Grid-side current harmonic suppression method based on five-phase permanent magnet synchronous motor driving system

Abstract

The invention discloses a grid-side current harmonic suppression method based on a five-phase permanent magnet synchronous motor driving system, and belongs to the technical field of motor driving and control. Firstly, a five-phase permanent magnet synchronous motor and non-electrolytic capacitor driving system model is established, and LC resonance analysis is carried out; extracting grid-side characteristic sub-harmonics through a band-pass filter, generating virtual damping through a PR resonance controller, and converting the virtual damping into a shaft voltage compensation instruction; extracting a grid-side input current harmonic component in real time, and combining the grid-side input current harmonic component with the output of a rotating speed loop through a PI regulator to form a final given inverter power; the compensation power is decoupled and injected into a motor shaft voltage component, and driving control is achieved in cooperation with five-phase carrier pulse width modulation. According to the invention, the grid-side current harmonic suppression under the drive system of the five-phase permanent magnet synchronous motor without the electrolytic capacitor is realized, the size of the electrolytic capacitor is saved, no extra hardware equipment is needed to carry out bus voltage resonance suppression, and the stability under the condition that the power grid is unbalanced is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of motor drive and control, and particularly belongs to a method for suppressing grid-side current harmonics based on a five-phase permanent magnet synchronous motor drive system. BACKGROUND

[0002] Permanent magnet synchronous motor (PMSM) is widely used in electric vehicles, industrial manufacturing, especially in traditional industrial fields due to its high efficiency and high power density. Currently, the solutions to the LC resonance phenomenon in the electrolytic capacitor-free circuit topology mainly fall into two categories: the resonance suppression method based on motor negative impedance characteristics regulation and the resonance suppression method based on virtual impedance. The first method can suppress the harmonic components in the grid-side current by changing the motor current or voltage command using the bus voltage information according to the system characteristic equation, and can enhance the stability of the system by regulating the negative impedance characteristics of the motor. However, the regulation of negative impedance may couple with the motor's own vector control and field weakening control, leading to increased speed fluctuation or torque ripple. The second method can improve the stability of the system by increasing the system damping, which can be achieved by constructing a bus voltage and current feedback control loop to improve the damping characteristics of the system. This method can suppress the system resonance but is only effective for specific order harmonics near the LC resonance frequency, and has little effect on other low-frequency or non-characteristic order harmonics caused by grid imbalance. The invention patent CN116094416B invents a harmonic suppression method for electrolytic capacitor-free permanent magnet synchronous motor based on steady-state point adaptation, which does not optimize the dynamic changes of multiple frequency harmonics under grid imbalance conditions, and only extracts the six times frequency harmonics of the bus voltage to adjust the current vector angle. It relies on small signal model and pre-set harmonic processing function, and has weak robustness to parameter drift and nonlinear disturbance, making it difficult to adapt to harmonic suppression under complex conditions such as grid voltage sag. Moreover, the scene is limited to three-phase permanent magnet synchronous motor, and the multiple harmonic space and conduction angle transformation requirements of five-phase motor are not considered, which lacks universality. The invention patent CN113098365B invents a harmonic suppression method and system for grid-side current of electrolytic capacitor-free motor drive system, the core technology of which is power waveform correction combined with PR regulator. This method has weak adaptability to grid imbalance, and only suppresses harmonics by extracting grid-side current harmonics and correcting initial power of inverter, assuming maximum power factor and ignoring power loss of thin film capacitor. Especially under voltage sag, power disturbance can easily lead to increased bus voltage fluctuation, and the characteristics only rely on power error and q-axis current given, without integrating input current harmonic information, which has single harmonic suppression dimension and insufficient sensitivity to LC resonance frequency drift.Invention patent CN119010717B invented a harmonic suppression method for electrolytic capacitor-free permanent magnet synchronous motor drive systems based on multi-port impedance optimization. The core technology of this invention is the entropy weight TOPSIS method to optimize the voltage regulation of the machine-grid side port impedance. This method is computationally complex and relies on machine-side input admittance modeling. Although active damping synergistically suppresses machine-grid side harmonics, it is prone to increasing machine-side torque ripple. Especially under grid imbalance, the optimization angle selection is easily affected by steady-state point parameters, resulting in weak robustness. Moreover, it is only for three-phase motors and does not integrate conduction angle transformation and power compensation mechanisms, making it insufficiently adaptable to the multi-dimensional harmonic space of five-phase motors.

