Field weakening control method and system of permanent magnet synchronous motor and vehicle

Abstract

The invention provides a field weakening control method and system of a permanent magnet synchronous motor and a vehicle, and relates to the technical field of automobiles. The method comprises the following steps: performing feedforward control according to a voltage signal of the permanent magnet synchronous motor to obtain a feedforward current value; determining a current voltage utilization rate according to a current direct-axis voltage value and a current quadrature-axis voltage value of the permanent magnet synchronous motor, and determining a feedback current value according to a target voltage utilization rate and the current voltage utilization rate; determining a stator direct-axis current request value according to the feedforward current value and the feedback current value, and determining a stator quadrature-axis current request value according to the request torque value and the stator direct-axis current request value, and the direct-axis voltage value and the quadrature-axis voltage value are updated based on the stator direct-axis current request value and the stator quadrature-axis current request value respectively, and the permanent magnet synchronous motor is driven to operate based on the updated direct-axis voltage value and the updated quadrature-axis voltage value. The field weakening control efficiency is improved.

Description

Technical Field

[0001] The present disclosure relates to the technical field of automobiles, and particularly to a field-weakening control method, system and vehicle for a permanent magnet synchronous motor. Background Art

[0002] The permanent magnet synchronous motor (PMSM) has the advantages of high power density, high efficiency, small pulsating torque and a relatively wide field-weakening speed regulation range, and is the best choice for new energy drive motors. The control of the permanent magnet synchronous motor can be divided into cross-torque control below the base speed and constant power control above the base speed.

[0003] As the speed of the permanent magnet synchronous motor increases, since the DC side voltage of the inverter reaches the maximum value and causes saturation of the current regulator, in order to obtain a wider speed regulation range and achieve constant power speed regulation during high-speed operation above the base speed, field-weakening control of the permanent magnet synchronous motor is required. Summary of the Invention

[0004] In view of this, the embodiments of the present disclosure provide a field-weakening control method, system and vehicle for a permanent magnet synchronous motor, which can improve the field-weakening control efficiency of the permanent magnet synchronous motor.

[0005] In a first aspect, the present disclosure provides a field-weakening control method for a permanent magnet synchronous motor, including:

[0006] Performing feedforward control according to the voltage signal of the permanent magnet synchronous motor to obtain a feedforward current value for field-weakening control;

[0007] Determining the current voltage utilization rate according to the current direct-axis voltage value and quadrature-axis voltage value of the permanent magnet synchronous motor, and determining a feedback current value for field-weakening control according to the target voltage utilization rate and the current voltage utilization rate;

[0008] Determining a stator direct-axis current request value according to the feedforward current value and the feedback current value, and determining a stator quadrature-axis current request value according to the requested torque value and the stator direct-axis current request value, respectively updating the direct-axis voltage value and the quadrature-axis voltage value based on the stator direct-axis current request value and the stator quadrature-axis current request value, and driving the permanent magnet synchronous motor to operate based on the updated direct-axis voltage value and quadrature-axis voltage value.

[0009] In a second aspect, the present disclosure provides a field-weakening control system for a permanent magnet synchronous motor, including:

[0010] A field-weakening feedforward module for performing feedforward control according to the voltage signal of the permanent magnet synchronous motor to obtain a feedforward current value for field-weakening control;

[0011] A field-weakening feedback module is configured to determine a current voltage utilization rate according to a current direct-axis voltage value and a quadrature-axis voltage value of the permanent magnet synchronous motor, and determine a feedback current value for field-weakening control according to a target voltage utilization rate and the current voltage utilization rate;

[0012] A driving module is configured to determine a stator direct-axis current request value according to the feedforward current value and the feedback current value, and determine a stator quadrature-axis current request value according to the requested torque value and the stator direct-axis current request value. The direct-axis voltage value and the quadrature-axis voltage value are updated respectively based on the stator direct-axis current request value and the stator quadrature-axis current request value, and the permanent magnet synchronous motor is driven to operate based on the updated direct-axis voltage value and quadrature-axis voltage value.

[0013] In a third aspect, the present disclosure provides a vehicle, including a permanent magnet synchronous motor and the control system of the permanent magnet synchronous motor described in the second aspect.

[0014] Optionally, the computer program may be stored in a readable storage medium or the cloud of a computer device; a processor of the computer device reads the computer program from the readable storage medium or the cloud.

