A method for controlling a compressor-driven motor

Abstract

This invention relates to the field of electric motor control technology and discloses an electric motor control method for compressor drive, comprising: acquiring stator current signal and DC bus voltage signal; extracting voltage ripple characteristics based on DC bus voltage signal and determining initial value of quadrature axis current compensation; calculating the amplitude of stator current signal; when the amplitude crosses the linear magnetization current threshold, retrieving the inductor magnetization characteristic table to determine the inductor drop ratio; correcting the initial value of quadrature axis current compensation using the inductor drop ratio; and injecting the corrected compensation command into the current regulating loop. This invention, by integrating voltage ripple sensing and magnetic saturation correction mechanisms, synergistically cancels the pulse load interference of the compressor's single-cycle, fills the torque output gap under magnetic circuit saturation, suppresses stator current oscillation under low-frequency operation, and maintains torque response stiffness under all operating conditions.

Description

Technical Field

[0001] This invention relates to a method for controlling an electric motor for driving a compressor, belonging to the field of electric motor control technology. Background Technology

[0002] Currently, in compressor motor control systems driven by variable frequency technology, field-oriented control and space vector pulse width modulation (SVM) techniques are commonly used. By establishing a mathematical model of the motor, the stator current vector is adjusted to control the output torque of the motor. When the compressor operates at low frequency, its load torque exhibits pulse characteristics that vary with the cycle. During the exhaust stroke, the instantaneous value of the load torque is significantly higher than the average value. Existing control systems mainly rely on closed-loop feedback regulation of the speed loop to eliminate load disturbances. Due to the limitations of the sampling period of the digital controller and the calculation period of the current loop, the feedback regulation has a phase lag in the time domain. When the motor is operating under low frequency and high load pressure conditions, this lag causes the electromagnetic torque to be unable to accurately offset the changes in load torque, resulting in torque fluctuations and mechanical vibrations.

[0003] While shifting from hardware limitations to software compensation, existing methods still have shortcomings. For example, Chinese invention patent CN105529980B discloses a motor control device, compressor, air conditioner, and program that estimates vibration corresponding quantities and switches between different control modes to balance noise suppression and power consumption reduction. This technology is based on mechanical vibration results or speed deviation feedback switching, making it a result-oriented adjustment. It cannot achieve a physically quasi-synchronous response to sudden load changes. This scheme ignores the physical parameter drift caused by transient magnetic saturation of the stator core during the high current output range of the motor and does not define the distortion effect of nonlinear drop in quadrature-axis inductance on torque gain calculation. Current control methods have the following main technical limitations when dealing with such operating conditions: 1. Phase delay in the feedback loop causes spatial misalignment between the compensation signal and the actual load pulse; 2. During the high current output range, transient saturation of the stator core magnetic circuit causes nonlinear drops in physical parameters such as quadrature-axis inductance, leading to inaccurate torque gain calculation; 3. The system typically filters out DC bus voltage ripple and treats it as interference, failing to effectively utilize the load characteristic information contained within it.

[0004] Therefore, the technical problem to be solved by this invention is how to dynamically correct the control deviation caused by phase delay and magnetic circuit saturation on the basis of establishing a real-time load sensing mechanism using the inherent electrical characteristic signals of the system, so as to maintain the stable operation of the drive system under all working conditions. Summary of the Invention

[0005] To address the problems mentioned in the background art, the technical solution of the present invention is as follows: A method for controlling an electric motor for driving a compressor, comprising the following steps:

[0006] Step S1: The signal acquisition unit acquires the stator current signal of the motor and the DC bus voltage signal of the power conversion unit.

[0007] Step S2: Calculate the DC bus voltage pulsation within a single compressor cycle based on the DC bus voltage signal. The DC bus voltage pulsation includes the amplitude and frequency fluctuation characteristics of the DC bus voltage signal within a single cycle.

[0008] Step S3: Based on the DC bus voltage ripple, determine the initial value of the quadrature axis current compensation command through a preset voltage-to-torque mapping function. The initial value of the quadrature axis current compensation command is used to generate an electromagnetic torque component that is opposite in direction to the transient load torque of the compressor.

[0009] Step S4: Real-time detection of the amplitude of the stator current signal and determination of whether the amplitude exceeds the preset core linear magnetization current threshold. The core linear magnetization current threshold represents the current critical point at which the stator core enters the magnetic saturation state.

[0010] Step S5: If the amplitude exceeds the core linear magnetization current threshold, the cross-axis inductance drop ratio is extracted from the preset inductance magnetization characteristic mapping table based on the amplitude of the stator current signal.

