CN112311271A - Three-level bidirectional buck-boost AC/DC converter and control method thereof - Google Patents

Three-level bidirectional buck-boost AC/DC converter and control method thereof Download PDF

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CN112311271A
CN112311271A CN202011098423.3A CN202011098423A CN112311271A CN 112311271 A CN112311271 A CN 112311271A CN 202011098423 A CN202011098423 A CN 202011098423A CN 112311271 A CN112311271 A CN 112311271A
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switching tube
driving signal
frequency switching
tube driving
frequency
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CN112311271B (en
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郭小强
陈兆文
王怀宝
王宝诚
伞国成
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Yanshan University
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Yanshan University
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    • 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
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/66—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal
    • H02M7/68—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters
    • H02M7/72—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • 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
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
    • 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
    • H02M1/12—Arrangements for reducing harmonics from ac input or output
    • 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
    • H02M1/12—Arrangements for reducing harmonics from ac input or output
    • H02M1/126—Arrangements for reducing harmonics from ac input or output using passive filters
    • 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
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/66—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal
    • H02M7/68—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters
    • H02M7/72—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/79—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal 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
    • H02M7/797—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal 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
    • 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
    • H02M1/12—Arrangements for reducing harmonics from ac input or output
    • H02M1/123—Suppression of common mode voltage or current

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Inverter Devices (AREA)

Abstract

The invention relates to a three-level bidirectional buck-boost AC/DC converter which comprises a direct-current power supply, an alternating-current power supply, a first inductor, a second inductor, a first low-frequency switching tube, a second low-frequency switching tube, a first high-frequency switching tube, a second high-frequency switching tube, a third high-frequency switching tube, a fourth high-frequency switching tube, a fifth high-frequency switching tube, a sixth high-frequency switching tube, a seventh high-frequency switching tube, an eighth high-frequency switching tube, a first capacitor, a second capacitor, a third capacitor, a fourth capacitor, a first voltage sensor, a second voltage sensor, a third voltage sensor, a first current sensor, a second current sensor and a third current sensor. The bidirectional flow of energy on the direct current side and the alternating current side and the current sine degree of the alternating current side can be ensured through modulation, and bidirectional voltage boosting and reducing can be realized. The invention can effectively reduce high-frequency common mode voltage and leakage current, overcomes the defect of large stress of the traditional buck-boost topological switch tube, can effectively reduce the ripple value of inductive current compared with two levels, and improves the efficiency.

Description

Three-level bidirectional buck-boost AC/DC converter and control method thereof
Technical Field
The invention belongs to the technical field of converters, and particularly relates to a three-level bidirectional buck-boost AC/DC converter and a control method thereof.
Background
The AC/DC bidirectional converter integrates two basic converters of AC-DC and DC-AC, wherein the AC-DC converter is a rectifier for converting alternating current into direct current, and the DC-AC converter is an inverter for converting the direct current into the alternating current.
Conventional bidirectional AC/DC converters are usually based on Buck circuits, Boost circuits only, and therefore have only Boost or Buck functions; the Buck-Boost AC/DC converter based on the Buck-Boost circuit generally has the defects of large voltage stress of a switching tube, discontinuous current on the alternating current input side and the like, and simultaneously, due to the high-frequency switching action of the switching tube, a high-frequency common-mode voltage can be generated between the negative polarity end of the direct current side and the reference ground end of the alternating current side, so that a large leakage current is generated, the safety performance and the inversion efficiency of an inversion system are reduced, and the safety of related equipment and personnel can be endangered even in serious cases. Therefore, it is necessary to design a bidirectional buck-boost AC/DC converter with small voltage stress of the switching tube, continuous current on the alternating current side and effective suppression of common mode voltage.
Disclosure of Invention
In view of the above situation, the invention provides a three-level bidirectional buck-boost AC/DC converter, which has the advantages of effectively reducing the voltage stress of a switching tube of a buck-boost circuit, realizing the continuity of alternating-current side current, inhibiting high-frequency common-mode voltage and leakage current and the like.
The technical scheme adopted by the invention is that the three-level bidirectional buck-boost AC/DC converter comprises a direct-current power supply, an alternating-current power supply, a first inductor, a second inductor, a first low-frequency switching tube, a second low-frequency switching tube, a first high-frequency switching tube, a second high-frequency switching tube, a third high-frequency switching tube, a fourth high-frequency switching tube, a fifth high-frequency switching tube, a sixth high-frequency switching tube, a seventh high-frequency switching tube, an eighth high-frequency switching tube, a first capacitor, a second capacitor, a third capacitor, a fourth capacitor, a first voltage sensor, a second voltage sensor, a third voltage sensor, a first current sensor, a second current sensor and a third current sensor, wherein the L end of the alternating-current power supply is respectively connected with the emitter of the first low-frequency switching tube, the drain of the first high-frequency switching tube and the input end of the first voltage sensor, and the N end of the alternating-current power supply is respectively connected with the emitter of the second low-frequency switching tube, the drain of, The drain electrode of the second high-frequency switching tube is connected with the output end of the first voltage sensor; the source electrode of the first high-frequency switching tube is respectively connected with the input end of the first current sensor and the drain electrode of the third high-frequency switching tube, and the source electrode of the second high-frequency switching tube is respectively connected with the input end of the second current sensor and the drain electrode of the fourth high-frequency switching tube; the output end of the first current sensor is connected with the output end of the first inductor, and the output end of the second current sensor is connected with the output end of the second inductor; the input end of the first capacitor is respectively connected with the collector of the first low-frequency switching tube, the collector of the second low-frequency switching tube and the input end of the second voltage sensor, and the output end of the first capacitor is respectively connected with the input end of the second capacitor, the output end of the third capacitor, the input end of the fourth capacitor, the output end of the second voltage sensor and the input end of the third voltage sensor; the output end of the second capacitor is respectively connected with the source electrode of the fifth high-frequency switching tube, the source electrode of the sixth high-frequency switching tube and the output end of the third voltage sensor; the drain electrode of the fifth high-frequency switching tube is respectively connected with the input end of the second inductor and the source electrode of the eighth high-frequency switching tube, and the drain electrode of the sixth high-frequency switching tube is respectively connected with the input end of the first inductor and the source electrode of the seventh high-frequency switching tube; the positive electrode of the direct current power supply is connected with the output end of the third current sensor, and the negative electrode of the direct current power supply is respectively connected with the source electrode of the third high-frequency switching tube, the source electrode of the fourth high-frequency switching tube and the output end of the fourth capacitor; and the input end of the third current sensor is respectively connected with the drain electrode of the seventh high-frequency switching tube, the drain electrode of the eighth high-frequency switching tube and the input end of the third capacitor.
Preferably, the capacitance values of the first capacitor and the second capacitor are the same, the capacitance values of the third capacitor and the fourth capacitor are the same, and the inductance values of the first inductor and the second inductor are equal.
Preferably, the first low-frequency switching tube, the second low-frequency switching tube, the first high-frequency switching tube, the second high-frequency switching tube, the third high-frequency switching tube, the fourth high-frequency switching tube, the fifth high-frequency switching tube, the sixth high-frequency switching tube, the seventh high-frequency switching tube and the eighth high-frequency switching tube are all fully-controlled devices.
Preferably, the control method further comprises performing high-low level modulation on the first low-frequency switching tube and the second low-frequency switching tube, wherein a gate of the first low-frequency switching tube inputs a first low-frequency switching tube driving signal, and a gate of the second low-frequency switching tube inputs a second low-frequency switching tube driving signal; in the positive half period of the alternating current power supply, the driving signal of the first low-frequency switching tube is at a high level, and the driving signal of the second low-frequency switching tube is at a low level; in the negative half period of the alternating current power supply, the driving signal of the first low-frequency switching tube is at a low level, and the driving signal of the second low-frequency switching tube is at a high level.
Preferably, the PWM modulation is performed by the first high-frequency switch tube, the second high-frequency switch tube, the third high-frequency switch tube, the fourth high-frequency switch tube, the fifth high-frequency switch tube, the sixth high-frequency switch tube, the seventh high-frequency switch tube and the eighth high-frequency switch tube, the gate of the first high-frequency switch tube is inputted with the first high-frequency switch tube driving signal, the gate of the second high-frequency switch tube is inputted with the second high-frequency switch tube driving signal, the gate of the third high-frequency switch tube is inputted with the third high-frequency switch tube driving signal, the gate of the fourth high-frequency switch tube is inputted with the fourth high-frequency switch tube driving signal, the gate of the fifth high-frequency switch tube is inputted with the fifth high-frequency switch tube driving signal, the gate of the sixth high-frequency switch tube is inputted with the sixth high-frequency switch tube driving signal, and the gate of the seventh high-frequency switch tube is inputted with the seventh high-frequency switch tube driving signal, and a grid electrode of the eighth high-frequency switching tube inputs an eighth high-frequency switching tube driving signal.
