Torque ripple collaborative optimization method suitable for MMC and CCV cascade drive system

Abstract

The invention discloses a torque ripple collaborative optimization method suitable for an MMC and CCV cascade drive system, and relates to the field of motor control, and the method comprises the steps: on the basis of MMC intermediate frequency operation and CCV variable frequency operation, calculating and correcting an intermediate frequency voltage outputted by an MMC in real time according to a motor side current frequency and a rotor electrical angle, and compensating a CCV modulation wave, so as to achieve the optimal control of the CCV. According to the method, the electric energy quality of the output side of the converter of the MMC and CCV cascade drive system can be effectively improved, collaborative optimization of the torque ripple is achieved, the control accuracy is ensured, the hardware cost of the converter does not need to be increased, the algorithm is simple and easy to achieve, and high practicability is achieved.

Description

Technical Field

[0001] This application relates to the field of marine motor control, and in particular to a torque ripple collaborative optimization method applicable to MMC and CCV cascaded drive systems. Background Art

[0002] The motor drive system, consisting of a drive converter and a propulsion motor, is a crucial component of a ship's integrated electrical system. As ships increasingly move towards full electrification, the voltage and power ratings of drive converters and propulsion motors are constantly increasing. In medium- and high-voltage drive applications, drive converters based on Modular Multilevel Converters (MMCs) are widely used due to their advantages such as high modularity, strong redundancy, and low component voltage stress. However, in low-speed drive applications, the capacitor voltage within the MMC submodule exhibits a low-frequency component that coincides with the motor-side current frequency. This can lead to excessive capacitor voltage fluctuations, causing overvoltage in the submodule components and affecting the reliable operation of the motor drive system. To address this issue, an effective method is to cascade the MMC and a Cycloconverter (CCV) to construct the drive converter. This solution outputs a medium-frequency voltage through the MMC under low-speed motor conditions, and the CCV down-converts the medium-frequency voltage provided by the MMC to the low-frequency voltage required by the motor, effectively avoiding the capacitor fluctuation problem of the MMC.

[0003] However, the CCV output line voltage contains harmonics caused by thyristor commutation, which can lead to torque ripple on the motor side, and this ripple increases with speed. Existing torque ripple optimization for cascaded MMC and CCV drive systems involves changing the operating mode based on different speeds. A speed threshold is set in the drive system's control logic. When the motor speed is below the threshold and in a low-speed state, the MMC operates at medium frequency, and the CCV operates at variable frequency. When the motor speed reaches the threshold and is in a medium-to-high-speed state, the CCV is bypassed, and the motor is directly driven by the MMC, which has lower output harmonics, thus preventing further increases in torque ripple. While this approach improves torque ripple at higher speeds in cascaded MMC and CCV drive systems, torque ripple at low speeds remains unsatisfactory. Summary of the Invention

[0004] To address the aforementioned problems and technical requirements, this application proposes a torque ripple collaborative optimization method applicable to MMC and CCV cascaded drive systems. The technical solution of this application is as follows:

[0005] A torque ripple co-optimization method applicable to MMC and CCV cascaded drive systems, comprising the following steps during the operation of a drive motor using an MMC and CCV cascaded drive system:

[0006] When the motor's current angular frequency ω m >ω lim At that time, according to the angular frequency ω of the motor current m and the electric angle θ of the motor rotor m Determine the dynamic amplitude U of the intermediate frequency voltage g_mod According to the electric angle θ of the motor rotor m Calculate the compensation component y of the CCV three-phase modulation wave. mj_comp ; where ω lim It is the current angular frequency threshold, j = a, b, c represent the A, B, and C phases of the motor, respectively;

[0007] Based on the dynamic amplitude U of the intermediate frequency voltage g_mod The three-phase reference voltage u of the MMC is determined using a medium-frequency voltage closed-loop control strategy. gj_ref And combined with the MMC modulation strategy, control the on / off state of the switching transistors inside the MMC;

[0008] According to the frequency command value Determining the CCV three-phase reference voltage u using a motor current vector control strategy mj_ref At the CCV three-phase reference voltage u mj_ref The normalized three-phase modulated wave y mj_ref Based on the superposition of CCV three-phase modulation wave compensation component y mj_comp It also combines a CCV modulation strategy to control the on / off state of the switching transistors within the CCV.

