Servo system current harmonic suppression system and method
By designing current sampling noise identification and third-order current observer in the servo system, and using notchers to process current sampling noise, the problem of insufficient current harmonic suppression is solved, and better current harmonic suppression and control performance are achieved.
Patent Information
- Application Number
- CN202510348794.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-24
- Publication Date
- 2025-07-11
AI Technical Summary
The current harmonics have not been effectively suppressed in the prior art, especially the impact of current sampling noise and sampling filtering on current harmonic suppression, resulting in increased motor loss and decreased control performance.
Design a servo system current harmonic suppression system, including upper computer software, servo drivers and servo motors, use the current sampling noise identification module and third-order current observer to process the current sampling noise through the notch, and conduct real-time observation of current signals and current loop disturbances before filtering to realize current closed-loop control.
Effectively reduce current sampling noise, improve current harmonic suppression effect, improve current loop control bandwidth, and improve motor system performance.
Smart Images
Figure CN120301296A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of servo motor control, and particularly to a servo system current harmonic suppression system and method. Background Art
[0002] Due to advantages such as small volume, high efficiency, and high power density, permanent magnet synchronous motors have been widely studied and applied in high-performance servo drive applications such as electric drive, electric vehicles, numerical control machine tools, and aerospace. However, factors such as machining deviations in the motor structure, non-linearity of the inverter, and current measurement errors can generate significant 5th and 7th phase current harmonics, resulting in increased motor losses and torque fluctuations, deteriorating the control performance of the system, and even shortening the service life of the motor. Therefore, suppressing current harmonics to improve the performance of the motor system is extremely important.
[0003] Currently, there are various control strategies for studying the suppression of current harmonics. Common methods include dead-time effect compensation of the inverter and constructing an ESO. Among them, dead-time effect compensation of the inverter is an effective means of suppressing current harmonics. The compensation voltage is calculated through the dead-time compensation algorithm to further improve the dead-time compensation performance. However, the above-mentioned dead-time effect compensation method based on voltage calculation can only compensate for the 5th and 7th phase current harmonics caused by the dead-time effect, and is not applicable to the suppression of current harmonics caused by factors other than the dead-time (such as magnetic flux). In addition, constructing an ESO on the current loop to observe the disturbance on the current loop is also a common method. The disturbance on the current loop is observed and compensated to suppress current harmonics. However, this method is affected and limited by current sampling noise. When there is a certain fixed high-frequency noise in the current sampling signal, it will instead deteriorate the effect of current harmonic suppression. At the same time, this method does not consider the influence of current sampling filtering, and uses the filtered current feedback as the input of the observer, so the observed disturbance will also have a lag.
[0004] Therefore, there are problems in the prior art of insufficient suppression of current harmonics and failure to consider current sampling noise and current sampling filtering. Summary of the Invention
[0005] The purpose of the present invention is to: in order to solve the problem that the existing current harmonic suppression does not consider current sampling noise and current sampling filtering, a servo system current harmonic suppression system is proposed, including:
[0006] A host computer software, a servo driver, and a servo motor; the host computer software is provided with a current sampling noise identification module, including: a motor speed regulation unit, a current waveform recording unit, a current waveform FFT unit, and a current harmonic suppression unit; the current harmonic suppression unit includes: a notch filter and a third-order current observer;
[0007] The motor speed control unit sends 5 different speed commands to the driver, the current waveform recording unit performs recording and sampling of the current waveform, the current waveform FFT unit performs FFT analysis on the 5 groups of current waveforms obtained by recording and sampling respectively, and the result output unit outputs the results of the 5 groups of FFT analysis, identifying the frequency of the noise signal;
[0008] The motor speed control unit sends 5 different speed commands to the driver, the current waveform recording unit performs recording and sampling of the current waveform, the current waveform FFT unit performs FFT analysis on the 5 groups of current waveforms obtained by recording and sampling respectively, and outputs the results of the 5 groups of FFT analysis, identifying the frequency of the noise signal;
[0009] The frequency of the noise signal identified is used as the notch frequency of the notch filter. The sampled current feedback of the servo driver processes the noise signal through the notch filter, and the processed sampled current feedback is input into the third-order current observer to perform real-time observation of the current signal before filtering and the current loop disturbance, and perform current closed-loop control based on the observed current signal before filtering and the current loop disturbance.