Preferably, when the three-level bidirectional buck-boost AC/DC converter operates in a rectification mode, i.e., energy is transferred from the AC power source to the DC power source, the PWM modulation sequentially performs a first operation mode, a second operation mode, a third operation mode, and a fourth operation mode during a positive half cycle of the AC power source; in the negative half period of the alternating current power supply, the PWM modulation sequentially executes a fifth working mode, a sixth working mode, a seventh working mode and an eighth working mode; the first working mode comprises that the first high-frequency switching tube driving signal, the second high-frequency switching tube driving signal, the fifth high-frequency switching tube driving signal and the sixth high-frequency switching tube driving signal are at high level, and the third high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the seventh high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level; the second working mode comprises that the first high-frequency switching tube driving signal, the second high-frequency switching tube driving signal and the fifth high-frequency switching tube driving signal are at high level, and the third high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the sixth high-frequency switching tube driving signal, the seventh high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level; the third working mode comprises that the second high-frequency switching tube driving signal, the fifth high-frequency switching tube driving signal and the sixth high-frequency switching tube driving signal are at high level, and the first high-frequency switching tube driving signal, the third high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the seventh high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level; the fourth working mode comprises that the second high-frequency switching tube driving signal and the fifth high-frequency switching tube driving signal are at high level, and the first high-frequency switching tube driving signal, the third high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the sixth high-frequency switching tube driving signal, the seventh high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level; the fifth working mode comprises that the first high-frequency switching tube driving signal, the second high-frequency switching tube driving signal, the fifth high-frequency switching tube driving signal and the sixth high-frequency switching tube driving signal are at high level, and the third high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the seventh high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level; the sixth working mode comprises that the first high-frequency switching tube driving signal, the second high-frequency switching tube driving signal and the sixth high-frequency switching tube driving signal are at high level, and the third high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the fifth high-frequency switching tube driving signal, the seventh high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level; the seventh working mode comprises that the first high-frequency switching tube driving signal, the fifth high-frequency switching tube driving signal and the sixth high-frequency switching tube driving signal are at high level, and the second high-frequency switching tube driving signal, the third high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the seventh high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level; the eighth working mode comprises that the first high-frequency switching tube driving signal and the sixth high-frequency switching tube driving signal are at high level, and the second high-frequency switching tube driving signal, the third high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the fifth high-frequency switching tube driving signal, the seventh high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level.
When the three-level bidirectional buck-boost AC/DC converter works in an inversion mode, namely energy is transmitted from the direct-current power supply to the alternating-current power supply, in a positive half period of the alternating-current power supply, the PWM modulation sequentially executes a ninth working mode, a tenth working mode, an eleventh working mode and a twelfth working mode; in the negative half period of the alternating current power supply, the PWM modulation sequentially executes a thirteenth working mode, a fourteenth working mode, a fifteenth working mode and a sixteenth working mode; the ninth working mode comprises that the second high-frequency switching tube driving signal, the third high-frequency switching tube driving signal, the fifth high-frequency switching tube driving signal and the seventh high-frequency switching tube driving signal are at high level, and the first high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the sixth high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level; the tenth working mode comprises that the second high-frequency switching tube driving signal, the fifth high-frequency switching tube driving signal and the seventh high-frequency switching tube driving signal are at high level, and the first high-frequency switching tube driving signal, the third high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the sixth high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level; the eleventh working mode comprises that the second high-frequency switching tube driving signal, the third high-frequency switching tube driving signal and the fifth high-frequency switching tube driving signal are at high level, and the first high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the sixth high-frequency switching tube driving signal, the seventh high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level; the twelfth working mode comprises that the second high-frequency switching tube driving signal and the fifth high-frequency switching tube driving signal are at high level, and the first high-frequency switching tube driving signal, the third high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the sixth high-frequency switching tube driving signal, the seventh high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level; the thirteenth working mode comprises that the first high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the sixth high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at high level, and the second high-frequency switching tube driving signal, the third high-frequency switching tube driving signal, the fifth high-frequency switching tube driving signal and the seventh high-frequency switching tube driving signal are at low level; the fourteenth working mode comprises that the first high-frequency switching tube driving signal, the sixth high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at high level, and the second high-frequency switching tube driving signal, the third high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the fifth high-frequency switching tube driving signal and the seventh high-frequency switching tube driving signal are at low level; the fifteenth working mode comprises that the first high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal and the sixth high-frequency switching tube driving signal are at high level, and the second high-frequency switching tube driving signal, the third high-frequency switching tube driving signal, the fifth high-frequency switching tube driving signal, the seventh high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level; the sixteenth working mode comprises that the first high-frequency switching tube driving signal and the sixth high-frequency switching tube driving signal are at high level, and the second high-frequency switching tube driving signal, the third high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the fifth high-frequency switching tube driving signal, the seventh high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level.
Preferably, in the first operating mode, the second operating mode, the third operating mode, the fourth operating mode, the fifth operating mode, the sixth operating mode, the seventh operating mode and the eighth operating mode, the PWM modulation specifically includes the following steps:
and S11, acquiring a rectification mode network side current reference value by double closed-loop control.
S111, subtracting a value of the third current sensor from a power supply current reference value of the given direct-current power supply, and obtaining a current reference value through a first proportional integral controller according to the obtained value;
and S112, multiplying the unit sinusoidal signal which is acquired by the first voltage sensor and has the same frequency and phase as the alternating current power supply by the current reference value to obtain a network side current reference value.
And S12, obtaining a first duty ratio through an active damping link.
S121, subtracting the grid-side current reference value from the grid-side current, and obtaining a first voltage reference value through a second proportional-integral controller, wherein the grid-side current is the value of the second current sensor in the first working mode, the second working mode, the third working mode and the fourth working mode; under the fifth working mode, the sixth working mode, the seventh working mode and the eighth working mode, the grid side current is the value of the first current sensor;
s122, subtracting the sum of the data of the second voltage sensor and the data of the third voltage sensor from the data of the first voltage sensor to obtain a first voltage comparison result; subtracting the data of the second voltage sensor from the data of the third voltage sensor to obtain a second voltage comparison result;
and S123, subtracting the comparison result of the first voltage from the reference value of the first voltage to obtain a first duty ratio.
S13, setting the first sawtooth wave as a signal with amplitude of 1 and frequency of 1/T, setting the second sawtooth wave as a signal with amplitude of 1, frequency of 1/T and phase lag of 180 degrees of the first sawtooth wave, balancing input capacitance voltage, and obtaining a first driving signal and a second driving signal.
S131, subtracting the comparison result of the first duty ratio and the second voltage to obtain a second duty ratio; adding the first duty ratio and the second voltage comparison result to obtain a third duty ratio
S132, comparing the second duty ratio with the first sawtooth wave, and when the second duty ratio is greater than or equal to the first sawtooth wave, the first driving signal is at a high level; when the second duty ratio is smaller than the first sawtooth wave, the first driving signal is at a low level;
and S133, comparing the third duty ratio with the second sawtooth wave, wherein when the third duty ratio is greater than or equal to the second sawtooth wave, the second driving signal is at a high level, and when the third duty ratio is less than the second sawtooth wave, the second driving signal is at a low level.
And S14, switching on the first driving signal and the second driving signal to corresponding positions respectively.
And S141, when the alternating current power supply voltage is positive, the first driving signal is connected with the grid electrode of the first high-frequency switching tube, and the second driving signal is connected with the grid electrode of the sixth high-frequency switching tube. At the moment, the first low-frequency switching tube, the second high-frequency switching tube and the fifth high-frequency switching tube are switched on, and the second low-frequency switching tube is switched off;
and S142, when the alternating current power supply voltage is negative, the first driving signal is connected with the grid electrode of the second high-frequency switching tube, and the second driving signal is connected with the grid electrode of the fifth high-frequency switching tube. At the moment, the first low-frequency switching tube is turned off, and the first high-frequency switching tube and the sixth high-frequency switching tube of the second low-frequency switching tube are turned on.
