Electrolytic capacitor-free motor control method and system based on capacitor current harmonic suppression

Abstract

The invention discloses a non-electrolytic capacitor motor control method and system based on capacitor current harmonic suppression, and the method comprises the steps: building a dynamic equation of DC bus voltage based on an equivalent model of a non-electrolytic capacitor driving system, generating a capacitor current compensation signal, and carrying out the correction processing, and obtaining a corrected inverter current reference value; shaft current prediction is carried out based on the motor discrete model to obtain the shaft current of the predicted motor at the next moment; and in combination with the predicted shaft current of the motor at the next moment and the corrected inverter current reference value, capacitance current adjustment and voltage vector adjustment are carried out, and non-electrolytic capacitor motor control for capacitor current harmonic suppression is realized. According to the inverter current controller, direct voltage vector adjustment and capacitance current adjustment can be combined, direct-current bus voltage distortion is restrained, and the control precision of a motor without an electrolytic capacitor is improved. The electrolytic capacitor-free motor control method and system based on capacitor current harmonic suppression can be widely applied to the technical field of motor control.

Description

Technical Field

[0001] This invention relates to the field of motor control technology, and in particular to a method and system for controlling electrolytic capacitor-free motors based on capacitor current harmonic suppression. Background Technology

[0002] In permanent magnet synchronous motor (IPMSM) drive systems, traditional single-phase inverters commonly use large-capacity electrolytic capacitors (typically hundreds to thousands of microfarads) for DC bus voltage regulation in their front-end rectifier circuits. However, electrolytic capacitors have inherent drawbacks such as large size, high cost, high temperature sensitivity, and short lifespan, becoming a weak link in system reliability. To address this, electrolytic capacitorless inverters have emerged, using small-capacity film capacitors to replace electrolytic capacitors. This solution eliminates switching devices and heat dissipation systems, significantly improving power density and reliability. However, the small-capacity film capacitors result in a lower DC bus capacitance (C... dc The reduction is significant, therefore, the related technologies have the following problems:

[0003] 1) LC resonance distortion: grid-side inductance (L g ) and the DC bus capacitor form a resonant circuit (resonant frequency approximately This causes severe distortion of the grid current (THD>40%) and DC bus voltage oscillation;

[0004] 2) Insufficient voltage dynamics: Severe fluctuations in bus voltage cause uncontrolled current on the motor side, and the traditional current loop becomes saturated due to insufficient voltage margin.

[0005] 3) System overvoltage and overcurrent: Severe oscillations in bus voltage can lead to overvoltage problems, while resonance of grid-side current can lead to overcurrent problems. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a control method and system for electrolytic capacitor-free motors based on capacitor current harmonic suppression. This method combines inverter current controllers with direct voltage vector regulation and capacitor current regulation to expand the equivalent control bandwidth, suppress DC bus voltage distortion, and improve the control accuracy of electrolytic capacitor-free motors.

[0007] The first technical solution adopted in this invention is: a capacitor-free motor control method based on capacitor current harmonic suppression, comprising the following steps:

[0008] Based on the equivalent model of the electrolytic capacitor-free drive system, a dynamic equation for the DC bus voltage is constructed, a capacitor current compensation signal is generated and corrected, and the corrected inverter current reference value is obtained.

[0009] Based on the discrete model of the motor, the shaft current is predicted to be the predicted shaft current of the motor at the next moment.

[0010] The capacitor current adjustment and voltage vector adjustment are performed in combination with the predicted motor shaft current at the next moment and the corrected inverter current reference value, so that the electrolytic capacitor-free motor control with capacitor current harmonic suppression is realized.

[0011] Further, the step of constructing the dynamic equation of the DC bus voltage based on the equivalent model of the electrolytic capacitor-free driving system, generating the capacitor current compensation signal and performing correction processing to obtain the corrected inverter current reference value specifically includes:

[0012] Based on the equivalent model of the electrolytic capacitor-free driving system, the LC resonance loop composed of the grid-side inductance and the DC bus capacitor is obtained, and the dynamic equation of the DC bus voltage is derived in combination with Kirchhoff's law;

[0013] Based on the dynamic equation of the DC bus voltage, the ideal capacitor current value is obtained by using the absolute value calculation of the grid voltage;

[0014] The actual capacitor current value is obtained by extracting from the dynamic equation of the DC bus voltage through a low-pass filter;

[0015] The ideal capacitor current value and the actual capacitor current value are calculated by difference to generate the capacitor current compensation signal;

[0016] The capacitor current compensation signal is injected into the inverter to calculate the distortion component, and the corrected inverter current reference value is obtained.