[0009] Its further technical solution is to base the motor's current angular frequency ω on... m and the electric angle θ of the motor rotor m Determine the dynamic amplitude U of the intermediate frequency voltage g_mod include:

[0010] According to the angular frequency ω of the motor's current m and the electric angle θ of the motor rotor m Determine the voltage command correction factor k mod And determine the dynamic amplitude U of the intermediate frequency voltage. g_mod =k mod ×U g U g It is to ensure the intermediate frequency voltage amplitude required for CCV frequency conversion and U m_N It is the amplitude of the fundamental frequency component of the phase voltage of the motor under rated operating conditions.

[0011] Its further technical solution is to base the motor's current angular frequency ω on... m and the electric angle θ of the motor rotor m Determine the voltage command correction factor k mod include:

[0012] According to the electric angle θ of the motor rotorm Determine the CCV three-phase modulation wave y mj_ref Phase angle of the fundamental frequency component of the A-phase modulated wave And based on the phase angle The corresponding time variable w is obtained by conversion, and the time variable w is combined with the current angular frequency ω. m The voltage command correction factor k is calculated. mod .

[0013] Its further technical solution is, based on the phase angle The corresponding time variable w obtained by transformation is:

[0014]

[0015] Where k is an integer not less than 0.

[0016] A further technical solution involves using the time variable w in conjunction with the current angular frequency ω. m The voltage command correction factor k is calculated. mod include:

[0017] Calculate the angular frequency ω of the current m With respect to the rated angular frequency ω of the motor current m_N ratio And in accordance with The voltage command correction factor k is calculated. mod , k margin It is a modulation margin coefficient less than 1.

[0018] Its further technical solution is, based on the electric angle θ of the motor rotor m Calculate the compensation component y of the CCV three-phase modulation wave. mj_comp for:

[0019]

[0020] Where Y represents the CCV three-phase modulation wave y mj_ref The amplitude of the fundamental frequency component and u md_ref It is the CCV three-phase reference voltage u mj_ref The d-axis component, u mq_ref It is the CCV three-phase reference voltage u mj_ref The q-axis component; the three-phase phase angle of the fundamental frequency component of the CCV three-phase modulated wave. CCV three-phase modulation wave y mj_ref Phase angle of the fundamental frequency component of the A-phase modulated wave According to the electric angle θ of the motor rotor m To determine.

[0021] Its further technical solution is, based on the electric angle θ of the motor rotorm Determine the CCV three-phase modulation wave y mj_ref Phase angle of the fundamental frequency component of the A-phase modulated wave This includes calculating the phase angle using the following formula.

[0022]

[0023] Among them, u md_ref It is the CCV three-phase reference voltage u mj_ref The d-axis component, u mq_ref It is the CCV three-phase reference voltage u mj_ref The q-axis component.

[0024] A further technical solution is that when the angular frequency ω of the motor current... m ≤ω lim Time based on constant amplitude U of intermediate frequency voltage g_lim The switching of the internal switching transistor of the MMC is controlled by a closed-loop control strategy using intermediate frequency voltage combined with an MMC modulation strategy, and the intermediate frequency voltage has a constant amplitude U. g_lim and current angular frequency threshold ω lim The following relationship must be satisfied:

[0025]

[0026] Among them, U m_N It is the amplitude of the fundamental frequency component of the phase voltage of the motor under rated operating conditions, ω m_N It is the rated angular frequency of the motor current.

[0027] Its further technical solution is based on the dynamic amplitude U of the intermediate frequency voltage. g_mod The three-phase reference voltage u of the MMC is determined using a medium-frequency voltage closed-loop control strategy. gj_ref include:

[0028] Based on the dynamic amplitude U of the intermediate frequency voltage g_mod Determine the d-axis intermediate frequency voltage command value and q-axis intermediate frequency voltage command value The three-phase intermediate frequency voltage u output by the MMC gj Performing a dq transformation yields the actual value u of the d-axis intermediate frequency voltage. gd and the actual value of the q-axis intermediate frequency voltage u gq ; d-axis intermediate frequency voltage error The PI controller receives the d-axis capacitor current command value. q-axis intermediate frequency voltage error The q-axis capacitor current command value is obtained by inputting the PI controller.

[0029] The three-phase capacitor current i of the three-phase filter capacitor of the MMCcj The d-axis capacitor current i is obtained by performing a dq transformation. cd and q-axis capacitor current i cq d-axis capacitance current error The d-axis reference voltage u is obtained by inputting the PI controller. gd_ref q-axis capacitance current error The q-axis reference voltage u is obtained by inputting the PI controller. gq_ref , for u gd_ref and u gq_ref The inverse dq transformation is performed to obtain the MMC three-phase reference voltage u. gj_ref .