And S15, detecting the alternating voltage, and repeating the operations from S11 to S14 to realize the transfer of energy from the alternating current side to the direct current side.
Preferably, in the ninth operating mode, the tenth operating mode, the eleventh operating mode, the twelfth operating mode, the thirteenth operating mode, the fourteenth operating mode, the fifteenth operating mode and the sixteenth operating mode, the PWM modulation specifically includes the following steps:
s21, acquiring the reference value of the lifting piezoelectric induction current of the inversion mode by the double closed loops: and subtracting the product of the given network side current reference value and the network side unit sinusoidal signal from the network side current, and multiplying the product by the network side unit sinusoidal signal after passing through the first proportional resonant controller to obtain the buck-boost inductive current reference value.
And S22, balancing the voltage of the output capacitor, and acquiring a fourth duty ratio and a fifth duty ratio.
S221, subtracting the buck-boost inductive current from the buck-boost inductive current to obtain a second voltage reference, where in the ninth working mode, the tenth working mode, the eleventh working mode, and the twelfth working mode, the buck-boost inductive current is a value of the first current sensor; in the thirteenth working mode, the fourteenth working mode, the fifteenth working mode and the sixteenth working mode, the lifting piezoelectric induction current is the value of the second current sensor;
s222, subtracting the data of the second voltage sensor from the data of the third voltage sensor to obtain a second voltage comparison result; and adding the second voltage reference value and the second voltage comparison result to obtain a fourth duty ratio, and subtracting the second voltage reference value and the second voltage comparison result to obtain a fifth duty ratio.
S23, acquiring a third driving signal and a fourth driving signal:
s231, comparing the fourth duty ratio with the first sawtooth wave, and when the fourth duty ratio is greater than or equal to the first sawtooth wave, enabling the third driving signal to be at a high level; when the fourth duty ratio is smaller than the first sawtooth wave, the third driving signal is at a low level;
s231, comparing the fifth duty ratio with the second sawtooth wave, and when the fifth duty ratio is greater than or equal to the second sawtooth wave, enabling the fourth driving signal to be at a high level; when the fifth duty ratio is less than the second saw-tooth wave, the fourth driving signal is at a low level.
And S24, switching on the third driving signal and the fourth driving signal to corresponding positions respectively.
And S241, when the voltage of the alternating current power supply is positive, a third driving signal is connected with the grid electrode of the third high-frequency switching tube, and a fourth driving signal is connected with the grid electrode of the seventh high-frequency switching tube. At the moment, the first low-frequency switching tube, the second high-frequency switching tube and the fifth high-frequency switching tube are switched on, and the second low-frequency switching tube is switched off;
and S242, when the voltage of the alternating current power supply is negative, a third driving signal is connected with the grid electrode of the fourth high-frequency switching tube, and a fourth driving signal is connected with the grid electrode of the eighth high-frequency switching tube. At the moment, the first low-frequency switching tube is turned off, and the second low-frequency switching tube, the first high-frequency switching tube and the sixth high-frequency switching tube are turned on.
And S25, detecting the alternating voltage, and repeating the operations from S21 to S24 to realize the transfer of energy from the direct current side to the alternating current side.
The invention has the characteristics and beneficial effects that:
1. according to the three-level bidirectional buck-boost AC/DC converter provided by the invention, the topological structure of the bidirectional AC/DC converter has the characteristics of small voltage stress of the switching tube, continuous alternating current side current and the like, high-frequency common mode voltage and leakage current can be effectively inhibited, the inductor ripple current is small, and the overall efficiency is favorably improved.
2. The three-level bidirectional buck-boost AC/DC converter provided by the invention has the advantages that the three-level structure circuit is beneficial to reducing the volume of the magnetic element, and has important significance for improving the power density of a system.
Drawings
FIG. 1 is a schematic diagram of the overall topology of a three-level bidirectional buck-boost AC/DC converter of the present invention;
FIG. 2 is a flow chart of a forward control method of the present invention;
FIG. 3 is a flow chart of a reverse control method of the present invention;
FIG. 4 is a schematic diagram of a control method of the present invention;
FIG. 5 is a schematic diagram of the operation of the positive half cycle of the AC power source in the rectification mode of the present invention;
FIG. 6 is a schematic diagram of the operation of the negative half cycle of the AC power source in the rectification mode of the present invention;
FIG. 7 is a schematic diagram of the operation of the positive half cycle of the AC power supply in the inversion mode according to the present invention;
FIG. 8 is a schematic diagram illustrating the operation of the negative half cycle of the AC power supply in the inversion mode according to the present invention;
FIG. 9 is a schematic diagram of the driving signal generation of the present invention;
FIG. 10A is a schematic diagram of driving signals in a rectifying mode according to the present invention; and
fig. 10B is a schematic diagram of driving signals in the inversion mode according to the present invention.
In the figure:
VG-an alternating current power source; vDC-a direct current power supply; l1 — first inductance; l2 — second inductance; sL1-a first low frequency switching tube; sL2-a second low frequency switching tube; s1-a first high frequency switching tube; s2-a second high frequency switching tube; s3-a third high frequency switching tube; s4-a fourth high frequency switching tube; s5-a fifth high frequency switching tube; s6-a sixth high frequency switching tube; s7-a seventh high frequency switching tube; s8-an eighth high frequency switching tube; c1 — first capacitance; c2 — second capacitance; c3-third capacitance and C4-fourth capacitance; VT1 — first voltage sensor; VT2 — second voltage sensor; -VT3 third voltage sensor; CT1 — first current sensor; CT2 — second current sensor; CT3 — third current sensor; CONT1 — first drive signal; CONT2 — first drive signal; CONT3 — first drive signal; CONT 4-first drive signal.
Detailed Description
The technical contents, structural features, attained objects and effects of the present invention are explained in detail below with reference to the accompanying drawings.
The three-level bidirectional buck-boost AC/DC converter provided by the invention comprises a direct-current power supply V as shown in figure 1DCAC power supply VGA first inductor L1Second, secondInductor L2A first low frequency switch tube SL1A second low frequency switch tube SL2A first high-frequency switch tube S1A second high-frequency switch tube S2And the third high-frequency switch tube S3And a fourth high-frequency switch tube S4The fifth high frequency switch tube S5Sixth high frequency switch tube S6Seventh high frequency switch tube S7Eighth high frequency switch tube S8A first capacitor C1A second capacitor C2A third capacitor C3A fourth capacitor C4A first voltage sensor VT1, a second voltage sensor VT2, a third voltage sensor VT3, a first current sensor CT1, a second current sensor CT2 and a third current sensor CT3, an alternating current power supply VGL ends of the first and second low-frequency switching tubes SL1Emitter electrode of (1), first high-frequency switching tube S1Is connected with the input end of a first voltage sensor VT1, and the N ends of the first voltage sensor VT1 are respectively connected with a second low-frequency switching tube SL2Emitter electrode of, second high-frequency switching tube S2Is connected to the output of the first voltage sensor VT 1; a first high-frequency switch tube S1Respectively with the input terminal of the first current sensor CT1 and the third high-frequency switching tube S3Is connected to the drain of the second high-frequency switching tube S2Respectively with the input of the second current sensor CT2 and the fourth high-frequency switching tube S4Is connected with the drain electrode of the transistor; the output of the first current sensor CT1 and the first inductance L1Is connected to the output of the second current sensor CT2 and the second inductance L2The output ends of the two-way valve are connected; a first capacitor C1Respectively connected with the first low-frequency switching tube SL1Collector electrode of the first low-frequency switching tube SL2Is connected to the input of a second voltage sensor VT2, the output of which is connected to a second capacitor C, respectively2Input terminal of, third capacitor C3Output terminal of, fourth capacitor C4Is connected to the input of a third voltage sensor VT3, to the output of a second voltage sensor VT 2; second capacitor C2Respectively connected with the fifth high-frequency switch tube S5Source electrode of (1), sixth high frequency switching tube S6And the output of the third voltage sensor VT3End connection; fifth high-frequency switch tube S5Respectively with the second inductor L2And an eighth high-frequency switching tube S8Is connected to the source of the sixth high-frequency switching tube S6Respectively with the first inductor L1And a seventh high-frequency switching tube S7Is connected to the source of (a); DC power supply VDCIs connected with the output end of a third current sensor CT3, and the negative electrodes of the current sensors are respectively connected with a third high-frequency switching tube S3Source electrode of, fourth high frequency switching tube S4Source electrode of and fourth capacitor C4The output ends of the two-way valve are connected; the input end of the third current sensor CT3 is respectively connected with the seventh high-frequency switch tube S7Drain electrode of (1), eighth high frequency switching tube S8Drain electrode of and third capacitor C3Is connected to the input terminal of the controller.
