Bus voltage oscillation suppression method and system for driving system without electrolytic capacitor

Abstract

The invention discloses a bus voltage oscillation suppression method and system for a driving system without an electrolytic capacitor, and the method comprises the steps: obtaining a torque current reference value of a motor and a phase angle of a power grid, and carrying out the multiplication calculation, and obtaining a preliminary q-axis current reference value of the motor; obtaining a power grid capacitance power reference value and a power grid capacitance power actual value, and performing compensation through a proportional resonance controller to obtain a power grid power compensation value; and combining the initial q-axis current reference value of the motor with the power grid power compensation value, performing feed-forward compensation control through a current controller, generating a pulse width PWM control signal to drive the motor to operate, and realizing motor control of voltage oscillation suppression. According to the invention, the oscillation trend of the capacitor voltage can be pre-judged, so that the controller can respond to the high-frequency oscillation of the capacitor voltage, and the suppression capability of the high-frequency oscillation component is improved. The bus voltage oscillation suppression method and system of the non-electrolytic capacitor driving system can be widely applied to the technical field of voltage oscillation suppression.

Description

Technical Field

[0001] The present invention relates to the technical field of voltage oscillation suppression, and particularly to a method and a system for suppressing bus voltage oscillation of a drive system without electrolytic capacitors. Background Art

[0002] Generally, the input source of the front stage of a single-phase frequency converter is industrial-frequency alternating current. After passing through an uncontrolled rectifier bridge, a pulsating bus voltage is obtained, and a large electrolytic capacitor is used to stabilize the bus voltage. However, the large electrolytic capacitor has a large volume and is sensitive to temperature, resulting in a limited service life, which greatly limits the service life and reliability of the system. Therefore, in order to improve the quality of the grid-side current, the frequency converter needs to add a power factor correction (PFC) circuit, which increases the loss and cost of the system and reduces the system reliability. Therefore, related methods have proposed a motor drive topology without electrolytic capacitors. This topology uses small-capacity thin-film capacitors to replace large electrolytic capacitors and eliminates the PFC circuit. Although this solution has low cost, high life, and high reliability, due to the lack of decoupling of large-capacity electrolytic capacitors, it is easy to form an LC high-frequency resonance between the bus capacitor and the grid-side inductor, resulting in unstable phenomena such as overvoltage of the system and out-of-control of the motor. Summary of the Invention

[0003] In order to solve the above technical problems, the object of the present invention is to provide a method and a system for suppressing bus voltage oscillation of a drive system without electrolytic capacitors, which can predict the oscillation trend of the capacitor voltage, so that the controller can respond to the high-frequency oscillation of the capacitor voltage and improve the suppression ability of the high-frequency oscillation component.

[0004] The first technical solution adopted by the present invention is: a method for suppressing bus voltage oscillation of a drive system without electrolytic capacitors, comprising the following steps:

[0005] Obtain the torque current reference value of the motor and the grid phase angle and perform a multiplication calculation to obtain the preliminary q-axis current reference value of the motor;

[0006] Obtain the grid capacitor power reference value and the actual value of the grid capacitor power and perform compensation through a proportional-resonant controller to obtain the grid power compensation value;

[0007] Combine the preliminary q-axis current reference value of the motor and the grid power compensation value and perform feedforward compensation control through a current controller to generate a pulse-width PWM control signal to drive the motor to operate, and realize motor control for voltage oscillation suppression.

[0008] Further, the step of obtaining the torque current reference value of the motor and the grid phase angle and performing a multiplication calculation to obtain the preliminary q-axis current reference value of the motor specifically includes:

[0009] Detect and process the rotational speed of the motor, obtain the actual rotational speed of the motor and calculate the difference from the motor speed command value to obtain the motor speed error value;

[0010] Convert and process the motor speed error value through a PI controller to obtain the reference value of the torque current of the motor;

[0011] Obtain the high-voltage AC signal of the power grid and perform conversion and sampling through an operational amplifier conditioning circuit to obtain the power grid voltage;

[0012] Perform phase tracking on the power grid voltage through a phase-locked loop PLL to obtain the power grid phase angle;

[0013] Multiply the reference value of the torque current of the motor by the power grid phase angle to obtain the preliminary reference value of the q-axis current of the motor.

