CN114825963A

CN114825963A - Open-circuit fault diagnosis and fault-tolerant operation method for TAB converter

Info

Publication number: CN114825963A
Application number: CN202210481912.XA
Authority: CN
Inventors: 马建军; 朱淼; 杨伟业; 陈奕嘉; 蔡旭
Original assignee: Shanghai Jiaotong University
Current assignee: Shanghai Jiaotong University
Priority date: 2022-05-05
Filing date: 2022-05-05
Publication date: 2022-07-29

Abstract

The invention provides a method for diagnosing open-circuit fault and fault-tolerant operation of a TAB converter, which relates to the technical field of fault diagnosis and fault tolerance of power electronic converters, and comprises the following steps: step S1: locating an open circuit fault of the TAB converter; step S2: after positioning is completed, direct current bias generated by open circuit faults is eliminated by locking driving signals of fault bridge arms and changing the range of phase shift angles, the problem of overcurrent is solved, and power transmitted among three ports is distributed to realize fault-tolerant operation. The method can quickly and accurately position the open-circuit fault of the three-active-bridge converter switching device, eliminate the influence of the open-circuit fault, reasonably distribute the power flow among the three ports and realize the fault-tolerant operation of the open-circuit fault.

Description

Open-circuit fault diagnosis and fault-tolerant operation method for TAB converter

Technical Field

The invention relates to the technical field of fault diagnosis and fault tolerance of power electronic converters, in particular to an open-circuit fault diagnosis and fault tolerance operation method of a TAB converter.

Background

With the increase of the proportion of new energy and stored energy to be accessed into the power system, the traditional alternating current power system faces huge challenges in the aspect of operation stability performance. The distributed direct current system can conveniently, flexibly and efficiently realize the access of a distributed power supply and a direct current load, and has wide application prospect. In the power system architecture including the distributed dc system shown in fig. 1, there are a large number of dc converters connecting the dc bus to various sources and loads.

The three-active-bridge (TAB) converter is an isolated three-port direct-current converter, has the advantages of high power density, bidirectional energy transfer and the like, and is widely applied to multi-port access scenes of renewable energy power generation, uninterruptible power supplies and electric vehicles.

Due to the nature of the power electronics, the switching elements are the most vulnerable components of the converter. Statistically, about 46% of converter failures are caused by switching elements. There can be a classification into a short-circuit fault and an open-circuit fault. In practical application, the short-circuit fault is usually removed through a protection function integrated inside a power switch tube. The open-circuit fault can cause the current in the converter to generate a direct current component and increase a current peak value, and a fault-tolerant strategy is required to eliminate the influence caused by the fault. The existing research on open-circuit fault detection and fault reconstruction means is limited to a two-port converter. The operation of the TAB converter relates to 3 access ports, the fault ride-through of the converter can be ensured when fault reconstruction is carried out, and the influence on the power transmission process of other two ports is minimum when one port is in fault, so that higher requirements are put forward on the reliable operation of the TAB converter.

In the existing literature [1] a Zhao nan, Xie Wei, Zheng ze Dong, Li Chi, Liu Jian Wei, Huang Xu Dong, a double-active-bridge converter and an open-circuit fault redundancy processing method thereof [ P ]. Sichuan province: CN112600437A,2021-04-02, this document studies an open-circuit fault tolerance strategy of a dual active bridge converter, which blocks all driving signals of a bridge arm where a fault switch is located and limits a maximum duty ratio of a driving pulse when an open-circuit fault occurs in a switching device of a secondary side full bridge, and blocks only the driving signal of the fault switching device itself when an open-circuit fault occurs in a switching device of a primary side full bridge, and limits a current by limiting the maximum duty ratio of the driving pulse. The scheme described in the document cannot solve the problem of generating a direct current component when the primary full-bridge is in an open circuit fault, cannot ensure that the power of a normal port is consistent with that before the fault, and does not provide an accurate positioning scheme of the open circuit fault.

The prior document [2] Mantengfeng, auspicious, Guanyupeng, Hope, Wang schmei, an open-circuit fault analysis and fault-tolerant control strategy of an isolated double-active-bridge DC-DC converter considering parasitic parameters [ J ] power automation equipment 2021,41(08):149-155.

The research on the open-circuit fault diagnosis of the three active bridge converters and the fault-tolerant operation strategy thereof is not found in the existing literature.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a method for diagnosing open-circuit fault and fault-tolerant operation of a TAB converter.

According to the method for diagnosing the open-circuit fault and carrying out fault-tolerant operation on the TAB converter, the scheme is as follows:

step S1: locating an open circuit fault of the TAB converter;

step S2: after positioning is completed, direct current bias generated by open circuit faults is eliminated by locking driving signals of fault bridge arms and changing the range of phase shift angles, the problem of overcurrent is solved, and power transmitted among three ports is distributed to realize fault-tolerant operation.

Preferably, the step S1 includes: analyzing open-circuit fault waveforms of the switch tubes of the TAB, and realizing TAB open-circuit fault location by using midpoint voltages of the bridge arms;

when the upper bridge arm runs normally, when current flows through the upper bridge arm, the midpoint voltage value of the corresponding bridge arm is equal to the direct-current side voltage; when the lower bridge arm flows current, the corresponding midpoint voltage value is 0;

when an open-circuit fault occurs, the midpoint voltage of the bridge arm is newly added with a state equal to 0, and the average value of the midpoint voltage of the corresponding fault bridge arm deviates from a normal value.

