Mtpa - field weakening feedforward control method, system, and storage medium

Abstract

The application discloses a kind of MTPA-weak magnetic feedforward control method, system based on model parameter updating, storeable medium, it is related to motor control field.The present application includes two stages: MTPA stage control and weak magnetic stage control respectively.Specifically, on the basis of MTPA control, judge whether current point is in the overlapping region of voltage limit circle and current limit circle, if meet then continue to execute MTPA mode, if not meet then jump to weak magnetic region control, according to the interrelation of target torque and voltage limit region, current limit region, real-time solution updates the current operating point of weak magnetic area.In the present application, the smoothness of two-stage transition and the responsiveness of the system under varying conditions are improved.In the case of inductance parameter variation, the present application can update the current operating point based on inductance variation in real time, effectively suppress the working condition fluctuation, and show good application prospect.

Description

Technical Field

[0001] This invention relates to the field of motor control, and more specifically to an MTPA-field weakening feedforward control method, system, and storage medium. Background Technology

[0002] Permanent magnet synchronous motors (PMSMs) are characterized by high torque, high power, high functionality, and miniaturization. They do not require excitation windings, have a simple structure, no heat source in the magnetic field, do not require cooling devices, and utilize materials with high coercivity. They have been widely used in the electric vehicle field. The power density and performance of synchronous motors have become a research hotspot in the current motor industry. However, due to limitations imposed by the inverter and stator voltage, above the turning speed, the stator current cannot track the target current, leading to unstable motor operation. Field weakening control can achieve wide-range field weakening speed regulation while maintaining the highest possible torque output.

[0003] The most common field weakening method both domestically and internationally is the voltage feedback method. Sun Xuxia et al. used a field weakening control method that corrects the current value using voltage feedback. This method uses AC and DC axis currents and voltages to correct the current, and the control algorithm is simple, with fast response and good robustness. Lin FaaJeng et al. designed a voltage control loop for field weakening control in the constant power region, which can limit the inverter output voltage to the maximum output voltage at high speed. Zhang Chuanpu proposed a traditional lead angle field weakening control, which uses the difference between the voltage feedback value and the maximum stator voltage to obtain the modulation coefficient through PI regulation, thereby correcting the space current vector angle. Li Tao et al., based on the poor dynamic performance and large fluctuations in d-axis current and torque in the field weakening region caused by the traditional current phase angle method, proposed a current phase angle adaptive field weakening control strategy. Through steady-state small-signal analysis, the voltage amplitude is differentiated with respect to the current phase angle to derive the adaptive gain value, thereby achieving adaptive control of the current phase angle. The system responsiveness of the above methods depends on the degree of gain optimization of the PI feedback regulator. Wang Hui et al. introduced Model Predictive Control (MPC) into the speed loop and designed a field weakening control system based on voltage feedback. Finally, simulation results show that under field weakening control, the MPC controller has better robustness and stronger anti-interference ability than the PI controller, thus improving system stability. Addressing the PMSM responsiveness problem, Lin Li et al., combining the advantages of feedforward control, introduced feedforward voltage compensation into field weakening control, realizing a novel field weakening control strategy. Wang Ying et al. proposed a feedforward field weakening control strategy based on a table showing the relationship between AC and DC axis currents and torque and stator flux linkage, effectively improving the system's fast response capability. However, the lookup table method requires a large amount of experimental data and high accuracy, and cannot cope with errors caused by changes in motor parameters. Shi Xinhua et al. proposed a fast adaptive field weakening control method, obtaining the maximum value of the stator current component id through feedforward control of the stator current component iq, allowing it to be adjusted within this range, thereby achieving a fast system response and obtaining an accurate id value more quickly, realizing fast adaptive control. Ren Shaomeng et al. designed an improved field weakening structure, combining feedforward control with limiting voltage feedback control to improve system control performance. Direm Chaima et al. proposed a combined control strategy (MTPA-FW) based on IPMSM vector control powered by a two-level inverter, which can provide excellent traction system dynamics over a wide operating speed range. While the above methods significantly improve system response characteristics through feedforward control, they neglect the transition between the MTPA operation phase and the field weakening control phase. Furthermore, the effectiveness of the feedforward control strategy under varying motor parameters and its responsiveness under transient operating conditions warrants further investigation. Summary of the Invention

[0004] In view of this, the present invention provides an MTPA-weakening feedforward control method, system, and storable medium.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A model parameter update-based MTPA-weakening feedforward control method includes the following steps:

[0007] Obtain the difference between the target speed and the current speed of the motor;

[0008] A PI controller is used to adjust and generate the target torque for correcting the difference.

