A chopper control method and device

Abstract

The application relates to a chopper control method and device, which comprises the following steps: calculating a braking power coefficient according to a motor braking force and a motor rotating speed; setting a chopper control mode according to a traction braking state and the braking power coefficient; if the current traction braking state is a traction mode or a braking mode and the braking power coefficient is less than a first preset threshold, setting the current chopper control mode as a first chopper control mode; if the current traction braking state is a braking mode and the braking power coefficient is greater than a second preset threshold, setting the current chopper control mode as a second chopper control mode; if the current traction braking state is a braking mode and the braking power coefficient is not less than the first preset threshold and not greater than the second preset threshold, keeping the last chopper control mode as the current chopper control mode; and performing chopper control according to a chopper duty cycle calculated according to the current chopper control mode.

Description

A chopper control method and device Technical Field

[0001] This invention relates to the field of rail vehicle braking, and more particularly to a chopper control method and apparatus. Background Technology

[0002] Braking methods for urban rail transit vehicles are divided into mechanical braking and electric braking. Mechanical braking is mainly achieved by the braking system controlling the mechanical brake shoes to apply friction through hydraulic or air pressure. Electric braking, on the other hand, is achieved by the traction system controlling the traction motor to generate electric braking force. Electric braking can convert the vehicle's kinetic energy into electrical energy and regenerate it back to the power grid. It can also avoid the wear and tear of mechanical brake shoes. Therefore, electric braking is the preferred braking method for vehicles. However, when the grid's absorption capacity is insufficient, electric braking can cause the grid voltage to rise continuously, leading to regenerative failure. Therefore, a braking resistor must be installed to dissipate the excess regenerative energy to ensure the continuous operation of electric braking.

[0003] Due to heat dissipation limitations, the frequency of the power switching devices in the chopper circuit must be as low as possible. However, low switching frequency chopper control can lead to larger capacitor voltage fluctuations, and the increased delay may also cause instability in the chopper control. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a chopper control method and system that can stabilize the chopper duty cycle even with lower switching frequencies of the power devices in the chopper circuit, while avoiding frequent switching of the chopper mode in the chopper control strategy, thereby improving the stability of chopper control.

[0005] To achieve the above objectives, the first aspect of the present invention provides a chopper control method, the method comprising:

[0006] The braking power coefficient is calculated based on the electric motor's power and motor speed.

[0007] The chopper control mode is set according to the traction braking state and the braking power coefficient;

[0008] If the current traction braking state is traction mode, or braking mode and the braking power coefficient is less than the first preset threshold, the current chopper control mode is set to the first chopper control mode.

[0009] If the current traction braking state is braking mode and the braking power coefficient is greater than the second preset threshold, set the current chopper control mode to the second chopper control mode.

[0010] If the current traction braking state is braking mode and the braking power coefficient is not less than the first preset threshold and not greater than the second preset threshold, the previous chopper control mode is kept as the current chopper control mode.

[0011] Chopper control is performed based on the chopper duty cycle calculated according to the current chopper control mode.

[0012] Furthermore, the first chopper control mode calculates the chopper duty cycle based on the real-time voltage value of the supporting capacitor.

[0013] Furthermore, the second chopper control mode calculates the chopper duty cycle based on real-time braking power feedforward.

[0014] Furthermore, the calculation of the chopper duty cycle based on the real-time voltage value of the supporting capacitor is specifically as follows:

[0015] The voltage deviation value is generated by subtracting the real-time voltage value of the supporting capacitor from the preset chopping start threshold.

[0016] The chopper duty cycle is calculated based on the Kp control value and the voltage deviation value.

[0017] Furthermore, the preset chopping start threshold is set according to the real-time braking power.

[0018] Furthermore, the specific calculation formula for the chopper duty cycle based on real-time braking power feedforward is as follows:

[0019]

[0020] Where D is the chopper duty cycle, R is the cold resistance of the braking resistor, and P 制动 For electric braking power, U dc To support the instantaneous value of the capacitor voltage, I dc_HPF U is the extracted value of the high-frequency component of the network flow. dc_fil To support the capacitor voltage filtering value, U coeff This is the chopper power adjustment coefficient.

