balanced distribution of the loss of the switching tubes of the bridge arm of the inverter is realized. The average minimum loss of a single switching tube is as follows:

P_{ave_tli}＝[k(P_{t11_type1}+P_{t11_type4})+(1-k)(P_{t11_type2}+P_{t11_type3})]/2

wherein, P_{ave_tli}The average loss of the bridge arm switching tube Ta1i in the level switching mode 1-4 running according to a certain proportion is shown, and the minimum value is P_{ave_tli_min}。

The optimal value of k can be found as:

k＝(2P_{ave_tli_min}-P_{t11_type2}-P_{t11_type3})/(P_{t11_type1}+P_{t11_type4}-P_{t11_type2}-P_{t11_type3})

the four level switching modes are according to k: (1-k): (1-k): and k operates in the action time proportion, so that the loss balance distribution of the switching tubes of the single-phase bridge arm of the inverter can be realized.

Drawings

FIG. 1 is a diagram of a three-phase five-level active neutral point clamped H-bridge inverter topology;

FIG. 2 is a schematic diagram of a five-level single-phase carrier stacking method;

FIG. 3 is the operation of each tube of the first arm of phase a in the case of level switching mode 1;

fig. 4 shows the operation of each tube of the a-phase first arm in the case of the level switching mode 2;

fig. 5 shows the operation of each tube of the a-phase first arm in the case of the level switching mode 3;

fig. 6 shows the operation of each tube of the a-phase first arm in the case of the level switching mode 4;

fig. 7 is a loss distribution diagram of the a-phase first arm in the case of the level switching mode 1;

fig. 8 is a loss distribution diagram of the a-phase first arm in the case of the level switching mode 2;

fig. 9 is a loss distribution diagram of the a-phase first arm in the case of the level switching mode 3;

fig. 10 is a loss distribution diagram of the a-phase first arm in the case of the level switching scheme 4;

FIG. 11 is a graph of loss distribution of the a-phase first leg when used in four switching modes in a 1:1:1:1 rotation;

fig. 12 is a graph of the loss profile of the a-phase first leg when the four switching schemes are used in 2:1:1:2 turns.

Detailed Description

The invention is further described with reference to the following figures and detailed description.

As shown in fig. 1, the three-phase five-level active midpoint H-bridge inverter applying the control method of the present invention includes three dc power supplies Vdc1, Vdc2, Vdc3, six voltage-dividing capacitors with the same parameters, and a, b, c three-phase H-bridge. In practical application, the three dc power supplies Vdc1, Vdc2 and Vdc3 are generally equal. Each phase H bridge is composed of 2 bridge arms, each bridge arm is composed of 6 switching tubes, each switching tube is reversely connected with a diode in parallel, the corresponding relation between the switching tubes and the diodes is that the switching tubes Taji are reversely connected with the diodes Daji in parallel, j is 1 or 2, i is 1,2,3, 4, 5 or 6.

For a phase-a H bridge, a first switching tube Ta11, a second switching tube Ta12, a third switching tube Ta13 and a fourth switching tube Ta14 are connected in series to form a first bridge arm of the H bridge, the anode of the first switching tube Ta11 is connected to the positive electrode of a direct-current power supply Vdc1, the cathode of the first switching tube Ta11 is connected to the anode of Ta12, the cathode of the second switching tube Ta12 is connected to the output of phase-a alternating current and the anode of the third switching tube Ta13, the cathode of the second switching tube Ta12 is connected to the anode of the fourth switching tube Ta14, the cathode of the fourth switching tube Ta14 is connected to the negative electrode of the direct-current power supply Vdc1, the anode of the fifth switching tube Ta15 is connected between the first switching tube Ta11 and the second switching tube Ta12, the cathode of the fifth switching tube Ta15 is connected to a potential midpoint O and the anode of the sixth switching tube Ta16, and the cathode of the sixth switching tube Ta 5 is connected between the fourth switching tube 5857324 and the fourth switching tube Ta 13. A seventh switching tube Ta21, an eighth switching tube Ta22, a ninth switching tube Ta23 and a tenth switching tube Ta24 are connected in series to form a second bridge arm of the H bridge, the anode of the seventh switching tube Ta21 is connected to the positive electrode of the Vdc1, the cathode of the seventh switching tube Ta21 is connected to the anode of the eighth switching tube Ta22, the cathode of the eighth switching tube Ta22 is connected to the common output terminal n of the three-phase alternating current and the anode of the ninth switching tube Ta23, the cathode of the ninth switching tube Ta23 is connected to the anode of the tenth switching tube Ta24, the cathode of the tenth switching tube Ta24 is connected to the negative electrode of the dc power supply, the anode of the eleventh switching tube Ta25 is connected between the seventh switching tube 737ta 6 and the eighth switching tube Ta22, the cathode of the eleventh switching tube Ta25 is connected to the midpoint potential O and the anode of the twelfth switching tube 26, and the cathode of the twelfth switching tube Ta26 is connected between the ninth switching tube 24.