[0003] Currently, existing research mainly focuses on single-phase or three-phase input electrolytic capacitor-free drive systems, and the controlled objects are mainly three-phase motors. There is still no effective solution to the problem of grid-side current fluctuation when a five-phase motor experiences a voltage drop in one phase input. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of the prior art. This invention provides a method for suppressing harmonics caused by grid imbalance in a five-phase permanent magnet synchronous motor without electrolytic capacitors. This method is the first to directly correlate the conduction angle offset caused by grid imbalance with the actual input current harmonics in a five-phase system. By using a simple PI closed-loop real-time correction of the inverter power setpoint, it eliminates LC resonance and harmonic degradation caused by power disturbance amplification at the source. At the same time, it retains traditional virtual damping as an auxiliary, achieving stable operation under all operating conditions with reduced total harmonic distortion of grid-side current, significantly reduced bus voltage fluctuations, and extremely low generator-side torque pulsation when the grid is severely unbalanced.

[0005] The technical solution to achieve the purpose of this invention is as follows:

[0006] The method for suppressing grid-side current harmonics in a five-phase permanent magnet synchronous motor drive system includes the following steps:

[0007] Step S1: Establish a grid imbalance model for a five-phase permanent magnet synchronous motor;

[0008] Step S2: Model the electrolytic capacitor-free motor drive system and perform LC resonance analysis;

[0009] Step S3: By analyzing the harmonic composition of the drive system, the mechanism of the change of harmonic content of the system input voltage and grid-side current is analyzed, the grid-side power parameters are calculated, the grid-side output impedance of the system is reshaped, and grid-side current harmonic suppression is performed.

[0010] Step S4: Derive the conduction angle transformation relationship of the five permanent magnet synchronous motors under the condition of power grid imbalance;

[0011] Step S5: Extract harmonic information from the input current, combine it with grid-side power calculation to construct a suitable compensation component, suppress the impact of input current harmonic disturbances on the grid-side power compensation circuit, and reduce bus voltage fluctuations under grid imbalance conditions.

[0012] Step S6: Detect and compare the actual speed of the five-phase permanent magnet motor with the given speed, and output the given value of the q-axis current through the PI controller;

[0013] Step S7: After comparing the feedback current with the reference current, the voltage in the synchronous rotating coordinate system is obtained through PI regulation and then transformed to... The axis is simultaneously injected with mesh-side compensation power to cancel out the resonant component;

[0014] Step S8 The shaft voltage is used to generate a switching signal via the CPWM module, which drives the inverter to control the motor and complete the system resonance control under grid imbalance.

[0015] A method for suppressing grid-side current harmonics in a five-phase permanent magnet synchronous motor drive system. The main components of the electrolytic capacitor-free drive system are an uncontrolled rectifier bridge, a filter inductor, a thin-film capacitor, an inverter, and a five-phase permanent magnet synchronous motor.

[0016] The method for suppressing grid-side current harmonics in a five-phase permanent magnet synchronous motor drive system, the specific process of step S1 is as follows:

[0017] Step S11: The voltage source can be considered as a DC voltage source. The inverter and the five-phase motor can be considered as current sources. According to Kirchhoff's laws, the grid-side current and voltage formulas are as follows:

[0018]

[0019]

[0020] In the formula, Indicates a DC voltage source. It is an equivalent current source. Indicates the inverter current source. It is the capacitor current. and It is the equivalent series impedance of the input power supply. It is the bus voltage.

[0021] Step S12: Express the inverter current in terms of bus voltage to obtain the following relationship:

[0022]

[0023] In the formula, For a constant power load of the motor system, This represents the average DC bus voltage at the film capacitor terminals. The signal component of the bus voltage at the end of the thin-film capacitor;

[0024] Linearize the relationship obtained in step S12 to obtain the inverter input current:

[0025]

[0026] For the small-signal component of the DC bus voltage at the thin-film capacitor terminal, the characteristic equation of the drive system can be obtained by simultaneously solving and expanding the above equations:

[0027]

[0028] The method for suppressing harmonic imbalance in a five-phase permanent magnet synchronous motor without electrolytic capacitors, specifically step S2, is as follows:

[0029] Step S21: In a capacitor-free motor drive system, a small-value film capacitor replaces a large-value electrolytic capacitor. The state equation is:

[0030]

[0031] in, Indicates grid-side voltage; Indicates inductor current; Indicates the bus voltage; Indicates the inverter current; Indicates bus inductance; Indicates the line resistance; Indicates a thin-film capacitor;

[0032] Step S22, derive the characteristic equation of the system as follows:

[0033]

[0034] in, This represents the average DC bus voltage at the film capacitor terminals. Equivalent power;

[0035] Step S23: Perform stability testing on the characteristic equation in step S22 according to the Routh criterion, and obtain:

[0036]

[0037] Step S24: The electrolytic capacitor-free drive system exhibits significant resonance, with a substantial increase in harmonic amplitudes near the resonant frequency in the grid-side current, affecting grid-side power quality. (LC resonant frequency...) It can be represented as:

[0038] .