[0010] Further, the 5 different speed commands are 10%, 30%, 50%, 80%, and 100% of the rated speed of the motor respectively.
[0011] Further, it is judged whether the notch filter is turned on according to the proportion of the overlapping frequency bands in the 5 groups of FFT analysis results.
[0012] Further, the transfer function of the notch filter is as follows:
[0013]
[0014] Among them, G(s) represents the transfer function of the notch filter, ω c is the notch frequency of the notch filter, ξ1 and ξ2 respectively represent the parameters used to set the notch width of the notch filter, s is a complex variable, Q represents the quality factor of the notch filter, D p represents the notch depth of the notch filter;
[0015] In the ideal state:
[0016]
[0017] Among them, i q represents the actual q-axis current of the motor, n q represents the current sampling noise signal, T f represents the filtering time constant of the current sampling filtering link.
[0018] Further, the third-order current observer is expressed as:
[0019]
[0020] Obtained:
[0021]
[0022] Among them, the disturbance observation output of the observer is:
[0023]
[0024] Among them, U q represents the q-axis command voltage, f q represents the total disturbance, L s represents the inductance value of the servo motor, s represents the complex variable, T f represents the filtering time constant of the current sampling and filtering link, i qf represents the sampled current feedback at the driver end, K p represents the proportional parameter of the observer, K i represents the integral parameter of the observer, K d represents the differential parameter of the observer, i qfob represents the i observed by the observer qf , f qob represents the f observed by the observer q .
[0025] Furthermore,
[0026]
[0027] K d = 2ω n L s T f - L s ;
[0028] Among them, w n represents the observer bandwidth setting value.
[0029] Furthermore, the current observation value before the filtering link is:
[0030]
[0031] Among them, i qfob2 represents the current observation value before the filtering link;
[0032] Feed i qfob2 and f qob back to the current loop for current closed-loop control, among which,
[0033] PI(i qref - i qfob2 ) - f qob = U q ;
[0034] Among them, PI() represents a PI controller.
[0035] The present invention also proposes a method for suppressing current harmonics in a servo system. The method is implemented based on the above system, and the method includes:
[0036] The motor speed regulation unit sends 5 different speed commands to the driver, the current waveform recording unit performs recording and sampling of the current waveform, the current waveform FFT unit performs FFT analysis on the 5 groups of current waveforms obtained by the recording and sampling respectively, outputs the results of the 5 groups of FFT analysis, and identifies the frequency of the noise signal;
[0037] The identified noise signal frequency is used as the notch frequency of the notch filter. The sampled current feedback of the servo driver processes the noise signal through the notch filter, and the processed sampled current feedback is input into the third-order current observer to perform real-time observation of the current signal before filtering and the disturbance of the current loop, and perform current closed-loop control based on the observed current signal before filtering and the disturbance of the current loop.
[0038] The beneficial effects brought by the technical solution provided by the present invention are:
[0039] In view of the current sampling link, the present invention designs a current observer and a notch filter, finds the common frequency band with higher harmonic components in the FFT analysis results of the current at different fundamental frequencies as the notch frequency, and effectively reduces the current sampling noise through the notch filter, improving the overall current harmonic suppression effect. The current observer performs real-time observation of the current signal before filtering and the disturbance of the current loop, and performs current closed-loop control based on the observed current signal before filtering and the disturbance of the current loop, eliminating the phase lag effect brought by the current sampling and filtering link, further improving the control bandwidth of the current loop, and achieving a better current harmonic suppression effect. Description of the Drawings
[0040] Figure 1 is a block diagram of a current harmonic suppression system for a servo system according to an embodiment of the present invention;
[0041] Figure 2 is a Bode diagram of the disturbance observation output versus the noise input in the simulation of an embodiment of the present invention;
[0042] Figure 3 is the time-domain result of the disturbance observation output versus the noise input in an embodiment of the present invention. The current harmonic suppression unit introduces the current harmonic suppression unit at the 1s moment, adds a 2000Hz current sampling noise at the 3s moment, and turns on the notch filter in the current harmonic suppression unit at the 5s moment. Detailed Embodiments
[0043] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described below in conjunction with the accompanying drawings.
