A full-speed range current optimization control method for a permanent magnet assisted synchronous reluctance motor with improved operating region judgment

Abstract

An optimized full-speed range current control method for a permanent magnet assisted synchronous reluctance motor with improved operating region judgment, which relates to the technical field of motor control. The present invention is to solve the problem of the decline in motor performance caused by the region judgment based on the critical speed obtained offline. The present invention constructs a mathematical model of the motor, describes the curve equations respectively, and calculates the characteristic points of the operating region; determines the current operating region of the motor and the state demarcation points within the region according to the magnitude relationship between the voltage of each characteristic point and the current voltage limit value; compares the torque of the state demarcation points within the current operating region with the reference torque value to determine the optimal operating point for the full-speed range current optimization, and takes the coordinates of the optimal operating point as the current reference value of the permanent magnet assisted synchronous reluctance motor, so as to realize the optimized control of the permanent magnet assisted synchronous reluctance motor.

Description

Technical Field

[0001] The present invention belongs to the technical field of motor control. Background Art

[0002] The permanent magnet-assisted synchronous reluctance motor (PMaSynRM) has the characteristics of simple structure, low cost and wide speed range, and has received extensive attention in the fields of industrial drive and electric vehicle applications in recent years. Thanks to its excellent field weakening performance, the motor can operate stably in a wide speed range. Therefore, it is of practical significance to study the current optimization method in the full speed range.

[0003] The full speed range current optimization method is to design the optimal operating current point according to the operating state of the motor in different operating regions. This method includes two key steps: operating region judgment and operating point determination. In different operating regions, the optimal performance indexes pursued by the motor system are not the same, so the methods for determining the optimal operating point are also different. Therefore, accurate operating region judgment is crucial for determining the operating point.

[0004] At present, the full speed range current optimization method of the permanent magnet-assisted synchronous reluctance motor judges the operating region based on the rotation speed critical results obtained offline. The critical speed is calculated a priori according to the motor parameters, and it includes the switching speed between the maximum torque per ampere (MTPA) control, the field weakening control and the maximum torque per voltage (MTPV) control. However, the critical speed obtained offline cannot be updated in real time, which leads to inaccurate judgment results of the motor operating region when the motor parameters change.

[0005] At the same time, the change of the bus voltage will also significantly affect the results of the critical speed. The critical speed is directly related to the bus voltage, and the DC bus voltage affected by the load fluctuation is a dynamic curve. Therefore, the real critical speed is a dynamic result. The critical speed determined based on the constant designed value of the bus voltage also leads to inaccurate judgment of the motor operating region. The inaccurate judgment of the operating region results in the designed motor operating point not being the optimal operating point, and even the operating point may exceed the effective operating region, leading to system instability and further affecting the operating performance of the motor system.

[0006] Based on the introduction of the above background technology, it can be seen that in the current full-speed range current trajectory planning method of permanent magnet assisted synchronous reluctance motors, the critical speed obtained offline is often used for operating region determination, and the change of the bus voltage is ignored, which leads to the decline of the motor operating performance. In order to ensure the accuracy of speed switching and improve the motor operating performance, it is of great significance to propose a real-time operating region judgment method. Summary of the Invention

[0007] The present invention is to solve the problem that in the existing full-speed range current optimization method of permanent magnet assisted synchronous reluctance motors, the critical speed obtained offline is used for operating region determination, and the change of the bus voltage is ignored, resulting in the decline of the motor operating performance. Now, an improved full-speed range current optimization control method for permanent magnet assisted synchronous reluctance motors with operating region judgment is provided.