[0009] The MTPA current is calculated using the target torque; where the MTPA current is the maximum torque current ratio to the control current.

[0010] Determine whether the MTPA current node is within the overlapping area of ​​the voltage limiting circle and the current limiting circle. If it is, then the MTPA current node is the operating point.

[0011] Optionally, it also includes determining whether the MTPA current node is within the overlapping area of ​​the voltage limiting circle and the current limiting circle. If not, the operating point query of the feedforward method is initiated.

[0012] Optionally, the working point query of the feedforward method is as follows:

[0013] The feedforward target torque is obtained by integrating the difference between the target speed and the current speed of the motor.

[0014] The intersection point of the feedforward target torque and the voltage limiting circle is determined in the second quadrant.

[0015] If an intersection point exists, continue to determine whether the current limiting region is satisfied;

[0016] If the conditions are met, the intersection point is the working point;

[0017] If an intersection exists, but the intersection does not satisfy the current limiting region or there is no intersection in the second quadrant, then the intersection of the current limiting circle and the voltage limiting circle in the second quadrant is the operating point.

[0018] Optionally, the formula for determining whether the MTPA current node is within the overlapping area of ​​the voltage limiting circle and the current limiting circle is as follows:

[0019]

[0020] Among them, i d Let i be the d-axis current. q U is the q-axis current. max L is the maximum allowable value of the stator terminal voltage. d For the d-axis inductance, L q It is the q-axis inductance.

[0021] A model parameter update-based MTPA-field weakening feedforward control system is characterized by comprising an MTPA real-time calculation module and a current operating point query module; wherein, the MTPA real-time calculation module is used to obtain the target torque through PI regulation based on the difference between the target speed and the current speed, and calculate the MTPA current; the operating area judgment module is used to determine whether the MTPA current is within the overlapping area of ​​the voltage limiting circle and the current limiting circle.

[0022] Optionally, a current operating point query module is also included to calculate the spatial geometric location of the operating point.

[0023] A computer storage medium storing a computer program, wherein the computer program, when executed by a processor, implements the steps of the MTPA-weakening feedforward control method based on model parameter updates.

[0024] As can be seen from the above technical solution, compared with the prior art, this invention discloses an MTPA-field weakening feedforward control method, system, and storable medium. By judging the geometric relationship between the target torque operating line and the voltage limiting circle and current limiting circle, the intersection point with the minimum current loss during stable operation is selected in real time as the operating point. Specifically, this means the intersection point of the torque line and the voltage limiting circle when the current point is located within the overlapping area of ​​the spatial voltage limiting circle and current limiting circle, and the intersection point of the voltage limiting circle and current limiting circle in the second quadrant when the limiting condition is not met. A simulation environment is built based on a built-in permanent magnet synchronous motor model, and the designed MTPA-field weakening feedforward control strategy is compared with the lead angle field weakening control method. Simulation results show that the online-updated MTPA-field weakening feedforward control strategy has better smoothness during mode switching and a 60% improvement in responsiveness under transition conditions compared to the lookup table method MTPA-lead angle field weakening control method. When the inductance parameter changes, this invention can update the current operating point in real time based on the inductance change, effectively suppressing operating condition fluctuations and showing good application prospects.

[0025] Furthermore, the present invention also has the following beneficial effects:

[0026] 1. Improved smoothness of the two-stage transition.

[0027] 2. Improved system transient response.

