A method and system for suppressing direct current side current ripple for motor drive systems

Abstract

The application discloses a direct-current side current pulsation suppression method and system suitable for a motor driving system and belongs to the field of modular multilevel converters, and comprises the following steps: step one, calculating the average value of the capacitor voltage of each phase unit sub-module of the MMC, and obtaining the sub-module capacitor voltage feedback value through a wave trap; step two, setting the sub-module capacitor voltage reference value of the MMC, and subtracting the sub-module capacitor voltage feedback value, and obtaining the direct-current component reference value of the circulating current after adjusting the obtained difference value; step three, subtracting 1 / 3 of the direct-current component reference value of the circulating current from the direct-current side current of the MMC, and obtaining the direct-current component control signal of the MMC circulating current after adjusting the obtained difference value, and obtaining the conduction signal of the MMC through modulation strategy and voltage sharing control after superimposing the signal with other control signals of the MMC. The application can effectively suppress the direct-current side current pulsation of the MMC caused by harmonic current in the driving system, improve the direct-current side power quality of the MMC, and improve the reliability of the control system.

Description

Technical Field

[0001] This invention relates to the field of modular multilevel converters, and more specifically to a method and system for suppressing DC-side current ripple in motor drive systems. Background Technology

[0002] Modular multilevel converters (MMCs) are widely used in motor drive applications due to their high degree of modularity, low device voltage stress, and strong redundancy. However, when driving low-speed motors, MMCs exhibit low-frequency pulsation components in the capacitor voltage of their submodules, and the amplitude of these pulsations is inversely proportional to the motor speed. In severe cases, this can lead to overvoltage in the submodule devices, affecting the reliability of the drive system.

[0003] To address the low-frequency voltage ripple issue of the capacitor voltage in a multi-channel converter (MMC) driving a low-speed motor, an effective approach is a cascaded drive system based on the MMC and a cycloconverter (CCV). The MMC provides the intermediate-frequency voltage to the CCV, while the CCV provides the low-frequency voltage required to drive the motor. However, in this scheme, the MMC outputs harmonic current, resulting in multiple frequency ripple components in the active power output, causing current ripple on the MMC's DC side. This DC current ripple affects the power quality on the MMC's input side, increases the current stress on the bridge arms, and poses a potential threat to the reliability of the drive system. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a method and system for suppressing DC-side current ripple in motor drive systems.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] In a first aspect, this application discloses a method for suppressing DC-side current ripple in a motor drive system, comprising:

[0007] The average value of the capacitor voltage of each phase unit submodule of MMC is processed by a notch filter to obtain the feedback value of the capacitor voltage of each phase unit submodule.

[0008] Set the reference value of the submodule capacitor voltage of the MMC, and subtract the submodule capacitor voltage reference value from the feedback value of the submodule capacitor voltage of each phase unit to obtain the reference value of the DC component of the circulating current of each phase unit of the MMC.

[0009] The DC component control signal of the MMC circulating current is obtained by subtracting the reference value of the DC component of the circulating current of each phase unit of the MMC from 1 / 3 of the DC side current of the MMC.

[0010] The DC component control signal of the MMC circulating current is superimposed with the MMC output voltage control signal and the second harmonic circulating current control signal, and then the MMC conduction signal is obtained through modulation strategy and voltage equalization control.

[0011] The switching devices within each submodule of the MMC are turned on or off based on the conduction signal.

[0012] In some embodiments, the DC component reference value of the circulating current of each phase unit of the MMC is obtained by adjusting the difference between the submodule capacitor voltage reference value and the submodule capacitor voltage feedback value of each phase unit through a proportional-integral controller.

[0013] In some embodiments, the DC component control signal of the MMC circulating current is obtained by subtracting the reference value of the DC component of the circulating current of each phase unit of the MMC from 1 / 3 of the DC side current of the MMC and adjusting it through a proportional-integral controller.

[0014] In some embodiments, the transfer function of the notch filter satisfies the following:

[0015] G(s)=G1(s)G2(s)G3(s)G4(s)

[0016] Transfer function G n (s)(n=1,2,3,4) is represented as:

[0017]

[0018] Where, ω n For G n The center angular frequency of (s), ξ is the damping ratio, and s is the differential operator.

