Beat frequency suppression method for permanent magnet traction system of electric locomotive

Abstract

The invention provides a beat frequency suppression method for a permanent magnet traction system of an electric locomotive, which comprises the following steps of: S1, sampling three-phase current of a motor in real time, and performing park conversion on the three-phase current of the motor to obtain d-axis current and q-axis current; s2, subtracting the fundamental current from the d-axis current and the q-axis current, and then processing through a vector control region to obtain beat frequency current; and S3, adjusting the d-axis voltage and the q-axis voltage through a discrete proportional resonance controller so as to control the amplitude of the beat frequency current to be 0. The method is specially used for beat frequency suppression of an electric locomotive permanent magnet synchronous motor traction system without an LC absorption circuit, the control purpose is that the beat frequency current is equal to 0, compensation adjustment is conducted on the reference voltage according to the actual d-axis and q-axis beat frequency current, suppression of the beat frequency current is achieved, and the control method is simple and easy to achieve.

Description

Technical Field

[0001] The present invention relates to the technical field of electric locomotives, and in particular to a method for suppressing beat frequency of a permanent magnet traction system of an electric locomotive. Background Art

[0002] Compared with asynchronous motors, permanent magnet synchronous motors have the advantages of high power density and high efficiency. In the field of rail transit, there is a trend of replacing asynchronous motors. In order to achieve lightweight and low-cost electric locomotive converters, it is necessary to cancel the LC absorption circuit in the traditional traction system. The rail transit converter uses a single-phase PWM rectifier to provide DC power to the inverter, which will bring pulsation to the DC voltage twice the grid frequency. The pulsation of DC voltage will cause the beat frequency phenomenon of the inverter, especially when the motor runs near 100Hz, which will cause the motor torque to pulsate greatly and even burn the motor. Generally, the beat frequency phenomenon of the motor is weakened from the hardware or software. The capacitance of the support capacitor needs to be increased in hardware, but at the same time, the space and cost of the converter are increased. Therefore, it is necessary to suppress the beat frequency phenomenon from the software control algorithm.

[0003] A method in the prior art, such as Figure 1 As shown, a closed-loop frequency compensation algorithm is used to suppress the beat frequency. In order to eliminate the torque pulsation component caused by the beat frequency, the beat frequency current of the d and q axes is first extracted through a generalized integrator, the input reference value of the resonant controller G(s) is set to zero, and the feedback value is set to i q2 -ki d2 To realize the current component i q2 -ki d2 The minimum value control. q2 -ki d2 When it is 0, the motor torque pulsation caused by DC voltage fluctuation is eliminated. The disadvantages are as follows: 1. The selection of k depends on the motor parameters, which affects the beat frequency suppression effect of the control system. 2. The output compensation wave frequency of the resonant controller, for the permanent magnet motor control system, if the compensation of the wave frequency is inaccurate, it is easy to cause the control system to oscillate, and the beat frequency suppression effect is not ideal.

[0004] Another method in the prior art, such as Figure 2As shown in the figure, the collected three-phase motor current is converted into d and q axis current, a reference voltage is generated by a current controller, and a quasi-PR controller is used to directly suppress the double frequency fluctuation of the power grid in the d and q axis currents. The output of the current controller and the output of the quasi-resonant controller are superimposed to obtain the final output voltage, thereby realizing the beat frequency current suppression of the permanent magnet traction system. The disadvantages are as follows: 1. The beat frequency current component is not extracted, and the quasi-resonant controller is directly used to control the d and q axis currents. The control accuracy is low and it is easily affected by current sampling glitches. 2. The impact of load mutation on the resonant controller is not considered, and the torque mutation has a greater impact on the compensation adjustment of the beat frequency voltage. Summary of the invention

[0005] In view of this, the purpose of the present invention is to propose a beat frequency suppression method for a permanent magnet traction system of an electric locomotive, so as to solve the technical problems of low beat frequency suppression effect and control accuracy of the existing methods.

[0006] The technical means adopted by the present invention are as follows:

[0007] A method for suppressing beat frequency of a permanent magnet traction system of an electric locomotive comprises the following steps:

[0008] S1, real-time sampling of the three-phase current of the motor, and obtaining the d-axis current and q-axis current through park transformation of the three-phase current of the motor;

[0009] S2, subtracting the fundamental current from the d-axis current and the q-axis current and processing them through the vector control area to obtain the beat frequency current;

[0010] S3. The d-axis voltage and the q-axis voltage are adjusted by a discrete proportional resonant controller to control the amplitude of the beat frequency current to be 0.

