CN115694301A - Beat frequency suppression method for permanent magnet synchronous motor traction system of motor train unit - Google Patents
Beat frequency suppression method for permanent magnet synchronous motor traction system of motor train unit Download PDFInfo
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Abstract
The invention provides a beat frequency suppression method for a permanent magnet synchronous motor traction system of a motor train unit. The method comprises the following steps: obtaining d-axis and q-axis currents under a synchronous rotating coordinate system according to the three-phase currents of the permanent magnet motor collected by the sensor; generating reference voltage regulating values of d and q axes through a PI controller according to the given current of the d and q axes and the current error of the d and q axes; restraining the double-frequency fluctuation of the power grid existing in the d-axis current and the q-axis current by using a preset quasi-resonant controller, and superposing the output of the PI controller and the output of the quasi-resonant controller to obtain final d-axis reference voltage and q-axis reference voltage; and finally realizing beat frequency suppression of the permanent magnet synchronous motor traction system of the motor train unit through a PWM (pulse-Width modulation) link. Compared with the prior art, the invention inhibits the beat frequency current through the proposed control algorithm on the basis of removing the LC resonance circuit, reduces the torque ripple and improves the system stability.
Description
Technical Field
The invention belongs to the field of motor train units, and particularly relates to a beat frequency suppression method for a permanent magnet synchronous motor traction system of a motor train unit.
Background
Because the traction transmission system of the motor train unit adopts a topological structure of a single-phase rectifier, the input power can be changed along with the frequency of a double-power grid, so that the voltage frequency of a double-power grid side of the direct-current bus voltage fluctuates. The pulsating intermediate direct current bus voltage will be further coupled with the motor side inverter, resulting in an obvious beat frequency phenomenon of the traction motor, and the motor torque and current will pulsate. The beat frequency problem not only reduces the performance of the traction converter, but also seriously influences the safety, reliability and high efficiency of the running of the motor train unit.
At present, induction motor traction systems are adopted in high-speed trains running in China, and permanent magnet motors have the advantages of high efficiency, low energy consumption, light weight, good starting characteristics, low noise, good maintainability and the like, so that the development of high-speed motor train units of the high-efficiency and energy-saving permanent magnet motor traction systems becomes a development trend along with the continuous rise of high-speed rail capacity and the continuous increase of the use amount of the high-speed trains.
Aiming at the beat frequency phenomenon of a traction system of a motor train unit, the prior art mainly has a hardware solution and a software solution. The hardware solution mainly adopts a mode of connecting an LC resonance circuit in parallel in an intermediate direct-current link or increasing the capacitance of a direct-current side bus to reduce voltage fluctuation, the method is simple and effective, but the LC resonance circuit is large in size, increases cost and is not beneficial to light weight of a vehicle. The software solution is to compensate the output voltage harmonic wave caused by the direct current voltage fluctuation through a control algorithm on the basis of not increasing any hardware configuration, and the solution can reduce the cost, has great practical value and belongs to the research hotspot.
The existing beat frequency suppression algorithm is multi-purpose for an induction motor traction system, and a patent document 'a beat frequency suppression system and method for an electric transmission system of a motor train unit' (CN 112311292A) extracts a bus voltage signal double frequency fluctuation component, frequency and phase compensation is carried out through a beat frequency suppression controller to realize beat frequency suppression, and the beat frequency suppression method essentially belongs to an open-loop algorithm and depends on the extracted bus voltage fluctuation component; the patent document 'motor beat frequency suppression method and system, electric transmission control system and storage medium' (CN 112751519B) compensates based on static compensation coefficients and dynamic compensation coefficients for given torque or given slip corresponding to the given torque, but the realization is more complex, the beat frequency suppression method facing to the permanent magnet synchronous motor traction system of the motor train unit can meet the requirement of the future high-speed motor train unit.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, and provides a beat frequency suppression method for a permanent magnet synchronous motor traction system of a motor train unit, which can effectively reduce low-frequency beat frequency current and torque fluctuation under asynchronous modulation, synchronous modulation and square wave control.
In order to achieve the purpose, the invention adopts the following technical scheme:
firstly, coordinate transformation is carried out on three-phase current of a permanent magnet motor collected by a current sensor to obtain d-axis current and q-axis current under a synchronous rotating coordinate system; generating reference voltage regulating quantities of the d axis and the q axis by a PI (proportional integral) controller according to the given current quantities of the d axis and the q axis and the current error quantities of the d axis and the q axis; the method comprises the steps that a preset quasi-resonant controller is used for restraining grid double frequency fluctuation existing in d-axis and q-axis currents, and the output of a PI controller and the output of the quasi-resonant controller are superposed to obtain final d-axis and q-axis reference voltages; and finally realizing beat frequency suppression of the permanent magnet synchronous motor traction system of the motor train unit through a PWM link.