[0021] Furthermore, the chopper power adjustment coefficient is set according to the voltage filtering value of the supporting capacitor.

[0022] Furthermore, the step of setting the chopper power adjustment coefficient based on the support capacitor voltage filter value specifically means that the chopper power adjustment coefficient is positively correlated with the support capacitor voltage filter value.

[0023] A second aspect of the present invention provides a chopper control device, the device comprising:

[0024] The data processing module is used to calculate and generate a braking power coefficient based on the motor power and motor speed; and to set the chopper control mode based on the traction braking state and the braking power coefficient.

[0025] If the current traction braking state is traction mode, or braking mode and the braking power coefficient is less than the first preset threshold, the current chopper control mode is set to the first chopper control mode.

[0026] If the current traction braking state is braking mode and the braking power coefficient is greater than the second preset threshold, set the current chopper control mode to the second chopper control mode.

[0027] If the current traction braking state is braking mode and the braking power coefficient is not less than the first preset threshold and not greater than the second preset threshold, the previous chopper control mode is kept as the current chopper control mode.

[0028] The control execution module is used to perform chopping control based on the chopping duty cycle calculated and generated according to the current chopping control mode.

[0029] The present invention provides a chopper control method and apparatus that can stabilize the chopper duty cycle when the switching frequency of the power devices in the chopper circuit is lower. The switching between two chopper modes is determined by the traction braking state and the magnitude of the braking power coefficient, thereby avoiding frequent switching of chopper modes in the chopper control strategy and improving the stability of chopper control. Attached Figure Description

[0030] Figure 1 is a hardware schematic diagram of the chopper system of the chopper control method provided in Embodiment 1 of the present invention;

[0031] Figure 2 is a flowchart of the chopper control method provided in Embodiment 1 of the present invention;

[0032] Figure 3 is a schematic diagram of the chopper control mode switching of the chopper control method provided in Embodiment 1 of the present invention;

[0033] Figure 4 is a schematic diagram of the PWM generation unit of the chopper control method provided in Embodiment 1 of the present invention;

[0034] Figure 5 is one of the structural schematic diagrams of the chopper control device provided in Embodiment 2 of the present invention;

[0035] Figure 6 is a second schematic diagram of the chopper control device provided in Embodiment 2 of the present invention. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0037] The chopper control method and apparatus provided in this invention determine the switching between two chopper modes by considering the traction braking state and the magnitude of the braking power coefficient. This avoids frequent switching of chopper modes in the chopper control strategy, thereby improving the stability of chopper control and resulting in smoother electric braking force, thus increasing vehicle ride comfort. Furthermore, by employing a chopper control method based on a composite calculation of the instantaneous value of the supporting capacitor voltage and the real-time braking power feedforward duty cycle, the chopper switching frequency is reduced while ensuring stable chopper control. This reduces the heat generation of the chopper switch, lowers the heat dissipation design requirements of the switch, reduces the design space requirements, and improves chopper performance. Extending the lifespan of the switching transistor can reduce the maintenance costs throughout the system's lifecycle by more than 30%, thus reducing the likelihood of vehicle malfunctions. By detecting and judging network current changes, high-frequency components in the network current are extracted in real time. Combined with the instantaneous value of the supporting capacitor voltage, the power for dynamic compensation is calculated to compensate for the feedforward chopper power, improving the system's dynamic response capability and enabling control under extreme industrial control conditions such as sudden changes in network-side regenerative capacity. Through dynamic adjustment control of the chopper power adjustment coefficient, the influence of braking resistor changes with temperature can be ignored, making control simpler. At the same time, it maximizes the utilization of the same-side regenerative capacity, feeding back as much regenerative energy as possible and reducing vehicle energy consumption.

[0038] Example 1

[0039] The chopper control method of the present invention can be applied to rail transit vehicles that are electrically braked, and is not limited to EMU trains and electric locomotives.