[0015] In the embodiments provided by the present disclosure, a current voltage utilization rate is determined according to a current direct-axis voltage value and a quadrature-axis voltage value of the permanent magnet synchronous motor, and a feedback current value for field-weakening control is determined according to a target voltage utilization rate and the current voltage utilization rate, so that the target voltage utilization rate is used as the target during field-weakening control, ensuring the field-weakening control efficiency. Moreover, feedforward control is performed according to the voltage signal of the permanent magnet synchronous motor to obtain a feedforward current value for field-weakening control. A stator direct-axis current request value is determined according to the feedforward current value and the feedback current value, and a stator quadrature-axis current request value is determined according to the requested torque value and the stator direct-axis current request value. The direct-axis voltage value and the quadrature-axis voltage value are updated respectively based on the stator direct-axis current request value and the stator quadrature-axis current request value, and the permanent magnet synchronous motor is driven to operate based on the updated direct-axis voltage value and quadrature-axis voltage value. Therefore, during the field-weakening control process, the feedforward current value is superimposed on the feedback current value, so that the achievement rate of the target voltage utilization rate is accelerated through feedforward, further improving the field-weakening control efficiency. Description of the Drawings

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present disclosure. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0017] Figure 1 The figure shows a schematic structural diagram of a dual-motor hybrid power system in the related art;

[0018] Figure 2 The figure shows a schematic diagram of the field-weakening control method for a permanent magnet synchronous motor in an embodiment of the present disclosure;

[0019] Figure 3 The figure shows a schematic block diagram of the working principle of a phase-locked loop in the related art;

[0020] Figure 4 The figure shows a block diagram of the structure of a phase-locked loop in an embodiment of the present disclosure;

[0021] Figure 5 The figure shows a schematic structural diagram of a PID regulator in an embodiment of the present disclosure;

[0022] Figure 6 The figure shows a schematic diagram of the current circle and voltage circle limitations in an embodiment of the present disclosure;

[0023] Figure 7 The figure shows a schematic diagram of the field-weakening control process in an embodiment of the present disclosure;

[0024] Figure 8 The figure shows a schematic diagram of the field-weakening control system for a permanent magnet synchronous motor in an embodiment of the present disclosure. Detailed implementation manners

[0025] Next, the technical solutions in the embodiments of the present disclosure will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present disclosure without creative efforts shall fall within the protection scope of the present disclosure.

[0026] Without conflict, the embodiments of the present disclosure and the features in the embodiments can be combined with each other.

[0027] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0028] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. As used herein, the singular forms "a" and "the" are also intended to include the plural forms unless the context clearly indicates otherwise. It will also be understood that when the terms "comprising" and / or "consisting of" are used in this specification, the specified features, wholes, steps, operations, elements, and / or components are present, but one or more other features, wholes, steps, operations, elements, components, and / or groups thereof are not excluded. Terms such as "connected" or "coupled" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect.

[0029] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art. It will also be understood that terms such as those defined in common dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted as having an idealized or overly formal meaning unless expressly so defined herein.

[0030] Overview

[0031] With the increasingly strict requirements for vehicle fuel consumption and emissions, as well as the development of electrification systems, hybrid technology is the key to achieving energy conservation and emissions reduction. To meet the emission requirements, vehicle manufacturers and component suppliers are seeking solutions. However, the battery technology in pure electric vehicle systems is currently complex and costly, and hybrid systems are being vigorously promoted due to their relative advantages.

[0032] Figure 1 The structure diagram of a dual-motor hybrid system is shown. In a dual-motor hybrid system, the permanent magnet synchronous motor has three modes, namely, pure electric mode, series mode, and parallel mode. In the pure electric mode, the dual-motor hybrid system uses the power provided by the motor to drive the vehicle, and the internal combustion engine (denoted as ENG) is in the off state and does not directly participate in driving. Therefore, fuel consumption and emissions can be minimized, which is suitable for low-speed driving. In the series mode, the clutch (C0) is not engaged, and the internal combustion engine serves as an energy source to drive the generator (denoted as P1) to charge the battery (Battery), and the motor (denoted as P2) uses the electrical energy of the battery to drive the wheels. The overall efficiency of the series mode is relatively low. In the parallel mode, the clutch (C0) is engaged, and the internal combustion engine can directly drive the wheels. The advantage of the parallel mode lies in efficient energy utilization and diverse driving modes.

[0033] As the speed of the permanent magnet synchronous motor increases, since the saturation of the current regulator will be caused after the DC side voltage of the inverter reaches the maximum value, in order to obtain a wide speed regulation range and achieve constant power speed regulation during high-speed operation above the base speed, field weakening control of the motor is required.