[0028] 3. Improved system stability when motor parameters change abruptly. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the process of the present invention;

[0031] Figure 2 This is a diagram showing the trajectories of the orthogonal axes of the present invention;

[0032] Figure 3 This is a schematic diagram of the bisection method of the present invention;

[0033] Figure 4a This is a schematic diagram showing the intersection point of the present invention outside the current limiting circle;

[0034] Figure 4b This is a schematic diagram showing that the torque line and the voltage limiting circle of the present invention do not intersect.

[0035] Figure 5 This is a schematic diagram of the peak operating point of the motor during the high-speed phase of this invention; Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] This invention discloses an MTPA-weak magnetic feedforward control method, system, and storable medium.

[0038] First, this embodiment provides an MTPA-weakening feedforward control method based on model parameter updates, such as... Figure 1 The above includes the following steps:

[0039] Obtain the difference between the target speed and the current speed of the motor;

[0040] A PI controller is used to adjust and generate the target torque for correcting the difference.

[0041] Calculate the MTPA current using the target torque;

[0042] Determine whether the MTPA current node is within the overlapping area of ​​the voltage limiting circle and the current limiting circle. If it is, then the MTPA current node is the operating point.

[0043] The MTPA control principle is as follows:

[0044] MTPA is a commonly used current control strategy in salient-pole permanent magnet synchronous motors. It requires only minimal stator current to achieve the desired torque control, thus reducing losses, facilitating the operation of converter switching devices, improving efficiency, and fully utilizing reluctance torque to enhance the motor's torque output capability.

[0045] The minimum current equation under the same torque is:

[0046]

[0047] Substituting equation (4) into equation (3), we obtain the relationship between the target torque and iq:

[0048]

[0049] By rearranging terms in equation (5), we can obtain:

[0050]

[0051] In engineering, if the quartic equation (6) is solved numerically and then a map is generated, a large amount of data and high accuracy are required, which is not effective in dealing with changes in motor parameters. Therefore, the analytical solution of the quartic equation is obtained by using Ferrari's method and Tartaglia's formula, and real-time calculation is used to improve accuracy and obtain better robustness.

[0052] The principle of field weakening control is as follows:

[0053] The excitation flux of a permanent magnet synchronous motor is provided by permanent magnets, and this flux is constant. If we want to reduce the flux intensity, we can only weaken the air gap flux by increasing the demagnetizing component of the stator current, thus achieving the field weakening equivalence with a separately excited DC motor.

[0054] The formula for induced electromotive force is:

[0055]

[0056] Where ω r Let ψ be the angular velocity. s For total flux linkage,

[0057] φ d , φ q The stator flux linkage is for the dq axis.

[0058] Given a fixed DC bus voltage, the maximum stator voltage Umax that the inverter can output remains constant; furthermore, due to heat generated during motor operation, the maximum allowable current Imax flowing through the stator windings also remains constant within a certain temperature rise tolerance. Thus, when the motor operates in the field-weakening region, the stator current is and terminal voltage Us are limited by the following conditions:

[0059] |i s |≤I max (8)

[0060] |u s |≤U max (9)

[0061] In the formula: Imax is the maximum allowable value of stator current; Umax is the maximum allowable value of stator terminal voltage.

[0062] As can be seen from the above formula, the current is limited by a circle, and the voltage is limited by an ellipse:

[0063]

[0064]

[0065] Among them, i d Let i be the d-axis current. q U is the q-axis current. max L is the maximum allowable value of the stator terminal voltage. d For the d-axis inductance, L q It is the q-axis inductance.

[0066] Figure 2 In the diagram, T1 and T2 represent different constant torque lines, with T1 > T2. ω1, ω2, and ω3 represent three different speeds, with ω1 < ω2 < ω3. Points A and C are the intersections of the constant torque lines T1 and T2 with the MTPA curve; points B and D are the intersections of the constant torque lines T1 and T2 with the voltage limiting circle, respectively. At speed ω1 and load torque T1, the entire MTPA curve lies within the overlapping area of ​​the voltage and current limiting circles, so field weakening control is not required. When accelerating to a stable ω2, the load torque T1 line intersects the MTPA curve at point A. Clearly, point A is not within the overlapping area of ​​the voltage and current limiting circles, so this operating point cannot be properly tracked. The current point should be planned to point B, the intersection of the load torque T1 line and the voltage limiting circle, as this point minimizes the current consumption on the load torque T1 line. Similarly, when the load torque decreases to T2 and the torque increases to ω3, point C no longer meets the requirements, and the current point should be planned to point D.