[0040] Figure 1 is a hardware schematic diagram of the chopper system of the chopper control method provided in Embodiment 1 of the present invention. As shown in Figure 1, the grid-side Unet forms a filter circuit through the main contactor K, the filter reactor L and the supporting capacitor C, and then supplies power to the motor M through the inverter module. The chopper module and the inverter module share the intermediate DC link. The chopper module is divided into two independent chopper bridge arms a1a2 and b1b2. The two chopper bridge arms are respectively connected to two braking resistors R1 and R2. When the electric braking energy cannot be completely returned to the grid side, the two chopper bridge arms are opened to consume the regenerative capacity in the braking resistor circuit to achieve the purpose of stabilizing the voltage.

[0041] Figure 2 is a flowchart of the chopper control method provided in Embodiment 1 of the present invention. As shown in Figure 2, it includes:

[0042] Step 110: Calculate and generate the braking power coefficient based on the electric motor's power and speed.

[0043] Specifically, the system obtains the motor power, motor speed, and maximum braking power of the electric motor; it calculates the actual braking power based on the motor power and motor speed, and then calculates the braking power coefficient based on the ratio of the actual braking power to the maximum braking power of the system.

[0044] Step 120: Set the chopper control mode according to the traction braking status and braking power coefficient.

[0045] The traction and braking status includes traction mode and braking mode.

[0046] Step 130: If the current traction braking state is traction mode, or braking mode and the braking power coefficient is less than the first preset threshold, set the current chopper control mode to the first chopper control mode.

[0047] The first chopper control mode calculates the chopper duty cycle based on the real-time voltage value of the supporting capacitor. The first preset threshold can be set according to the practical debugging of a specific engineering project. Optionally, the first preset threshold is 0.35. The first chopper control mode is used for chopper stages requiring rapid deployment but with relatively low braking power.

[0048] Specifically, the voltage deviation value is generated by subtracting the real-time voltage value of the supporting capacitor from the preset chopping start threshold; the chopping duty cycle is then calculated based on the Kp control value and the voltage deviation value. Here, the Kp control value is the control parameter of the proportional-integral (PI) controller.

[0049] In one possible implementation, the preset chopping start threshold is set based on the real-time braking power. The chopping duty cycle formula in the first chopping control mode is D = Kp * ΔU, ΔU = Vdc - Vset, Vset = f(P) 制动 ), where Vdc is the real-time voltage value of the supporting capacitor, Vset is the preset chopping start threshold, and ΔU is the voltage deviation value. The chopping enable signal is given high only when ΔU is greater than or equal to zero, i.e., chopping is allowed.

[0050] Step 140: If the current traction braking state is braking mode and the braking power coefficient is greater than the second preset threshold, set the current chopper control mode to the second chopper control mode.

[0051] The second chopper control mode calculates the chopper duty cycle based on real-time braking power feedforward. The second preset threshold can be set according to the practical debugging of a specific engineering project. The optional second preset threshold is 0.4. The second chopper control mode is mainly used in the chopper stage where the braking power is large and the chopper duty cycle needs to be stably controlled. The specific calculation formula is shown in formula (1):

[0052]

[0053] Where D is the chopper duty cycle, R is the cold resistance of the braking resistor, and P 制动 For electric braking power, U dc To support the instantaneous value of the capacitor voltage, I dc_HPF U is the extracted value of the high-frequency component of the network flow. dc_fil To support the capacitor voltage filtering value, U coeff This is the chopper power adjustment coefficient.

[0054] In one possible implementation, the chopper power adjustment coefficient, U, is set according to the filter value of the supporting capacitor voltage. coeff =f(U dc_fil Furthermore, the chopper power adjustment coefficient is positively correlated with the support capacitor voltage filter value. Based on the support capacitor voltage filter value U... dc_fil The size is adjusted in real time. When the grid voltage is low, it can be assumed that the grid side still has sufficient absorption capacity. At this time, the chopper power adjustment coefficient U is reduced. coeff The chopping duty cycle decreases, resulting in a decrease in actual chopping power, thus fully utilizing the grid-side absorption capacity. When the grid voltage gradually increases, it is assumed that the grid-side absorption capacity cannot meet the current braking power requirements, and the chopping power adjustment coefficient U is rapidly increased. coeff The chopper duty cycle increases, dissipating the energy that the grid side cannot absorb into the braking resistor, thus achieving voltage stabilization.