[0034] The idea of field-weakening control of permanent magnet synchronous motors is derived from the field control of separately excited DC motors. When the terminal voltage of a separately excited DC motor reaches its maximum value, the motor can only operate at a constant power at a higher speed by reducing the excitation current of the motor, changing the excitation magnetic flux, and ensuring voltage balance. That is to say, a separately excited DC motor can achieve the purpose of field-weakening speed increase by reducing the excitation current. For a permanent magnet synchronous motor, the excitation magnetomotive force is generated by permanent magnets and cannot be adjusted. It can only achieve the purpose of field-weakening speed increase by adjusting the stator current, that is, increasing the direct-axis demagnetizing current component of the stator to maintain voltage balance during high-speed operation. As the speed increases, the back electromotive force of the stator increases. When the back electromotive force is higher than the maximum voltage that the inverter can provide at its end, the inverter cannot feed energy into the motor, and at this time, the motor cannot continue to operate at high speed. The basic idea of field-weakening control is that when the speed exceeds the rated speed, due to the limitation of the maximum voltage output by the frequency converter, the voltage output value of the current loop quickly reaches saturation. To enable the motor to continue to increase its speed, it is necessary to increase the reverse current id (i.e., the direct-axis demagnetizing current component of the stator) and make the current loop exit the saturation state. It can be seen that when the stator voltage reaches its maximum value, by controlling and increasing the field-weakening speed, the stator quadrature-axis current component iq can be reduced, and at the same time, the amplitude of the direct-axis demagnetizing current component id of the stator can be increased, thereby achieving the purpose of increasing the speed.

[0035] During the field-weakening control process, increasing the direct-axis current will have a canceling effect on the magnetic flux of the permanent magnet, thereby reducing the total magnetic flux, further reducing the back electromotive force, and enabling the motor to operate at a higher speed.

[0036] Based on the idea of field-weakening control, the embodiments of the present disclosure provide a field-weakening control method for a permanent magnet synchronous motor, which can perform field-weakening control with the goal of improving voltage utilization and improving system control performance. This method can be applied to the field-weakening control of permanent magnet synchronous motors in vehicles.

[0037] Exemplary Method

[0038] The field-weakening control method for a permanent magnet synchronous motor provided by the embodiments of the present disclosure, as Figure 2 shown, mainly includes the following steps:

[0039] Step 201, perform feedforward control according to the voltage signal of the permanent magnet synchronous motor to obtain a feedforward current value for field-weakening control.

[0040] In some embodiments, the feedforward control is performed based on the voltage signal of the permanent magnet synchronous motor to obtain a feedforward current value for field weakening control, including: generating a current rotational speed value of the permanent magnet synchronous motor according to the voltage signal of the permanent magnet synchronous motor; determining a feedforward current value for field weakening control according to the bus voltage value of the permanent magnet synchronous motor, the current rotational speed value, and the requested torque value.

[0041] The voltage signal of the permanent magnet synchronous motor can be collected from the permanent magnet synchronous motor through an eddy current sensor.

[0042] In some embodiments, the voltage signal of the permanent magnet synchronous motor includes a sine voltage signal and a cosine voltage signal. The generating of the current rotational speed value of the permanent magnet synchronous motor according to the voltage signal of the permanent magnet synchronous motor includes: collecting the sine voltage signal and the cosine voltage signal of the permanent magnet synchronous motor, determining a current rotor angle value according to the sine voltage signal and the cosine voltage signal, subtracting the current rotor angle value from the rotor angle value output by the phase-locked loop in the previous period, and inputting the obtained difference into the phase-locked loop to obtain the current rotational speed value of the permanent magnet synchronous motor output by the phase-locked loop.

[0043] The phase-locked loop also outputs a motor angle value of the permanent magnet synchronous motor, denoted as θ.

[0044] In some embodiments, the method further includes: subtracting the current rotor angle value from the rotor angle value output by the phase-locked loop in the previous period delayed by one cycle duration, and in the case where the obtained difference is greater than a set value for a certain duration, resetting the rotor angle value output by the phase-locked loop by using the rotor angle value determined according to the latest collected sine voltage signal and cosine voltage signal.

[0045] Here, the current rotor angle value θ(t) is subtracted from the rotor angle value calculated by the phase-locked loop in the previous period to obtain a difference, and proportional-integral-integral (PII) control is performed to obtain the rotational speed and the angle is obtained after integration delayed by one cycle and input to the input end for closed-loop control. This can ensure that the angle of the phase-locked loop is one cycle ahead of the original position. At the same time, the difference between the angle calculated by the phase-locked loop and the rotor angle value θ(t) collected by the eddy current sensor is judged. When the difference is greater than the set value and lasts for more than a certain time threshold, the rotor angle value output by the phase-locked loop is reset to the rotor angle value θ(t) calculated after the latest collection by the eddy current sensor.

[0046] Figure 3The figure shows a schematic diagram of the working principle of a phase-locked loop (PLL). The PLL structure consists of three parts: a phase detector (PD), a loop filter (LF), and a voltage-controlled oscillator (VCO). The role of the PD section is to calculate and output the equivalent position error between the input signal and the output signal to the LF section. The frequency of the output signal is obtained through the LF section, and the output obtained by integrating this frequency through the VCO section is the phase angle of the output signal. Once the frequency of the output signal tracks the frequency of the input signal, the phase error between the two will eventually converge to zero, and at this time, the PLL has completed the phase-locking function. In the open-loop transfer function of the LF section, the total number of poles of the function is called the order, and the number of poles at the origin is called the type (class). Therefore, generally speaking, under the condition that the VCO section is an integral section, the order and type number of the PLL are both increased by 1 based on the LF section. When the phase-locked loop (Phase-locked Loop, PLL) is applied in different fields, its structural manifestation is different. It is widely used in the field of motor control and is usually used to estimate the motor speed and rotor angle value (i.e., rotor position).