[0017] Further, the expression of the dynamic equation of the DC bus voltage is specifically as follows:

[0018]

[0019] In the above formula, U dc represents the DC bus voltage, C dc represents the DC bus capacitor, L g represents the grid-side inductance, U g represents the grid voltage, L g represents the grid current, i inv represents the inverter output current, R g represents the grid-side equivalent resistance, and t represents the time variable.

[0020] Further, the expression of the ideal capacitor current value is specifically as follows:

[0021]

[0022] In the above formula, represents the ideal capacitor current value, C dc represents the DC bus capacitor, U grepresents the grid voltage.

[0023] Further, the expression of the actual capacitor current value is specifically as follows:

[0024]

[0025] In the above formula, i dc represents the actual capacitor current value, ω s represents the low-pass filter cutoff frequency, C dc represents the DC bus capacitor, U dc represents the DC bus voltage, s represents the Laplace operator.

[0026] Further, the step of predicting the shaft current of the motor at the next moment based on the discrete model of the motor specifically includes:

[0027] The motor phase current at the current moment is obtained through a sensor, and Clarke-Park transformation processing is performed to obtain the motor shaft current at the current moment;

[0028] The output voltage instruction of the current controller and the rotor electric angular velocity obtained through an encoder are obtained;

[0029] The motor shaft current at the current moment, the output voltage instruction of the current controller, and the rotor electric angular velocity are input to the discrete model of the motor for calculation to obtain the predicted shaft current of the motor at the next moment.

[0030] Further, the expression of the predicted shaft current of the motor at the next moment is specifically as follows:

[0031]

[0032]

[0033] In the above formula, represents the predicted d-axis current of the motor at the next moment, represents the predicted q-axis current of the motor at the next moment, represents the motor d-axis current at the current moment, represents the motor q-axis current at the current moment, ω r represents the rotor electric angular velocity, represents the output voltage instruction of the current controller, T sc represents the control period, L d represents the d-axis inductance of the motor, L q represents the q-axis inductance of the motor, R s represents the stator resistance, ψ f represents the permanent magnet flux linkage.

[0034] Further, the step of realizing the electrolytic capacitor-free motor control with capacitor current harmonic suppression combines the predicted motor next-time shaft current with the corrected inverter current reference value to perform capacitor current adjustment and voltage vector adjustment, which specifically includes:

[0035] According to the dynamic equation of the DC bus voltage, the current error is calculated by combining the corrected inverter current reference value and the predicted motor next-time shaft current, and the inverter current error value is obtained.

[0036] According to the inverter current error value, the cross-axis adjustment of the motor is performed to determine the d-axis correction amount and the q-axis correction amount of the motor.

[0037] The grid voltage, DC bus voltage and three-phase current are resampled and Clarke and Park transformations are performed to obtain the direct-axis current of the motor and the quadrature-axis current of the motor.

[0038] Based on the direct-axis current of the motor and the quadrature-axis current of the motor, the capacitor current adjustment is performed, the ideal capacitor current is calculated using the absolute value of the grid voltage, the inverter current reference value is updated, and the adjusted predicted motor next-time shaft current is obtained.

[0039] Based on the d-axis correction amount and the q-axis correction amount of the motor, the voltage vector adjustment is performed to obtain the corrected voltage vector.

[0040] Combining the adjusted predicted motor next-time shaft current and the corrected voltage vector, the electrolytic capacitor-free motor control with capacitor current harmonic suppression is realized.

[0041] Further, the calculation expression of the inverter current error value is specifically as follows:

[0042]

[0043] In the above formula, Δi inv represents the inverter current error value, represents the corrected inverter current reference value, U dc represents the current DC bus voltage, represents the predicted motor next-time d-axis current, represents the predicted motor next-time q-axis current, represents the corrected d-axis voltage reference value, represents the corrected q-axis voltage reference value.

