A current conversion circuit for a motor

Abstract

The present invention provides a current conversion circuit for a motor, which relates to the technical field of motors. The circuit includes: a PI control module, which is used to take the actual induced current and the command induced current of the motor as inputs, adjust the actual induced current, and output a first voltage; a harmonic suppression module, which is connected in parallel with the PI control module, and is used to take the output torque fluctuation coefficient of the motor and a first current difference as inputs, compensate the first voltage, and output a second voltage, where the first current difference is the difference between the actual induced current and the command induced current. The current conversion circuit for the motor in the embodiment of the present invention realizes harmonic suppression by connecting a harmonic suppression module in parallel with the PI regulator of the permanent magnet synchronous motor. It solves the problem that the harmonic suppression scheme for permanent magnet synchronous motors in the prior art is difficult to be applied to electric vehicles. It can reduce the high-order harmonics in the motor current in electric vehicles, improve the driving experience, and reduce the noise of the motor.

Description

Technical Field

[0001] The present invention relates to the technical field of motors, and particularly to a current conversion circuit for a motor. Background Art

[0002] For electric vehicles, the smoothness of power output and the vehicle operation noise are important performance indicators for measuring the driving experience of passengers in the vehicle. For electric vehicles using a permanent magnet synchronous motor as the power core of the drive system, the high-order harmonics in the motor current during driving will damage the smoothness of the vehicle power output and cause noise problems at the same time. The algorithms required for harmonic suppression of permanent magnet synchronous motors are complex and have a large amount of calculation, which will greatly increase the hardware load rate of the motor controller. Limited by the hardware performance and cost of the electric vehicle motor controller, it is difficult to apply to electric vehicles. At the same time, electric vehicles need to adjust the power output of the drive system in real time according to the driver's needs, and the output of the motor is variable. Fixed-load harmonic suppression methods cannot be applied to the vehicle system. Although there are currently relatively mature solutions for harmonic suppression of permanent magnet synchronous motors, it is difficult to apply them to electric vehicles. Summary of the Invention

[0003] An embodiment of the present invention provides a current conversion circuit for a motor, which can solve the problem that the solution for harmonic suppression of a permanent magnet synchronous motor in the prior art is difficult to apply to electric vehicles.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] An embodiment of the present invention provides a current conversion circuit for a motor, including:

[0006] A PI control module, configured to use the actual induced current and the command induced current of the motor as inputs, adjust the current of the actual induced current, and output a first voltage;

[0007] A harmonic suppression module, connected in parallel with the PI control module, configured to use the output torque fluctuation coefficient and the first current difference of the motor as inputs, compensate the first voltage, and output a second voltage, where the first current difference is the difference between the actual induced current and the command induced current.

[0008] Further, the harmonic suppression module includes:

[0009] A phase compensation unit and a torque fluctuation coefficient compensation unit.

[0010] Further, the circuit further includes:

[0011] A space vector pulse width modulation module, an insulated gate bipolar transistor, and a permanent magnet synchronous motor;

[0012] The output end of the PI control module is successively connected to the space vector pulse width modulation module, the insulated gate bipolar transistor, and the permanent magnet synchronous motor.

[0013] Further, the harmonic suppression module takes the output torque fluctuation coefficient of the motor and the first current difference as inputs to compensate the first voltage, including:

[0014] Taking the output torque fluctuation coefficient and the first current difference as inputs to the objective function of the harmonic suppression module to obtain a compensation voltage;

[0015] Compensating the first voltage according to the compensation voltage.

[0016] Further, the objective function is:

[0017] U s (k) = b0·E(k) + b1·E(k - 1) + b2·E(k - 2) + a1·U s (k - 1) - a2·U s (k - 2);

[0018] Where, Us(k) represents the voltage compensation value in the k-th control period, and E(k) represents the first current difference in the k-th control period; b0, b1, b2, a1, a2 are the system parameters of the objective transfer function of the harmonic suppression module.