In the three-level bidirectional buck-boost AC/DC converter circuit topology provided by the invention, the first inductor L1 and the second inductor L2 respectively form a buck-boost inductor and a network side inductor, so that the circuit has buck-boost capacity and the alternating current side current is continuous; from the circuit structure, the high-voltage end of the alternating current power supply is always connected with the positive electrode of the direct current side through the first capacitor C1 or the second capacitor C2, and the purpose of suppressing leakage current can be achieved by suppressing the high-frequency quantity of the voltage of the first capacitor C1 and the voltage of the second capacitor C2.
The voltage stress of a switching tube of a conventional Buck-Boost circuit-based AC/DC converter is the sum of input voltage and output voltage, and the embodiment is based on a three-level Buck-Boost converter, so that a first high-frequency switching tube S1A second high-frequency switch tube S2And the third high-frequency switch tube S3And a fourth high-frequency switch tube S4The fifth high frequency switch tube S5Sixth high frequency switch tube S6Seventh high frequency switch tube S7And an eighth high-frequency switching tube S8The maximum voltage stress of which is an alternating current power supply VGMaximum voltage and DC power supply VDCHalf of the sum of the voltages.
For system stability and uniform current distribution, the first inductor L1 is preferably equal to the second inductor L2 when selecting the inductor, and the first capacitor C1 is preferably equal to the second capacitor C2 and the third capacitor C3 is preferably equal to the fourth capacitor C4 when selecting the capacitor, although of courseThe invention is not limited to the inductance and capacitance values, and is determined according to actual needs; first low frequency switch tube SL1And a second low frequency switching tube SL2Are all fully controlled devices, preferably IGBT (Insulated Gate Bipolar Transistor), a first high frequency switching tube S1A second high-frequency switch tube S2And the third high-frequency switch tube S3And a fourth high-frequency switch tube S4The fifth high frequency switch tube S5Sixth high frequency switch tube S6Seventh high frequency switch tube S7And an eighth high-frequency switching tube S8Are all fully-controlled devices, preferably Metal-Oxide-Semiconductor Field-Effect transistors (MOSFETs).
Based on the three-level bidirectional buck-boost AC/DC converter provided by the invention, a corresponding control method is provided, and the control method comprises a first low-frequency switching tube SL1And a second low frequency switching tube SL2High-low level modulation is carried out, and a first low-frequency switching tube SL1The grid electrode inputs a first low-frequency switching tube driving signal QL1Second low frequency switch tube SL2The grid electrode inputs a second low-frequency switching tube driving signal QL2(ii) a In an AC power supply VGOf the first low-frequency switching tube drive signal QL1At high level, the second low-frequency switch tube drives the signal QL2Is low level; in an AC power supply VGNegative half period of (1), first low frequency switching tube drive signal QL1At low level, the second low-frequency switch tube drives the signal QL2Is at a high level; at the same time, the device also comprises a first high-frequency switch tube S1A second high-frequency switch tube S2And the third high-frequency switch tube S3And a fourth high-frequency switch tube S4The fifth high frequency switch tube S5Sixth high frequency switch tube S6Seventh high frequency switch tube S7And an eighth high-frequency switching tube S8Performing PWM modulation, and switching tube S1The grid electrode inputs a first high-frequency switching tube driving signal Q1A second high-frequency switching tube S2The grid electrode of the first high-frequency switching tube is input with a second high-frequency switching tube driving signal Q2The third high frequency switch tube S3Grid input third high frequency switchTube driving signal Q3Fourth high frequency switching tube S4The grid electrode of the grid electrode inputs a fourth high-frequency switching tube driving signal Q4Fifth high frequency switch tube S5The grid electrode of the grid electrode inputs a fifth high-frequency switching tube driving signal Q5Sixth high frequency switching tube S6The grid electrode of the grid electrode inputs a sixth high-frequency switching tube driving signal Q6Seventh high frequency switching tube S7The grid electrode of the grid electrode inputs a seventh high-frequency switching tube driving signal Q7Eighth high frequency switch tube S8The grid electrode inputs an eighth high-frequency switching tube driving signal Q8。
In order to ensure the bidirectional buck-boost characteristic of the three-level bidirectional buck-boost AC/DC converter topology provided by the invention, two high-frequency switching tubes are required to be ensured to be in high-frequency switching action and be continuously conducted during working. Therefore, the three-level bidirectional buck-boost AC/DC converter has sixteen working modes of PWM (pulse-width modulation) during working, and the working modes are as follows:
when the three-level bidirectional buck-boost AC/DC converter operates in the rectification mode, i.e. energy is supplied from the AC power supply VGTo a DC power supply VDCDuring transmission, in an AC power supply VGAs shown in fig. 5, the PWM modulation sequentially performs the first operation mode M1A second operating mode M2A third operating mode M3And a fourth operating mode M4(ii) a In an AC power supply VGAs shown in fig. 6, the PWM modulation sequentially performs a fifth operation mode M5And a sixth operating mode M6And a seventh operating mode M7And an eighth operating mode M8(ii) a First mode of operation M1Comprises a first high-frequency switch tube driving signal Q1A second high frequency switch tube driving signal Q2A fifth high frequency switching tube driving signal Q5And a sixth high frequency switching tube driving signal Q6At high level, the third high-frequency switch tube drives the signal Q3A fourth high frequency switching tube driving signal Q4A seventh high frequency switching tube driving signal Q7And an eighth high frequency switching tube driving signal Q8Is low level; second mode of operation M2Comprises a first high-frequency switch tube driving signal Q1The first stepTwo high frequency switch tube driving signal Q2And a fifth high-frequency switching tube driving signal Q5At high level, the third high-frequency switch tube drives the signal Q3A fourth high frequency switching tube driving signal Q4A sixth high frequency switching tube driving signal Q6A seventh high frequency switching tube driving signal Q7And an eighth high frequency switching tube driving signal Q8Is low level; third mode of operation M3Comprising a second high-frequency switching tube drive signal Q2A fifth high frequency switching tube driving signal Q5And a sixth high frequency switching tube driving signal Q6At high level, the first high-frequency switch tube drives the signal Q1And a third high-frequency switching tube driving signal Q3A fourth high frequency switching tube driving signal Q4A seventh high frequency switching tube driving signal Q7And an eighth high frequency switching tube driving signal Q8Is low level; fourth mode of operation M4Comprising a second high-frequency switching tube drive signal Q2And a fifth high-frequency switching tube driving signal Q5At high level, the first high-frequency switch tube drives the signal Q1And a third high-frequency switching tube driving signal Q3A fourth high frequency switching tube driving signal Q4A sixth high frequency switching tube driving signal Q6A seventh high frequency switching tube driving signal Q7And an eighth high frequency switching tube driving signal Q8Is low level; fifth mode of operation M5Comprises a first high-frequency switch tube driving signal Q1A second high frequency switch tube driving signal Q2A fifth high frequency switching tube driving signal Q5A sixth high frequency switching tube driving signal Q6At high level, the third high-frequency switch tube drives the signal Q3A fourth high frequency switching tube driving signal Q4A seventh high frequency switching tube driving signal Q7And an eighth high frequency switching tube driving signal Q8Is low level; sixth operating mode M6Comprises a first high-frequency switch tube driving signal Q1A second high frequency switch tube driving signal Q2A sixth high frequency switching tube driving signal Q6At high level, the third high-frequency switch tube drives the signal Q3A fourth high frequency switching tube driving signal Q4A fifth high frequency switching tube driving signalQ5A seventh high frequency switching tube driving signal Q7And an eighth high frequency switching tube driving signal Q8Is low level; seventh operating mode M7Comprises a first high-frequency switch tube driving signal Q1A fifth high frequency switching tube driving signal Q5A sixth high frequency switching tube driving signal Q6At a high level, a second high-frequency switch tube drives a signal Q2And a third high-frequency switching tube driving signal Q3A fourth high frequency switching tube driving signal Q4A seventh high frequency switching tube driving signal Q7And an eighth high frequency switching tube driving signal Q8Is low level; eighth mode of operation M8Comprises a first high-frequency switch tube driving signal Q1And a sixth high frequency switching tube driving signal Q6At a high level, a second high-frequency switch tube drives a signal Q2And a third high-frequency switching tube driving signal Q3A fourth high frequency switching tube driving signal Q4A fifth high frequency switching tube driving signal Q5A seventh high frequency switching tube driving signal Q7And an eighth high frequency switching tube driving signal Q8Is low.