The invention comprises the following steps:
step 1: and converting the three-phase current of the motor collected by the current sensor into a rotating coordinate system.
Due to the inherent problem of the single-phase rectifier, the voltage on the direct current side has double frequency fluctuation, and w is generated in the motor current e -2w g Low frequency current ripple component of and w e +2w g Neglecting high frequency harmonic wave, the three-phase current of the motor can be expressed as:
wherein i a ，i b ，i c Is three-phase current of motor, and t is time w e As angular velocity of the motor, w g To the grid frequency, I s And I h Respectively a fundamental current amplitude and a ripple current amplitude,
the phases of the low-frequency fluctuation component and the high-frequency fluctuation component;
the constant amplitude transformation is used as follows:
where θ is an electrical angle.
The d-axis and q-axis currents in the rotating coordinate system can be obtained by combining the formulas (1) and (2):
wherein i d ，i q Is d, q axis current, i d0 ，i q0 As can be seen from the d-axis and q-axis fundamental wave currents, the d-axis and q-axis currents have double frequency components in the rotating coordinate system.
Step 2: and performing PI control on the basis of the d and q current set values and the d and q axis currents after low-pass filtering processing to output d and q axis voltage regulating values.
Firstly, designing a low-pass filter to filter i d ，i q Double frequency components and other high frequency components. The first order low pass filter transfer function is:
wherein, w f ＝2πf c ，f c S is the complex variable for the cut-off frequency of the low-pass filter.
And performing proportional integral control on the filtered d-axis and q-axis currents to obtain d-axis and q-axis voltage regulating values, and calculating as follows:
wherein k is p ，k i In order to be the PI-controller coefficients,
given for d, q-axis currents, i dLPF ，i qLPF Is d, q axis current after passing through a low pass filter, u dPI ，u qPI Is the output of the PI controller. By adjusting the coefficient of the PI controller, good tracking of the fundamental frequency current can be realized.
And step 3: aiming at the frequency doubling component of the d-axis current and the q-axis current, a quasi-resonance controller is designed for suppressing beat frequency current.
The resonant controller being capable of operating at a single frequency w n High gain is generated to realize unsteady state error tracking of alternating current signals, other frequency signals are obviously attenuated, the frequency band of the controller is too narrow, and due to the fact that harmonic waves exist in a traction power grid, the anti-interference performance of a control system is reduced, so that the quasi-resonance controller is adopted to improve the stability of the systemAnd (4) sex. Meanwhile, in order to compensate the phase angle lag existing in the control system, a quasi-resonant controller with delay compensation is adopted, and the transfer function of the quasi-resonant controller is as follows:
wherein, w n Is the resonant frequency, w c Quasi-resonant controller bandwidth, θ n Is the lagging phase angle present in the control system.
In order to restrain the frequency doubling component of d-axis and q-axis currents, a resonant frequency of 2w is adopted g The quasi-resonant controller of (2), calculated as follows:
wherein u is dQRSC ，u qQRSC Output of the quasi-resonant controller, k r For quasi-resonant controller coefficients, by adjusting k r Suppression of the beat frequency current can be achieved.
In addition, when the resonance controller is digitally implemented, resonance point shift exists, a transfer function of the formula (6) is discretized by adopting double-linear transformation with predistortion, and the discretization method specifically comprises the following steps:
wherein, T s For discrete step size, z is a discrete system complex variable, and the discrete quasi-resonant controller transfer function can be obtained according to equations (6) and (8) as follows:
wherein, a n1 ，a n2 ，b n0 ，b n1 ，b n2 Is a coefficient, specifically:
and 4, step 4: and superposing the output of the PI controller and the output of the quasi-resonant controller to obtain the final d-axis and q-axis reference voltages.
The tracking of fundamental wave current is realized through a PI controller, the suppression of beat frequency current is realized through a quasi-resonance controller, the output phases of the two are superposed to obtain final reference voltage, and the calculation is as follows:
wherein u is d ，u q Is the final reference voltage.
And 5: and finally realizing beat frequency suppression of the permanent magnet synchronous motor traction system of the motor train unit through a PWM link.
According to the generated reference voltage and the collected direct-current side voltage, the modulation ratio and the angle are calculated as follows:
wherein u is dc Is a DC side bus voltage, k v And theta v Modulation ratio and angle, respectively.
