Transition method for permanent magnet synchronous motor control and permanent magnet synchronous motor

Abstract

A transition method for permanent magnet synchronous motor control and a permanent magnet synchronous motor are disclosed. The method comprises: when a switching condition is determined to be reached, calculating a first reference current based on a current first control method, and determining a total number of times of transition reference current output for transition control; outputting the transition reference current in turn for controlling the motor, the transition reference current being calculated by weighting the first reference current and a second reference current, wherein the second reference current is calculated based on a second control method for target control motor, and the weight of the second reference current is a transition function f(k), and the weight of the first reference current is 1-f(k); and when the number of times k of transition reference current output reaches the total number, using the reference current output by the second control method to control the motor. The present disclosure realizes smooth transition based on the iteration of the number of times of transition reference current output via the transition function. The transition function and the number of iterations can be flexibly selected according to the specific scenarios faced by the motor acceleration and deceleration, and the present disclosure has universality.

Description

Technical Field

[0001] This disclosure relates to the field of electric motors, and more particularly to a transition method for switching between different control methods of a permanent magnet synchronous motor and the permanent magnet synchronous motor itself. Background Technology

[0002] Permanent magnet synchronous motors (PMSMs) are widely used in new energy vehicles, robot servos, and home appliances due to their advantages such as low noise and high energy efficiency. In order to make the PMSM rotor rotate continuously and smoothly, FOC (Field-Oriented Control) is required to control the motor.

[0003] FOC (Free-Oriented Control) can be achieved using different principles at different motor speeds. For example, existing motor control products require motors to have a wide speed range (such as controllers for new energy electric vehicles). These products use field weakening control to keep the motor operating above the base speed, and MTPA (Medium-to-Medium Actuation) control to ensure efficient and stable operation below the base speed. Because different control methods are used above and below the base speed, directly switching between these two methods will cause significant fluctuations in the motor's output torque and speed, leading to adverse consequences.

[0004] Therefore, an improved method is needed to smoothly switch between different control methods. Summary of the Invention

[0005] One technical problem this disclosure aims to solve is to provide a transition method when switching between different control methods for a motor, achieving a smooth transition through iteration of the transition function based on the number of transition reference current outputs. The transition function and the number of iterations can be flexibly selected according to the specific scenario of motor acceleration and deceleration, thus possessing versatility and avoiding the problem of calculating the transition curve for each motor in existing methods.

[0006] According to a first aspect of this disclosure, a transition method for switching between different control methods of a permanent magnet synchronous motor is provided, comprising: when determining that a motor control method switching condition has been reached, calculating a first reference current based on a first control method currently controlling the motor, and determining the total number of transition reference current outputs for transition control; sequentially outputting the transition reference current to control the motor, wherein the transition reference current is obtained by weighting the first reference current and a second reference current, wherein the second reference current is calculated based on a second control method for controlling the target motor, the weight of the second reference current is a transition function f(k), and the weight of the first reference current is 1-f(k); and when the number of transition reference current outputs k reaches the total number of transition reference current outputs, using the reference current output by the second control method to control the motor.

[0007] Optionally, during the transition control process, the transition reference current is output once in each calculation cycle or an integer multiple of the calculation cycle of the first control method and / or the second control method.

[0008] Optionally, the successive output of the transition reference current for controlling the motor includes: acquiring the first reference current at the initial moment of the transition; calculating the second reference current at the moment when the transition reference current is output for the kth time; and obtaining and outputting the transition reference current at the kth output based on the second reference current calculated at the moment of the kth output.

[0009] Optionally, when the first control method is MTPA control, the second control method is field weakening control; when the first control method is field weakening control, the second control method is MTPA control. The determination of the conditions for switching the motor control method includes: when the motor is currently being controlled using MTPA control, the synthesized voltage u... s Increase to the maximum value u max The system determines that the motor has reached the switching condition; and when the motor is currently being controlled by the field weakening control, the synthesized voltage u... s Reduce to the maximum value u max Under these conditions, it is determined that the motor has reached the switching condition, wherein the synthesized voltage Among them, u q U is the q-axis voltage. q This is the voltage along the d-axis.

[0010] Optionally, the first reference current calculated based on the first control method for the current motor includes: calculating a first q-axis reference current and a first d-axis reference current based on the first control method; the second reference current calculated based on the second control method for the target motor includes: calculating a second q-axis reference current and a second d-axis reference current based on the second control method, and the obtained transition reference current includes a q-axis transition reference current obtained by weighting the first q-axis reference current and the second q-axis reference current, and a d-axis transition reference current obtained by weighting the first d-axis reference current and the second d-axis reference current.

