A method for suppressing the beat frequency of a busless motor drive system

Abstract

The application provides a bus voltage sensor-free motor driving system beat frequency suppression method, a double closed-loop control system based on a power current loop is constructed by moving a q-axis current feedback node forward, additional current loop PI parameters are not needed to be set, and control loop design is greatly simplified; meanwhile, a bus voltage observer derived from the system architecture uses system existing signals such as power current reference values, motor dq-axis currents and voltages, and accurately calculates bus voltage observation values through specific mathematical relations, high-precision voltage estimation values can be obtained without physical sensors, the modulation coefficient errors of a space vector pulse width modulation unit can be accurately compensated as feedforward values, the beat frequency effect caused by a single-phase rectifier double-frequency bus voltage pulsation is effectively suppressed, motor torque and rotating speed pulsation is significantly reduced, and the drawbacks of a high cost, large sampling delay and insufficient dynamic performance of simple feedback compensation of a traditional scheme are overcome.

Description

Technical Field

[0001] This invention relates to the field of servo drives and traction converters, and in particular to a method for suppressing beat frequency in a motor drive system without a bus voltage sensor. Background Technology

[0002] In a motor drive system powered by a single-phase rectifier, the rectifier and inverter are interconnected via an intermediate DC bus. Due to the inherent nonlinear operating characteristics of the single-phase rectifier, its output DC bus voltage is not a smooth DC signal but contains abundant harmonic components, among which the voltage ripple component at twice the grid frequency is the most significant. This bus voltage ripple, through the inverter's modulation process, generates a frequency of 2 in the inverter output phase voltage and the motor stator phase current. ω g ± ω The beat frequency component introduces a second-harmonic voltage disturbance in the motor's dq coordinate system, thereby exciting periodic oscillations in the q-axis current. Since the motor's output torque is directly related to the q-axis current, the pulsation of the q-axis current will directly cause low-frequency pulsations in the motor's output torque, resulting in additional noise and mechanical vibration, reducing the smoothness of equipment operation and control accuracy, and increasing the losses of the motor and transmission components.

[0003] To suppress bus voltage ripple, traditional solutions typically involve connecting large-capacity electrolytic capacitors in parallel with the DC bus. However, electrolytic capacitors have inherent drawbacks such as large size, short lifespan, limited current handling capacity, and temperature sensitivity, which restricts the improvement of system power density. In recent years, electrolytic capacitor-free designs have gained attention, employing alternatives such as thin-film capacitors. However, their capacitance per unit volume is relatively low, and with the trend of reducing capacitance values, the bus voltage ripple problem becomes more prominent, placing higher demands on control algorithms. In existing technologies, to address torque ripple caused by beat frequency, bus voltage sensors are often introduced for feedforward compensation. However, this method increases hardware costs, and sampling delays affect the real-time performance of compensation. Some technologies propose introducing repetitive voltage observers to compensate by predicting the bus voltage, but the observation accuracy depends on a high sampling rate, further increasing hardware performance requirements. In addition, there are resonant control methods based on current-specified harmonic feedback, which, while possessing good robustness, have poor dynamic performance and often require feedforward compensation in conjunction with bus voltage sensors.

[0004] Therefore, how to simplify the control system structure, eliminate dependence on physical sensors of bus voltage, and effectively suppress motor beat frequency problems caused by bus voltage pulsation while ensuring the dynamic response performance of the system has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a beat frequency suppression method for a motor drive system without a bus voltage sensor, so as to solve the problems existing in the prior art.

[0006] To achieve the above objectives, the present invention provides the following solution: This invention provides a beat frequency suppression method for a motor drive system without a bus voltage sensor, applicable to a motor drive system consisting of a rectifier and a three-phase inverter cascaded together, comprising the following steps: S1. Construct a dual closed-loop control system for a motor based on power current control. The dual closed-loop control system includes a speed loop and a power current loop arranged sequentially. S2. The speed loop outputs a power current reference value based on the motor speed error; S3. Receive the power current reference value through the power current loop, and generate the motor q-axis voltage command based on the power current feedback signal and the built-in PI controller. S4. Based on the power current reference value, motor d-axis current, motor q-axis current, motor d-axis voltage, and motor q-axis voltage, the observed bus voltage value is calculated using the bus voltage observer. S5. The observed bus voltage value is input as a feedforward quantity to the space vector pulse width modulation unit to compensate for the calculation error of the modulation coefficient.