For a b-phase H bridge, a thirteenth switching tube Tb11, a fourteenth switching tube Tb12, a fifteenth switching tube Tb13 and a sixteenth switching tube Tb14 are connected in series to form a first bridge arm of the H bridge, the anode of the thirteenth switching tube Tb11 is connected to the anode of a direct current power supply Vdc2, the cathode of a thirteenth switching tube Tb11 is connected to the anode of a fourteenth switching tube Tb12, the cathode of the fourteenth switching tube Tb12 is connected to the output of b-phase alternating current and the anode of a fifteenth switching tube Tb13, the cathode of a fifteenth switching tube Tb13 is connected to the anode of a sixteenth switching tube Tb14, the cathode of a sixteenth switching tube Tb14 is connected to the cathode of a direct current power supply Vdc2, connected between the thirteenth switching tube Tb11 and the fourteenth switching tube Tb12 is the anode of the seventeenth switching tube Tb15, the cathode of the seventeenth switching tube Tb15 is connected to the midpoint potential O and the anode of the eighteenth switching tube Tb16, and the cathode of the eighteenth switching tube Tb16 is connected between the fifteenth switching tube Tb13 and the sixteenth switching tube Tb 14. A nineteenth switching tube Tb21, a twentieth switching tube Tb22, a twenty-first switching tube Tb23 and a twenty-second switching tube Tb24 are connected in series to form a second bridge arm of the H bridge, the anode of the nineteenth switching tube Tb21 is connected to the positive electrode of a direct current power supply Vdc2, the cathode of the nineteenth switching tube Tb21 is connected to the anode of the twentieth switching tube Tb22, the cathode of the twentieth switching tube Tb22 is connected to the common output terminal n of three-phase alternating current and the anode of the twenty-first switching tube Tb23, the cathode of the twenty-first switching tube Tb23 is connected to the anode of the twenty-second switching tube Tb24, and the cathode of the twenty-second switching tube Tb24 is connected to the negative electrode of the direct current power supply Vdc, connected between the nineteenth switching tube Tb21 and the twentieth switching tube Tb22 is the anode of the twentieth switching tube Tb25, the cathode of which is connected to the midpoint potential O and the anode of the twenty-fourth switching tube Tb26, and the cathode of the twenty-fourth switching tube Tb26 is connected between the twenty-first switching tube Tb23 and the twenty-second switching tube Tb 24.

For a c-phase H bridge, a twenty-fifth switching tube Tc11, a twenty-sixth switching tube Tc12, a twenty-seventh switching tube Tc13 and a twenty-eighth switching tube Tc14 are connected in series to form a first bridge arm of the H bridge, the anode of the twenty-fifth switching tube Tc11 is connected to the anode of a direct-current power supply Vdc3, the cathode of the twenty-fifth switching tube Tc11 is connected to the anode of the twenty-sixth switching tube Tc12, the cathode of the twenty-sixth switching tube Tc12 is connected to the output of c-phase alternating current and the anode of the twenty-seventh switching tube Tc13, the cathode of the twenty-seventh switching tube Tc13 is connected to the anode of the twenty-eighth switching tube Tc14, and the cathode of the twenty-eighth switching tube Tc14 is connected to the cathode of the, connected between the twenty-fifth switching tube Tc11 and the twenty-sixth switching tube Tc12 is an anode of a twenty-ninth switching tube Tc15, a cathode of the twenty-ninth switching tube Tc15 is connected to the midpoint potential O and an anode of the thirty-fourth switching tube Tc16, and a cathode of the thirty-third switching tube Tc16 is connected between the twenty-seventh switching tube Tc13 and the twenty-eighth switching tube Tc 14. A thirty-first switching tube Tc21, a thirty-second switching tube Tc22, a thirty-third switching tube Tc23 and a thirty-fourth switching tube Tc24 are connected in series to form a second bridge arm of the H bridge, the anode of the thirty-first switching tube Tc21 is connected to the positive electrode of a direct current power supply Vdc3, the cathode of the thirty-first switching tube Tc21 is connected to the anode of the thirty-second switching tube Tc22, the cathode of the thirty-second switching tube Tc22 is connected to the common output end n of three-phase alternating current and the anode of the thirty-third switching tube Tc23, the cathode of the thirty-third switching tube Tc23 is connected to the anode of the thirty-fourth switching tube Tc 7, and the cathode of the thirty-fourth switching tube Tc24 is connected to the, connected between the thirty-first switching tube Tc21 and the thirty-second switching tube Tc22 is an anode of a thirty-fifth switching tube Tc25, a cathode of the thirty-fifth switching tube Tc25 is connected to the midpoint potential O and an anode of the thirty-sixth switching tube Tc26, and a cathode of the thirty-sixth switching tube Tc26 is connected between the thirty-fourth switching tube Tc23 and the thirty-fourth switching tube Tc 24.

The invention discloses a five-level active midpoint H-bridge inverter loss balance control method, which comprises the following steps of: the method comprises the steps of defining the output state of a five-level active neutral point clamping H-bridge inverter, analyzing the switching loss of each switching device in each switching mode, determining four level switching modes and reasonably selecting the operation proportion of the four level switching modes.

Each step is described in detail below:

The control method is suitable for any five-level pulse width modulation. In order to simplify the calculation, a five-level carrier stacking modulation method is adopted, and fig. 2 is a schematic diagram of a five-level single-phase carrier stacking method. Wherein four triangular waves tr 1-tr 4 with the same phase and the amplitude of 0.5 are superposed between-1 and 1, and a modulation wave u_refIs a sine wave. When modulating wave u_refWhen the voltage is larger than the triangular carrier tr1, the inverter bridge arm outputs Vdc; when u is_refWhen the voltage is greater than tr2 and less than tr1, the inverter bridge arm outputs Vdc/2; when u is_refWhen the voltage is greater than tr3 and less than tr2, the bridge arm of the inverter outputs 0 level; when u is_refWhen the output is less than tr3 and greater than tr4, the output of the bridge arm of the inverter is-Vdc/2, and when u is greater than tr4_refAnd when the output voltage is less than tr4, the inverter bridge arm outputs-Vdc.

Since each of the above output levels can be implemented by different switching tubes being turned on and off, there is a state redundancy, thus further defining the output state. The switching state and the level output state of the switching tube of the phase-a H bridge are defined as follows, and the phase-b and the phase-c have the same reason:

(1) the output voltage Van is Vdc

In the first bridge arm, when the first switching tube Ta11, the second switching tube Ta12 and the sixth switching tube Ta16 are turned on, and the third switching tube Ta13, the fourth switching tube Ta14 and the fifth switching tube Ta15 are turned off; in the second bridge arm, when a ninth switching tube Ta23, a tenth switching tube Ta24 and an eleventh switching tube Ta25 are turned on, and a seventh switching tube Ta21, an eighth switching tube Ta22 and a twelfth switching tube Ta26 are turned off; the output level of the a-phase H-bridge is Vdc, and the output state is defined as 2.