[0011] Optionally, the transition function f(k) is a function that increases between 0 and 1 as the number of transition reference current outputs k increases. When the transition function f(k) reaches the total number of reference current outputs k, it takes the value of 1, and may include at least one of the following: a linear transition function; or an exponential transition function.

[0012] Optionally, the total number of reference current outputs for the transition control and / or the function type of the transition function are determined based on at least one of the following: the calculation frequency of the first control method and / or the second control method; the difference between the first reference current and the second reference current when the motor control method is switched; the power of the motor when the motor control method is switched; and the operating mode of the motor.

[0013] Optionally, the transition function of the motor control method when switching from the first control method to the second control method is different from the transition function when switching from the second control method to the first control method.

[0014] According to a second aspect of this disclosure, a permanent magnet synchronous motor is provided, comprising: a motor; a motor control circuit, the motor control circuit comprising: a first control module for calculating a reference current for controlling the motor based on a first control method; a second control module for calculating a reference current for controlling the motor based on a second control method; and a transition module for performing the method according to the first aspect of the present invention to perform a transition between the first control method and the first control method.

[0015] Optionally, the motor control circuit further includes: a switching control module, comprising a first switch controlling the first control module and a second switch controlling the second control module, for: disconnecting the first switch after acquiring the first reference current of the first control module at the initial moment of transition; and keeping the second switch closed during the transition control process.

[0016] Therefore, when faced with current fluctuations during the switch from the first control method to the second control method, the transition switching scheme of the present invention can suppress torque pulsations during the switch based on an iterative transition function, thus keeping the motor speed stable during the switch. Furthermore, by appropriately selecting the number of iterations and the type of transition function, it can adapt to different switching requirements in various motor models and scenarios, avoiding motor speed jitter during the switch. Attached Figure Description

[0017] The above and other objects, features and advantages of this disclosure will become more apparent from the more detailed description of exemplary embodiments thereof taken in conjunction with the accompanying drawings, wherein like reference numerals generally denote like parts.

[0018] Figure 1 The FOC control principle diagram for PMSM is shown.

[0019] Figure 2 Examples of the current control trajectories for MTPA and field weakening control are shown.

[0020] Figure 3 A schematic flowchart of a transition method between MTPA control and field weakening control according to an embodiment of the present invention is shown.

[0021] Figure 4 The specific process of switching from point A controlled by MTPA to point B controlled by weak magnetic field is shown.

[0022] Figure 5 The transition trajectory points using different transition functions are shown.

[0023] Figure 6 A schematic diagram of the composition of a permanent magnet synchronous motor according to an embodiment of the present invention is shown.

[0024] Figure 7 A schematic diagram of the permanent magnet synchronous motor of the present invention performing state switching based on determination conditions is shown. Detailed Implementation

[0025] Preferred embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While preferred embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0026] As mentioned earlier, in order to make the PMSM rotor rotate continuously and smoothly, FOC (Field-Oriented Control) is required to control the motor.

[0027] Figure 1 The FOC control principle diagram for PMSM is shown.

[0028] As shown in the figure, a position sensor, such as a magnetic encoder, acquires the rotor speed n and rotor position θ of motor M. In practical applications, for example, a speed reference n obtained from user input... ref The difference between the measured rotor speed n and the actual rotor speed is calculated and input to PID1 (i.e., the speed loop PID). The output of the speed loop PID is the q-axis reference current i. qref For simplicity, without additional control, the d-axis reference current i can be set. dref =0. At this point, the reference currents i on the q-axis and d-axis can be set to 0. qref and i dref The actual feedback of the motor's q-axis and d-axis currents i q and i d (This can also be referred to as the q-axis feedback current i) q and d-axis feedback current i dThe difference is calculated, and after being regulated by PID2 (i.e., q-axis current loop) and PID3 (i.e., d-axis current loop) respectively, the output q-axis and d-axis voltages U are obtained. d and U q Then, through the inverse Park transform, it is converted into α-axis and β-axis voltages U. α and U β Then, the three-phase voltage U is obtained through SVPWM (Space Vector Modulation). a U b U c The motor M is driven to rotate via a three-phase inverter bridge. In FOC control, the three-phase current i is collected. a i b i c After Clark transformation, the α-axis and β-axis currents i are obtained. α and i β Then, after Park transformation, the q-axis and d-axis currents i are obtained as feedback. d and i q The inputs are used in the current loop PID2 and PID3 control, respectively. The rotor position θ obtained by the position sensor is used in the Park transform and inverse Park transform.