[0008] An improved full-speed range current optimization control method for permanent magnet assisted synchronous reluctance motors with operating region judgment includes:

[0009] Construct a mathematical model of the permanent magnet assisted synchronous reluctance motor, and respectively describe the maximum torque current ratio curve equation, maximum torque voltage ratio curve equation, current limit curve equation, voltage limit curve equation and constant torque curve equation of the permanent magnet assisted synchronous reluctance motor according to the mathematical model;

[0010] Calculate the intersection point M of the maximum torque current ratio curve and the current limit curve, the intersection point N of the maximum torque voltage ratio curve and the current limit curve, and the intersection point O of the maximum torque current ratio curve and the origin in the current plane, and use the intersection points M, N and O as the operating region characteristic points;

[0011] Calculate the voltages of each operating region characteristic point respectively, and determine the current operating region of the permanent magnet assisted synchronous reluctance motor and the state demarcation point within the region according to the magnitude relationship between the voltage of each characteristic point and the current voltage limit value u lim ;

[0012] Compare the torque of the state demarcation point in the current operating region with the reference torque value to determine the optimal operating point for full-speed range current optimization, and use the coordinates of the optimal operating point as the current reference value of the permanent magnet assisted synchronous reluctance motor to realize the optimization control of the permanent magnet assisted synchronous reluctance motor.

[0013] Furthermore, the mathematical model of the above permanent magnet assisted synchronous reluctance motor includes a voltage equation and a torque equation;

[0014] The expression of the voltage equation is:

[0015]

[0016] where, Rs is the stator resistance, ω e is the electrical angular velocity, u d and u q are the voltages on the d-axis and q-axis respectively, i d and i q are the currents on the d-axis and q-axis respectively, and are the magnetic fluxes on the d-axis and q-axis respectively;

[0017] The expression of the torque equation is:

[0018]

[0019] where, T e is the motor torque, P n is the number of pole pairs of the motor.

[0020] Furthermore, the expression of the maximum torque current ratio curve equation is:

[0021]

[0022] The expression of the maximum torque voltage ratio curve equation is:

[0023]

[0024] The expression of the current limit curve equation is:

[0025]

[0026] where, I lim is the current limit value;

[0027] The expression of the voltage limit curve equation is:

[0028]

[0029] The expression of the constant torque curve equation is:

[0030]

[0031] Furthermore, the coordinates of the intersection point M are calculated by the following formula:

[0032]

[0033] The coordinates of the intersection point N are calculated by the following formula:

[0034]

[0035] The coordinates of the intersection point O are expressed as: O=(0,0).

[0036] Further, calculating the voltages of the characteristic points in each operating region respectively includes:

[0037] Calculating the voltages of the characteristic points in each operating region through the following formula:

[0038]

[0039] where u y represents the voltage of the characteristic point y in the operating region, y = M, N, O, i d,y and i q,y respectively represent the d-axis and q-axis currents of the characteristic point y in the operating region, R s is the stator resistance, ω e is the electrical angular velocity, and are the d-axis and q-axis magnetic fluxes respectively.

[0040] Further, the method for obtaining the above-mentioned current voltage limit value u lim is as follows:

[0041] Collect the current bus voltage u dc , and calculate the current voltage limit value u lim through the following formula:

[0042]

[0043] Further, when u M ≤u lim , the operating region is I;

[0044] When u M >u lim ≥u N , the operating region is II;

[0045] When u N >u lim ≥u O , the operating region is III;

[0046] When u O >u lim , the operating region is IV.

[0047] Further, the state demarcation point in the operating region I is the intersection point of the maximum torque current ratio curve and the current limit curve;

[0048] The state demarcation points in the operating region II are the intersection points of the voltage limit curve and the current limit curve and the intersection points of the voltage limit curve and the maximum torque current ratio curve;

[0049] The state demarcation points in operating region III are the intersections of the voltage limit curve with the maximum torque voltage ratio curve and the voltage limit curve with the maximum torque current ratio curve;

[0050] The state demarcation point in operating region IV is the intersection of the voltage limit curve with the maximum torque voltage ratio curve.