(2) The output voltage Van is Vdc/2

In the first bridge arm, when the first switching tube Ta11, the second switching tube Ta12 and the sixth switching tube Ta16 are turned on, and the third switching tube Ta13, the fourth switching tube Ta14 and the fifth switching tube Ta15 are turned off; in the second bridge arm, when the eighth switching tube Ta22 and the eleventh switching tube Ta25 are turned on, the seventh switching tube Ta21, the ninth switching tube Ta23 and the twelfth switching tube Ta26 are turned off, and the tenth switching tube Ta24 is turned on or turned off, the output level of the a-phase H-bridge is Vdc/2, and the output state is defined as "1 _ 1".

In the first bridge arm, when the first switching tube Ta11, the second switching tube Ta12 and the sixth switching tube Ta16 are turned on, and the third switching tube Ta13, the fourth switching tube Ta14 and the fifth switching tube Ta15 are turned off; in the second bridge arm, when a ninth switching tube Ta23 and a twelfth switching tube Ta26 are turned on, an eighth switching tube Ta22, a tenth switching tube Ta24 and an eleventh switching tube Ta25 are turned off, and a seventh switching tube Ta21 is turned on or turned off, the output level of the a-phase H bridge is Vdc/2, and the output state is defined as '1 _ 2'.

In the first bridge arm, when the second switching tube Ta12 and the fifth switching tube Ta15 are turned on, the first switching tube Ta11, the third switching tube Ta13 and the sixth switching tube Ta16 are turned off, and the fourth switching tube Ta14 is turned on or turned off; in the second bridge arm, when the ninth switching tube Ta23, the tenth switching tube Ta24 and the eleventh switching tube Ta25 are turned on, and the seventh switching tube Ta21, the eighth switching tube Ta22 and the twelfth switching tube Ta26 are turned off, the output level of the a-phase H-bridge is Vdc/2, and the output state is defined as "1 _ 3".

In the first bridge arm, when the third switching tube Ta13 and the sixth switching tube Ta16 are turned on, the second switching tube Ta12, the fourth switching tube Ta14 and the fifth switching tube Ta15 are turned off, and the first switching tube Ta11 is turned on or turned off, in the second bridge arm, when the ninth switching tube Ta23, the tenth switching tube Ta24 and the eleventh switching tube Ta25 are turned on, and the seventh switching tube Ta21, the eighth switching tube Ta22 and the twelfth switching tube Ta26 are turned off, the output level of the a-phase H bridge is Vdc/2, and the output state is defined as "1 _ 4".

(3) An output voltage Van of 0

In the first bridge arm, when the second switching tube Ta12 and the fifth switching tube Ta15 are turned on, the first switching tube Ta11, the third switching tube Ta13 and the sixth switching tube Ta16 are turned off, and the fourth switching tube Ta14 is turned on or turned off, in the second bridge arm, when the eighth switching tube Ta22 and the eleventh switching tube Ta25 are turned on, the seventh switching tube Ta21, the ninth switching tube Ta23 and the twelfth switching tube Ta26 are turned off, and the tenth switching tube Ta24 is turned on or turned off, the output level of the a-phase H bridge is 0, and the output state is defined as "0 _ 1".

In the first bridge arm, when the third switching tube Ta13 and the sixth switching tube Ta16 are turned on, the second switching tube Ta12, the fourth switching tube Ta14 and the fifth switching tube Ta15 are turned off, and the first switching tube Ta11 is turned on or turned off; in the second bridge arm, when a ninth switching tube Ta23 and a twelfth switching tube Ta26 are turned on, an eighth switching tube Ta22, a tenth switching tube Ta24 and an eleventh switching tube Ta25 are turned off, and a seventh switching tube Ta21 is turned on or turned off; the output level of the a-phase H-bridge is 0, and the output state is defined as 0_ 2.

In the first bridge arm, when the second switching tube Ta12 and the fifth switching tube Ta15 are turned on, the first switching tube Ta11, the third switching tube Ta13 and the sixth switching tube Ta16 are turned off, and the fourth switching tube Ta14 is turned on or turned off; in the second bridge arm, when a ninth switching tube Ta23 and a twelfth switching tube Ta26 are turned on, an eighth switching tube Ta22, a tenth switching tube Ta24 and an eleventh switching tube Ta25 are turned off, and a seventh switching tube Ta21 is turned on or turned off; the output level of the a-phase H-bridge is 0, and the output state is defined as 0_ 3.

In the first bridge arm, when the third switching tube Ta13 and the sixth switching tube Ta16 are turned on, the second switching tube Ta12, the fourth switching tube Ta14 and the fifth switching tube Ta15 are turned off, and the first switching tube Ta11 is turned on or turned off; in the second bridge arm, when a ninth switching tube Ta23 and a twelfth switching tube Ta26 are turned on, an eighth switching tube Ta22, a tenth switching tube Ta24 and an eleventh switching tube Ta25 are turned off, and a seventh switching tube Ta21 is turned on or turned off; the output level of the a-phase H-bridge is 0, and the output state is defined as 0-4.

In the first bridge arm, when the first switching tube Ta11, the second switching tube Ta12 and the sixth switching tube Ta16 are turned on, and the third switching tube Ta13, the fourth switching tube Ta14 and the fifth switching tube Ta15 are turned off; in the second bridge arm, when the seventh switching tube Ta21, the eighth switching tube Ta22 and the twelfth switching tube Ta26 are turned on, and the ninth switching tube Ta23, the tenth switching tube Ta24 and the eleventh switching tube Ta25 are turned off, the output level of the a-phase H-bridge is 0, and the output state is defined as "0 _ 5".