[0039] The specific process of step S3 in the grid-side current harmonic suppression method based on a five-phase permanent magnet synchronous motor drive system is as follows:

[0040] Step S31: Extract the damping current from the equivalent parallel virtual resistance of the 6th and 12th harmonics using a bandpass filter. Send the error to the PR controller to increase the damping of the drive system and suppress the LC resonance phenomenon on the grid side. The expression for the PR controller is:

[0041]

[0042] In the formula, This represents the proportional coefficient of the resonant controller. This represents the resonance coefficient of the resonant controller. Indicates the bandwidth of the resonant controller. This indicates the center frequency of the resonant controller;

[0043] Step S32: Convert the damping current into damping power, then into voltage command, and use the voltage command to achieve control;

[0044] Damping power can be expressed as:

[0045]

[0046] In the formula, It is damping power. It is the damping current;

[0047] Step S33: Ignoring the inverter's switching losses, the motor power can be considered as the inverter power, as shown below:

[0048]

[0049] in, , These represent voltage and current in a stationary coordinate system, respectively.

[0050] Step S34, the form of the injected voltage command is:

[0051]

[0052] In the formula, , It is a voltage command used for correction in a stationary coordinate system.

[0053] The method for suppressing grid-side current harmonics in a five-phase permanent magnet synchronous motor drive system, the specific process of step S4 is as follows:

[0054] Step S41: Under grid imbalance conditions, significant harmonic components appear on the DC bus, exacerbating harmonic distortion of the grid current. When the U-phase voltage drops, the three-phase grid voltage after the fault can be expressed as:

[0055]

[0056] In the formula, The drop coefficient, The fundamental frequency of the grid input voltage. This represents the effective value of the grid input voltage for the non-slip phase. , and These are the input voltages of the three-phase power grid. When the phase voltage drops sharply, the conduction angle of the rectifier bridge diodes will deviate from the balanced operating state. This deviation will cause the rectified voltage to drop. The waveform is significantly distorted, and the diode conduction angle is... The offset is:

[0057]

[0058] In the formula, It can be represented as:

[0059]

[0060] Based on the output characteristics of the uncontrolled rectifier bridge, the rectified voltage can be expressed as a periodic function of the line voltage, and its Fourier series expansion can be expressed as:

[0061]

[0062] Step S42, voltage droop of U-phase voltage amplitude After that, the rectified voltage It has the properties of an even function, and its coefficients Naturally zero, coefficient and It can be represented as:

[0063]

[0064] exist After the phase voltage droops, the conduction angle of the rectifier diodes adaptively adjusts to maintain the stability of the DC link on the grid side. Phase current and grid voltage Waveform distortion occurs, resulting in a significant amplification of harmonics in the grid-side current.

[0065] The method for suppressing grid-side current harmonics in a five-phase permanent magnet synchronous motor drive system, the specific process of step S5 is as follows:

[0066] Step S51: We first process the grid-side signal. The inverter power signal can be expressed as:

[0067]

[0068] In the formula, Peak voltage, For the power grid frequency, The initial phase angle;

[0069] When the grid power factor reaches its maximum value, the input power of the power source can be expressed as:

[0070]

[0071] In the formula, The peak value of the grid input current is given. The grid input power is mainly contributed by the thin-film capacitors and the inverter, and can be expressed as:

[0072]

[0073] In the formula, For input power, For inverter power, For the power of the thin-film capacitor;

[0074] The formula for calculating the DC link voltage during active rectification is as follows:

[0075]

[0076] The specific expression for the power loss of the capacitor is derived as follows:

[0077]

[0078] The capacitance of a thin-film capacitor is extremely small, and its power loss is negligible. Therefore, the inverter's power is approximately equal to the grid-side input power, as shown in the following formula:

[0079]

[0080] Step S52: Filter the acquired grid-side current signal and then calculate the harmonic components in the input current. formula:

[0081]

[0082] The harmonic components are subtracted from zero, and the result is processed by a PI controller to obtain the correction term for the inverter power waveform. Its expression is as follows:

[0083]

[0084] in For the proportional gain of the PI controller, The integral gain of the PI controller, the inverter power signal Through algebraic operations, the initial inverter power signal Subtract the term used to correct the inverter power waveform The corrected given inverter power is:

[0085]

[0086] In the formula, This is the corrected inverter power. This is the reference speed. That is the actual rotational speed. To simplify the proportional gain of the PI controller, This simplifies the integral gain of the PI controller.