[0011] Step S6: The cross-axis inductance drop ratio is used as a gain factor to apply to the initial value of the cross-axis current compensation command to generate a corrected cross-axis current compensation command, thereby making up for the electromagnetic torque compensation gap caused by the transient saturation of the stator core.

[0012] Step S7: The corrected quadrature-axis current compensation command is injected as the feedforward compensation amount into the command terminal of the current regulation loop to adjust the output duty cycle of the power conversion unit.

[0013] Preferably, after step S6 and before step S7, the following steps are also included: Step S201, obtaining the rotor electrical angle to identify the electrical angle phase interval where the peak load torque of the compressor is located; Step S202, performing high-pass filtering on the estimated speed of the motor to extract the speed harmonic residual; Step S203, calculating the compensation phase deviation value based on the speed harmonic residual, and using the compensation phase deviation value to perform advance correction on the injection phase of the corrected quadrature axis current compensation command, so that the generated electromagnetic torque is aligned with the mechanical load torque in spatial phase.

[0014] Preferably, after step S6 and before step S7, the following steps are also included: step S301, detecting the DC offset in the DC bus voltage signal and the hot resistance drift value of the stator winding; step S302, adjusting the compensation gain of the corrected quadrature axis current compensation command by normalization coefficient according to the DC offset and the hot resistance drift value, so as to maintain the consistency of torque response under different operating conditions.

[0015] Preferably, during the execution of steps S1 to S7, and when the compressor load torque valley value is identified, the following steps are also included: Step S401, injecting a high-frequency carrier signal into the stator winding within the electrical angle range corresponding to the compressor load torque valley value; Step S402, identifying the real-time resistance value of the stator winding based on the response characteristics of the stator current signal to the high-frequency carrier signal, and using the real-time resistance value as the basis for adjusting the current regulating loop control parameters.

[0016] Preferably, step S2 specifically includes: performing bandpass filtering on the DC bus voltage signal to extract the voltage pulsation component corresponding to a single revolution cycle; performing synchronous coordinate transformation on the voltage pulsation component according to the rotor electrical angle to construct a rotating energy feature vector synchronized with the compressor mechanical load pulse frequency.

[0017] Preferably, the cross-axis inductance drop ratio η is determined by the following rule: Where η is the sag ratio of the quadrature-axis inductance. This is the preset nominal quadrature-axis inductance value of the motor in the linear region of the magnetic field. The real-time quadrature-axis inductance value is obtained by retrieving the inductor magnetization characteristic mapping table from the amplitude of the stator current signal.

[0018] Preferably, the inductance magnetization characteristic mapping table contains multiple sets of inductance characteristic curves corresponding to different compressor discharge pressures; the method further includes: estimating the real-time pressure ratio based on the condensing temperature and evaporating temperature of the compressor system, and dynamically switching from the inductance magnetization characteristic mapping table to the target characteristic curve that matches the real-time pressure ratio.

[0019] Preferably, the method further includes: when the operating frequency of the motor is below 10Hz, increasing the control bandwidth of the speed regulation loop, and using the corrected quadrature axis current compensation command as a feedforward term to directly apply to the duty cycle generation logic of the voltage space vector modulation, so as to shorten the response delay to load torque pulsation.

[0020] Preferably, step S203 specifically includes: performing a second-order differential operation on the speed harmonic residual to determine the extreme point of the speed fluctuation, and determining the compensation phase deviation value based on the geometric offset of the extreme point relative to the electrical angle phase interval where the load torque peak is located.

[0021] Preferably, before executing step S7, the method further includes: limiting the modified quadrature-axis current compensation command based on the maximum allowable output current of the power conversion unit and the real-time temperature rise protection threshold of the motor.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] 1. In the control of the motor driven by the compressor, the energy fluctuation characteristic vector is determined based on the periodic fluctuation component of the DC bus voltage and converted into the compensation component of the stator current. This allows the pulsating energy on the DC side of the inverter to be actively offset at the physical instant of electromagnetic torque generation. This breaks the traditional feedback logic that relies on speed deviation for lag adjustment and realizes real-time response to the pulse load within a single rotation cycle of the compressor. This suppresses the forced oscillation of the stator current vector under low-frequency conditions and reduces the low-frequency electromagnetic noise of the system.

[0024] 2. By aligning the rotor electrical angle with the spatial quadrant of the load torque peak and combining it with the harmonic fluctuation residual in the estimated speed to establish a phase correction closed loop, the physical phase lag caused by sampling delay and algorithm calculation cycle is automatically corrected. This phase self-optimization mechanism enables the injected electromagnetic torque and mechanical load torque to achieve zero-error alignment in spatial phase, avoiding additional torque pulsation induced by phase shift, ensuring the torque smoothing effect of the motor during the switching process between high-speed and low-speed domains, and making the micro-acceleration of the rotor during rotation more stable.