[0029] However, in many cases, additional control of the motor is required; that is, the d-axis reference current i is adjusted. dref ≠0, and the output of the speed loop PID is not directly used as the q-axis reference current i. qref .

[0030] Since existing motor control products require motors to have a wide speed range (such as controllers for new energy electric vehicles), these products use field weakening control to make the motor work above the base speed, and use MTPA control to make the motor work efficiently and stably below the base speed.

[0031] MTPA (Maximum Torque Per Ampere) control strategy is the optimal control strategy in the constant torque region. It maximizes the output electromagnetic torque using the same current, and similarly, minimizes the current required to output the same torque. MTPA-based FOC control typically uses an MTPA search strategy to find the MTPA operating point. The basic process of the MTPA search strategy is as follows:

[0032] When the motor is running stably (motor body temperature and speed are constant), change i dref The reference value, the motor output torque changes slightly, the speed changes slightly, and through the adjustment of the speed PID loop, when the motor speed stabilizes again, i qref It also changes, the composite current It also changes. By constantly changing idref The value of i is eventually found to be the smallest. s At this time, the corresponding i dref and i qref This refers to the MTPA control point (i.e., the reference current i calculated based on the MTPA control method, as described below). dref_mtpa and i qref_mtpa ).

[0033] When the motor speed is low, the synthesized voltage u s (in The increase of ) can make the resultant current i s Increasing the voltage u increases the torque and speed of the motor. In other words, this can be achieved in the constant torque region by increasing the combined voltage u. s Increase the motor speed. When the motor speed reaches a certain speed (usually called "base speed"), the combined voltage u... s Increase to the maximum value u max (where u) max It is a maximum voltage value defined by the user based on the specific application, usually u mc (This is the DC bus voltage), and it cannot be increased by adding the synthesized voltage u. s The rotational speed can be increased by increasing the value of the reference current i on the d-axis. At this point, the only way is to increase the reference current i on the d-axis. dref By weakening the air gap magnetic field, the motor can operate at a higher speed under constant power conditions. This is called flux-weaking control.

[0034] The basic principle of field weakening control is to use the field weakening angle β to vectorize the PID output current i of the speed loop. s Assigned to the q-axis and d-axis as reference currents for the q-axis and d-axis, respectively (i qref =i s *cosβ,i dref =i s *sinβ), the included angle β equals 0°, and the current vector i s All assigned to the q-axis (e.g.) Figure 1 The state shown is i. dref =i s *sinβ=0, indicating no field weakening control is performed; β equals 90°, current vector i s All are assigned to the d-axis. Current vector i s The angle β with the q-axis represents the depth of entry into field weakening control. After entering field weakening control, β increases from 0. Based on β and the current vector i output by the speed loop... s The d-axis reference current i can be determined. dref and q-axis reference current i qref The β angle value is generally determined by the field weakening control module ( Figure 1(Not shown) Calculation of u max with u s The difference is the output value after PI adjustment.

[0035] Because different control methods are used at the base speed, and the control trajectories of MTPA and field weakening control do not intersect near the baseline, directly switching between the two control methods will cause significant fluctuations in the motor's output torque and speed, leading to adverse consequences, such as unintended rapid acceleration or deceleration in new energy electric vehicles. Therefore, when switching control methods at the base speed, a smooth transition method is generally required to ensure a smooth change in motor torque and speed.

[0036] Figure 2 Examples of the current control trajectories for MTPA control and field weakening control are shown. As illustrated, when switching between MTPA control and field weakening control, the target current becomes discontinuous, as shown at points A and B in the figure. Here, point A can be considered a point on the MTPA control trajectory at the start of the switch, and point B can be considered a point on the field weakening control trajectory at the start of the switch. If the target current switches directly from point A to point B, problems such as motor stalling and short-term current surges will occur. Therefore, when switching directly between MTPA control and field weakening control, a smooth transition is required to fill the gap in the target current.

[0037] In existing technologies, a d-axis current i is typically established through methods such as experiments and theoretical calculations. d and q-axis current i q The current comparison table can achieve a smooth transition between MTPA control and field weakening control through repeated testing. However, obtaining such a table requires a lot of manpower and resources, and it is usually only effective for the same type of motor and controller, so its versatility is poor.

