Electronic follow-up and method for controlling the same

Abstract

The application discloses a novel electronic traction substation and a control method thereof. The electronic traction substation is a three-phase inverter structure. An input end of the electronic traction substation is connected with a direct-current traction network, and an output end of the electronic traction substation is connected with a 380V power lighting system. The direct-current traction network is connected with a 35kV medium-voltage loop network through a pulse rectifier set. The electronic traction substation is used for transmitting power of the direct-current traction network to the 380V power lighting system, and providing electric energy for the 380V power lighting system. In the application, the existing traction substation is transformed into the electronic traction substation, so that the construction area of the 35kV line can be greatly reduced, the difficulty of the rail transit construction is reduced, the urban subway construction is optimized, the urban civil engineering demand is reduced, the operation of the existing traction substation and traction substation of the power supply system is not affected, and the instability problem of the existing power supply system is avoided.

Description

Technical Field

[0001] This invention relates to the field of power supply for rail transit, specifically to an electronic following device and its control method. Background Technology

[0002] The field of metro following has already yielded numerous research results and application cases in the field of rail transit construction. Transforming existing following systems into electronic following systems is a relatively new research direction.

[0003] Domestic subway systems currently draw power directly from the 35kV medium-voltage ring network at existing substations. This 35kV ring network then steps down the voltage through the existing substation's power frequency transformer to supply power to the 380V section lighting system. Therefore, it is necessary to construct 35kV lines near these existing substations. Given the limited capacity and large number of existing substations, a significant number of 35kV lines are required. Rail transit construction must consider factors such as high altitude, high seismic intensity, adverse geological conditions, fragile and sensitive ecological environments, and landscape requirements, overcoming challenges such as harsh natural environments, weak power supply capacity, and significant construction difficulties.

[0004] How to efficiently reduce the difficulty of rail transit construction in remote mountainous areas and the transformation of existing traction substations is a current research hotspot in the rail transit field. Moreover, the existing power supply system, including traction substations, traction substations, and other substations, draws power independently from the 35kV medium-voltage ring network, so they can also be constructed independently. It is highly feasible to transform existing traction substations separately. Summary of the Invention

[0005] To address the aforementioned shortcomings in existing technologies, the present invention provides an electronic follower substation and its control method, which reduces the construction area of ​​35kV lines, lowers the difficulty of rail transit construction in remote mountainous areas, and stabilizes the output voltage of the electronic follower substation under relatively simple operating conditions, providing a stable voltage for the 380V section power lighting system.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is: a novel electronic follower, wherein the electronic follower is an integrated three-phase inverter structure;

[0007] The input end of the electronic follower is connected to the DC traction network, and its output end is connected to the 380V interval power lighting system. The DC traction network is connected to the 35kV medium-voltage ring network through a pulse rectifier unit.

[0008] The electronic follower is used to transmit DC traction power to the 380V range power lighting system, providing it with electrical energy.

[0009] Furthermore, the integrated three-phase inverter includes switching transistors. S 1- S 6. Diode D 1-D3, Capacitor Cdc and inductor L in ;

[0010] The switching transistor S The collector of 1 is connected to the positive input terminal of the electronic follower at point A, the positive voltage terminal of the DC traction network, and is connected to the diode. D The negative terminal of 2 is connected, and the switching transistor is... S The emitter of 1 is connected to the inductor respectively. l in One end of the capacitor C dc negative terminal, switching transistor S 5's emitter and switching transistor S 3's emitter and diode D 3. Positive terminal connection;

[0011] The inductor L in The other end serves as the negative input terminal of the electronic follower, connected to the negative voltage point B of the DC traction network, and is connected to the diode. D The positive terminal of 1 is connected, and the diode is... D The negative terminal of 1 is connected to the capacitor respectively. C dc positive terminal, switching transistor S 6 collector and switching transistor S 4's collector and switching transistor S 2. Collector connection, the switching transistor S 5's collector and switching transistor S The emitter connection of 6, the switching transistor S 3 collector and switching transistor S The emitter connection of 4, the switching transistor S The emitter of 2 is connected to the diode respectively. D 3's positive terminal and diode D 2. Positive terminal connection;

