CN110545040A - three-level Buck circuit and control method thereof - Google Patents

three-level Buck circuit and control method thereof Download PDF

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Publication number
CN110545040A
CN110545040A CN201910859287.6A CN201910859287A CN110545040A CN 110545040 A CN110545040 A CN 110545040A CN 201910859287 A CN201910859287 A CN 201910859287A CN 110545040 A CN110545040 A CN 110545040A
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CN
China
Prior art keywords
buck circuit
charging unit
level buck
capacitor
outer tube
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Pending
Application number
CN201910859287.6A
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Chinese (zh)
Inventor
王腾飞
庄加才
李江松
徐君
谷雨
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Sungrow Power Supply Co Ltd
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Sungrow Power Supply Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Application filed by Sungrow Power Supply Co Ltd filed Critical Sungrow Power Supply Co Ltd
Priority to CN201910859287.6A priority Critical patent/CN110545040A/en
Publication of CN110545040A publication Critical patent/CN110545040A/en
Priority to CN201911359302.7A priority patent/CN111181396B/en
Pending legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
    • H02M3/1584—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load with a plurality of power processing stages connected in parallel
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/06—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using resistors or capacitors, e.g. potential divider
    • H02M3/07—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using resistors or capacitors, e.g. potential divider using capacitors charged and discharged alternately by semiconductor devices with control electrode, e.g. charge pumps
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
    • H02M3/1584—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load with a plurality of power processing stages connected in parallel
    • H02M3/1586—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load with a plurality of power processing stages connected in parallel switched with a phase shift, i.e. interleaved

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)
  • Inverter Devices (AREA)

Abstract

The invention provides a three-level Buck circuit and a control method thereof, wherein the three-level Buck circuit comprises: input capacitance, output capacitance and at least one bridge arm, the bridge arm includes: the device comprises a charging unit, a suspension capacitor, two inner pipes, two outer pipes and an inductor; the charging unit is connected in parallel with two ends of the outer tube which is not connected with the low-voltage side, when the three-level Buck circuit is connected with a power supply, most of the voltage which is originally added in the input voltage at the two ends of the outer tube is greatly reduced by dividing the voltage through the charging unit and the suspension capacitor, and therefore the outer tube is prevented from being damaged by overvoltage; simultaneously, carry out the precharge for the suspended capacitor through this charging unit, still can avoid leading to another outer tube overvoltage damage's problem because of switching on this outer tube and charge for the suspended capacitor to improve three level Buck circuit security.

Description

Three-level Buck circuit and control method thereof
Technical Field
the invention belongs to the technical field of power electronics, and particularly relates to a three-level Buck circuit and a control method thereof.
background
with the rise of the system voltage of the power electronic converter, the voltage withstanding requirements of related switching devices are gradually raised, but due to the influence of semiconductor process performance and the like, the development of high-cost performance devices has certain hysteresis, and the related voltage withstanding requirements cannot be met in a short period of time, so that how to realize high-voltage power conversion by using lower-voltage-level devices and lower cost becomes a research hotspot, and the problem can be better solved by the proposal of the multilevel technology.
in the three-level Buck circuit shown in FIG. 1, the first outer tube K1 and the first inner tube K2 are alternately conducted in normal operation, and under ideal conditions, the conduction duty ratios of the first outer tube K1 and the first inner tube K2 are the same, so that the voltage stress of each switching tube is only half of the output voltage in normal operation. However, when the three-level Buck circuit is started, since the voltage Vf across the floating capacitor Cf is zero, if the input voltage Vin is greater than the withstand voltage of the first outer tube K1, the first outer tube K1 may be over-voltage broken; moreover, the first outer tube K1 is turned on to charge the floating capacitor, and then the voltage at the two ends of the first outer tube K1 is instantaneously transferred to the two ends of the second outer tube K4, so that the second outer tube K4 is damaged by overvoltage, therefore, the first outer tube K1 and the second outer tube K4 of the three-level Buck circuit are easily damaged by overvoltage, and further the three-level Buck circuit is failed.
Disclosure of Invention
In view of the above, an object of the present invention is to provide a three-level Buck circuit and a control method thereof, so as to solve the problems that the first outer tube is prone to overvoltage breakdown during starting, which results in failure of the first outer tube, and the flying capacitor type three-level Buck circuit is caused by overvoltage breakdown failure of the second outer tube due to conduction of the first outer tube for charging the floating capacitor.
the first aspect of the invention discloses a three-level Buck circuit, comprising: an input capacitance, an output capacitance, and at least one leg, the leg comprising: the device comprises a charging unit, a suspension capacitor, two inner pipes, two outer pipes and an inductor; wherein:
Two ends of the input capacitor are respectively used as the positive electrode and the negative electrode of the high-voltage side of the three-level Buck circuit;
two ends of the output capacitor are respectively used as the positive electrode and the negative electrode of the low-voltage side of the three-level Buck circuit;
In the bridge arm, the suspension capacitor is connected in parallel with the series branch of the two inner tubes, a connecting point between the two inner tubes is connected with one end of the inductor, the other end of the inductor is connected with one of the positive and negative electrodes of the low-voltage side, one outer tube is used for respectively connecting the other of the positive and negative electrodes of the low-voltage side and the corresponding one of the positive and negative electrodes of the high-voltage side, and the other outer tube is used for connecting the other of the positive and negative electrodes of the high-voltage side and is connected with the charging unit in parallel.
optionally, the charging unit includes: a balancing capacitor and a charging diode connected in series;
If one end of the balance capacitor is connected with the anode of the charging diode, the other end of the balance capacitor is used as the input end of the charging unit, and the cathode of the charging diode is used as the output end of the charging unit;
And if one end of the balance capacitor is connected with the cathode of the charging diode, the other end of the balance capacitor is used as the output end of the charging unit, and the anode of the charging diode is used as the input end of the charging unit.
Optionally, the method further includes: and the discharging unit is used for discharging the balance capacitor after the three-level Buck circuit is powered off.
Optionally, the discharge unit includes: a discharge diode;
If the negative electrode of the low-voltage side of the three-level Buck circuit is connected with the negative electrode of the high-voltage side of the three-level Buck circuit, the anode of the discharge diode is connected with the negative electrode of the low-voltage side and the negative electrode of the high-voltage side, and the cathode of the discharge diode is connected with the charged negative electrode of the balance capacitor;
If the low-voltage side anode of the three-level Buck circuit is connected with the high-voltage side anode of the three-level Buck circuit, the cathode of the discharge diode is connected with the low-voltage side anode and the high-voltage side anode, and the anode of the discharge diode is connected with the anode of the charged balance capacitor.