[0087] The method for suppressing grid-side current harmonics in a five-phase permanent magnet synchronous motor drive system, specifically step S6, involves detecting the rotational speed of the five-phase permanent magnet motor as the feedback speed of the motor. , give the speed With feedback speed The motor speed error was obtained by comparison. A PI controller is used based on the speed error. The calculation of the five-phase permanent magnet motor The shaft current, the output of the PI controller is given. shaft current .

[0088] The method for suppressing grid-side current harmonics in a five-phase permanent magnet synchronous motor drive system, specifically step S7, involves: comparing the obtained feedback current component with a given reference current, sending the error to a PI controller to obtain a given voltage signal in a synchronous rotating coordinate system, and then transforming the obtained given voltage signal in the rotating orthogonal coordinate system to obtain the motor... In the shaft voltage component, the grid-side compensation power is simultaneously decoupled and injected into the motor. The resonant component is canceled out in the axial voltage component.

[0089] The method for suppressing grid-side current harmonics in a five-phase permanent magnet synchronous motor drive system, wherein the specific process of step S7 is as follows: [The text abruptly ends here, likely due to an incomplete sentence or missing information.] The shaft voltage signal is input to the continuous pulse width modulation (CPWM) module to obtain the switching signals for each phase. These switching signals are then input to the inverter to control the motor, achieving resonant control of the electrolytic capacitor-free five-phase permanent magnet synchronous motor drive system under grid imbalance. Compared with existing technologies, this invention has the following advantages:

[0090] 1. This invention proposes a grid-side current harmonic suppression method for a five-phase permanent magnet synchronous motor electrolytic capacitor-free drive system, which combines input current harmonic extraction with grid-side power compensation. Addressing the issue of input voltage drop in a certain phase, the method extracts harmonic information from the input current and constructs a suitable compensation component based on grid-side power calculation. This suppresses the impact of input current harmonic disturbances on the grid-side power compensation circuit. Furthermore, it uses a grid-side power compensation method based on a resonant controller to suppress excessive grid-side current resonance fluctuations during faults, thereby achieving stable operation under grid imbalance conditions.

[0091] 2. This invention employs a grid-side power compensation method based on a resonant controller to suppress grid-side current resonance fluctuations when the grid is unbalanced. Compared with traditional passive damping or purely active damping methods, this invention can achieve equivalent damping without any additional hardware, completely eliminating bulky passive components, significantly reducing system size and weight, and greatly increasing power density. At the same time, it avoids the constant heat loss caused by passive damping and the large amount of parallel computation for multiple harmonics in active damping. It is particularly suitable for scenarios such as mining ventilation fans, air conditioning outdoor units, and electric drives for new energy vehicles where size, weight, and reliability requirements are stringent.

[0092] 3. This invention employs a carrier-based pulse width modulation (CPWM) method optimized for multiphase motors. Compared with the current hysteresis modulation commonly used in traditional three-phase systems or the random PWM and hysteresis PWM used in some literature, CPWM has a fixed switching frequency and optimized five-phase harmonic cancellation characteristics. This not only reduces switching losses but also results in a cleaner output voltage harmonic spectrum, with almost no excitation in the third harmonic plane. The iron and copper losses of the motor are significantly reduced, and the temperature rise is lowered. At the same time, the fixed switching frequency leads to strong EMI predictability and greatly reduces the difficulty of filter design. The overall system efficiency, thermal management, and electromagnetic compatibility performance are all superior to hysteresis or random PWM schemes, making it more suitable for industrial mass production and long-life operation conditions. Attached Figure Description

[0093] Figure 1 This is a block diagram of a grid-side current harmonic suppression method based on a five-phase permanent magnet synchronous motor drive system.

[0094] Figure 2 The motor load is Under certain circumstances, a voltage drop occurs in the U-phase phase, and the motor transitions from normal operation to voltage drop to resonance suppression. The waveform diagram shows the bus voltage and grid-side current.

[0095] Figure 3 The motor load is Under normal operating conditions, the amplified waveforms of the motor bus voltage and grid-side current are shown.

[0096] Figure 4 The motor load is The waveform diagram of the motor bus voltage and grid-side current when the motor experiences a U-phase voltage drop.