[0038] To address this, the present invention proposes a transition method for switching between different control methods, achieving a smooth transition through iteration of the transition function based on the number of control cycles. In a further embodiment, the transition function and the number of iterations can be flexibly selected according to the specific scenario faced by the motor acceleration and deceleration, thus possessing versatility and avoiding the need to calculate the transition curve for each motor in existing methods.

[0039] Figure 3 A schematic flowchart illustrating a transition method between different control methods according to an embodiment of the present invention is shown. This method can be viewed as part of a permanent magnet synchronous motor control method, or as an optimization thereof.

[0040] In step S310, when the switching condition for the motor control method is determined, the first reference current obtained based on the first control method of the currently controlled motor is calculated, and the total number of reference current outputs for transition control is determined. It should be clarified that this method can be used for switching from MTPA control to field weakening control during acceleration, and also for switching from field weakening control to MTPA control during deceleration. The "first control method" and "second control method" can be MTPA control and field weakening control methods, respectively. When the first control method of the currently controlled motor is MTPA control, the second control method of the target controlled motor is the field weakening method; correspondingly, if the first control method of the currently controlled motor is the field weakening control method, the second control method of the target (i.e., the target method to which the transition is needed) controlled motor is the MTPA control method. However, it is worth noting that the transition method of this invention is not limited to the switching between MTPA control and field weakening control methods; it can also be used for other applications where the reference current (including the d-axis reference current i) is calculated using different algorithms. dref and q-axis reference current i qref When switching between control methods for motor control, the transition method of this invention can also be used.

[0041] For ease of explanation, it can be assumed that the current situation is a switch from MTPA control to field weakening control during motor acceleration. Therefore, the current control method, i.e., the "first control method," is the MTPA control method. It should be understood that using the example of switching from field weakening control to MTPA control is also feasible. Thus, in step S310, if it is determined that the motor control method switching condition has been met, for example, the motor has reached its base speed, the reference current calculated based on the MTPA control method (e.g., the d-axis reference current i) can be applied. dref_mtpa and q-axis reference current i qref_mtpa This serves as the first reference current. Simultaneously, it's necessary to determine the total number of times the reference current is output during transition control (which can be expressed as "N" times), i.e., how many times the reference current needs to be output during the transition process. Understandably, for a smooth transition, it's desirable to connect... Figure 2 The transition curve between points A and B remains smooth. Therefore, the larger the value of N, the more reference current output points there are from point A to point B, and the smoother the transition curve obtained from this connection is.

[0042] Subsequently, in step S320, a transitional reference current is output sequentially to control the motor. This transitional reference current is obtained by weighting the first reference current and the second reference current. Specifically, the second reference current can be calculated based on a second control method for controlling the motor. If the first control method is the MTPA control method, the second control method is the field weakening method. Therefore, the d-axis reference current i obtained based on field weakening control can be calculated. dref_fw and q-axis reference current iqref_fw The first reference current is used as the second reference current, and the transition reference current is obtained by weighting the first reference current and the second reference current.

[0043] In this invention, the weights are determined using a transition function f(k) that iterates based on the output of each transition reference current. The transition function f(k) is defined as follows: the weight of the second reference current is f(k), and the weight of the first reference current is 1-f(k). That is, the transition reference current = f(k) * second reference current + (1-f(k)) * first reference current.

[0044] In step S330, when the number of transition reference current outputs k reaches the total number of reference current outputs N, the reference output current output by the second control method is used to control the motor, thereby completing the switching. In a further embodiment, the transition function f(k) can be a function that increases between 0 and 1 as the number of transition reference current outputs k increases (especially monotonically increasing); when the transition function f(k) reaches a value of 1 when k increases to the total number of reference current outputs N, specifically, when iterating to the Nth iteration, that is, when the output of the transition reference current reaches the total number of outputs N determined in step S310 (at this time, k = N), the transition function f(k) takes a value of 1, the weight of the second reference current is 1, and the weight of the first reference circuit is 0, representing the end of the transition control process. Therefore, in step S330, the reference current output by the second control method can be used to control the motor.