[0030] Its further technical solution is to, based on the frequency command value Determining the CCV three-phase reference voltage u using a motor current vector control strategy mj_ref include:

[0031] frequency command value With current angular frequency ω m angular frequency error The input to the PI controller obtains the q-axis motor current command value. Get the d-axis motor current command value

[0032] For the three-phase motor current i mj The actual value of the d-axis motor current i is obtained by performing a dq transformation. md and the actual value of the q-axis motor current i mq ; d-axis motor current error The d-axis reference voltage u is obtained by inputting the PI controller. md_ref q-axis motor current error The q-axis reference voltage u is obtained by inputting the PI controller. mq_ref ;

[0033] For the d-axis reference voltage u md_ref and q-axis reference voltage u mq_ref The inverse dq transformation is performed to obtain the CCV three-phase reference voltage u. mj_ref .

[0034] The beneficial technical effects of this application are:

[0035] This application discloses a torque ripple co-optimization method applicable to MMC and CCV cascaded drive systems. Based on the intermediate frequency operation of the MMC and the variable frequency operation of the CCV, this method calculates and corrects the intermediate frequency voltage output by the MMC in real time according to the motor side current frequency and rotor electrical angle, and compensates for the CCV modulation wave. This can effectively improve the power quality on the output side of the converter in the MMC and CCV cascaded drive system, realize the co-optimization of torque ripple, ensure the accuracy of control, and eliminate the need to increase the hardware cost of the converter. The algorithm is simple and easy to implement, and has strong practicality. Attached Figure Description

[0036] Figure 1 This is the circuit diagram of the cascaded drive system of MMC and CCV.

[0037] Figure 2 This is a control block diagram for traditional methods.

[0038] Figure 3 This is a control block diagram of the intermediate frequency voltage closed-loop control in one embodiment.

[0039] Figure 4 This is a control block diagram of motor current vector control in one embodiment.

[0040] Figure 5 This is a control block diagram of a torque ripple collaborative optimization method in one embodiment of this application.

[0041] Figure 6 This is a simulation waveform of the intermediate frequency voltage, CCV modulation compensation component, and motor current at a motor speed of 0.25 pu in a simulation example.

[0042] Figure 7 yes Figure 6 The simulation example shows the waveforms of the intermediate frequency voltage, CCV modulation compensation component, and motor current at a motor speed of 0.5 pu.

[0043] Figure 8 yes Figure 6 The simulation example shows the waveforms of the intermediate frequency voltage, CCV modulation compensation component, and motor current at a motor speed of 0.75 pu.

[0044] Figure 9 yes Figure 6 The simulation example shows the torque pulsation waveform at motor speeds of 0.1–1 p.u. Detailed Implementation

[0045] The specific embodiments of this application will be further described below with reference to the accompanying drawings.

[0046] This application discloses a torque ripple collaborative optimization method applicable to MMC and CCV cascaded drive systems, utilizing the system circuit diagram of the drive motor of the MMC and CCV cascaded drive system as shown in the figure. Figure 1 As shown, the torque ripple collaborative optimization method of this application is implemented on this circuit structure.

[0047] This method utilizes a medium-frequency voltage closed-loop control strategy combined with an MMC modulation strategy to control the on / off state of each switch within the MMC, and a motor current vector control strategy combined with a CCV modulation strategy to control the on / off state of each switch within the CCV. After starting the motor, the method continuously collects the motor's current angular frequency ω during motor operation. m , motor rotor electrical angle θ m Three-phase motor current i mj And the three-phase intermediate frequency voltage u output by MMC gj And the three-phase capacitor current i of the three-phase filter capacitor of MMC. cj In this application, variables j = a, b, c represent the A, B, and C phases of the motor, respectively.

[0048] The current angular frequency ω m With current angular frequency threshold ω lim The comparison will determine whether to activate the torque ripple collaborative optimization method of this application.