[0014] Furthermore, the transfer function of the phase-locked loop PLL is as follows:

[0015]

[0016] In the above formula, H(s) represents the transfer function of the phase-locked loop PLL, θ g represents the phase angle of the power grid voltage, k p represents the proportional coefficient of the speed loop, s represents the differential operator, k i represents the integral coefficient of the speed loop, θ grid (s) represents the input of the actual phase angle of the power grid voltage, K pd represents the gain coefficient of the phase detector.

[0017] Furthermore, the step of obtaining the reference value of the power grid capacitor power and the actual value of the power grid capacitor power and compensating through a proportional-resonant controller to obtain the power grid power compensation value specifically includes:

[0018] Perform a differential operation on the power grid voltage and multiply it by the capacitance value of the power grid capacitor to obtain the reference value of the capacitor charge and discharge current;

[0019] Multiply the reference value of the capacitor charge and discharge current by the power grid voltage to obtain the reference value of the capacitor power;

[0020] Sample the bus voltage, perform a differential operation and multiply it by the capacitance value of the power grid capacitor to obtain the actual value of the capacitor charge and discharge current;

[0021] Multiply the actual value of the capacitor charge and discharge current by the bus voltage to obtain the actual value of the capacitor power;

[0022] Calculate the difference between the reference value of the capacitor power and the actual value of the capacitor power and compensate through a proportional-resonant controller to obtain the power grid power compensation value.

[0023] Furthermore, the transfer function of the proportional-resonant controller is as follows:

[0024]

[0025] In the above formula, k pr represents the proportional coefficient of the resonant controller, k rr represents the resonant coefficient of the resonant controller, ω c represents the cut-off frequency, s represents the differential operator, and ω0 represents the center frequency.

[0026] Furthermore, the step of combining the initial q-axis current reference value of the motor and the grid power compensation value and performing feed-forward compensation control through a current controller to generate a pulse-width PWM control signal to drive the motor to operate and achieve voltage oscillation suppression of the motor control specifically includes:

[0027] Obtain the d-axis power error term of the motor and perform a difference calculation with the grid power compensation value, and divide the result of the difference calculation by the q-axis voltage of the motor to obtain the q-axis current compensation value of the motor;

[0028] Add the q-axis current compensation value of the motor to the initial q-axis current reference value of the motor to obtain the q-axis current reference value of the motor;

[0029] Obtain the d-axis current reference value of the motor and combine it with the q-axis current reference value of the motor, input it into the current controller for feed-forward compensation control, and generate a pulse-width PWM control signal;

[0030] Transmit the pulse-width PWM control signal to the inverter to drive the motor to operate and achieve voltage oscillation suppression of the motor control.

[0031] Furthermore, the expression of the feed-forward compensation control of the current controller is specifically as follows:

[0032]

[0033] In the above formula, represents the d-axis current reference value of the motor, represents the q-axis current reference value of the motor, i d (s) represents the d-axis current value of the motor, i q (s) represents the q-axis current value of the motor, s represents the differential operator, ω r represents the actual speed of the motor, ψ f represents the permanent magnet flux linkage, represents the d-axis voltage reference value, represents the q-axis voltage reference value, represents the d-axis current loop proportional gain, represents the q-axis current loop proportional gain, represents the d-axis current loop integral gain, Represents the integral gain of the q-axis current loop, L q Represents the d-axis inductance, L d Represents the q-axis inductance.

[0034] The second technical solution adopted by the present invention is: a system for suppressing bus voltage oscillation of an electrolytic-capacitorless drive system, comprising:

[0035] A first module, configured to obtain a reference value of the torque current of the motor and the phase angle of the power grid and perform a multiplication calculation to obtain a preliminary reference value of the q-axis current of the motor;

[0036] A second module, configured to obtain a reference value of the grid capacitor power and an actual value of the grid capacitor power and perform compensation through a proportional-resonant controller to obtain a grid power compensation value;

[0037] A third module, configured to combine the preliminary reference value of the q-axis current of the motor and the grid power compensation value and perform feedforward compensation control through a current controller to generate a pulse-width PWM control signal to drive the motor to operate, so as to achieve motor control for suppressing voltage oscillation.