[0044] The block diagram of a current harmonic suppression system for a servo system according to an embodiment of the present invention is as follows Figure 1 and specifically includes: a host computer software, a servo driver, and a servo motor. The host computer software on the PC communicates with the servo driver through the RS-485 method or the USB method. The servo driver is used to receive the speed command sent by the host computer software to control the rotation of the servo motor. The host computer software is provided with a current sampling noise identification module, including: a motor speed regulation unit, a current waveform recording unit, a current waveform FFT unit, and a current harmonic suppression unit; the current harmonic suppression unit includes: a notch filter and a third-order current observer.
[0045] According to the relationship between the fundamental frequency f0 of the permanent magnet synchronous motor, the motor speed n, and the number of pole pairs p of the motor:
[0046]
[0047] The current harmonics in the motor are usually integer multiples of the motor fundamental frequency. Specifically, the frequency of the current harmonics can be expressed as:
[0048] f h = h × f0,
[0049] where f h is the frequency of the hth harmonic, and h is the harmonic order.
[0050] The transfer function of the notch filter is as follows:
[0051]
[0052] where G(s) represents the transfer function of the notch filter, ω c is the notch frequency of the notch filter, ξ1 and ξ2 respectively represent the parameters used to set the notch width of the notch filter, s is a complex variable, Q represents the quality factor of the notch filter. The larger the quality factor of the notch filter, the better the notch characteristics, but the stability will decrease accordingly. D p represents the notch depth of the notch filter.
[0053] Since the current sampling noise is generated by the current sampling circuit and is usually introduced by the hardware noise of the sampling circuit, it has nothing to do with the motor fundamental frequency. No matter how large the motor fundamental frequency is, the frequency of the current sampling noise is basically unchanged. Therefore, the present invention utilizes the difference characteristics of the relationship between the current harmonics and the current sampling noise and the motor fundamental frequency. By performing FFT analysis on the currents under several different motor fundamental frequencies, the common frequency band with higher harmonic components in the FFT analysis results of the currents under different fundamental frequencies is found, so as to screen out the frequency of the current sampling noise.
[0054] The motor speed regulation unit sends 5 different speed commands to the driver, which are 10%, 30%, 50%, 80%, and 100% of the rated speed of the motor, so that the motor operates at 5 different base frequencies. The current waveform recording unit performs recording and sampling of the current waveform at different base frequencies when the motor is working. The current waveform FFT unit performs FFT analysis on the 5 groups of current waveforms obtained by the recording and sampling respectively, outputs the results of the 5 groups of FFT analysis, and identifies the frequency of the noise signal.
[0055] The identified noise signal frequency is used as the notch frequency of the notch filter. The sampled current feedback of the servo driver processes the noise signal through the notch filter, and the processed sampled current feedback is input into the third-order current observer for real-time observation of the current signal before filtering and the current loop disturbance, and current closed-loop control is performed based on the observed current signal before filtering and the current loop disturbance.
[0056] The main function of the notch filter is to process the noise signal in the current sampling circuit. The frequency band of the noise signal can be known through the FFT result output by the current sampling noise identification module. The identified noise signal frequency is set as the notch frequency of the notch filter, and then the noise part in the current sampling signal can be eliminated, thus avoiding the deterioration of the observation effect of the observer caused by the noise part.
[0057] After correctly setting the notch frequency of the notch filter, it can be approximately obtained that:
[0058]
[0059] where, i q represents the actual q-axis current of the motor, n q represents the current sampling noise signal, and T f represents the filtering time constant of the current sampling filtering link.