[0007] Preferably, the bus voltage observer calculates the observed bus voltage value using the following formula: ; in, P e This refers to the instantaneous electromagnetic power of the motor. i p * This is a reference value for power current. u d For the d-axis voltage value of the motor, u q This is the q-axis voltage value of the motor. i d For the d-axis current value of the motor, i q This is the q-axis current value of the motor.

[0008] Preferably, in the space vector pulse width modulation unit, the modulation coefficient is feedforward compensated using the bus voltage observation value, and the formula for calculating the compensated modulation coefficient is as follows: ; in, u sref Let be the expected value of the inverter output voltage vector magnitude. u dobThis is the observed value of the bus voltage.

[0009] Preferably, the feedforward channel of the power current loop includes a variable gain circuit and a PI controller, and the gain value of the variable gain circuit is determined according to the ratio of the rated value of the bus voltage to the q-axis voltage of the motor.

[0010] Preferably, the power current feedback signal is obtained by calculating the ratio of the instantaneous power on the inverter side to the rated value of the bus voltage.

[0011] Preferably, the single-phase rectifier is a single-phase diode rectifier, and the observed bus voltage is used to compensate for the modulation coefficient error caused by the second harmonic bus voltage pulsation generated by the single-phase diode rectifier.

[0012] Preferably, the power current reference value is obtained by the speed loop after processing the square error of the motor speed through a PI regulator.

[0013] The present invention also provides a motor drive system configured to perform the beat frequency suppression method for a motor drive system without a bus voltage sensor.

[0014] The present invention achieves the following beneficial technical effects compared to the prior art: This invention provides a beat frequency suppression method for a motor drive system without a bus voltage sensor, characterized by simplified structure, fast dynamic response, and low cost. This method constructs a dual closed-loop control system based on the power current loop by moving the q-axis current feedback node forward, eliminating the need to tune additional current loop PI parameters and significantly simplifying the control loop design. Simultaneously, the bus voltage observer derived from the system architecture utilizes existing system signals such as power current reference values, motor dq-axis currents and voltages, and more, to accurately calculate the observed bus voltage values ​​through specific mathematical relationships. This not only provides high-precision voltage estimates without physical sensors but also uses these estimates as feedforwards to accurately compensate for modulation coefficient errors in the space vector pulse width modulation unit, effectively suppressing the beat frequency effect caused by the second harmonic bus voltage pulsation of the single-phase rectifier. This significantly reduces motor torque and speed pulsation, overcoming the drawbacks of traditional solutions such as high cost, large sampling delay, and insufficient dynamic performance of simple feedback compensation. It is particularly suitable for cost-sensitive motor drive systems with high control performance requirements, such as those without electrolytic capacitors or with small-capacity capacitors. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of beat frequency suppression in a motor control system based on a power current loop. Figure 2 This is a schematic diagram of power current closed-loop control; Figure 3 This is a schematic diagram of modulation coefficient compensation based on a voltage observer; Figure 4 Simulation waveforms of a motor drive system based on power current control under rated operating conditions: voltage observer starts at 1.5s; Figure 5 Spectral analysis of stator A-phase current before starting voltage observer; Figure 6 Spectral analysis of stator A-phase current after starting the voltage observer. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] The purpose of this invention is to provide a beat frequency suppression method for a motor drive system without a bus voltage sensor, so as to solve the problems existing in the prior art.

[0019] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] Example 1: This embodiment takes a permanent magnet synchronous motor drive system as an example, specifically a motor drive system consisting of a single-phase diode rectifier and a three-phase inverter cascaded together. This system includes a power grid, a single-phase diode rectifier, and a DC bus with a bus capacitor. C dc The system includes a three-phase inverter, a permanent magnet synchronous motor (PMSM), and a control unit. The control unit adopts a dual closed-loop control architecture based on the power current loop, including a speed loop and a power current loop, and integrates a bus voltage observer. This control architecture enables the suppression of motor beat frequency current without the need for a bus voltage sensor.