[0049] When the motor's current angular frequency ω m ≤ω lim If the torque ripple co-optimization method is not enabled, the MMC and CCV cascaded drive system will be controlled using traditional control methods. Please refer to [reference needed]. Figure 2 The control block diagram shown is based on the three-phase intermediate frequency voltage u. gj and three-phase capacitor current i cj A closed-loop control strategy for intermediate frequency voltage is implemented by combining an intermediate frequency voltage closed-loop control strategy with an MMC modulation strategy, thereby ensuring that the MMC output has a constant intermediate frequency voltage amplitude U. g_lim Three-phase intermediate frequency voltage u gj And based on the current angular frequency ω m , motor rotor electrical angle θ m and three-phase motor current i mj Motor current vector control is achieved by combining a motor current vector control strategy with a CCV modulation strategy.

[0050] The intermediate frequency voltage closed-loop control strategy employs a dual-loop control strategy consisting of an outer loop for intermediate frequency voltage and an inner loop for capacitor current. Please refer to the detailed control logic block diagram of the intermediate frequency voltage closed-loop control strategy. Figure 3 This includes: based on the constant amplitude U of the intermediate frequency voltage. g_lim Determine the d-axis intermediate frequency voltage command value And retrieve the q-axis intermediate frequency voltage command value. The three-phase intermediate frequency voltage u output by the MMC gj The phase θ of the A-phase intermediate frequency voltage output by the MMC g Performing a dq transformation yields the actual value u of the d-axis intermediate frequency voltage. gd and the actual value of the q-axis intermediate frequency voltage u gq Then calculate the d-axis intermediate frequency voltage error. and q-axis intermediate frequency voltage error The d-axis intermediate frequency voltage error Δu gd The PI controller receives the d-axis capacitor current command value. The q-axis intermediate frequency voltage error Δu gq The q-axis capacitor current command value is obtained by inputting the PI controller. The three-phase capacitor current i of the three-phase filter capacitor of the MMC cj The phase θ of the A-phase intermediate frequency voltage output by the MMC g The d-axis capacitor current i is obtained by performing a dq transformation. cd and q-axis capacitor current i cq Then calculate the d-axis capacitance current error. and q-axis capacitance current error The d-axis capacitance current error Δi cd The d-axis reference voltage u is obtained by inputting the PI controller. gd_ref The q-axis capacitance current error Δi cq The q-axis reference voltage u is obtained by inputting the PI controller. gq_ref Then for u gd_ref and u gq_ref The phase θ of the A-phase intermediate frequency voltage output by the MMC g The inverse dq transformation is performed to obtain the MMC three-phase reference voltage u. gj_ref The obtained MMC three-phase reference voltage u gj_ref The MMC modulation strategy outputs the turn-on signals of each switch in the MMC. The MMC modulation strategy used includes capacitor voltage balancing and pulse width modulation.

[0051] The motor current vector control strategy is a dual-loop control strategy consisting of an outer speed loop and an inner motor current loop. Please refer to the detailed control logic block diagram of the motor current vector control strategy. Figure 4 This includes: setting the frequency command value With current angular frequency ω m angular frequency error The input to the PI controller obtains the q-axis motor current command value. Get the d-axis motor current command value For the three-phase motor current i mj Combined with the electric angle θ of the motor rotor m The actual value of the d-axis motor current i is obtained by performing a dq transformation.md and the actual value of the q-axis motor current i mq Then, the d-axis motor current error was calculated. The d-axis reference voltage u is obtained by inputting the PI controller. md_ref q-axis motor current error The q-axis reference voltage u is obtained by inputting the PI controller. mq_ref Finally, the d-axis reference voltage u... md_ref and q-axis reference voltage u mq_ref Combined with the electric angle θ of the motor rotor m The inverse dq transformation is performed to obtain the CCV three-phase reference voltage u. mj_ref Finally, the turn-on signals of each switch within the CCV are output via a CCV modulation strategy. This is achieved by using the CCV modulation strategy based on the CCV three-phase reference voltage u. mj_ref When the CCV switch is turned on, the CCV three-phase reference voltage u is first checked. mj_ref Third harmonic injection is performed to improve voltage utilization. Then, normalization is performed to obtain the three-phase modulated wave y. mj_ref Then, the cosine intersection method is used to output the CCV switch turn-on signal.

[0052] When the motor's current angular frequency ω m >ω lim When the torque ripple co-optimization method of this application is enabled, please refer to [reference needed]. Figure 5 The control block diagram shown optimizes the control logic for both MMC and CCV.