[0060] For the noise existing in the current sampling circuit, a third-order current observer is designed in the current signal filtering link to perform real-time observation of the current signal before filtering and the current loop disturbance, so as to improve the suppression effect on current harmonics. The current harmonic suppression unit of the embodiment of the present invention refers to Figure 1 , which is expressed as:
[0061]
[0062] to obtain:
[0063]
[0064] where, the disturbance observation output of the observer is:
[0065]
[0066] where, Uq represents the q-axis command voltage, f q represents the total disturbance, L s represents the inductance value of the servo motor, s represents the complex variable, T f represents the filtering time constant of the current sampling filter section, i qf represents the sampled current feedback at the driver end, K p represents the proportional parameter of the observer, K i represents the integral parameter of the observer, K d represents the differential parameter of the observer, i qfob represents the i observed by the observer qf , f qob represents the f observed by the observer q .
[0067] The current observation value before the filtering section is:
[0068]
[0069] where, i qfob2 represents the current observation value before the filtering section;
[0070] Feed i qfob2 and f qob back to the current loop for current closed-loop control. i qfob2 is the current observation value before the filtering section, which can eliminate the phase lag effect brought by the current sampling filter section, so that the control bandwidth of the current loop can be further improved, and a better current harmonic suppression effect can be achieved.
[0071] PI(i qref -i qfob2 )-f qob = U q ,
[0072] where, PI() represents the PI controller, i qref represents the q-axis command current.
[0073] The transfer function of the disturbance observation and the actual total disturbance input can be obtained as:
[0074]
[0075] The expressions of the proportional parameter, integral parameter, and differential parameter of the observer are:
[0076]
[0077] K d = 2ω n L s T f -L s,
[0078] Among them, w n represents the set value of the observer bandwidth.
[0079] It can be obtained that:
[0080]
[0081] Finally, it can be obtained that the form between the observed disturbance and the actual total disturbance is a third-order Butterworth filter. At this time, the disturbance input can be observed better. Then, the observed disturbance is compensated into the loop, and the compensation of the current loop disturbance input can be realized, so as to achieve a better current harmonic suppression effect.
[0082] The present invention also proposes a method for suppressing current harmonics in a servo system. The method is implemented based on the above system, and the method includes:
[0083] The motor speed control unit sends 5 different speed commands to the driver. The current waveform recording unit performs recording and sampling of the current waveform. The current waveform FFT unit performs FFT analysis on the 5 groups of current waveforms obtained by recording and sampling respectively, outputs the results of 5 groups of FFT analysis, and identifies the noise signal frequency;
[0084] The identified noise signal frequency is used as the notch frequency of the notch filter. The sampled current feedback of the servo driver processes the noise signal through the notch filter, and the processed sampled current feedback is input into the third-order current observer to perform real-time observation of the pre-filtering current signal and the current loop disturbance, and perform current closed-loop control based on the observed pre-filtering current signal and the current loop disturbance.
[0085] Use Matlab / Simulink simulation software to build a model for analysis. In the simulation, the current sampling noise is set to 2000 Hz, and the notch frequency of the notch filter is also set to 2000 Hz. First, the Bode plot of the disturbance observation output with respect to the noise input can be obtained. The Bode plot of the disturbance observation output with respect to the noise input simulated in the embodiment of the present invention is as Figure 2 shown. It can be seen that after adding the notch filter, the amplitude response of the disturbance observation output with respect to the noise input at 2000 Hz has been greatly attenuated, so the deterioration of the sampling noise on the disturbance observation output of the current observer is greatly reduced. Then, perform simulation analysis in the time domain. The current harmonic suppression unit is introduced at 1 s, the 2000 Hz current sampling noise is increased at 3 s, and the notch filter is turned on in the current harmonic suppression unit at 5 s. The time domain results are as Figure 3As shown, it can be seen from the time-domain results that without introducing current sampling noise, the current harmonic suppression unit can achieve good current harmonic suppression effects. However, when current sampling noise is introduced at the 3s mark, the suppression performance of the current harmonic suppression unit deteriorates significantly, which is consistent with the previous theoretical analysis. Current sampling noise can lead to the deterioration of the observed output of the current harmonic suppression unit, thereby affecting the harmonic suppression effect. After the notch filter is turned on in the current harmonic suppression unit at the 5s mark, it can be seen that the deterioration caused by current sampling noise is effectively reduced, thus improving the overall current harmonic suppression effect.