[0045] In practice, the calculation frequencies of MTPA control and field weakening control are usually the same (although they can be different). Therefore, the transition reference current output can be based on the operating frequencies of MTPA control and / or field weakening control. For example, the transition reference current can be output once per calculation cycle (or an integer multiple thereof) of MTPA control and / or field weakening control. With the calculation frequencies of MTPA control and field weakening control relatively fixed, the value of N determines the length of the switching time. For example, if the calculation frequency of MTPA control and field weakening control is 5kHz, meaning that MTPA / field weakening control calculates the first reference current / second reference current every 200µs respectively, then during the transition process, the transition reference current is calculated and output every 200µs. When N is 10,000, it means that the transition reference current is calculated and output 10,000 times at 200µs intervals. In each transition reference current output, the weight of the second reference current increases compared to the previous one, and the switching from MTPA to field weakening control is completed within a 2s (200µs*10000) transition time. In other embodiments, during the transition process, the transition reference current can be calculated and output by dividing the calculation frequency of MTPA control and field weakening control, for example, once every 400µs or 800µs, that is, once every integer multiple of the calculation cycle of MTPA control and field weakening control.

[0046] In one embodiment, the second reference current used to generate the transition reference current can be a second reference current calculated based on a second control method to determine the timing of switching. However, due to the d-axis current i d and q-axis current i q It will change as the transition proceeds, generating the second reference current i. qref_fw and i dref_fw This can also change, so in a preferred embodiment, a first reference current (e.g., the d-axis reference current i calculated by the MTPA control method) is first obtained at the time when switching is determined or at the initial transition time (k=0). dref_mtpa and q-axis reference current i qref_mtpa The second reference current is calculated at the moment when the transition reference current is output for the kth time; and based on the second reference current calculated at the moment of the kth output, the transition reference current at the kth output is obtained and output. In other words, the real-time second reference current needs to be calculated first when calculating and outputting the transition reference current (e.g., the d-axis reference current i calculated by the field weakening control method). dref_fw(k) and q-axis reference current i qref_fw(k)Then, based on the current second reference current and the current value of the transition function f(k), the transition reference current is calculated. (It should be noted that the first reference circuit is fixed at this time, which is the first reference current calculated by the first control method when the motor control method switching condition is reached or at the initial moment of transition (k=0).)

[0047] As previously stated, the motor reaching its base speed can be considered as fulfilling the switching condition. In one embodiment, when the first control method is MTPA control and the second control method is field weakening control, and when the first control method is field weakening control and the second control method is MTPA control, the value of the synthesized voltage can be used to determine whether the motor is running at its base speed. In this case, determining whether the motor control method switching condition has been met includes: when the motor is currently being controlled using MTPA, the synthesized voltage u... s Increase to the maximum value u max The system determines that the motor has reached the switching condition; and when the motor is currently being controlled by field weakening, the synthesized voltage u... s Reduce to the maximum value u max Under these conditions, it is determined that the motor has reached the switching condition, wherein the synthesized voltage Among them, u q U is the q-axis voltage. q This represents the d-axis voltage.

[0048] Accordingly, since the reference current includes the q-axis reference current and the d-axis reference current, calculating the first reference current obtained based on the first control method for the current motor control includes: calculating the first q-axis reference current and the first d-axis reference current obtained based on the first control method; calculating the second reference current based on the second control method for the target motor control includes: calculating the second q-axis reference current and the second d-axis reference current based on the second control method, and the obtained transition reference current includes the q-axis transition reference current obtained by weighting the first q-axis reference current and the second q-axis reference current, and the d-axis transition reference current obtained by weighting the first d-axis reference current and the second d-axis reference current.

[0049] As mentioned earlier, the transition function f(k) takes a value of 1 when k increases to the total number of times the reference current is output N, thereby completing the switch from the first control method to the second control method. In specific implementations, the type of the transition function f(k) can be selected to control the transition curve. For example, the transition function f(k) can be a linear transition function or an exponential transition function.

[0050] Figure 4The diagram illustrates the specific process of switching from point A under MTPA control to point B under field weakening control. The figure uses the switch from MTPA to field weakening control as an example to explain the switching process based on the transient function. Point A represents the value of the MTPA control trajectory before the switch, i.e., A = (i... dref_mtpa i qref_mtpa Since k = 0 at this moment, the MTPA control point at this time can be regarded as the initial magnetic weakening control point, therefore A = (i dref_mtpa i qref_mtpa )=(i d0_fw i q0_fw )

[0051] Point B is a point on the weak magnetic control trajectory, i.e., B = i dref_fw(k) During the transition, each i dref_fw(k) The values ​​will vary, ultimately forming a region, as shown in the elliptical region in the figure. It should be understood that the elliptical distribution region here is just an example; the actual region may have other irregular shapes. The two dashed lines above and below the elliptical region represent the two extreme cases of the transition trajectory; all transition trajectories will fall between these two limiting curves. The gray curve in the middle represents an example of the actual transition curve. The curve will differ for each transition case.