[0011] Furthermore, the specific steps of S1 are as follows:

[0012] Ignoring the current generated by the high-frequency part of the beat frequency voltage, the three-phase beat frequency current of the motor is expressed as follows:

[0013]

[0014] Among them, i a1 、i b1 、i c1 They are the three-phase beat frequency current of the motor, Δu dc is the DC voltage pulsation amplitude, A is the coefficient, ω is the grid frequency, ω e is the motor fundamental frequency, Z1 is the motor impedance;

[0015] Transform the three-phase beat frequency current to the d and q axis coordinate system:

[0016]

[0017]

[0018] Among them, i d1 is the d-axis beat frequency current, i q1 is the q-axis beat frequency current, I is the beat frequency current amplitude;

[0019] It is concluded that the beat frequency current is twice the grid voltage frequency in the d and q axis coordinate system, which is about 100Hz; therefore, the beat frequency voltage is also about 100Hz in the d and q axis coordinate system;

[0020] In summary, the beat frequency phenomenon can be suppressed by controlling the beat frequency current near 100 Hz to 0.

[0021] Further, in S2, the vector control area uses a low-pass filter and a band-pass filter to extract the d-axis current and the q-axis current that are not affected by the load mutation through calculation processing, which specifically includes the following steps:

[0022] The d-axis current and the q-axis current are processed by a low-pass filter to obtain the fundamental current;

[0023] The d-axis current and q-axis current are subtracted from the fundamental current to obtain the high-frequency component of the current that is different from the load mutation.

[0024] The high-frequency component current signal is processed by a 100 Hz bandpass filter with a bandwidth of 10 Hz to filter out the high-frequency components caused by the switching frequency and noise, and obtain the beat frequency current.

[0025] Further, in S3, the discrete proportional resonant controller is designed based on the characteristics of the beat frequency current 100 Hz pulsation, and the design steps are as follows:

[0026] The quasi-PR controller is:

[0027]

[0028] Among them, K p is the proportional coefficient of the controller, K r is the resonance coefficient of the controller, ω c is the cut-off angular frequency, ω is the resonant angular frequency, ω=2π*100;

[0029] The zero-order holder method is used to discretize the controller s function, that is,

[0030]

[0031] Complete the discrete design of PR controller.

[0032] Furthermore, in S3, the specific steps of adjusting the d-axis voltage and the q-axis voltage by the discrete proportional resonant controller are as follows:

[0033] The output of the discrete quasi-PR controller is applied as a compensation voltage to the permanent magnet traction system current control output voltage and Thus generating the vector controlled output voltage u d1 and u q1 , so as to achieve the purpose of suppressing the beat frequency current;

[0034] The weak magnetic field area of ​​the motor running at high speed adopts single-axis current control, which only controls the q-axis current. The output of the q-axis current loop is After calculating the limit with umax, we get Realize the control of motor current and torque;

[0035] The q-axis beat frequency current is extracted in the same way as the vector area. At this time, the output of the q-axis PR controller is Δu d , applied to Generate u d2 The q-axis high-frequency current is controlled and the u is obtained after limiting the calculation with umax. q2 , thereby achieving the beat frequency current suppression in the weak magnetic control area;

[0036] The principle of suppressing the beat frequency current in the weak magnetic field region is as follows: the extracted q-axis beat frequency current is used as the input of the beat frequency controller, and the output of the beat frequency controller performs real-time compensation on the current loop output voltage, adjusts the single-axis current control output voltage, and suppresses the beat frequency current;

[0037] Vector control and flux weakening control use a designed switching algorithm to smoothly switch voltage and current;

[0038] The switching algorithm steps are as follows: When vector control switches to weak magnetic control, save the u before switching d1 、u q1 , gradually transition to the weak magnetic control u according to the proportional relationship d2 、u q2 ; When the weak magnetic control is switched to the vector control, the u before the switch is also saved d2 、u q2 , the initial value of the current loop is assigned to u at the switching moment d2 、u q2 , outputted by the current controller u d1 、u q1 , generating the u required for the final modulation d and u q , to achieve smooth switching of voltage and ensure that there is no current impact during the switching process.