When the three-level bidirectional buck-boost AC/DC converter works in an inversion mode, namely energy is converted from a direct current power supply VDCTo an alternating current source VGDuring transmission, in an AC power supply VGAs shown in fig. 7, the PWM modulation sequentially performs the ninth operation mode M9The tenth operating mode M10Eleventh operating mode M11And a twelfth operating mode M12(ii) a In an AC power supply VGNegative half-cycles of (1), as shown in fig. 8, the PWM modulation sequentially performs a thirteenth operation mode M13Fourteenth operating mode M14Fifteenth operating mode M15And a sixteenth mode of operation M16(ii) a Ninth operating mode M9Comprising a second high-frequency switching tube drive signal Q2And a third high-frequency switching tube driving signal Q3A fifth high frequency switching tube driving signal Q5And a seventh high frequency switching tube driving signal Q7At high level, the first high-frequency switch tube drives the signal Q1A fourth high frequency switching tube driving signal Q4A sixth high frequency switching tube driving signal Q6And an eighth high frequency switching tube driving signal Q8Is low level; tenth operating mode M10Comprising a second high-frequency switching tube drive signal Q2A fifth high frequency switching tube driving signal Q5And a seventh high frequency switching tube driving signal Q7At high level, the first high-frequency switch tube drives the signal Q1And a third high-frequency switching tube driving signal Q3A fourth high frequency switching tube driving signal Q4A sixth high frequency switching tube driving signal Q6And an eighth high frequency switching tube driving signal Q8Is low level; eleventh operating mode M11Comprising a second high-frequency switching tube drive signal Q2And a third high-frequency switching tube driving signal Q3And a fifth high-frequency switching tube driving signal Q5At high level, the first high-frequency switch tube drives the signal Q1A fourth high frequency switching tube driving signal Q4A sixth high frequency switching tube driving signal Q6A seventh high frequency switching tube driving signal Q7And an eighth high frequency switching tube driving signal Q8Is low level; twelfth operating mode M12Comprising a second high-frequency switching tube drive signal Q2And a fifth high-frequency switching tube driving signal Q5At high level, the first high-frequency switch tube drives the signal Q1And a third high-frequency switching tube driving signal Q3A fourth high frequency switching tube driving signal Q4A sixth high frequency switching tube driving signal Q6A seventh high frequency switching tube driving signal Q7And an eighth high frequency switching tube driving signal Q8Is low level; thirteenth operating mode M13Comprises a first high-frequency switch tube driving signal Q1A fourth high frequency switching tube driving signal Q4A sixth high frequency switching tube driving signal Q6And an eighth high frequency switching tube driving signal Q8At a high level, a second high-frequency switch tube drives a signal Q2And a third high-frequency switching tube driving signal Q3A fifth high frequency switching tube driving signal Q5And a seventh high frequency switching tube driving signal Q7Is low level; fourteenth operating mode M14Comprises a first high-frequency switch tube driving signal Q1A sixth high frequency switching tube driving signal Q6And eighth highFrequency switching tube driving signal Q8At a high level, a second high-frequency switch tube drives a signal Q2And a third high-frequency switching tube driving signal Q3A fourth high frequency switching tube driving signal Q4A fifth high frequency switching tube driving signal Q5And a seventh high frequency switching tube driving signal Q7Is low level; fifteenth operating mode M15Comprises a first high-frequency switch tube driving signal Q1A fourth high frequency switching tube driving signal Q4And a sixth high frequency switching tube driving signal Q6At a high level, a second high-frequency switch tube drives a signal Q2And a third high-frequency switching tube driving signal Q3A fifth high frequency switching tube driving signal Q5Seventh high frequency switch tube Q7And an eighth high frequency switching tube driving signal Q8Is low level; sixteenth mode of operation M16Comprises a first high-frequency switch tube driving signal Q1And a sixth high frequency switching tube driving signal Q6At a high level, a second high-frequency switch tube drives a signal Q2And a third high-frequency switching tube driving signal Q3A fourth high frequency switching tube driving signal Q4A fifth high frequency switching tube driving signal Q5A seventh high frequency switching tube driving signal Q7And an eighth high frequency switching tube driving signal Q8Is low.
As shown in FIG. 2, when the three-level bidirectional buck-boost AC/DC converter operates in the rectification mode, i.e., in the first operation mode M1A second operating mode M2A third operating mode M3And a fourth operation mode M4The fifth operating mode M5And a sixth operating mode M6And a seventh operating mode M7And an eighth operating mode M8Next, the PWM modulation specifically includes the steps of:
s11, obtaining a rectification mode network side current reference value i by double closed loop controlG*。
S111, setting a direct current power supply VDCSubtracting the value of the third current sensor CT3 from the power supply current reference value I, and obtaining a current reference value I from the obtained value through a first proportional integral controller;
s112, sensing the first voltageCollected by the CT1 and connected with an alternating current power supply VGMultiplying unit sinusoidal signals with same frequency and phase with a current reference value i to obtain a grid-side current reference value iG*。
S12, obtaining a first duty ratio D1, a second duty ratio D2 and a third duty ratio D3 through an active damping link.
S121, network side current reference value iGAnd net side current iGSubtracting, and obtaining a first voltage reference value U by a second proportional-integral controllerREF1Wherein in the first, second, third and fourth operating modes the grid side current iGIs the value of the second current sensor CT 2; under a fifth working mode, a sixth working mode, a seventh working mode and an eighth working mode, the network side current iGIs the value of the first current sensor CT 1;
s122, subtracting the sum of the data of the second voltage sensor VT2 and the data of the third voltage sensor VT3 from the data of the first voltage sensor VT1 to obtain a first voltage comparison result delta v1(ii) a Subtracting the data of the second voltage sensor VT2 from the data of the third voltage sensor VT3 to obtain a second voltage comparison result Δ v2；
S123, converting the first voltage reference value UREF1Comparison result Δ v with the first voltage1The subtraction results in the first duty cycle D1.
S13, as shown in FIG. 9, the first sawtooth wave is set to be a signal with amplitude of 1 and frequency of 1/T, the second sawtooth wave is a signal with amplitude of 1 and frequency of 1/T and phase lag of 180 degrees of the first sawtooth wave, the input capacitor voltage is balanced, and the first driving signal CONT1 and the second driving signal CONT2 are obtained.
S131, comparing the first duty ratio D1 with the second voltage2Subtracting to obtain a second duty ratio D2; comparing the first duty ratio D1 with the second voltage Δ v2Adding to obtain a third duty ratio D3;
s132, comparing the second duty ratio D2 with the first sawtooth wave, and when the second duty ratio D2 is greater than or equal to the first sawtooth wave, the first driving signal CONT1 is at a high level; when the second duty ratio is smaller than the first sawtooth wave, the first driving signal CONT1 is low;
and S133, comparing the third duty ratio D3 with the second sawtooth wave, wherein the second driving signal CONT2 is at a high level when the third duty ratio D3 is greater than or equal to the second sawtooth wave, and the second driving signal CONT2 is at a low level when the third duty ratio D3 is less than the second sawtooth wave.
S14, as shown in fig. 10A, the first drive signal CONT1 and the second drive signal CONT2 are respectively turned on to corresponding positions.
S141, AC power supply VGWhen the voltage is positive, the first driving signal CONT1 is connected with the first high-frequency switch tube S1The second driving signal CONT2 is connected to the sixth high-frequency switch tube S6A gate electrode of (1). At the moment, the first low-frequency switch tube SL1A second high-frequency switch tube S2And a fifth high-frequency switching tube S5Conducting the second low-frequency switch tube SL2Turning off;
s142, AC power supply VGWhen the voltage is negative, the first driving signal CONT1 is connected with the second high-frequency switch tube S2The second driving signal CONT2 is connected to the fifth high-frequency switch tube S5A gate electrode of (1). At the moment, the first low-frequency switch tube SL1Turn-off, second low-frequency switching tube SL2A first high-frequency switch tube S1And a sixth high-frequency switching tube S6And conducting.