Optionally, when the three-level Buck circuit access voltage source is a stable input voltage source, between the stable input voltage source and the input capacitor, the three-level Buck circuit further includes: a current limiting unit;
and the current limiting unit is used for limiting the charging current of the parallel parasitic capacitor of the outer tube which is not connected with the charging unit when the three-level Buck circuit is connected to the input voltage source.
optionally, the current limiting unit includes: the circuit comprises a first switch, a second switch and a current-limiting resistor;
the first switch is connected with the current-limiting resistor in series;
And the series branch of the first switch and the current-limiting resistor is connected with the second switch in parallel.
Optionally, the number of the bridge arms is n, and n is a positive integer greater than or equal to 2.
Optionally, the inner tube and the outer tube connected to the charging unit are respectively reverse conducting transistors, and are in a staggered conducting state during normal operation;
the inner tube and the outer tube which are not connected with the charging unit are respectively a diode or a reverse conducting transistor.
the second aspect of the present invention discloses a control method for a three-level Buck circuit, which is applied to a controller of the three-level Buck circuit in any one of the first aspect, and the control method includes:
Controlling the three-level Buck circuit to be connected to an input voltage source;
and when the difference between the voltage of the floating capacitor and half of the input voltage is reduced to be smaller than a threshold value, controlling the inner tube and the outer tube which are connected with the charging unit in the three-level Buck circuit to be conducted in a staggered mode.
Optionally, the controlling of the staggered conduction of the inner tube and the outer tube in the three-level Buck circuit, which have a connection relationship with the charging unit, includes:
controlling the conduction of an outer pipe connected with the charging unit and the disconnection of an inner pipe connected with the charging unit to charge the floating capacitor of the three-level Buck circuit;
Controlling the inner pipe and the outer pipe which are connected with the charging unit to be turned off, and charging the suspension capacitor and the charging unit;
Controlling the outer pipe connected with the charging unit to be switched off and the inner pipe connected with the charging unit to be switched on to charge the charging unit;
And returning to the step of controlling the conduction of the outer pipe connected with the charging unit and the disconnection of the inner pipe connected with the charging unit until the voltage of the floating capacitor rises to be equal to half of the input voltage.
optionally, the method further includes the following three steps executed in a cycle after the voltage of the floating capacitor rises to be equal to half of the input voltage:
controlling the conduction of an outer pipe connected with the charging unit and the disconnection of an inner pipe connected with the charging unit to charge the floating capacitor;
Controlling the inner pipe and the outer pipe which are connected with the charging unit to be turned off, so that the suspension capacitor and the charging unit are not charged and discharged;
and controlling the outer pipe connected with the charging unit to be switched off and the inner pipe connected with the charging unit to be switched on so as to discharge the suspension capacitor.
optionally, if the three-level Buck circuit includes a current limiting unit, after the controlling the three-level Buck circuit to access the input voltage source, the method further includes:
Controlling a first switch of the current limiting unit to be closed;
and when the difference between the voltage of the floating capacitor and half of the input voltage is reduced to be smaller than a threshold value, a second switch of the current limiting unit is controlled to be closed, and then the step of controlling the inner tube and the outer tube which are connected with the charging unit in the three-level Buck circuit to be conducted in a staggered mode is executed.
Optionally, if the inner tube and the outer tube that are not connected to the charging unit are reverse conducting transistors, the method further includes, while controlling the inner tube and the outer tube that are connected to the charging unit in the three-level Buck circuit to be alternately conducted:
And controlling the complementary conduction of the two inner tubes and the complementary conduction of the two outer tubes in the three-level Buck circuit.
from the above technical solution, the three-level Buck circuit provided by the present invention is characterized by comprising: input capacitance, output capacitance and at least one bridge arm, the bridge arm includes: the device comprises a charging unit, a suspension capacitor, two inner pipes, two outer pipes and an inductor; wherein: the three-level Buck circuit is connected with a power supply, most of input voltage which is originally applied to two ends of the outer tube which is not connected with the low-voltage side is divided into partial voltage by the charging unit and the suspension capacitor, so that the outer tube is prevented from being damaged by overvoltage; simultaneously, carry out the precharge for the suspension capacitor through the unit that charges, still can avoid leading to another outer tube overvoltage damage's problem because of switching on this outer tube and charge for the suspension capacitor to improve three level Buck circuit security.
drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a schematic diagram of a three-level Buck circuit provided in the prior art;
FIG. 2 is a timing diagram illustrating the conduction of a first outer tube and a first inner tube in a three-level Buck circuit provided by the prior art;
FIG. 3 is a schematic diagram of a three-level Buck circuit according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of another three-level Buck circuit provided by an embodiment of the present invention;
FIG. 5 is a schematic diagram of another three-level Buck circuit provided by an embodiment of the present invention;
FIG. 6 is a schematic diagram of another three-level Buck circuit provided by an embodiment of the present invention;
FIG. 7 is a schematic diagram of another three-level Buck circuit provided by an embodiment of the present invention;
FIG. 8 is a schematic diagram of another three-level Buck circuit provided by an embodiment of the present invention;
FIG. 9 is a schematic diagram of another three-level Buck circuit provided by an embodiment of the present invention;
FIG. 10 is a schematic diagram of another three-level Buck circuit provided by an embodiment of the present invention;
FIG. 11 is a schematic diagram of another three-level Buck circuit provided by an embodiment of the present invention;
FIG. 12 is a schematic diagram of another three-level Buck circuit provided by an embodiment of the present invention;
FIG. 13 is a flowchart of a control method for a three-level Buck circuit according to an embodiment of the present invention;
FIG. 14 is a flow chart of another control method for a three-level Buck circuit according to an embodiment of the present invention;
Fig. 15 is a schematic diagram of another three-level Buck circuit provided by the prior art.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In this application, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
it should be noted that, in the three-level Buck circuit shown in fig. 1, during normal operation, the first outer tube K1 and the first inner tube K2 are alternately turned on. Under ideal working conditions, the conduction duty cycles of the first outer tube K1 and the first inner tube K2 are the same and are both D, and the conduction timing diagram is shown in fig. 2, then:
The output voltage Vout and the input voltage Vin satisfy: vout ═ D × Vin.
The voltage across the floating capacitor Cf is:
The voltage stress of each switching tube is as follows:
vf is a voltage of the floating capacitor Cf, Vk1 is a voltage stress of the first outer tube K1, Vk2 is a voltage stress of the first inner tube K2, Vk3 is a voltage stress of the second inner tube K3, and Vk4 is a voltage stress of the second outer tube K4.