[0025] 3. By monitoring the DC bias drift of the DC bus voltage and the thermal offset of the stator resistance, the self-normalization adjustment of the compensation gain is achieved. Combined with the transient reconstruction logic of the quadrature axis inductor under high current conditions, the nonlinear distortion of torque output caused by magnetic circuit saturation is eliminated. The synergistic effect of multiple technical features enables the control system to have adaptive sensing capabilities under all pressure conditions and the entire temperature rise cycle. Utilizing the existing voltage sampling circuit in the system, the physical stiffness of the motor output torque under the extreme pressure ratio environment is maintained without the need to add a pressure sensor, thus solving the problem of compensation failure caused by operating environment drift. Attached Figure Description

[0026] Figure 1 This is a flowchart of the torque compensation control method for the compressor drive motor of the present invention;

[0027] Figure 2 This is the logic diagram for the quadrature axis current compensation correction under stator core magnetic saturation in this invention.

[0028] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0029] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0030] A method for controlling an electric motor for a compressor drive includes the following steps:

[0031] Step S1: The signal acquisition unit acquires the stator current signal of the motor and the DC bus voltage signal of the power conversion unit.

[0032] Step S2: Calculate the DC bus voltage pulsation within a single compressor cycle based on the DC bus voltage signal. The DC bus voltage pulsation includes the amplitude and frequency fluctuation characteristics of the DC bus voltage signal within a single cycle.

[0033] Step S3: Based on the DC bus voltage ripple, determine the initial value of the quadrature axis current compensation command through a preset voltage-to-torque mapping function. The initial value of the quadrature axis current compensation command is used to generate an electromagnetic torque component that is opposite in direction to the transient load torque of the compressor.

[0034] Step S4: Real-time detection of the amplitude of the stator current signal and determination of whether the amplitude exceeds the preset core linear magnetization current threshold. The core linear magnetization current threshold represents the current critical point at which the stator core enters the magnetic saturation state.

[0035] Step S5: If the amplitude exceeds the core linear magnetization current threshold, the cross-axis inductance drop ratio is extracted from the preset inductance magnetization characteristic mapping table based on the amplitude of the stator current signal.

[0036] Step S6: The cross-axis inductance drop ratio is used as a gain factor to apply to the initial value of the cross-axis current compensation command to generate a corrected cross-axis current compensation command, thereby making up for the electromagnetic torque compensation gap caused by the transient saturation of the stator core.

[0037] Step S7: The corrected quadrature-axis current compensation command is injected as the feedforward compensation amount into the command terminal of the current regulation loop to adjust the output duty cycle of the power conversion unit.

[0038] Preferably, after step S6 and before step S7, the following steps are also included: Step S201, obtaining the rotor electrical angle to identify the electrical angle phase interval where the peak load torque of the compressor is located; Step S202, performing high-pass filtering on the estimated speed of the motor to extract the speed harmonic residual; Step S203, calculating the compensation phase deviation value based on the speed harmonic residual, and using the compensation phase deviation value to perform advance correction on the injection phase of the corrected quadrature axis current compensation command, so that the generated electromagnetic torque is aligned with the mechanical load torque in spatial phase.

[0039] Preferably, after step S6 and before step S7, the following steps are also included: step S301, detecting the DC offset in the DC bus voltage signal and the hot resistance drift value of the stator winding; step S302, adjusting the compensation gain of the corrected quadrature axis current compensation command by normalization coefficient according to the DC offset and the hot resistance drift value, so as to maintain the consistency of torque response under different operating conditions.

[0040] Preferably, during the execution of steps S1 to S7, and when the compressor load torque valley value is identified, the following steps are also included: Step S401, injecting a high-frequency carrier signal into the stator winding within the electrical angle range corresponding to the compressor load torque valley value; Step S402, identifying the real-time resistance value of the stator winding based on the response characteristics of the stator current signal to the high-frequency carrier signal, and using the real-time resistance value as the basis for adjusting the current regulating loop control parameters.

[0041] Preferably, step S2 specifically includes: performing bandpass filtering on the DC bus voltage signal to extract the voltage pulsation component corresponding to a single revolution cycle; performing synchronous coordinate transformation on the voltage pulsation component according to the rotor electrical angle to construct a rotating energy feature vector synchronized with the compressor mechanical load pulse frequency.

[0042] Preferably, the cross-axis inductance drop ratio η is determined by the following rule: Where η is the sag ratio of the quadrature-axis inductance. This is the preset nominal quadrature-axis inductance value of the motor in the linear region of the magnetic field. The real-time quadrature-axis inductance value is obtained by retrieving the inductor magnetization characteristic mapping table from the amplitude of the stator current signal.