[0019] Further, the objective transfer function is a function obtained by discretizing the transfer function of the harmonic suppression module;

[0020] The transfer function is:

[0021]

[0022] Where, K R represents the resonance coefficient of the motor; K T represents the torque fluctuation coefficient of the motor; ω0 represents the resonance angular frequency of the motor, represents the compensation angle of the motor.

[0023] Further, the objective transfer function is:

[0024]

[0025]

[0026]

[0027] Where,

[0028] a1 = 1.999;

[0029] a2 = 1;

[0030] Wherein, T s represents the control period.

[0031] Furthermore, the torque ripple coefficient of the motor is determined by the following formula:

[0032]

[0033] Wherein, F lim is the target torque ripple parameter after restricting the torque ripple parameter of the motor; F max is the maximum value of the torque ripple parameter of the motor; F min is the minimum value of the torque ripple parameter of the motor;

[0034] The torque ripple parameter of the motor is determined by the following formula:

[0035]

[0036] Wherein, F represents the torque ripple parameter of the motor; F H (i) is the second torque signal after high-pass filtering the output torque of the motor.

[0037] Furthermore, the second torque signal is:

[0038] F H (n) = f H (n) - f H (n - 1);

[0039] Wherein, f H (n) = F L (n)K Ha -K Hb f H (n - 1); F H (n) represents the torque signal after high-pass filtering; K Ha and K Hb are high-pass filter coefficients; F L (n) is the first torque signal after second-order low-pass filtering the output torque of the motor.

[0040] Furthermore, the first torque signal is:

[0041] F L (n) = f L (n) - f L (n - 2);

[0042] Wherein, fL T(n) = e K(n) La - K Lb f L (n - 1) - K Lc f L (n - 2); T e(n) represents the motor output torque of the current control cycle; K La and K Lb and K Lc represent the filtering coefficients.

[0043] The beneficial effects of the present invention are as follows:

[0044] For the current conversion circuit of the motor in the embodiment of the present invention, harmonic suppression is achieved by connecting a harmonic suppression module in parallel to the PI regulator of the permanent magnet synchronous motor. The high gain of the harmonic suppression module at the resonance point is utilized to suppress the current harmonics. It solves the problem that the existing solutions for harmonic suppression of permanent magnet synchronous motors are difficult to be applied to electric vehicles. It can reduce the high-order harmonics in the motor current of electric vehicles, improve the smoothness of vehicle power output, thereby enhancing the driving experience and reducing the noise of the motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 represents one of the schematic structural diagrams of the current conversion circuit of the motor in the embodiment of the present invention;

[0046] Figure 2 represents the schematic structural diagram of the harmonic suppression module in the embodiment of the present invention;

[0047] Figure 3 represents another schematic structural diagram of the current conversion circuit of the motor in the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] To make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the accompanying drawings and specific embodiments. In the following description, specific details such as specific configurations and components are provided only to assist in a comprehensive understanding of the embodiments of the present invention. Therefore, those skilled in the art should clearly understand that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present invention. Additionally, descriptions of known functions and structures are omitted for clarity and conciseness.

[0049] It should be understood that the "one embodiment" or "an embodiment" mentioned throughout the specification means that the specific features, structures or characteristics related to the embodiment are included in at least one embodiment of the present invention. Therefore, the appearances of "in one embodiment" or "in an embodiment" throughout the specification do not necessarily refer to the same embodiment. In addition, these specific features, structures or characteristics can be combined in one or more embodiments in any suitable manner.

[0050] As Figure 1 shown, an embodiment of the present invention provides a current conversion circuit for a motor, including:

[0051] A PI control module, which uses the actual induced current and the commanded induced current of the motor as inputs, adjusts the current of the actual induced current, and outputs a first voltage;

[0052] A harmonic suppression module HS, which is connected in parallel with the PI control module, uses the output torque fluctuation coefficient of the motor and the first current difference as inputs, compensates the first voltage, and outputs a second voltage, where the first current difference is the difference between the actual induced current and the commanded induced current.

