Cascaded H-bridge current sharing circuit and method based on voltage feedforward control

Abstract

The invention discloses a cascaded H-bridge current sharing circuit and method based on voltage feedforward control, the circuit comprises a master controller, a plurality of slave controllers and H-bridge power modules, the master controller is connected with each slave controller, each slave controller is correspondingly connected with one H-bridge power module, and the H-bridge power modules are connected in parallel to form a cascaded H-bridge and output; according to the circuit, current sharing control among the H-bridge power modules connected in parallel is achieved through voltage feed-forward control. The method comprises the following steps: according to a connection principle of a transformer and an H-bridge power module, carrying out cascade H-bridge current-sharing circuit connection; the slave controller acquires an input bus voltage signal of each H-bridge power module in real time, and inversely calculates the duty ratio of each H-bridge power module according to the input bus voltage signal and a preset target voltage sent by the master controller; and outputting a corresponding PWM control signal from the controller according to the duty ratio of each H-bridge power module. According to the invention, accurate and rapid current balance control of each power module of the cascaded H bridge is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of cascaded H-bridge, and specifically relates to a cascaded H-bridge current sharing circuit and method based on voltage feedforward control. Background Art

[0002] The cascaded H-bridge is a multilevel converter topology widely used in high-voltage and high-power applications. By connecting multiple H-bridge power units in series, it realizes the multilevel output voltage, thereby reducing the harmonic content of the output voltage and improving the power factor. However, in practical applications, due to the incomplete consistency of the parameters of each power unit, such as component parameter differences, drive circuit delay differences, etc., the currents borne by each power unit are unbalanced. This current imbalance will cause some units to overheat due to overload, affecting the reliability and lifespan of the entire system.

[0003] Traditional current sharing control schemes mainly rely on adding passive current sharing inductors. However, adding current sharing inductors will increase the volume and cost of the system and cannot be dynamically adjusted. In addition, traditional control strategies also have deficiencies in dynamic response and control accuracy, making it difficult to meet the requirements of high-performance applications.

[0004] In view of this, the present application is specifically proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a cascaded H-bridge current sharing circuit and method based on voltage feedforward control, aiming to solve the problems of reduced system reliability and efficiency caused by current imbalance in each power module of the cascaded H-bridge in the prior art. Specifically, it overcomes the disadvantages of traditional current sharing control methods that rely on passive components, have slow response speed, low control accuracy, and poor fault tolerance, and realizes precise and fast current balancing control for each power module of the cascaded H-bridge, and uses voltage feedforward control to achieve current sharing control between parallel modules.

[0006] The present invention is achieved through the following technical solutions:

[0007] In a first aspect, the present invention provides a cascaded H-bridge current sharing circuit based on voltage feedforward control. The circuit includes a main controller, several slave controllers, and H-bridge power modules. The main controller is connected to each slave controller, and each slave controller is correspondingly connected to an H-bridge power module, and the H-bridge power modules are connected in parallel to form a cascaded H-bridge and output.

[0008] The circuit uses voltage feedforward control to achieve current sharing control between the parallel H-bridge power modules. The main controller provides a synchronous clock and start / stop signals for the slave controllers, and the slave controllers respectively control the corresponding H-bridge power modules to calculate and output the duty cycle.

[0009] Further, a single H-bridge power module includes a transformer T 1 ~Tm / 2 、m rectifiers AC / DC and H-bridge unit Hu 1 ~Hu m ,transformer T m / 2 The primary side of which is connected to the alternating current, and the transformer T m / 2 The first secondary side of which is connected to the first rectifier AC / DC, and the transformer T m / 2 The second secondary side of which is connected to the second rectifier AC / DC, and the first rectifier AC / DC is connected to the H-bridge unit Hu m-1 ,The second rectifier AC / DC is connected to the H-bridge unit Hu m ; The H-bridge units are connected in series in turn, so as to form a single H-bridge power module;

[0010] Wherein, the output of the rectifier AC / DC serves as the input U m of each H-bridge unit Hu in_Hum ,The output of the H-bridge unit Hu m is U out_HUm 。

[0011] Furthermore, a voltage stabilizing capacitor C is also connected in parallel on each rectifier AC / DC m 。

[0012] Furthermore, the secondary side voltages of the transformers T 1 ~T mn / 2 of the n H-bridge power modules are equal.