From the above equations, it can be seen that the voltage stress of each switching tube is only half of the input voltage during normal operation. However, when the three-level Buck circuit is started, since the voltage Vf between the two ends of the floating capacitor Cf is zero, the difference between the withstand voltage of each switching tube and the steady-state operating time is large, which is:
Vk1＝Vin-Vf＝Vin
Vk2＝Vf＝0
Vk3＝0
Vk4＝0
at this time, if the input voltage Vin is greater than the withstand voltage of the first outer tube K1, the first outer tube K1 will fail due to overvoltage breakdown, and the three-level Buck circuit will fail.
Therefore, the embodiment of the invention discloses a three-level Buck circuit, which aims to solve the problem that the first outer tube K1 fails due to the fact that the first outer tube K1 is prone to overvoltage breakdown when being started, and further the three-level Buck circuit fails.
The three-level Buck circuit, see fig. 3 or fig. 4, includes: input capacitance Cin, output capacitance Co and at least one bridge arm 310, bridge arm 310 includes: the charging unit 311, the floating capacitor Cf, two inner tubes (a first inner tube K2 and a second inner tube K3), two outer tubes (a first outer tube K1 and a second outer tube K4), and an inductor L; wherein:
two ends of the input capacitor Cin are respectively used as the positive electrode and the negative electrode of the high-voltage side of the three-level Buck circuit. Two ends of the output capacitor Co are respectively used as the positive electrode and the negative electrode of the low-voltage side of the three-level Buck circuit. In bridge arm 310, charging unit 311 is connected in parallel to first outer tube K1. The suspension capacitor Cf is connected with a series branch of the two inner tubes (the first inner tube K2 and the second inner tube K3) in parallel, a connecting point between the two inner tubes (the first inner tube K2 and the second inner tube K3) is connected with one end of an inductor L, and the other end of the inductor L is connected with one of the positive pole and the negative pole of the low-voltage side. The second outer tube K4 is used to connect the other of the low-voltage side positive and negative electrodes and the one of the high-voltage side positive and negative electrodes with the same polarity. The first outer tube K1 is used to connect the other of the high-voltage-side positive and negative electrodes, and is connected in parallel with the charging unit 311.
specifically, referring to fig. 3 as an example, the first outer tube K1, the first inner tube K2, the second inner tube K3, and the second outer tube K4 are connected in series. One end of an input capacitor Cin of the three-level Buck circuit, which is connected with the first outer tube K1, is used as the high-voltage side anode of the three-level Buck circuit, and one end of the input capacitor Cin of the three-level Buck circuit, which is connected with the second outer tube K4, is used as the high-voltage side cathode of the three-level Buck circuit. One end of the output capacitor Co connected with the inductor L is used as the low-voltage side anode of the three-level Buck circuit, and one end of the output capacitor Co connected with the second outer tube K4 is used as the low-voltage side cathode of the three-level Buck circuit. The charging unit 311 is connected in parallel to the first outer tube K1. One end of the floating capacitor Cf is connected with the connection point of the first outer tube K1 and the first inner tube K2, and the other end of the floating capacitor Cf is connected with the connection point of the second inner tube K3 and the second outer tube K4. The other end of the inductance L is connected with the connection point of the first inner tube K2 and the second inner tube K3.
more specifically, one end of the input capacitor Cin is connected to one end of the charging unit 311 and one end of the first outer tube K1, respectively, and the connection point is used as a high-voltage side positive electrode, the other end of the input capacitor Cin is connected to one end of the second outer tube K4 and a low-voltage side negative electrode, respectively, and the connection point is used as a high-voltage side negative electrode.
The other end of the first outer tube K1 is connected to the other end of the charging unit 311, one end of the first inner tube K2 and one end of the floating capacitor Cf, respectively; the other end of the first inner tube K2 is respectively connected with one end of the second inner tube K3 and one end of an inductor L, the other end of the inductor L is connected with one end of an output capacitor Co, the connection point is used as a low-voltage side anode, and the other end of the output capacitor Co is used as a low-voltage side cathode.
the other end of the second inner tube K3 is connected to the other end of the floating capacitor Cf and the other end of the second outer tube K4, respectively.
Referring to fig. 4, the circuit shown in fig. 4 is a dual circuit with the circuit shown in fig. 3, and the connection relationship of each device in the circuit shown in fig. 4 is similar to that of each device in the circuit shown in fig. 3, which can be referred to the description of the drawing in fig. 3 and is not repeated herein; the difference is that one end of the input capacitor Cin is connected to one end of the charging unit 311 and one end of the first outer tube K1, the connection point is used as a high-voltage side cathode, the other end of the input capacitor Cin is connected to one end of the second outer tube K4 and a low-voltage side anode, the connection point is used as a high-voltage side anode, one end of the inductor L is connected to the output capacitor Co, the connection point is used as a high-voltage side cathode, and the other end of the output capacitor Co is used as a low-voltage side anode.
in practical applications, the first inner tube K2 and the first outer tube K1 connected to the charging unit 311 are reverse conducting transistors respectively, and are in a staggered conducting state during normal operation; the second inner tube K3 and the second outer tube K4, which are not connected to the charging unit 311, are diodes or transistors of a reverse conducting type, respectively.
in this embodiment, when the three-level Buck circuit is connected to the power supply, most of the input voltages originally applied to the two ends of the first outer tube K1 are greatly reduced in voltage by dividing the voltage through the charging unit 311 and the floating capacitor Cf, so as to prevent the first outer tube K1 from being damaged by overvoltage; meanwhile, the floating capacitor Cf is precharged through the charging unit 311, and the problem that the second outer tube K4 is damaged due to overvoltage caused by conducting the first outer tube K1 to charge the floating capacitor Cf can be solved, so that the safety of the three-level Buck circuit is improved, the restrictive condition of the three-level Buck circuit in actual use is low, and the advantages of the three-level Buck circuit are fully exerted.
It should be noted that, as shown in fig. 15, in the prior art, the precharge circuit 10 is provided at both ends of the floating capacitor Cf. In the three-level Buck circuit, before an input voltage source is connected to the three-level Buck circuit, the pre-charging circuit 10 charges the floating capacitor Cf, and when the voltage of the floating capacitor Cf is reduced, the pre-charging circuit 10 needs to charge the floating capacitor Cf again to ensure that the floating capacitor Cf is reserved with a corresponding voltage in advance, so that the first outer tube K1 is prevented from being damaged by overvoltage. Specifically, an additional branch is needed to provide power for the pre-charge circuit 10, so as to pre-charge the floating capacitor Cf by the pre-charge circuit 10. Before the input end of the three-level Buck circuit is connected to an input voltage source, the three-level Buck circuit needs to be controlled to start working, that is, the pre-charging circuit 10 is controlled to charge the floating capacitor Cf, so that the operation is very inconvenient.
in the embodiment, an additional branch circuit is not needed, and the three-level Buck circuit is not needed to be controlled to start working before the three-level Buck circuit is connected to a power supply, so that the operation is very convenient.