[0047] In the embodiments of the present disclosure, the structural block diagram of the PLL is as shown in Figure 4 shown. The loop filter LF used is a PII controller. This PLL is a typical third-order type-3 control system. The closed-loop transfer function of the PLL can be expressed as Equation 1:

[0048]

[0049] In the formula, k p , k i , k ii are the proportional gain, integral gain, and quadratic integral gain of the quadrature PLL in sequence, and τ is the delay time. For example, the delay time is set to one period of 100 μs.

[0050] The input of the PLL is the sine voltage signal and cosine voltage signal collected by the eddy current sensor. The rotor angle value θ is obtained through the arctangent operation of Equation 2:

[0051]

[0052] Among them, U sin is the sine voltage signal collected by the eddy current sensor, and U cos is the cosine voltage signal collected by the eddy current sensor.

[0053] The rotor angle value of the motor is estimated using the PLL After a delay of τ, it is subtracted from the currently calculated rotor angle value to obtain the position error, which is expressed as Equation 3:

[0054]

[0055] The phase - locked loop is gradually phase - locked by controlling the position error.

[0056] The PII controller adopted by the LF part obtains the rotational speed estimation value ω(t) based on the position error obtained by the PD part. After integrating the rotational speed estimation value by the VCO, the rotor angle value is obtained. Differentiating the rotor angle value to obtain the current rotational speed value of the permanent - magnet synchronous motor.

[0057] In some embodiments, determining the feed - forward current value for field - weakening control according to the bus voltage value, the current rotational speed value, and the requested torque value of the permanent - magnet synchronous motor includes: determining the ratio of the bus voltage value and the current rotational speed value of the permanent - magnet synchronous motor to obtain the target voltage - frequency ratio; obtaining the tabular data corresponding to the target voltage utilization rate, where the tabular data includes the mapping relationship among the voltage - frequency ratio, the torque value, and the direct - axis feed - forward current value; looking up the tabular data according to the target voltage - frequency ratio and the requested torque value to obtain the target direct - axis feed - forward current value; multiplying the target direct - axis feed - forward current value by the feed - forward proportionality coefficient to obtain the feed - forward current value for field - weakening control. In the embodiments of the present disclosure, the tabular data used for feed - forward look - up is pre - determined using real motor data, which can achieve fast transient response and has a significant field - weakening effect. In the selection of the look - up table scheme, compared with data such as flux linkage parameters, rotational speed, and torque, it is easier to calibrate, more intuitive and understandable, and has higher engineering application value.

[0058] In the existing related technologies, the influence of bus voltage change on the calibration parameter accuracy is usually not considered. If multiple look - up tables under different bus voltages are used, although the accuracy can be improved, it will lead to a large increase in data volume, the calibration process becomes complex, and the switching strategy between different tables will also become more cumbersome. To solve the influence of bus voltage change on the calibration parameters, in the embodiments of the present disclosure, following the equal voltage - frequency ratio principle, the field - weakening feed - forward is designed based on the voltage - frequency ratio. By using the off - line calculation method, the tabular data corresponding to the voltage - frequency ratio and the requested torque value of the target voltage utilization rate (assuming a value of 1.05) is obtained. The tabular data includes three - dimensional data, namely the voltage - frequency ratio, the requested torque value, and the feed - forward current value. The target direct - axis (i.e., d - axis) feed - forward current value is directly obtained by looking up the tabular data.

[0059] The constant V / f principle means that when performing variable-frequency speed regulation, a constant V / f control method is adopted. The main reason is that when regulating speed downward from the base frequency, it is necessary to keep the magnetic flux constant. According to the formula U = E = 4.44 * f * N * Φ, it can be seen that the magnetic flux Φ is proportional to the electromotive force E / f (approximately proportional to the bus voltage U / f). Therefore, by keeping the ratio of E / f (U / f) constant, the magnetic flux can be ensured to remain unchanged, where N is the number of turns of the coil and is regarded as a constant here. The constant V / f and the direct-axis feedforward current value corresponding to the same requested torque value are the same. In the embodiments of the present disclosure, a data table is pre-formulated using the constant V / f principle, so that the data in the same table can be queried under different voltages. In the existing related technologies, when querying a fixed table based on the bus voltage, speed, and torque command, it is necessary to set corresponding tables for different bus voltages, which requires looking up multiple tables under different voltages. The table data formulated by the present disclosure according to the constant V / f significantly reduces the number of tables to be looked up, reduces the difficulty of looking up tables, and improves the efficiency.