[0051] Furthermore, in operating region I, when the optimal operating point is the intersection of the maximum torque current ratio curve and the current limit curve, and when the optimal operating point is the intersection of the maximum torque current ratio curve and the constant torque curve with a torque value of ;

[0052] In operating region II, when the optimal operating point is the intersection of the voltage limit curve and the current limit curve, and when the optimal operating point is the intersection of the voltage limit curve and the constant torque curve with a torque value of and when the optimal operating point is the intersection of the maximum torque current ratio curve and the constant torque curve with a torque value of ;

[0053] In operating region III, when the optimal operating point is the intersection of the voltage limit curve and the maximum torque voltage ratio curve, and when the optimal operating point is the intersection of the voltage limit curve and the constant torque curve with a torque value of and when the optimal operating point is the intersection of the maximum torque current ratio curve and the constant torque curve with a torque value of ;

[0054] In operating region IV, when the optimal operating point is the intersection of the voltage limit curve and the maximum torque voltage ratio curve; when the optimal operating point is the intersection of the voltage limit curve and the constant torque curve with a torque value of ;

[0055] wherein, T e,M is the torque at intersection point M, T e,A is the torque at intersection point A, T e,B is the torque at intersection point B, T e,C is the torque at intersection point C, T e,D is the torque at intersection point D, T e,E is the torque at intersection point E;

[0056] Intersection point A is the intersection of the voltage limit curve and the current limit curve in operating region II,

[0057] Intersection point B is the intersection of the voltage limit curve and the maximum torque current ratio curve in operating region II.

[0058] Intersection point C is the intersection of the voltage limit curve and the maximum torque voltage ratio curve in operating region III.

[0059] Intersection point D is the intersection of the voltage limit curve and the maximum torque current ratio curve in operating region III.

[0060] Intersection point E is the intersection of the voltage limit curve and the maximum torque voltage ratio curve in operating region IV.

[0061] The present invention provides a determination process for the optimal operating point in the full-speed range current optimization of a permanent magnet assisted synchronous reluctance motor. Based on the voltage relationship, the operating regions of the motor are determined, and a selection scheme for the optimal current operating points in each operating region is given. The proposed method has a smooth switching process and a stable operating process. At the same time, the proposed method does not require additional signal injection and complex controller design, with a simple principle and easy implementation.

[0062] Compared with the traditional method of judging the operating region based on the prior obtained speed, the present invention fully considers the motor parameter changes and the bus voltage fluctuations, can online judge the operating region where the motor is located based on the real-time voltage relationship, and the zoning result is more accurate, ensuring the accuracy of the online optimization result.

[0063] The online optimization control method of the present invention considers the magnetic saturation effect and the motor resistance term. The adopted MTPA curve and MTPV curve consider the magnetic saturation influence, and the motor resistance term is also considered in the voltage trajectory curve, which ensures the accuracy of the modeling standard in the optimization process, and further ensures the accurate calculation of the optimized operating point. Brief Description of the Drawings

[0064] Figure 1 Schematic diagrams of different operating regions, where (a) is operating region I, (b) is operating region II, (c) is operating region III, and (d) is operating region IV;

[0065] Figure 2 Flowchart for determining the operating working point described in the present invention;

[0066] Figure 3 Schematic diagram of the influence of bus voltage change on the voltage limit curve, where (a) is at a speed of 3800 rpm and (b) is at a speed of 7000 rpm;

[0067] Figure 4 Flowchart of an improved permanent magnet assisted synchronous reluctance motor full-speed range current optimization control method for operating region judgment. Detailed Embodiment

[0068] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are only a part rather than all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments may be combined with each other.

[0069] Refer to Figures 1 to 4 Specifically describe this embodiment. The full-speed range current optimization control method for a permanent magnet assisted synchronous reluctance motor with improved operating region judgment described in this embodiment includes:

[0070] Step 1, establish a mathematical model of the permanent magnet assisted synchronous reluctance motor to describe the voltage equation and torque equation of the motor.

[0071] In this embodiment, the specific expression of the voltage equation is:

[0072]

[0073] Among them, R s is the stator resistance, ω e is the electrical angular velocity, u d and u q are the voltages on the d-axis and q-axis respectively, i d and i q are the currents on the d-axis and q-axis respectively, and are the magnetic fluxes on the d-axis and q-axis respectively.

[0074] The specific expression of the torque equation is:

[0075]

[0076] Among them, T e is the motor torque, and P n is the number of pole pairs of the motor.

[0077] Step 2, according to the motor mathematical model described in Step 1, give the equations of the maximum torque per ampere (MTPA) curve, maximum torque per voltage (MTPV) curve, current limit (CL) curve, voltage limit (VL) curve, and constant torque curve of the motor.