Optionally, the charging unit 311 referred to in fig. 3 or fig. 4 in the embodiment of the present invention, referring to fig. 5 to 8, may include: a balancing capacitor C1 and a charging diode D1 connected in series.
Referring to fig. 6 or 7, one end of the balancing capacitor C1 is connected to the anode of the charging diode D1, the other end of the balancing capacitor C1 serves as the input terminal of the charging unit 311, and the cathode of the charging diode D1 serves as the output terminal of the charging unit 311.
Specifically, referring to fig. 6, one end of a balance capacitor C1 is connected to the anode of the charging diode D1, the other end of the balance capacitor C1 is connected to the high-voltage-side anode and one end of the first outer tube K1, respectively, and the cathode of the charging diode D1 is connected to the other end of the first outer tube K1, one end of the floating capacitor Cf, and one end of the first inner tube K2, respectively; at this time, one end of the balance capacitor C1 connected to the high-voltage side positive electrode serves as an input end of the charging unit 311, and the cathode of the charging diode D1 serves as an output end of the charging unit 311.
Referring to fig. 7, one end of a balance capacitor C1 is connected to the anode of the charging diode D1, the other end of the balance capacitor C1 is connected to one end of the first outer tube K1, one end of the floating capacitor Cf, and one end of the first inner tube K2, respectively, the cathode of the charging diode D1 is connected to the high-voltage negative electrode and the other end of the first outer tube K1, at this time, one end of the balance capacitor C1 connected to the floating capacitor Cf serves as the input end of the charging unit 311, and the cathode of the charging diode D1 serves as the output end of the charging unit 311.
Referring to fig. 5 or 8, one end of the balancing capacitor C1 is connected to the cathode of the charging diode D1, the other end of the balancing capacitor C1 is the output terminal of the charging unit 311, and the anode of the charging diode D1 is the input terminal of the charging unit 311.
Specifically, referring to fig. 5, one end of a balance capacitor C1 is connected to the cathode of the charging diode D1, the other end of the balance capacitor C1 is connected to one end of the first outer tube K1, one end of the first inner tube K2 and one end of the floating capacitor Cf, respectively, and the anode of the charging diode D1 is connected to the high-voltage-side anode and the other end of the first outer tube K1, respectively; at this time, the anode of the charging diode D1 is used as the input terminal of the charging unit 311, and the end of the balance capacitor C1 connected to the floating capacitor Cf is used as the output terminal of the charging unit 311.
Referring to fig. 8, one end of a balance capacitor C1 is connected to the cathode of the charging diode D1, the other end of the balance capacitor C1 is connected to the high-voltage side negative electrode and one end of the first outer tube K1, respectively, and the anode of the charging diode D1 is connected to the other end of the first outer tube K1, one end of the first inner tube K2, and one end of the floating capacitor Cf, respectively; at this time, the anode of the charging diode D1 is used as the input terminal of the charging unit 311, and the terminal of the balance capacitor C1 connected to the high-voltage side cathode is used as the output terminal of the charging unit 311.
In the embodiment, the floating capacitor Cf is charged through the balancing capacitor C1 and the charging diode D1 which are connected in series, so that the problems that the voltage stress of the first outer tube K1 is too high when the first outer tube K is started and the floating capacitor Cf is pre-charged to cause overvoltage damage are solved; and under the condition of not increasing the circuit loss, the number of sampling paths and the control complexity, the charging speed of the floating capacitor Cf is increased, and the dynamic response of the circuit is improved.
It should be noted that, in the above embodiments of fig. 5-8, the balancing capacitor C1 cannot be discharged after being powered down, and based on the implementation of fig. 5 or 7, see fig. 9 (shown on the basis of fig. 5) or fig. 10 (shown on the basis of fig. 7), the method may further include: and a discharge unit 312.
And the discharge unit 312 is used for discharging the balance capacitor C1 after the three-level Buck circuit is powered down.
in practical applications, the discharge unit 312 may include: a discharge diode D2.
Referring to fig. 9, the negative electrode of the low-voltage side of the three-level Buck circuit is connected to the negative electrode of the high-voltage side of the three-level Buck circuit, the anode of the discharge diode D2 is connected to the negative electrode of the low-voltage side and the negative electrode of the high-voltage side, the cathode of the discharge diode D2 is connected to the charged negative electrode of the balancing capacitor C1, that is, the cathode of the discharge diode D2 is connected to the connection point of the balancing capacitor C1 and the charging diode D1, and the cathode of the charging diode D1 is connected to one end of the first outer tube K1, one end of the floating capacitor Cf and one end of the first inner tube K.
After the three-level Buck circuit is powered on, the discharge diode D2 is cut off, after the three-level Buck circuit is powered off, the discharge diode D2 is turned on, and the discharge diode D2 discharges for the balance capacitor C1.
Referring to fig. 10, the low-voltage side positive electrode of the three-level Buck circuit is connected to the high-voltage side positive electrode of the three-level Buck circuit, the cathode of the discharge diode D2 is connected to the low-voltage side positive electrode and the high-voltage side positive electrode, the anode of the discharge diode D2 is connected to the charged positive electrode of the balancing capacitor C1, that is, the anode of the discharge diode D2 is connected to the connection point of the balancing capacitor C1 and the charging diode D1, and the anode of the charging diode D1 is connected to one end of the first outer tube K1, one end of the floating capacitor Cf, and one end of the first inner tube K2, respectively.
After the three-level Buck circuit is powered on, the discharge diode D2 is cut off, and when the three-level Buck circuit is powered off, the discharge diode D2 is turned on, and the discharge diode D2 discharges for the balance capacitor C1.
after the balance capacitor C1 is charged, the two ends of the balance capacitor C1 are respectively used as the positive electrode and the negative electrode, the end closer to the positive electrode on the high-voltage side is used as the positive electrode, and the end closer to the negative electrode on the high-voltage side is used as the negative electrode.
in this embodiment, after the three-level Buck circuit was powered down, discharge unit 312 was discharged for balanced capacitor C1 fast, avoided among the three-level Buck circuit balanced capacitor C1 to be electrified for a long time, had the problem of potential safety hazard when causing the maintenance.
optionally, on the basis of any one of fig. 3 to 10, referring to fig. 11 (which is shown on the basis of fig. 9 as an example), when the input voltage source connected to the three-level Buck circuit is a stable input voltage source DC, between the stable input voltage source DC and the input capacitor Cin, the method may further include: a current limiting unit 313.