[0043] Preferably, the inductance magnetization characteristic mapping table contains multiple sets of inductance characteristic curves corresponding to different compressor discharge pressures; the method further includes: estimating the real-time pressure ratio based on the condensing temperature and evaporating temperature of the compressor system, and dynamically switching from the inductance magnetization characteristic mapping table to the target characteristic curve that matches the real-time pressure ratio.

[0044] Preferably, the method further includes: when the operating frequency of the motor is below 10Hz, increasing the control bandwidth of the speed regulation loop, and using the corrected quadrature axis current compensation command as a feedforward term to directly apply to the duty cycle generation logic of the voltage space vector modulation, so as to shorten the response delay to load torque pulsation.

[0045] Preferably, step S203 specifically includes: performing a second-order differential operation on the speed harmonic residual to determine the extreme point of the speed fluctuation, and determining the compensation phase deviation value based on the geometric offset of the extreme point relative to the electrical angle phase interval where the load torque peak is located.

[0046] Preferably, before executing step S7, the method further includes: limiting the modified quadrature-axis current compensation command based on the maximum allowable output current of the power conversion unit and the real-time temperature rise protection threshold of the motor.

[0047] Example 1: When the heat pump system is operating in an extremely low-temperature environment and the compressor drive motor is operating at an extremely low frequency (below 10Hz), due to the pressure difference between the compressor's suction and discharge pressures, the piston generates a pulsed mechanical torque load during discharge. Limited by the switching frequency of the power conversion unit (i.e., the space vector pulse width modulation system) and the calculation delay of the current regulating loop, the compensation command generated by the control system experiences phase lag in the time domain. This results in the electromagnetic torque being unable to offset the changes in load torque in real time, causing forced oscillations in the stator current along the space vector trajectory, inducing low-frequency electromagnetic noise. This motor control method adjusts the fluctuations under the above conditions through a coherent quadrature-axis current pre-distortion mechanism related to the DC bus ripple. The signal acquisition unit collects the DC bus voltage of the power conversion unit. In addition to the stator current signal of the motor, the DC bus voltage is synchronously sampled at the symmetrical center point of the pulse width modulation carrier to eliminate incoherent noise generated by the switching action of the power transistor. The periodic fluctuation component is extracted from the DC bus voltage using a linear differential operator. Based on the initial voltage value in the resting state Average DC bus voltage during operation The difference determines the load characterization factor. The mapping gain of the quadrature-axis current compensation term is corrected using this load characterization factor. The initial value of the quadrature axis current compensation command is calculated. This allows the compensation command to be normalized and adjusted according to changes in the load reference, maintaining the torque response strength.

[0048] To achieve quantization and extraction of frequency fluctuation characteristics in DC bus voltage ripple, the controller, after acquiring the DC bus voltage signal, uses a bandpass filter with adaptive bandwidth characteristics to lock the center frequency of the DC bus ripple. The center frequency of this bandpass filter is locked in real-time at twice the motor's electrical frequency, with a fixed quality factor of 10.0 and a dynamically set bandwidth of 15% of the center frequency, with a minimum bandwidth threshold of no less than 4Hz. The filter coefficients are updated every 5 milliseconds, rapidly switching between 10 preset coefficient groups covering the range of 10Hz to 120Hz in memory, thereby stabilizing the signal group delay of the filter within the range of 1.2 to 1.8 milliseconds. The frequency fluctuation coefficient, used to characterize the spatial distribution of the load torque, is determined based on the deviation of the center frequency from the motor stator frequency. The quantization mapping logic for this frequency fluctuation coefficient... The controller stores the input in a 1D linear lookup table. The input is the difference between the center frequency of the DC bus voltage pulsation and the real-time electric frequency of the motor. When this difference varies within the range of 0Hz to 15Hz, the frequency fluctuation coefficient increases from 1.00 to 1.675 in linear steps of 0.045. If the difference exceeds 15Hz, the coefficient is forcibly locked at 1.675. The real-time pressure ratio is estimated based on a comparison table of the thermodynamic properties of the R32 working fluid. The condensing temperature sampling range is 30.0℃ to 65.0℃, the evaporating temperature sampling range is -25.0℃ to 15.0℃, and the sampling grid accuracy is 5.0℃. The controller uses a 2D bilinear interpolation algorithm to calculate the current pressure ratio value. If the calculated value is greater than 4.5, the image gain of the quadrature-axis current compensation command is automatically multiplied by a correction factor of 1.25. The voltage-to-torque mapping function integrates multi-dimensional sensing parameters and incorporates periodic fluctuation components. Mapping gain Load characterization factor With frequency fluctuation coefficient Perform chained multiplication operations to calculate the initial value of the quadrature-axis current compensation command. Its calculation process satisfies the following arithmetic constraints: ,in, This is the initial value for the quadrature-axis current compensation command. As a periodic fluctuation component, For mapping gain, As the load characterization factor, This is the frequency fluctuation coefficient.