[0038] The beneficial effects of the method and system of the present invention are as follows: By obtaining the reference value of the torque current of the motor and the phase angle of the power grid and performing a multiplication calculation, the present invention obtains a preliminary reference value of the q-axis current of the motor. The reference value samples the actually sampled AC voltage, and there is no amplitude extraction process. Its response to the change of the AC voltage is instantaneous, and the actual feedback value is also obtained by real-time sampling. Therefore, the amplitude extraction and reconstruction processes are avoided. Further, the reference value of the grid capacitor power and the actual value of the grid capacitor power are obtained and compensated through a proportional-resonant controller to obtain a grid power compensation value. It is proposed to use a PR resonant controller to track the reference value of the capacitor power, use the real-time sampled grid to calculate the reference value of the capacitor power, with fast dynamic response, and use the capacitor power as the control target, which can directly suppress the oscillation of the capacitor voltage and can predict the oscillation trend of the capacitor voltage, enabling the controller to respond to the high-frequency oscillation of the capacitor voltage. Finally, the preliminary reference value of the q-axis current of the motor and the grid power compensation value are combined and feedforward compensation control is performed through a current controller to generate a pulse-width PWM control signal to drive the motor to operate, so as to achieve motor control for suppressing voltage oscillation and improve the suppression ability for high-frequency oscillation components. Description of the Drawings

[0039] Figure 1 Is a flowchart of the steps of a method for suppressing bus voltage oscillation of an electrolytic-capacitorless drive system according to the present invention;

[0040] Figure 2 Is a structural block diagram of a system for suppressing bus voltage oscillation of an electrolytic-capacitorless drive system according to the present invention;

[0041] Figure 3It is a schematic diagram of permanent magnet synchronous motor control provided by a specific embodiment of the present invention;

[0042] Figure 4 It is a schematic diagram of the experimental effect of disabling voltage oscillation suppression provided by a specific embodiment of the present invention;

[0043] Figure 5 It is a schematic diagram of the experimental effect of enabling the voltage oscillation suppression algorithm provided by a specific embodiment of the present invention. Specific Embodiments

[0044] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. For the step numbers in the following embodiments, they are only set for the convenience of elaboration and explanation, and no limitation is imposed on the order between the steps. The execution order of each step in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art.

[0045] First of all, it should be noted that the prior art mainly uses a PI controller to adjust the control target. One kind of command reference value is the grid-side current, which is a standard steamed bun wave |sinθ g |, and the frequency component is mainly 100Hz. However, the control gain of the PI controller at this frequency is low and it cannot perform error-free tracking. Another kind of command reference value is the input power, and its components mainly include a 100Hz alternating current component and a direct current component. The PI control cannot track the alternating current component either. In addition, when the prior art method uses the grid-side current as the control target, the bus voltage is an indirect control variable. Although the grid-side current can be controlled to be relatively sinusoidal, there will still be a situation of sacrificing the bus voltage, and even causing the bus voltage to oscillate and overvoltage. And the prior art method also includes the bus voltage information. When the voltage oscillates, the actual power will deviate from the reference power, and the controller can suppress the voltage oscillation. However, the control bandwidth of this method is limited. The PI controller only responds when the voltage oscillation occurs and cannot predict in advance. Therefore, it is still unable to effectively suppress the high-frequency voltage oscillation, and the reconstruction calculation amount of the prior art method is very large. First, the fundamental wave values of the bus voltage and the grid-side current are extracted, and then multiplied by the phase reference |sinθ g | to obtain the reference value. However, the process of extracting the fundamental wave amplitude has a very large calculation amount, and there will be a delay problem in the process of extracting the amplitude when the AC voltage changes dynamically. Therefore, the dynamic performance is insufficient.

[0046] Therefore, the embodiment of the present invention first proposes to use a PR resonant controller to track the capacitance power reference value, and further proposes to use the capacitance power as the control target. The derivative of the capacitance current is used in the process of calculating the capacitance power. Therefore, the oscillation of the capacitance voltage can be predicted in advance, with a fast response and strong suppression ability for high-frequency oscillation components. Finally, the reference value samples the actual sampled AC voltage, and there is no amplitude extraction process. Its response to the change of the AC voltage is instantaneous, and the actual feedback value is also obtained by real-time sampling. Therefore, the amplitude extraction and reconstruction processes are avoided.