And the current limiting unit 313 is used for limiting the charging current of the parallel parasitic capacitance of the outer tube (namely, the second outer tube K4) which is not connected with the charging unit when the three-level Buck circuit is connected with the input voltage source DC.
in practical applications, the current limiting unit 313 includes: a first switch S1, a second switch S2, and a current limiting resistor R.
the first switch S1 is connected in series with the current limiting resistor R, and the series branch of the first switch S1 and the current limiting resistor R is connected in parallel with the second switch S2.
the reason why the current limiting resistor R is connected between the stable input voltage source DC and the input capacitor Cin is that when the stable input voltage source DC is a voltage source with a capacitor, and when the initial voltage of the stable input voltage source DC is very high, such as 1500V, at this time, if the current limiting resistor R is not provided, at the moment that the three-level Buck circuit is connected to the input voltage source, the capacitor of the stable input voltage source DC charges the balance capacitor C1, the floating capacitor Cf and the parasitic capacitors at the two ends of the second outer tube K4 with a very large charging current, because the capacitance values of the balance capacitor C1 and the floating capacitor Cf are much larger than those of the parasitic capacitors at the two ends of the second outer tube K4, the smaller the capacitance value is, and the higher the voltage division is performed according; therefore, the main voltage of the stabilized input voltage source DC is applied across the second external tube K4, causing it to be damaged by overvoltage.
If the current-limiting resistor R is arranged, the charging current of the second outer tube K4 is reduced, the second outer tube K4 and a second inner tube K3-inductor L-output capacitor Co loop are in a parallel connection relationship, the capacitance of the output capacitor Co is extremely large and is generally far larger than the capacitance of the balance capacitor C1 and the capacitance of the suspension capacitor Cf, the voltage at two ends of the second outer tube K4 is restrained from being rapidly increased, and the second outer tube K4 is guaranteed against overvoltage damage. For the three-level Buck circuit, which is connected to the input voltage source and is a photovoltaic input voltage source, the current limiting unit 313 may be omitted, and the current limiting unit 313 may also be omitted for other three-level Buck circuits with input voltage sources having limited output current or slowly increasing output voltage.
The circuit added with the current limiting unit 313 in fig. 3-8 and 10 is similar to the circuit shown in fig. 11, and is not described again here, and is within the scope of the present application.
it should be noted that any one or more of the above circuits may be selected to be used in combination according to the application environment and the user's requirements, and certainly not limited to the above exemplary circuits, other circuits that can pre-charge the floating capacitor Cf to avoid the overvoltage damage of the first outer tube K1 can be implemented, and are within the scope of the present application.
Optionally, in the embodiments of fig. 3 to 12 of the present invention, referring to fig. 13 (which is shown by taking fig. 5 as an example), the number of the bridge arms 310 is n, and n is a positive integer greater than or equal to 2, such as 3.
The n bridge arms 310 are connected in parallel, the n bridge arms 310 share one input capacitor Cin and one output capacitor Co, and the three-level Buck circuit can be used for a parallel interleaving system; compared with a topology with different input and output grounds, the n-path parallel topology is more easily applied to a multi-path interleaving parallel system, the number of the inductors L is reduced, and meanwhile, the size and the cost of the inductors L can be saved.
because one of the input end and the output end of the three-level Buck circuit is directly electrically connected, the n bridge arms 310 are independent from each other, and the phase shift is driven by corresponding switching tubes (namely a first outer tube K1, a first inner tube K2, a second inner tube K3 and a second outer tube K4) among the n bridge arms 310, so that the staggered parallel connection can be realized.
In the embodiment, the bridge arms 310 are ensured to be independent and not coupled, the advantage of reducing the L-inductance value of the output inductor by frequency multiplication of the three-level Buck circuit is fully utilized, and the staggered parallel structure reduces input and output current ripples, so that the current stress of the input capacitor Cin and the output capacitor Co is reduced, the cost is further saved, and the power density is improved.
The invention discloses a control method of a three-level Buck circuit, which is applied to a controller of the three-level Buck circuit, wherein the three-level Buck circuit is the three-level Buck circuit in any one of the embodiments shown in figures 1 to 13. Referring to fig. 14, the control method includes:
s801, controlling a three-level Buck circuit to be connected to an input voltage source;
in the initial situation, that is, before the input voltage source is connected, the voltage of each device in the three-level Buck circuit is 0, when the input voltage source is connected to the three-level Buck circuit, the three-level Buck circuit is still in a standby state, the voltage of the input capacitor Cin is rapidly charged to the voltage of the input voltage source, and the input voltage source charges the floating capacitor Cf through the charging unit 311.
for convenience of illustration, the setting of capacitance values of the respective capacitors in the three-level Buck circuit may be C1 ═ Cf, Co > > C1; wherein, C1 is the capacitance of the balance capacitance C1, Cf is the capacitance of the floating capacitance Cf, and Co is the capacitance of the output capacitance Co; in addition, the parasitic capacitance of the first outer tube K1, the first inner tube K2, the second inner tube K3 and the second outer tube K4 is much smaller than that of the balance capacitor C1, and the maximum input voltage may be 1500V; of course, the values of the capacitance and the maximum input voltage of each device of the three-level Buck circuit can be other values, and the values are determined according to actual requirements and are all within the protection range of the application.