[0060] When formulating the table data, considering the influence of the magnitude of different bus voltages on the d-axis feedforward current value, the lowest voltage value is used to convert different bus voltages. When looking for the feedforward current value at a certain speed and a certain requested torque value under a certain bus voltage, it can be equivalent to the operating point of the same requested torque value under the same V / f ratio, and the two have the same feedforward current value. In this way, only the table data needs to be made for the data under the lowest bus voltage, greatly reducing the amount of motor calibration data required.

[0061] The horizontal axis of the table data is the requested torque value, and the vertical axis is the V / f ratio. To more conveniently follow the constant V / f principle, the V / f ratio can be converted into the ratio of the mechanical speed to the bus voltage. In this way, the look-up table can more directly reflect the control requirements of the motor under different speeds and voltages. During the process of formulating the table data, first, a set of reference data is obtained through the sweep-point data of the target voltage utilization rate (assumed to be 1.05). The sweep-point data is obtained by testing the motor under different speeds, torques, and voltage conditions and recording the actual response of the motor. The reference data is the direct-axis feedforward current value obtained according to the recorded actual response of the motor. Secondly, for safety reasons, this reference data is multiplied by 0.9 as the actual direct-axis fixed feedforward current value for output. This method can ensure that the motor can obtain sufficient feedforward current in most cases, while leaving a certain margin to prevent overload. For parts not covered by the feedforward look-up table or parts that require more refined adjustment, a PID regulator can be used to further control the current and torque output of the motor. The PID regulator monitors the difference between the actual output and the desired output of the motor and adjusts the control parameters accordingly to achieve more precise control.

[0062] Step 202: Determine the current voltage utilization rate according to the current direct-axis voltage value and quadrature-axis voltage value of the permanent magnet synchronous motor, and determine the feedback current value for field weakening control according to the target voltage utilization rate and the current voltage utilization rate.

[0063] In some embodiments, the determining the feedback current value for field weakening control according to the target voltage utilization rate and the current voltage utilization rate includes: determining the difference between the current voltage utilization rate and the target voltage utilization rate; inputting the difference into an integral regulator to obtain the feedback current value for field weakening control output by the integral regulator.

[0064] The integral coefficient of the integral regulator (also known as the I regulator), denoted as k i , is obtained by looking up a mapping relationship table according to the requested torque value and the current speed value. The mapping relationship among the torque value, speed value, and integral coefficient is pre-stored in the mapping relationship table.

[0065] Here, the feedback current value for field weakening control is allowed to be a positive value.

[0066] As Figure 5 shown in the structural schematic diagram of the PID regulator, the PID regulator includes a proportional regulator, an integral regulator, and a derivative regulator. The formula (4) for the PID regulator to calculate the control output according to the error function e(t) is as follows:

[0067]

[0068] u(t) is the feedback current value for field weakening control. Converting the behavior of the PID controller to the frequency domain gives the transfer function, which is expressed by formula (5) as follows:

[0069]

[0070] Among them, U(s) is the Laplace transform of u(t), and E(s) is the Laplace transform of e(t). K p is the proportional coefficient, T i is the integral time constant, T d is the derivative time constant, K i =K p / T i is the integral coefficient, K d =K p *T d is the derivative coefficient.

[0071] Removing the proportional and derivative terms in formula 5 gives the I-term regulator. The allowable value ranges of the parameters of the I-term regulator are pre-configured, and the feedback current value obtained through the I-term regulator is restricted by the upper and lower limits of the allowable value ranges of these parameters.

[0072] Step 203: Determine the stator direct-axis current request value according to the feedforward current value and the feedback current value, and determine the stator quadrature-axis current request value according to the requested torque value and the stator direct-axis current request value. Update the direct-axis voltage value and the quadrature-axis voltage value respectively based on the stator direct-axis current request value and the stator quadrature-axis current request value, and drive the permanent magnet synchronous motor to operate based on the updated direct-axis voltage value and quadrature-axis voltage value.

[0073] In some embodiments, input the stator direct-axis current request value and the stator quadrature-axis current request value into a proportional-integral regulator to update the direct-axis voltage value and the quadrature-axis voltage value through the proportional-integral regulator, and drive the permanent magnet synchronous motor to operate based on the updated direct-axis voltage value and quadrature-axis voltage value.

[0074] In some embodiments, the step of determining the stator direct-axis current request value according to the feedforward current value and the feedback current value includes: adding the feedforward current value and the feedback current value to obtain a current adjustment value; determining the stator direct-axis current request value according to the current adjustment value and a control strategy.

[0075] The control strategy can be one or both of the maximum torque per ampere (MTPA) and the maximum torque per voltage (MTPV). When the control strategy includes MTPV, the final stator direct-axis current request value is not less than the limit of the current calibrated with the speed in the MTPV stage; when the control strategy includes MTPA, the final stator direct-axis current request value is not greater than the limit of the calibrated current in the MTPA stage.