[0044] The second technical solution adopted by the present application is: an electrolytic capacitor-free motor control system based on capacitor current harmonic suppression, comprising:

[0045] The first module is used for constructing a dynamic equation of a DC bus voltage based on an equivalent model of a non-electrolytic capacitor driving system, generating a capacitor current compensation signal and performing correction processing to obtain a corrected inverter current reference value;

[0046] The second module is used for predicting a shaft current based on a discrete model of the motor to obtain a predicted shaft current of the motor at a next moment;

[0047] The third module is used for combining the predicted shaft current of the motor at the next moment and the corrected inverter current reference value to perform capacitor current adjustment and voltage vector adjustment, so as to realize non-electrolytic capacitor motor control with capacitor current harmonic suppression.

[0048] The method and system have the following beneficial effects: the equivalent model of the non-electrolytic capacitor driving system is used to construct the dynamic equation of the DC bus voltage, generate the capacitor current compensation signal and perform the correction processing to obtain the corrected inverter current reference value, the discrete model of the motor is used to predict the shaft current to obtain the predicted shaft current of the motor at the next moment, the direct voltage vector adjustment is used to quickly correct the inverter current error in one control cycle, and the voltage reference trajectory is optimized to increase the voltage margin, so as to solve the problem of insufficient bandwidth of the controller, improve the dynamic response capability of the system, and finally combine the predicted shaft current of the motor at the next moment and the corrected inverter current reference value to perform the capacitor current adjustment and the voltage vector adjustment, so as to combine the inverter current controller with the direct voltage vector adjustment and the capacitor current adjustment, expand the equivalent control bandwidth, suppress the DC bus voltage distortion, and improve the non-electrolytic capacitor motor control precision. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 is a step flow chart of the non-electrolytic capacitor motor control method based on capacitor current harmonic suppression according to the present application;

[0050] Figure 2 is a structural block diagram of the non-electrolytic capacitor motor control system based on capacitor current harmonic suppression according to the present application;

[0051] Figure 3 is a non-electrolytic capacitor control schematic diagram provided by the embodiment of the present application for capacitor current harmonic suppression;

[0052] Figure 4 is an experimental result schematic diagram of the non-CCR method provided by the embodiment of the present application;

[0053] Figure 5 is an experimental result schematic diagram of the CCR method provided by the embodiment of the present application. DETAILED DESCRIPTION

[0054] The application will be further described in detail below in combination with the drawings and specific embodiments. For the step numbers in the following embodiments, they are only set for the convenience of description, and the order between the steps is not limited in any way, and the execution order of each step in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art.

[0055] First of all, it needs to be pointed out that the prior art proposes a voltage vector regulation to realize output power correction. The adjustment of the output instantaneous power is realized by simultaneously correcting the dq-axis voltages, and the principle of voltage regulation is to make the adjustment direction perpendicular to the output power curve, so as to ensure that the amplitude of the adjusted voltage is minimum, but it has the following disadvantages:

[0056] 1) Indirect control strategy (such as q-axis current regulation, power balance control), open-loop control (such as trapezoidal wave modulation) cannot eliminate current error in real time, resulting in residual voltage distortion. Closed-loop power control needs to convert power reference into current reference (different dimensions), which depends on the accuracy of motor speed observation and is complex in parameter setting.

[0057] 2) Active damping control (suppress LC resonance), only designed for grid-side resonance (such as controlling inductance current), ignoring the voltage distortion caused by charging and discharging on the inverter side, and the suppression is not comprehensive. The feedback gain needs to be dynamically adjusted, which is high in calculation complexity and poor in real-time performance.

[0058] 3) Traditional voltage vector correction method, the voltage correction direction is aligned with the current vector, which may introduce q-axis current disturbance, leading to current loop saturation, and the bandwidth of PI controller is limited, which cannot effectively suppress high-frequency harmonics.

[0059] Based on this, the embodiment of the application proposes an inverter current controller combining direct voltage vector regulation and capacitor current regulation to suppress DC bus voltage distortion. The capacitor current is calculated, and the extracted distortion component is compensated into the inverter current reference value. The grid-side current harmonics and motor-side current are simultaneously controlled through inverter current compensation. In addition, the voltage vector is directly regulated to reduce the inverter current error in one control period. The voltage reference trajectory is modified in the d-axis direction to increase the voltage margin, which can solve the problem of insufficient bandwidth of the current controller.