[0053] Optionally, the actual induced current includes the actual induced current i d on the d-axis and the actual induced current i q on the q-axis;

[0054] In the synchronous rotating d-q axis synchronous coordinate system, the voltage equations of the d-axis and q-axis of a permanent magnet synchronous motor can be expressed as:

[0055]

[0056] where, u d represents the d-axis voltage; u q represents the q-axis voltage; R s represents the stator winding resistance; L d represents the d-axis inductance; L q represents the q-axis inductance; Ψ s represents the magnetic flux linkage of the permanent magnet of the motor rotor; ω e represents the electrical angular velocity.

[0057] Optionally, the harmonic suppression module is a resonant controller.

[0058] It should be noted that when the motor operates at a stable speed, the motor phase current and flux linkage only contain fundamental components, and the d-axis and q-axis currents and voltages are direct currents. In fact, due to the non-linear factors of the inverter and the uneven air-gap magnetic field inside the motor, the three-phase stator current contains a large number of harmonics.

[0059] The current conversion circuit of the motor in the embodiment of the present invention realizes harmonic suppression by connecting a harmonic suppression module in parallel with the PI regulators of the d-axis and q-axis current loops in the vector control of the permanent magnet synchronous motor, and uses the high gain of the harmonic suppression module at the resonance point to suppress current harmonics. It solves the problem that the harmonic suppression scheme for permanent magnet synchronous motors in the prior art is difficult to be applied to electric vehicles. It can reduce the high-order harmonics in the motor current in the electric vehicle, improve the smoothness of the vehicle power output, thereby improving the driving experience and reducing the noise of the motor.

[0060] Optionally, the harmonic suppression module includes:

[0061] A phase compensation unit and a torque ripple coefficient compensation unit.

[0062] It should be noted that considering the stability of the current conversion circuit, the harmonic suppression module has the functions of phase angle compensation and torque ripple coefficient compensation.

[0063] For the current conversion circuit of the motor in the embodiment of the present invention, considering the feasibility of the control method in actual engineering applications and ensuring the stability of the system when the resonance frequency is relatively high, the phase angle compensation is added to the harmonic suppression module, and at the same time, it is discretized through bilinear transformation. Finally, the compensation values of the d-axis and q-axis voltages are calculated with a small amount of computation, which will not significantly increase the hardware load rate of the motor while meeting the control performance, so that this method has good engineering application value.

[0064] Optionally, the transfer function of the harmonic suppression module is:

[0065]

[0066] where K R represents the resonance coefficient of the motor; K T represents the torque ripple coefficient of the motor; ω0 represents the resonance angular frequency of the motor, represents the compensation angle of the motor.

[0067] Optionally, the torque ripple coefficient of the motor is used to solve the problem that the overall control effect deteriorates due to the excitation of other order harmonics during the harmonic suppression process.

[0068] In an embodiment of the present invention, it is defined that the input and output of the harmonic suppression module are u and y respectively. Then, the harmonic suppression module based on phase and torque ripple coefficient compensation is as Figure 2 shown. The harmonic suppression module is a continuous system. In order to apply this harmonic suppression module to an embedded digital motor controller, it is necessary to discretize the transfer function to obtain the target transfer function, and at the same time ensure the resonance frequency accuracy after discretization and the stability of the discrete control system.

[0069] Optionally, the target transfer function is:

[0070]

[0071]

[0072]

[0073] where

[0074] a1 = 1.999;

[0075] a2 = 1;

[0076] where T s represents the control period; b0, b1, b2, a1, a2 are the system parameters of the target transfer function of the harmonic suppression module; ω0 represents the resonant angular frequency.