Preferably, the step S2 of eliminating the open-circuit fault in the dc offset generated by the open-circuit fault includes: a direct current bus side open circuit fault and an energy storage side open circuit fault;

when an open-circuit fault occurs at the direct-current bus side or the energy storage side, the driving signals of the bridge arm where the fault switching tube is located are locked to form a symmetrical circuit, so that the direct-current component is eliminated;

preferably, after the direct current bus side and the energy storage side open circuit have faults, the maximum inductive current of each port is not larger than the maximum inductive current in normal operation when the fault-tolerant operation is performed. When an open circuit fault occurs at the side of the direct current bus, changing a phase shift angle to ensure that the direct current bus normally absorbs power; when an open-circuit fault occurs on the energy storage side, the phase shift angle is changed to cut off the fault energy storage side, and the other two ports normally transmit power.

Compared with the prior art, the invention has the following beneficial effects:

1. the open-circuit fault of the switching device in the TAB converter is accurately and quickly positioned by detecting the midpoint voltage of each bridge arm;

2. the fault-tolerant operation of the open-circuit fault of the switch device of the TAB converter is realized by locking a bridge arm driving signal where the fault device is located;

3. and in fault-tolerant operation, the reasonable power distribution among the three ports after the open-circuit fault of the TAB converter is realized by changing the range of the phase shift angle.

Drawings

Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:

FIG. 1 is a diagram of a power system architecture including a distributed DC system;

FIG. 2 is a view of a TAB converter topology;

FIG. 3 is a TAB converter equivalent circuit diagram (Y & delta type);

FIG. 4 is a waveform diagram of a TAB normal operation;

FIG. 5 is a current loop diagram for TAB under single phase shift control;

FIG. 6 is S ₂₁ An open circuit fault waveform;

FIG. 7 is S ₂₁ The state of the change of the midpoint voltage of the open-circuit fault bridge arm;

FIG. 8 is S ₁₁ Open circuit fault operation oscillogram;

FIG. 9 is S ₁₁ The state of the change of the midpoint voltage of the open-circuit fault bridge arm;

FIG. 10 is an open circuit fault detection flow diagram;

FIG. 11 is S ₂₁ A circuit topology diagram when an open circuit fault is locked;

FIG. 12 is S ₂₁ Open circuit fault tolerant operating waveforms;

FIG. 13 is S ₁₁ Open circuit fault tolerant operating waveforms;

FIG. 14 is S ₂₁ 、S ₁₁ Detecting an open-circuit fault simulation waveform;

FIG. 15 is S ₂₁ An open-circuit fault-tolerant operation simulation waveform;

FIG. 16 is S ₁₁ Fault-tolerant operation simulation waveform of open circuit fault;

fig. 17 is a graph of three port power change during open fault tolerant operation.

Detailed Description

The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.

The embodiment of the invention provides a method for diagnosing open-circuit fault and fault-tolerant operation of a TAB converter, which is shown in figure 2 and comprises the following steps:

step S1: an open circuit fault of the TAB converter is located.

In step S1: analyzing open-circuit fault waveforms of the switch tubes of the TAB, and realizing TAB open-circuit fault location by using midpoint voltages of the bridge arms; when the upper bridge arm runs normally, when current flows through the upper bridge arm, the midpoint voltage value of the corresponding bridge arm is equal to the direct-current side voltage; when the lower bridge arm flows current, the corresponding midpoint voltage value is 0; when an open-circuit fault occurs, the midpoint voltage of the bridge arm is newly added with a state equal to 0, and the average value of the midpoint voltage of the corresponding fault bridge arm deviates from a normal value.

The elimination of the open-circuit fault in the dc offset generated by the open-circuit fault in step S2 includes: a direct current bus side open circuit fault and an energy storage side open circuit fault; when a direct current bus side open circuit fault occurs, locking driving signals of a bridge arm where a fault switch tube is located to form a symmetrical circuit, so that a direct current component is eliminated; when the open-circuit fault of the port at the energy storage side occurs, the direct current component is eliminated by locking the driving signal of the bridge arm where the fault switching tube is located. On the basis of locking a fault bridge arm driving signal, the phase shift angle range is changed, fault current is limited, when an open-circuit fault occurs on a direct-current bus side, the direct-current bus side can normally absorb power, when the open-circuit fault occurs on an energy storage side, fault energy storage is cut off, and the rest two ports normally transmit power.

Next, the present invention will be described in more detail.

A method for diagnosing open-circuit fault and fault-tolerant running of TAB converter includes such steps as locking the drive signal of faulty bridge arm and changing the range of phase shift angle to eliminate DC bias generated by open-circuit fault, solving overcurrent problem, and reasonably distributing the power transmitted between three ports.

As shown in fig. 2, the TAB converter has one or three ports connected to the energy storage system such as the battery and the super capacitor, and the second port connected to the dc bus side.