[0013] Furthermore, a voltage sensor is arranged on the input side of each H-bridge unit for measuring the input bus voltage.

[0014] Furthermore, the transformer is a three-winding transformer, and its two secondary sides adopt delta-star connection with a phase difference of 30°.

[0015] Furthermore, the rectifier is a diode rectifier.

[0016] In the second aspect, the present invention further provides a cascaded H-bridge current sharing method based on voltage feedforward control, and the current sharing method includes:

[0017] According to the connection principle of the transformer and the H-bridge power module, the cascaded H-bridge current sharing circuit is wired;

[0018] The input bus voltage signals of each H-bridge power module are collected in real time from the controller, and according to the input bus voltage signals and the preset target voltage sent by the main controller, the duty ratios of each H-bridge power module are calculated inversely;

[0019] According to the duty ratios of each H-bridge power module, corresponding PWM control signals are output from the controller.

[0020] Furthermore, the connection principle between the transformer and the H-bridge power module includes: according to the number of series and parallel connections of the H-bridge power modules, distribute the connection between the secondary output of the pre-stage transformer and the H-bridge power modules, so that the input bus voltages of the pre-stage of the parallel H-bridge power modules are kept basically the same.

[0021] Furthermore, the calculation formula for the duty cycle d% of each H-bridge power module is:

[0022]

[0023] where U ref is the preset target voltage value, and the duty cycle of each H-bridge power module is calculated separately to ensure that the voltages between the H-bridge power modules are equal; U Hu1 is the input bus voltage of the H-bridge power module Hu1; U Hu2 is the input bus voltage of the H-bridge power module Hu2; U Hum is the input bus voltage of the H-bridge power module Hum.

[0024] Furthermore, the current sharing method further includes:

[0025] Based on the synchronous clock control in the master controller and the slave controller, so that the PWM control signals of each H-bridge power module are kept consistent in phase and frequency.

[0026] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0027] 1. The present invention is based on the cascaded H-bridge current sharing circuit and method using voltage feedforward control, which realizes accurate and fast current equalization control for each power module of the cascaded H-bridge, and uses voltage feedforward control to realize current sharing control between parallel modules.

[0028] 2. The present invention is based on the cascaded H-bridge current sharing circuit and method using voltage feedforward control. A synchronous clock control module is set in the controller (used for sending in the master controller and receiving in the slave controller) to ensure that the PWM signals of each H-bridge power module are kept consistent in phase and frequency, and to avoid current imbalance caused by phase deviation. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, form a part of this application, and do not constitute a limitation to the embodiments of the present invention. In the drawings:

[0030] Figure 1 is the circuit diagram of the cascaded H-bridge current sharing based on the voltage feedforward control of the present invention;

[0031] Figure 2 is the schematic diagram of a single H-bridge power module (series unit) of the present invention;

[0032] Figure 3 Schematic diagram of a single H-bridge unit of the present invention;

[0033] Figure 4 Flowchart of the cascaded H-bridge current sharing method based on the use of voltage feedforward control of the present invention;

[0034] Figure 5 Example diagram of the cascaded H-bridge current sharing circuit corresponding to the method of Embodiment 2 of the present invention. Detailed implementation manners

[0035] Hereinafter, the term "comprising" or "may comprise" that may be used in various embodiments of the present invention indicates the presence of the functions, operations or elements of the present invention, and does not limit the addition of one or more functions, operations or elements. In addition, as used in various embodiments of the present invention, the terms "comprising", "having" and their cognates are only intended to indicate a specific feature, number, step, operation, element, component or combination of the foregoing items, and should not be construed as precluding the existence or addition of one or more other features, numbers, steps, operations, elements, components or combinations of the foregoing items first.

[0036] In various embodiments of the present invention, the expression "or" or "at least one of A or / and B" includes any combination or all combinations of the recited words. For example, the expression "A or B" or "at least one of A or / and B" may include A, may include B, or may include both A and B.

[0037] Expressions (such as "first", "second", etc.) used in various embodiments of the present invention may modify various components in various embodiments, but do not limit the corresponding components. For example, the above expressions do not limit the order and / or importance of the elements. The above expressions are only used for the purpose of distinguishing one element from other elements. For example, the first user device and the second user device indicate different user devices, although both are user devices. For example, without departing from the scope of various embodiments of the present invention, the first element may be referred to as the second element, and similarly, the second element may also be referred to as the first element.