[0039] The present invention also provides a storage medium, which includes a stored program, wherein when the program is run, any of the above-mentioned methods for suppressing beat frequency of a permanent magnet traction system of an electric locomotive is executed.

[0040] The present invention also provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes any of the above-mentioned methods for suppressing beat frequency of a permanent magnet traction system of an electric locomotive through the operation of the computer program.

[0041] Compared with the prior art, the present invention has the following advantages:

[0042] The present invention is specifically aimed at the beat frequency suppression of the electric locomotive permanent magnet synchronous motor traction system without LC absorption circuit. The beat frequency current is equal to 0 as the control purpose. The reference voltage is compensated and adjusted according to the actual d and q axis beat frequency currents, so as to achieve the suppression of the beat frequency current. The control method is simple and easy to implement. The application of this solution reduces the current and torque pulsation of the motor running near 2 times the power grid frequency, improves the system stability, and provides strong support for the lightweight design of the electric locomotive traction converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0044] Figure 1 It is a block diagram of a closed-loop frequency compensation strategy in the prior art.

[0045] Figure 2 The figure is a block diagram of a beat frequency current suppression strategy for a permanent magnet traction system in the prior art.

[0046] Figure 3 This is a block diagram of the beat frequency suppression control principle of the permanent magnet motor of the present invention.

[0047] Figure 4 This is a diagram of the beat frequency current extraction of the permanent magnet motor of the present invention.

[0048] Figure 5 This is a schematic diagram of the beat frequency current control principle of the present invention.

[0049] Figure 6 The U-phase and V-phase current diagrams before and after adding beat frequency suppression during 96 Hz full load operation in the embodiment.

[0050] Figure 7 In this embodiment, beat frequency suppression is not enabled and the motor is fully loaded and the speed scan of U-phase and V-phase current is 90 Hz-110 Hz.

[0051] Figure 8For the embodiment, the beat frequency suppression is enabled and the motor is fully loaded at 90 Hz-110 Hz and the U-phase and V-phase current diagrams are scanned. DETAILED DESCRIPTION

[0052] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0053] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0054] The purpose of the present invention is to propose a method for suppressing the motor beat frequency phenomenon for a permanent magnet traction system of an electric locomotive without an LC absorption circuit. The three-phase current of the motor is sampled in real time, and the d-axis current and the q-axis current are obtained by park transformation. In order to reduce the influence of load mutation on the extraction of the beat frequency current, the d-axis current and the q-axis current are subtracted from the fundamental current and processed by a 100Hz bandpass filter to obtain the beat frequency current, and then the d-axis and q-axis voltages are adjusted by a discrete proportional resonant controller to control the amplitude of the beat frequency current to 0, thereby suppressing the motor beat frequency phenomenon of the traction system without an LC absorption circuit and reducing the pulsation of the motor torque and current.

[0055] The principle of beat frequency suppression of permanent magnet motor is as follows Figure 3 As shown, the dotted line part is the vector control beat frequency suppression principle, and the solid line part is the single-axis current control beat frequency suppression principle.

[0056] The present invention provides a method for suppressing beat frequency of a permanent magnet traction system of an electric locomotive, comprising the following steps:

[0057] S1. Sample the three-phase current of the motor in real time and rotate it to the d and q axis coordinate system.

[0058] Ignoring the current generated by the high-frequency part of the beat frequency voltage, the three-phase beat frequency current can be expressed as:

[0059]

[0060] Transform the three-phase beat frequency current to the d and q axis coordinate system, then

[0061]

[0062] It can be seen that the beat frequency current is twice the grid voltage frequency in the d and q axis coordinate system, which is about 100Hz. It can also be deduced that the beat frequency voltage is also about 100Hz in the d and q axis coordinate system. Therefore, the beat frequency phenomenon can be suppressed by controlling the beat frequency current near 100Hz to 0.

[0063] S2. The vector control area uses a low-pass filter and a band-pass filter with a certain bandwidth to extract the d and q axis beat frequency currents that are not affected by load mutations through calculation processing.