[0097] Figure 5 The motor load is The waveforms of the motor bus voltage and grid-side current after the motor resonant suppression are shown in the figure. When the U-phase voltage drops, the motor bus voltage and grid-side current are amplified. Detailed Implementation

[0098] To more clearly describe the ideas, technical solutions, and advantages of the present invention, specific embodiments are illustrated through examples and accompanying drawings. Obviously, the described embodiments are only a portion, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0099] Figure 1 A block diagram of a grid-side current harmonic suppression method based on a five-phase permanent magnet synchronous motor drive system is shown. The specific implementation steps of this method are described in detail below with reference to the control block diagram:

[0100] The method for suppressing grid-side current harmonics in a five-phase permanent magnet synchronous motor drive system includes the following steps:

[0101] Step S1: Establish a grid imbalance model for a five-phase permanent magnet synchronous motor.

[0102] Step S11: Treat the voltage source as a DC voltage source Therefore, the inverter and the five-phase motor can be considered as current sources. According to Kirchhoff's laws, the grid-side current and voltage formulas are as follows:

[0103]

[0104]

[0105] In the formula, Indicates a DC voltage source. It is an equivalent current source. Indicates the inverter current source. It is the capacitor current. and It is the equivalent series impedance of the input power supply. It is the bus voltage.

[0106] Step S12: Express the inverter current in terms of bus voltage to obtain the following relationship:

[0107]

[0108] Linearize the relationship obtained in step S12 to obtain the inverter input current:

[0109]

[0110] In the formula, For a constant power load of the motor system, This represents the average DC bus voltage at the film capacitor terminals. This is the signal component of the bus voltage at the end of the thin-film capacitor. For the small-signal component of the DC bus voltage at the thin-film capacitor terminal, the characteristic equation of the drive system can be obtained by simultaneously solving and expanding the above equations:

[0111]

[0112] Step S2: Model the electrolytic capacitor-free motor drive system and perform LC resonance analysis;

[0113] Step S21: In a capacitor-free motor drive system, a small-value film capacitor replaces a large-value electrolytic capacitor. The state equation is:

[0114]

[0115] in, Indicates grid-side voltage; Indicates inductor current; Indicates the bus voltage; Indicates the inverter current; Indicates bus inductance; Indicates the line resistance; Indicates a thin-film capacitor;

[0116] Step S22, derive the characteristic equation of the system as follows:

[0117]

[0118] in, This is the average value of the DC bus voltage at the end of the film capacitor.

[0119] Step S23: Perform stability testing on the characteristic equation in step S22 according to the Routh criterion, and obtain:

[0120]

[0121] Step S24: The electrolytic capacitor-free drive system exhibits significant resonance, with a substantial increase in harmonic amplitudes near the resonant frequency in the grid-side current, affecting grid-side power quality. (LC resonant frequency...) It can be represented as:

[0122] .

[0123] Step S3 involves analyzing the harmonic composition of the drive system to elucidate the mechanism of changes in the harmonic content of the system input voltage and grid-side current. Based on this, the grid-side power parameters are calculated, the system grid-side output impedance is reshaped, and grid-side current harmonic suppression is performed.

[0124] Step S31: Extract the damping current from the equivalent parallel virtual resistance of the 6th and 12th harmonics using a bandpass filter. Send the error to the PR controller to increase the damping of the drive system and suppress the LC resonance phenomenon on the grid side. The expression for the PR controller is:

[0125]

[0126] in This represents the proportional coefficient of the resonant controller. This represents the resonance coefficient of the resonant controller. Indicates the bandwidth of the resonant controller. This indicates the center frequency of the resonant controller;

[0127] Step S32: Convert the damping current into damping power, then into voltage command, and use the voltage command to achieve control;

[0128] Damping power can be expressed as:

[0129]

[0130] in, It is damping power. It is the damping current.

[0131] Step S33: Ignoring the inverter's switching losses, the motor power can be considered as the inverter power, as shown below:

[0132]

[0133] in, , These represent voltage and current in a stationary coordinate system, respectively.

[0134] Step S34, the form of the injected voltage command is:

[0135]

[0136] in, , It is a voltage command used for correction in a stationary coordinate system.

[0137] Step S4: In order for the electrolytic capacitor-free five-phase permanent magnet synchronous motor drive system to operate under grid imbalance, explain the conduction angle transformation relationship of the motor under grid imbalance.