[0038] It should be noted that: If it is described that one component is "connected" to another component, the first component may be directly connected to the second component, and a third component may be "connected" between the first component and the second component. Conversely, when one component is "directly connected" to another component, it can be understood that there is no third component between the first component and the second component.

[0039] The terms used in various embodiments of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the various embodiments of the present invention. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the various embodiments of the present invention pertain. The terms (such as those defined in a commonly used dictionary) will be interpreted as having the same meaning as the contextual meaning in the relevant technical field and will not be interpreted as having an idealized meaning or being overly formal, unless clearly defined in the various embodiments of the present invention.

[0040] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to embodiments and drawings. The illustrative embodiments and descriptions thereof of the present invention are only for the purpose of explaining the present invention and do not constitute a limitation to the present invention.

[0041] The present invention aims to solve the problem of reduced system reliability and efficiency caused by current imbalance in each power module of a cascaded H-bridge in the prior art. Specifically, it overcomes the disadvantages of traditional current sharing control methods, such as relying on passive components, slow response speed, low control accuracy, and poor fault tolerance, and realizes precise and fast current balance control for each power module of the cascaded H-bridge, and uses voltage feedforward control to achieve current sharing control between parallel modules.

[0042] The current sharing method designed by the present invention includes the following steps:

[0043] ①Specific connection principle of the transformer and the H-bridge power module: According to the series and parallel numbers of the H-bridge power modules, reasonably allocate the connection method between the secondary output of the pre-stage transformer and the H-bridge power modules to ensure that the input bus voltages of the pre-stage of the parallel H-bridge power modules remain basically the same.

[0044] ②Real-time acquisition of the input voltage signals of each H-bridge power module: Real-time monitor the input bus voltage of each H-bridge power module through a megahertz voltage sensor to obtain accurate voltage data.

[0045] ③Calculate the voltage output control value (i.e., duty cycle): Calculate the duty cycle of each H-bridge power module based on the input bus voltage.

[0046] ④Adjust the PWM control signal: Output the corresponding PWM control signal from the controller according to the duty cycle of each H-bridge power module.

[0047] ⑤Synchronous coordination control: A synchronous clock control module is set in the controller (used for sending in the main controller and receiving in the slave controller) to ensure that the PWM signals of each H-bridge power module are consistent in phase and frequency, avoiding current imbalance caused by phase deviation.

[0048] Through the above solutions, the present invention achieves the following technical effects:

[0049] (1) Improve current balance: By adopting a digital control algorithm to control the output voltage of each H-bridge power module, the actual output current deviation is significantly reduced, ensuring that each H-bridge power module evenly shares the load.

[0050] (2) Enhance system reliability: Through real-time monitoring and fault detection mechanisms, the fault tolerance of the system is improved, preventing system shutdown caused by unit failures.

[0051] (3) Improve control response speed: The digital feedforward control method enables faster voltage regulation, can respond to load changes and external disturbances in a timely manner, maintain the stability of output performance, and at the same time significantly reduce the system delay caused by algorithm control.

[0052] (4) Reduce system cost and volume: Avoid the use of traditional passive current sharing components, reduce hardware costs, reduce system volume, and improve overall economy.

[0053] Embodiment 1

[0054] As Figure 1 shown, the present invention is based on a cascaded H-bridge current sharing circuit using voltage feedforward control. The circuit includes a main controller, several slave controllers, and H-bridge power modules. The main controller is connected to each slave controller, and each slave controller is correspondingly connected to an H-bridge power module, and the H-bridge power modules are connected in parallel to form a cascaded H-bridge and output;

[0055] This circuit uses voltage feedforward control to achieve current sharing control among the parallel H-bridge power modules. The main controller provides synchronous clocks and start / stop signals for the slave controllers, and the slave controllers respectively control the corresponding H-bridge power modules to calculate and output the duty cycle.

