Multi-module parallel synchronous control method for high-power converter

Abstract

The invention provides a multi-module parallel synchronous control method for a high-power converter, and the method comprises the steps: enabling a centralized control subsystem to calculate and output a q-axis current given value, a d-axis current given value and a phase angle for controlling each sub-module according to the voltage and current of a motor, issuing the q-axis current given value, the d-axis current given value and the phase angle to each sub-module control system; and according to the q-axis current given value, the d-axis current given value and the phase angle, each sub-module control system calculates and outputs a control duty ratio for controlling each sub-module, and based on the control duty ratio, the corresponding sub-module is controlled. According to the collected voltage and current of the output ends of the sub-modules and the voltage and current of the motor, power device control signals of all the sub-modules are output through a double-closed-loop control algorithm, frequency conversion and speed regulation control over the motor load is achieved, parallel circulation can be effectively reduced, the current of the sub-modules can be balanced, and the output electric energy quality of the frequency converter is improved.

Description

Technical Field

[0001] The present invention relates to the field of frequency converter control, and more particularly, to a multi-module parallel synchronous control method for high-power converters. Background Art

[0002] The multi-module parallel technology is one of the key technologies to improve the power rating of frequency converters. A high-power frequency converter can be achieved by paralleling multiple power modules with low power ratings. However, when modules are paralleled, due to the inability to ensure complete electrical and structural consistency among sub-modules, problems such as inter-module circulating current and current imbalance will occur, affecting the output power quality of the frequency converter. Summary of the Invention

[0003] In order to reduce the parallel circulating current, balance the currents of sub-modules, and improve the output power quality of the frequency converter, the present invention provides a multi-module parallel synchronous control method for high-power converters.

[0004] The present invention provides a multi-module parallel synchronous control method for high-power converters, including: According to the motor voltage and motor current, the centralized control subsystem calculates and outputs the q-axis current reference value, d-axis current reference value, and phase angle for controlling each sub-module, and sends the q-axis current reference value, d-axis current reference value, and phase angle to each sub-module control system; According to the q-axis current reference value, d-axis current reference value, and phase angle, each sub-module control system calculates and outputs the control duty cycle for controlling each sub-module, and controls the corresponding sub-module based on the control duty cycle.

[0005] A multi-module parallel synchronous control method for high-power converters provided by the present invention, according to the voltage and current at the output end of the sub-module and the motor voltage and current collected, through a double closed-loop control algorithm, outputs the control signals of the power devices of each sub-module, realizes the variable frequency speed control of the motor load, can effectively reduce the parallel circulating current, balance the currents of sub-modules, and improve the output power quality of the frequency converter. Brief Description of the Drawings

[0006] Figure 1 It is a flowchart of a multi-module parallel synchronous control method for high-power converters provided by an embodiment of the present invention; Figure 2 It is a schematic diagram of a multi-module parallel synchronous control system for high-power converters provided by an embodiment of the present invention. Detailed Description

[0007] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. Additionally, the technical features in each embodiment or individual embodiment provided by the present invention can be combined with each other arbitrarily to form a feasible technical solution. Such combination is not restricted by the order of steps and / or the structural composition mode, but must be based on the fact that those of ordinary skill in the art can implement it. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the protection scope required by the present invention.

[0008] See Figure 1 , a flowchart of a multi-module parallel synchronous control method for a high-power converter according to an embodiment of the present invention is provided. This control method is based on a multi-module parallel synchronous control system as shown in Figure 2 . Among them, Figure 2 the number of sub-module control systems in it is four. This is only one embodiment of the present invention. In fact, more sub-module control systems can be used in this control system, which should not limit the present invention.

[0009] Figure 2 In

[0010] a multi-module parallel synchronous control system includes a centralized control system and multiple sub-module control systems. Each system shares one CAN bus and two RS485 buses. Step 1: According to the motor voltage and motor current, the centralized control subsystem calculates and outputs the q-axis current reference value, d-axis current reference value, and phase angle for controlling each sub-module, and sends the q-axis current reference value, d-axis current reference value, and phase angle to each sub-module control system.