[0019] In some embodiments, the formula for selecting the center angular frequency in the transfer function of the notch filter is as follows:

[0020]

[0021] Where, ω g ω is the angular frequency of the MMC output voltage. m ω is the electrical angular frequency of the motor.

[0022] In some embodiments, ω g The voltage reference value controlled by the MMC output voltage is obtained, ω m The speed is obtained from the motor speed sensor.

[0023] In some embodiments, the average value of the capacitor voltage of each phase unit submodule of the MMC is obtained by averaging the real-time monitoring values ​​of the capacitor voltage of each phase unit submodule of the MMC; the DC side current of the MMC is the real-time monitoring value of the DC side current of the MMC.

[0024] Secondly, this application discloses a DC-side current ripple suppression system as described in the first aspect, comprising:

[0025] Submodule capacitor voltage feedback module: The average value of the submodule capacitor voltage of each phase unit of MMC is processed by a notch filter to obtain the submodule capacitor voltage feedback value of each phase unit.

[0026] DC component reference module: Set the reference value of the submodule capacitor voltage of MMC, and calculate the difference between the reference value of the submodule capacitor voltage and the feedback value of the submodule capacitor voltage of each phase unit to obtain the reference value of the DC component of the circulating current of each phase unit of MMC.

[0027] DC component control signal module: The DC component control signal of the MMC circulating current is obtained by subtracting the reference value of the DC component of the circulating current of each phase unit of the MMC from 1 / 3 of the DC side current of the MMC.

[0028] Turn-on signal module: The DC component control signal of the MMC circulating current is superimposed with the MMC output voltage control signal and the second harmonic circulating current control signal, and then the MMC turn-on signal is obtained through modulation strategy and voltage equalization control;

[0029] Drive module: Controls the switching devices in each submodule of the MMC to turn on or off based on the conduction signal.

[0030] Thirdly, this application discloses a terminal device, including a memory, a processor, and a computer program stored in the memory and capable of running on the processor. The memory stores the computer program capable of running on the processor. When the processor loads and executes the computer program, it employs a DC-side current ripple suppression method applicable to a motor drive system as described in the first aspect.

[0031] Fourthly, this application discloses a computer-readable storage medium storing a computer program, which, when loaded and executed by a processor, employs a DC-side current ripple suppression method applicable to a motor drive system as described in the first aspect.

[0032] The beneficial effects of this invention are:

[0033] This invention can effectively suppress DC-side current ripple caused by harmonic current in the MMC and CCV cascaded drive system, and improve the DC-side power quality of the MMC.

[0034] This invention uses a notch filter to filter the feedback signal, removing harmonic-related frequency components from the capacitor voltage, thus avoiding their introduction into the DC-side current ripple suppression stage and improving the reliability of the control system.

[0035] The DC-side current ripple suppression method for motor drive systems proposed in this invention does not require additional system construction costs, the algorithm is easy to implement, and the control is simple and direct, making it highly practical. Attached Figure Description

[0036] The invention will now be further described with reference to the accompanying drawings.

[0037] Figure 1 This is a circuit diagram of the MMC and CCV cascaded drive system of this application;

[0038] Figure 2 This is a control block diagram of the DC-side current ripple suppression method applicable to the motor drive system of this application. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0041] This invention relates to a method for suppressing DC-side current ripple in a suitable motor drive system applicable to MMC and CCV cascaded drive systems. The circuit diagram of the drive system is shown below. Figure 1 As shown, the control block diagram of the DC-side current ripple suppression method applicable to motor drive systems is as follows: Figure 2 As shown. The DC-side current ripple suppression method for a motor drive system according to the present invention includes the following steps:

[0042] Real-time monitoring of the capacitor voltage of each phase submodule of the MMC, and averaging the capacitor voltage of each phase submodule to obtain u. cj_avg (j=a,b,c), and after filtering out harmonic-related frequency components by a notch filter G(s), the submodule capacitor voltage feedback value u of each phase unit is obtained. cj_filtered ;

[0043] The transfer function of the notch filter is:

[0044] G(s)=G1(s)G2(s)G3(s)G4(s)

[0045] Transfer function G n (s)(n=1,2,3,4) is represented as:

[0046]

[0047] Where, ω n For G n The center angular frequency of (s), ξ is the damping ratio, and s is the differential operator; the formula for selecting the center angular frequency of the notch filter is:

[0048]

[0049] Where, ω g ω is the angular frequency of the MMC output voltage. m ω is the electrical angular frequency of the motor; where ω g The voltage reference value controlled by the MMC output voltage is obtained, ω m The speed is obtained from the motor speed sensor.