[0064] The vector control area extracts and suppresses the d-axis and q-axis beat frequency currents. In order to reduce the impact of load mutations on beat frequency current extraction, the extraction process takes current mutations into account. First, the actual d-axis current and q-axis current are processed through a low-pass filter to obtain the fundamental current. The actual d-axis current and q-axis current are subtracted from the fundamental current to obtain the high-frequency component of the current that is different from the load mutation. The high-frequency component current signal is processed through a 100Hz bandpass filter with a bandwidth of 10Hz to filter out the high-frequency components caused by the switching frequency and noise to obtain the beat frequency current. The beat frequency current extraction process is as follows: Figure 4 shown.

[0065] S3. According to the 100Hz pulsation characteristics of the beat frequency current, a quasi-discrete PR controller is designed as a beat frequency current controller. The beat frequency current controller controls the beat frequency current to the minimum value by adjusting the output voltage. The output Δu of the beat frequency controller d Superimposed on the current loop output Generate u d1 and u q1 ; Single-axis current control is adopted in the weak magnetic field area, and the q-axis beat frequency current is extracted by the same method to control the q-axis beat frequency current. The beat frequency controller outputs Δu d Superimposed on the output of the single-axis current controller Generate u d2 and u q2 ; Design a smooth control switching strategy to output the required u d and u q , thereby achieving the purpose of suppressing the beat frequency current in the motor control process.

[0066] The extracted beat frequency current is adjusted to 0 amplitude, and the PI controller fails to control the AC signal, so a quasi-proportional resonant controller is used to adjust the beat frequency current. The designed quasi-PR controller is:

[0067]

[0068] Among them, K p and K r are the proportional coefficient and resonance coefficient of the controller, ω c is the cut-off angular frequency, ω is the resonant angular frequency, ω=2π*100. The zero-order holder method is used to discretize the controller s function, that is,

[0069]

[0070] In this way, the discrete design of the PR controller is completed. The beat frequency current control regulation principle is shown in Figure 5.

[0071] The output of the discrete quasi-PR controller is applied as a compensation voltage to the control system. and Thus generating the vector controlled output voltage u d1 and u q1 , so as to achieve the purpose of suppressing the beat frequency current.

[0072] The weak magnetic field area of ​​the motor running at high speed adopts single-axis current control, which only controls the q-axis current. The output of the q-axis current loop is After calculating the limit with umax, we get Realize the control of motor current and torque. Figure 4 and Figure 5 The q-axis beat frequency current is extracted and controlled by the method. At this time, the output of the q-axis PR controller is Δu d , applied to Generate u d2 The q-axis high-frequency current is controlled and the u is obtained after limiting the calculation with umax. q2 , thereby achieving the beat frequency current suppression in the weak magnetic field control area. The principle of beat frequency current suppression in the weak magnetic field area is shown in the single-axis current control part in 3. Vector control and weak magnetic field control use the designed switching algorithm to smoothly switch the voltage and current to generate the u required for the final modulation d and u q .

[0073] The experimental results of a permanent magnet traction system are used to illustrate the effectiveness of the beat frequency control algorithm. Figure 6 Current waveforms of a permanent magnet motor before and after applying the beat frequency algorithm at full load at 96 Hz. Figure 7 and Figure 8 The full-load sweep frequency current waveforms are shown in Figure 1 and 2 respectively. It can be seen that after applying the beat frequency algorithm, the motor current of the permanent magnet motor under full-load steady-state operation and full-load sweep frequency dynamic operation has been greatly improved.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for suppressing beat frequency of a permanent magnet traction system of an electric locomotive, characterized in that: The steps include: S1, real-time sampling of the three-phase current of the motor, and obtaining the d-axis current and q-axis current through park transformation of the three-phase current of the motor; S2, subtracting the fundamental current from the d-axis current and the q-axis current and processing them through the vector control area to obtain the beat frequency current; S3. The d-axis voltage and the q-axis voltage are adjusted by a discrete proportional resonant controller to control the amplitude of the beat frequency current to be 0.