[0055] By detecting and judging changes in grid current, high-frequency components in the grid current are extracted in real time to compensate for the feedforward chopping power, thereby improving the system's dynamic response capability and enabling control under extreme industrial control conditions such as sudden changes in grid-side regeneration capacity. By dynamically adjusting the chopping power coefficient, the system can automatically identify the grid-side absorption capacity based on the grid voltage and make dynamic adjustments to achieve energy saving. The resistance of the braking resistor increases with its own temperature in actual use. Since the chopping power adjustment coefficient in the chopping duty cycle expression of the second chopping control mode can automatically adapt to the influence of the braking resistor's resistance change, the feedforward power can be calculated using the cold resistance value, making the calculation simpler.

[0056] Step 150: If the current traction braking state is braking mode and the braking power coefficient is not less than the first preset threshold and not greater than the second preset threshold, keep the previous chopper control mode as the current chopper control mode.

[0057] Specifically, if the traction braking state and braking power coefficient do not meet the requirements of steps 130 and 140, the previous chopper control mode is retained as the current chopper control mode.

[0058] Frequent switching of the chopper mode is avoided by using the braking power coefficient hysteresis method in steps 130 to 150. Figure 3 is a schematic diagram of the chopper control mode switching of the chopper control method provided in Embodiment 1 of the present invention. As shown in Figure 3, when the current mode is braking and the braking power coefficient is less than 0.35 or when the current mode is traction, i.e. (Brake_power_coeff<0.35&&Barke_command==1)||(Traction_command==1), the first chopper control mode Chop_Mode 0 is selected. When the current mode is braking and the braking power coefficient is greater than 0.4, i.e. Brake_power_coeff>0.4&&Barke_command==1, the second chopper control mode Chop_Mode 1 is selected. Otherwise, the previous chopper control mode is maintained.

[0059] Step 160: Perform chopping control based on the chopping duty cycle calculated according to the current chopping control mode.

[0060] Specifically, a pulse width modulation (PWM) drive signal is generated based on the chopper duty cycle, chopper period, and chopper enable signal to control the two chopper bridge arms of the chopper module. The chopper period, i.e., the chopper switching frequency, is a fixed set value.

[0061] In one possible implementation, to reduce the fluctuation of DC voltage during chopping, the activation of the two chopping channels is phase-shifted. Two sawtooth wave signals with a 180-degree phase difference are independently generated based on the chopping period value. These sawtooth wave signals are compared with a chopping comparison value, which is generated based on the chopping duty cycle. When the sawtooth wave count value is lower than the chopping comparison value and the chopping enable signal is high, a chopping activation signal is triggered to control the chopping bridge arm operation of the chopping system hardware circuit.

[0062] In a specific example, Figure 4 is a schematic diagram of the PWM generation unit of the chopper control method provided in Embodiment 1 of the present invention. As shown in Figure 4, it includes two sawtooth wave signals, A and B, with a chopper period of Ts. The sawtooth wave signals A and B are 180 degrees out of phase. From (k-1)Ts to T0, the sawtooth wave count is lower than the chopper comparison value. When the chopper enable signal is high, i.e., chopper is allowed, the chopper bridge arm of A is turned on. From T0 to KTs, the sawtooth wave count is higher than the chopper comparison value, and the chopper bridge arm of A remains closed. From (k-1)Ts+π to T1, the sawtooth wave count is lower than the chopper comparison value. When the chopper enable signal is high, the chopper bridge arm of B is turned on. From T1 to KTs+π, the sawtooth wave count is higher than the chopper comparison value, and the chopper bridge arm of B remains closed. The chopper bridge arms A and B are turned on once each within one cycle Ts.

[0063] Example 2

[0064] Embodiment 2 of the present invention provides a chopper control device. Figure 5 is a schematic diagram of the structure of the chopper control device provided in Embodiment 2 of the present invention. As shown in Figure 5, the chopper control device 200 includes a data processing module 201 and a control execution module 202.