[0049] The voltage-to-torque mapping function is established based on the instantaneous power balance relationship between the inverter's DC-side pulse energy and the motor's mechanical shaft torque fluctuation. The controller acquires the DC bus voltage pulsation in real time and determines the conversion coefficient using a chain product of mapping gain, load characterization factor, and frequency fluctuation coefficient. The mapping gain is calibrated based on the ratio of pulse torque amplitude to voltage fluctuation peak value and stored in non-volatile memory. The load characterization factor is the ratio of the real-time DC bus voltage sliding average to the no-load reference voltage, characterizing the torque gain offset under different DC bus voltage drops. The frequency fluctuation coefficient is determined based on the offset of the DC bus voltage ripple center frequency relative to the stator frequency. The voltage domain fluctuation signal is converted into the initial value of the quadrature-axis current compensation command. To address the torque output nonlinearity problem caused by the stator core entering transient magnetic saturation due to large current injection, the controller compares the vector synthesis amplitude of the stator current with the preset core linear magnetization current threshold in real time. When the amplitude exceeds the core linear magnetization current threshold, the controller retrieves the preset inductor magnetization characteristic mapping table to determine the real-time quadrature-axis inductance value and calculates the quadrature-axis inductance drop ratio η, the formula of which is as follows: Where η is the cross-axis inductance drop ratio. This is the nominal quadrature axis inductance value. The real-time quadrature-axis inductance value is obtained by searching the inductor magnetization characteristic mapping table based on the amplitude of the stator current signal. The controller uses this ratio η as a gain factor to correct the initial value of the quadrature-axis current compensation command, generating a corrected quadrature-axis current compensation command to fill the torque output gap caused by transient saturation of the stator core. The method for determining the core linear magnetization current threshold and the inductor magnetization characteristic mapping table is to set the stator current amplitude to increase from zero to 2.5 times the rated current in 0.5 ampere steps, collect the motor terminal voltage response, and calculate the real-time quadrature-axis inductance value under each current gradient according to the stator voltage equation. Select Decay to the nominal quadrature axis inductance value 95% corresponds to the current amplitude threshold of the linear magnetization current of the iron core. High-pass filtering is used to extract the speed harmonic residuals from the speed estimate. The extreme points of speed fluctuations are determined using second-order differentials, and the phase correction angle is searched in 0.1-degree steps. Until The modulus value drops to a local minimum point, thus determining... To correct the phase advance of the quadrature-axis current compensation command, a phase advance is injected to offset the time-domain phase lag caused by signal sampling and algorithm iteration. To eliminate the phase difference caused by computational delay, this method corrects the execution phase through a self-alignment mechanism for compensating for speed fluctuation residuals, obtains the rotor electrical angle to identify the electrical angle phase interval where the compressor's load torque peak is located, and performs high-pass filtering on the estimated motor speed to extract the speed harmonic residuals. The phase deviation value is calculated based on the speed harmonic residual, and the phase correction angle characterizing the processing delay is determined. The phase correction angle is used to perform advance correction on the injection phase of the corrected quadrature axis current compensation command, ensuring that the generated electromagnetic torque is aligned with the mechanical load torque in spatial phase, maintaining the current vector roundness under motor operation, and attenuating electromagnetic noise under low frequency conditions.

[0050] Example 2: Measurements were performed on a 2.2kW permanent magnet synchronous motor experimental platform. This platform included a magnetic powder brake simulating a compressor load and a torque sensor for monitoring torque characteristics, simulating the load conditions of a heat pump system under extreme low-temperature environments. The input electrical signal of the motor was acquired using a power analyzer with a measurement accuracy better than 0.1%. The current sampling rate was set to 20kHz, and Gaussian random noise with a signal-to-noise ratio of 25dB was superimposed on the signal path. A 50Hz power frequency interference harmonic was also introduced to establish a benchmark for evaluating anti-interference capability. The sampling frequency of the DC bus voltage was set to twice the switching frequency, i.e., 10kHz. This frequency selection was based on the need to capture the highest frequency of the DC bus voltage pulsation component and the balance between the controller's computational load and the required frequency. To achieve a balance and satisfy the Nyquist sampling theorem to prevent frequency aliasing during signal reconstruction, the cutoff frequency of the high-pass filter is set to 0.5Hz, which is determined by the mechanical frequency corresponding to the lowest speed of the motor. The sampling frequency of the speed data is set to 2000Hz. A sliding window with a length of 256 sampling points is used to store the real-time speed data. A sliding calculation is performed every 0.5 milliseconds, and the data overlap rate is set to 75%. When extracting the speed harmonic residual, the controller performs a 3-point center difference operation on the speed data in the buffer to replace the second-order derivative. The time interval of the difference is fixed at 4 milliseconds to filter out high-frequency electromagnetic interference above 100Hz generated by the power transistor switching in the control loop. This is used to filter out DC offset and retain the dynamic fluctuation component generated by the rotor rotation.