[0012] The switching transistor S 1. Switching transistor S 2. Diode D 2 and diode D 3. The first bridge arm of the integrated three-phase inverter, the diode D The negative terminal of 3 serves as the first output port of the integrated three-phase inverter. a Point through inductor L fa Connect to a 380V zone-controlled lighting system;

[0013] The switching transistor S 3 and switching transistors S4. The second bridge arm of the integrated three-phase inverter, the switching transistor S The collector of phase 3 serves as the first output port of the integrated three-phase inverter. b Point through inductor L fb Connect to a 380V zone-controlled lighting system;

[0014] The switching transistor S 5 and switching transistors S 6 forms the third bridge arm of the integrated three-phase inverter, and the switching transistor S The collector of 5 serves as the first output port of the integrated three-phase inverter. c Point through inductor L fc Connect to a 380V zone power lighting system.

[0015] Furthermore, the integrated three-phase inverter, in continuous current-inductance mode, according to... i fa , i fb , i fc The relationship between the value of 0 and the configuration of the integrated three-phase inverter's operating process is determined, with each operating process corresponding to 8 operating modes; where, where i fa , i fb , i fc Inductance L fa L fb L fc The current.

[0016] A novel electronic follower control method, wherein the switching transistor S 1. S 2. Controlling the capacitor via PWM modulation C dc The voltage of the switching transistor S 3. S 4. S 5. S 6. Using SPWM modulation and in conjunction with a switching transistor S 1 and S The output control of 2 is electronically controlled to follow the output three-phase voltage.

[0017] Furthermore, the switching transistor S 1. S The modulation method of 2 is:

[0018] pulse width modulation signal V r1and bipolar triangular carrier signal V c1 The output signal of the first comparator is then input to the non-inverting input and the inverting input respectively. V s1 As a switch. S The drive signal of 1 will output the signal. V s1 The inverted signal is used as a switch. S 2. Drive signal.

[0019] Furthermore, the switching transistor S 3. S 4. S 5. S The modulation method of 6 is:

[0020] sinusoidal modulation signal V r2 and bipolar triangular carrier signal V c2 By inputting the non-inverting and inverting inputs of the second comparator respectively, the output signal of the second comparator can be obtained. V s3 ;

[0021] sinusoidal modulation signal V r3 and bipolar triangular carrier signal V c2 By inputting the non-inverting and inverting inputs of the third comparator respectively, the output signal of the third comparator can be obtained. V s5 ;

[0022] Output signal v s3 and output signal v s5 As switching transistors respectively S 3. S The drive signal of 5 will output the signal. V s3 and output signal V s5 The inverted signals are used as switching transistors. S 4. S The drive signal for 6.

[0023] The beneficial effects of this invention are as follows:

[0024] 1. Transforming existing substations into electronic substations can significantly reduce the construction area of ​​35kV lines, lower the civil engineering and building construction costs required for 35kV lines in remote mountainous areas, and reduce the difficulty of rail transit construction.

[0025] 2. Converting existing substations into electronic substations can reduce the land area occupied by 35kV lines in urban rail transit construction, optimize urban subway construction, and reduce urban civil engineering needs.

[0026] 3. Modify the existing traction substation separately without affecting the operation of the existing power supply system's traction substations and follower substations, thus avoiding instability issues to the existing power supply system;

[0027] 4. Convert the bridge arm voltage from the traction network voltage V i Transform into the supporting capacitor voltage V c This can reduce the withstand voltage requirements of switching transistors S2, S3, S4, S5, and S6, while simultaneously improving the utilization rate of the DC side voltage of the bridge arm to cope with the working conditions of large voltage fluctuation range of the traction network.

[0028] 5. The DC traction network is connected to the 380V range power lighting system after being controlled by the electronic follower. The electronic follower can suppress the influence of DC traction network voltage fluctuations, stabilize the input voltage of the 380V range power lighting system, and ensure the normal operation of the 380V range power lighting system. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the connection of the novel electronic follower provided by the present invention.

[0030] Figure 2 A schematic diagram of a pulse rectifier unit is provided for this invention.

[0031] Figure 3 This is a schematic diagram of the novel electronic follower structure provided by the present invention.

[0032] Figure 4 This is a schematic diagram of an existing follower connection provided by the present invention.