[0065] The data processing module 201 is used to calculate and generate the braking power coefficient based on the motor power and motor speed; and to set the chopper control mode based on the traction braking state and the braking power coefficient.

[0066] If the current traction braking state is traction mode, or is braking mode and the braking power coefficient is less than the first preset threshold, set the current chopper control mode to the first chopper control mode.

[0067] If the current traction braking state is braking mode and the braking power coefficient is greater than the second preset threshold, set the current chopper control mode to the second chopper control mode.

[0068] If the current traction braking state is braking mode and the braking power coefficient is not less than the first preset threshold and not greater than the second preset threshold, the previous chopper control mode is kept as the current chopper control mode.

[0069] The control execution module 202 is used to perform chopping control based on the chopping duty cycle calculated and generated according to the current chopping control mode.

[0070] In a specific example, Figure 6 is a second schematic diagram of the chopper control device structure provided in Embodiment 2 of the present invention. As shown in Figure 6, the data processing module 201 of the chopper control device 200 includes a digital signal processor (DSP) 2011, and the control execution module 202 includes a field programmable gate array (FPGA) 2021. The FPGA includes a dual-port RAM unit 20211, an analog sampling unit 20212, a fault discrimination unit 20213, and a PWM generation unit 20214.

[0071] As shown in Figure 6, the chopper control device 200 is connected to the traction control system 300 and the chopper system hardware circuit 300 respectively. Data such as motor power, motor speed and traction braking status of the traction control system 300 are sent to the DSP 2011 through the dual-port RAM unit 20211. Data such as mains voltage, mains current and chopper current of the chopper system hardware circuit 300 are sampled and processed by the analog sampling unit 20212 and then sent to the DSP 2011 through the dual-port RAM unit 20211. The DSP 2011 calculates and generates the chopper duty cycle, chopper period and chopper enable based on the received data, and sends them to the PWM generation unit 20214 through the dual-port RAM unit 20211. The PWM generation unit 20214 generates PWM drive signals based on the chopper duty cycle, chopper period and chopper enable signals to control the two chopper bridge arms of the chopper system hardware circuit 300.

[0072] The chopper control device provided in Embodiment 2 of the present invention is used to execute the steps of the method provided in Embodiment 1 of the present invention. Its implementation principle and technical effect are similar, and will not be described again here.

[0073] It should be noted that the division of the various modules in the above-described device is merely a logical functional division. In actual implementation, they can be fully or partially integrated into a single physical entity, or they can be physically separated. Furthermore, these modules can be implemented entirely in software via processing element calls; they can be fully implemented in hardware; or some modules can be implemented by processing element calls to software, while others are implemented in hardware. For example, the data processing module can be a separate processing element, or it can be integrated into a chip in the above-described device. Alternatively, it can be stored as program code in the memory of the above-described device, and called and executed by a processing element of the device. The implementation of other modules is similar. Moreover, these modules can be fully or partially integrated together, or they can be implemented independently. The processing element described here can be an integrated circuit with signal processing capabilities. In the implementation process, the steps of the method provided in the embodiments of the present invention or the various modules of the device provided in the embodiments of the present invention can be completed by the integrated logic circuits in the hardware of the processor element or by software instructions.

[0074] For example, the modules of the apparatus provided in the embodiments of the present invention may be one or more integrated circuits configured as the methods provided in the embodiments of the present invention, such as: one or more application-specific integrated circuits (ASICs), or one or more digital signal processors (DSPs), or one or more field-programmable gate arrays (FPGAs), etc. As another example, when a module of the apparatus provided in the embodiments of the present invention is implemented in the form of processing element scheduler code, the processing element may be a general-purpose processor, such as a central processing unit (CPU) or other processor capable of calling program code. Furthermore, these modules of the apparatus provided in the embodiments of the present invention may be integrated together and implemented in the form of a system-on-a-chip (SOC).