[0047] Referring to Figure 1 and Figure 3 , the present invention provides a method for suppressing the bus voltage oscillation of a drive system without electrolytic capacitors, and the method includes the following steps:

[0048] S100. Obtain the torque current reference value of the motor and the grid phase angle, and perform a multiplication calculation to obtain the preliminary q-axis current reference value of the motor;

[0049] Specifically, detect and process the speed of the motor, obtain the actual speed of the motor and perform a difference calculation with the motor speed command value to obtain the motor speed error value; perform a conversion process on the motor speed error value through a PI controller to obtain the torque current reference value of the motor; obtain the high-voltage AC signal of the grid and perform conversion and sampling through an operational amplifier conditioning circuit to obtain the grid voltage; perform phase tracking on the grid voltage through a phase-locked loop PLL to obtain the grid phase angle; perform a multiplication calculation on the torque current reference value of the motor and the grid phase angle to obtain the preliminary q-axis current reference value of the motor.

[0050] In this embodiment, according to the motor speed command value and the detected actual speed ω r perform a difference operation, and pass through a PI controller. The transfer function of the PI controller is:

[0051] k p +k i / s

[0052] In the above formula, k p represents the speed loop proportionality coefficient, k i represents the speed loop integral coefficient, and s represents the differential operator.

[0053] Convert the speed error to obtain the torque current reference value Convert the high-voltage AC signal to a low-voltage DC signal through an operational amplifier conditioning circuit for sampling to obtain the grid voltage U g , and use a phase-locked loop PLL to obtain the grid phase angle θ g, The phase-locked loop PLL is a closed-loop control system used to make the phase of the output signal accurately track the phase of the input signal. The transfer function of the phase-locked loop is:

[0054]

[0055] In the above formula, H(s) represents the transfer function of the phase-locked loop PLL, and θ g represents the phase angle of the grid voltage, k p represents the proportional coefficient of the speed loop, s represents the differential operator, and k i represents the integral coefficient of the speed loop, and θ grid (s) represents the actual phase angle input of the grid voltage, and K pd represents the gain coefficient of the phase detector.

[0056] Finally, multiply the motor torque current reference value by |sinθ g | 2 to obtain the preliminary q-axis current reference value.

[0057] S200. Obtain the grid capacitor power reference value and the actual value of the grid capacitor power and compensate them through a proportional-resonant controller to obtain the grid power compensation value;

[0058] S210. Differentiate the grid voltage and multiply it by the capacitance value of the grid capacitor to obtain the reference value of the capacitor charge and discharge current;

[0059] S220. Multiply the reference value of the capacitor charge and discharge current by the grid voltage to calculate the reference value of the capacitor power;

[0060] In this embodiment, differentiate the sampled grid voltage U g and then multiply it by the capacitance value C dc . The formula is:

[0061] i g = C dc (du / dt)

[0062] In the above formula, C dc represents the capacitance value, and i g represents the reference value of the capacitor charge and discharge current.

[0063] After obtaining the reference value of the capacitor charge and discharge current, multiply it by the grid voltage U g to obtain the reference value of the capacitor power

[0064] S230. Sample the bus voltage, perform a differentiation operation, and multiply it by the capacitance value of the grid capacitor to obtain the actual value of the capacitor charge and discharge current;

[0065] S240. Multiply the actual value of the capacitor charge and discharge current by the bus voltage to obtain the actual value of the capacitor power;

[0066] In this embodiment, the sampled bus voltage U dc is differentiated and then multiplied by the capacitance value C dc to obtain the actual value of the capacitor charge and discharge current, and then multiplied by the bus voltage U dc to obtain the actual value of the capacitor power P dc .

[0067] S250. Calculate the difference between the reference value and the actual value of the capacitor power and compensate it through a proportional-resonant controller to obtain the power compensation value for the power grid.

[0068] In this embodiment, the difference between the reference value and the actual value of the capacitor power is calculated and passed through a proportional-resonant controller (PR), that is, the difference between the reference value and the actual value of the capacitor power is multiplied by the transfer function of the PR controller, and its expression is:

[0069]

[0070] In the above formula, k pr represents the proportional coefficient of the resonant controller, k rr represents the resonant coefficient of the resonant controller, ω c represents the cut-off frequency, s represents the differential operator, and ω0 represents the center frequency.