After the input voltage source is connected, the voltage of the charging unit 311 is equal to the voltage of the floating capacitor Cf; at this time, the parasitic capacitance of the second outer tube K4 is in parallel with the branch of the anti-parallel diode, the inductor L, and the output capacitor Co of the second inner tube K3. Because the output capacitor Co exists and the capacitance thereof is much larger than that of the charging unit 311, according to the capacitance voltage division principle, the voltage difference between the common terminal of the second inner tube K3 and the second outer tube K4 and the negative electrode of the input voltage source is zero; therefore, the input voltage is mainly applied to the charging unit 311 and the floating capacitor Cf, that is, the voltages of the charging unit 311 and the floating capacitor Cf are equal to and approximately equal to one half of the input voltage, the voltage across the first outer tube K1 is clamped by the charging unit 311, and the voltage of the first outer tube K1 is equal to the voltage of the charging unit 311 and approximately equal to one half of the input voltage, so that the first outer tube K1 is not damaged by over voltage.
in fact, the output capacitor Co cannot be infinite, so that after the input voltage source is connected, there will be a small voltage on the output capacitor Co, resulting in the voltages on the charging unit 311 and the floating capacitor Cf being slightly lower than Vin/2. The three-level Buck circuit enters the operation mode to charge the charging unit 311 and the floating capacitor Cf, and the specific implementation and principle are described below.
it should be noted that before the three-level Buck circuit is connected to the input voltage source, both the inner tube and the outer tube in the three-level Buck circuit are in the off state, and then before the difference between the voltage of the floating capacitor Cf and half of the input voltage drops to be less than the threshold, both the inner tube and the outer tube in the three-level Buck circuit are kept in the off state, that is, before the difference between the voltage of the floating capacitor Cf and half of the input voltage drops to be less than the threshold, both the inner tube and the outer tube are kept in the off state, and whether the difference between the voltage of the floating capacitor Cf and half of the input voltage drops to be less than the threshold is continuously determined.
In practical applications, if the three-level Buck circuit includes the current limiting unit 313, after step S801, the method may further include:
The first switch S1 of the current limiting unit 313 is controlled to be closed, so that the current limiting resistor R is connected between the regulated input voltage source DC and the input capacitor Cin, and the charging current of the second outer tube K4 is further reduced.
when the difference between the voltage of the floating capacitor Cf and half of the input voltage is decreased to be smaller than the threshold, the second switch S2 of the current limiting unit 313 is first controlled to be closed, so that the current limiting resistor R is separated from the voltage-stabilizing input voltage source DC and the input capacitor Cin, power loss caused by the current limiting resistor R is avoided, and then step S802 is executed.
And S802, when the difference between the voltage of the floating capacitor Cf and half of the input voltage is reduced to be smaller than a threshold value, controlling the inner tube and the outer tube which are connected with the charging unit 311 in the three-level Buck circuit to be conducted in a staggered mode.
In one switching period, the conduction duty ratios of the inner tube and the outer tube connected to the charging unit 311 may be equal or unequal, depending on the specific application environment, and are all within the protection scope of the present application.
specifically, the inner tube connected to the charging unit 311 is the first inner tube K2, and the outer tube connected to the charging unit 311 is the first outer tube K1, that is, the first outer tube K1 and the first inner tube K2 are alternately turned on, assuming that the turn-on duty ratios of the first outer tube K1 and the first inner tube K2 are the same and are D, and 0< D <0.5, the turn-on timing charts of the first outer tube K1 and the first inner tube K2 are shown in fig. 2: dividing a switching period T into three parts, such as a first part with 0< T < D T, a second part with D T < 0.5T and 0.5T + D T < T, and a third part with 0.5T < 0.5T + D T; the first outer pipe K1 and the first inner pipe K2 are communicated in a staggered mode in the three parts.
In practical applications, referring to fig. 15, step S802 may include three steps S904 to S906.
For convenience of description, fig. 5 is taken as an example to illustrate that the second inner tube K3 and the second outer tube K4 are diodes, and the implementation processes and principles of fig. 3, 4, 6-13, and the second inner tube K3 and the second outer tube K4 are inverse conducting transistors are the same, and are not repeated here, and the operating principle of the three-level Buck circuit is as follows:
And S901, controlling an outer tube connected with the charging unit 311 to be connected and an inner tube connected with the charging unit 311 to be disconnected, and charging the floating capacitor Cf of the three-level Buck circuit.
the outer tube connected to the charging unit 311 is a first outer tube K1, and the inner tube connected to the charging unit 311 is a first inner tube K2, i.e. the first outer tube K1 is controlled to be turned on and the first inner tube K2 is controlled to be turned off; the loop current trend at this time is: the input capacitor Cin → the first outer tube K1 → the floating capacitor Cf → the second inner tube K3 → the inductor L → the output capacitor Co → the input capacitor Cin, i.e., the floating capacitor Cf charges;
and S902, controlling the inner pipe and the outer pipe which are connected with the charging unit 311 to be closed, and charging the floating capacitor Cf and the charging unit 311.
Specifically, the first outer tube K1 and the first inner tube K2 are both controlled to be turned off, and the loop current trend at this time is as follows: the input capacitor Cin → the charging diode D1 of the charging unit 311 → the balance capacitor C1 of the charging unit 311 → the floating capacitor Cf → the second outer tube K4 → the input capacitor Cin, that is, the balance capacitor C1 and the floating capacitor Cf of the charging unit 311 are charged simultaneously; meanwhile, the inductor L → the output capacitor Co → the second outer tube K4 → the second inner tube K3 → the inductor L, i.e. the inductor L is in current freewheeling.
S903, controlling the outer tube connected with the charging unit 311 to be turned off and the inner tube connected with the charging unit 311 to be turned on to charge the charging unit 311;
specifically, the first outer tube K1 is controlled to be turned off, and the first inner tube K2 is controlled to be turned on; the loop current trend at this time is: the input capacitor Cin → the charging diode D1 of the charging unit 311 → the balance capacitor C1 of the charging unit 311 → the first inner tube K2 → the inductor L → the output capacitor Co → the input capacitor Cin, i.e., the balance capacitor C1 of the charging unit 311.
After step S903 is completed, the process returns to step S901, i.e., steps S901 to S903 are executed in a loop until the voltage of the floating capacitor Cf rises to be equal to half of the input voltage. Since the conduction time of the first outer tube K1 and the first inner tube K2 in one switching period T is equal to D × T, and D is a conduction duty ratio, the voltage division of the balance capacitor C1 of the charging unit 311 and the voltage division of the floating capacitor Cf are equal, and increase with the accumulation of the working time until the voltage is half of the input voltage.
therefore, when the voltages of the floating capacitor Cf and the balance capacitor C1 are half lower than the input voltage, in the working process of the three-level Buck circuit, only the floating capacitor Cf charging loop but not the floating capacitor Cf discharging loop is provided, and the speed of charging the floating capacitor Cf to the steady state in the dynamic adjustment of the three-level Buck circuit is accelerated through the charging unit 311.
After the voltage of the floating capacitor Cf rises to be equal to half of the input voltage, step S802 may further include steps S904 to S906 that are cyclically performed.
It should be noted that, after the voltage of the balance capacitor C1 of the charging unit 311 and the voltage of the floating capacitor Cf rise to half of the input voltage, the first inner tube K2 is turned on, so that the voltage of the balance capacitor C1 is greater than Vin/2, at this time, Vc1+ Vf > Vin, Vc1 is the voltage of the balance capacitor C1, Vf is the voltage of the floating capacitor Cf, and Vin is the input voltage, therefore, the charging diode D1 is turned off in the reverse direction, for convenience of description, in the following description, Vc1 is the voltage of the balance capacitor C1, Vf is the voltage of the floating capacitor Cf, Vin is the input voltage, and Vout is the output voltage.