The basic operating principle of TAB:

as shown in FIG. 2, TAB is composed of three H-bridges and a high frequency transformer, wherein the three H-bridges are respectively H ₁ 、H ₂ 、H ₃ ，S ₁₁ ～S ₁₄ Is a primary side H ₁ Switch tube of S ₂₁ ～S ₂₄ Is a secondary side H ₂ Switch tube of S ₃₁ ～S ₃₄ Is the third side H ₃ Switch tube of, D ₁₁ ～D ₁₄ 、D ₂₁ ～D ₂₄ 、D ₃₁ ～D ₃₄ Are respectively H ₁ 、H ₂ 、H ₃ And the middle switch tube corresponds to the anti-parallel diode. The high-frequency transformer is a three-winding transformer, and the turn ratio of the three windings is N ₁ :N ₂ :N ₃ . Wherein each winding is connected with one H bridge, and the transformer enables the three H bridges to realize electrical isolation and match the voltage ratio among the three. In the figure V _H1 、V′ _H2 、V′ _H3 Respectively representing the difference of the midpoint voltages of the bridge arms of the three H-bridges, L in FIG. 2 ₁ 、L′ ₂ 、L′ ₃ The sum of the leakage inductance and the auxiliary inductance of the three windings of the transformer is respectively. By means of L ₁ 、L′ ₂ 、L′ ₃ Effecting the transfer of energy, i _L1 、i′ _L2 、i′ _L3 The currents of the three windings are shown with reference to the direction shown in fig. 2.

In the following analysis, f denotes the switching frequency and T denotes the switching period. TAB usually employs single phase shift control, under which S is ₁₁ And S ₁₄ 、S ₁₂ And S ₁₃ 、S ₂₁ And S ₂₄ 、S ₂₂ And S ₂₃ 、S ₃₁ And S ₃₄ 、S ₃₂ And S ₃₃ The driving signals are respectively kept consistent, and the duty ratio is 0.5. d _ij (i, j ≠ 1, 2, 3, i ≠ j) is expressed as the phase shift angle between three H-bridges, d ₁₂ +d ₂₃ ＝d ₁₃ 。S ₁₁ And S ₂₁ The time difference between the drive signals is 0.5d ₁₂ T，S ₁₁ And S ₃₁ The time difference of the driving signals is 0.5d ₁₃ T，S ₂₁ And S ₃₁ The time difference between the drive signals is 0.5d ₂₃ And T. Tong (Chinese character of 'tong')By adjusting the phase shift angle between any two H-bridges, the direction and magnitude of power can be controlled, e.g. when d ₁₂ When the power is greater than 0, the port transmits power to the port two, and when the power is less than 0, the opposite is true. d ₂₃ When the transmission power is larger than 0, the transmission power is transmitted to the two-way port of the port, and when the transmission power is smaller than 0, the operation modes of the TAB converter can be divided into six modes according to the relative magnitude of the phase shift angle, as shown in the following formula (1). The actual power transmission direction in TAB needs to be taken into account ₁₂ ，d ₁₃ ，d ₂₃ 。

Operating state of TAB:

a: TAB normal operating state:

when the TAB converter normally operates, power can be transmitted between the ports in a two-way mode, the mode I is taken as an example here, the inductive current of each port is analyzed in detail, the switch tube and the transformer are assumed to be ideal elements, dead time is ignored, and the voltage difference between the midpoint of the bridge arms of the three ports can be equivalent to three square wave voltages with the duty ratio of 0.5. FIG. 3 shows an equivalent circuit, V, of the TAB converter _H2 、V _H3 Is V' _H2 、V′ _H3 Converted to a value on the primary side, L ₂ 、L ₃ Is L' ₂ 、L′ ₃ Converted to the value on the primary side. Note i _L1 Is a primary side inductor current i _L2 、i _L3 Are secondary side and tertiary side inductor currents i 'respectively' _L2 、i′ _L3 Converted to the value on the primary side. V can be obtained by applying KCL theorem in FIG. 3(a) ₀ The value of (c):

where M is the defined equivalent inductance,

the direction indicated by the arrow in fig. 3(a) is the reference positive direction of the current. The inductance L can be known from the figure ₁ 、L ₂ 、L ₃ The voltage and current expressions (4) and (5) below:

the drive signal and key voltage current waveforms are shown in FIG. 4 during normal operation, m _ij And (i is 1 to 3, and j is 1 to 6) represents the inductance current change rate at the corresponding time of each port. The corresponding current loop in normal operation is shown in fig. 5, and one cycle in normal operation can be divided into 12 states according to the current path, which correspond to N in fig. 4 respectively _a ～N _l . Where the dark part is the actual return path for the current. With i _L1 Specific calculations are performed for the examples:

primary side inductor current i in one cycle _L1 (t) is of the formula (7), wherein V ₁ 、V ₂ 、V ₃ Three square wave voltages V respectively _H1 、V _H2 、V _H3 Amplitude of (FIG. 4 is V) ₁ >V ₂ >V ₃ Waveform under the conditions):

from the symmetry of the inductor current, the average inductor current is 0 in one period, so that i is _L1 (t ₀ )＝-i _L1 (t ₃ )、i _L1 (t ₁ )＝-i _L1 (t ₄ )、i _L1 (t ₂ )＝-i _L1 (t ₅ ) Let t ₀ When t is equal to 0 ₁ ＝d ₁₂ /2f，t ₂ ＝d ₁₃ And/2 f, in combination with the above formula:

the inductance current of the secondary side winding and the inductance current of the tertiary side winding at corresponding time can be obtained by the same calculation method, and the change rate of the inductance current of each port is as the following formula (9).