[0033] Figure 5 This is a schematic diagram of the modified connection for the electronic follower provided by the present invention.

[0034] Figure 6 The integrated three-phase inverter provided by this invention operates in continuous inductor current mode and in i fa > i fb >0> i fc The working process of the time has 8 modal diagrams.

[0035] Figure 7 The diagram shows the simulation results of the integrated three-phase inverter provided by the present invention; wherein, (a) is the supporting capacitor of an integrated three-phase inverter provided by the present invention, (b) is the steady-state waveform of the output voltage, and (c) is the THD analysis diagram of the output voltage.

[0036] Figure 8 The transient waveform of the output voltage of the integrated three-phase inverter provided by this invention. Detailed Implementation

[0037] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0038] Example 1:

[0039] This invention provides a novel electronic follower, such as... Figure 1 As shown, the electronic follower is an integrated three-phase inverter structure;

[0040] The input end of the electronic follower is connected to the DC traction network, and its output end is connected to the 380V interval power lighting system. The DC traction network is connected to the 35kV medium-voltage ring network through a pulse rectifier unit.

[0041] The electronic follower is used to transmit DC traction power to the 380V range power lighting system, providing it with electrical energy.

[0042] In this embodiment of the invention, the 35kV medium-voltage ring network is used to provide power to the entire subway system. The input end of the pulse rectifier unit is connected to the 35kV medium-voltage ring network, and the output end is connected to the DC traction network, which is used to transmit the power from the 35kV medium-voltage ring network to the DC traction network. One end of the DC traction network is connected to the pulse rectifier unit, so that the power is transmitted from the pulse rectifier unit to the DC traction network, which is used to provide power to the DC locomotive. The other end is connected to the electronic following substation, which provides input power to the electronic following substation.

[0043] In embodiments of the present invention, such as Figure 2 As shown, the pulse rectifier unit includes phase transformers and pulse rectifiers. The phase-shifting transformers include transformer 1 and transformer 2. The 35kV medium-voltage ring network is stepped down by transformer 1 and then connected to the midpoints a1, b1, and c1 of the rectifier bridge arm, and then passes through diode D. A1 D A2 D A3 D A4 D A5 D A6 The rectified output DC voltage V1; the 35kV medium-voltage ring network, after phase shifting and voltage reduction by transformer #2, is connected to the midpoints a2, b2, and c2 of the rectifier bridge arm, and then passes through diode D. B1 DB2 D B3 D B4 D B5 D B6 After rectification, the output DC voltage V2 is used. The output DC voltage V1 and the output DC voltage V2 are connected in parallel and then connected to the DC traction network to provide power to the DC traction network.

[0044] In embodiments of the present invention, such as Figure 3 As shown, the integrated three-phase inverter includes switching transistors. S 1- S 6. Diode D 1-D3, Capacitor C dc and inductor L in ;

[0045] The switching transistor S The collector of 1 is connected to the positive input terminal of the electronic follower at point A, the positive voltage terminal of the DC traction network, and is connected to the diode. D The negative terminal of 2 is connected, and the switching transistor is... S The emitter of 1 is connected to the inductor respectively. l in One end of the capacitor C dc negative terminal, switching transistor S 5's emitter and switching transistor S 3's emitter and diode D 3. Positive terminal connection;

[0046] The inductor L in The other end serves as the negative input terminal of the electronic follower, connected to the negative voltage point B of the DC traction network, and is connected to the diode. D The positive terminal of 1 is connected, and the diode is... D The negative terminal of 1 is connected to the capacitor respectively. C dc positive terminal, switching transistor S 6 collector and switching transistor S 4's collector and switching transistor S 2. Collector connection, the switching transistor S 5's collector and switching transistor S The emitter connection of 6, the switching transistor S 3 collector and switching transistor S The emitter connection of 4, the switching transistor S The emitter of 2 is connected to the diode respectively. D 3's positive terminal and diode D 2. Positive terminal connection;

[0047] The switching transistorS 1. Switching transistor S 2. Diode D 2 and diode D 3. The first bridge arm of the integrated three-phase inverter, the diode D The negative terminal of 3 serves as the first output port of the integrated three-phase inverter. a Point through inductor L fa Connect to a 380V zone-controlled lighting system;

[0048] The switching transistor S 3 and switching transistors S 4. The second bridge arm of the integrated three-phase inverter, the switching transistor S The collector of phase 3 serves as the first output port of the integrated three-phase inverter. b Point through inductor L fb Connect to a 380V zone-controlled lighting system;

[0049] The switching transistor S 5 and switching transistors S 6 forms the third bridge arm of the integrated three-phase inverter, and the switching transistor S The collector of 5 serves as the first output port of the integrated three-phase inverter. c Point through inductor L fc Connect to a 380V zone power lighting system.