In the first bridge arm, when the third switching tube Ta13, the fourth switching tube Ta14 and the fifth switching tube Ta15 are turned on, and the first switching tube Ta11, the second switching tube Ta12 and the sixth switching tube Ta16 are turned off; in the second arm, when the ninth switching tube Ta23, the tenth switching tube Ta24 and the eleventh switching tube Ta25 are turned on, and the seventh switching tube Ta21, the eighth switching tube Ta22 and the twelfth switching tube Ta26 are turned off, the output level of the a-phase H-bridge is 0, and the output state is defined as "0 _ 6".

(4) The output voltage Van is-Vdc/2

In the first bridge arm, when the third switching tube Ta13, the fourth switching tube Ta14 and the fifth switching tube Ta15 are turned on, and the first switching tube Ta11, the second switching tube Ta12 and the sixth switching tube Ta16 are turned off; in the second bridge arm, when a ninth switching tube Ta23 and a twelfth switching tube Ta26 are switched on, an eighth switching tube Ta22, a tenth switching tube Ta24 and an eleventh switching tube Ta25 are switched off, and a seventh switching tube Ta21 is switched on or switched off, the output level of the a-phase H bridge is-Vdc/2, and the output state is defined as "-1 _ 1".

In the first bridge arm, when the third switching tube Ta13, the fourth switching tube Ta14 and the fifth switching tube Ta15 are turned on, and the first switching tube Ta11, the second switching tube Ta12 and the sixth switching tube Ta16 are turned off; in the second bridge arm, when a ninth switching tube Ta23 and a twelfth switching tube Ta26 are switched on, an eighth switching tube Ta22, a tenth switching tube Ta24 and an eleventh switching tube Ta25 are switched off, and a seventh switching tube Ta21 is switched on or switched off, the output level of the a-phase H bridge is-Vdc/2, and the output state is defined as "-1 _ 2".

In the first bridge arm, when the third switching tube Ta13 and the sixth switching tube Ta16 are turned on, the second switching tube Ta12, the fourth switching tube Ta14 and the fifth switching tube Ta15 are turned off, and the first switching tube Ta11 is turned on or turned off; in the second bridge arm, when a seventh switching tube Ta21, an eighth switching tube Ta22 and a twelfth switching tube Ta26 are turned on, and a ninth switching tube Ta23, a tenth switching tube Ta24 and an eleventh switching tube Ta25 are turned off, the output level of the a-phase H bridge is-Vdc/2, and the output state is defined as "-1 _ 3".

In the first bridge arm, when the second switching tube Ta12 and the fifth switching tube Ta15 are turned on, the first switching tube Ta11, the third switching tube Ta13 and the sixth switching tube Ta16 are turned off, and the fourth switching tube Ta14 is turned on or turned off; in the second bridge arm, when a seventh switching tube Ta21, an eighth switching tube Ta22 and a twelfth switching tube Ta26 are turned on, and a ninth switching tube Ta23, a tenth switching tube Ta24 and an eleventh switching tube Ta25 are turned off, the output level of the a-phase H bridge is-Vdc/2, and the output state is defined as "-1 _ 4".

(5) The output voltage Van is-Vdc

In the first bridge arm, when the third switching tube Ta13, the fourth switching tube Ta14 and the fifth switching tube Ta15 are turned on, and the first switching tube Ta11, the second switching tube Ta12 and the sixth switching tube Ta16 are turned off; in the second bridge arm, when the seventh switch tube Ta21, the eighth switch tube Ta22 and the twelfth switch tube Ta26 are turned on, and the ninth switch tube Ta23, the tenth switch tube Ta24 and the eleventh switch tube Ta25 are turned off, the output level of the a-phase H-bridge is-Vdc, and the output state is defined as "-2".

Four level switching situations exist in a single-phase H bridge of a five-level active midpoint H bridge inverter, namely

For the switching combination of different output states, the switching tubes generating the switching loss are different, and for different switching directions, the switching tubes generating the switching loss are also different; according to the level switching principle, screening out applied level switching modes, analyzing the commutation process of each switching mode, and obtaining that only one switching tube and one diode generate switching loss in the commutation process of each level switching and have a symmetrical relation. The following describes the switching loss of the switch tube and the diode under different switching conditions。

And

four level switching modes.

Switching mode

When the output state 2 is switched to the state 1_1, the ninth switching tube Ta23 is firstly turned off, after a dead time, the eighth switching tube Ta22 is turned on, if the output current direction is from a to n, the ninth switching tube Ta23 and the eighth diode Da22 generate a switching loss, and if the current direction is opposite, the ninth diode Da23 and the eighth switching tube Ta22 generate a switching loss.

Switching mode

When the output state 2 is switched to the state 1_2, the eleventh switching tube Ta25 is firstly turned off, no current flows through the eleventh switching tube Ta25 at this time, so that no turn-off loss is generated when the eleventh switching tube Ta25 is turned off, then the tenth switching tube Ta24 is turned off, the twelfth switching tube Ta26 is turned on after a dead time, if the output current direction is from a to n, the tenth switching tube Ta24 and the twelfth diode Da26 generate switching loss, and if the current direction is opposite, the twelfth diode Ta24 and the twelfth switching tube Ta26 generate switching loss.

Switching mode

When the output state 2 is switched to the state 1_3, the first switch tube Ta11 is turned off first, and no current flows through the first switch tube Ta11, so that the first switch tube Ta11 is turned off at this timeAnd a turn-off loss is generated, then the sixth switching tube Ta16 is turned off, after a dead time, the fifth switching tube Ta15 is turned on, if the direction of output current is from a to n, the sixth switching tube Ta16 and the fifth diode Da15 generate a switching loss, and if the direction of current is opposite, the sixth diode Da16 and the fifth switching tube Ta15 generate a switching loss.