TABLE 1 i _L1 (t) expression

TABLE 2 i _L2 (t) expression

TABLE 3 i _L3 (t) expression

The expressions of the inductance and current of each port are as shown in table 1, table 2 and table 3. Power calculation by the Delta-type circuit shown in FIG. 3(b), P ₁ 、P ₂ 、P ₃ Referring to the direction as shown in the figure, referring to the power calculation formula of DAB, the transmission powers of three ports of TAB are respectively:

to facilitate the analysis of the comparative power characteristics and current stress, assume electricityThe road is operated in an ideal condition, L ₁ ＝L ₂ ＝L ₃ ＝L，V ₁ ＝V ₂ ＝V ₃ ＝V。

According to the formula (10), when d ₁₂ ＝0.5，d ₁₃ When 0.5, the output power of port one is maximum, when d ₁₂ ＝-0.5，d ₁₃ When the power is-0.5, the absorbed power of the port I is maximum; d ₁₂ ＝-0.5，d ₂₃ When the output power of the port two is maximum, d is 0.5 ₁₂ ＝0.5，d ₂₃ When the power is-0.5, the absorption power of the second port is maximum; d ₁₃ ＝-0.5，d ₂₃ When-0.5, the output power of three ports is maximum, d ₁₃ ＝0.5，d ₂₃ When the power is 0.5, the absorption power of the port three is maximum; the maximum power that each port can reach is as follows:

according to the table 1, the table 2 and the table 3, the inductive current of the TAB converter working in the mode one at each moment of three ports can be calculated, and when d is ₁₂ ＝0.5，d ₂₃ When the peak value of the inductor current at the port one is maximum, the three ports are completely symmetrical, and the phase shift angle range is also symmetrical, so that the maximum peak currents of the inductor currents at the ports of the TAB converter are equal, and the results are as follows:

b: open circuit fault of the side of the direct current bus:

the situation that the internal anti-parallel diode can still work normally when the switching tube has an open circuit fault is assumed, and the state that the anti-parallel diode cannot work normally is not considered.

With secondary side winding S ₂₁ Open circuit faults were analyzed as an example. FIG. 6 is S ₂₁ And the waveform diagram of the drive signal after the circuit is opened and the voltage and the current of the inductor. The shaded part on the left represents the transient process of the fault, and the shaded part on the right represents the state that the fault reaches the stable state, and the voltage waveform can be used forKnowing that the rate of change of current over time is consistent with normal operation, but S ₂₁ After the open-circuit fault reaches steady state, i _L2 (t ₄ ) When the current in the second inductor is equal to 0, the dc bias is generated in the second inductor. Now will S ₂₁ The process of open circuit failure is analyzed in detail as follows:

S ₂₁ at the moment of open circuit fault, N _a ～N _g State is not affected, N _g When the state is finished, the secondary side inductance current is converted from positive to negative, and the current should pass through S ₂₁ Due to S ₂₁ An open circuit fault occurs, at which time D ₂₂ And S ₂₄ Providing a current loop, secondary side voltage V _H2 When the voltage becomes 0, the secondary side inductance voltage decreases in amplitude and the direction becomes negative as shown in the formula (4), and therefore the secondary side inductance current conversion rate becomes smaller than that in normal operation, and the circuit state at this time is recorded as

The state continues until t ₄ Time of day t ₄ ～t ₅ The time period is divided into four circuit states t ₄ At that time, the circuit goes into N _i The state is then entered by the three times of zero crossing of the inductor current, the primary side of zero crossing of the inductor current, and the secondary side of zero crossing of the inductor current

N _k 、

Status. t is t ₅ ～t ₆ In the time period, the secondary side inductance current is converted from positive to negative, and the circuits are respectively recorded as

N _l Status. The inductive current has DC bias and passes through several periods until the secondary side S ₂₂ And S ₂₃ At the moment of rising edge of driving signal, the secondary side current is justIf the voltage drops to zero, the circuit enters a fault steady state, and D is not needed in the circuit ₂₂ A freewheeling circuit is provided. As indicated by the right-hand shaded portion, S ₂₁ The circuit operation sequence when the open circuit fault reaches the steady state operation is

Above with symbol E ₂₁ For the state of the subscript, S is expressed ₂₁ And newly adding a state after the open circuit fault. S ₂₁ The current loop for the bridge arm voltage change during an open circuit fault transient is shown in fig. 7.