And S904, controlling the outer tube connected with the charging unit 311 to be conducted and the inner tube connected with the charging unit 311 to be disconnected, and charging the floating capacitor Cf.
specifically, the first outer tube K1 is controlled to be on, and the first inner tube K2 is controlled to be off, at this time, the loop current trend is as follows: the input capacitor Cin → the first outer tube K1 → the floating capacitor Cf → the second inner tube K3 → the inductor L → the output capacitor Co → the input capacitor Cin, i.e. the floating capacitor Cf, is charged, and the voltage of the inductor L is Vin-Vf-Vout.
And S905, controlling the inner pipe and the outer pipe which are connected with the charging unit 311 to be both closed, so that the floating capacitor Cf and the charging unit 311 are not charged or discharged.
specifically, the first outer tube K1 and the first inner tube K2 are both controlled to be turned off, and the loop current trend at this time is as follows: the inductor L → the output capacitor Co → the second outer tube K4 → the second inner tube K3 → the inductor L, i.e. the inductor L has current flowing, the balance capacitor C1 and the floating capacitor Cf have no charge or discharge, the voltage thereof remains unchanged, and the voltage of the inductor L is-Vout.
And S906, controlling the outer tube connected with the charging unit 311 to be turned off, and controlling the inner tube connected with the charging unit 311 to be turned on, so as to discharge the floating capacitor Cf.
Specifically, the first outer tube K1 is controlled to be turned off, the first inner tube K2 is controlled to be turned on, and the loop current trend at this time is as follows: the floating capacitor Cf → the first inner tube K2 → the inductor L → the output capacitor Co → the second outer tube K4 → the floating capacitor Cf, i.e. the floating capacitor Cf discharges, and the voltage of the inductor L is Vf-Vout.
It should be noted that the output voltage can be obtained according to the inductive volt-second balance principle; the formula adopted is as follows: the expression can be derived in the same way when the value is 0.5< D <1, and is not repeated herein, and is within the protection scope of the present application.
therefore, if the parameters of the three-level Buck circuit are ideal, the balance capacitor C1 of the charging unit 311 does not participate in the three-level Buck circuit during normal operation, i.e., no charging and discharging process occurs, and the voltage remains unchanged; the floating capacitor Cf is charged and discharged equally during the period of the first outer tube K1 and the first inner tube K2 being alternately conducted, and the average voltage of the floating capacitor Cf is kept at half the input bus voltage.
In practical application, due to parameter difference, the voltage Vf of the floating capacitor Cf slightly deviates from the half-input bus voltage Vin/2; as can be seen from the above analysis, the floating capacitor Cf is charged when only the first outer tube K1 is turned on, the floating capacitor Cf is discharged when only the first inner tube K2 is turned on, and if the on duty ratios of the first outer tube K1 and the first inner tube K2 are the same as D, the gain of the output voltage and the input voltage is fixed, and at this time, the duty ratio fine adjustment amount Δ D with opposite signs is superimposed on the on duty ratios D of the first outer tube K1 and the first inner tube K2, so that the charge and discharge control of the floating capacitor Cf can be realized, and the voltage control of the floating capacitor Cf can be further realized.
During normal operation, if the floating capacitor Cf is not in a steady state when the input voltage suddenly changes, the floating capacitor Cf only has a charging loop, and the floating capacitor Cf quickly enters the steady state, which is described in detail with reference to steps S901 to S903 and is not described herein again.
in the embodiment, the three-level Buck circuit still rapidly enters a steady state even when the voltage of the input voltage source suddenly changes, the normal operation complexity of the circuit is not increased, and the performance of the three-level Buck circuit is improved.
In addition, in this embodiment, if the inner tube and the outer tube that are not connected to the charging unit 311 are MOS (Metal Oxide Semiconductor) tubes, the two inner tubes and the two outer tubes in the three-level Buck circuit are controlled to be complementarily turned on, or the inner tube and the outer tube that are not connected to the charging unit are controlled to maintain an off state.
Specifically, the outer tube connected to the charging unit 311 and the inner tube not connected to the charging unit 311 are both controlled to be turned on, and the inner tube connected to the charging unit 311 and the outer tube not connected to the charging unit 311 are both controlled to be turned off. Namely, the first outer tube K1 and the second inner tube K3 are both turned on, and the first inner tube K2 and the second outer tube K4 are both turned off. Then controlling the two inner pipes and the two outer pipes to be closed; namely, the first outer tube K1, the first inner tube K2, the second inner tube K3 and the second outer tube K4 are all closed. Then, the outer tube connected with the charging unit 311 and the inner tube not connected with the charging unit 311 are controlled to be turned off, and the inner tube connected with the charging unit 311 and the outer tube not connected with the charging unit 311 are controlled to be turned on; namely, the first outer tube K1 and the second inner tube K3 are both off, and the first inner tube K2 and the second outer tube K4 are both on.
Or the outer tube which is connected with the charging unit is firstly controlled to be switched on, and the two inner tubes and the outer tube which is not connected with the charging unit are both controlled to be switched off; namely, the first outer tube K1 is turned on, and the first inner tube K2, the second inner tube K3 and the second outer tube K4 are all turned off. And controlling the two inner pipes and the two outer pipes to be closed, namely the first outer pipe K1, the first inner pipe K2, the second inner pipe K3 and the second outer pipe K4 to be closed. And then controlling the inner tube connected with the charging unit to be switched on, switching off the two outer tubes and the inner tube not connected with the charging unit, namely switching on the first inner tube K2, and switching off the first outer tube K1, the second inner tube K3 and the second outer tube K4.
The structure and principle of the three-level Buck circuit can be obtained by referring to the above embodiments, and are not described in detail herein.