[0060] With reference to Figure 1 and Figure 3 , the application provides a capacitor-free motor control method based on capacitor current harmonic suppression, which comprises the following steps:

[0061] S100, based on the equivalent model of the capacitor-free driving system, a dynamic equation of the DC bus voltage is constructed, a capacitor current compensation signal is generated and modified, and a modified inverter current reference value is obtained;

[0062] S110, based on the equivalent model of electrolytic capacitor-free driving system, LC resonance loop composed of grid-side inductance and DC bus capacitor is obtained, and the dynamic equation of DC bus voltage is derived based on Kirchhoff's law;

[0063] In this embodiment, based on the equivalent model of electrolytic capacitor-free driving system, the dynamic equation of DC bus voltage is established, LC resonance loop is composed of grid-side inductance (L g ) and DC bus capacitor (C dc ), and the dynamic equation of DC bus voltage is derived based on Kirchhoff's law as follows:

[0064]

[0065] In the above formula, U dc represents the DC bus voltage, C dc represents the DC bus capacitor, L g represents the grid-side inductance, U g represents the grid voltage, L g represents the grid current, i inv represents the inverter output current, R g represents the grid-side equivalent resistance, and t represents the time variable.

[0066] S120, based on the dynamic equation of DC bus voltage, the ideal capacitor current value is obtained by calculating the absolute value of grid voltage;

[0067] In this embodiment, the ideal capacitor current is calculated, in order to avoid introducing noise by directly differentiating U dc , the absolute value of grid voltage is calculated, and its expression is as follows:

[0068]

[0069] In the above formula, i represents the ideal capacitor current value, C dc represents the DC bus capacitor, and U g represents the grid voltage.

[0070] S130, the actual capacitor current value is obtained by extracting from the dynamic equation of DC bus voltage through a low-pass filter;

[0071] In this embodiment, the actual capacitor current is extracted: the actual capacitor current is extracted from U s through a low-pass filter (cutoff frequency ω dc ), and its expression is as follows:

[0072]

[0073] In the above formula, i ac represents the actual capacitor current value, and ωs represents the low-pass filter cutoff frequency, C dc represents the DC bus capacitor, U dc represents the DC bus voltage, s represents the Laplace operator.

[0074] S140, difference calculation is performed on the ideal capacitor current value and the actual capacitor current value to generate a capacitor current compensation signal;

[0075] S150, the capacitor current compensation signal is injected into the inverter to calculate the distortion component, and a corrected inverter current reference value is obtained.

[0076] In this embodiment, a compensation signal is generated, a distortion component is calculated, and an inverter current reference value is injected. The calculation expression of the capacitor current compensation signal is:

[0077]

[0078] The calculation expression of the corrected inverter current reference value is:

[0079]

[0080] In the above formula, represents the corrected inverter current reference value.

[0081] S200, based on the motor discrete model, the shaft current is predicted to obtain the predicted motor shaft current at the next time;

[0082] Specifically, the motor phase current at the current time is obtained through a sensor, and Clarke-Park transformation processing is performed to obtain the motor shaft current at the current time. The output voltage command of the current controller and the rotor electric angular velocity obtained through an encoder are obtained. The motor shaft current at the current time, the output voltage command of the current controller, and the rotor electric angular velocity are input into the motor discrete model for calculation to obtain the predicted motor shaft current at the next time.

[0083] In this embodiment, based on the motor discrete model, the motor phase current (i a , i b , i c at the current time is measured through a sensor, and Clarke-Park transformation is performed to obtain the d-axis current and the q-axis current The output voltage command of the current controller The rotor electric angular velocity ω r is obtained through an encoder or an observer. The above parameters are substituted into the discretization equation to directly calculate the predicted shaft current at the next time, and the expression is:

[0084]

[0085] In the above formula, This indicates a prediction of the motor's d-axis current at the next moment. This indicates a prediction of the motor's q-axis current at the next moment. This represents the d-axis current of the motor at the current moment. ω represents the q-axis current of the motor at the current moment. r Indicates the rotor's electrical angular velocity. T represents the current controller's output voltage command. sc L represents the control period. d L represents the d-axis inductance of the motor. q R represents the q-axis inductance of the motor. s ψ represents the stator resistance. f This indicates the magnetic flux linkage of a permanent magnet.