[0050] In this embodiment, based on the above-described integrated three-phase inverter structure, the process of outputting the three-phase voltage is as follows: DC traction grid voltage V dc1 The capacitor voltage is controlled to V by the switching transistors S1 and S2 of the integrated three-phase inverter. c At the same time, the port voltage V is obtained. an Simultaneously, it controls switching transistors S3, S4, S5, and S6, controlling the port voltage V. bn V cn This makes the voltage V ab V bc V ca It controls the output three-phase voltage to power the 380V range lighting system.

[0051] Example 2:

[0052] This embodiment is a further improvement on the basis of embodiment 1. Based on the existing rail transit, the existing following depot is transformed into the electronic following depot in embodiment 1. This transformation process does not involve the transformation of the traction network and is easy to implement in engineering.

[0053] like Figure 4As shown, there are interconnected circuit breakers and power frequency transformers included in the system. The circuit breakers are directly connected to the 35kV medium-voltage ring network, and the output of the power frequency transformer is connected to the 380V range power lighting system.

[0054] like Figure 5 As shown, during the renovation, the three-phase output voltage of the integrated three-phase inverter is connected to the power frequency transformer, and the output terminal of the power frequency transformer is connected to the 380V range power lighting system.

[0055] In this embodiment, the circuit breaker is used to disconnect the existing follower to ensure that the 380V section power lighting system can be safely disconnected in the event of a power supply system failure; the power frequency transformer steps down the 35kV medium voltage ring network voltage to 380V to supply power to the 380V section power lighting system.

[0056] Example 3:

[0057] This embodiment is a further improvement on Embodiment 1, providing the specific working process of the integrated three-phase inverter in Embodiment 1. In specific operation, the integrated three-phase inverter operates in continuous current-inductance mode, according to... i fa , i fb , i fc The relationship between the value of 0 and the value of 0 determines the working process of the integrated three-phase inverter, and each working process corresponds to 8 working modes;

[0058] Specifically, with i fa > i fb >0> i fc For example, Figure 6 As shown, its operating modes are as follows:

[0059] (1) Mode 1: Switches S1, S3, and S5 are off, while S2, S4, and S6 are on; L in Because it is subjected to reverse voltage V c In linear discharge, the anti-parallel diode of S6, S2, and S4 form a freewheeling circuit;

[0060] (2) Mode 2: Switches S1, S3, and S6 are off, while S2, S4, and S5 are on, L in Because it is subjected to reverse voltage V i Linear discharge. S2, S4, S5, capacitor C dc This forms an inverter circuit;

[0061] (3) Mode 3: Switches S1, S4, and S5 are off, while S2, S3, and S6 are on, Lin Because it is subjected to reverse voltage V c Linear discharge. The anti-parallel diode of S6, S2, S3, and capacitor C. dc Forming an inverter circuit;

[0062] (4) Mode 4: Switches S1, S4, and S6 are off, while S2, S3, and S5 are on, L in Because it is subjected to reverse voltage V i Linear discharge. The anti-parallel diode of S3, S2, S5, and capacitor C. dc This forms an inverter circuit;

[0063] (5) Mode 5: Switches S2, S3, and S5 are off, while S1, S4, and S6 are on, L in Because it is subjected to a positive voltage V i Linear charging. The anti-parallel diode of S6, D3, S4, and capacitor C. dc This forms an inverter circuit;

[0064] (6) Mode 6: Switches S2, S3, and S6 are off, while S1, S4, and S5 are on, L in Because it is subjected to a positive voltage V i Linear charging. D3, S4, S5, capacitor C dc This forms an inverter circuit;

[0065] (7) Mode 7: Switches S2, S4, and S5 are off, while S1, S3, and S6 are on, L in Because it is subjected to a positive voltage V i Linear charging. The anti-parallel diodes S3 and S6, D3, and capacitor C. dc Forming an inverter circuit;

[0066] (8) Mode 8: Switches S2, S4, and S6 are off, while S1, S3, and S5 are on, L in Because it is subjected to a positive voltage V i Linear charging. The anti-parallel diode of S3, D3, and S5 form a freewheeling circuit.