[0071] The difference between the reference value and the actual value of the capacitor power is multiplied by the transfer function of the PR controller to obtain the power compensation value

[0072] S300. Combine the preliminary q-axis current reference value of the motor with the power compensation value of the power grid and perform feed-forward compensation control through a current controller to generate a pulse-width PWM control signal to drive the motor to operate, realizing motor control for suppressing voltage oscillation.

[0073] Specifically, obtain the d-axis power error term of the motor. To obtain the d-axis power error term, first measure the actual d-axis voltage u d and current i d , and then calculate the d-axis voltage error and multiply them to obtain the power error term Δu d i d, and perform a difference calculation with the power compensation value of the power grid. Divide the result of the difference calculation by the q-axis voltage of the motor to obtain the q-axis current compensation value of the motor; add the q-axis current compensation value of the motor to the preliminary q-axis current reference value of the motor to obtain the q-axis current reference value of the motor; obtain the d-axis current reference value of the motor and combine it with the q-axis current reference value of the motor, and input it into the current controller for feedforward compensation control to generate a pulse width PWM control signal; transmit the pulse width PWM control signal to the inverter to drive the motor to operate, realizing the motor control for suppressing voltage oscillation.

[0074] In this embodiment, subtract the d-axis power error term Δu d i d , and then divide it by the q-axis voltage U q to obtain the q-axis current compensation value Finally, add the obtained initial current reference value and the compensation value to obtain the q-axis current reference value

[0075] Pass the motor current reference value through the current controller, and the current controller is used to convert the current reference value ( set to 0) and convert it into a PWM drive signal. Its core is a current loop PI controller. The design of the current controller adopts a combined strategy of PI control + feedforward compensation + decoupling term, and its formula can be expressed as:

[0076]

[0077] In the above formula, represents the d-axis current reference value of the motor, represents the q-axis current reference value of the motor, i d (s) represents the d-axis current value of the motor, i q (s) represents the q-axis current value of the motor, s represents the differential operator, ω r represents the actual speed of the motor, ψ f represents the permanent magnet flux linkage, represents the d-axis voltage reference value, represents the q-axis voltage reference value, represents the d-axis current loop proportional gain, represents the q-axis current loop proportional gain, represents the d-axis current loop integral gain, represents the q-axis current loop integral gain, L q represents the d-axis inductance, L d represents the q-axis inductance.

[0078] Finally, generate the pulse width signal PWM and send it to the inverter to drive the permanent magnet motor PMSM.

[0079] In summary, in the embodiment of the present invention, by using the power grid to calculate the reference value of the capacitive power through real-time sampling, the dynamic response is fast, and there is no need for the voltage reference value reconstruction process of the traditional technology. This process has a large amount of calculation and poor real-time performance, resulting in inaccurate reconstructed amplitude when the grid voltage suddenly changes, seriously affecting the control performance. Second, by using the capacitive power as the control target, the oscillation of the capacitive voltage can be directly suppressed. The traditional method uses the capacitive voltage control, which has a lag effect and insufficient bandwidth. Especially when the voltage oscillates at high frequency, the PI control cannot respond. The capacitive power of the present invention is obtained by multiplying the differential of the capacitive current by the voltage, which has an advanced effect and can predict the oscillation trend of the capacitive voltage, enabling the controller to respond to the high-frequency oscillation of the capacitive voltage. Third, compared with the traditional method, the use of the PR controller makes the control gain of the controller higher at 100 Hz, which cannot be achieved by the traditional method. Fourth, the traditional method obtains the compensation current through PI from the voltage, but the parameters are not universal under different operating conditions because the physical meaning from voltage to current is not clear and the parameter debugging is complex. The compensated capacitive power obtained by the present invention, by subtracting the d-axis power error term Δu d i d , and then dividing by the q-axis voltage to obtain the accurate compensation current Therefore, the physical meaning is clear and the parameters are relatively easy to set.

[0080] As Figure 4 shown, when the method of the present invention is not adopted, the bus voltage shows obvious periodic high-frequency oscillation, the voltage fluctuation amplitude is large, the peak-to-peak voltage difference is significant, and there are obvious overshoot and undershoot phenomena. Due to the influence of the voltage oscillation, the motor current (such as the q-axis current) fluctuates accordingly, with a high harmonic content and obvious waveform distortion, resulting in an increase in torque ripple and affecting the smooth operation of the motor. The violent fluctuations of the voltage and current indicate that there is an LC resonance problem in the system, which may cause the overvoltage protection to trigger or the motor control to become unstable, affecting the reliability of the drive system.