[0086] S300 combines the predicted motor shaft current at the next moment with the corrected inverter current reference value to adjust the capacitor current and voltage vector, thereby achieving electrolytic capacitor-free motor control with capacitor current harmonic suppression.

[0087] Specifically, the current DC bus voltage is obtained based on the dynamic equation of the DC bus voltage. Combined with the corrected inverter current reference value and the predicted motor shaft current at the next moment, the current error is calculated to obtain the inverter current error value. Based on the inverter current error value, the motor is cross-axis adjusted to determine the motor's d-axis and q-axis corrections. The grid voltage, DC bus voltage, and three-phase current are resampled and subjected to Clarke and Park transformations to obtain the motor's direct-axis and quadrature-axis currents. Based on the motor's direct-axis and quadrature-axis currents, the capacitor current is regulated. Using the absolute value of the grid voltage, the ideal capacitor current is calculated, and the inverter current reference value is updated to obtain the adjusted predicted motor shaft current at the next moment. Based on the motor's d-axis and q-axis corrections, the voltage vector is adjusted to obtain the corrected voltage vector. Combining the adjusted predicted motor shaft current at the next moment with the corrected voltage vector, electrolytic capacitor-free motor control with capacitor current harmonic suppression is achieved.

[0088] In this embodiment, the inverter current error is calculated by first obtaining the predicted d-axis and q-axis currents. and Then read the current DC bus voltage U dc Obtain the corrected inverter current reference value. Finally, the current error is calculated, and its expression is as follows:

[0089]

[0090] In the above formula, Δi inv This indicates the inverter current error value. represents the corrected inverter current reference value, U dc represents the current DC bus voltage, represents the predicted next moment d-axis current of the motor, represents the predicted next moment q-axis current of the motor, represents the corrected d-axis voltage reference value, represents the corrected q-axis voltage reference value.

[0091] If the d-axis regulation is insufficient, adjust the q-axis in proportion: If Δu d > Δu dmax , otherwise, first calculate the current error Then confirm the d-axis correction amount

[0092] Sample U g , U dc , i abc , perform Clarke transformation and Park transformation to obtain i d and i q ; using the absolute value of the grid voltage, calculate the ideal capacitor current: Calculate At the same time, update the inverter current reference value Then predict and Finally, correct the voltage vector Δu d and Δu q .

[0093] In summary, the embodiments of the present application have the following differences in technical features compared with the prior art:

[0094] 1) Harmonic cooperative suppression, through capacitor current regulation (CCR) to synchronously extract grid side and inverter side harmonics, compensate to the current reference value, solve the problem of parameter regulation, the parameters of this strategy have clear physical meaning.

[0095] 2) Dynamic voltage margin optimization, using direct voltage vector regulation (DVR), preferentially correcting the d-axis voltage, avoiding saturation caused by q-axis disturbance.

[0096] 3) Calculation efficiency is improved, based on the absolute value of the grid voltage to calculate the ideal capacitor current, avoiding deep filtering delay, improving response speed.

[0097] 4) Closed-loop control combining CCR and DVR, expanding the equivalent control bandwidth, effectively suppressing high-frequency resonance components.

[0098] In addition, the key point of the embodiments of the present application is:

[0099] 1) Capacitor current compensation mechanism: By extracting the distortion component and compensating to the inverter current reference value, harmonic suppression is achieved.

[0100] 2) Direct voltage vector regulation: Dynamically adjust the d-axis voltage to improve current tracking ability and avoid voltage saturation.

[0101] 3) Joint control strategy: Combine capacitor current regulation and voltage vector regulation to optimize grid-side and motor-side performance simultaneously.