[0086] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.
Claims
1. A current harmonic suppression system for a servo system, characterized in that, Including: Host computer software, servo driver, and servo motor; the host computer software is provided with a current sampling noise identification module, including: a motor speed regulation unit, a current waveform recording unit, a current waveform FFT unit, and a current harmonic suppression unit; the current harmonic suppression unit includes: a notch filter and a third-order current observer; The motor speed regulation unit sends 5 different speed commands to the driver, the current waveform recording unit performs recording and sampling of the current waveform, the current waveform FFT unit performs FFT analysis on the 5 groups of recorded current waveforms respectively, outputs the results of 5 groups of FFT analysis, and identifies the noise signal frequency; The identified noise signal frequency is used as the notch frequency of the notch filter. The sampled current feedback of the servo driver processes the noise signal through the notch filter, and the processed sampled current feedback is input into the third-order current observer to perform real-time observation of the current signal before filtering and the current loop disturbance, and perform current closed-loop control based on the observed current signal before filtering and the current loop disturbance.
2. The current harmonic suppression system of a servo system according to claim 1, wherein The 5 different speed commands are respectively 10%, 30%, 50%, 80%, and 100% of the rated speed of the motor.
3. A current harmonic suppression system for a servo system according to claim 1, wherein According to the proportion of the overlapping frequency bands in the 5 groups of FFT analysis results, it is judged whether the notch filter is turned on.
4. A current harmonic suppression system of a servo system according to claim 1, characterized in that The transfer function of the notch filter is as follows: where, G(s) represents the notch filter transfer function, ω c is the notch frequency of the notch filter, ξ1 and ξ2 respectively represent the parameters used to set the notch width of the notch filter, s is the complex variable, Q represents the quality factor of the notch filter, D p represents the notch depth of the notch filter; Under ideal conditions: Among them, i q represents the actual q-axis current of the motor, n q represents the current sampling noise signal, T f represents the filtering time constant of the current sampling filtering section.
5. A current harmonic suppression system for a servo system according to claim 1, characterized in that, The third-order current observer is expressed as: Obtained: Among them, the disturbance observation output of the observer is: Among them, U q represents the q-axis command voltage, f q represents the total disturbance, L s represents the inductance value of the servo motor, s represents the complex variable, T f represents the filtering time constant of the current sampling filter section, i qf represents the sampled current feedback at the driver end, K p represents the proportional parameter of the observer, K i represents the integral parameter of the observer, K d represents the differential parameter of the observer, i qfob represents the i observed by the observer qf , f qob represents the f observed by the observer q .
6. A servo system current harmonic suppression system according to claim 5, characterized in that Among them, w n represents the set value of the observer bandwidth.
7. A current harmonic suppression system for a servo system according to claim 5, characterized in that, The current observation value before the filtering link is: Among them, i qfob2 represents the current observation value before the filtering link; Feed i qfob2 and f qob back to the current loop for current closed-loop control, where PI(i qref -i qfob2 )-f qob =U q ; Among them, PI() represents a PI controller.
8. A method for suppressing current harmonics in a servo system, characterized in that, The method is implemented based on the system according to any one of claims 1-7, and the method includes: The motor speed regulation unit sends 5 different speed commands to the driver, the current waveform recording unit performs recording and sampling of the current waveform, the current waveform FFT unit performs FFT analysis on the 5 groups of recorded current waveforms respectively, outputs the results of 5 groups of FFT analysis, and identifies the noise signal frequency; The identified noise signal frequency is used as the notch frequency of the notch filter. The sampled current feedback of the servo driver processes the noise signal through the notch filter, and the processed sampled current feedback is input into the third-order current observer to perform real-time observation of the current signal before filtering and the current loop disturbance, and perform current closed-loop control based on the observed current signal before filtering and the current loop disturbance.