Asynchronous modulation, synchronous modulation and square wave modulation are achieved according to the modulation ratio, the angle and the frequency, PWM signals are generated, the on-off of a switch tube is controlled, and finally beat frequency suppression of a permanent magnet synchronous motor traction system of the motor train unit is achieved.
Has the beneficial effects that:
the invention discloses a permanent magnet synchronous motor traction system for a motor train unit, which aims at minimizing the output current pulse component and obtaining the required compensation voltage through closed-loop control of a frequency doubling quasi-resonant controller, can effectively inhibit beat current and pulse torque, is simple to realize, is convenient to combine with other control strategies, and can meet the requirements of future high-speed motor train units.
Drawings
Fig. 1 is a control block diagram of a beat suppression method according to the present invention.
Fig. 2 is a flowchart illustrating the operation of the beat suppression method according to the present invention.
FIG. 3 is a bode plot of a continuous quasi-resonant controller and a discrete quasi-resonant controller at a resonant frequency of 100 Hz.
FIG. 4 is a plot of motor current, torque, and line voltage waveforms without beat suppression algorithm for asynchronous modulation.
FIG. 5 is a plot of motor current, torque, and line voltage waveforms using the beat suppression algorithm of the present application for asynchronous modulation.
FIG. 6 is a plot of motor current, torque, and line voltage waveforms for the no beat suppression algorithm with synchronous modulation.
FIG. 7 is a plot of motor current, torque, and line voltage waveforms using the beat suppression algorithm of the present application for synchronous modulation.
FIG. 8 is a plot of motor current, torque, and line voltage waveforms without beat suppression algorithm for square wave modulation.
FIG. 9 is a plot of motor current, torque, and line voltage waveforms using the beat suppression algorithm of the present application for a square wave modulation.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The beat frequency suppression algorithm control block diagram is shown in an attached drawing 1, the implementation flow of the beat frequency suppression algorithm control block diagram is shown in an attached drawing 2, firstly, coordinate transformation is carried out on three-phase currents of a permanent magnet motor, which are collected by a current sensor, so that d-axis currents and q-axis currents under a synchronous rotation coordinate system are obtained; generating reference voltage regulating quantities of the d axis and the q axis by a PI (proportional integral) controller according to the given current quantities of the d axis and the q axis and the current error quantities of the d axis and the q axis; the method comprises the steps that a preset quasi-resonant controller is used for restraining grid double frequency fluctuation existing in d-axis and q-axis currents, and the output of a PI controller and the output of the quasi-resonant controller are superposed to obtain final d-axis and q-axis reference voltages; and finally realizing beat frequency suppression of the permanent magnet synchronous motor traction system of the motor train unit through a PWM (pulse-Width modulation) link.
The specific implementation mode of the invention comprises the following steps:
step 1: and transforming the three-phase current of the motor acquired by the current sensor into a rotating coordinate system.
Due to the inherent problem of the single-phase rectifier, the voltage on the direct current side has double frequency fluctuation, and w is generated in the motor current e -2w g Low frequency current ripple component of and w e +2w g Neglecting high frequency harmonic wave, the three-phase current of the motor can be expressed as:
wherein i a ，i b ，i c Is three-phase current of motor, t is time, w e As angular velocity of the motor, w g To the grid frequency, I s And I h Respectively a fundamental current amplitude and a ripple current amplitude,
the phases of the low-frequency fluctuation component and the high-frequency fluctuation component;
the use of the constant amplitude transform is as follows:
where θ is an electrical angle.
The d-axis and q-axis currents in the rotating coordinate system can be obtained by combining the formulas (1) and (2):
wherein i d ，i q Is d, q axis current, i d0 ，i q0 As can be seen from the d-axis and q-axis fundamental wave currents, the d-axis and q-axis currents have double frequency components in the rotating coordinate system.
And 2, step: and performing PI control on the basis of the d-axis and q-axis current set values and the d-axis and q-axis currents after low-pass filtering to output d-axis and q-axis voltage regulating values.
Firstly, a low-pass filter is designed to filter i d ，i q Double frequency components and other high frequency components. The first order low pass filter transfer function is:
wherein, w f ＝2πf c ，f c S is the complex variable for the cut-off frequency of the low-pass filter.
And performing proportional integral control on the filtered d-axis and q-axis currents to obtain d-axis and q-axis voltage regulating values, and calculating as follows:
wherein k is p ，k i In order to be the PI-controller coefficients,
given for d, q-axis currents, i dLPF ，i qLPF Is d, q axis current after passing through a low pass filter, u dPI ，u qPI Is the output of the PI controller. By adjusting the coefficient of the PI controller, good tracking of the fundamental frequency current can be realized.