[0102] Therefore, the embodiments of the present application have the following advantages compared with the prior art:

[0103] 1) Simultaneous suppression of grid harmonics and motor current error: The prior art usually uses indirect control strategies (such as adjusting the q-axis current reference) or open-loop control (such as trapezoidal wave modulation), which cannot completely eliminate current error, resulting in residual voltage distortion. However, the present application combines capacitor current regulation and direct voltage vector regulation to simultaneously suppress grid-side harmonics and motor-side current error, significantly reducing total harmonic distortion (THD). As shown in Figure 4 and Figure 5 the experimental data show that the THD of grid current is reduced from 43.02% to 20.074%, which is significant.

[0104] 2) Improve control bandwidth and dynamic response: Traditional PI controllers have limited bandwidth and cannot suppress high-frequency harmonics, and closed-loop power balance control has the problem of inconsistent dimensions. The present application uses direct voltage vector regulation to quickly correct inverter current error within one control cycle, and increases voltage margin by optimizing voltage reference trajectory (adjusting along the d-axis direction), thereby solving the problem of insufficient controller bandwidth and improving the dynamic response ability of the system.

[0105] 3) Adapt to low voltage conditions: When the DC bus voltage is insufficient, traditional methods are prone to current out of control due to voltage saturation. The present application avoids voltage saturation problems by preferentially adjusting the d-axis voltage (deep field weakening control) and dynamically correcting the voltage vector, ensuring stable operation of the system under low voltage conditions.

[0106] Referring to Figure 2 , the electrolytic capacitor-free motor control system based on capacitor current harmonic suppression includes:

[0107] The first module 201 is used to construct the dynamic equation of the DC bus voltage based on the equivalent model of the electrolytic capacitor-free drive system, generate a capacitor current compensation signal and perform correction processing to obtain a corrected inverter current reference value;

[0108] The second module 202 is used to predict the shaft current based on the discrete model of the motor to obtain the predicted shaft current of the motor at the next time;

[0109] The third module 203 is configured to combine the predicted motor shaft current at the next moment and the corrected inverter current reference value to perform capacitance current adjustment and voltage vector adjustment, so as to realize the control of the electrolytic-free motor with harmonic suppression of the capacitance current.

[0110] The content in the method embodiments is applicable to the system embodiments, the system embodiments specifically realize the same functions as the method embodiments, and achieve the same beneficial effects as the method embodiments.

[0111] The above is a specific description of the preferred implementation of the application, but the application is not limited to the embodiments described, and those skilled in the art can make various equivalent modifications or replacements without departing from the spirit of the application. These equivalent modifications or replacements are all included in the scope defined by the claims of the present application.

Claims

1. A method of electrolysis-free capacitor motor control based on capacitor current harmonic suppression, characterized by, The method comprises the following steps: Based on the equivalent model of electrolytic capacitor-free driving system, the dynamic equation of DC bus voltage is constructed, the capacitor current compensation signal is generated and modified, and the modified inverter current reference value is obtained; Based on the discrete model of the motor, the shaft current of the predicted motor at the next moment is obtained; The capacitor current adjustment and voltage vector adjustment are combined with the predicted motor shaft current at the next moment and the modified inverter current reference value to realize the electrolytic capacitor-free motor control of capacitor current harmonic suppression.

2. The method of claim 1, wherein the method is characterized by: The step of constructing the dynamic equation of the DC bus voltage based on the equivalent model of the electrolytic capacitor-free driving system, generating the capacitor current compensation signal and modifying the capacitor current compensation signal to obtain the modified inverter current reference value, specifically comprises: Based on the equivalent model of electrolytic capacitor-free driving system, the LC resonance loop composed of grid-side inductance and DC bus capacitor is obtained, and the dynamic equation of DC bus voltage is derived based on Kirchhoff's law; Based on the dynamic equation of the DC bus voltage, the ideal capacitor current value is obtained by calculating the absolute value of the grid voltage; The actual capacitor current value is extracted from the dynamic equation of the DC bus voltage through a low-pass filter; The ideal capacitor current value and the actual capacitor current value are calculated by difference to generate the capacitor current compensation signal; The capacitor current compensation signal is injected into the inverter to calculate the distortion component, and the modified inverter current reference value is obtained.

3. The method of claim 2, wherein the method further comprises: The expression of the dynamic equation of the DC bus voltage is specifically as follows: In the above equation, U dc represents the DC bus voltage, C dc represents the DC bus capacitance, L g represents the grid-side inductance, U g represents the grid voltage, L g represents the grid current, i inv represents the inverter output current, R g represents the grid-side equivalent resistance, t represents the time variable.