C: energy storage side open circuit failure:

with primary winding S ₁₁ Analysis was performed by taking an open circuit as an example, and S is shown in FIG. 8 ₁₁ And the waveform diagram of the drive signal after the circuit is opened and the voltage and the current of the inductor. In the figure, the left shaded part represents the transient process of the fault, the right shaded part represents the state after the fault is stabilized, the voltage waveform shows that the current change rate of each period of time after the fault reaches the steady state is consistent with that in normal operation, but S ₁₁ After open circuit fault, S ₁₂ And S ₁₃ When the primary side inductor current is zero at the rising edge of the driving signal, the inductor current is known to generate a dc bias. Now will S ₁₁ The process of open circuit failure is analyzed in detail as follows:

S ₁₁ at the moment of open circuit fault, N _a ～N _c State is not affected, N _c When the state is over, until t ₃ At this time, the primary-side inductor current is maintained at zero. Now will t ₁ ～t ₃ The process over the time period is analyzed as follows, N _c At the end of the state, the primary side inductor current should be switched from negative to positive, but since S is ₁₁ An open circuit fault has occurred, with only D present ₁₂ And S ₁₄ Providing a forward current loop, assuming current flows through D ₁₂ And S ₁₄ On the primary side V _H1 When the primary-side inductor voltage becomes 0, it is found from the equation (4) that the primary-side inductor current should decrease from positive to negative, and thus the current does not flow through D ₁₂ And S ₁₄ (ii) a Assuming that the current flows in the negative direction D ₁₁ And D ₁₄ On the primary sideV _H1 Becomes V ₁ From the equation (4), it can be seen that if the primary side inductor voltage is greater than zero, the primary side inductor current should be increased from negative to positive, so that the current will not flow through D ₁₁ And D ₁₄ Is maintained at zero, during this time period V _H1 Equal to the voltage on the primary winding of the transformer, the circuit is switched to S and S respectively because the primary side inductive current is reduced to zero, and the secondary side and the tertiary side inductive currents are reversed ₃₁ And S ₃₄ The change of the driving signal enters the state respectively

t ₃ ～t ₄ Within a period of time, is recorded as

And

state, t ₄ ～t ₅ During the time period, the circuit is N _k State, t ₅ ～t ₆ In the time period, the circuit state is kept consistent with that in the normal state. Due to the presence of a DC bias of the inductor current, over several cycles, until S ₁₂ And S ₁₃ At the rising edge of the driving signal, the primary side current just rises to zero, which indicates that the circuit enters a fault steady state. As shown by the shaded portion on the right side of the figure, the circuit operation sequence in steady state is

Above with symbol E ₁₁ For the state of the subscript, S is represented ₁₁ And newly increased state in case of open circuit fault. S ₁₁ The current loop corresponding to the time period when the bridge arm voltage changes during the open-circuit fault transient is shown in fig. 9.

Open fault diagnosis and fault tolerance strategy of TAB:

after an open-circuit fault occurs, in order to reduce the influence of the fault on a circuit as much as possible, the position of the open-circuit fault needs to be accurately positioned, and then the influence caused by the fault is reduced through a fault-tolerant strategy. As can be seen from the foregoing analysis, the occurrence of an open-circuit fault of a switch tube in TAB may cause a dc bias of an inductor current and an increase of the current, and the dc bias of the current may cause a transformer to be saturated, while the increase of the current may cause a risk of over-current burning other devices, so that after the open-circuit fault occurs, it is required to ensure that the fault current is not greater than the maximum inductor current of each port during normal operation, and to eliminate the dc component of the current.

a. Open-circuit fault diagnosis:

the analysis of open-circuit fault waveforms of the switch tubes of the TAB shows that when an open-circuit fault occurs, the midpoint voltage difference and the inductance current of the corresponding bridge arm are obviously changed, and whether the fault occurs can be judged by utilizing the midpoint voltage difference and the inductance current change of the bridge arm, because the number of the TAB switch devices is up to 12, S _i1 And S _i4 ，S _i2 And S _i3 When the open-circuit fault occurs, (i ═ 1, 2, 3), the bridge arm midpoint voltage difference and the inductor current waveform are consistent, so that the open-circuit faults of the switching tubes cannot be distinguished. To solve this problem, a method for accurately positioning the TAB open circuit fault by using the midpoint voltage of each bridge arm is proposed, i.e. V shown in fig. 2 _AG1 、V _BG1 、V _AG2 、V _BG2 、V _AG3 、V _BG3 . As can be seen from the figure, V _AG1 、V _BG1 、V _AG2 、V _BG2 、V _AG3 、V _BG3 The magnitude of the voltage is determined by the states of the switching devices of the upper and lower bridge arms respectively, when the upper bridge arm runs normally and current flows through the upper bridge arm, the midpoint voltage value of the corresponding bridge arm is equal to the direct-current side voltage, and the midpoint voltage value is V ₁ 、V ₂ 、V ₃ . When the lower bridge arm flows current, the corresponding midpoint voltage value is 0, and the relationship between the bridge arm midpoint voltage and the corresponding square wave voltage can be known as follows:

the TAB open circuit fault can be accurately positioned by using the average value of the midpoint voltage of the bridge arm in one period. From the above equation (13), when the bridge is in normal operation, the average value of the midpoint voltage of each bridge arm is as follows:

from S ₂₁ And S ₁₁ In the transient process of the open-circuit fault, the newly added current loop state (fig. 7 and 9) shows that when the open-circuit fault occurs, the midpoint voltage of the bridge arm is newly added to be equal to 0, and the average value of the midpoint voltage of the corresponding fault bridge arm deviates from the normal value. For example, S ₂₁ When open-circuit fault occurs, V _CG2 The average value in one period is obviously reduced, and the midpoint voltage of other bridge arms has little influence, S ₂₂ When open-circuit fault occurs, V _CG2 The average value in one period is obviously increased, and the midpoint voltage of other bridge arms has little influence. S ₂₄ The change of the inductor voltage and inductor current and S when open-circuit fault occurs ₂₁ Is consistent when an open circuit fault occurs, but at this time V _DG2 The average value in one period is obviously increased, and V _CG2 Without significant change, therefore, S can be distinguished ₂₁ And S ₂₄ Open circuit fault of S ₂₃ At fault V _DG2 The voltage of other middle points is not obviously changed, and the positions of open-circuit faults can be positioned by the middle point voltages of corresponding bridge arms on the primary side and the tertiary side by the same principle. The information of the midpoint voltage of the bridge arm when each switching tube is open is summarized as shown in table 4 below. Considering that switching noise, electromagnetic interference, the influence of parasitic parameters and measurement errors of a sensor exist in an actual power electronic system, certain deviation may occur in voltage measurement values when the TAB converter operates normally, and therefore corresponding threshold values alpha, beta and gamma are set to avoid misjudgment of faults. Accordingly, a flowchart of open circuit fault detection positioning can be obtained as shown in fig. 10.

TABLE 4 average value of midpoint voltage of bridge arm in open-circuit fault of each switching device

b. A fault tolerance strategy of an open circuit at the side of a direct current bus:

according to the analysis process, the root cause of the generated direct current component is the asymmetry of the circuit after the open circuit fault, so that the driving signals of the bridge arm where the fault switch tube is positioned are all locked when the open circuit fault occurs, so as to form a symmetrical circuit, and further eliminate the direct current component. When the direct current bus side is opened, the direct current bus side is turned to S ₂₁ An open circuit is taken as an example, and both of the driving signals of the failed bridge arm are locked, and the circuit topology is shown in fig. 11. And the second port is connected with the direct current bus, and the fault-tolerant control target is that the energy storage system transmits energy to the direct current bus. Therefore, it is necessary to change the phase shift angle to d ₁₂ ≥0、d ₂₃ ≤0、d ₁₃ Not less than 0, or d ₁₂ ≥0、d ₂₃ ≤0、d ₁₃ Is less than or equal to 0. To be at d ₁₂ ≥0、d ₂₃ ≤0、d ₁₃ Error-tolerant operation example in the range of not less than 0, S ₂₁ The current waveform at the time of open-circuit fault blocking is shown in FIG. 12, where the left shaded portion is S ₂₁ Open circuit fault transients, which are described in detail above; the shaded portion on the right is S ₂₁ Compared with the normal operation state, the fault-tolerant operation stable state of the open circuit fault has the change of the phase shift angle, and the fault-tolerant operation stable state can be divided into 12 states according to the current loop of the converter, but only the power characteristic and the current characteristic during fault-tolerant operation need to be analyzed, so that the power characteristic and the current characteristic during fault-tolerant operation are only classified according to the voltage difference of the middle points of bridge arms in a graph, and the fault-tolerant operation stable state of the open circuit fault can be divided into 8 operation states, for example, the fault-tolerant operation stable state of the open circuit fault can be divided into 8 operation states in the graph

As shown. In the drawings

The state corresponds to S ₂₃ The driving signal is effective and the secondary side inductive current is positive, and the circuit is S ₂₃ And D ₂₁ Providing a current loop, thus V _H2 And becomes zero, and the voltage of the power supply is changed into zero,

the state corresponds to S ₂₄ The driving signal is effective and the secondary side inductive current is negative, and the circuit is S ₂₄ And D ₂₂ Providing a current loop, r in the figure _ij Indicating the rate of change of the inductor current for each time segment of the ith port. The current value at each time can be calculated by the equation (4), and taking the secondary side inductance current as an example, the relationship between the secondary side inductance currents is as follows:

the inductance current at port two can be obtained from equation (15), the calculation results are shown in appendix a, and the inductance current expressions at each port are equations (a1), (a2), and (A3). Ideally, S ₂₁ When the open-circuit fault-tolerant operation is carried out, the power expression of each port is (A4), the inductance current expression of each port is (A5), and the maximum values of the inductance currents of the three ports are calculated according to (A5) and are respectively as follows:

in practical application, the device model is generally selected according to a normal operation mode, so that the maximum inductive current of each port is not greater than the maximum inductive current in normal operation during fault-tolerant operation. Then there are:

under the fault-tolerant strategy, the phase shift angle range satisfies d is more than or equal to 0 ₁₂ ≤0.5，d ₂₃ ≤0，d ₁₃ Not less than 0 or d ₁₂ ≥0，d ₂₃ ≤0，0≤d ₁₃ Less than or equal to 0.5. It is found by calculation that all satisfy the above formula (17). According to (A4), the relation between the power of each port and the phase shift angle is satisfied with the formula (18) when d ₁₂ ＝0.5，d ₂₃ When the output power is equal to 0, the first port reaches the maximum output power; when d is ₁₂ ＝0.5，d ₂₃ When the power is-0.5, the second port reaches the maximum absorption power; when d is ₁₂ ＝0.5，d ₂₃ When the output power of the port three is-0.5, the maximum transmission power expression of each port is as follows:

according to calculation, S ₂₁ The maximum inductive current of each port during open-circuit fault-tolerant operation is as follows:

c. an energy storage side open circuit fault tolerance strategy:

and after the port at the energy storage side has an open-circuit fault, the direct-current component is eliminated by locking the driving signal of the bridge arm where the fault switching tube is positioned. The fault-tolerant control target is to cut off a fault energy storage side and enable power to be transmitted on the energy storage side and the direct current bus side without faults. By port one S ₁₁ For open-circuit fault, for example, the phase shift angle should be changed to d is greater than or equal to 0 ₁₂ ≤0.5，0≤d ₂₃ ≤0.5，d ₁₃ D is more than or equal to 0 or more than or equal to 0 ₁₂ ≤0.5，-0.5≤d ₂₃ ≤0，d ₁₃ And the range is more than or equal to 0, and the two states of the power transmission from the bus to the normal operation energy storage side and the power transmission from the normal operation energy storage side to the bus are respectively corresponded. Where d is 0. ltoreq. d ₁₂ ≤0.5，0≤d ₂₃ ≤0.5，d ₁₃ For example, S is not less than 0 ₁₁ The waveforms for open-circuit fault-tolerant operation are shown in fig. 13, and the detailed process analysis is as follows:

S ₁₁ in the event of an open circuit fault, the fault transient is shown in the left shaded portion of the figure, which has been described in detail above and is omitted here. And locking the fault bridge arm, and after a period of time, the circuit reaches a steady state as shown by a shaded part at the right side in the figure. With S ₁₄ The rising edge of the driving signal is taken as a steady-state starting point for analysis, and the driving signal can be divided into eight operating states according to the voltage difference of the bridge arms, and the eight operating states are respectively recorded as

An inductive current loop corresponding to the port is S ₁₄ And D ₁₂ Three states of (a). t is t ₃ At that moment, the current drops to zero and is maintained until S ₁₃ Driving the rising edge of the signal during a time period V _H1 Equal to the voltage of the primary winding of the transformer, and the state is recorded as

This state analysis is as follows: t is t ₃ At that time, the primary side inductor current drops to zero, and if the current continues to drop, the current should pass through D ₁₁ And D ₁₄ ，V _H1 Is a V ₁ If the current rises according to equation (4), the current returns to zero, so that the current remains zero during this period.

An inductive current loop corresponding to the port is S ₁₃ And D ₁₁ Three states of (a). t is t ₇ At that moment, the current rises to zero and is maintained until S ₁₄ Driving the rising edge of the signal during a time period V _H1 Equal to the voltage of the primary winding of the transformer, and the state is recorded as

The status analysis process and

similarly, no further details are given. S ₁₁ The expressions of the inductance current of each port in open-circuit fault-tolerant operation are (A6), (A7) and (A8) under the ideal condition of S ₁₁ The open-circuit fault-tolerant operation power expression is (A9), and the inductance current expression of each port is (A10).

Likewise, S is compared in the ideal case ₁₁ Current stress and power characteristics during open-circuit fault blocking operation, wherein the maximum inductive current of the three windings respectively appears at t ₁ ，t ₁ ，t ₂ Time:

according to the calculation, the maximum value of the fault current does not exceed the maximum value of the current in normal operation at the same time, and the expression of the relation between the power of the three ports and the phase shift angle, P, can be obtained by combining the formula (A9) ₁ Is constantly equal to zero, i.e. no power flows at the port, P ₂ 、P ₃ The expression (21) (22) is as follows, power flows only between port two and port three, when d ₁₂ ＝0，d ₂₃ When the power is 0.5, the output power of the second port is maximum, and the absorption power of the third port is maximum:

according to the symmetry of the port, if the adopted fault tolerance strategy is d is more than or equal to 0 ₁₂ ≤0.5，-0.5≤d ₂₃ D is less than or equal to 0 ₁₃ ＝0，d ₂₃ When the power is equal to-0.5, the output power of the port three is maximum, and the absorption power of the port two is maximum:

according to calculation, S ₁₁ The maximum current of each port in open-circuit fault-tolerant operation is as follows:

examples are:

in order to verify the technical scheme provided by the invention, a TAB converter simulation model is established based on MATLAB-Simulink environment. The TAB port dc voltages are seen in table 5.

TABLE 5 TAB Port DC voltages

Designing parameters of TAB:

1. designing parameters of the TAB inductor:

TAB auxiliary inductor L ₁ 、L ₂ 、L ₃ The power transmission index needs to be satisfied, the maximum port transmission power is designed to be 100W, and ideally, the maximum power that the TAB can transmit is known from equation (11):

here, take L ₁ ＝L ₃ ＝240μH，L ₂ ＝160μH。

2. Designing a direct current side capacitor of TAB:

the DC side capacitor mainly has the functions of filtering and reducing the influence of load disturbance on voltage and is required to meet the requirement

In the formula I _o -the output current of the direct current is,

ΔU _max the anti-interference index is generally 5% of the direct current voltage when the load of the converter is disturbed.