[0067] The rest according to i fa , i fb , i fc There are 7 working processes related to the magnitude of 0, and each working process has 8 working modes. The analysis process is similar, so it will not be repeated here.

[0068] Example 4:

[0069] This embodiment provides a control method for the electronic follower in operation, specifically, the switching transistor...S 1. S 2. Controlling the capacitor via PWM modulation C dc The voltage of the switching transistor S 3. S 4. S 5. S 6. Using SPWM modulation and in conjunction with a switching transistor S 1 and S The output control of 2 is electronically controlled to follow the output three-phase voltage.

[0070] Specifically, switching transistor S 1. S The modulation method of 2 is:

[0071] pulse width modulation signal V r1 and bipolar triangular carrier signal V c1 The output signal of the first comparator is then input to the non-inverting input and the inverting input respectively. V s1 As a switch. S The drive signal of 1 will output the signal. V s1 The inverted signal is used as a switch. S 2. Drive signal.

[0072] Specifically, switching transistor S 3. S 4. S 5. S The modulation method of 6 is:

[0073] sinusoidal modulation signal V r2 and bipolar triangular carrier signal V c2 By inputting the non-inverting and inverting inputs of the second comparator respectively, the output signal of the second comparator can be obtained. V s3 ;

[0074] sinusoidal modulation signal V r3 and bipolar triangular carrier signal V c2 By inputting the non-inverting and inverting inputs of the third comparator respectively, the output signal of the third comparator can be obtained. V s5 ;

[0075] Output signal v s3 and output signal v s5 As switching transistors respectively S3. S The drive signal of 5 will output the signal. V s3 and output signal V s5 The inverted signals are used as switching transistors. S 4. S The drive signal for 6.

[0076] The first to third comparators in the above embodiments are three comparators of the same type, and there are no special requirements in terms of model and parameters.

[0077] In this embodiment, based on the above modulation method, on the one hand, the DC side voltage of the bridge arm is changed from... V i Become V c This can reduce the switching transistor S 2. S 3. S 4. S 5. S The voltage withstand requirement of 6 is met, which simultaneously improves the utilization rate of DC side voltage of the bridge arm and achieves the purpose of wide voltage input range. On the other hand, it solves the problem of voltage instability of electronic follower output voltage due to the large voltage fluctuation range of DC traction network, and provides stable voltage for 380V range power lighting system.

[0078] In this embodiment, a simulation example of an electronic follower based on the above control method is also provided, and its simulation parameters are shown in Table 1.

[0079] Table 1. Simulation parameters of an integrated three-phase inverter

[0080]

[0081] The simulation results obtained are as follows Figure 7 As shown, from Figure 7 As can be seen from this, the integrated three-phase inverter in this embodiment has good steady-state performance, supports stable capacitor voltage, outputs a three-phase voltage of AC380V, and has a THD of only 0.56%.

[0082] The simulated input voltage waveform, H-bridge output voltage waveform, buck chopper circuit + H-bridge output voltage waveform, and integrated three-phase inverter output voltage waveform are as follows: Figure 8 As shown in the figure, the comparison reveals that the integrated three-phase inverter exhibits excellent transient characteristics, which can be divided into five stages:

[0083] 0s-3s: Input voltage is 1000V;

[0084] 3s-6s: The input voltage is 1200V. After the input voltage changes in 3s, the adjustment time is 66ms.

[0085] 6s-9s: The input voltage is 1400V. After the input voltage changes at 6s, the adjustment time is 33ms.

[0086] 9s-11s; the input voltage is 1600V, and the adjustment time after the input voltage changes at 9s is 53ms.

[0087] 11s-13s; the input voltage is 1800V, and the adjustment time after the input voltage changes at 11s is 53ms.