[0052] In one example, a linear function can be chosen: f(k) = k / N. The dynamic process of a linear transition can be adjusted by controlling the size of N. The larger N is, the smoother the transition process, but the longer the transition time. The smaller N is, the smoother the transition process, but the shorter the transition time. In another example, an exponential transition function can be chosen, such as f(k) = exp(5*k / N-5).

[0053] Figure 5 The figure shows the transition trajectory points using different transition functions. "*" indicates the output point of the linear transition function, and "o" indicates the output point of the linear transition function. The horizontal axis in the figure represents i. d The vertical axis represents i q As can be seen from the figure, the trajectories of the transition reference currents are basically the same, but the spacing (steps) between every two points are not the same, resulting in different transition effects. Specifically, the linear transition function changes with the same step size throughout the process, while the exponential transition function has longer steps at the beginning of the switch, followed by shorter steps, thus achieving a faster switch. Therefore, with the same step size (i.e., the transition effect, manifested as motor jitter), the exponential function can achieve a smaller N (faster transition process) than the linear function.

[0054] It should be understood that, Figure 2 and Figure 4This only provides a schematic diagram of the relationship between the MTPA control trajectory and the field weakening control trajectory for a certain type of motor. In practical applications, the smoothness of the transition process can be adjusted by selecting the total number of transition reference current outputs N and the function type of the transition function f(k) according to the actual situation.

[0055] In one embodiment, the value of the total number of times the reference current output N for transition control and / or the function type of the transition function can be determined based on at least one of the following factors: the calculation frequency of the first control method and / or the second control method (e.g., the FOC calculation frequency of the aforementioned first / second control method); the difference between the first reference current and the second reference current when the motor control method switches; the power of the motor during switching; and the operating mode of the motor. For example, the larger the difference between the first and second reference currents during switching (e.g., ... Figure 4 The larger the value of N (the difference in coordinates between points A and B), the smoother the transition process (e.g., a linear function) should be. For example, the greater the motor power, the larger the value of N or the smoother the transition process (e.g., a linear function). Regarding the motor's operating mode, for example, in the application scenario of new energy vehicles, if the user adjusts the vehicle's operating state to sport mode, it means the user expects stronger control and faster acceleration and deceleration; therefore, a smaller N or an exponential transition function should be selected. Considering the current environment, faster switching or even no switching may be allowed when emergency braking is detected, while smoother acceleration and deceleration may be allowed when the driver assistance system determines there are no obstacles in front or behind.

[0056] The present invention can also be implemented as a permanent magnet synchronous motor. Figure 6 A schematic diagram of the composition of a permanent magnet synchronous motor according to an embodiment of the present invention is shown. Besides being similar to... Figure 1 In addition to the motor and FOC control circuitry, the control circuitry further includes an MTPA control module (first control module) 610, a field weakening control module (second control module) 620, and a transition module 630. The MTPA control module 610 calculates a reference current for motor control based on MTPA (first control method). The field weakening control module 620 calculates a reference current for motor control based on field weakening control (second control method). The transition module 630 can be used to perform the switching method described above, transitioning between MTPA control and field weakening control.

[0057] Furthermore, the motor control circuit also includes a switching control module 640, comprising a first switch controlling the first control module 610 and a second switch controlling the second control module 620. The first switch S1 is opened after acquiring the reference current of the first control module 610 at the initial moment of the transition; and the second switch S2 remains closed during the transition control process. In the case of transitioning from MTPA control to field weakening control, the first switch corresponds to S1 as shown in the figure, and the second switch corresponds to S2 as shown in the figure. In the case of transitioning from field weakening control to MTPA control, the first switch corresponds to S2 as shown in the figure, and the second switch corresponds to S1 as shown in the figure.

[0058] Specifically, the switching control module 640 can be combined with the transition module 630 to achieve a smooth transition for field weakening and the MTPA algorithm. When the target motor speed is relatively low, after the motor starts, the reference current i will be gradually increased through MTPA control. qref and i dref This allows the motor to reach the target speed. If the target speed gradually increases, the reference current i... qref and i dref It will gradually increase, and when it increases to a certain level, the motor will reach its base speed, for example, u. s Reaching the maximum value u max In this situation, the current cannot continue to increase (because the voltage is limited to u). max If you want to continue increasing the speed at this point, you can only do so by using field weakening control.