2. The beat frequency suppression method of the electric locomotive permanent magnet traction system according to claim 1 is characterized in that: The specific steps of S1 are as follows: Ignoring the current generated by the high-frequency part of the beat frequency voltage, the three-phase beat frequency current of the motor is expressed as follows: Among them, i a1 、i b1 、i c1 They are the three-phase beat frequency current of the motor, Δu dc is the DC voltage pulsation amplitude, A is the coefficient, ω is the grid frequency, ω e is the motor fundamental frequency, Z1 is the motor impedance; Transform the three-phase beat frequency current to the d and q axis coordinate system: Among them, i d1 is the d-axis beat frequency current, i q1 is the q-axis beat frequency current, I is the beat frequency current amplitude; It is concluded that the beat frequency current frequency in the d and q axis coordinate system is twice the grid frequency, that is, 2ω; the grid frequency ω fluctuates around 50Hz, so the d and q axis beat frequency current frequency is about 100Hz; it can also be deduced that the beat frequency voltage frequency is also about 100Hz in the d and q axis coordinate system; In summary, the beat frequency phenomenon can be suppressed by controlling the 100 Hz beat frequency current to 0.

3. The beat frequency suppression method of the electric locomotive permanent magnet traction system according to claim 1, characterized in that: In S2, the vector control area uses a low-pass filter and a band-pass filter to extract the d-axis current and the q-axis current that are not affected by the load mutation through calculation processing, which specifically includes the following steps: The d-axis current and the q-axis current are processed by a low-pass filter to obtain the fundamental current; The d-axis current and q-axis current are subtracted from the fundamental current to obtain the high-frequency component of the current that is different from the load mutation. The high-frequency component current signal is processed by a 100 Hz bandpass filter with a bandwidth of 10 Hz to filter out the high-frequency components caused by the switching frequency and noise, and obtain the beat frequency current.

4. The beat frequency suppression method of the electric locomotive permanent magnet traction system according to claim 2 is characterized in that: In S3, the discrete proportional resonant controller is designed based on the characteristics of the beat frequency current 100Hz pulsation, and the design steps are as follows: The quasi-PR controller is: Among them, K p is the proportional coefficient of the controller, K r is the resonance coefficient of the controller, ω c is the cut-off angular frequency, ω is the resonant angular frequency, ω=2π*100; The zero-order holder method is used to discretize the controller s function, that is, Complete the discrete design of PR controller.

5. The beat frequency suppression method of the electric locomotive permanent magnet traction system according to claim 4 is characterized in that: In S3, the specific steps of adjusting the d-axis voltage and the q-axis voltage by the discrete proportional resonant controller are as follows: The output of the discrete quasi-PR controller is applied as a compensation voltage to the current control output voltage of the permanent magnet traction control system and Thus generating the vector controlled output voltage u d1 and u q1 , so as to achieve the purpose of suppressing the beat frequency current; The weak magnetic field area of ​​the motor running at high speed adopts single-axis current control, which only controls the q-axis current. The output of the q-axis current loop is After calculating the limit with umax, we get Realize the control of motor current and torque; The q-axis beat frequency current is extracted in the same way as the vector area. At this time, the output of the q-axis PR controller is Δu d , applied to Generate u d2 The q-axis high-frequency current is controlled and the u is obtained after limiting the calculation with umax. q2 , thereby achieving the beat frequency current suppression in the weak magnetic control area; The principle of suppressing the beat frequency current in the weak magnetic field region is as follows: the extracted q-axis beat frequency current is used as the input of the beat frequency controller, and the output of the beat frequency controller performs real-time compensation on the current loop output voltage, adjusts the single-axis current control output voltage, and suppresses the beat frequency current; Vector control and flux weakening control use a designed switching algorithm to smoothly switch voltage and current; The switching algorithm steps are as follows: When vector control switches to weak magnetic control, save the u before switching d1 、u q1 , gradually transition to the weak magnetic control u according to the proportional relationship d2 、u q2 ; When the weak magnetic control is switched to the vector control, the u before the switch is also saved d2 、u q2 , the initial value of the current loop is assigned to u at the switching moment d2 、u q2 , outputted by the current controller u d1 、u q1 , generating the u required for the final modulation d and u q , to achieve smooth switching of voltage and ensure that there is no current impact during the switching process.

6. A storage medium, characterized in that: The storage medium includes a stored program, wherein when the program is run, the beat frequency suppression method of the permanent magnet traction system of an electric locomotive as described in any one of claims 1 to 5 is executed.

7. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: The processor executes the beat frequency suppression method of the permanent magnet traction system of an electric locomotive as described in any one of claims 1 to 5 through the operation of the computer program.

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