[0011] Among them, motors can be mainly divided into permanent magnet synchronous motors and asynchronous motors. When the types of motors are different, the methods for the centralized control system to calculate the q-axis current reference value, d-axis current reference value, and phase angle are different.

[0012] In a possible embodiment of the present invention, when the motor is a permanent magnet synchronous motor, the centralized control system uses an outer-loop closed-loop control algorithm to calculate and output the q-axis current reference value, d-axis current reference value, and phase angle for controlling each sub-module according to the motor voltage and motor current, including: Step 11: According to the current moment Axis estimated current and at the current moment Axis estimated current, and the motor at the current moment Axis actual current and the motor at the current moment Axis actual current, calculate at the current moment Axis disturbance loop proportional-integral output and at the current moment Axis disturbance loop proportional-integral output.

[0013] In an embodiment of the present invention, according to the at the current moment Axis estimated current and at the current moment Axis estimated current, and the motor at the current moment Axis actual current and the motor at the current moment Axis actual current, calculate at the current moment Axis disturbance loop proportional-integral output and at the current moment Axis disturbance loop proportional-integral output, including:

[0014]

[0015] Wherein, is the at the current moment Axis disturbance loop proportional-integral output, is the at the current moment Axis disturbance loop proportional-integral output, is the motor d-axis inductance, is the motor q-axis inductance, is the disturbance loop proportionality coefficient, is the disturbance loop integral coefficient, is the motor at the current moment Axis actual current, is the motor at the current moment Axis actual current, is the at the current moment Axis estimated current, is the at the current moment Axis estimated current.

[0016] Wherein, calculate the at the current moment Axis estimated current and the at the current moment Axis estimated current , including: According to the motor current at the current moment, the motor voltage at the current moment, the motor estimated angular velocity at the previous moment, the at the previous moment Axis disturbance loop proportional-integral output, the at the previous moment The axis disturbance loop proportional integral output and motor parameters are used to calculate the current moment Axis estimated current and current Estimated axis current.

[0017] Calculate the current time Estimated axis current and the current moment Estimated axis current The specific formula is:

[0018]

[0019] in, Estimate the angular velocity of the motor at the last moment, For the previous moment Shaft disturbance loop proportional integral output, For the previous moment Shaft disturbance loop proportional-integral output.

[0020] Step 12: Based on the current Axis disturbance loop proportional integral output, current moment The proportional integral output of the axis disturbance loop and the phase angle of the previous moment are used to calculate the phase-locked loop output at the current moment.

[0021] In one embodiment of the present invention, the Axis disturbance loop proportional integral output, current moment The proportional integral output of the axis disturbance loop and the phase angle of the previous moment are used to calculate the phase-locked loop output at the current moment, including:

[0022]

[0023] in, For the current moment Shaft disturbance loop proportional integral output, For the current moment Shaft disturbance loop proportional integral output, is the phase-locked loop input at the current moment, is the phase-locked loop output at the current moment, is the phase-locked loop proportional coefficient, is the phase-locked loop integral coefficient, is the phase angle at the previous moment.

[0024] Step 13, calculating the estimated angular velocity of the motor at the current moment according to the phase-locked loop output at the current moment and the estimated angular velocity of the motor at the previous moment.

[0025] In an embodiment of the present invention, calculating the estimated angular velocity of the motor at the current moment based on the output of the phase-locked loop at the current moment and the estimated angular velocity of the motor at the previous moment includes:

[0026] where, is the estimated angular velocity of the motor at the current moment, is the estimated angular velocity of the motor at the previous moment, is the observer bandwidth.

[0027] Step 14, calculating the given value of the q-axis current at the current moment and the given value of the d-axis current at the current moment based on the estimated angular velocity of the motor at the current moment and the given angular velocity of the motor.