[0077] In an embodiment of the present invention, taking the d-axis as an example, the input of the harmonic suppression module is the difference between the d-axis current command and the actual d-axis current, and this difference is defined as E, and the output corresponds to Figure 1 the d-axis voltage compensation value U ds in, then the expression of the d-axis voltage compensation value in the k-th control period is as follows:

[0078] U s (k) = b0·E(k) + b1·E(k - 1) + b2·E(k - 2) + a1·U s (k - 1) - a2·U s (k - 2);

[0079] where Us(k) represents the voltage compensation value in the k-th control period, and E(k) represents the first current difference in the k-th control period; b0, b1, b2, a1, a2 are the system parameters of the target transfer function of the harmonic suppression module.

[0080] An electric vehicle itself is a complex non-linear system. In the actual control process, considering that the harmonic suppression module may excite other order harmonics due to different vehicle operating states while solving specific order harmonics, thus destroying the driving experience of the vehicle. To solve this problem, the present invention introduces the driving motor output torque fluctuation coefficient K T . In the harmonic suppression method provided by the present invention, the d-q axis voltage compensation amount of the harmonic suppression module is adaptively adjusted through the torque fluctuation coefficient. When it is detected that the torque fluctuation degree increases, the d-q axis voltage compensation value is reduced to avoid the problem of deteriorating the overall control effect due to harmonic suppression control.

[0081] Optionally, asFigure 3 As shown, the circuit further includes:

[0082] a space vector pulse width modulation module, an insulated gate bipolar transistor (IGBT), and a permanent magnet synchronous motor (PMSM);

[0083] The output end of the PI control module is sequentially connected to the space vector pulse width modulation module, the insulated gate bipolar transistor, and the permanent magnet synchronous motor.

[0084] Optionally, the circuit further includes a rotor position sensor.

[0085] i d * and i q * represents the given d-q axis current command, which is determined by the maximum torque current ratio control, the maximum torque voltage ratio control, and the field weakening control according to the required torque of the vehicle at that time and the state of the drive system (how to determine the d and q axis current commands does not belong to the content of the present invention); the three-phase currents i A 、i B 、i C of the permanent magnet synchronous motor are transformed through two coordinate transformations (Clark transformation, Park transformation) to obtain the actual d-q axis currents i d and i q ; the difference between the d-q axis command current and the actual current is used as the input of the PI controller for current loop regulation, aiming to make the actual output d-q axis currents of the motor consistent with the command current through the PI control module; the initial values U d and U q of the d-q axis voltage commands are obtained through two PI control modules, and then the compensation voltages U ds and U qs are added respectively to obtain the final d-q axis voltage commands U d * and U q *; U d * and U q * are transformed through coordinate transformation and then the control signals of the IGBT module are obtained through space vector pulse width modulation. By controlling the conduction states of the U, V, and W three-phase bridge arms of the IGBT module, currents (i A 、i B 、i C ) are generated in the three-phase windings of the motor under the action of the constant DC bus voltage UDC at the input end of the motor, so that the motor outputs the expected torque.

[0086] In addition to the above, considering the practical problem that the harmonic suppression method may exacerbate other order harmonics while solving specific order harmonics, the present invention introduces the concept of the output torque fluctuation coefficient of the drive motor. By performing band-pass filtering on the output torque of the motor, the pulsation condition of the torque is obtained and the torque fluctuation coefficient is calculated. Then, the torque fluctuation coefficient is used to adaptively adjust the compensation amount of the harmonic suppression control, and the intervention degree of the harmonic suppression control is controlled, so as to avoid deteriorating the overall control effect due to the harmonic suppression control.

[0087] Optionally, the output torque of the motor is determined according to the DC bus voltage at the input end of the motor;

[0088] The output torque is:

[0089] T e = 1.5·p·[(L d - L q )·i d ·i q + ψ s ·i q ;

[0090] The first output torque is filtered to obtain a torque pulsation parameter F;

[0091] The torque fluctuation coefficient is determined according to the torque pulsation parameter;

[0092] Among them, T e represents the output torque of the motor; p represents the number of pole pairs of the motor; L d and L q represent the d-axis and q-axis inductances; i d and i q represent the d-axis and q-axis actual currents; Ψ s represents the permanent magnet flux linkage of the motor rotor.