[0056] Specifically, as Figure 2 shown, a single H-bridge power module includes a transformer T 1 ~T m / 2 , m rectifiers AC / DC, voltage stabilizing capacitors C 1 ~C m and an H-bridge unit Hu 1 ~Hu m , the primary side of the transformer T m / 2 is connected to the alternating current, and the first secondary side of the transformer T m / 2 is connected to the first rectifier AC / DC, the transformer Tm / 2 The second secondary side is connected to the second rectifier AC / DC, and a voltage stabilizing capacitor C is also connected in parallel on each rectifier AC / DC. m ; The first rectifier AC / DC is connected to the H-bridge unit Hu m-1 , and the second rectifier AC / DC is connected to the H-bridge unit Hu m ; Specifically, the transformer is a three-winding transformer, and its two secondary sides adopt a corner-joined star connection with a phase difference of 30°; the rectifier is a diode rectifier.

[0057] The H-bridge units are connected in series in sequence to form a single H-bridge power module; among them, the output of the rectifier AC / DC serves as the input U m of each H-bridge unit Hu in_HUm , and the output of the H-bridge unit Hu m is U out_Hum .

[0058] As Figure 1 shown, n H-bridge power modules (H 1 ~H n ) are connected in parallel to form a cascaded H-bridge. A single H-bridge unit (Hu 1 ~Hu m ) contains four IGBT switching devices S1~S4. U i is the output of the pre-stage rectifier AC / DC, and U o is the output of the H-bridge power module. First, it is clear that the total number of H-bridge power modules is j, where m H-bridge units are connected in series to form 1 H-bridge power module, and n H-bridge power modules are connected in parallel to form the final output;

[0059] A single H-bridge unit is as Figure 3 shown, m H-bridge units connected in series form 1 H-bridge power module as Figure 2 shown, and n modules connected in parallel form the total output as Figure 1 shown, m×n = j;

[0060] To reduce the harmonic of the input bus voltage of the H-bridge unit and ensure the quality of the backend DC conversion, 2 rectifiers AC / DC are used to form 12 pulses, and j rectifiers AC / DC are respectively connected in parallel with the H-bridge units (Hu 1 ~Hu j );

[0061] To improve the input voltage consistency of the H-bridge power module, the sum of the secondary side voltage values of the transformers that supply power to the n H-bridge power modules should be equal. Further, the secondary side voltages of the transformers T 1 ~T mn / 2 of the first module, the second module, the third module,..., the nth module should be equal;

[0062] Furthermore, the connection method of the H-bridge unit (Hu 1 ~Hu j ) and the transformer T 1 ~T mn / 2 should not only consider phase shifting to form 12 pulses, but also ensure that the sum of the secondary side voltages is equal;

[0063] One main controller (main digital controller) and n slave controllers (slave digital controllers) serve as the control system. The n slave controllers respectively control n H-bridge power modules, and the main controller provides synchronous clocks and start / stop signals for the slave controllers;

[0064] Voltage sensors are arranged on the input side of each H-bridge unit to measure the input bus voltage U Hu1 ~U Huj . The bus voltage U Hu1 ~U Hum of a single H-bridge power module is sent to its slave controller for duty cycle calculation; according to the duty cycle calculation formula where U ref is the preset target voltage value. The duty cycle of each H-bridge power module is calculated separately to ensure equal voltage between modules.

[0065] In addition, a synchronous clock control module is provided in the main controller and the slave controllers, that is, the main controller sends synchronous clock signals to the n slave controllers to ensure that the n parallel modules are consistent in phase and frequency, and avoid current imbalance caused by phase deviation.

[0066] Embodiment 2

[0067] As Figure 4 shown, the difference between this embodiment and Embodiment 1 is that this embodiment provides a cascaded H-bridge current sharing method based on voltage feedforward control. This current sharing method is based on the cascaded H-bridge current sharing circuit based on voltage feedforward control in Embodiment 1; this current sharing method includes:

[0068] Step 1: According to the connection principle of the transformer and the H-bridge power module, connect the cascaded H-bridge current sharing circuit;

[0069] Step 2: The slave controller collects the input bus voltage signals of each H-bridge power module in real time, and calculates the duty cycle of each H-bridge power module by back-calculating according to the input bus voltage signals and the preset target voltage sent by the main controller;

[0070] Step 3: According to the duty cycle of each H-bridge power module, the slave controller outputs corresponding PWM control signals.