And 3, step 3: aiming at the frequency doubling component of the d-axis current and the q-axis current, a quasi-resonance controller is designed for suppressing beat frequency current.
The resonant controller being capable of operating at a single frequency w n High gain is generated to realize unsteady state error tracking of alternating current signals, other frequency signals are obviously attenuated, the frequency band of the controller is too narrow, and due to the fact that harmonic waves exist in a traction power grid, the anti-interference performance of a control system is reduced, so that the stability of the system is improved by adopting a quasi-resonance controller. Meanwhile, in order to compensate the phase angle lag existing in the control system, a quasi-resonant controller with delay compensation is adopted, and the transfer function of the quasi-resonant controller is as follows:
wherein, w n Is the resonant frequency, w c Quasi-resonant controller bandwidth, θ n Is the lagging phase angle present in the control system.
In order to restrain the frequency doubling component of d-axis and q-axis currents, a resonant frequency of 2w is adopted g The quasi-resonant controller of (2), calculated as follows:
wherein u is dQRSC ，u qQRSC Output of the quasi-resonant controller, k r For quasi-resonant controller coefficients, by adjusting k r Suppression of the beat current can be achieved.
In addition, the resonance controller has resonance point shift during digital implementation, and the transfer function of the formula (6) is discretized by adopting bilinear transformation with predistortion, wherein the discretization method specifically comprises the following steps:
wherein, T s For discrete step size, z is a discrete system complex variable, and according to equations (6) and (8), a discrete quasi-resonant controller transfer function can be obtained as follows:
wherein, a n1 ，a n2 ，b n0 ，b n1 ，b n2 The coefficients are specifically:
FIG. 3 is a bode plot of the resonant frequency of the continuous quasi-resonant controller and the discrete quasi-resonant controller at 100Hz, the bode plots of the continuous quasi-resonant controller and the discrete quasi-resonant controller are basically consistent, and only the bode plots are different at the point close to the Nyquist frequency, so that the accuracy of the discrete method adopted by the invention is proved.
And 4, step 4: and superposing the output of the PI controller and the output of the quasi-resonant controller to obtain the final d-axis and q-axis reference voltages.
The tracking of fundamental wave current is realized through a PI controller, the suppression of beat frequency current is realized through a quasi-resonance controller, the output phases of the two are superposed to obtain final reference voltage, and the calculation is as follows:
wherein u is d ，u q Is the final reference voltage.
And 5: and finally realizing beat frequency suppression of the permanent magnet synchronous motor traction system of the motor train unit through a PWM link.
According to the generated reference voltage and the collected direct-current side voltage, the modulation ratio and the angle are calculated as follows:
wherein u is dc Is a DC side bus voltage, k v And theta v Are respectively in toneThe aspect ratio and the angle.
Asynchronous modulation, synchronous modulation and square wave modulation are achieved according to the modulation ratio, the angle and the frequency, PWM signals are generated, the on-off of a switch tube is controlled, and finally beat frequency suppression of the permanent magnet synchronous motor traction system of the motor train unit is achieved.
As an embodiment of the application, a beat frequency suppression effect of current and torque under the same traction power supply network voltage and load working condition under three conditions of asynchronous modulation, synchronous modulation and square wave modulation by using a beat frequency suppression algorithm without a beat frequency suppression algorithm and by using the beat frequency suppression algorithm is verified. The motor a-phase current, output torque, and line voltage results are shown in fig. 4 without beat frequency suppression algorithm under asynchronous modulation, fig. 5 with beat frequency suppression algorithm of the present application under asynchronous modulation, fig. 6 with beat frequency suppression algorithm under synchronous modulation, fig. 7 with beat frequency suppression algorithm of the present application under synchronous modulation, fig. 8 with beat frequency suppression algorithm under square wave modulation, and fig. 9 with beat frequency suppression algorithm of the present application under square wave modulation. The comparison results of the fundamental wave amplitude, the beat frequency current amplitude, the average torque and the double-frequency torque of the motor phase current are shown in the following table 1, and it can be seen that the method has a good beat frequency suppression effect.