[0078] The expression of the established MTPA curve equation is:

[0079]

[0080] The expression of the established MTPV curve equation is as follows:

[0081]

[0082] The expression of the established CL curve equation is as follows:

[0083]

[0084] Among them, I lim is the current limit value. In this embodiment, the rated current of the 5.5kW permanent magnet assisted synchronous reluctance motor is selected as 14.7A, and the determined current limit equation is:

[0085] The VL curve equation is related to the voltage limit value u lim obtained in real time. Therefore, the equation expression of the VL curve is:

[0086]

[0087] In this embodiment, the constant torque curve equation is a series of equations under different reference torque values , and its general expression is:

[0088]

[0089] Step 3: Before real-time calculation, calculate the current coordinates of the characteristic points in the operating region according to the MTPA curve trajectory, MTPV curve trajectory, and CL curve trajectory in the current plane, including: the intersection point M of the MTPA curve and the CL curve, the intersection point N of the MTPV curve and the CL curve, and the intersection point O of the MTPA curve and the origin. The intersection points M, N, and O are used as the characteristic points for calculating each operating region.

[0090] The coordinate calculation equations of the characteristic points M and N are described as:

[0091]

[0092] Among them, C x represents the curve x, where x = MTPA, MTPV, CL. Then C x1 ∩C x2 represents the intersection point of curve x1 and curve x2.

[0093] The characteristic point O is the origin, and its coordinates are O = (i d,O , i q,O) = (0, 0). The characteristic points M and N are obtained by an iterative calculation method, and the coordinates of the characteristic points M and N are respectively described as: (i d,M , i q,M ) and (i d,N , i q,N ).

[0094] In this embodiment, based on the selected 5.5 kW permanent magnet assisted synchronous reluctance motor, the current coordinates of the three characteristic points can be calculated, which are respectively:

[0095] M = (i d,M , i q,M ) = (-15.04, 14.36)

[0096] N = (i d,N , i q,N ) = (20.22, 4.40).

[0097] O = (i d,O , i q,O ) = (0, 0)

[0098] Step 4, in the real-time calculation process, calculate the voltage limit value according to the bus voltage obtained by sampling.

[0099] In this embodiment, the bus voltage u dc is obtained by real-time sampling through a voltage Hall sensor, and the real-time voltage limit value is obtained based on the following formula:

[0100] Step 5, according to the coordinates of the three characteristic points M, N, and O obtained before the real-time calculation, calculate the voltage values at each point by using the voltage equation.

[0101] In this embodiment, according to the coordinates of the characteristic points M, N, and O, and the real-time obtained rotational speed, the voltage equations of the characteristic points are calculated as:

[0102]

[0103] where y = M, N, O.

[0104] Step 6, determine the operating region of the motor based on the relationship between the voltage at the characteristic point and the voltage limit value u lim .

[0105] When u M ≤ u lim , the operating region is I;

[0106] When u M > u lim ≥ u N , the operating region is II;

[0107] When u N > u lim ≥ u O the operating region is III;

[0108] When u O > u lim the operating region is IV;

[0109] The diagrams of different operating regions are as Figure 1 shown.

[0110] Step 7, determine the state demarcation points in each operating region according to the planned operating region.

[0111] For operating region I, there is a state demarcation point M (the intersection of the maximum torque current ratio curve and the current limit curve, denoted as C MTPA ∩ C CL ).

[0112] For operating region II, there are two state demarcation points A (the intersection of the voltage limit curve and the current limit curve, denoted as C VL ∩ C CL ) and B (the intersection of the voltage limit curve and the maximum torque current ratio curve, denoted as C VL ∩ C MTPA ).

[0113] For operating region III, there are two state demarcation points C (the intersection of the voltage limit curve and the maximum torque voltage ratio curve, denoted as C VL ∩ C MTPV ) and D (the intersection of the voltage limit curve and the maximum torque current ratio curve, denoted as C VL ∩ C MTPA );

[0114] For operating region IV, there is a state demarcation point E (the intersection of the voltage limit curve and the maximum torque voltage ratio curve, denoted as C VL ∩ C MTPV ).