[0088] Specific embodiments have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

[0089] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. An electronic follower, characterized in that, The electronic follower is an integrated three-phase inverter structure; The input end of the electronic follower is connected to the DC traction network, and its output end is connected to the 380V interval power lighting system. The DC traction network is connected to the 35kV medium-voltage ring network through a pulse rectifier unit. The electronic follower is used to transmit DC traction power to the 380V range power lighting system to provide it with electrical energy. The integrated three-phase inverter includes switching transistors. S 1- S 6. Diode D 1-D3, Capacitor C dc and inductor L in ; The switching transistor S The collector of 1 is connected to the positive input terminal of the electronic follower at point A, the positive voltage terminal of the DC traction network, and is connected to the diode. D The negative terminal of 2 is connected, and the switching transistor is... S The emitter of 1 is connected to the inductor respectively. l in One end of the capacitor C dc negative terminal, switching transistor S 5's emitter and switching transistor S 3's emitter and diode D 3. Positive terminal connection; The inductor L in The other end serves as the negative input terminal of the electronic follower, connected to the negative voltage point B of the DC traction network, and is connected to the diode. D The positive terminal of 1 is connected, and the diode is... D The negative terminal of 1 is connected to the capacitor respectively. C dc positive terminal, switching transistor S 6 collector and switching transistor S 4's collector and switching transistor S 2. Collector connection, the switching transistor S 5's collector and switching transistor S The emitter connection of 6, the switching transistor S 3 collector and switching transistor S The emitter connection of 4, the switching transistor S The emitter of 2 is connected to the diode respectively. D 3's positive terminal and diode D 2. Positive terminal connection; The switching transistor S 1. Switching transistor S 2. Diode D 2 and diode D 3. The first bridge arm of the integrated three-phase inverter, the diode D The negative terminal of 3 serves as the first output port of the integrated three-phase inverter. a Point through inductor L fa Connect to a 380V zone-controlled lighting system; The switching transistor S 3 and switching transistors S 4. The second bridge arm of the integrated three-phase inverter, the switching transistor S The collector of phase 3 serves as the first output port of the integrated three-phase inverter. b Point through inductor L fb Connect to a 380V zone-controlled lighting system; The switching transistor S 5 and switching transistors S 6 forms the third bridge arm of the integrated three-phase inverter, and the switching transistor S The collector of 5 serves as the first output port of the integrated three-phase inverter. c Point through inductor L fc Connect to a 380V zone power lighting system.

2. The electronic follower according to claim 1, characterized in that, The integrated three-phase inverter, in continuous current-inductance mode, according to i fa , i fb , i fc The relationship between the value of 0 and the configuration of the integrated three-phase inverter's operating process is determined, with each operating process corresponding to 8 operating modes; where, where i fa , i fb , i fc Inductance L fa L fb L fc The current.

3. A control method based on the electronic follower as described in any one of claims 1 to 2, characterized in that, The switching transistor S 1. S 2. Controlling the capacitor via PWM modulation C dc The voltage of the switching transistor S 3. S 4. S 5. S 6. Using SPWM modulation and in conjunction with a switching transistor S 1 and S The output control of 2 is electronically controlled to follow the output three-phase voltage.

4. The control method according to claim 3, characterized in that, The switching transistor S 1. S The modulation method of 2 is: pulse width modulation signal V r1 and bipolar triangular carrier signal V c1 The output signal of the first comparator is then input to the non-inverting input and the inverting input respectively. V s1 As a switch. S The drive signal of 1 will output the signal. V s1 The inverted signal is used as a switch. S 2. Drive signal.

5. The control method according to claim 4, characterized in that, The switching transistor S 3. S 4. S 5. S The modulation method of 6 is: sinusoidal modulation signal V r2 and bipolar triangular carrier signal V c2 By inputting the non-inverting and inverting inputs of the second comparator respectively, the output signal of the second comparator can be obtained. V s3 ; sinusoidal modulation signal V r3 and bipolar triangular carrier signal V c2 By inputting the non-inverting and inverting inputs of the third comparator respectively, the output signal of the third comparator can be obtained. V s5 ; Output signal v s3 and output signal v s5 As switching transistors respectively S 3. S The drive signal of 5 will output the signal. V s3 and output signal V s5 The inverted signals are used as switching transistors. S 4. S The drive signal for 6.

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