[0067] Specifically, it is divided into the following two stages, such as Figure 1 As shown.

[0068] First stage: Control within the MTPA region. In this stage, the target torque is obtained through PI regulation based on the difference between the target speed and the current speed, and input into the MTPA real-time calculation module to solve the quartic equation (6). Since this equation is a special form of a quartic equation, lacking quadratic and cubic terms, it is easy to obtain an analytical solution using the Ferrari completion method. The variant of equation (6) is as follows:

[0069] a*i q 4 +d*i q -e=0 (12)

[0070] In the formula, the coefficient of the fourth term is a = 9 * Pn 2 *(Ld-Lq) 2 coefficient of the first term Te; constant term e = -4*Te 2 The coefficients of the cubic term b and the quadratic term c are both 0.

[0071] Dividing both sides by a, we get

[0072]

[0073] Move to the back

[0074]

[0075] According to Ferrari's method of completing the square, add to both sides of the equation simultaneously have to:

[0076]

[0077] This gives us the form of a perfect square on the left. If the right side is also a perfect square, then taking the square root of both sides yields two quadratic equations. To make the polynomial in iq on the right side of equation (15) also a perfect square, its discriminant should be equal to zero, i.e. Organized

[0078]

[0079] According to Tartaglia's formula, the cubic equation y 3 The solution to +p*y+q=0 is:

[0080]

[0081] The value of y in the completing the square method is obtained. From this, we can derive the formula where both sides of the equation are perfect squares. After taking the square root, we can solve the two linear equations in two variables:

[0082]

[0083] We obtain the quadratic formula:

[0084]

[0085] Where z = 3*a*y

[0086] From this, we can obtain the q-axis current of MTPA, and then substitute it into equation (4) to obtain the d-axis current.

[0087] Then, based on MTPA control, it is determined whether the current point is within the overlapping area of ​​the voltage limit circle and the current limit circle. The determination method is whether the current point at this moment satisfies equation (11).

[0088] If the conditions are met, the MTPA mode continues; otherwise, it jumps to the next stage. It should be explained that the MTPA real-time calculation module uses Ferrari's method and Tartaglia's formula to calculate the analytical solution under MTPA control. The current operating point query module can effectively update and correct the motor parameters involved in both control methods.

[0089] Second stage: Field weakening region control. The voltage limiting circle shrinks continuously as the rotational speed increases, and the motor's operating range also decreases accordingly. The motor's peak torque capability continuously decreases. When the circulating current no longer satisfies equation (11), the judgment module cuts off the current value provided by the MTPA module and starts the output value calculation module, such as... Figure 3 As shown, Nr* is the real-time motor speed; Nr** is the target speed; Ld and Lq are the real-time motor inductances obtained by the parameter identification method; and the switching signal γ is the switching signal between MTPA and field weakening control.

[0090] The core current operating point query module of the feedforward method calculates the spatial geometric location of the reasonable operating point through programming. The specific program functions are divided into the following three steps:

[0091] Step 1: Signal γ judgment. The switching signal obtained from the judgment module is used as the switch to start the current operating point query module. If signal 1 is received, it is turned on.

[0092] Step 2: Determining the intersection point of the target torque and the voltage limiting circle. Based on the feedforward target torque obtained by integrating the speed difference, the intersection point of the voltage limiting circle is determined in the second quadrant. If an intersection point exists, it is further determined whether it meets the current limiting region. If it does, this intersection point is the optimal operating point at this time. Specifically... Figure 3 As shown.