TABLE 1 fundamental amplitude, beat frequency current amplitude, average torque, and double frequency torque of motor phase current under different working conditions
Therefore, the beat frequency suppression method applied to the traction system of the permanent magnet synchronous motor of the motor train unit, which is provided by the application example of the application example, introduces the frequency doubling quasi-resonant controller into a permanent magnet synchronous motor current closed-loop control strategy based on a rotating coordinate system, so that good dynamic response can be obtained, low-frequency harmonics in three-phase current of the motor under the condition that secondary ripples exist in direct-current voltage of a single-phase rectifier can be effectively eliminated, torque double-frequency ripple is suppressed, and the stability of the system is improved.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (7)
1. A beat frequency suppression method for a permanent magnet synchronous motor traction system of a motor train unit is characterized by comprising the following steps:
step 1: converting the three-phase current of the motor collected by the current sensor into a rotating coordinate system;
step 2: performing PI control on the basis of d-axis and q-axis current set values and d-axis and q-axis currents after low-pass filtering processing to output d-axis and q-axis voltage regulating values;
and step 3: aiming at the frequency doubling components of the d-axis current and the q-axis current, a quasi-resonance controller is designed for inhibiting beat frequency current;
and 4, step 4: superposing the output of the PI controller and the output of the quasi-resonant controller to obtain final d-axis and q-axis reference voltages;
and 5: and finally realizing beat frequency suppression of the permanent magnet synchronous motor traction system of the motor train unit through a PWM link.
2. The beat frequency suppressing method as claimed in claim 1, wherein in said step 1: neglecting high frequency harmonic wave, omega exists in three-phase current of motor e -2ω g Low frequency current ripple component of and ω e +2ω g Is expressed as:
wherein i a ，i b ，i c Is three-phase current of motor, and t is time omega e Is electricityAngular velocity of machine, omega g To the grid frequency, I s And I h Respectively a fundamental current amplitude and a ripple current amplitude,
the phases of the low-frequency fluctuation component and the high-frequency fluctuation component;
the use of the constant amplitude transform is as follows:
wherein θ is an electrical angle;
combining the formulas (1) and (2), the d-axis current and the q-axis current under the rotating coordinate system are obtained as follows:
wherein i d ，i q Is d, q axis current, i d0 ，i q0 Is d and q axis fundamental wave current;
under the rotating coordinate system, the d-axis current and the q-axis current have double frequency components.
3. The beat frequency suppression method according to claim 2, wherein in said step 2, the first order low pass filter transfer function is:
wherein, ω is f ＝2πf c ，f c Is the cut-off frequency of the low-pass filter, s is a complex variable;
and performing proportional integral control on the filtered d-axis and q-axis currents to obtain d-axis and q-axis voltage regulating values, and calculating as follows:
wherein k is p ，k i In order to be a PI-controller coefficient,
given for d, q-axis currents, i drpF ，i qLPF Is d, q axis current after passing through a low pass filter, u dPI ，u qPI Is the output of the PI controller.
4. A beat frequency suppression method according to claim 3, wherein in step 3, the quasi-resonant controller with delay compensation is used to suppress the second harmonic component, and the transfer function is:
wherein, ω is n To the resonant frequency, ω c Quasi-resonant controller bandwidth, θ n Is the lag phase angle present in the control system;
in order to suppress the frequency doubling component of the d-and q-axis currents, a resonant frequency of 2 omega is adopted g The quasi-resonant controller of (2), calculated as follows:
wherein u is dQRSC ，u qQRSC Output of the quasi-resonant controller, k r For quasi-resonant controller coefficients, by adjusting k r Suppression of the beat current can be achieved.
5. The beat frequency suppressing method according to claim 4, wherein in step 3, the transfer function of the formula (6) is discretized by a bilinear transformation with predistortion, and the discretization method is specifically:
wherein, T s For discrete step size, z is a discrete system complex variable according to equations (6) and (8), and the discrete quasi-resonant controller transfer function is obtained as follows:
wherein, a n1 ，a n2 ，b n0 ，b n1 ，b n2 The coefficients are specifically:
6. the beat frequency suppression method according to claim 5, wherein in step 4, the PI controller of step 2 is used to track the fundamental current, the quasi-resonant controller of step 3 is used to suppress the beat frequency current, and the outputs of the two are superposed to obtain the final reference voltage:
wherein u is d ，u q Is the final reference voltage.
7. The beat suppression method according to claim 6, wherein said step 5 comprises: and 4, calculating a modulation ratio and an angle by using the final reference voltage obtained in the step 4 and the collected direct-current side voltage as follows:
wherein u is dc Is a DC-side bus voltage, k v And theta v Modulation ratio and angle, respectively;
asynchronous modulation, synchronous modulation and square wave modulation are achieved according to the modulation ratio, the angle and the frequency, PWM signals are generated, the on-off of a switch tube is controlled, and finally beat frequency suppression of the permanent magnet synchronous motor traction system of the motor train unit is achieved.
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