[0028] In an embodiment of the present invention, calculating the given value of the q-axis current at the current moment and the given value of the d-axis current at the current moment based on the estimated angular velocity of the motor at the current moment and the given angular velocity of the motor includes:

[0029] where, is the estimated angular velocity of the motor at the current moment, is the given angular velocity of the motor, is the proportional coefficient of the speed loop, is the integral coefficient of the speed loop, is the given value of the q-axis current at the current moment.

[0030] When the motor is a permanent magnet synchronous motor, the given value of the d-axis current is set to:

[0031] Calculating the phase angle is:

[0032] where, is the given value of the d-axis current at the current moment, is the phase angle at the current moment.

[0033] The foregoing embodiments describe the method for the centralized control system to calculate the given value of the q-axis current at the current moment, the given value of the d-axis current at the current moment, and the phase angle at the current moment when the motor is a synchronous permanent magnet motor. The following introduces the method for calculating the given value of the q-axis current at the current moment, the given value of the d-axis current at the current moment, and the phase angle at the current moment when the motor is an asynchronous motor.

[0034] In one embodiment of the present invention, when the motor is an asynchronous motor, calculating and outputting the q-axis current reference value, d-axis current reference value, and phase angle for controlling each sub-module based on the motor voltage and motor current includes: Step 11', calculating the voltage reference value based on the motor reference current.

[0035] In one embodiment of the present invention, calculating the voltage reference value based on the motor reference current includes:

[0036] where, is the voltage reference value, is the voltage-frequency proportionality coefficient, is the motor reference angular velocity value.

[0037] Step 12', calculating the voltage feedback value at the current moment through angle transformation based on the motor voltage at the current moment.

[0038] In one embodiment of the present invention, calculating the voltage feedback value at the current moment through angle transformation based on the motor voltage at the current moment includes:

[0039] where, is the voltage feedback value at the current moment, is the actual voltage of the motor axis at the current moment, is the actual voltage of the motor axis at the current moment.

[0040] Step 13', calculating the q-axis current reference value at the current moment, the d-axis current reference value at the current moment, and the phase angle at the current moment based on the voltage reference value and the voltage feedback value at the current moment.

[0041] In one embodiment of the present invention, calculating the q-axis current reference value at the current moment, the d-axis current reference value at the current moment, and the phase angle at the current moment based on the voltage reference value and the voltage feedback value at the current moment includes:

[0042] When the motor is an asynchronous motor, the d-axis current reference value is set to: Calculating the phase angle:

[0043]

[0044] where, is the voltage-loop proportionality coefficient, is the integral coefficient of the voltage loop, is the given value of the q-axis current at the current moment, is the given value of the d-axis current at the current moment, is the phase angle at the current moment.

[0045] Step 2: According to the given value of the q-axis current, the given value of the d-axis current, and the phase angle, each sub-module control system calculates and outputs the control duty cycle for controlling each sub-module, and based on the control duty cycle, controls the corresponding sub-module.

[0046] In an embodiment of the present invention, the calculating and outputting, by each sub-module control system, the control duty cycle for controlling each sub-module according to the given value of the q-axis current, the given value of the d-axis current, and the phase angle includes: Step 21: Calculate the given value of the q-axis voltage for each sub-module according to the given value of the q-axis current and the actual q-axis current of each sub-module.

[0047] Step 22: Calculate the given value of the d-axis voltage for each sub-module according to the given value of the d-axis current and the actual d-axis current of each sub-module.

[0048] In an embodiment of the present invention, calculating the given value of the q-axis voltage for each sub-module according to the given value of the q-axis current and the actual q-axis current of each sub-module includes:

[0049] Calculating the given value of the d-axis voltage for each sub-module according to the given value of the d-axis current and the actual d-axis current of each sub-module includes:

[0050] Wherein, is the given value of the q-axis voltage of the nth sub-module at the current moment, is the given value of the d-axis voltage of the nth sub-module at the current moment, N is the number of sub-modules, is the actual q-axis current of the nth sub-module at the current moment, is the actual d-axis current of the nth sub-module at the current moment, is the proportional coefficient of the current loop, is the integral coefficient of the current loop. Wherein, and are obtained by coordinate transformation of the real-time measured current of the nth sub-module through the phase angle coordinate transformation.