[0115] The diagrams of different state demarcation points are as Figure 1 shown.

[0116] Step 8, give the optimal operating points for full-speed range current optimization according to the divided operating regions and state demarcation points.

[0117] For operating region I, when the optimal operating point is: the intersection of the maximum torque current ratio curve and the current limit curve (C MTPA ∩ C CL ); when When, the optimal operating point is: the intersection of the maximum torque current ratio curve and the constant torque curve with a torque value of T e * For the operating region II, when

[0118] For the operating region II, when When, the optimal operating point is: the intersection of the voltage limit curve and the current limit curve (C VL ∩C CL );when When, the optimal operating point is: the intersection of the voltage limit curve and the constant torque curve with a torque value of For the operating region III, when When When, the optimal operating point is: the intersection of the maximum torque current ratio curve and the constant torque curve with a torque value of For the operating region III, when

[0119] For the operating region III, when When, the optimal operating point is: the intersection of the voltage limit curve and the maximum torque voltage ratio curve (C VL ∩C MTPV );when When, the optimal operating point is: the intersection of the voltage limit curve and the constant torque curve with a torque value of For the operating region IV, when When When, the optimal operating point is: the intersection of the maximum torque current ratio curve and the constant torque curve with a torque value of For the operating region IV, when

[0120] For the operating region IV, when When, the optimal operating point is: the intersection of the voltage limit curve and the maximum torque voltage ratio curve (C VL ∩C MTPV );when When, the optimal operating point is: the intersection of the voltage limit curve and the constant torque curve with a torque value of For the operating region IV, when

[0121] Among them, represents the constant torque curve with a torque value of , T e,M is the torque at the intersection point M, T e,A is the torque at the intersection point A, T e,B is the torque at the intersection point B, T e,C is the torque at the intersection point C, T e,D is the torque at the intersection point D, T e,E is the torque at the intersection point E.

[0122] Thus, the coordinates of the optimal operating point can be obtained and used as the current reference for the permanent magnet assisted synchronous reluctance motor to optimize the motor control performance.

[0123] Although the present invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. It should thus be understood that numerous modifications can be made to the exemplary embodiments, and that other arrangements can be designed, without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that the features described herein can be combined in different ways from those described in the original claims. It should also be understood that the features described in connection with separate embodiments can be used in other described embodiments.

Claims

1. A method for optimizing the current control of a permanent magnet assisted synchronous reluctance motor in full speed range with improved operation area judgment, characterized in that: include: Constructing a mathematical model of a permanent magnet assisted synchronous reluctance motor, and describing a maximum torque current ratio curve equation, a maximum torque voltage ratio curve equation, a current limit curve equation, a voltage limit curve equation and a constant torque curve equation of the permanent magnet assisted synchronous reluctance motor according to the mathematical model; Under the current plane, the intersection point M between the maximum torque current ratio curve and the current limit curve, the intersection point N between the maximum torque voltage ratio curve and the current limit curve, and the intersection point O between the maximum torque current ratio curve and the origin are calculated respectively, and the intersection points M, N and O are used as characteristic points of the operating area; Calculate the voltage of each characteristic point in the operating area respectively, and calculate the voltage of each characteristic point according to the current voltage limit value u lim The size relationship between them determines the current operation area of ​​the permanent magnet assisted synchronous reluctance motor and determines the state demarcation point within the area; Compare the torque at the state boundary point in the current operating area with the reference torque value The size of the permanent magnet assisted synchronous reluctance motor is determined, and the optimal operating point of the full-speed domain current optimization is determined, and the coordinates of the optimal operating point are used as the current reference value of the permanent magnet assisted synchronous reluctance motor to achieve optimized control of the permanent magnet assisted synchronous reluctance motor; The step of respectively calculating the voltages of the characteristic points of each operating area includes: The voltage at the characteristic point of each operating area is calculated by the following formula: Among them, u y Represents the voltage at the characteristic point y in the operating area, y=M,N,O,i d,y and i q,y They represent the d-axis and q-axis currents of the characteristic point y in the operating area, respectively, and R s is the stator resistance, ω e is the electrical angular velocity, and are the magnetic flux of d-axis and q-axis respectively; The current voltage limit value u lim The method to obtain is: Collect the current bus voltage u dc , the current voltage limit value u is calculated by the following formula lim : When u M ≤u lim When , the operating area is I, and its state boundary point is the intersection of the maximum torque current ratio curve and the current limit curve; When u M >u lim ≥u N When , the operation area is II, and its state boundary points are the intersection of the voltage limit curve and the current limit curve and the intersection of the voltage limit curve and the maximum torque current ratio curve; When u N >u lim ≥u O When , the operation area is III, and its state boundary points are the intersection points of the voltage limit curve and the maximum torque voltage ratio curve and the intersection points of the voltage limit curve and the maximum torque current ratio curve; When u O >u lim When , the operating area is IV, and its state dividing point is the intersection of the voltage limit curve and the maximum torque voltage ratio curve.