[0093] Since the equations of the voltage limiting circle and the torque line are combined to form a general quartic equation, which is difficult to solve analytically, the bisection method is introduced to find the intersection point coordinates. Seven coordinates X1, X2…X7 are evenly divided within the current horizontal coordinate limit region, forming six intervals. The difference between the voltage limiting circle and the torque line corresponding to the left endpoint of the interval where the intersection point is located is always the smallest compared to other points on the left, and the difference between the torque line and the voltage limiting circle corresponding to the right endpoint is always the smallest compared to other points on the right. Therefore, based on the operating conditions in the diagram, the tangent point position is limited to between X3 and X4. Then, the midpoint coordinate Xmid of X3 and X4 is calculated. The difference between the voltage limiting circle and the torque line function value corresponding to Xmid is calculated. If it is positive, the value of the midpoint coordinate Xmid is assigned to the left endpoint X3; if it is negative, the value of the midpoint coordinate Xmid is assigned to the right endpoint X4. This calculation is repeated cyclically. When the difference between the right endpoint X4 and the left endpoint X3 is less than a certain precision, the next midpoint coordinate Xmid is the final intersection point coordinate Xfinal.

[0094] Step 3: Other operating conditions, including cases where the feedforward target torque and the voltage limiting circle intersect but do not meet the current limiting region, and cases where they do not intersect in the second quadrant. The spatial distribution of these two cases is as follows: Figure 4a and Figure 4b As shown:

[0095] When the system is in the third operating condition, the intersection of the current limiting circle and the voltage limiting circle in the second quadrant should be taken as the peak torque current point, which is the optimal operating point at this moment. Figure 5 As shown.

[0096] By using online calculation methods, the operating point in the field weakening zone was accurately calculated, the maximum starting torque in the acceleration mode was maintained, and the final stable point was the point where the stator current consumption was minimized, thus preventing the situation where the actual current could not track the target current and thus caused loss of control during the high-speed stage.

[0097] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0098] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A model parameter update-based MTPA-field-weakening feedforward control method, characterized in that, The method comprises the following steps: obtaining a difference between a target rotating speed and a current rotating speed of the motor; adjusting a target torque for correcting the difference by using a PI regulator; calculating an MTPA current by using the target torque; judging whether the MTPA current node is in an overlapping area of a voltage limit circle and a current limit circle, and if yes, the MTPA current node is a working point; further comprising judging whether the MTPA current node is in the overlapping area of the voltage limit circle and the current limit circle, and if no, starting a working point query of a feedforward method; the working point query of the feedforward method is specifically as follows: integrating the difference between the target rotating speed and the current rotating speed of the motor to obtain a feedforward target torque; obtaining an intersection point of the feedforward target torque and the voltage limit circle in a second quadrant; continuing to judge whether a current limit area is met if the intersection point exists; if yes, the intersection point is the working point; if the intersection point exists, but the intersection point does not meet the current limit area or no intersection point exists in the second quadrant, an intersection point of the current limit circle and the voltage limit circle in the second quadrant is the working point; judging whether the MTPA current node is in the overlapping area of the voltage limit circle and the current limit circle, and a formula is as follows: ； wherein i d is d shaft current, i q is q shaft current, U max is a stator end voltage allowable maximum, L d is d shaft inductance, L q is q shaft inductance.

2. A model parameter updating based MTPA-field-weakening feedforward control system using the model parameter updating based MTPA-field-weakening feedforward control method of claim 1, characterized in that, The method comprises an MTPA real-time calculation module and a working area judgment module; the MTPA real-time calculation module is used for obtaining a target torque by PI adjustment according to a difference between a target rotating speed and a current rotating speed, and calculating an MTPA current; the working area judgment module is used for judging whether the MTPA current is in an overlapping area of a voltage limit circle and a current limit circle.

3. The MTPA - field weakening feedforward control system based on model parameter updating according to claim 2, characterized in that, The method further comprises a current working point query module for calculating a spatial geometric position of the working point.

4. A computer storage medium, characterized in that, The computer storage medium stores a computer program, and the computer program is executed by a processor to realize the steps of the MTPA-weak magnetic feedforward control method based on model parameter updating.

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