As shown in fig. 4, during the forward rectification operation, the generated first driving signal CONT1 and second driving signal CONT2 are first inverted and then respectively connected to the first low-frequency switching tube driving signal QL1And a second low frequency switching tube driving signal QL2Performing NAND gate operation to generate four paths of signals as the first low-frequency switch tube S in the modeL1A second low frequency switch tube SL2A first high-frequency switch tube S1And a sixth high-frequency switching tube S6The signals of the four action switching tubes are totally.
And S15, detecting the alternating voltage, and repeating the operations from S11 to S16 to realize the transfer of energy from the alternating current side to the direct current side.
In summary, in the first operation mode M1A second operating mode M2A third operating mode M3And a fourth operating mode M4Lower, second high frequency switching tube driving signal Q2And a fifth high-frequency switching tube driving signal Q5Constant high level, first high frequency switch tube driving signal Q1Is equal to the first driving signal CONT1 and the sixth high-frequency switching tube driving signal Q6Equal to the second drive signal CONT 2; in a fifth operating mode M5And a sixth operating mode M6And a seventh operating mode M7And an eighth operating mode M8The first high frequency switch tube driving signal Q1A sixth high frequency switching tube driving signal Q6Constant high level, second high frequency switch tube driving signal Q2Equal to the first driving signal CONT1 and the fifth high-frequency switching tube driving signal Q5Equal to the second drive signal CONT 2. Therefore, the first eight working modes simultaneously ensure that two high-frequency switching tubes act in a high-frequency switching mode and are continuously conducted during working, so that the bidirectional buck-boost characteristic of the three-level bidirectional buck-boost AC/DC converter topology provided by the invention is ensured.
As shown in FIG. 3, when the three-level bidirectional buck-boost AC/DC converter operates in the inverter mode, i.e., in the ninth operating mode M9The tenth operating mode M10Eleventh operating mode M11And the twelfth operating mode M12Thirteenth operating mode M13Fourteenth operating mode M14Fifteenth operating mode M15And a sixteenth mode of operation M16Next, the PWM modulation specifically includes the steps of:
s21, obtaining the lifting piezoelectric induction current reference value i of the inversion mode through double closed loopsB*: will give the net side current reference value iGMultiplication of unit sine signal on grid side and current i on grid sideGSubtracting, and multiplying the difference by a unit sine signal at the network side after passing through a first proportional resonant controller to obtain a buck-boost inductive current reference value iB*。
S22, balancing the voltage of the output capacitor, and acquiring a fourth duty ratio D4 and a fifth duty ratio D5.
S221, lifting the piezoelectric inductance current reference value iBAnd step-up/step-down inductor current iBSubtract to obtain the secondReference value of voltage UREF2In a ninth operating mode M9The tenth operating mode M10Eleventh operating mode M11And a twelfth operating mode M12Step-down buck-boost inductive current iBIs the value of the first current sensor CT 1; in a thirteenth operating mode M13Fourteenth operating mode M14Fifteenth operating mode M15And a sixteenth mode of operation M16Step-down buck-boost inductive current iBIs the value of the second current sensor CT 2;
s222, subtracting the data of the second voltage sensor VT2 from the data of the third voltage sensor VT3 to obtain a second voltage comparison result delta v2(ii) a Reference value U of the second voltageREF2Comparison result Δ v with the second voltage2Adding to obtain a fourth duty ratio D4, a second voltage reference value UREF2Comparison result Δ v with the second voltage2The subtraction results in the fifth duty cycle D5.
S23, as shown in FIG. 9, the first sawtooth wave is set to be a signal with amplitude of 1 and frequency of 1/T, the second sawtooth wave is set to be a signal with amplitude of 1 and frequency of 1/T and phase lag of 180 degrees of the first sawtooth wave, and the third driving signal CONT3 and the fourth driving signal CONT4 are obtained:
s231, comparing the fourth duty ratio D4 with the first sawtooth wave, and when the fourth duty ratio D4 is greater than or equal to the first sawtooth wave, the third driving signal CONT3 is at a high level; when the fourth duty ratio D4 is less than the first sawtooth wave, the third driving signal CONT3 is low;
s231, comparing the fifth duty ratio D5 with the second sawtooth wave, and when the fifth duty ratio D5 is greater than or equal to the second sawtooth wave, the fourth driving signal CONT4 is at a high level; when the fifth duty ratio D5 is less than the second sawtooth wave, the fourth drive signal CONT4 is low.
S24, as shown in fig. 10B, the third driving signal CONT3 and the fourth driving signal CONT4 are respectively turned on to corresponding positions.
S241, AC power supply VGWhen the voltage is positive, the third driving signal CONT3 is connected with the third high-frequency switch tube S3The fourth driving signal CONT4 is connected to the seventh high-frequency switch tube S7A gate electrode of (1). At the moment, the first low-frequency switch tube SL1A second high-frequency switch tube S2And a fifth high-frequency switching tube S5Conducting the second low-frequency switch tube SL2Turning off;
s242, alternating current power supply VGWhen the voltage is negative, the third driving signal CONT3 is connected with the fourth high-frequency switching tube S4The fourth driving signal CONT4 is connected to the eighth high-frequency switch tube S8A gate electrode of (1). At the moment, the first low-frequency switch tube SL1Turn-off, second low-frequency switching tube SL2A first high-frequency switch tube S1And a sixth high-frequency switching tube S6And conducting.
As shown in fig. 4, during the reverse inversion operation, the generated driving signals CONT3 and CONT4 are respectively connected to the first low-frequency switching tube driving signal QL1And a second low frequency switching tube driving signal QL2And operation is carried out to generate a first low-frequency switching tube SL1A second low frequency switch tube SL2A first high-frequency switch tube S1And a sixth high-frequency switching tube S6Four groups of signals of the four action switching tubes jointly form a driving signal in an inversion mode.
And S25, detecting the alternating voltage, and repeating the operations from S21 to S26 to realize the transfer of energy from the direct current side to the alternating current side.
In summary, in the ninth operation mode M9The tenth operating mode M10Eleventh operating mode M11And a twelfth operating mode M12Lower, second high frequency switching tube driving signal Q2A fifth high frequency switching tube driving signal Q5Constant high level, third high frequency switch tube driving signal Q3Is equal to the third driving signal CONT3 and the seventh high-frequency switching tube driving signal Q7Equal to the fourth drive signal CONT 4; in a thirteenth operating mode M13Fourteenth operating mode M14Fifteenth operating mode M15And a sixteenth mode of operation M16The first high frequency switch tube driving signal Q1A sixth high frequency switching tube driving signal Q6Constant high level, fourth high frequency switch tube driving signal Q4Is equal to the third drive signal CONT3Eighth high frequency switching tube driving signal Q8Equal to the fourth drive signal CONT 4. Therefore, the latter eight working modes also ensure that the two high-frequency switching tubes act in a high-frequency switching mode and are continuously conducted during working, so that the bidirectional buck-boost characteristic of the three-level bidirectional buck-boost AC/DC converter topology provided by the invention is ensured.
The direct current output reference current I ═ 1A and the alternating current output reference current I of the three-level bidirectional buck-boost AC/DC converter are usedGEach of 1A is exemplified.
In a direct current output mode, given that the alternating current power supply voltage is 220V, the frequency is 50Hz, the direct current power supply voltage is 400V, and the reference current I is 1A, the current sensor CT3 collects the current IGAfter subtraction, a current outer ring is formed through a PI controller, the output voltage of the current outer ring is multiplied by a unit sinusoidal signal with the same frequency and phase as the current power grid, and a power grid current reference value i is obtainedGA first step of; and the current value i of the power gridGAfter subtraction, a current inner loop is formed through a PI controller, and a comparison result delta v of the output voltage reference value and the first voltage is output1Subtracting to form active damping for suppressing the first voltage comparison result Δ v1Thereby suppressing the leakage current; the first duty ratio D1 is then compared with the second voltage respectively2Adding to obtain a second duty ratio D2, subtracting to obtain a third duty ratio D3 for balancing the input capacitor voltage; and finally, respectively modulating the first duty ratio D1 and the second duty ratio D2 to obtain a first driving signal CONT1 and a second driving signal CONT2, wherein the output direct current can be stabilized at 1A, the sine degree of an alternating current input waveform can meet the national standard requirement, and the power factor is more than 0.99.