The embodiments in the present specification are described in a progressive manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments. In particular, the system or system embodiments are substantially similar to the method embodiments and therefore are described in a relatively simple manner, and reference may be made to some of the descriptions of the method embodiments for related points. The above-described system and system embodiments are only illustrative, wherein the units described as separate parts may or may not be physically separate, and the parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.
those of skill would further appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that the various illustrative components and steps have been described above generally in terms of their functionality in order to clearly illustrate this interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (13)

1. A three-level Buck circuit, comprising: an input capacitance, an output capacitance, and at least one leg, the leg comprising: the device comprises a charging unit, a suspension capacitor, two inner pipes, two outer pipes and an inductor; wherein:
Two ends of the input capacitor are respectively used as the positive electrode and the negative electrode of the high-voltage side of the three-level Buck circuit;
Two ends of the output capacitor are respectively used as the positive electrode and the negative electrode of the low-voltage side of the three-level Buck circuit;
in the bridge arm, the suspension capacitor is connected in parallel with the series branch of the two inner tubes, a connecting point between the two inner tubes is connected with one end of the inductor, the other end of the inductor is connected with one of the positive and negative electrodes of the low-voltage side, one outer tube is used for respectively connecting the other of the positive and negative electrodes of the low-voltage side and the one of the positive and negative electrodes of the high-voltage side with the same polarity, and the other outer tube is used for connecting the other of the positive and negative electrodes of the high-voltage side and is connected with the charging unit in parallel.
2. The three-level Buck circuit according to claim 1, wherein the charging unit comprises: a balancing capacitor and a charging diode connected in series;
If one end of the balance capacitor is connected with the anode of the charging diode, the other end of the balance capacitor is used as the input end of the charging unit, and the cathode of the charging diode is used as the output end of the charging unit;
And if one end of the balance capacitor is connected with the cathode of the charging diode, the other end of the balance capacitor is used as the output end of the charging unit, and the anode of the charging diode is used as the input end of the charging unit.
3. the three-level Buck circuit according to claim 2, further comprising: and the discharging unit is used for discharging the balance capacitor after the three-level Buck circuit is powered off.
4. The three-level Buck circuit according to claim 3, wherein said discharge unit comprises: a discharge diode;
if the negative electrode of the low-voltage side of the three-level Buck circuit is connected with the negative electrode of the high-voltage side of the three-level Buck circuit, the anode of the discharge diode is connected with the negative electrode of the low-voltage side and the negative electrode of the high-voltage side, and the cathode of the discharge diode is connected with the charged negative electrode of the balance capacitor;
If the low-voltage side anode of the three-level Buck circuit is connected with the high-voltage side anode of the three-level Buck circuit, the cathode of the discharge diode is connected with the low-voltage side anode and the high-voltage side anode, and the anode of the discharge diode is connected with the anode of the charged balance capacitor.
5. The three-level Buck circuit according to claim 1, wherein when the input voltage source connected to the three-level Buck circuit is a stable input voltage source, between the stable input voltage source and the input capacitor, the three-level Buck circuit further comprises: a current limiting unit;
And the current limiting unit is used for limiting the charging current of the parallel parasitic capacitor of the outer tube which is not connected with the charging unit when the three-level Buck circuit is connected to the input voltage source.
6. The three-level Buck circuit according to claim 5, wherein said current limiting unit comprises: the circuit comprises a first switch, a second switch and a current-limiting resistor;
The first switch is connected with the current-limiting resistor in series;
and the series branch of the first switch and the current-limiting resistor is connected with the second switch in parallel.
7. the three-level Buck circuit according to claim 1, wherein the number of the bridge arms is n, and n is a positive integer greater than or equal to 2.
8. The three-level Buck circuit according to any one of claims 1 to 7, wherein the inner tube and the outer tube connected to the charging unit are reverse conducting transistors respectively, and are in a staggered conducting state during normal operation;
The inner tube and the outer tube which are not connected with the charging unit are respectively a diode or a reverse conducting transistor.
9. A control method of a three-level Buck circuit, which is applied to the controller of the three-level Buck circuit according to any one of claims 1 to 8, the control method comprising:
Controlling the three-level Buck circuit to be connected to an input voltage source;
and when the difference between the voltage of the floating capacitor and half of the input voltage is reduced to be smaller than a threshold value, controlling the inner tube and the outer tube which are connected with the charging unit in the three-level Buck circuit to be conducted in a staggered mode.
10. The method for controlling the three-level Buck circuit according to claim 9, wherein the step of controlling the inner tube and the outer tube of the three-level Buck circuit, which are connected with the charging unit, to conduct alternately, comprises the steps of:
controlling the conduction of an outer pipe connected with the charging unit and the disconnection of an inner pipe connected with the charging unit to charge the floating capacitor of the three-level Buck circuit;
Controlling the inner pipe and the outer pipe which are connected with the charging unit to be turned off, and charging the suspension capacitor and the charging unit;
controlling the outer pipe connected with the charging unit to be switched off and the inner pipe connected with the charging unit to be switched on to charge the charging unit;
and returning to the step of controlling the conduction of the outer pipe connected with the charging unit and the disconnection of the inner pipe connected with the charging unit to charge the floating capacitor of the three-level Buck circuit until the voltage of the floating capacitor rises to be equal to half of the input voltage.
11. The method of controlling a three-level Buck circuit according to claim 9, wherein the controlling of the conduction of the inner tube and the outer tube of the three-level Buck circuit in a connection relationship with the charging unit alternately comprises the following three steps performed in a cycle after the voltage of the floating capacitor rises to equal to half of the input voltage:
controlling the conduction of an outer pipe connected with the charging unit and the disconnection of an inner pipe connected with the charging unit to charge the floating capacitor;
Controlling the inner pipe and the outer pipe which are connected with the charging unit to be turned off, so that the suspension capacitor and the charging unit are not charged and discharged;
And controlling the outer pipe connected with the charging unit to be switched off and the inner pipe connected with the charging unit to be switched on so as to discharge the suspension capacitor.
12. The method for controlling a three-level Buck circuit according to claim 9, wherein if the three-level Buck circuit includes a current limiting unit, after the controlling the three-level Buck circuit to be connected to an input voltage source, the method further comprises:
Controlling a first switch of the current limiting unit to be closed;
And when the difference between the voltage of the floating capacitor and half of the input voltage is reduced to be smaller than a threshold value, a second switch of the current limiting unit is controlled to be closed, and then the step of controlling the inner tube and the outer tube which are connected with the charging unit in the three-level Buck circuit to be conducted in a staggered mode is executed.
13. The method according to any one of claims 10 to 12, wherein if the inner tube and the outer tube which are not connected to the charging unit are field effect transistor MOS tubes, respectively, the method further comprises the step of controlling the inner tube and the outer tube which are connected to the charging unit in the three-level Buck circuit to be alternately turned on:
controlling two inner tubes and two outer tubes in the three-level Buck circuit to be in complementary conduction; or controlling the inner pipe and the outer pipe which are not connected with the charging unit to keep a closed state.
CN201910859287.6A 2019-09-11 2019-09-11 three-level Buck circuit and control method thereof Pending CN110545040A (en)

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