[0093] The present invention filters the output torque of the motor through a band-pass filter to extract the pulsation condition of the motor torque in a specified frequency range interval. In the design of the band-pass filter, an embodiment of the present invention is implemented in a series manner of a second-order low-pass filter and a first-order high-pass filter. The motor torque signal is first subjected to second-order low-pass filtering, and then first-order high-pass filtering. After the above two steps, the unexpected disturbance signals in a fixed frequency interval are screened out.

[0094] Optionally, the torque pulsation parameter of the motor is determined by the following formula:

[0095]

[0096] Among them, F represents the torque pulsation parameter of the motor; F H(i) The first torque signal after high-pass filtering the output torque of the motor.

[0097] Optionally, the first torque signal is obtained by performing a second-order low-pass filtering process on the output torque of the motor;

[0098] Perform a first-order high-pass filtering process on the first torque signal to obtain the second torque signal.

[0099] Optionally, the first torque signal is:

[0100] F L (n) = f L (n) - f L (n - 2);

[0101] where f L (n) = T e (n)K La -K Lb f L (n - 1) - K Lc f L (n - 2); F L (n) is the first torque signal after performing a second-order low-pass filtering process on the output torque of the motor; T e(n) represents the motor output torque of the current control cycle; K La 、K Lb and K Lc represent filter coefficients for adjusting the cut-off frequency of the low-pass filter.

[0102] Optionally, the first torque signal is:

[0103] F H (n) = f H (n) - f H (n - 1);

[0104] where f H (n) = F L (n)K Ha -K Hb f H (n - 1); F H (n) represents the second torque signal; K Ha and K Hb are high-pass filter coefficients for adjusting the cut-off frequency of the high-pass filter; the motor output torque obtained through band-pass filtering no longer contains low-frequency and high-frequency signals. Therefore, in an ideal situation, F H should be 0. However, if there is torque pulsation, F will increase sharply as the degree of torque pulsation intensifies. Therefore, it is necessary to limit the torque pulsation parameter F within a reasonable range.

[0105] Specifically,

[0106] F lim is the target torque ripple parameter after the torque ripple parameter of the motor is restricted; F max is the maximum value of the torque ripple parameter of the motor, and F max > 0; F min is the minimum value of the torque ripple parameter of the motor, and F min > 0.

[0107] Optionally, the torque fluctuation coefficient is calculated through normalization processing. Specifically:

[0108]

[0109] In an embodiment of the present invention, K T linearly changes within the range of [0, 1] as the torque ripple degree varies. When F min reaches F max , at this time K T = 0. In this case, considering the aggravation of the torque ripple degree caused by harmonic suppression, the harmonic suppression is exited to prevent the overall control effect from deteriorating due to harmonic suppression control; when F lim decreases to F min , K T = 1. At this time, the harmonic suppression control does not cause unexpected torque ripple, that is, the torque ripple situation remains within a reasonable range. In this case, 100% harmonic suppression control is executed.

[0110] Optionally, the harmonic suppression module takes the output torque fluctuation coefficient and the first current difference of the motor as inputs and compensates the first voltage, including:

[0111] Taking the output torque fluctuation coefficient and the first current difference as inputs of the objective function of the harmonic suppression module to obtain a compensation voltage;

[0112] Compensating the first voltage according to the compensation voltage.

[0113] In an embodiment of the present invention, for a permanent magnet synchronous motor, ideally, the three-phase stator current has half-wave symmetry, so there are even harmonics. If the three-phase windings are connected in star, without a neutral line and with a symmetric structure, there are no harmonics that are integer multiples of 3. Therefore, in the permanent magnet synchronous motor control system, there are only current harmonics of order 6k±1 (k = 1, 2...), where the current of order 6k - 1 is the negative sequence current and the current of order 6k + 1 is the positive sequence current. For a vehicle system, the main harmonics of the stator current are the 5th, 7th, 11th, and 13th harmonics, among which the 5th and 7th harmonics have a greater impact. Therefore, mainly the 5th and 7th harmonics are suppressed.