[0051] The control group used the field-oriented control method, while the experimental group used the method of this invention. When the motor operating frequency was 5Hz and the load torque was 1.2 times the rated torque, the control group exhibited stator current oscillation, with a total harmonic distortion rate of 16.8% and a DC bus voltage fluctuation amplitude of 12.5V. Correspondingly, the experimental group extracted periodic fluctuation components... The peak value is 12.2V, and the calculated load characterization factor is... The initial value of the quadrature-axis current compensation command generated was 1.45A, resulting in a value of 0.85. Under the feedforward compensation, the total harmonic distortion of the stator current in the test group was reduced to 3.8%, and the circularity of the spatial trajectory of the current vector was corrected. Gradient verification of the magnetic saturation effect showed that when the stator current amplitude increased within the range of 5.0A to 12.0A, the quadrature-axis inductance... Maintain at the nominal quadrature axis inductance value Near the same point, the cross-axis inductance drop ratio η is close to 1.0. When the amplitude exceeds the core linear magnetization current threshold of 12.5A, the core enters a transient magnetic saturation state. Under overload conditions with a stator current amplitude of 20.0A, the control group experiences a 15.5% torque shortfall due to a decrease in the torque constant, and the speed fluctuation increases from the initial 8.2 rpm to 35.1 rpm. The experimental group, using the inductance magnetization characteristic mapping table, determines the cross-axis inductance drop ratio η to be 1.42. The corrected cross-axis current compensation command reduces the speed fluctuation from 35.1 rpm to 9.6 rpm. When the current amplitude exceeds the deep saturation region of 25.0A, the growth slope of the cross-axis inductance drop ratio η decreases, indicating that the magnetic circuit is approaching the physical saturation limit. At an operating frequency of 8Hz, the experimental group uses high-pass filtering to extract the speed harmonic residuals. The phase correction angle was determined by calculation and was set at 6.5 rpm. With an accuracy of 11.8 degrees, after injecting this lead correction into the quadrature axis current compensation command, the low-frequency harmonic component in the speed estimate is reduced from 6.5 rpm to 1.2 rpm. The resulting electromagnetic torque is aligned with the mechanical load torque in spatial phase, suppressing the current oscillation of the system across the entire load range and maintaining the stability of the torque response during the dynamic process.

[0052] Example 3: In the operating conditions involving high-power multi-split heat pump compressors, the stator resistance undergoes thermal drift due to continuous heat generation in the stator windings. Simultaneously, the DC bus support capacitor experiences electrical parameter fluctuations as the ambient temperature rises, causing a gain shift in the voltage-to-torque mapping relationship. This results in the compensation amount generated by the pre-distortion mechanism being unable to offset the actual load pulsation. This method establishes an inductor magnetization characteristic mapping table through a parameter identification procedure during the system startup phase. The controller controls the power conversion unit to sequentially inject step current signals with amplitudes ranging from 0.1 to 2.5 times the rated current into the stator windings. A voltage sensor monitors the motor terminal voltage response and calculates the real-time quadrature-axis inductance value under each current gradient based on the stator voltage equation. The acquired current amplitude points and corresponding real-time quadrature-axis inductance values ​​are stored in the controller's address space as key-value pairs. During this process, the linear magnetization current threshold of the iron core is determined by calculating the rate of change of the real-time quadrature-axis inductance value with increasing current. Specifically, the current value corresponding to when the real-time quadrature-axis inductance value drops to 95% of the nominal quadrature-axis inductance value is selected as the critical point for entering magnetic saturation. (Load characterization factor) The calculation formula is as follows: ,in, As the load characterization factor, This is the real-time moving average value of the DC bus voltage under motor operating conditions. This is the static reference value of the DC bus voltage under no-load conditions. The controller uses this load characterization factor to characterize the dynamic state of the DC side energy reserve in real time.

[0053] When the hot-state resistance drift of the stator winding is detected to exceed the preset 10% deviation threshold, the controller initiates a compensation gain correction program. This program calculates a normalized coefficient using the resistance change and adds it to the image gain of the quadrature-axis current compensation command. In this process, the feedforward injection intensity is enhanced to offset the effect of increased stator voltage drop on torque response. After parameter reconstruction and gain correction, under the condition that the motor winding temperature rise reaches 80℃, the injected space vector electromagnetic torque and the mechanical torque at the moment of compressor exhaust are matched in amplitude. The axial deviation of the stator current vector trajectory is maintained within 2.5%. The system establishes balance under hot conditions and maintains the quiet characteristics of low-frequency operation.