In the AC output mode, the voltage of an AC power supply is set to be 220V, the frequency is 50Hz, the voltage of a DC power supply is set to be 400V, and the reference value i of the AC input current is setG1A, first of all, the current reference value iGMultiplying unit sine signal with same frequency and phase with current power grid and then multiplying unit sine signal with current power grid current value iGSubtracting, and multiplying the unit sine signal after the subtraction by a PR controller to obtain a buck-boost inductive current reference value iBForming a current outer loop; then the current is connected with a lifting piezoelectric induction current iBSubtracting the first voltage reference value U from the second voltage reference value U to obtain a second voltage reference value U after the first voltage reference value U is subtracted from the second voltage reference value U through a PI controllerREF2Forming a current inner ring; the values are respectively equal to Δ v2Adding to obtain a fourth duty ratio D4, and subtracting to obtain a fifth duty ratio D5; and finally, respectively modulating the fourth duty ratio D4 and the fifth duty ratio D5 to obtain a third driving signal CONT3 and a fourth driving signal CONT4, wherein the peak value of the output alternating current can be stabilized at 1A, and the sine degree of the alternating current output waveform can meet the national standard requirement.
The three-level bidirectional buck-boost AC/DC converter provided by the invention adopts 8 high-frequency switching tubes and 2 low-frequency switching tubes, has the characteristics of small voltage stress of the switching tubes, continuous alternating current side current and the like in a topological structure, can effectively inhibit high-frequency common-mode voltage and leakage current, has small inductance ripple current, and is beneficial to improving the overall efficiency; the three-level structure circuit is beneficial to reducing the volume of the magnetic element and has important significance for improving the power density of a system.
The above-mentioned embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements made to the technical solution of the present invention by those skilled in the art without departing from the spirit of the present invention shall fall within the protection scope defined by the claims of the present invention.

Claims (8)

1. A three-level bidirectional buck-boost AC/DC converter is characterized by comprising an alternating current power supply, a first capacitor, a second capacitor, a third capacitor, a fourth capacitor and a direct current power supply,
the L end of the alternating current power supply is respectively connected with the emitting electrode of the first low-frequency switching tube, the drain electrode of the first high-frequency switching tube and the input end of the first voltage sensor, and the N end of the alternating current power supply is respectively connected with the emitting electrode of the second low-frequency switching tube, the drain electrode of the second high-frequency switching tube and the output end of the first voltage sensor; the source electrode of the first high-frequency switching tube is respectively connected with the input end of the first current sensor and the drain electrode of the third high-frequency switching tube, and the source electrode of the second high-frequency switching tube is respectively connected with the input end of the second current sensor and the drain electrode of the fourth high-frequency switching tube; the output end of the first current sensor is connected with the output end of the first inductor, and the output end of the second current sensor is connected with the output end of the second inductor;
the input end of the first capacitor is respectively connected with the collector electrode of the first low-frequency switching tube, the collector electrode of the second low-frequency switching tube and the input end of the second voltage sensor, and the output end of the first capacitor is respectively connected with the input end of the second capacitor, the output end of the third capacitor, the input end of the fourth capacitor, the output end of the second voltage sensor and the input end of the third voltage sensor; the output end of the second capacitor is respectively connected with the source electrode of the fifth high-frequency switching tube, the source electrode of the sixth high-frequency switching tube and the output end of the third voltage sensor; the drain electrode of the fifth high-frequency switching tube is respectively connected with the input end of the second inductor and the source electrode of the eighth high-frequency switching tube, and the drain electrode of the sixth high-frequency switching tube is respectively connected with the input end of the first inductor and the source electrode of the seventh high-frequency switching tube;
the positive electrode of the direct current power supply is connected with the output end of the third current sensor, and the negative electrode of the direct current power supply is respectively connected with the source electrode of the third high-frequency switching tube, the source electrode of the fourth high-frequency switching tube and the output end of the fourth capacitor; and the input end of the third current sensor is respectively connected with the drain electrode of the seventh high-frequency switching tube, the drain electrode of the eighth high-frequency switching tube and the input end of the third capacitor.
2. The three-level bidirectional buck-boost AC/DC converter of claim 1, wherein said first capacitor has the same capacitance value as said second capacitor, said third capacitor has the same capacitance value as said fourth capacitor, and said first inductor has the same inductance value as said second inductor.
3. The three-level bidirectional buck-boost AC/DC converter according to claim 1, wherein the first low-frequency switch tube, the second low-frequency switch tube, the first high-frequency switch tube, the second high-frequency switch tube, the third high-frequency switch tube, the fourth high-frequency switch tube, the fifth high-frequency switch tube, the sixth high-frequency switch tube, the seventh high-frequency switch tube and the eighth high-frequency switch tube are all fully-controlled devices.
4. The three-level bidirectional buck-boost AC/DC converter according to claim 1, wherein a gate of the first low-frequency switch tube inputs a first low-frequency switch tube driving signal, and a gate of the second low-frequency switch tube inputs a second low-frequency switch tube driving signal; in the positive half period of the alternating current power supply, the driving signal of the first low-frequency switching tube is at a high level, and the driving signal of the second low-frequency switching tube is at a low level; in the negative half period of the alternating current power supply, the driving signal of the first low-frequency switching tube is at a low level, and the driving signal of the second low-frequency switching tube is at a high level.
5. The three-level bidirectional buck-boost AC/DC converter according to claim 4, wherein a gate of the first high-frequency switch tube receives a first high-frequency switch tube driving signal, a gate of the second high-frequency switch tube receives a second high-frequency switch tube driving signal, a gate of the third high-frequency switch tube receives a third high-frequency switch tube driving signal, a gate of the fourth high-frequency switch tube receives a fourth high-frequency switch tube driving signal, a gate of the fifth high-frequency switch tube receives a fifth high-frequency switch tube driving signal, a gate of the sixth high-frequency switch tube receives a sixth high-frequency switch tube driving signal, a gate of the seventh high-frequency switch tube receives a seventh high-frequency switch tube driving signal, and a gate of the eighth high-frequency switch tube receives an eighth high-frequency switch tube driving signal.
6. A control method for a three-level bidirectional buck-boost AC/DC converter as recited in any one of claims 1 to 5 wherein when said three-level bidirectional buck-boost AC/DC converter is operating in a rectification mode, i.e., energy is transferred from said AC power source to said DC power source, PWM modulation sequentially performs a first operation mode, a second operation mode, a third operation mode and a fourth operation mode during a positive half cycle of said AC power source; in the negative half period of the alternating current power supply, the PWM modulation sequentially executes a fifth working mode, a sixth working mode, a seventh working mode and an eighth working mode; the first working mode comprises that the first high-frequency switching tube driving signal, the second high-frequency switching tube driving signal, the fifth high-frequency switching tube driving signal and the sixth high-frequency switching tube driving signal are at high level, and the third high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the seventh high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level; the second working mode comprises that the first high-frequency switching tube driving signal, the second high-frequency switching tube driving signal and the fifth high-frequency switching tube driving signal are at high level, and the third high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the sixth high-frequency switching tube driving signal, the seventh high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level; the third working mode comprises that the second high-frequency switching tube driving signal, the fifth high-frequency switching tube driving signal and the sixth high-frequency switching tube driving signal are at high level, and the first high-frequency switching tube driving signal, the third high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the seventh high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level; the fourth working mode comprises that the second high-frequency switching tube driving signal and the fifth high-frequency switching tube driving signal are at high level, and the first high-frequency switching tube driving signal, the third high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the sixth high-frequency switching tube driving signal, the seventh high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level; the fifth working mode comprises that the first high-frequency switching tube driving signal, the second high-frequency switching tube driving signal, the fifth high-frequency switching tube driving signal and the sixth high-frequency switching tube driving signal are at high level, and the third high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the seventh high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level; the sixth working mode comprises that the first high-frequency switching tube driving signal, the second high-frequency switching tube driving signal and the sixth high-frequency switching tube driving signal are at high level, and the third high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the fifth high-frequency switching tube driving signal, the seventh high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level; the seventh working mode comprises that the first high-frequency switching tube driving signal, the fifth high-frequency switching tube driving signal and the sixth high-frequency switching tube driving signal are at high level, and the second high-frequency switching tube driving signal, the third high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the seventh high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level; the eighth working mode comprises that the first high-frequency switching tube driving signal and the sixth high-frequency switching tube driving signal are at high level, and the second high-frequency switching tube driving signal, the third high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the fifth high-frequency switching tube driving signal, the seventh high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level;
when the three-level bidirectional buck-boost AC/DC converter works in an inversion mode, namely energy is transmitted from the direct-current power supply to the alternating-current power supply, in a positive half period of the alternating-current power supply, the PWM modulation sequentially executes a ninth working mode, a tenth working mode, an eleventh working mode and a twelfth working mode; in the negative half period of the alternating current power supply, the PWM modulation sequentially executes a thirteenth working mode, a fourteenth working mode, a fifteenth working mode and a sixteenth working mode; the ninth working mode comprises that the second high-frequency switching tube driving signal, the third high-frequency switching tube driving signal, the fifth high-frequency switching tube driving signal and the seventh high-frequency switching tube driving signal are at high level, and the first high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the sixth high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level; the tenth working mode comprises that the second high-frequency switching tube driving signal, the fifth high-frequency switching tube driving signal and the seventh high-frequency switching tube driving signal are at high level, and the first high-frequency switching tube driving signal, the third high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the sixth high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level; the eleventh working mode comprises that the second high-frequency switching tube driving signal, the third high-frequency switching tube driving signal and the fifth high-frequency switching tube driving signal are at high level, and the first high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the sixth high-frequency switching tube driving signal, the seventh high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level; the twelfth working mode comprises that the second high-frequency switching tube driving signal and the fifth high-frequency switching tube driving signal are at high level, and the first high-frequency switching tube driving signal, the third high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the sixth high-frequency switching tube driving signal, the seventh high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level; the thirteenth working mode comprises that the first high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the sixth high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at high level, and the second high-frequency switching tube driving signal, the third high-frequency switching tube driving signal, the fifth high-frequency switching tube driving signal and the seventh high-frequency switching tube driving signal are at low level; the fourteenth working mode comprises that the first high-frequency switching tube driving signal, the sixth high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at high level, and the second high-frequency switching tube driving signal, the third high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the fifth high-frequency switching tube driving signal and the seventh high-frequency switching tube driving signal are at low level; the fifteenth working mode comprises that the first high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal and the sixth high-frequency switching tube driving signal are at high level, and the second high-frequency switching tube driving signal, the third high-frequency switching tube driving signal, the fifth high-frequency switching tube driving signal, the seventh high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level; the sixteenth working mode comprises that the first high-frequency switching tube driving signal and the sixth high-frequency switching tube driving signal are at high level, and the second high-frequency switching tube driving signal, the third high-frequency switching tube driving signal, the fourth high-frequency switching tube driving signal, the fifth high-frequency switching tube driving signal, the seventh high-frequency switching tube driving signal and the eighth high-frequency switching tube driving signal are at low level.