[0114] The above are the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements are also within the protection scope of the present invention.

Claims

1. A current conversion circuit of a motor, characterized in that, Including: A PI control module, which takes the actual induced current and the commanded induced current of the motor as inputs, adjusts the actual induced current, and outputs a first voltage; A harmonic suppression module, which is connected in parallel with the PI control module, takes the output torque fluctuation coefficient and the first current difference of the motor as inputs, compensates the first voltage, and outputs a second voltage, where the first current difference is the difference between the actual induced current and the commanded induced current; The harmonic suppression module takes the output torque fluctuation coefficient and the first current difference of the motor as inputs to compensate the first voltage, including: Taking the output torque fluctuation coefficient and the first current difference as inputs of the objective function of the harmonic suppression module to obtain a compensation voltage; Compensating the first voltage according to the compensation voltage; The objective function is: U s U(k) = b0·E(k) + b1·E(k - 1) + b2·E(k - 2) + a1·U s (k - 1) - a2·U s (k - 2); where Us(k) represents the voltage compensation value in the kth control cycle, and E(k) represents the first current difference in the kth control cycle; b0, b1, b2, a1, a2 are the system parameters of the objective transfer function of the harmonic suppression module.

2. The current conversion circuit of the motor according to claim 1, wherein The harmonic suppression module includes: A phase compensation unit and a torque fluctuation coefficient compensation unit.

3. The current conversion circuit of the motor according to claim 1, characterized in that, The circuit further includes: A space vector pulse width modulation module, an insulated gate bipolar transistor, and a permanent magnet synchronous motor; The output end of the PI control module is sequentially connected to the space vector pulse width modulation module, the insulated gate bipolar transistor, and the permanent magnet synchronous motor.

4. The current conversion circuit of the motor according to claim 1, characterized in that, The objective transfer function is a function obtained by discretizing the transfer function of the harmonic suppression module; The transfer function is: Among them, K R represents the resonance coefficient of the motor; K T represents the torque ripple coefficient of the motor; ω0 represents the resonance angular frequency of the motor, represents the compensation angle of the motor.

5. The current conversion circuit of the motor according to claim 1 or 4, characterized in that, The objective transfer function is: Among them, a1＝1.999； a2＝1； Among them, T s represents the control period.

6. The current conversion circuit of the motor according to claim 5, characterized in that The torque fluctuation coefficient of the motor is determined by the following formula: Among them, F lim is the target torque ripple parameter after the torque ripple parameter of the motor is restricted; F max is the maximum value of the torque ripple parameter of the motor; F min is the minimum value of the torque ripple parameter of the motor; The torque ripple parameter of the motor is determined by the following formula: where F represents the torque ripple parameter of the motor; F H (i) is the second torque signal after high-pass filtering the output torque of the motor.

7. The current conversion circuit of the motor according to claim 6, characterized in that The second torque signal is: F H f(n) = f H f(n) - f H f(n - 1); Among them, f H (n)=F L (n)K Ha -K Hb f H (n - 1); F H (n) represents the torque signal after high - pass filtering; K Ha and K Hb are high - pass filter coefficients; F L (n) is the first torque signal after second - order low - pass filtering of the output torque of the motor.

8. The current conversion circuit of the motor according to claim 7, characterized in that, The first torque signal is: F L f(n) = f L f(n) - f L (n - 2); Among them, f L (n) = T e (n)K La -K Lb f L (n - 1)-K Lc f L (n - 2); T e(n) represents the motor output torque of the current control cycle; K La , K Lb and K Lc represent the filtering coefficients.

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