[0053] 1. Optimization of MMC control logic

[0054] According to the angular frequency ω of the motor's current m and the electric angle θ of the motor rotor m Perform intermediate frequency voltage correction to obtain the dynamic amplitude U of the intermediate frequency voltage. g_mod ,include:

[0055] First, based on the motor's current angular frequency ω m and the electric angle θ of the motor rotor m Determine the voltage command correction factor k mod Then take the dynamic amplitude U of the intermediate frequency voltage. g_mod =k mod ×U g U here g This ensures the required intermediate frequency voltage amplitude for CCV frequency conversion, and U m_N It is the amplitude of the fundamental frequency component of the phase voltage of the motor under rated operating conditions.

[0056] Determine the voltage command correction factor k mod The methods include:

[0057] (1) Based on the electric angle θ of the motor rotor m Determine the CCV three-phase modulation wave y mj_ref Phase angle of the fundamental frequency component of the A-phase modulated wave Phase angle The calculation formula is:

[0058]

[0059] Among them, u md_ref It is the CCV three-phase reference voltage u mj_ref The d-axis component, u mq_ref It is the CCV three-phase reference voltage u mj_ref The q-axis component.

[0060] (2) Based on phase angle The transformation yields the corresponding time variable w:

[0061]

[0062] Where k is an integer not less than 0.

[0063] (3) Finally, the time variable w is combined with the current angular frequency ω. m The voltage command correction factor k is calculated. mod This includes calculations based on the following formula:

[0064]

[0065] Where m is the current angular frequency ω m With respect to the rated angular frequency ω of the motor current m_N The ratio and written as k margin It is a modulation margin coefficient less than 1, used to avoid CCV overmodulation, with a typical value of 0.9 to 0.95.

[0066] Determining the dynamic amplitude U of the intermediate frequency voltage g_mod Then, based on the three-phase intermediate frequency voltage u gj and three-phase capacitor current i cj Achieving closed-loop control of the intermediate frequency voltage allows the MMC output to have a dynamic amplitude U of the intermediate frequency voltage. g_mod Three-phase intermediate frequency voltage u gj Similarly, it is based on traditional intermediate frequency voltage closed-loop control, based on the dynamic amplitude U of the intermediate frequency voltage. g_mod The three-phase reference voltage u of the MMC is determined using a medium-frequency voltage closed-loop control strategy. gj_ref This is combined with an MMC modulation strategy to generate an MMC switch on / off signal to control the switching on / off state of the internal MMC switch. For details, please refer to... Figure 3 According to the dynamic amplitude U of the intermediate frequency voltage g_modDetermine the d-axis intermediate frequency voltage command value And similarly, the q-axis intermediate frequency voltage command value is taken. The subsequent intermediate frequency voltage closed-loop control strategy is the same. Figure 3 The details are omitted here, but this allows for dynamic adjustment of the intermediate frequency voltage waveform output by the MMC.

[0067] 2. Optimization of CCV control logic

[0068] After obtaining the CCV three-phase reference voltage u mj_ref Then, similarly, third harmonic injection and normalization are performed first, but the normalization method used in this application is different from the traditional method:

[0069] In traditional methods, the normalized CCV three-phase modulation wave y mj_ref dq axis component y md_ref and y mq_ref for:

[0070]

[0071] In this application, the normalized CCV three-phase modulation wave y mj_ref dq axis component y md_ref and y mq_ref for:

[0072]

[0073] The CCV three-phase modulation wave y is obtained after normalization. mj_ref Then, the electric angle θ of the motor rotor was also considered. m Calculate the compensation component y of the CCV three-phase modulation wave. mj_comp Then, the CCV three-phase modulated wave y mj_ref Based on the superposition of CCV three-phase modulation wave compensation component y mj_comp Then, the cosine intersection method is used to adjust and generate the CCV switch conduction signal to control the switching on and off of the CCV internal switch.

[0074] CCV three-phase modulation wave compensation component y mj_comp for:

[0075]

[0076] Where Y represents the CCV three-phase modulation wave y mj_ref The amplitude of the fundamental frequency component and

[0077] y md_ref and y mq_ref The definition and calculation method are described above.

[0078] The three-phase phase angle of the fundamental frequency component of the CCV three-phase modulated wave

[0079] CCV three-phase modulation wave y mj_ref Phase angle of the fundamental frequency component of the A-phase modulated wave According to the electric angle θ of the motor rotor m To determine this, please refer to the above introduction for specific methods.