[0051] Step 23: Calculate the control duty cycle for each sub-module according to the given value of the q-axis voltage and the given value of the d-axis voltage of each sub-module.

[0052] In an embodiment of the present invention, according to the q-axis voltage reference value and the d-axis voltage reference value of each sub-module, the control duty ratio of each sub-module is calculated by using the prior art, which will not be elaborated here. Each sub-module is controlled according to the calculated control duty ratio of each sub-module to achieve current balance among multiple sub-modules.

[0053] See Figure 2 , a multi-module parallel synchronous control system for a high-power converter according to an embodiment of the present invention is provided. The system includes a centralized control system and multiple sub-module control systems; The centralized control system is configured to calculate and output the q-axis current reference value, d-axis current reference value and phase angle for controlling each sub-module based on the outer-loop closed-loop control algorithm according to the motor voltage and motor current, and send the q-axis current reference value, d-axis current reference value and phase angle to each sub-module control system; each sub-module control system is configured to calculate and output the control duty ratio for controlling each sub-module based on the inner-loop closed-loop control algorithm according to the q-axis current reference value, d-axis current reference value and phase angle, and control the corresponding sub-module based on the control duty ratio.

[0054] In an embodiment of the present invention, the centralized control system and multiple sub-module control systems share one CAN bus and two RS485 buses. Among them, the CAN bus is used for medium- and low-speed point-to-point communication. The centralized control system receives the status feedback and fault feedback uploaded by the sub-module control system through the CAN bus, and the sub-module control system receives the enable signal sent by the centralized control system through the CAN bus. Each sub-module control system takes turns to communicate with the centralized control system in a point-to-point manner.

[0055] In the RS485 buses, one RS485 bus is used to achieve carrier signal synchronization, and the other 485 bus is used to achieve high-speed broadcast communication. Among them, the centralized control system outputs the carrier synchronization signal to the PWM-SyncIn pin of the sub-module control circuit through the No. 1 485 bus, and the synchronization interval is an integer number of carrier cycles. The centralized control system sends control instructions such as the q-axis current reference value, d-axis current reference value, and phase angle to the sub-module control circuit through the No. 2 485 bus. The number of communication bytes per time is not less than 8 bytes, and the communication rate is not less than 75 kB / s.

[0056] The control timing of the multi-module parallel synchronous control system is as follows: At the k-th PWM interruption, the centralized control system sequentially executes: broadcasting and sending the (k - 1)-th control instruction, collecting voltage and current signals, executing the outer-loop closed-loop control algorithm, and calculating the k-th control instruction. Meanwhile, at the k-th PWM interruption, the sub-module control system sequentially executes: reading the (k - 2)-th control instruction sent by the centralized control system, collecting voltage and current signals, executing the inner-loop closed-loop control algorithm, feeding back the k-th status and fault data, and outputting power device control signals.

[0057] A multi-module parallel synchronous control method for high-power converters provided by the present invention outputs power device control signals of each sub-module through a double closed-loop control algorithm according to the collected voltages and currents at the output ends of the sub-modules and the motor voltages and currents, realizes variable-frequency speed regulation control of the motor load, can effectively reduce parallel circulating current, balance the sub-module currents, and improve the power quality of the inverter output.

[0058] It should be noted that in the above embodiments, the descriptions of each embodiment have their own focuses. For the parts not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0059] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0060] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, and the combination of processes and / or blocks in the flowchart and / or block diagram, can be realized by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded computer, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate means for realizing the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0061] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory generate a manufactured article including instruction means, and the instruction means realizes the functions in the process Figure 1One or more processes and / or blocks Figure 1 The functions specified in one block or more blocks.

[0062] These computer program instructions can also be loaded onto a computer or other programmable data processing device, so that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process. Thus, the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one process Figure 1 One or more processes and / or blocks Figure 1 The steps of the functions specified in one block or more blocks.