[0071] As a further implementation, the duty cycle d% calculation formula of each H-bridge power module is:

[0072]

[0073] Among them, U ref is the preset target voltage value, and the duty ratio of each H-bridge power module is calculated separately to ensure that the voltages between the H-bridge power modules are equal; U Hu1 is the input bus voltage of the H-bridge power module Hu1; U Hu2 is the input bus voltage of the H-bridge power module Hu2; U Hum is the input bus voltage of the H-bridge power module Hum.

[0074] During specific implementation, Figure 5 an example is given. Taking 2 strings in parallel and 4 strings in series as an example, at this time m = 2, n = 4, j = 8: Transformers T1 to T4 are three-winding transformers, and their two secondary sides adopt delta-star connection with a phase difference of 30°, which can make the backend AC / DC form a 12-pulse output and reduce power supply harmonics;

[0075] In this embodiment, the connection principle between the transformer and the H-bridge power module in step 1 includes: according to the series and parallel quantities of the H-bridge power modules, the connection between the output of the secondary side of the pre-stage transformer and the H-bridge power module is allocated, which can ensure that the input bus voltages of the pre-stage of the parallel H-bridge power modules are basically the same.

[0076] Specifically, Hu1 and Hu2 are respectively powered by the delta-connected secondary side and the star-connected secondary side of transformer T1 after being converted by a diode rectifier AC / DC, and then are connected in series; Hu3 and Hu4 are respectively powered by the delta-connected secondary side and the star-connected secondary side of transformer T2 after being converted by a diode rectifier AC / DC, and then are connected in series; Hu5 and Hu6 are respectively powered by the delta-connected secondary side and the star-connected secondary side of transformer T3 after being converted by a diode rectifier AC / DC, and then are connected in series; Hu7 and Hu8 are connected in series and are respectively powered by the delta-connected secondary side and the star-connected secondary side of transformer T4 after being converted by a diode rectifier AC / DC, and then are connected in series;

[0077] After Hu1 and Hu2 are connected in series, they form the H-bridge power module H1. After Hu3 and Hu4 are connected in series, they form the H-bridge power module H2. After Hu5 and Hu6 are connected in series, they form the H-bridge power module H3. After Hu7 and Hu8 are connected in series, they form the H-bridge power module H4; H1 - H4 are connected in parallel to form the total output of the system;

[0078] Adopting this connection method of transformers T1 - T4 and H-bridge power modules Hu1 - Hu8 can make the sum of the incoming line voltages of Hu1 and Hu2 (i.e., U Hu1 +U Hu2 ), the sum of the voltages of Hu3 and Hu4 (i.e., U Hu1 +U Hu4 ), the sum of the voltages of Hu5 and Hu6 (i.e., U Hu5+U Hu6 ) The sum of the voltages of Hu7 and Hu8 (i.e., U Hu7 +U Hu8 ) is equal, that is, the incoming line bus voltages of the H-bridge power modules H1 - H4 are equal;

[0079] In this embodiment, in step 2, each of the H-bridge power modules H1 - H4 is equipped with 1 slave controller, and 1 master controller interacts with the 4 slave digital controllers to provide them with synchronous clock signals, start / stop signals, etc.; The present invention ensures the synchronization of the PWM control signals of each power module, avoiding the asynchronous switching of devices caused by phase differences, and further avoiding large voltage output deviations and current imbalances.

[0080] The master controller respectively sends the preset target voltage (i.e., U ref ) The voltage sensors measure the incoming line voltages of Hu1 - Hu8 (U Hu1 -U Hu8 ) and send them to the corresponding slave controllers. The slave controllers of each H-bridge power module perform their respective calculations according to the duty cycle d% calculation formula:

[0081] The slave controller of the H-bridge power module H1 calculates the duty cycles of the H-bridge units Hu1 and Hu2 according to ;

[0082] The slave controller of the H-bridge power module H2 calculates the duty cycles of the H-bridge units Hu3 and Hu4 according to ;

[0083] The slave controller of the H-bridge power module H3 calculates the duty cycles of the H-bridge units Hu5 and Hu6 according to ;

[0084] The slave controller of the H-bridge power module H4 calculates the duty cycles of the H-bridge units Hu7 and Hu8 according to ;

[0085] For the above technical solutions, the present invention uses an independent controller to separately control the H-bridge power module, ensuring that the output voltages of each H-bridge power module are consistent.

[0086] In this embodiment, in step 3, the slave controller generates a PWM control signal according to the calculated duty cycle, and the H-bridge units Hu1 - Hu8 output according to the PWM control signal.