[0059] Figure 7 A schematic diagram illustrating the state switching of the permanent magnet synchronous motor based on decision conditions according to the present invention is shown. The current control method is divided into four cases based on whether algorithm switching is required:

[0060] TransMode=0: Simple MTPA control mode

[0061] TransMode=1: Switches from MTPA control to field weakening control.

[0062] TransMode=2: Simple field weakening control

[0063] TransMode=3: Switches from field weakening control to MTPA control.

[0064] Different approaches can be taken for each situation.

[0065] Specifically, first determine the resultant current u s Relative to u max The magnitude of the resultant current u. s Greater than or equal to u maxThis means that MTPA control can no longer be performed. If TransMode is not at 0 at this time, it indicates that the current reference current output is based on field weakening control, so TransMode can continue to be 2, i.e., simple field weakening control. When TransMode is 2, Figure 7 The switch s2 shown is normally closed, and the switch s1 is normally open. This is a simple field weakening control mode, with the d-axis reference current i... dref =i dref_fw q-axis reference current i qref =i qref_fw .

[0066] If TransMode = 0 at this time, it indicates that the reference current output is currently based on MTPA control, and a switch from MTPA to field weakening control is required. That is, enter TransMode = 1: the state of switching from MTPA control to field weakening control. When TransMode = 1, switch s1 closes once and then opens, while s2 remains closed. When switch s1 closes once, the current value output by the MTPA module is recorded, and i... d0_fw =i dref_mtpa i q0_fw =i qref_mtpa .

[0067] At this time, the output transition reference current is as follows:

[0068] i dref(k) =i d0_fw +f(k)*(i dref_fw(k) -i d0_fw )=f(k)*i dref_fw(k) +(1-f(k))*i d0_fw ;

[0069] i qref(k) =i q0_fw +f(k)*(i qref_fw(k) -i q0_fw )=f(k)*i qref_fw(k) +(1-f(k))*i q0_fw ;

[0070] Where k = 0, 1, 2…N; f(k) is a function with k as independent variable, which satisfies the following properties: 1. Monotonically increasing; 2. The range of k is 0 to N, and when k reaches its maximum value N, f(k) = 1. When k = N, the transition algorithm is completed, TransMode = 2, and the system fully switches to the field weakening module for control.

[0071] Returning to the composite current u s Decision box. If the combined current u s Less than u maxThis means that MTPA control is required. If TransMode is not currently set to 2, it indicates that the reference current output is based on MTPA control, and therefore TransMode can remain at 0, i.e., simple MTPA control. When TransMode = 0, Figure 7 The switch s2 shown is normally open, and the switch s1 is normally closed. This is a simple field weakening control mode, with the d-axis reference current i... dref =i dref_mtpa q-axis reference current i qref =i qref_mtpa .

[0072] If TransMode=2 is currently active, it indicates that the reference current output is based on field weakening control. A switch from field weakening control to MTPA control is needed, i.e., entering TransMode=3: the state of switching from field weakening control to MTPA control. When TransMode=3, switch s2 closes once and then opens, while s1 remains closed. When switch s2 closes once, the current value output by the field weakening module is recorded, and i... d0_mtpa =i dref_fw i q0_mtpa =i qref_fw .

[0073] At this time, the output transition reference current is as follows:

[0074] i dref(k) =i d0_mtpa +f(k)*(i dref_mtpa(k) -i d0_fw )=f(k)*i dref_mtpaf(k) +(1-f(k))*i d0_mtpa ;

[0075] i qref(k) =i q0_mtpa +f(k)*(i qref_mtpa(k) -i q0_fw )=f(k)*i qref_mtpaf(k) +(1-f(k))*i q0_mtpa ;

[0076] Where k = 0, 1, 2…N; f(k) is a function with independent variable k, satisfying the following properties: 1. Monotonically increasing; 2. k ranges from 0 to N, and when k reaches its maximum value N, f(k) = 1. When k = N, the transition algorithm is completed, TransMode = 0, and the system fully switches to the MTPA module for control. It is worth noting that for the same motor, the transition function f(k) when switching from the first control method to the second control method (e.g., when TransMode = 1) is the same as the transition function f(k) when switching from the second control method to the first control method (e.g., when TransMode = 3). In some application scenarios, such as when the required speed of motor acceleration and deceleration transitions differs, the transition function f(k) when switching from the first control method to the second control method (e.g., when TransMode = 1) may be different from the transition function f(k) when switching from the second control method to the first control method (e.g., when TransMode = 3).