[0054] Example 4: In applications where motor control methods are adapted to power conversion units with different distributed inductance properties, manufacturing tolerances in the DC bus electrolytic capacitors lead to differences in equivalent series resistance. This causes a deviation in the linear mapping function between the DC bus voltage ripple and the required electromagnetic torque compensation. The mapping gain is determined through calibration procedures during the system commissioning phase. The system controls a motor to drive a simulated load with known torque characteristics and obtains the DC bus voltage fluctuation component. The peak-to-peak value is used to calculate the mapping gain using a linear relationship. The initial value, where the mapping gain The following linear computational relationship must be satisfied: ,in, For mapping gain, To simulate the amplitude of the pulse torque generated by the load, To synchronously acquire the peak value of the DC bus voltage fluctuation, the controller maps this gain. Stored in non-volatile memory as the basic mapping operator under operating conditions.

[0055] When the DC bus capacitor's capacitance decreases due to thermal effects from the operating environment, the controller initiates a reference calibration procedure to maintain consistent load sensing. During a preset detection period when the motor is stationary, the DC bus voltage signal is acquired, and the arithmetic mean of the voltage data over 100 consecutive sampling periods is calculated to determine the current static reference value of the DC bus voltage. If the deviation between the measured arithmetic mean of the voltage data and the stored historical reference value reaches 5%, the controller uses this arithmetic mean to update the calculation reference of the load characterization factor, and corrects the voltage offset by monitoring the physical bias level of the sampling circuit to ensure the periodic fluctuation component. The extraction always uses the physical DC level as the reference origin, and corrects the mapping gain using the updated load characterization factor. Generate adaptive compensation coefficients to suppress current oscillations caused by hardware parameter drift over time and maintain torque fluctuation suppression performance under low-frequency operating conditions.

[0056] Example 5: When the system faces the initial calibration conditions of deploying the motor control method to a new model of variable frequency compressor, due to the physical differences in the crankshaft rotational inertia and flux linkage distribution characteristics, the controller establishes the control matrix through a standardized automatic parameter alignment procedure. Under the quasi-static condition where the stator current vector angle is locked at 0 degrees, the controller uses a high-frequency carrier injection method to measure the stator impedance characteristics, calculates the direct-axis inductance and quadrature-axis inductance parameters, and performs a speed residual closed-loop search algorithm at a 5Hz operating frequency, stepwise adjusting the phase correction angle. To find the speed harmonic residual The physical alignment point where the modulus reaches the local minimum, where, For phase correction angle, For the speed harmonic residual, in this stage, the controller calculates the mapping gain using DC bus voltage data sampled at a frequency of 20kHz. The sensitivity coefficient, where, To map the gain, the ratio of DC bus voltage ripple to transient load torque is locked by linear extrapolation at two characteristic values: no-load point and rated load point.

[0057] To address the nonlinear boundary of the stator core entering magnetic saturation, the controller initiates a controlled current ramp scan procedure, increasing the stator current amplitude from zero to the rated peak in 0.5A increments, while continuously monitoring the decay curve of the real-time quadrature-axis inductance. The real-time quadrature-axis inductance value is used. When the second-order change of the real-time quadrature-axis inductance value with the increase of current crosses the preset saturation sensitivity threshold, the controller automatically locks the current amplitude as the core linear magnetization current threshold and generates an inductance magnetization characteristic mapping table based on the slope characteristics of the drop curve. This engineering procedure based on the identification of underlying physical properties eliminates the prediction error caused by the manufacturing deviation of motor parameters, so that the generated quadrature-axis current compensation command can be dynamically matched with the torque pulsation characteristics of a specific mechanical structure. As the calibration program ends, the stator current trajectory driven by the power conversion unit maintains the spatial vector roundness in the full load range, suppresses the frequency fluctuation in a single revolution cycle, and thus keeps the motor in a silent operation state.