[0087] The present invention uses digital control to perform real-time feedforward control on the output voltages of the cascaded H-bridge power modules. Each H-bridge power module reasonably distributes its respective output voltage according to the level of the incoming line bus voltage, ensuring that the output currents of each H-bridge power module are basically the same, while simplifying the control algorithm and greatly improving the power output response speed.

[0088] The specific embodiments described above further elaborate on the object, technical solution, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A cascaded H-bridge current sharing circuit based on voltage feedforward control, characterized in that: The circuit includes a master controller, several slave controllers and an H-bridge power module. The master controller is connected to each slave controller, each slave controller is correspondingly connected to an H-bridge power module, and each H-bridge power module is connected in parallel to form a cascade H-bridge and output; The circuit uses voltage feedforward control to achieve current sharing control between parallel H-bridge power modules. The master controller provides a synchronous clock and start / stop signals to the slave controller, and the slave controller controls the corresponding H-bridge power modules to calculate and output the duty cycle.

2. The cascaded H-bridge current sharing circuit based on voltage feedforward control according to claim 1, characterized in that: A single H-bridge power module includes transformers T1 to T m / 2 , m rectifiers AC / DC and H-bridge units Hu1~Hu m , transformer T m / 2 The primary side of the transformer is connected to the AC m / 2 The first secondary side is connected to the first rectifier AC / DC, transformer T m / 2 The second secondary side is connected to the second rectifier AC / DC, and the first rectifier AC / DC is connected to the H bridge unit Hu m-1 , the second rectifier AC / DC connects the H bridge unit Hu m ; Each H-bridge unit is connected in series in sequence to form a single H-bridge power module; The output of the rectifier AC / DC is used as each H-bridge unit Hu m Input U in_Hum , H-bridge unit Hu m The output is U out_HUm .

3. The cascaded H-bridge current sharing circuit based on voltage feedforward control according to claim 2, characterized in that: Each rectifier AC / DC is also connected in parallel with a voltage stabilizing capacitor C m .

4. The cascaded H-bridge current sharing circuit based on voltage feedforward control according to claim 2, characterized in that: Each transformer T1~T of n H-bridge power modules mn / 2 The secondary voltage is equal.

5. The cascaded H-bridge current sharing circuit based on voltage feedforward control according to claim 2, characterized in that: A voltage sensor is arranged on the input side of each H-bridge unit to measure the input bus voltage.

6. The cascaded H-bridge current sharing circuit based on voltage feedforward control according to claim 2, characterized in that: The rectifier is a diode rectifier; The transformer is a three-winding transformer, and its two secondary sides are corner-connected and star-connected, with a phase difference of 30°.

7. The current sharing method based on the cascaded H-bridge current sharing circuit using voltage feedforward control as claimed in any one of claims 1 to 6; characterized in that: The current sharing method includes: According to the connection principle between the transformer and the H-bridge power module, the cascaded H-bridge current sharing circuit is connected; The slave controller collects the input bus voltage signal of each H-bridge power module in real time, and reversely calculates the duty cycle of each H-bridge power module according to the input bus voltage signal and the preset target voltage sent by the master controller; According to the duty cycle of each H-bridge power module, the corresponding PWM control signal is output from the controller.

8. The current balancing method according to claim 7, characterized in that: The connection principle between the transformer and the H-bridge power module includes: allocating the connection between the secondary output of the front-stage transformer and the H-bridge power module according to the number of series and parallel connections of the H-bridge power modules, so that the front-stage input bus voltage of the parallel H-bridge power modules remains consistent.

9. The current balancing method according to claim 7, characterized in that: The calculation formula for the duty cycle d% of each H-bridge power module is: Among them, U ref To preset the target voltage value, the duty cycle of each H-bridge power module is calculated separately to ensure that the voltage between the H-bridge power modules is equal; U Hu1 is the input bus voltage of the H-bridge power module Hu1; U Hu2 is the input bus voltage of the H-bridge power module Hu2; U Hum is the input bus voltage of the H-bridge power module Hum.

10. The current balancing method according to claim 6, characterized in that: The current sharing method also includes: Based on the synchronous clock control in the master controller and the slave controller, the PWM control signals of each H-bridge power module are kept consistent in phase and frequency.

Images