Calculated by substitution

In an actual circuit, an alternating current interface is required to be provided on a direct current output side, the capacitance filtering and voltage stabilizing capacity is required to be stronger, and C is selected ₁ ＝C ₂ ＝C ₃ ＝400μF。

And (3) simulation results:

in order to verify the effectiveness of the proposed open-circuit fault diagnosis and fault tolerance strategy of the three-active-bridge converter, the effectiveness of an open-circuit fault detection strategy is verified firstly, and S is used ₂₁ And S ₁₁ For example, an open fault diagnosis simulation was performed, and an open fault occurred when 0.005s was set in the simulation.

As shown in FIG. 14, when S ₂₁ Or S ₁₁ When an open-circuit fault occurs, the inductive current generates obvious direct current bias, the amplitude is increased, and the open-circuit fault diagnosis strategy can rapidly position the fault position. Flag in the figure indicates the Flag bit of the fault, u _AB ,u _CD Are square wave voltages i corresponding to the primary side bridge and the secondary side bridge respectively _L1 ,i _L2 Primary side and secondary side inductor currents, respectively.

Respectively setting S for verifying the validity of the fault-tolerant strategy ₂₁ And S ₁₁ An open-circuit fault occurs, the open-circuit fault of the direct current bus side and the energy storage side is simulated, and d is carried out before the fault ₁₂ >0，d ₂₃ >0，d ₁₃ >0。S ₂₁ The fault tolerance target when an open circuit fault occurs is to make port two (dc bus side) absorb power and port one and three output power, and the result is shown in fig. 15. S ₁₁ The fault tolerance objective when an open circuit fault occurs is to make port one (energy storage side) not participate in power transmission any more, and power is only transmitted between port two and port three. The results are shown in FIG. 16. It can be seen from fig. 15 and 16 that the proposed fault tolerance strategy can rapidly eliminate dc offset, and fig. 17 is S ₂₁ And S ₁₁ The power of three ports in the open fault tolerant operation is referred to the power flow shown in fig. 3 (b). As can be seen from the figure, S ₁₁ When the circuit is open, the first port can not transmit power any more, and the power is transmitted between the second port and the third port only; s ₂₁ When the circuit is open, the first port and the second port output power.

Appendix A

Secondary side S ₂₁ The calculation result in the open-circuit fault-tolerant operation is as follows:

from equation (15), S can be calculated ₂₁ Zero-crossing time t of open-circuit fault-tolerant operation current ₂ And secondary side inductance current:

S ₂₁ the inductive current at each moment on the primary side during open-circuit fault-tolerant operation is as follows:

S ₂₁ the inductive current at each moment of the three sides in open-circuit fault-tolerant operation is as follows:

under ideal operating conditions, the power at each port is as follows:

under ideal operating conditions, the inductor current at each port is as follows:

a first port:

and a second port:

and a third port:

S ₁₁ the calculation result in the open-circuit fault-tolerant operation is as follows:

the primary side current at each time is as follows:

the secondary side current at each time is as follows:

the current at each moment of the third side is as follows:

ideally, the power expression of each port is as follows:

ideally, the inductance and current expression of each port is as follows:

a first port:

and a second port:

and a third port:

the embodiment of the invention provides a method for diagnosing open-circuit faults and fault-tolerant operation of a TAB converter, which can quickly and accurately position the open-circuit faults of three active bridge converter switching devices; the fault-tolerant operation of the open-circuit fault of the switching devices of the three-active-bridge converter can be realized; the reasonable power distribution among the three ports after the open circuit fault of the TAB converter can be realized.

The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.

Claims

1. A method for diagnosing open circuit fault and fault-tolerant operation of a TAB converter is characterized by comprising the following steps:

step S1: locating an open circuit fault of the TAB converter;

2. The method for diagnosing and fault-tolerant operation of an open circuit fault of a TAB converter as claimed in claim 1, wherein the step S1 comprises: analyzing open-circuit fault waveforms of the switch tubes of the TAB, and realizing TAB open-circuit fault location by using midpoint voltages of the bridge arms;

3. The method for diagnosing and fault-tolerant operation of an open circuit fault in a TAB converter as claimed in claim 1, wherein the step S2 eliminates a dc bias generated by the open circuit fault, solves an overcurrent problem, and reasonably distributes transmission power among three ports, wherein the open circuit fault includes: a direct current bus side open circuit fault and an energy storage side open circuit fault;

when an open-circuit fault occurs at the direct-current bus side or the energy storage side, the bridge arm driving signals where the fault switching tubes are located are locked to form a symmetrical circuit, so that direct-current components are eliminated.

4. The method for diagnosing and fault-tolerant operating an open circuit fault of a TAB converter according to claim 3, wherein after the open circuit fault occurs at the DC bus side and the energy storage side, the fault-tolerant operating ensures that the maximum inductive current of each port is not larger than the maximum inductive current in normal operating, and when the DC bus side fails, the DC bus can be ensured to normally absorb power, and when the energy storage side fails, the fault energy storage is cut off, and the power transmission is normally performed between the other two ports.