[0081] As Figure 5 shown, after adopting the method of the present invention, the high-frequency oscillation component of the bus voltage is significantly suppressed, the voltage waveform is smoother, the fluctuation amplitude is greatly reduced, the peak-to-peak voltage difference is significantly decreased, and the voltage stability is significantly improved. The harmonic content of the motor current (such as the q-axis current) is reduced, the waveform is closer to the ideal sine wave, the torque output is more stable, and the motor operation noise and vibration are reduced. Due to the adoption of the proportional resonance (PR) control and the capacitive power feedforward compensation, the system can quickly respond to the voltage fluctuation, suppress the oscillation trend in advance, and avoid the influence of the voltage mutation on the system.

[0082] Therefore, the differences between the embodiment of the present invention and the prior art are as follows:

[0083] 1) Calculating the reference value of the capacitive power through the sampled grid voltage.

[0084] 2) The calculation method is to obtain the current value by differentiating the grid voltage or the bus voltage, and then multiply it by the voltage to obtain the power value.

[0085] 3) The PR controller is used to control the capacitor power, so that the controller has a larger gain at a frequency of 100 Hz.

[0086] 4) The method for calculating the q-axis current based on the compensation power, by subtracting the d-axis power error term Δu d i d , and then dividing by the q-axis voltage to obtain the compensation current

[0087] Referring to Figure 2 , a bus voltage oscillation suppression system for a non-electrolytic capacitor drive system, comprising:

[0088] The first module 201 is used to obtain the torque current reference value of the motor and the grid phase angle and perform a multiplication calculation to obtain the preliminary q-axis current reference value of the motor;

[0089] The second module 202 is used to obtain the grid capacitor power reference value and the actual value of the grid capacitor power and perform compensation through a proportional-resonant controller to obtain the grid power compensation value;

[0090] The third module 203 is used to combine the preliminary q-axis current reference value of the motor and the grid power compensation value and perform feedforward compensation control through a current controller to generate a pulse width PWM control signal to drive the motor to operate, so as to realize the motor control for voltage oscillation suppression.

[0091] The content in the above method embodiments is applicable to the present system embodiment. The functions specifically implemented by the present system embodiment are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those of the above method embodiments.

[0092] The above is a specific description of the preferred embodiments of the present invention, but the present invention is not limited to the described embodiments. Those skilled in the art can make various equivalent deformations or substitutions without departing from the spirit of the present invention, and these equivalent deformations or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A method for suppressing bus voltage oscillation in an electrolytic-capacitorless drive system, characterized in that It includes the following steps: Obtain the torque current reference value of the motor and the grid phase angle, and perform a multiplication calculation to obtain the preliminary q-axis current reference value of the motor; Obtain the grid capacitor power reference value and the actual value of the grid capacitor power, and perform compensation through a proportional-resonant controller to obtain the grid power compensation value; Combine the preliminary q-axis current reference value of the motor and the grid power compensation value, and perform feedforward compensation control through a current controller to generate a pulse-width PWM control signal to drive the motor to operate, realizing motor control for suppressing voltage oscillation.

2. The method for suppressing bus voltage oscillation of an electrolytic-capacitorless drive system according to claim 1, wherein The step of obtaining the torque current reference value of the motor and the grid phase angle, and performing a multiplication calculation to obtain the preliminary q-axis current reference value of the motor specifically includes: Detect and process the speed of the motor, obtain the actual speed of the motor, and perform a difference calculation with the motor speed command value to obtain the motor speed error value; Perform a conversion process on the motor speed error value through a PI controller to obtain the torque current reference value of the motor; Obtain the high-voltage AC signal of the grid, and perform conversion and sampling through an operational amplifier conditioning circuit to obtain the grid voltage; Perform phase tracking on the grid voltage through a phase-locked loop PLL to obtain the grid phase angle; Perform a multiplication calculation on the torque current reference value of the motor and the grid phase angle to obtain the preliminary q-axis current reference value of the motor.