2. A method for optimizing the current control of a permanent magnet assisted synchronous reluctance motor in full speed range with improved operation area judgment according to claim 1, characterized in that: The mathematical model of the permanent magnet assisted synchronous reluctance motor includes a voltage equation and a torque equation; The voltage equation is expressed as: Among them, R s is the stator resistance, ω e is the electrical angular velocity, u d and u q are the voltages of the d-axis and q-axis respectively, i d and i q are the currents of the d-axis and q-axis respectively, and are the magnetic flux of d-axis and q-axis respectively; The torque equation is expressed as: Among them, T e is the motor torque, P n is the number of motor pole pairs.

3. A method for optimizing the current control of a permanent magnet assisted synchronous reluctance motor in full speed range with improved operation area judgment according to claim 2, characterized in that: The expression of the maximum torque current ratio curve equation is: The expression of the maximum torque voltage ratio curve equation is: The expression of the current limit curve equation is: Among them, I lim is the current limit value; The voltage limit curve equation is expressed as: The expression of the constant torque curve equation is:

4. A method for optimizing the current control of a permanent magnet assisted synchronous reluctance motor in full speed range with improved operation area judgment according to claim 3, characterized in that: The coordinates of the intersection point M are calculated by the following formula: The coordinates of the intersection point N are calculated by the following formula: The coordinates of the intersection point O are expressed as: O=(0,0).

5. The method for optimizing the current control of a permanent magnet assisted synchronous reluctance motor in full speed range with improved operation area judgment according to claim 1 is characterized in that: In operating region I, when When , the optimal working point is the intersection of the maximum torque current ratio curve and the current limit curve. When the optimal working point is the maximum torque current ratio curve and the torque value is The intersection of the constant torque curve; In operating region II, when When , the optimal working point is the intersection of the voltage limit curve and the current limit curve. When the optimal working point is the voltage limit curve and the torque value is The intersection of the constant torque curve is When the optimal working point is the maximum torque current ratio curve and the torque value is The intersection of the constant torque curve; In operating region III, when When , the optimal working point is the intersection of the voltage limit curve and the maximum torque voltage ratio curve. When the optimal working point is the voltage limit curve and the torque value is The intersection of the constant torque curve is When the optimal working point is the maximum torque current ratio curve and the torque value is The intersection of the constant torque curve; In operating region IV, when When , the optimal working point is the intersection of the voltage limit curve and the maximum torque voltage ratio curve; when When the optimal working point is the voltage limit curve and the torque value is The intersection of the constant torque curve; Among them, T e,M is the torque at the intersection point M, T e,A is the torque at the intersection point A, T e,B is the torque at the intersection point B, T e,C is the torque at the intersection point C, T e,D is the torque at the intersection point D, T e,E is the torque at the intersection point E; Intersection point A is the intersection of the voltage limit curve and the current limit curve in operation area II. Intersection point B is the intersection of the voltage limit curve and the maximum torque current ratio curve in operating area II. The intersection point C is the intersection point of the voltage limit curve and the maximum torque voltage ratio curve in the operating area III. The intersection point D is the intersection point of the voltage limit curve and the maximum torque current ratio curve in the operating area III. The intersection point E is the intersection point of the voltage limit curve and the maximum torque voltage ratio curve in the operating region IV.

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