[0077] The transition method for switching between different control methods of a motor according to the present invention, and the permanent magnet synchronous motor utilizing this method, have been described in detail above with reference to the accompanying drawings. When faced with current fluctuations during the switching between different motor control methods, the transition switching scheme of the present invention can suppress torque pulsations during switching based on an iterative transition function, thus maintaining a stable motor speed during the switching process. Furthermore, by appropriately selecting the number of iterations and the type of transition function, it can adapt to different switching requirements in various motor models and scenarios, avoiding motor speed jitter during the switching process.

[0078] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A transition method for switching between different control methods of a permanent magnet synchronous motor, comprising: When determining the conditions for switching the motor control method, the first reference current is calculated based on the first control method currently controlling the motor, and the total number of transition reference current outputs for transition control is determined. The transition reference current is output sequentially to control the motor. The transition reference current is obtained by weighting the first reference current and the second reference current. The second reference current is calculated based on a second control method for controlling the motor with a target. The weight of the second reference current is the transition function f(k), and the weight of the first reference current is 1-f(k). When the number of transitional reference current outputs k reaches the total number of transitional reference current outputs, the motor is controlled using the reference current output by the second control method. Wherein, the first reference current is a reference current calculated by the first control method at the moment when the motor control method switching condition is reached or at the transition initial moment when k=0, and which remains unchanged during the transition control period. When calculating and outputting the transition reference current each time, the current second reference current is first calculated in real time using the second control method, and then the transition reference current is calculated and output based on the current second reference current and the value of the current transition function f(k).

2. The method as described in claim 1, wherein during the transition control process, the transition reference current is output once in each calculation cycle or an integer multiple of the calculation cycle of the first control method and / or the second control method.

3. The method as described in claim 1, wherein when the first control method is MTPA control, the second control method is field weakening control; and when the first control method is field weakening control, the second control method is MTPA control, wherein... The conditions for determining when to switch the motor control method include: When the motor is currently being controlled using the MTPA control, the synthesized voltage... u s Increase to maximum value u max Determine that the motor has reached the switching condition; and When the motor is currently being controlled using the aforementioned field weakening control, the synthesized voltage u s Reduce to the maximum value u max Under these circumstances, it is determined that the motor has reached the switching condition. Wherein, the synthesized voltage ,in, u q This is the q-axis voltage. u q This is the voltage along the d-axis.

4. The method of claim 1, wherein, The first reference current calculated based on the current first control method for controlling the motor includes: The first q-axis reference current and the first d-axis reference current are calculated based on the first control method; The second control method for controlling the motor based on the target includes calculating the second reference current as follows: The second q-axis reference current and the second d-axis reference current are calculated based on the second control method, and The obtained transition reference current includes the q-axis transition reference current obtained by weighting the first q-axis reference current and the second q-axis reference current, and the d-axis transition reference current obtained by weighting the first d-axis reference current and the second d-axis reference current.

5. The method of claim 1, wherein, The transition function f(k) is a function that increases between 0 and 1 as the number of transition reference current outputs k increases. The transition function f(k) takes a value of 1 when k increases to the total number of reference current outputs, and includes at least one of the following: Linear transition function; or Exponential transition function.

6. The method of claim 1, wherein, The total number of reference current outputs for the transient control and / or the function type of the transient function are determined based on at least one of the following: The calculation frequency of the first control method and / or the second control method; The difference between the first reference current and the second reference current when the motor control method is switched; The power of the motor when the motor control method is switched; as well as The operating mode of the motor.

7. The method of claim 1, wherein, The transition function for switching the motor control method from the first control method to the second control method is different from the transition function for switching the motor control method from the second control method to the first control method.

8. A permanent magnet synchronous motor, comprising: Electric motor; Motor control circuit, the motor control circuit including: The first control module is used to calculate a reference current for controlling the motor based on the first control method; The second control module is used to calculate a reference current for motor control based on the second control method; and A transition module is configured to perform the method as described in any one of claims 1-7, transitioning between the first control method and the first control method.

9. The permanent magnet synchronous motor as described in claim 8, wherein the motor control circuit further comprises: A switching control module, including a first switch controlling the first control module and a second switch controlling the second control module, is used for: After acquiring the first reference current from the first control module at the initial moment of the transition, the first switch is disconnected; and The second switch remains closed during the transition control process.

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