[0076] In some embodiments, the control strategy includes the maximum torque per ampere and the maximum torque per voltage;

[0077] The step of determining the stator direct-axis current request value according to the current adjustment value and the control strategy includes: determining a first reference current value based on the maximum torque per ampere, and selecting the smaller value of the current adjustment value and the first reference current value; determining a second reference current value based on the maximum torque per voltage, and selecting the larger value of the smaller value and the second reference current value as the stator direct-axis current request value.

[0078] Figure 6The figure shows a schematic diagram of current circle and voltage circle limitations. When a permanent magnet synchronous motor operates in vector control, it is restricted by dual constraints of voltage and current. The voltage is restricted by the voltage limit ellipse and cannot exceed the maximum voltage that the inverter can output; the current is restricted by the current limit circle and cannot exceed the maximum current that the inverter can output. During high-speed operation, the direct-axis current is restricted by the voltage circle, and the maximum available direct-axis current of MTPV is pre-calibrated as the limit. Similarly, the minimum available direct-axis current of MTPA is pre-calibrated as the limit.

[0079] Determining a first reference current value based on MTPA includes: looking up the direct-axis current mapping table of MTPA according to the current speed value and the requested torque value to obtain the first reference current value; the direct-axis current mapping table of MTPA includes the mapping relationship among the pre-calibrated speed value, torque value, and direct-axis current value in the MTPA stage.

[0080] Determining a second reference current value based on the maximum torque voltage ratio includes: looking up the direct-axis current mapping table of MTPV according to the current speed value and the requested torque value to obtain the second reference current value; the direct-axis current mapping table of MTPV includes the mapping relationship among the pre-calibrated speed value, torque value, and direct-axis current value in the MTPV stage.

[0081] In some embodiments, determining the stator quadrature-axis current request value according to the requested torque value and the stator direct-axis current request value includes: calculating the stator quadrature-axis current request value according to the torque equation of the permanent magnet synchronous motor, and this torque equation is expressed as formula 6:

[0082] Tq=3 / 2p(ψ f iq+(Ld-Lq)idiq)) (6)

[0083] Wherein, Tq represents the electromagnetic torque, p represents the number of pole pairs of the motor, id represents the stator direct-axis current request value, iq represents the stator quadrature-axis current request value, Ld and Lq respectively represent the direct-axis inductance and the quadrature-axis inductance. ψ f represents the flux linkage coefficient, which is calculated through temperature and the requested torque value. In order to more precisely control the motor, the flux linkage coefficient is calibrated and compensated according to temperature and the requested torque value respectively. Subsequently, iq is restricted by the maximum allowable output current to keep the current amplitude within the current limit circle and the allowable current range.

[0084] In some embodiments, determining the current voltage utilization rate according to the current direct-axis voltage value and quadrature-axis voltage value of the permanent magnet synchronous motor includes:

[0085]

[0086] Wherein, R usage act ual represents the current voltage utilization rate, ud Represents the direct-axis voltage, u q Represents the quadrature-axis voltage, u dc act Represents the DC voltage.

[0087] The difference between the current voltage utilization rate and the target voltage utilization rate can be expressed as:

[0088] R usage error = R usage tar - R usage act ual (8)

[0089] Wherein, R usage error Represents the difference between the current voltage utilization rate and the target voltage utilization rate, R usage tar Represents the target voltage utilization rate, R usage act ual Represents the current voltage utilization rate.

[0090] The difference between the current voltage utilization rate and the target voltage utilization rate is subjected to I-term integral control through an I regulator to obtain a feedback current value for field-weakening control, which is expressed by the formula as follows:

[0091] id fw_i = ∫R usage error * I gain dt (9)

[0092] Wherein, id fw_i Represents the feedback current value, I gain Represents the integral coefficient.

[0093] The feedforward current value and the feedback current value are added together to obtain a current adjustment value, which is expressed as:

[0094] id final = id fw_fd + id fw_i (10)

[0095] Wherein, id final Represents the current adjustment value, id fw_fd Represents the feedforward current value.

[0096] In an exemplary embodiment, Figure 7 As shown is a schematic diagram of the field-weakening control process. The field-weakening control process includes collecting sine voltage signals and cosine voltage signals from a PMSM, calculating intermediate parameter values such as position and speed feedback signals through the sine voltage signals and cosine voltage signals, obtaining the current rotor angle value based on the intermediate parameter values, inputting the current rotor angle value into a phase-locked loop for control calculation, and using the current speed value of the permanent magnet synchronous motor output by the phase-locked loop for the field-weakening feedforward process.

[0097] During the field-weakening feedforward process, table data is looked up based on the voltage-frequency ratio and the requested torque value to obtain the target direct-axis feedforward current value, which is multiplied by the feedforward proportionality coefficient to obtain the feedforward current value for field-weakening control.