[0058] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for controlling an electric motor for driving a compressor, characterized in that, Includes the following steps: Step S1: The signal acquisition unit acquires the stator current signal of the motor and the DC bus voltage signal of the power conversion unit. Step S2: Calculate the DC bus voltage pulsation within a single compressor cycle based on the DC bus voltage signal. The DC bus voltage pulsation includes the amplitude and frequency fluctuation characteristics of the DC bus voltage signal within a single cycle. Step S3: Based on the DC bus voltage ripple, determine the initial value of the quadrature axis current compensation command through a preset voltage-to-torque mapping function. The initial value of the quadrature axis current compensation command is used to generate an electromagnetic torque component that is opposite in direction to the transient load torque of the compressor. Step S4: Real-time detection of the amplitude of the stator current signal and determination of whether the amplitude exceeds the preset core linear magnetization current threshold. The core linear magnetization current threshold represents the current critical point at which the stator core enters the magnetic saturation state. Step S5: If the amplitude exceeds the core linear magnetization current threshold, the cross-axis inductance drop ratio is extracted from the preset inductance magnetization characteristic mapping table based on the amplitude of the stator current signal. Step S6: The cross-axis inductance drop ratio is used as a gain factor to apply to the initial value of the cross-axis current compensation command to generate a corrected cross-axis current compensation command, thereby making up for the electromagnetic torque compensation gap caused by the transient saturation of the stator core. Step S7: The corrected quadrature-axis current compensation command is injected as the feedforward compensation amount into the command terminal of the current regulation loop to adjust the output duty cycle of the power conversion unit.

2. The electric motor control method for compressor drive according to claim 1, characterized in that, After step S6 and before step S7, the following steps are also included: Step S201, obtaining the rotor electrical angle to identify the electrical angle phase interval where the peak load torque of the compressor is located; Step S202, performing high-pass filtering on the estimated speed of the motor to extract the speed harmonic residual; Step S203, calculating the compensation phase deviation value based on the speed harmonic residual, and using the compensation phase deviation value to perform advance correction on the injection phase of the corrected quadrature axis current compensation command, so that the generated electromagnetic torque is aligned with the mechanical load torque in spatial phase.

3. The method for controlling an electric motor for driving a compressor according to claim 2, characterized in that, After step S6 and before step S7, the following steps are also included: Step S301, detecting the DC offset in the DC bus voltage signal and the hot resistance drift value of the stator winding; Step S302, adjusting the compensation gain of the corrected quadrature axis current compensation command by normalization coefficient according to the DC offset and the hot resistance drift value, so as to maintain the consistency of torque response under different operating conditions.

4. The electric motor control method for compressor drive according to claim 1, characterized in that, During the execution of steps S1 to S7, and when the compressor load torque valley value is identified, the following steps are also included: Step S401, injecting a high-frequency carrier signal into the stator winding within the electrical angle range corresponding to the compressor load torque valley value; Step S402, identifying the real-time resistance value of the stator winding based on the response characteristics of the stator current signal to the high-frequency carrier signal, and using the real-time resistance value as the basis for adjusting the current regulating loop control parameters.

5. The electric motor control method for compressor drive according to claim 1, characterized in that, Step S2 specifically includes: performing bandpass filtering on the DC bus voltage signal to extract the voltage pulsation component corresponding to a single revolution cycle; performing synchronous coordinate transformation on the voltage pulsation component according to the rotor electrical angle to construct a rotating energy feature vector synchronized with the compressor mechanical load pulse frequency.

6. The electric motor control method for compressor drive according to claim 1, characterized in that, The quadrature axis inductance drop ratio η is determined by the following rule: Where η is the sag ratio of the quadrature-axis inductance. This is the preset nominal quadrature-axis inductance value of the motor in the linear region of the magnetic field. The real-time quadrature-axis inductance value is obtained by retrieving the inductor magnetization characteristic mapping table from the amplitude of the stator current signal.

7. The method for controlling an electric motor for driving a compressor according to claim 1, characterized in that, The inductor magnetization characteristic mapping table contains multiple sets of inductor characteristic curves corresponding to different compressor discharge pressures; the method also includes: estimating the real-time pressure ratio based on the condensing temperature and evaporating temperature of the compressor system, and dynamically switching from the inductor magnetization characteristic mapping table to the target characteristic curve that matches the real-time pressure ratio.

8. The method for controlling an electric motor for driving a compressor according to claim 1, characterized in that, The method also includes: when the operating frequency of the motor is below 10Hz, increasing the control bandwidth of the speed regulation loop, and using the corrected quadrature axis current compensation command as a feedforward term to directly apply to the duty cycle generation logic of the voltage space vector modulation, so as to shorten the response delay to load torque pulsation.

9. A method for controlling an electric motor for driving a compressor according to claim 2, characterized in that, Step S203 specifically includes: performing a second-order differential operation on the speed harmonic residual to determine the extreme point of the speed fluctuation, and determining the compensation phase deviation value based on the geometric offset of the extreme point relative to the electrical angle phase interval where the load torque peak is located.

10. A method for controlling an electric motor for driving a compressor according to claim 1, characterized in that, Before executing step S7, the method further includes: limiting the modified quadrature axis current compensation command based on the maximum allowable output current of the power conversion unit and the real-time temperature rise protection threshold of the motor.

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