4. The method of claim 3, wherein the method further comprises: The expression of the ideal capacitor current value is specifically as follows: In the above formula, denotes the ideal capacitance current value, C dc denotes the DC bus capacitor, U g denotes the grid voltage.

5. The method of claim 4, wherein the method further comprises: The expression of the actual capacitor current value is specifically as follows: In the above formula, i dc represents the actual capacitance current value, ω s represents the low-pass filter cutoff frequency, C dc represents the DC bus capacitor, U dc represents the DC bus voltage, s represents the Laplace operator.

6. The method of claim 5, wherein the method further comprises: The step of obtaining the predicted motor shaft current at the next moment based on the discrete model of the motor, specifically comprises: The motor phase current at the current moment is obtained through a sensor, and Clarke-Park transformation processing is performed to obtain the motor shaft current at the current moment; The output voltage command of the current controller and the rotor electrical angular velocity obtained through the encoder are obtained; The motor shaft current at the current moment, the output voltage command of the current controller and the rotor electrical angular velocity are input into the motor discrete model for calculation to obtain the predicted motor shaft current at the next moment.

7. The method of claim 6, wherein the method further comprises: The expression of the predicted motor shaft current at the next moment is specifically as follows: In the above formulae, represents the predicted d-axis current of the motor at the next time, represents the predicted q-axis current of the motor at the next time, represents the d-axis current of the motor at the current time, represents the q-axis current of the motor at the current time, ω r represents the electrical angular velocity of the rotor, represents the output voltage command of the current controller, T sc represents the control period, L d represents the d-axis inductance of the motor, L q represents the q-axis inductance of the motor, R s represents the stator resistance, ψ f represents the permanent magnet flux linkage.

8. The method of claim 7, wherein the method further comprises: The step of combining the predicted motor shaft current at the next moment with the modified inverter current reference value to realize the electrolytic capacitor-free motor control of capacitor current harmonic suppression, specifically comprises: The current error value of the inverter is obtained by calculating the current error of the modified inverter current reference value and the predicted motor shaft current at the next moment based on the dynamic equation of the DC bus voltage; The d-axis correction amount and the q-axis correction amount of the motor are determined by cross-axis adjustment of the motor according to the inverter current error value; The grid voltage, the DC bus voltage and the three-phase current are resampled and Clarke transformed and Park transformed to obtain the direct-axis current of the motor and the quadrature-axis current of the motor; The motor-based direct-axis current and the motor-based quadrature-axis current are subjected to capacitor current regulation, the ideal capacitor current is calculated based on the absolute value of the grid voltage, the inverter current reference value is updated, and the adjusted predicted motor next-time-axis current is obtained; The motor-based d-axis correction amount and the motor-based q-axis correction amount are subjected to voltage vector regulation, and the corrected voltage vector is obtained; The adjusted predicted motor next-time-axis current and the corrected voltage vector are combined to achieve capacitor current harmonic suppression of the electrolytic capacitor-free motor control.

9. The method of claim 8, wherein the method further comprises: The calculation expression of the inverter current error value is specifically as follows: In the above formula, Δi inv represents the inverter current error value, represents the corrected inverter current reference value, U dc represents the current DC bus voltage, represents the predicted d-axis current of the motor at the next moment, represents the predicted q-axis current of the motor at the next moment, represents the corrected d-axis voltage reference value, represents the corrected q-axis voltage reference value.

10. An electrolysis-free capacitor motor control system based on capacitor current harmonic suppression, characterized by, The method comprises the following modules: A first module is configured to construct a dynamic equation of a DC bus voltage based on an equivalent model of an electrolytic capacitor-free driving system, generate a capacitor current compensation signal, and perform correction processing to obtain a corrected inverter current reference value; A second module is configured to perform axis current prediction based on a motor discrete model to obtain a predicted motor next-time-axis current; A third module is configured to combine the predicted motor next-time-axis current and the corrected inverter current reference value to perform capacitor current regulation and voltage vector regulation, and achieve electrolytic capacitor-free motor control of capacitor current harmonic suppression.

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