[0075] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented, in whole or in part, as a computer program product. This computer program product includes one or more computer instructions. When these computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the methods provided according to the embodiments of the present invention are generated. The computer described above can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The aforementioned computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the aforementioned computer instructions can be transmitted from one website, computer, server, or data center to another via wired (e.g., coaxial cable, fiber optic, Digital Subscriber Line (DSL)) or wireless (e.g., infrared, wireless, Bluetooth, microwave, etc.) means. The aforementioned computer-readable storage medium can be any available medium that a computer can access, or a data storage device such as a server or data center that integrates one or more available media. The aforementioned available media can be magnetic media (e.g., floppy disks, hard disks, magnetic tapes), optical media (e.g., high-density digital video discs (DVDs)), or semiconductor media (e.g., solid-state disks (SSDs)).

[0076] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0077] The steps of the methods or algorithms described in conjunction with the embodiments disclosed herein can be implemented in hardware, a software module executed by a processor, or a combination of both. The software module can be located in random access memory (RAM), main memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art.

[0078] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A chopper control method, characterized in that, The method includes: calculating a braking power coefficient based on the motor power and motor speed; setting a chopper control mode based on the traction braking state and the braking power coefficient; if the current traction braking state is a traction mode, or a braking mode and the braking power coefficient is less than a first preset threshold, setting the current chopper control mode to a first chopper control mode; if the current traction braking state is a braking mode and the braking power coefficient is greater than a second preset threshold, setting the current chopper control mode to a second chopper control mode; if the current traction braking state is a braking mode and the braking power coefficient is not less than the first preset threshold and not greater than the second preset threshold, maintaining the previous chopper control mode as the current chopper control mode; performing chopper control based on the chopper duty cycle calculated by the current chopper control mode; the first chopper control mode calculates the chopper duty cycle based on the real-time voltage value of the supporting capacitor; the second chopper control mode calculates the chopper duty cycle based on real-time braking power feedforward; the specific calculation formula for calculating the chopper duty cycle based on real-time braking power feedforward is as follows: Where D is the chopper duty cycle and R is the cold resistance of the braking resistor. For electric braking power, To support the instantaneous value of the capacitor voltage, This is the extracted value of the high-frequency components of the network stream. To support the capacitor voltage filtering value, This is the chopper power adjustment coefficient.

2. The chopper control method according to claim 1, characterized in that, The calculation of the chopper duty cycle based on the real-time voltage value of the supporting capacitor specifically involves: subtracting the real-time voltage value of the supporting capacitor from a preset chopper start threshold to generate a voltage deviation value; and calculating the chopper duty cycle based on the Kp control value and the voltage deviation value.

3. The chopper control method according to claim 2, characterized in that, The preset chopping start threshold is set according to the real-time braking power.

4. The chopper control method according to claim 1, characterized in that, The chopper power adjustment coefficient is set according to the voltage filtering value of the supporting capacitor.

5. The chopper control method according to claim 4, characterized in that, The step of setting the chopper power adjustment coefficient based on the support capacitor voltage filter value specifically means that the chopper power adjustment coefficient is positively correlated with the support capacitor voltage filter value.

6. A chopper control device, characterized in that, The device includes: a data processing module, used to calculate and generate a braking power coefficient based on the motor power and motor speed; set a chopper control mode based on the traction braking state and the braking power coefficient; if the current traction braking state is a traction mode, or a braking mode and the braking power coefficient is less than a first preset threshold, set the current chopper control mode to a first chopper control mode; if the current traction braking state is a braking mode and the braking power coefficient is greater than a second preset threshold, set the current chopper control mode to a second chopper control mode; if the current traction braking state is a braking mode and the braking power coefficient is not less than the first preset threshold and not greater than the second preset threshold, maintain the previous chopper control mode as the current chopper control mode; and a control execution module, used to perform chopper control based on the chopper duty cycle calculated according to the current chopper control mode; the first chopper control mode calculates the chopper duty cycle based on the real-time voltage value of the supporting capacitor; the second chopper control mode calculates the chopper duty cycle based on real-time braking power feedforward; the specific calculation formula for the chopper duty cycle based on real-time braking power feedforward is as follows: Where D is the chopper duty cycle and R is the cold resistance of the braking resistor. For electric braking power, To support the instantaneous value of the capacitor voltage, This is the extracted value of the high-frequency components of the network stream. To support the capacitor voltage filtering value, This is the chopper power adjustment coefficient.

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