[0050] Set the reference value u for the submodule capacitor voltage of the MMC. c * The voltage error is obtained by subtracting the voltage feedback value of the submodule capacitor of each phase unit. After proportional-integral (PI) adjustment, the DC component reference value i of the circulating current of each phase unit of the MMC is obtained. cir0_j * ,

[0051] Real-time monitoring of the DC-side current i of the MMC dc , change i cir0_j * DC component of the circulating current in each phase unit of MMC dc The difference between the two values ​​is calculated as / 3, and after proportional-integral adjustment, the DC component control signal u of the MMC circulating current is obtained. cir0_j , will u cir0_j With MMC output voltage control signal u ref_j and the second harmonic circulating current control signal u cir2_j After superposition, the MMC's turn-on signal is obtained through modulation strategy and voltage equalization control, which controls the switching devices in each sub-module of the MMC to turn on or off.

[0052] This application discloses a DC-side current ripple suppression system, including:

[0053] Submodule capacitor voltage feedback module: The average value of the submodule capacitor voltage of each phase unit of MMC is processed by a notch filter to obtain the submodule capacitor voltage feedback value of each phase unit.

[0054] DC component reference module: Set the reference value of the submodule capacitor voltage of MMC, and calculate the difference between the reference value of the submodule capacitor voltage and the feedback value of the submodule capacitor voltage of each phase unit to obtain the reference value of the DC component of the circulating current of each phase unit of MMC.

[0055] DC component control signal module: The DC component control signal of the MMC circulating current is obtained by subtracting the reference value of the DC component of the circulating current of each phase unit of the MMC from 1 / 3 of the DC side current of the MMC.

[0056] Turn-on signal module: The DC component control signal of the MMC circulating current is superimposed with the MMC output voltage control signal and the second harmonic circulating current control signal, and then the MMC turn-on signal is obtained through modulation strategy and voltage equalization control;

[0057] Drive module: Controls the switching devices in each submodule of the MMC to turn on or off based on the conduction signal.

[0058] This application also discloses a terminal device, including a memory, a processor, and a computer program stored in the memory and capable of running on the processor. When the processor executes the computer program, it employs any of the DC-side current ripple suppression methods applicable to motor drive systems described in the above embodiments.

[0059] The terminal device can be a computer device such as a desktop computer, a laptop computer, or a cloud server. The terminal device includes, but is not limited to, a processor and a memory. For example, the terminal device may also include input / output devices, network access devices, and buses.

[0060] The processor can be a central processing unit (CPU). Of course, depending on the actual use, it can also be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), off-the-shelf programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or any conventional processor, etc., and this application does not limit it in this regard.

[0061] The memory can be an internal storage unit of the terminal device, such as a hard disk or RAM of the terminal device, or an external storage device of the terminal device, such as a plug-in hard disk, smart memory card (SMC), secure digital card (SD), or flash memory card (FC) equipped on the terminal device. Furthermore, the memory can be a combination of internal storage units and external storage devices of the terminal device. The memory is used to store computer programs and other programs and data required by the terminal device. The memory can also be used to temporarily store data that has been output or will be output. This application does not limit this.

[0062] In this terminal device, any of the DC-side current ripple suppression methods applicable to motor drive systems in the above embodiments are stored in the terminal device's memory and loaded and executed on the terminal device's processor for convenient use.

[0063] This application also discloses a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, it employs any of the DC-side current ripple suppression methods applicable to motor drive systems described in the above embodiments.

[0064] The computer program can be stored in a computer-readable medium. The computer program includes computer program code, which can be in the form of source code, object code, executable file, or certain middleware. The computer-readable medium includes any entity or device capable of carrying computer program code, recording media, USB flash drive, portable hard drive, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc. It should be noted that the computer-readable medium includes, but is not limited to, the above-mentioned components.

[0065] The above-described DC-side current ripple suppression method for any of the applicable motor drive systems in the above embodiments is stored in the computer-readable storage medium and loaded and executed on the processor to facilitate the storage and application of the above methods.