[0138] Step S41: Under grid imbalance conditions, significant harmonic components appear on the DC bus, exacerbating harmonic distortion of the grid current. When the U-phase voltage drops, the three-phase grid voltage after the fault can be expressed as:

[0139]

[0140] in The drop coefficient, The fundamental frequency of the grid input voltage. This represents the effective value of the grid input voltage for the non-slip phase. , and These are the input voltages of the three-phase power grid, respectively. During a phase voltage drop, the conduction angle of the rectifier bridge diodes deviates from the balanced operating state. This deviation will cause the rectified voltage to drop. The waveform is significantly distorted, and the diode conduction angle is... The offset is:

[0141]

[0142] in, It can be represented as:

[0143]

[0144] Based on the output characteristics of the uncontrolled rectifier bridge, the rectified voltage can be expressed as a periodic function of the line voltage, and its Fourier series expansion can be expressed as:

[0145]

[0146] Step S42, with Phase voltage amplitude The voltage droop is analyzed because the rectified voltage It has the properties of an even function, and its coefficients Since the coefficient is zero, the coefficient is zero. and It can be represented as:

[0147]

[0148] exist After a phase voltage drop, the conduction angle of the rectifier diodes adaptively adjusts to maintain the stability of the DC link on the grid side. Phase current and grid voltage Waveform distortion occurs, which in turn leads to a significant amplification of harmonics in the grid-side current.

[0149] Step S5: In order to reduce bus voltage fluctuations under grid imbalance, the harmonic information in the input current is extracted and a suitable compensation component is constructed by combining it with grid-side power calculation to suppress the impact of input current harmonic disturbances on the grid-side power compensation circuit.

[0150] Step S51: We first process the grid-side signal. The inverter power signal can be expressed as:

[0151]

[0152] in, Peak voltage, For the power grid frequency, The initial phase angle;

[0153] When the grid power factor reaches its maximum value, the input power of the power source can be expressed as:

[0154]

[0155] in The peak value of the grid input current is given. The grid input power is mainly contributed by the thin-film capacitors and the inverter, and can be expressed as:

[0156]

[0157] in For input power, For inverter power, For the power of the thin-film capacitor;

[0158] The formula for calculating the DC link voltage during active rectification is as follows:

[0159]

[0160] The specific expression for the power loss of the capacitor is derived as follows:

[0161]

[0162] The capacitance of a thin-film capacitor is extremely small, and its power loss is negligible. Therefore, the inverter's power is approximately equal to the grid-side input power, as shown in the following formula:

[0163]

[0164] Step S52: Filter the acquired grid-side current signal and then calculate the harmonic components in the input current. formula:

[0165]

[0166] The harmonic components are subtracted from zero, and the result is processed by a PI controller to obtain the correction term for the inverter power waveform. Its expression is as follows:

[0167]

[0168] in For the proportional gain of the PI controller, The integral gain of the PI controller, the inverter power signal Through algebraic operations, the initial inverter power signal Subtract the term used to correct the inverter power waveform The corrected given inverter power is:

[0169]

[0170] in, This is the corrected inverter power. This is the reference speed. That is the actual rotational speed. To simplify the proportional gain of the PI controller, This simplifies the integral gain of the PI controller.

[0171] Step S6: Detect the speed of the five-phase permanent magnet motor as the speed feedback for the motor. , give the speed With feedback speed The motor speed error was obtained by comparison. A PI controller is used based on the speed error. The calculation of the five-phase permanent magnet motor The shaft current, the output of the PI controller is given. shaft current .

[0172] Step S7: Compare the obtained feedback current component with the given reference current, and send the error to the PI controller to obtain the given voltage signal in the synchronous rotating coordinate system. Then, transform the obtained given voltage signal in the rotating orthogonal coordinate system to obtain the motor... In the shaft voltage component, the grid-side compensation power is simultaneously decoupled and injected into the motor. The resonant component is canceled out in the axial voltage component;

[0173] Step S8, the obtained motor The shaft voltage signal is input to the CPWM module to obtain the switching signals for each phase. These switching signals are then input to the inverter to control the motor, achieving resonant control of the electrolytic capacitor-free five-phase permanent magnet synchronous motor drive system under grid imbalance.

[0174] Figure 2 For the motor under load torque of The rotational speed is Below are the bus voltage waveforms and motor bus voltage and grid-side current waveforms for the motor during normal operation, voltage drop, and resonance suppression. When the control strategy used in this invention is employed, the resonance fluctuation amplitudes of the bus voltage and grid-side current are significantly reduced after the voltage drop, proving the correctness of the proposed control strategy.

[0175] Figure 3 , Figure 4 and Figure 5 The motor is respectively under load torque of The rotational speed is Below is an enlarged view of the motor bus voltage and grid-side current waveforms during normal operation, voltage dip, and resonance suppression. When the resonance control strategy used in this invention is employed, the bus voltage fluctuation is... Descending to The grid-side current fluctuation is caused by Downgraded to It is basically close to the normal operating condition and can maintain stable operation.