[0098] During the field-weakening feedback process, based on the current direct-axis voltage value Ud and quadrature-axis voltage value Uq, the current voltage utilization rate is calculated. The difference between the target voltage utilization rate and the current voltage utilization rate is subjected to integral (I) control. The feedback current value obtained from the I control is limited by the upper and lower limits of the allowable value ranges of the various parameters of the I regulator to obtain the feedback current value for field-weakening control.

[0099] After adding the feedforward current value and the feedback current value, the smaller value is selected from the d-axis current values in the MPTA region, and the larger value is selected from the d-axis current values in the MTPV region to obtain the final stator direct-axis current request value, which is given to the PI regulator of the direct axis to update the direct-axis voltage value Ud. Using the final stator direct-axis current request value, the magnetic flux calculated through the magnetic flux, and the requested torque value, the stator quadrature-axis current request value is calculated according to the torque equation and given to the PI regulator of the quadrature axis to update the quadrature-axis voltage value Uq. Using the updated direct-axis voltage value Ud and the updated quadrature-axis voltage value Uq, the current voltage utilization rate is updated, and the field-weakening feedback process is performed again. In summary, the field-weakening control of the permanent magnet synchronous motor is combined with the field-weakening feedforward process and the field-weakening feedback process, and the purpose of the field-weakening control process is to achieve the target voltage utilization rate, improving the field-weakening control efficiency.

[0100] In the embodiments provided by the present disclosure, the current voltage utilization rate is determined according to the current direct-axis voltage value and quadrature-axis voltage value of the permanent magnet synchronous motor, and the feedback current value for field-weakening control is determined according to the target voltage utilization rate and the current voltage utilization rate, so that the target voltage utilization rate is used as the target during field-weakening control, ensuring the field-weakening control efficiency. Moreover, feedforward control is performed based on the voltage signal of the permanent magnet synchronous motor to obtain the feedforward current value for field-weakening control. According to the feedforward current value and the feedback current value, the stator direct-axis current request value is determined, and according to the requested torque value and the stator direct-axis current request value, the stator quadrature-axis current request value is determined. The direct-axis voltage value and the quadrature-axis voltage value are updated respectively based on the stator direct-axis current request value and the stator quadrature-axis current request value, and the permanent magnet synchronous motor is driven to operate based on the updated direct-axis voltage value and quadrature-axis voltage value. Thus, during the field-weakening control process, the feedforward current value is superimposed on the feedback current value, so that the achievement rate of the target voltage utilization rate is accelerated through feedforward, further improving the field-weakening control efficiency.

[0101] It can be understood that, without violating the principle logic, the above-mentioned method embodiments disclosed in the present disclosure can be combined with each other to form combined embodiments. Due to space limitations, the present disclosure will not elaborate further. Those skilled in the art can understand that in the above method of the specific implementation manner, the specific execution order of each step should be determined according to its function and possible internal logic, and the execution order between steps is not limited to being implemented according to the step numbers.

[0102] Exemplary system

[0103] An embodiment of the present disclosure provides a field-weakening control system for a permanent magnet synchronous motor, as Figure 8 shown, mainly including:

[0104] A field-weakening feedforward module 801, configured to perform feedforward control according to the voltage signal of the permanent magnet synchronous motor to obtain a feedforward current value for field-weakening control;

[0105] A field-weakening feedback module 802, configured to determine the current voltage utilization rate according to the current direct-axis voltage value and quadrature-axis voltage value of the permanent magnet synchronous motor, and determine a feedback current value for field-weakening control according to the target voltage utilization rate and the current voltage utilization rate;

[0106] A driving module 803, configured to determine a stator direct-axis current request value according to the feedforward current value and the feedback current value, and determine a stator quadrature-axis current request value according to the requested torque value and the stator direct-axis current request value, respectively update the direct-axis voltage value and the quadrature-axis voltage value based on the stator direct-axis current request value and the stator quadrature-axis current request value, and drive the permanent magnet synchronous motor to operate based on the updated direct-axis voltage value and quadrature-axis voltage value.

[0107] Exemplary Vehicle

[0108] An embodiment of the present disclosure provides a vehicle, including a permanent magnet synchronous motor and a controller of the permanent magnet synchronous motor, where the controller is configured to execute the field-weakening control method of the permanent magnet synchronous motor.

[0109] The above are only the preferred embodiments of the present disclosure and are not intended to limit the present disclosure. Any modifications, equivalent replacements, etc. made within the spirit and principle of the present disclosure shall be included within the protection scope of the present disclosure.

Claims

1. A method for weakening magnetic field of a permanent magnet synchronous motor, characterized in that: include: Performing feedforward control according to the voltage signal of the permanent magnet synchronous motor to obtain a feedforward current value for magnetic field weakening control; Determine a current voltage utilization rate according to a current direct-axis voltage value and a quadrature-axis voltage value of the permanent magnet synchronous motor, and determine a feedback current value for magnetic field weakening control according to a target voltage utilization rate and the current voltage utilization rate; A stator direct-axis current request value is determined according to the feedforward current value and the feedback current value, and a stator quadrature-axis current request value is determined according to the requested torque value and the stator direct-axis current request value; the direct-axis voltage value and the quadrature-axis voltage value are updated based on the stator direct-axis current request value and the stator quadrature-axis current request value, respectively; and the permanent magnet synchronous motor is driven to operate based on the updated direct-axis voltage value and the quadrature-axis voltage value.