[0021] First refer to Figure 1 A verification platform for beat frequency suppression of a motor drive system based on a power current loop was built, and a method based on... i d *The vector control structure with =0 has an outer loop that controls the square of the rotational speed, and the output of the speed controller is the power current reference value. i p * Power current i p The average power injected into the inverter is the current injected from the DC bus. P inv = U dc i p ,in U dc This is the rated value of the bus voltage. The expression for the instantaneous electromagnetic power of the motor is: P e = u q i q + u d i d ,in u q This is the q-axis voltage. i q For q-axis current, u d The voltage along the d-axis. i d For d-axis current, in steady state i d =0 and P e Average power injected by the inverter P inv They are approximately equal, if we let P inv = P e The power current can be derived by combining the two equations. i p = P e / U dc .

[0022] This embodiment uses a bus observation voltage feedforward method to correct the modulation coefficients calculated by the space vector pulse width modulation unit. The voltage observer derived from the power current loop uses the power current reference value. i p * and instantaneous electromagnetic power of motor P e As inputs, the instantaneous inverter injection power is defined respectively. P inv = udob i p * Instantaneous electromagnetic power of motor P e = u q i q + u d i d ,in u dob For the busbar observation voltage. Let P inv = P e The bus observation voltage can be derived by combining the two methods. u dob = P e / i p * ,Right now The observed bus voltage is used to correct the regulation coefficient, and the space vector pulse width modulation unit outputs drive signals S1 to S6 to control the inverter accordingly.

[0023] based on Figure 1 The vector control structure is constructed. Figure 2 The power current closed-loop control shown sets up a power current loop after the output of the speed controller, using the power current reference value. i p * Given a variable gain stage and a PI controller, the gain of the variable gain stage is determined by the ratio of the rated bus voltage to the q-axis voltage. In this invention, the virtual switch of the control system is defaulted to position I, meaning the inner loop uses power current control. When the virtual switch is shifted to position II, the inner loop uses the traditional control method, i.e., q-axis current control. If the q-axis current feedback node is moved forward and multiplied in the feedback channel... u q / U dc This allows for an equivalent transformation from traditional control to the proposed power current control. Clearly, the open-loop transfer functions of the two current inner-loop control methods are equal. This evolution process is equivalent to shifting the virtual switch position from II to I, at which point the q-axis current... i q To power current i p The transfer function can be written as: ; The power current feedback signal is obtained by calculating the instantaneous power on the inverter side and the rated value of the bus voltage.U dc The ratio is obtained and after being filtered by a low-pass filter to remove high-frequency harmonics, it enters the feedback comparison stage of the power current loop to generate the final q-axis voltage command.

[0024] The bus voltage observer based on power current control is another key component of this invention. It calculates the observed bus voltage value using system-measurable signals, eliminating the need for physical sensors. Specifically, refer to... Figure 3 The expression for the observed voltage of the bus is: u dob = P e / i p * ;in P e = u q i q + u d i d At this point, the modulation coefficient m calculated within the space vector pulse width modulation unit is corrected to... ,in u sref Let be the desired value of the inverter output voltage vector magnitude. By compensating for the modulation coefficient, the inverter output voltage vector magnitude can be reduced to the previous sin( ). φ dob )(sin( φ dob (<1) times, of which This compensation method helps to reduce motor torque pulsation caused by beat frequency issues in order to observe the phase angle of voltage lag behind the actual voltage.

[0025] To verify the effectiveness of this invention, a simulation experiment was conducted on a surface-mount permanent magnet synchronous motor drive system. This motor has 4 pole pairs, a rated speed of 4425 r / min (electric angular velocity of 295 Hz), a rated torque of 2.39 N·m, a permanent magnet flux linkage of 0.031 Wb, a stator phase inductance of 3.2 mH, and a stator phase resistance of 1.44 Ω. The switching frequency of the permanent magnet synchronous motor drive system is 2 kHz. The AC side of the single-phase diode rectifier is connected to the power grid through a 500 μH filter inductor. This rectifier converts 380V / 50Hz three-phase AC power to DC power to supply the inverter. The bus capacitor is a small 300 μF capacitor. Due to the small bus capacitance, the bus voltage pulsation reached as high as 146V. Before the voltage observer was activated at 1.5s, the speed pulsation was 117 r / min, the torque pulsation was 1.73 N·m, the stator A-phase current exhibited significant distortion, and the total harmonic distortion (THD) was as high as 22.51%. The stator current beat frequency distribution was located at the electrical angular frequency plus or minus twice the grid frequency, with beat current magnitudes of 1.81A and 1.39A, respectively. After the voltage observer was activated, the system entered a steady state after 0.2s. The voltage observer could track the actual voltage more accurately, the speed pulsation decreased to 33 r / min, the torque pulsation decreased to 0.74 N·m, the stator current THD decreased to 5.98%, and the beat current magnitudes decreased to 0.34A and 0.24A, respectively. By comparison, it can be seen that the present invention, through the bus voltage observer of the power current loop, effectively alleviates the motor beat frequency effect, suppresses motor torque and speed pulsation, and improves the system control accuracy and reliability in the absence of a bus voltage sensor.