7. The method of claim 6, wherein in the first, second, third, fourth, fifth, sixth, seventh and eighth operating modes, the PWM modulation specifically comprises the following steps:
s11, obtaining a rectification mode network side current reference value through double closed-loop control;
s111, subtracting a value of the third current sensor from a power supply current reference value of the given direct-current power supply, and obtaining a current reference value through a first proportional integral controller according to the obtained value;
s112, multiplying the unit sinusoidal signal which is acquired by the first voltage sensor and has the same frequency and phase as the alternating current power supply by a current reference value to obtain a network side current reference value;
s12, obtaining a first duty ratio through an active damping link;
s121, subtracting the grid-side current reference value from the grid-side current, and obtaining a first voltage reference value through a second proportional-integral controller, wherein the grid-side current is the value of the second current sensor in the first working mode, the second working mode, the third working mode and the fourth working mode; under the fifth working mode, the sixth working mode, the seventh working mode and the eighth working mode, the grid side current is the value of the first current sensor;
s122, subtracting the sum of the data of the second voltage sensor and the data of the third voltage sensor from the data of the first voltage sensor to obtain a first voltage comparison result; subtracting the data of the second voltage sensor from the data of the third voltage sensor to obtain a second voltage comparison result;
s123, subtracting the comparison result of the first voltage from the reference value of the first voltage to obtain a first duty ratio;
s13, balancing the voltage of the input capacitor to obtain a first driving signal and a second driving signal;
s131, subtracting the comparison result of the first duty ratio and the second voltage to obtain a second duty ratio; adding the first duty ratio and the second voltage comparison result to obtain a third duty ratio;
s132, comparing the second duty ratio with the first sawtooth wave, and when the second duty ratio is greater than or equal to the first sawtooth wave, the first driving signal is at a high level; when the second duty ratio is smaller than the first sawtooth wave, the first driving signal is at a low level;
s133, comparing the third duty ratio with the second sawtooth wave, wherein when the third duty ratio is greater than or equal to the second sawtooth wave, the second driving signal is at a high level, and when the third duty ratio is less than the second sawtooth wave, the second driving signal is at a low level;
s14, respectively connecting the first driving signal and the second driving signal to corresponding positions;
s141, when the alternating current power supply voltage is positive, a first driving signal is connected with a grid electrode of the first high-frequency switching tube, and a second driving signal is connected with a grid electrode of the sixth high-frequency switching tube; at the moment, the first low-frequency switching tube, the second high-frequency switching tube and the fifth high-frequency switching tube are switched on, and the second low-frequency switching tube is switched off;
s142, when the alternating current power supply voltage is negative, a first driving signal is connected with the grid electrode of the second high-frequency switching tube, and a second driving signal is connected with the grid electrode of the fifth high-frequency switching tube; at the moment, the first low-frequency switching tube is turned off, and the first high-frequency switching tube and the sixth high-frequency switching tube of the second low-frequency switching tube are turned on;
and S15, detecting the alternating voltage, and repeating the operations from S11 to S16 to realize the transfer of energy from the alternating current side to the direct current side.
8. The method of claim 6, wherein in the ninth operation mode, the tenth operation mode, the eleventh operation mode, the twelfth operation mode, the thirteenth operation mode, the fourteenth operation mode, the fifteenth operation mode, and the sixteenth operation mode, the PWM modulation specifically comprises the following steps:
s21, acquiring the reference value of the lifting piezoelectric induction current of the inversion mode by the double closed loops: subtracting the product of the given grid side current reference value and the grid side unit sinusoidal signal from the grid side current, and multiplying the product by the grid side unit sinusoidal signal after passing through a first proportional resonant controller to obtain a buck-boost inductive current reference value;
s22, balancing the voltage of the output capacitor, and acquiring a fourth duty ratio and a fifth duty ratio;
s221, subtracting the buck-boost inductive current from the buck-boost inductive current to obtain a second voltage reference, where in the ninth working mode, the tenth working mode, the eleventh working mode, and the twelfth working mode, the buck-boost inductive current is a value of the first current sensor; in the thirteenth working mode, the fourteenth working mode, the fifteenth working mode and the sixteenth working mode, the lifting piezoelectric induction current is the value of the second current sensor;
s222, subtracting the data of the second voltage sensor from the data of the third voltage sensor to obtain a second voltage comparison result; adding the second voltage reference value and the second voltage comparison result to obtain a fourth duty ratio, and subtracting the second voltage reference value and the second voltage comparison result to obtain a fifth duty ratio;
s23, acquiring a third driving signal and a fourth driving signal:
s231, comparing the fourth duty ratio with the first sawtooth wave, and when the fourth duty ratio is greater than or equal to the first sawtooth wave, enabling the third driving signal to be at a high level; when the fourth duty ratio is smaller than the first sawtooth wave, the third driving signal is at a low level;
s231, comparing the fifth duty ratio with the second sawtooth wave, and when the fifth duty ratio is greater than or equal to the second sawtooth wave, enabling the fourth driving signal to be at a high level; when the fifth duty ratio is smaller than the second sawtooth wave, the fourth driving signal is at a low level;
s24, respectively switching on the third driving signal and the fourth driving signal to corresponding positions;
s241, when the voltage of the alternating current power supply is positive, a third driving signal is connected with the grid electrode of the third high-frequency switching tube, and a fourth driving signal is connected with the grid electrode of the seventh high-frequency switching tube; at the moment, the first low-frequency switching tube, the second high-frequency switching tube and the fifth high-frequency switching tube are switched on, and the second low-frequency switching tube is switched off;
s242, when the voltage of the alternating current power supply is negative, a third driving signal is connected with the grid electrode of the fourth high-frequency switching tube, and a fourth driving signal is connected with the grid electrode of the eighth high-frequency switching tube; at the moment, the first low-frequency switching tube is turned off, and the second low-frequency switching tube, the first high-frequency switching tube and the sixth high-frequency switching tube are turned on;
and S25, detecting the alternating voltage, and repeating the operations from S21 to S26 to realize the transfer of energy from the direct current side to the alternating current side.
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