Claims

1. A method for suppressing the harmonic current of the grid side based on the five-phase permanent magnet synchronous motor drive system, characterized in that, It comprises the following steps: Step S1, establishing a five-phase permanent magnet synchronous motor grid imbalance model; Step S2, LC resonance analysis is performed on modeling of electrolytic capacitor-free motor drive system; Step S3, by analyzing the harmonic composition of the drive system, the change mechanism of the system input voltage and the harmonic content of the grid-side current is analyzed, the grid-side power parameters are calculated, the system grid-side output impedance is reshaped, and the grid-side current harmonic suppression is performed; Step S4, the conduction angle transformation relationship of the five-phase permanent magnet synchronous motor under the condition of grid imbalance is derived; Step S5, the harmonic information in the input current is extracted, and the compensation component is constructed by combining the grid-side power calculation to suppress the influence of input current harmonic disturbance on the grid-side power compensation loop and reduce the bus voltage fluctuation under the condition of grid imbalance; Step S6, the actual speed of the five-phase permanent magnet motor is compared with the given speed, and the given value of the q-axis current is output through the PI controller; Step S7, after the feedback current is compared with the reference current, PI adjustment is performed to obtain a synchronous rotating coordinate system voltage, which is transformed to The shaft, while injecting the grid side compensation power to offset the resonance component; Step S8, The shaft voltage generates a switching signal through a continuous pulse width modulation module, drives an inverter to control a motor, and completes system resonance control under unbalanced power grid.

2. The method for grid-side current harmonic suppression based on five-phase permanent magnet synchronous motor driving system according to claim 1, characterized in that, The electrolytic capacitor-free drive system comprises an uncontrollable rectifier bridge, a filter inductor, a film capacitor, an inverter and a five-phase permanent magnet synchronous motor.

3. The method for grid-side current harmonic suppression based on five-phase permanent magnet synchronous motor driving system according to claim 2, characterized in that, The specific process of step S1 is as follows: Step S11, the voltage source is a direct current voltage source According to Kirchhoff's law, the obtained network side current voltage formula is as follows: ， ， wherein represents a direct voltage source, is an equivalent current source, represents an inverter current source, is a capacitance current, and is an equivalent series impedance of the input power supply, is a bus voltage; Step S12, the inverter current is expressed by the bus voltage to obtain a relationship: ， wherein is a constant power load of the motor system, is the mean value of the DC bus voltage at the thin film capacitor terminal, is the signal component of the bus voltage at the thin film capacitor terminal; The relationship obtained in step S12 is linearized, and the inverter input side current is obtained: ， In the formula, The small signal component of the thin film capacitor terminal DC bus voltage is obtained, and the characteristic equation of the drive system is obtained. 。 4. The electrolytic capacitorless five-phase permanent magnet synchronous motor grid imbalance harmonic suppression method according to claim 3, characterized in that, The specific process of step S2 is as follows: Step S21, in the electrolytic capacitor-free motor drive system, the electrolytic capacitor is replaced by a film capacitor, the capacitance of the film capacitor is smaller than that of the electrolytic capacitor, and the state equation is: ， wherein, represents a grid voltage; represents an inductor current; represents a bus voltage; represents an inverter current; represents a bus inductor; represents a line resistance; represents a film capacitor; Step S22, the characteristic equation of the system is derived as: ， wherein is the mean value of the DC bus voltage at the thin-film capacitor end, is the equivalent power; Step S23, the characteristic equation in step S22 is subjected to stability discrimination according to the Routh criterion, and the following is obtained: ， Step S24, the resonant phenomenon exists in the electrolytic capacitor-free driving system, the harmonic amplitude near the resonant frequency of the grid-side current increases, which affects the grid-side power quality, and the LC resonant frequency is represented as: 。 5. The method for grid-side current harmonic suppression based on five-phase permanent magnet synchronous motor driving system according to claim 1, characterized in that, The specific process of step S3 is as follows: Step S31, the equivalent virtual resistance of the 6th and 12th harmonics is extracted through a band-pass filter to generate a damping current, and the error is sent into a PR controller to increase the damping of the drive system, suppress the LC resonance phenomenon of the grid side, and the expression of the PR controller is: ， wherein represents a proportional coefficient of the resonant controller, represents a resonant coefficient of the resonant controller, represents a bandwidth of the resonant controller, represents a center frequency of the resonant controller; Step S32, the damping current is converted into damping power, and the voltage instruction is converted into a voltage instruction to realize control; The damping power is expressed as: ， wherein is the damping power, is the damping current; Step S33, ignoring the switching loss of the inverter, the motor power is the inverter power, and the expression is: ， wherein , V and I represent the voltage and current in the stationary coordinate system, respectively; Step S34, the injection voltage instruction is in the form of: ， In the formula, , is a voltage command for correction in a stationary coordinate system.