[0080] Therefore, based on the MMC intermediate frequency operation and CCV variable frequency operation, this application optimizes the torque ripple of the cascaded drive system by adjusting the intermediate frequency voltage waveform according to the speed of the MMC and combining it with the improved CCV modulation strategy. This allows the CCV to reduce the conduction angle of the thyristor, reduce line voltage harmonics, and optimize torque ripple without affecting the fundamental frequency component of the output voltage.

[0081] To avoid CCV overmodulation, when the motor current angular frequency ω m ≤ω lim The intermediate frequency voltage used at that time has a constant amplitude U g_lim The current angular frequency threshold ω at the start of the optimization method lim The following relationship must be satisfied:

[0082]

[0083] Among them, U m_N It is the amplitude of the fundamental frequency component of the phase voltage of the motor under rated operating conditions, ω m_N It is the rated angular frequency of the motor current.

[0084] To verify the effectiveness of the method in this application, a simulation model of the torque ripple optimization method for a cascaded drive system was built in the professional simulation software PLECS. The actual system parameters are shown in Table 1 below.

[0085] Table 1 Simulation parameters of the drive system

[0086]

[0087]

[0088] After enabling the torque ripple optimization method, the simulation waveforms of the cascaded drive system at motor speeds of 0.25 pu, 0.5 pu, and 0.75 pu are as follows: Figure 6 , Figure 7 , Figure 8 As shown, the peak-to-peak torque ripple of the drive system at speeds of 0.1–1 p.u. is as follows: Figure 9 As shown in the simulation results, this method can effectively reduce torque pulsation at various speeds.

[0089] The above descriptions are merely preferred embodiments of this application, and this application is not limited to the above embodiments. It is understood that other improvements and variations that can be directly derived or conceived by those skilled in the art without departing from the spirit and concept of this application should be considered to be included within the protection scope of this application.

Claims

1. A torque ripple collaborative optimization method applicable to MMC and CCV cascaded drive systems, characterized in that, The torque ripple co-optimization method includes the following steps during the operation of the motor using an MMC and CCV cascaded drive system: When the motor's current angular frequency ω m >ω lim At that time, according to the angular frequency ω of the motor current m and the electric angle θ of the motor rotor m Determine the dynamic amplitude U of the intermediate frequency voltage g_mod According to the electric angle θ of the motor rotor m Calculate the compensation component y of the CCV three-phase modulation wave. mj_comp ; where ω lim It is the current angular frequency threshold, j = a, b, c represent the A, B, and C phases of the motor, respectively; Based on the dynamic amplitude U of the intermediate frequency voltage g_mod The three-phase reference voltage u of the MMC is determined using a medium-frequency voltage closed-loop control strategy. gj_ref And combined with the MMC modulation strategy, control the on / off state of the switching transistors inside the MMC; According to the frequency command value Determining the CCV three-phase reference voltage u using a motor current vector control strategy mj_ref At the CCV three-phase reference voltage u mj_ref The normalized three-phase modulated wave y mj_ref Based on the superposition of CCV three-phase modulation wave compensation component y mj_comp It also combines a CCV modulation strategy to control the on / off state of the switching transistors within the CCV.

2. The torque pulsation cooperative optimization method according to claim 1, characterized in that, According to the angular frequency ω of the motor's current m and the electric angle θ of the motor rotor m Determine the dynamic amplitude U of the intermediate frequency voltage g_mod include: According to the angular frequency ω of the motor's current m and the electric angle θ of the motor rotor m Determine the voltage command correction factor k mod And determine the dynamic amplitude U of the intermediate frequency voltage. g_mod =k mod ×U g U g It is to ensure the intermediate frequency voltage amplitude required for CCV frequency conversion and U m_N It is the amplitude of the fundamental frequency component of the phase voltage of the motor under rated operating conditions.

3. The torque ripple cooperative optimization method according to claim 2, characterized in that, According to the angular frequency ω of the motor's current m and the electric angle θ of the motor rotor m Determine the voltage command correction factor k mod include: According to the electric angle θ of the motor rotor m Determine the CCV three-phase modulation wave y mj_ref Phase angle of the fundamental frequency component of the A-phase modulated wave And based on the phase angle The corresponding time variable w is obtained by conversion, and the time variable w is combined with the current angular frequency ω. m The voltage command correction factor k is calculated. mod .

4. The torque ripple cooperative optimization method according to claim 3, characterized in that, According to the phase angle The corresponding time variable w obtained by transformation is: Where k is an integer not less than 0.