[0063] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they learn the basic creative concepts. Therefore, the appended claims are intended to be interpreted to include the preferred embodiments as well as all changes and modifications falling within the scope of the present invention.

[0064] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A multi-module parallel synchronous control method for high-power converters, characterized in that, including: Based on the motor voltage and motor current, calculate and output the q-axis current reference value, d-axis current reference value, and phase angle for controlling each sub-module according to the outer-loop closed-loop control algorithm, and send the q-axis current reference value, d-axis current reference value, and phase angle to each sub-module control system; According to the q-axis current reference value, d-axis current reference value, and phase angle, each sub-module control system calculates and outputs the control duty cycle for controlling each sub-module based on the inner-loop closed-loop control algorithm, and controls the corresponding sub-module based on the control duty cycle.

2. The multi-module parallel synchronous control method for high-power converters according to claim 1, wherein When the motor is a permanent magnet synchronous motor, the calculating and outputting the q-axis current reference value, d-axis current reference value, and phase angle for controlling each sub-module according to the motor voltage and motor current includes: According to the axis estimated current at the current moment and the axis estimated current at the current moment, and the axis actual current at the current moment and the axis actual current at the current moment, calculate the axis disturbance loop proportional-integral output at the current moment and the axis disturbance loop proportional-integral output; According to the current moment shaft disturbance loop proportional-integral output at the current moment, and the shaft disturbance loop proportional-integral output and the phase angle at the previous moment, calculate the phase-locked loop output at the current moment; Calculating the estimated motor angular velocity at the current moment according to the output of the phase-locked loop at the current moment and the estimated motor angular velocity at the previous moment; Based on the estimated motor angular velocity at the current moment and the given motor angular velocity, calculating the q-axis current reference value at the current moment and the d-axis current reference value at the current moment.

3. The multi-module parallel synchronous control method for high-power converters according to claim 2, wherein The shaft estimated current at the current moment and the shaft estimated current at the current moment, and the motor shaft actual current at the current moment and the motor shaft actual current at the current moment, calculate the shaft disturbance loop proportional-integral output at the current moment and the shaft disturbance loop proportional-integral output at the current moment, including: Among them, is the proportional-integral output of the axis disturbance loop at the current moment, is the proportional-integral output of the axis disturbance loop at the current moment, is the axis inductance of the motor, is the d-axis inductance of the motor, is the q-axis inductance of the motor, is the proportional coefficient of the disturbance loop, is the integral coefficient of the disturbance loop, is the actual current of the motor axis at the current moment, is the actual current of the motor axis at the current moment, is the estimated current of the axis at the current moment, is the estimated current of the axis at the current moment.

4. The multi-module parallel synchronous control method for high-power converters according to claim 3, characterized in that Calculate the axis estimated current at the current moment and the axis estimated current, including: Based on the motor current at the current moment, the motor voltage at the current moment, the estimated angular velocity of the motor at the previous moment, and the proportional-integral output of the shaft disturbance loop at the previous moment, and the proportional-integral output of the shaft disturbance loop at the previous moment and the motor parameters, calculate the estimated current of the shaft at the current moment and the estimated current of the shaft at the current moment.

5. The multi-module parallel synchronous control method for high-power converters according to claim 4, wherein, Based on the motor current at the current moment, the motor voltage at the current moment, the estimated motor angular velocity at the previous moment, and the axial disturbance loop proportional-integral output at the previous moment, and the axial disturbance loop proportional-integral output and motor parameters, calculate the axial estimated current at the current moment and the axial estimated current at the current moment, including: Among them, is the estimated angular velocity of the motor at the previous moment, is at the previous moment proportional-integral output of the shaft disturbance loop, is at the previous moment proportional-integral output of the shaft disturbance loop.