Switching mode

When the output state 2 is switched to the state 1_4, the second switching tube Ta12 is firstly turned off, after a dead time, the third switching tube Ta13 is turned on, if the output current direction is from a to n, the second switching tube Ta12 and the third diode Da13 generate switching loss, and if the current direction is opposite, the second diode Da12 and the third switching tube Ta13 generate switching loss.

the zero level state matching the level state 1_1 has three zero levels of 0_1, 0_4, and 0_ 5. When 1_1 → 0_1, the sixth switching tube Ta16 is turned off first, then the first switching tube Ta11 is turned off, after a dead time, the fifth switching tube Ta15 is turned on, and the first switching tube Ta11 and the fifth diode Da15 suffer the largest switching loss. When 1_1 → 0_4, the second switching tube Ta12 is turned off first, the first switching tube Ta11 is still in an on state, and after a dead time, the third switching tube Ta13 is turned on, and the second switching tube Ta12 and the third diode Da13 generate the largest turn-off loss. When 1_1 → 0_5, the eleventh switching tube Ta25 is turned off first, then the seventh switching tube Ta21 is turned on, and finally the twelfth switching tube Ta26 is turned on, and the seventh switching tube Ta21 and the eleventh diode Da25 generate major switching loss.

The zero level state matching the level state 1_2 has three zero levels of 0_2, 0_3, and 0_ 5. When 1_2 → 0_2, the second switching tube Ta12 is turned off first, the first switching tube Ta11 is still in an on state, and after a dead time, the third switching tube Ta13 is turned on, and the second switching tube Ta12 and the third diode Da13 generate the largest turn-off loss. When 1_2 → 0_3, the sixth switching tube Ta16 is turned off first, then the first switching tube Ta11 is turned off, after a dead time, the fifth switching tube Ta15 is turned on, and the first switching tube Ta11 and the fifth diode Da15 suffer the largest switching loss. When 1_2 → 0_5, the ninth switching tube Ta23 is turned off first, and then the eighth switching tube Ta22 is turned on, and the eighth switching tube Ta22 and the ninth diode Da23 generate major switching loss.

The zero level state matching the level state 1_3 has three zero levels of 0_1, 0_3, and 0_ 6. When 1_3 → 0_1, the ninth switching tube Ta23 is turned off first, the tenth switching tube Ta24 is still in an on state, and after a dead time, the eighth switching tube Ta22 is turned on, and the ninth switching tube Ta23 and the eighth diode Da22 generate the largest turn-off loss. When 1_3 → 0_3, the eleventh switching tube Ta25 is turned off first, then the tenth switching tube Ta24 is turned off, after a dead time, the twelfth switching tube Ta26 is turned on, and the tenth switching tube Ta24 and the twelfth diode Da26 suffer the largest switching loss. When 1_3 → 0_6, the second switching tube Ta12 is turned off first, and then the third switching tube Ta13 is turned on, the second switching tube Ta12 and the third diode Da13 generate major switching loss.

The zero level state matching the level state 1_4 has three zero levels of 0_2, 0_4, and 0_ 6. When 1_4 → 0_2, the eleventh switching tube Ta25 is turned off first, then the tenth switching tube Ta24 is turned off, after a dead time, the twelfth switching tube Ta26 is turned on, and the tenth switching tube Ta24 and the twelfth diode Da26 suffer the largest switching loss. When 1_4 → 0_4, the ninth switching tube Ta23 is turned off first, the tenth switching tube Ta24 is still in the on state, and after a dead time, the eighth switching tube Ta22 is turned on, and the ninth switching tube Ta23 and the eighth diode Da22 generate the largest turn-off loss. When 1_4 → 0_6, the sixth switching tube Ta16 is turned off first, the fourth switching tube Ta14 is turned on, the fifth switching tube Ta15 is turned on finally, and the fourth switching tube Ta14 and the sixth diode Da16 generate major switching loss.

there are three zero level states that match the level state-1 _1, 0_2, 0_3, and 0_ 6. When the voltage value is-1 _1 → 0_2, the fifth switching tube Ta15 is turned off first, then the fourth switching tube Ta14 is turned off, after a dead time, the sixth switching tube Ta16 is turned on, and the fourth switching tube Ta14 and the sixth diode Da16 suffer the largest switching loss. When-1 _1 → 0_3, the third switching tube Ta13 is turned off first, the fourth switching tube Ta14 is still in an on state, and after a dead time, the second switching tube Ta12 is turned on, and the third switching tube Ta13 and the second diode Da12 generate the largest turn-off loss. When-1 _1 → 0_6, the twelfth switching tube Ta26 is turned off first, then the tenth switching tube Ta24 is turned on, and finally the eleventh switching tube Ta25 is turned on, and the tenth switching tube Ta24 and the twelfth diode Da26 generate major switching loss.

There are three zero level states that match the level state-1 _2, 0_1, 0_4, and 0_ 6. When-1 _2 → 0_1, the third switching tube Ta13 is turned off first, the fourth switching tube Ta14 is still in an on state, and after a dead time, the second switching tube Ta12 is turned on, and the third switching tube Ta13 and the second diode Da12 generate the largest turn-off loss. When the voltage value is-1 _2 → 0_4, the fifth switching tube Ta15 is turned off first, then the fourth switching tube Ta14 is turned off, after a dead time, the sixth switching tube Ta16 is turned on, and the fifth switching tube Ta15 and the sixth diode Da16 suffer the largest switching loss. When 1_2 → 0_6, the eighth switching tube Ta22 is turned off first, and then the ninth switching tube Ta23 is turned on, and the ninth switching tube Ta23 and the eighth diode Da22 generate major switching loss.