3. The method for suppressing the bus voltage oscillation of an electrolytic-capacitorless drive system according to claim 2, characterized in that, The transfer function of the phase-locked loop PLL is as follows: In the above formula, H(s) represents the transfer function of the phase-locked loop (PLL), and θ g represents the phase angle of the grid voltage, k p represents the proportional coefficient of the speed loop, s represents the differential operator, k i represents the integral coefficient of the speed loop, θ grid (s) represents the actual phase angle input of the grid voltage, K pd represents the gain coefficient of the phase detector.

4. The method for suppressing the bus voltage oscillation of an electrolytic-capacitorless drive system according to claim 3, wherein The step of obtaining the grid capacitor power reference value and the actual value of the grid capacitor power, and performing compensation through a proportional-resonant controller to obtain the grid power compensation value specifically includes: Perform a differential operation on the grid voltage and multiply it by the capacitance value of the grid capacitor to obtain the reference value of the capacitor charging and discharging current; Perform a multiplication calculation on the reference value of the capacitor charging and discharging current and the grid voltage to obtain the grid capacitor power reference value; Sample the bus voltage, perform a differential operation, and multiply it by the capacitance value of the grid capacitor to obtain the actual value of the capacitor charging and discharging current; Perform a multiplication calculation on the actual value of the capacitor charging and discharging current and the bus voltage to obtain the actual value of the grid capacitor power; Calculate the difference between the grid capacitor power reference value and the actual value of the grid capacitor power, and perform compensation through a proportional-resonant controller to obtain the grid power compensation value.

5. A method for suppressing bus voltage oscillation in an electrolytic-capacitor-free drive system according to claim 4, characterized in that, The transfer function of the proportional-resonant controller is as follows: In the above formula, k pr represents the proportional coefficient of the resonant controller, k rr represents the resonant coefficient of the resonant controller, ω c represents the cut-off frequency, s represents the differential operator, and ω0 represents the center frequency.

6. A method for suppressing bus voltage oscillation in an electrolytic-capacitorless drive system according to claim 5, characterized in that, The step of combining the preliminary q-axis current reference value of the motor and the grid power compensation value, and performing feedforward compensation control through a current controller to generate a pulse-width PWM control signal to drive the motor to operate, realizing motor control for suppressing voltage oscillation specifically includes: Obtain the d-axis power error term of the motor, perform a difference calculation with the grid power compensation value, and divide the difference calculation result by the q-axis voltage of the motor to obtain the q-axis current compensation value of the motor; Perform an addition calculation on the q-axis current compensation value of the motor and the preliminary q-axis current reference value of the motor to obtain the q-axis current reference value of the motor; Obtain the d-axis current reference value of the motor, combine it with the q-axis current reference value of the motor, and input it to the current controller for feedforward compensation control to generate a pulse-width PWM control signal; Transmit the pulse-width PWM control signal to the inverter to drive the motor to operate, realizing motor control for suppressing voltage oscillation.

7. The method for suppressing bus voltage oscillation of an electrolytic-capacitorless drive system according to claim 6, wherein The expression of the feedforward compensation control of the current controller is specifically as follows: In the above formula, represents the d-axis current reference value of the motor, represents the q-axis current reference value of the motor, i d (s) represents the d-axis current value of the motor, i q (s) represents the q-axis current value of the motor, s represents the differential operator, ω r represents the actual speed of the motor, ψ f represents the permanent magnet flux linkage, represents the d-axis voltage reference value, represents the q-axis voltage reference value, represents the d-axis current loop proportional gain, represents the q-axis current loop proportional gain, represents the d-axis current loop integral gain, represents the q-axis current loop integral gain, L q represents the d-axis inductance, L d represents the q-axis inductance.

8. An electrolytic-capacitorless drive system bus voltage oscillation suppression system, characterized in that, It includes the following modules: The first module is used to obtain the torque current reference value of the motor and the grid phase angle and perform a multiplication calculation to obtain the preliminary q-axis current reference value of the motor; The second module is used to obtain the grid capacitor power reference value and the actual value of the grid capacitor power and perform compensation through a proportional-resonant controller to obtain the grid power compensation value; The third module is used to combine the preliminary q-axis current reference value of the motor and the grid power compensation value and perform feedforward compensation control through a current controller to generate a pulse-width PWM control signal to drive the motor to operate, realizing motor control for suppressing voltage oscillation.

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