6. The multi-module parallel synchronous control method for high-power converters according to claim 2, wherein The axis disturbance loop proportional-integral output at the current moment, the axis disturbance loop proportional-integral output at the current moment, and the phase angle at the previous moment to calculate the phase-locked loop output at the current moment, including: ； ； Among them, is the proportional-integral output of the shaft disturbance loop at the current moment, is the proportional-integral output of the shaft disturbance loop at the current moment, is the phase-locked loop input at the current moment, is the phase-locked loop output at the current moment, is the phase-locked loop input at the current moment, is the phase-locked loop output at the current moment, is the phase-locked loop proportional coefficient, is the phase-locked loop integral coefficient, is the phase angle at the previous moment; The calculating the estimated motor angular velocity at the current moment according to the output of the phase-locked loop at the current moment and the estimated motor angular velocity at the previous moment includes: wherein, is the estimated angular velocity of the motor at the current moment, is the estimated angular velocity of the motor at the previous moment, is the observer bandwidth.

7. The multi-module parallel synchronous control method for high-power converters according to claim 2, characterized in that The calculating the q-axis current reference value at the current moment and the d-axis current reference value at the current moment based on the estimated motor angular velocity at the current moment and the given motor angular velocity includes: Among them, is the estimated angular velocity of the motor at the current moment, is the given angular velocity of the motor, is the proportional coefficient of the speed loop, is the integral coefficient of the speed loop, is the given value of the q-axis current at the current moment, is the given value of the d-axis current at the current moment, is the phase angle at the current moment.

8. The multi-module parallel synchronous control method for high-power converters according to claim 1, characterized in that When the motor is an asynchronous motor, the calculating and outputting the q-axis current reference value, d-axis current reference value, and phase angle for controlling each sub-module according to the motor voltage and motor current includes: Calculating the given voltage value according to the given motor current; Calculating the voltage feedback value at the current moment according to the motor voltage at the current moment; Based on the given voltage value and the voltage feedback value at the current moment, calculating the q-axis current reference value at the current moment, the d-axis current reference value at the current moment, and the phase angle at the current moment.

9. The multi-module parallel synchronous control method for high-power converters according to claim 8, characterized in that The calculating the given voltage value according to the given motor current includes: Among them, is the voltage set value, is the voltage-frequency proportionality coefficient; The calculating the voltage feedback value at the current moment according to the motor voltage at the current moment includes: Among them, is the voltage feedback value at the current moment, is the actual voltage of the motor shaft at the current moment, is the actual voltage of the motor shaft at the current moment; Based on the given voltage value and the voltage feedback value at the current moment, calculating the q-axis current reference value at the current moment, the d-axis current reference value at the current moment, and the phase angle at the current moment includes: Among them, is the proportional coefficient of the voltage loop, is the integral coefficient of the voltage loop, is the given value of the q-axis current at the current moment, is the given value of the d-axis current at the current moment, is the phase angle at the current moment.

10. The multi-module parallel synchronous control method for high-power converters according to claim 1, characterized in that The calculating and outputting the control duty cycle for controlling each sub-module by each sub-module control system according to the q-axis current reference value, d-axis current reference value, and phase angle includes: Calculating the q-axis voltage reference value for each sub-module according to the q-axis current reference value and the actual q-axis current of each sub-module; Calculating the d-axis voltage reference value for each sub-module according to the d-axis current reference value and the actual d-axis current of each sub-module; Calculating the control duty cycle for each sub-module according to the q-axis voltage reference value and the d-axis voltage reference value of each sub-module; Among them, calculating the q-axis voltage reference value for each sub-module according to the q-axis current reference value and the actual q-axis current of each sub-module includes: The calculating the d-axis voltage reference value for each sub-module according to the d-axis current reference value and the actual d-axis current of each sub-module includes: wherein, is the q-axis voltage reference value of the nth sub-module at the current moment, is the d-axis voltage reference value of the nth sub-module at the current moment, N is the number of sub-modules, is the actual q-axis current of the nth sub-module at the current moment, is the actual d-axis current of the nth sub-module at the current moment, is the proportional coefficient of the current loop, is the integral coefficient of the current loop.

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