[0066] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for suppressing DC-side current ripple in a motor drive system, characterized in that, include: The average value of the capacitor voltage of each phase unit submodule of MMC is filtered out by a notch filter to remove the frequency components related to harmonics, and the feedback value of the capacitor voltage of each phase unit submodule is obtained. Set the reference value of the submodule capacitor voltage of the MMC, and subtract the submodule capacitor voltage reference value from the feedback value of the submodule capacitor voltage of each phase unit to obtain the reference value of the DC component of the circulating current of each phase unit of the MMC. The DC component control signal of the MMC circulating current is obtained by subtracting the reference value of the DC component of the circulating current of each phase unit of the MMC from 1 / 3 of the DC side current of the MMC. The DC component control signal of the MMC circulating current is superimposed with the MMC output voltage control signal and the second harmonic circulating current control signal, and then the MMC conduction signal is obtained through modulation strategy and voltage equalization control. The switching devices within each submodule of the MMC are turned on or off based on the conduction signal.

2. The method for suppressing DC-side current ripple in a motor drive system according to claim 1, characterized in that, The reference value of the submodule capacitor voltage is obtained by subtracting the feedback value of the submodule capacitor voltage of each phase unit and then adjusting it through the proportional-integral controller to obtain the reference value of the DC component of the circulating current of each phase unit of the MMC.

3. The method for suppressing DC-side current ripple in a motor drive system according to claim 1, characterized in that, The reference value of the DC component of the circulating current of each phase unit of the MMC is obtained by subtracting 1 / 3 of the DC side current of the MMC and then adjusting it through a proportional-integral controller to obtain the DC component control signal of the MMC circulating current.

4. The method for suppressing DC-side current ripple in a motor drive system according to claim 1, characterized in that, The transfer function of the notch filter satisfies: transfer function Represented as: in, for The center angular frequency, For the damping ratio, It is a differential operator.

5. The method for suppressing DC-side current ripple in a motor drive system according to claim 4, characterized in that, In the transfer function of a notch filter, the formula for selecting the center angular frequency is: in, The angular frequency of the MMC output voltage. ω is the electrical angular frequency of the motor.

6. The DC-side current ripple suppression method for a motor drive system according to claim 5, characterized in that, The voltage reference value is obtained from the output voltage of the MMC, and ωm is obtained from the motor speed sensor.

7. The method for suppressing DC-side current ripple in a motor drive system according to claim 1, characterized in that, The average value of the capacitor voltage of each phase unit submodule of MMC is obtained by averaging the real-time monitoring values ​​of the capacitor voltage of each phase unit submodule of MMC. The DC-side current of the MMC is the real-time monitoring value of the DC-side current of the MMC.

8. A DC-side current ripple suppression system applying the DC-side current ripple suppression method for a motor drive system as described in any one of claims 1 to 7, characterized in that, include; Submodule capacitor voltage feedback module: The average value of the submodule capacitor voltage of each phase unit of MMC is processed by a notch filter to obtain the submodule capacitor voltage feedback value of each phase unit. DC component reference module: Set the reference value of the submodule capacitor voltage of MMC, and calculate the difference between the reference value of the submodule capacitor voltage and the feedback value of the submodule capacitor voltage of each phase unit to obtain the reference value of the DC component of the circulating current of each phase unit of MMC. DC component control signal module: The DC component control signal of the MMC circulating current is obtained by subtracting the reference value of the DC component of the circulating current of each phase unit of the MMC from 1 / 3 of the DC side current of the MMC. Turn-on signal module: The DC component control signal of the MMC circulating current is superimposed with the MMC output voltage control signal and the second harmonic circulating current control signal, and then the MMC turn-on signal is obtained through modulation strategy and voltage equalization control; Drive module: Controls the switching devices in each submodule of the MMC to turn on or off based on the conduction signal.

9. A terminal device, comprising a memory, a processor, and a computer program stored in the memory and capable of running on the processor, characterized in that, When the processor loads and executes the computer program, it implements a DC-side current ripple suppression method for a motor drive system according to any one of claims 1 to 7.

10. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is loaded and executed by the processor, it implements a DC-side current ripple suppression method for a motor drive system according to any one of claims 1 to 7.

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