[0026] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0027] It should be noted that the components mentioned in the above embodiments are all general standard parts or parts known to those skilled in the art. Their structure and principle can be learned by those skilled in the art through technical manuals or conventional experimental methods.

[0028] This invention has illustrated its principles and implementation methods using specific examples. The descriptions of these embodiments are merely illustrative of the method and its core ideas; furthermore, those skilled in the art will recognize that modifications may be made to the specific implementation methods and application scope based on the principles of this invention. Therefore, the content of this specification should not be construed as limiting the invention.

Claims

1. A method for suppressing beat frequency in a motor drive system without a bus voltage sensor, characterized in that, Applied to a motor drive system consisting of a cascaded rectifier and a three-phase inverter, the method includes the following steps: S1. Construct a dual closed-loop control system for a motor based on power current control. The dual closed-loop control system includes a speed loop and a power current loop arranged sequentially. S2. The speed loop outputs a power current reference value based on the motor speed error; S3. Receive the power current reference value through the power current loop, and generate the motor q-axis voltage command based on the power current feedback signal and the built-in PI controller. S4. Based on the power current reference value, motor d-axis current, motor q-axis current, motor d-axis voltage, and motor q-axis voltage, the observed bus voltage value is calculated using the bus voltage observer. S5. The observed bus voltage value is input as a feedforward quantity to the space vector pulse width modulation unit to compensate for the calculation error of the modulation coefficient.

2. The beat frequency suppression method for a motor drive system without a bus voltage sensor according to claim 1, characterized in that, The bus voltage observer calculates the observed bus voltage value using the following formula: ； in, P e This refers to the instantaneous electromagnetic power of the motor. i p * This is a reference value for power current. u d For the d-axis voltage value of the motor, u q This is the q-axis voltage value of the motor. i d For the d-axis current value of the motor, i q This is the q-axis current value of the motor.

3. The beat frequency suppression method for a motor drive system without a bus voltage sensor according to claim 1, characterized in that, In the space vector pulse width modulation unit, the modulation coefficient is feedforward compensated using the bus voltage observation value. The formula for calculating the compensated modulation coefficient is as follows: ； in, u sref Let be the expected value of the inverter output voltage vector magnitude. u dob This is the observed value of the bus voltage.

4. The beat frequency suppression method for a motor drive system without a bus voltage sensor according to claim 1, characterized in that, The feedforward channel of the power current loop includes a variable gain circuit and a PI controller. The gain value of the variable gain circuit is determined based on the ratio of the rated bus voltage to the q-axis voltage of the motor.

5. The beat frequency suppression method for a motor drive system without a bus voltage sensor according to claim 1, characterized in that, The power current feedback signal is obtained by calculating the ratio of the instantaneous power on the inverter side to the rated value of the bus voltage.

6. The beat frequency suppression method for a motor drive system without a bus voltage sensor according to claim 1, characterized in that, The single-phase rectifier is a single-phase diode rectifier, and the bus voltage observation value is used to compensate for the modulation coefficient error caused by the second harmonic bus voltage pulsation generated by the single-phase diode rectifier.

7. The beat frequency suppression method for a motor drive system without a bus voltage sensor according to claim 1, characterized in that, The power current reference value is obtained by the speed loop after processing the square error of the motor speed through a PI regulator.

8. A motor drive system, characterized in that, The system is configured to perform the beat frequency suppression method for a motor drive system without a bus voltage sensor as described in any one of claims 1 to 7.

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