6. The method for grid-side current harmonic suppression based on five-phase permanent magnet synchronous motor driving system according to claim 1, characterized in that, The specific process of step S4 is as follows: Step S41, under the condition of grid imbalance, harmonic components appear on the DC bus, which aggravates the harmonic distortion of the grid current, and when the U-phase voltage drops, the three-phase grid voltage after the fault is expressed as: ， wherein is the drop coefficient, is the fundamental frequency of the grid input voltage, is the effective value of the grid input voltage of the non-dropped phase, , and are the three-phase grid input voltage, the conduction angle of the rectifier bridge diodes deviates from the balanced operating state when the U-phase voltage dips, this deviation leads to a significant distortion of the rectified voltage waveform, the amount of deviation of the diode conduction angle is: ， wherein may be represented as: ， According to the output characteristics of the uncontrollable rectifier bridge, the rectified voltage is expressed as a periodic function of the line voltage, and its Fourier series expansion is expressed as: ， Step S42, Voltage droop of phase voltage amplitude After rectification voltage Has even function characteristics, its coefficient b n Natural zero, coefficient a0 and a n Can be expressed as: ， In After the phase voltage droop, the conduction angle of the rectifier diode is adaptively adjusted to maintain the stability of the DC link, and the grid-side Phase current And grid voltage Waveform distortion occurs, resulting in significant amplification of harmonics in the grid-side current.

7. The method for grid-side current harmonic suppression based on five-phase permanent magnet synchronous motor driving system according to claim 1, characterized in that, The specific process of step S5 is as follows: Step S51, we first process the grid-side signal, and the inverter power signal can be expressed as: ， wherein is the peak voltage, is the grid frequency, is the initial phase angle; When the power factor of the grid reaches the maximum value, the input power of the power supply can be expressed as: ， wherein is the peak value of the grid input current, the grid input power is mainly contributed by the film capacitor and the inverter, and can be expressed as: ， wherein P in is the input power, P inv is the inverter power, P f is the thin film capacitor power; In the active rectification process, the calculation formula of the DC link voltage is as follows: ， The specific expression of the power loss of the capacitor is derived as follows: ， The capacitance of the film capacitor is extremely small, and the power loss of the film capacitor is negligible, and the power of the inverter is approximately equal to the input power of the grid side as follows: ， Step S52, the acquired grid-side current signal is filtered, and then the harmonic component in the input current is calculated Formula: ， The harmonic component is subtracted from the zero value, and the result is processed by a PI regulator to obtain the correction term of the inverter power waveform The expression is as follows: ， wherein is a proportional gain of the PI controller, is an integral gain of the PI controller, inverter power signal by algebraic operations, initial inverter power signal subtracting a term for correcting the inverter power waveform , the corrected given inverter power is: ， wherein is the modified inverter power, is the reference rotational speed, is the actual rotational speed, is a simplification of the proportional gain of the PI controller, is a simplification of the integral gain of the PI controller.

8. The method for grid-side current harmonic suppression based on five-phase permanent magnet synchronous motor driving system according to claim 1, characterized in that, The specific process of step S6 is as follows: Detect the speed of the five-phase permanent magnet synchronous motor as the feedback speed of the motor. , give the speed With feedback speed The motor speed error was obtained by comparison. A PI controller is used based on the speed error. The calculation of the five-phase permanent magnet motor The shaft current, the output of the PI controller is given. shaft current .

9. The method for grid-side current harmonic suppression based on five-phase permanent magnet synchronous motor driving system according to claim 1, characterized in that, The specific process of the step S7 is: comparing the obtained feedback current component with the given reference current, sending the obtained error into a PI controller to obtain a given voltage signal in the synchronous rotating coordinate system, and obtaining a given voltage signal in the rotating orthogonal coordinate system through coordinate transformation The network-side compensation power is decoupled and injected into the motor The resonance component is offset in the shaft voltage component.

10. The method for grid-side current harmonic suppression based on five-phase permanent magnet synchronous motor driving system according to claim 1, characterized in that, The specific process of the step S7 is: inputting the obtained motor The shaft voltage signal is input into a continuous pulse width modulation module to obtain switching signals of each phase, and the obtained switching signals are input into an inverter to control the motor, so as to realize the resonance control of the electrolytic capacitor-free five-phase permanent magnet synchronous motor driving system under the grid imbalance.

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