There are three zero level states that match the level state-1 _3, 0_2, 0_4, and 0_ 5. When-1 _3 → 0_2, the eighth switching tube Ta22 is turned off first, the seventh switching tube Ta21 is still in an on state, and after a dead time, the ninth switching tube Ta23 is turned on, and the eighth switching tube Ta22 and the ninth diode Da23 generate the largest turn-off loss. When-1 _3 → 0_4, the twelfth switching tube Ta26 is turned off first, then the seventh switching tube Ta21 is turned off, after a dead time, the eleventh switching tube Ta25 is turned on, and the seventh switching tube Ta21 and the eleventh diode Da25 suffer the largest switching loss. When-1 _3 → 0_5, the third switching tube Ta13 is turned off first, and then the second switching tube Ta12 is turned on, the third switching tube Ta13 and the second diode Da12 generate major switching loss.

There are three zero level states that match the level state-1 _4, 0_1, 0_3, and 0_ 5. When-1 _4 → 0_1, the twelfth switching tube Ta26 is turned off first, then the seventh switching tube Ta21 is turned off, after a dead time, the eleventh switching tube Ta25 is turned on, and the seventh switching tube Ta21 and the eleventh diode Da25 suffer the largest switching loss. When-1 _4 → 0_3, the eighth switching tube Ta22 is turned off first, the seventh switching tube Ta21 is still in an on state, and after a dead time, the ninth switching tube Ta23 is turned on, and the eighth switching tube Ta22 and the ninth diode Da23 generate the largest turn-off loss. When-1 _4 → 0_5, the fifth switching tube Ta15 is turned off first, then the first switching tube Ta11 is turned on, and finally the sixth switching tube Ta16 is turned on, and the first switching tube Ta11 and the fifth diode Da15 generate major switching loss.

Andthere are four types of level switching:

switching mode

When the output state-2 is switched to the state-1 _1, the eighth switching tube Ta22 is firstly turned off, after a dead time, the ninth switching tube Ta23 is turned on, if the output current direction is from a to n, the eighth switching tube Ta22 and the ninth diode Da23 generate switching loss, and if the current direction is opposite, the eighth diode Da22 and the ninth switching tube Ta23 generate switching loss.

Switching mode

When the output state-2 is switched to the state-1 _2, the twelfth switching tube Ta26 is firstly turned off, no current flows through the twelfth switching tube Ta26, so that no turn-off loss is generated when the twelfth switching tube Ta26 is turned off, then the seventh switching tube Ta21 is turned off, the eleventh switching tube Ta25 is turned on after a dead time, if the output current direction is from a to n, the seventh switching tube Ta21 and the eleventh diode Da25 generate a switching loss, and if the current direction is opposite, the seventh diode Da21 and the eleventh switching tube Ta25 generate a switching loss.

Switching mode

When the output state-2 is switched to the state-1 _3, the fifth switching tube Ta15 is firstly turned off, no current flows through the fifth switching tube Ta15, so that no turn-off loss is generated when the fifth switching tube Ta15 is turned off, then the fourth switching tube Ta14 is turned off, the sixth switching tube Ta16 is turned on after a dead time, if the output current direction is from a to n, the fourth switching tube Ta14 and the sixth diode Da16 generate a switching loss, and if the current direction is opposite, the fourth diode Da14 and the sixth switching tube Ta16 generate a switching loss.

Switching mode

When the output state-2 is switched to the state-1 _4, the third switching tube Ta13 is firstly turned off, after a dead time, the second switching tube Ta12 is turned on, if the output current direction is from a to n, the third switching tube Ta13 and the second diode Da12 generate switching loss, and if the current direction is opposite, the third diode Da13 and the second switching tube Ta12 generate switching loss.

3. Determining four level switching modes

Only one switching tube and one diode generate switching loss in the level switching process, and in order to improve the safe working area and the output capacity of the inverter, the loss value of the switching tube with the largest loss needs to be reduced to the minimum. With the loss of the switching tube as a main loss source, according to the level switching principle, sequentially screening four level switching combinations according to the sequence that the first switching tube Ta11 or the seventh switching tube Ta21, the second switching tube Ta12 or the eighth switching tube Ta22, the third switching tube Ta13 or the ninth switching tube Ta23, the fourth switching tube Ta14 or the tenth switching tube Ta24 generate the maximum loss, wherein the four level switching modes respectively comprise:

level switching method 1:

level switching method 2:

level switching method 3:

level switching method 4:

the first switching tube Ta11 and the seventh switching tube Ta21 generate the largest loss when the level switching mode 1 is applied, the second switching tube Ta12 and the eighth switching tube Ta22 generate the largest loss when the level switching mode 2 is applied, the third switching tube Ta13 and the ninth switching tube Ta23 generate the largest loss when the level switching mode 3 is applied, and the fourth switching tube switching device Ta14 and the tenth switching tube Ta24 generate the largest loss when the level switching mode 4 is applied.

4. Reasonably selecting operation proportion of four level switching modes

The loss of the bridge arm switching tubes with the level switching modes 1-4 is respectively P_{tli_typ00}、P_{tli_type2}、P_{tli_type3}And P_{tli_type4}. When the above four level switching modes are alternately used in a modulation voltage period in a ratio of 1:1:1:1, the average loss of the first switching tube Ta11, the second switching tube Ta12, the third switching tube Ta13 and the fourth switching tube Ta14 of each switching device in the a-phase first bridge arm can be represented as follows:

the maximum loss of each switching tube can be independently adjusted by the four selected switching modes, the loss of each switching tube can be further balanced by adjusting the action time of the four switching modes, and the minimum value of the loss average value of each switching tube is as follows:

P_{min_ave}＝(P_{ave_t11}+P_{ave_t12}+P_{ave_t13}+P_{ave_t14})/4

in a five-level active midpoint clamping H-bridge inverter topology, in an a-phase H-bridge, a first switching tube Ta11 and a fourth switching tube Ta14 have symmetry in structure, and the switching tube loss distribution when the level switching mode 1 and the switching mode 4 act also has symmetry, so that the two switching modes are implemented for the same time in the whole inverter working cycle. Similarly, the second switching tube Ta12 and the third switching tube Ta13 have symmetry in structure, and the switching tube loss distributions when the level switching manner 2 and the switching manner 3 act also have symmetry, so that the two switching manners are implemented for the same time in the whole inverter duty cycle.