2. The method according to claim 1, characterized in that The performing feedforward control according to the voltage signal of the permanent magnet synchronous motor to obtain a feedforward current value for magnetic field weakening control includes: Generating a current speed value of the permanent magnet synchronous motor according to a voltage signal of the permanent magnet synchronous motor; A feedforward current value for magnetic field weakening control is determined according to a bus voltage value of the permanent magnet synchronous motor, the current speed value, and a requested torque value.

3. The method according to claim 2, characterized in that The voltage signal of the permanent magnet synchronous motor includes a sine voltage signal and a cosine voltage signal; Generating a current speed value of the permanent magnet synchronous motor according to the voltage signal of the permanent magnet synchronous motor includes: The sine voltage signal and the cosine voltage signal of the permanent magnet synchronous motor are collected, and the current rotor angle value is determined according to the sine voltage signal and the cosine voltage signal. The current rotor angle value is input into the phase-locked loop after the difference between the current rotor angle value and the rotor angle value output by the phase-locked loop in the previous cycle is input to obtain the current speed value of the permanent magnet synchronous motor output by the phase-locked loop.

4. The method according to claim 3, characterized in that The method further comprises: The current rotor angle value is subtracted from the rotor angle value output by the phase-locked loop in the previous cycle that is delayed by one cycle. When the difference is greater than the set value for more than a certain period of time, the rotor angle value determined based on the most recently collected sinusoidal voltage signal and cosine voltage signal is used to reset the rotor angle value output by the phase-locked loop.

5. The method according to claim 2, characterized in that: The step of determining a feedforward current value for magnetic field weakening control according to a bus voltage value of the permanent magnet synchronous motor, the current speed value, and a requested torque value includes: Determine the ratio of the bus voltage value of the permanent magnet synchronous motor to the current speed value to obtain a target voltage-frequency ratio; Acquire table data corresponding to the target voltage utilization rate, wherein the table data includes a mapping relationship between a voltage-frequency ratio, a torque value, and a direct-axis feedforward current value; According to the target voltage-frequency ratio and the requested torque value, the table data is searched to obtain a target direct-axis feedforward current value; The target direct-axis feedforward current value is multiplied by the feedforward proportional coefficient to obtain a feedforward current value for magnetic field weakening control.

6. The method according to claim 1, characterized in that The step of determining the feedback current value for magnetic field weakening control according to the target voltage utilization rate and the current voltage utilization rate includes: Determining a difference between the current voltage utilization rate and the target voltage utilization rate; The difference is input into an integral regulator to obtain a feedback current value output by the integral regulator for magnetic field weakening control.

7. The method according to claim 1, characterized in that The step of determining a stator direct-axis current request value according to the feedforward current value and the feedback current value comprises: Adding the feedforward current value and the feedback current value to obtain a current regulation value; According to the current adjustment value and the control strategy, a stator direct-axis current request value is determined.

8. The method according to claim 7, characterized in that The control strategy includes a maximum torque current ratio and a maximum torque voltage ratio; Determining the stator direct-axis current request value according to the current adjustment value and the control strategy includes: Determine a first reference current value based on the maximum torque-to-current ratio, and select a smaller value between the current adjustment value and the first reference current value; A second reference current value is determined based on the maximum torque-to-voltage ratio, and a larger value between the smaller value and the second reference current value is selected as a stator direct-axis current request value.

9. A magnetic field weakening control system for a permanent magnet synchronous motor, characterized in that: include: A magnetic field weakening feedforward module, used for performing feedforward control according to the voltage signal of the permanent magnet synchronous motor to obtain a feedforward current value for magnetic field weakening control; A magnetic field weakening feedback module, used to determine a current voltage utilization rate according to a current direct-axis voltage value and a quadrature-axis voltage value of the permanent magnet synchronous motor, and to determine a feedback current value for magnetic field weakening control according to a target voltage utilization rate and the current voltage utilization rate; A driving module is used to determine a stator direct-axis current request value according to the feedforward current value and the feedback current value, and to determine a stator quadrature-axis current request value according to the requested torque value and the stator direct-axis current request value, to update the direct-axis voltage value and the quadrature-axis voltage value based on the stator direct-axis current request value and the stator quadrature-axis current request value, respectively, and to drive the permanent magnet synchronous motor to operate based on the updated direct-axis voltage value and the quadrature-axis voltage value.

10. A vehicle, characterized in that: It comprises a permanent magnet synchronous motor and the control system of the permanent magnet synchronous motor as claimed in claim 9.

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