5. The torque ripple cooperative optimization method according to claim 3, characterized in that, Using the time variable w in combination with the current angular frequency ω m The voltage command correction factor k is calculated. mod include: Calculate the angular frequency ω of the current m With respect to the rated angular frequency ω of the motor current m_N ratio And in accordance with The voltage command correction factor k is calculated. mod , k margin It is a modulation margin coefficient less than 1.

6. The torque ripple cooperative optimization method according to claim 5, characterized in that, According to the electric angle θ of the motor rotor m Calculate the compensation component y of the CCV three-phase modulation wave. mj_comp for: Where Y represents the CCV three-phase modulation wave y mj_ref The amplitude of the fundamental frequency component and u md_ref It is the CCV three-phase reference voltage u mj_ref The d-axis component, u mq_ref It is the CCV three-phase reference voltage u mj_ref q-axis component; CCV three-phase modulated wave y mj_ref The three-phase phase angle of the fundamental frequency component CCV three-phase modulation wave y mj_ref Phase angle of the fundamental frequency component of the A-phase modulated wave According to the electric angle θ of the motor rotor m To determine.

7. The torque ripple cooperative optimization method according to claim 3 or 6, characterized in that, According to the electric angle θ of the motor rotor m Determine the CCV three-phase modulation wave y mj_ref Phase angle of the fundamental frequency component of the A-phase modulated wave This includes calculating the phase angle using the following formula. Among them, u md_ref It is the CCV three-phase reference voltage u mj_ref The d-axis component, u mq_ref It is the CCV three-phase reference voltage u mj_ref The q-axis component.

8. The torque ripple cooperative optimization method according to claim 1, characterized in that, When the motor's current angular frequency ω m ≤ω lim Time based on constant amplitude U of intermediate frequency voltage g_lim The switching of the internal switching transistor of the MMC is controlled by a closed-loop control strategy using intermediate frequency voltage combined with an MMC modulation strategy, and the intermediate frequency voltage has a constant amplitude U. g_lim and current angular frequency threshold ω lim The following relationship must be satisfied: Among them, U m_N It is the amplitude of the fundamental frequency component of the phase voltage of the motor under rated operating conditions, ω m_N It is the rated angular frequency of the motor current.

9. The torque ripple cooperative optimization method according to claim 1, characterized in that, Based on the dynamic amplitude U of the intermediate frequency voltage g_mod The three-phase reference voltage u of the MMC is determined using a medium-frequency voltage closed-loop control strategy. gj_ref include: Based on the dynamic amplitude U of the intermediate frequency voltage g_mod Determine the d-axis intermediate frequency voltage command value and q-axis intermediate frequency voltage command value The three-phase intermediate frequency voltage u output by the MMC gj Performing a dq transformation yields the actual value u of the d-axis intermediate frequency voltage. gd and the actual value of the q-axis intermediate frequency voltage u gq ; d-axis intermediate frequency voltage error The PI controller receives the d-axis capacitor current command value. q-axis intermediate frequency voltage error The q-axis capacitor current command value is obtained by inputting the PI controller. The three-phase capacitor current i of the three-phase filter capacitor of the MMC cj The d-axis capacitor current i is obtained by performing a dq transformation. cd and q-axis capacitor current i cq d-axis capacitance current error The d-axis reference voltage u is obtained by inputting the PI controller. gd_ref q-axis capacitance current error The q-axis reference voltage u is obtained by inputting the PI controller. gq_ref , for u gd_ref and u gq_ref The inverse dq transformation is performed to obtain the MMC three-phase reference voltage u. gj_ref .

10. The torque ripple cooperative optimization method according to claim 1, characterized in that, According to the frequency command value Determining the CCV three-phase reference voltage u using a motor current vector control strategy mj_ref include: frequency command value With current angular frequency ω m angular frequency error The input to the PI controller obtains the q-axis motor current command value. Get the d-axis motor current command value For the three-phase motor current i mj The actual value of the d-axis motor current i is obtained by performing a dq transformation. md and the actual value of the q-axis motor current i mq ; d-axis motor current error The d-axis reference voltage u is obtained by inputting the PI controller. md_ref q-axis motor current error The q-axis reference voltage u is obtained by inputting the PI controller. mq_ref ; for the d-axis reference voltage u md_ref and q-axis reference voltage u mq_ref The inverse dq transformation is performed to obtain the CCV three-phase reference voltage u. mj_ref .

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