Introducing a loss distribution adjusting coefficient k, wherein 0< k <1, and making the ratio of the use frequencies of the level switching modes 1 and 4 to the use frequencies of the level switching modes 2 and 3 be k/(1-k), wherein the average loss of a single switch tube is as follows:

its minimum value is P_{ave_tli_min}And solving k optimal values:

the action time of the four level switching modes is as follows: (1-k): (1-k): the k mode can realize the balanced distribution of the loss of the single-phase bridge arm device of the inverter.

The loss balance control method of the a-phase bridge arm is explained above, and for the loss balance control of the b-phase bridge arm and the c-phase bridge arm, the same loss balance purpose as that of the a-phase bridge arm can be achieved by adopting the same output level state definition, four same level switching modes and the same loss distribution coefficient k.

The following examples are provided to illustrate the effects of the present invention.

The embodiment of the invention builds a simulation model of a five-level active midpoint clamping H bridge inverter, the selected active switching devices are 4500V and 4000A IGCTs, the model is 5SHY35L4510, the model of a diode is 5SDF10H4520, the bus voltage Vdc is 3000V, the effective value of output current Irms is 2kA, the output frequency is 50Hz, the carrier frequency is 1.2kHz, and the output capacity is 12 MVA.

Fig. 7, 8, 9, and 10 show individual arm loss profiles of a single-phase H-bridge in the five-level active midpoint clamp H-bridge inverter in the level switching method 1, the switching method 2, the switching method 3, and the switching method 4, respectively. Fig. 11 shows a power factor of 0.95 when the modulation ratio m is equal to

In the four switching modes, the loss distribution is in alternate use in a ratio of 1:1:1:1, and then the T12 and the T13 generate the same loss 2117W, and then the T11 and the T14 generate the loss 1842W. It can be found that when running alternately at a ratio of 1:1:1:1,the losses of the switching tubes of one bridge arm are still not balanced enough. Fig. 12 shows the distribution of losses when four switching modes are operated alternately at a ratio of 2:1:1:2 under the same modulation ratio and power factor, and when k is 0.65, the losses generated by the switching devices T11, T12, T13 and T14 are the same, 1994W, and simulation analysis shows that the loss is reduced by 21% compared with the maximum 2570W generated by the five-level NPC/H inverter loss balance control. Therefore, the loss balance control strategy of the invention realizes the balance of the loss of each bridge arm switch device and improves the output capacity and power density.

The loss balance control strategy provided by the invention is suitable for all five-level inverter modulation methods such as five-level carrier laminated modulation, carrier phase shift modulation, space vector pulse width modulation and the like.

Claims

1. A control method of a five-level active neutral point clamped H bridge inverter comprises the steps of firstly defining the output state of the five-level active neutral point clamped H bridge inverter, analyzing the loss distribution condition of a bridge arm switching tube of the inverter, determining a level switching mode, and reasonably using the proportion of the level switching mode; the method is characterized in that the method for determining the level switching modes of four five-level active neutral point clamped H-bridge inverters is as follows:

defining Ta11 as a first switch tube, Ta12 as a second switch tube, Ta13 as a third switch tube, Ta14 as a fourth switch tube, Ta15 as a fifth switch tube and Ta16 as a sixth switch tube in the first bridge arm; in the second bridge arm, Ta21 is a seventh switching tube, Ta22 is an eighth switching tube, Ta23 is a ninth switching tube, Ta24 is a tenth switching tube, Ta25 is an eleventh switching tube, and Ta26 is a twelfth switching tube; the loss of the switching tube is a main loss source, four level switching modes are screened out according to the sequence that the first switching tube (Ta11) or the seventh switching tube (Ta21), the second switching tube (Ta12) or the eighth switching tube (Ta22), the third switching tube (Ta13) or the ninth switching tube (Ta23), the fourth switching tube (Ta14) or the tenth switching tube (Ta24) generate the maximum loss in sequence, and the four level switching modes are respectively:

level switching method 1:

level switching method 2:

level switching method 3:

level switching method 4:

wherein 2, 1_1, 1_2, 1_3, 1_4, 0_1, 0_2, 0_6, -1_1, -1_2, -1_3, -1_4 and-2 are respectively the output states of the five-level active midpoint clamping H-bridge inverter; the state 2 corresponds to the switching tubes Ta11, Ta12, Ta16, Ta23, Ta24 and Ta25 being on, and the switching tubes Ta13, Ta14, Ta15, Ta21, Ta22 and Ta26 being off; the state 1_1 corresponds to the switching tubes Ta11, Ta12, Ta16, Ta22 and Ta25 being on, the switching tubes Ta13, Ta14, Ta15, Ta21, Ta23 and Ta26 being off, and the switching tube Ta24 being on or off; the state 1_2 corresponds to the switching tubes Ta11, Ta12, Ta16, Ta23 and Ta26 being on, the switching tubes Ta13, Ta14, Ta15, Ta22, Ta24 and Ta25 being off, and the switching tube Ta21 being on or off; the state 1_3 corresponds to the switching tubes Ta12, Ta15, Ta23, Ta24 and Ta25 being on, the switching tubes Ta11, Ta13, Ta16, Ta21, Ta22 and Ta26 being off, and the switching tube Ta14 being on or off; the state 1_4 corresponds to the switching tubes Ta13, Ta16, Ta23, Ta24 and Ta25 being on, the switching tubes Ta12, Ta14, Ta15, Ta21, Ta22 and Ta26 being off, and the switching tube Ta11 being on or off; the state 0_1 corresponds to the switching tubes Ta12, Ta15, Ta22 and Ta25 being turned on, the switching tubes Ta11, Ta13, Ta16, Ta21, Ta23 and Ta26 being turned off, and the switching tubes Ta14 and Ta24 being turned on or off; the state 0_2 corresponds to the switching tubes Ta13, Ta16, Ta23 and Ta26 being turned on, the switching tubes Ta12, Ta14, Ta15, Ta22, Ta24 and Ta25 being turned off, and the switching tubes Ta11 and Ta21 being turned on or off; the state 0_6 corresponds to the switching tubes Ta13, Ta14, Ta15, Ta23, Ta24 and Ta25 being on, and the switching tubes Ta11, Ta12, Ta16, Ta21, Ta22 and Ta26 being off; the state-1 _1 corresponds to the switching tubes Ta13, Ta14, Ta15, Ta23 and Ta26 being on, the switching tubes Ta11, Ta12, Ta16, Ta22, Ta24 and Ta25 being off, and the switching tube Ta21 being on or off; the state-1 _2 corresponds to the switching tubes Ta13, Ta14, Ta15, Ta23 and Ta26 being on, the switching tubes Ta11, Ta12, Ta16, Ta22, Ta24 and Ta25 being off, and the switching tube Ta21 being on or off; the state-1 _3 corresponds to the switching tubes Ta13, Ta16, Ta21, Ta22 and Ta26 being on, the switching tubes Ta12, Ta14, Ta15, Ta23, Ta24 and Ta25 being off, and the switching tube Ta11 being on or off; the state-1 _4 corresponds to the switching tubes Ta12, Ta15, Ta21, Ta22 and Ta26 being on, the switching tubes Ta11, Ta13, Ta16, Ta23, Ta24 and Ta25 being off, and the switching tube Ta14 being on or off; the state-2 corresponds to the switching tubes Ta13, Ta14, Ta15, Ta21, Ta22 and Ta26 being on, and the switching tubes Ta11, Ta12, Ta16, Ta23, Ta24 and Ta25 being off; when the level switching method 1 is applied, the first switching tube (Ta11) and the seventh switching tube (Ta21) generate the largest loss, when the level switching method 2 is applied, the second switching tube (Ta12) and the eighth switching tube (Ta22) generate the largest loss, when the level switching method 3 is applied, the third switching tube (Ta13) and the ninth switching tube (Ta23) generate the largest loss, and when the level switching method 4 is applied, the fourth switching tube (Ta14) and the tenth switching tube (Ta24) generate the largest loss.

2. The method for controlling the five-level active midpoint clamping H-bridge inverter according to claim 1, wherein the proportion of the level switching modes is reasonably used, and the proportion of the action time of the level switching modes is adjusted, so that the four level switching modes are operated in turn in proportion as follows:

when the level switching method 1, the level switching method 2, the level switching method 3, and the level switching method 4 are alternately used at a ratio of 1:1:1:1 in a modulation voltage unit cycle, the average loss of the first switching tube (Ta11), the second switching tube (Ta12), the third switching tube (Ta13), and the fourth switching tube (Ta14) of the first arm is expressed as:

P_{ave_ta1i}＝(P_{ta1i_type1}+P_{ta1i_type2}+P_{ta1i_type3}+P_{ta1i_type4})/4

wherein, P_{ave_ta1i}The average loss of the arm switching tube Ta1i in four level switching modes is shown, i is the switching tube number, i is 1,2,3 or 4, and P is_{ta1i_type1}、P_{ta1i_type2}、P_{ta1i_type3}、P_{ta1i_type4}Respectively representing the loss of the bridge arm switching tube Ta1i in the level switching modes 1-4;

the maximum loss of each switching tube can be independently adjusted by the four selected switching modes, the loss of each switching tube is further balanced by adjusting the running time proportion of the four switching modes, and the minimum value which can be reached by the loss average value of each switching tube is as follows:

P_{min_ave}＝(P_{ave_ta11}+P_{ave_ta12}+P_{ave_ta13}+P_{ave_ta14})/4

wherein, P_{min_ave}The average value of the average losses of the first bridge arm switching tubes Ta 11-Ta 14 is the minimum value;

introducing a loss distribution adjusting coefficient k, wherein 0< k <1, and enabling four level switching modes to be according to k: (1-k): (1-k): k, when i is 1, the average loss of a single switching tube Ta11 is:

P_{ave_ta1i}＝[k(P_{ta11_type1}+P_{ta11_type4})+(1-k)(P_{ta11_type2}+P_{ta11_type3})]/2

obtaining the average loss of a single switching tube when i is 2,3 or 4 by the same method;

when i is 1,2,3 or 4, P_{ave_ta1i}Minimum value of (A) is P_{ave_ta1i_min}；

Obtaining a k-best value:

k＝(2P_{ave_ta1i_min}-P_{ta11_type2}-P_{ta11_type3})/(P_{ta11_type1}+P_{ta11_type4}-P_{ta11_type2}-P_{ta11_type3})

the action time of the four level switching modes is as follows: (1-k): (1-k): the balanced distribution of the loss of the single-phase bridge arm devices of the inverter is realized in a k mode;

the loss balance control method of the a-phase bridge arm is explained above, and for the loss balance control of the b-phase bridge arm and the c-phase bridge arm, the same output level state definition, four same level switching modes and the same loss distribution adjustment coefficient k are adopted, so that the same loss balance purpose as that of the a-phase bridge arm is achieved.