Field weakening control method combining magnetization state selection and maximum torque current ratio of memory motor

Abstract

The invention discloses a field weakening control method combining magnetization state selection and maximum torque current ratio of a memory motor, which comprises the following steps of: firstly, selecting a proper magnetization state according to different rotating speed intervals of the motor, and then reasonably distributing direct-axis and quadrature-axis current by combining a control method of the maximum torque current ratio under each magnetization state. Compared with a traditional segmented magnetic adjustment control method of the memory motor under the control of id = 0, the method has the advantages that the torque output capacity of the motor at different rotating speeds is improved, the speed adjustment range of the motor is increased under the condition of constant load, and the method has good application prospects in the industries of electric automobiles and the like.

Description

Technical Field

[0001] The invention relates to the technical field of electric transmission, and in particular to a magnetic flux partitioning and magnetic field weakening control method for a memory motor. Background Art

[0002] With the introduction of the "dual carbon" policy, permanent magnet synchronous motors are being widely used in electric vehicles, aerospace, military and other fields due to their small size, light weight and high efficiency. Among them, the memory motor can adjust the magnetization state of the aluminum nickel cobalt permanent magnet by adjusting the charging and demagnetization current, thereby changing the operating characteristics of the motor and attracting widespread attention. Its characteristics are that the load capacity of the motor is improved by applying a magnetizing pulse current to the permanent magnet in the low-speed zone, and the speed adjustment range is expanded by applying a demagnetization current in the high-speed zone. However, although the traditional id=0 segmented weak magnetic field has improved the speed regulation range of the motor to a certain extent, it cannot output the maximum torque under a given speed, which reduces the efficiency of the system to a certain extent. This design selects the appropriate magnetization state for different states of the motor, and on this basis, performs weak magnetic field through the maximum torque current ratio to improve the control performance of the motor. Summary of the invention

[0003] Purpose of the invention: The present invention provides a control method combining the magnetization state selection of a memory motor and MTPA weak magnetic control, which can improve the speed output under a constant load torque and improve the load capacity under a fixed speed.

[0004] Technical solution: To achieve this purpose, the present invention adopts the following technical solution:

[0005] The control method combining the magnetization state selection of the memory motor and the MTPA weak magnetic control of the present invention comprises the following steps:

[0006] S1: By analyzing the current limit circle and voltage limit ellipse under the constant magnetization state, the operating area under this magnetization state is obtained as follows Figure 2 As shown, it includes the constant torque area and the constant power area. Three speed points ω are calculated according to the operating area. b ,ω0,ω m , and the boundary line T between constant torque and transverse power i .

[0007] S2: Three speed points ω in the operating area according to the constant magnetization state b ,ω0,ω m , and the boundary line T between constant torque and transverse power i , and discuss the current working conditions of the motor under various operating conditions.

[0008] S3: According to the different magnetization states of the permanent magnets of the motor during the charging and demagnetization process, two magnetization states are selected and recorded as MS1 and MS2, and the flux linkage is recorded as ψ pm (i f1 ),ψ pm (i f2 ), and ψ pm (i f1 )>ψ pm (i f2 ), the operating area boundaries under the two magnetization states can be obtained by analyzing steps S1-S2 as follows Figure 6 As shown, the turning speed and the corresponding magnetic flux of the motor under each magnetization state are stored in the speed-magnetic flux table, and the current of the magnetization and demagnetization is corresponding to the magnetic flux-magnetization and demagnetization current table. The corresponding relationship is as follows Figure 8 shown.

[0009] S4: Figure 6 As shown, combined with steps S1-S3, assuming that the motor is at point A in the MS1 magnetization state at the beginning, at this time, according to the speed-flux linkage-charge and demagnetization current correspondence, by applying appropriate charge and demagnetization current, the permanent magnet flux linkage is ψ pm (i f1 ); When the speed needs to be increased to point B, due to the limitation of the MS1 operating area, a reverse demagnetization current i must be applied to the permanent magnet first f2 , so that the motor is in MS2 state. On the contrary, when the speed is reduced, the magnetizing current is applied to increase the load capacity in the low speed area.

[0010] S5: Combined with steps S1-S4, the magnetization state selection and the motion trajectory of the maximum torque current ratio of the motor under constant torque are analyzed, such as Figure 7As shown. The motor starts to work in the MS1 magnetization state, accelerates with a constant torque, and the motor working point stabilizes at the intersection A of the torque curve and the MTPA curve. As the speed increases, the voltage limit ellipse shrinks. When the speed reaches n1, the voltage limit ellipse passes through point A. At this time, the maximum output torque of the motor is limited by the DC bus voltage, and the magnetization state of the motor needs to be changed. According to the magnetic modulation strategy proposed above, a demagnetization pulse current is applied to the motor. At this time, the motor working point is located at the intersection B of the MTPA curve and the torque curve in this magnetization state. According to the voltage limit ellipse expression, it can be seen that in this magnetization state, the voltage limit ellipse expands, and the motor works stably at point B and maintains torque output. As the speed further increases, the voltage limit ellipse shrinks again to pass through point B. When the speed increases again, in order to maintain the torque output, the motor working point continues to work on the torque curve as the speed increases. At this time, the dq axis currents change until the motor works at the intersection C of the current limit circle and the torque curve. Afterwards, the motor operates at the change point D along the intersection of the current limit circle and the voltage limit ellipse. At this time, the torque output cannot be maintained and decreases as the speed n2 increases.

[0011] The relationship between the dq axis currents in various states can be analyzed and obtained in step S2.

[0012] S2.11: Speed ​​range: ω<ω b

[0013] Depend on Figure 3 It can be seen that when the speed ω<ω b When the motor runs at a relatively low speed, it will not be limited by the bus voltage. At this time, the maximum output torque of the motor is at the intersection A of the MTPA curve and the current limit circle. At this time, the AC and DC axis reference currents are calculated respectively. for:

[0014]

[0015] The maximum torque is:

[0016]

[0017] When point A is within the voltage limit ellipse, as the speed increases, the voltage limit ellipse shrinks, and the maximum torque remains at point A until point A is outside the voltage limit ellipse. At this time, the maximum speed in the constant torque zone ω b for:

[0018]

[0019] S2.12: Speed ​​range: ω b <ω<ω0

[0020] Depend on Figure 4 It can be seen that when the speed ωb When <ω<ω0, as the speed increases, the voltage limit ellipse begins to shrink until it finally passes through the origin, at which point the maximum speed ω0 in this interval is reached:

[0021]

[0022] In this range, for a fixed speed ω, the motor operates at the intersection B of the voltage limit ellipse and the MTPA curve, and the maximum output torque curve T i It also passes through point B. At this time, the AC and DC axis reference currents are calculated respectively. for:

[0023]

[0024] The torque expression on the dividing line between constant torque and constant power is:

[0025]

[0026] In this torque range, for a fixed speed ω:

[0027] When T * <T i When the motor works Figure 4 At point C, the dq current distribution is the same as in equation (5), and the torque output is the same as in equation (6).

[0028] When T * >T i When the motor works Figure 4 Point D is shown. At this time, the motor operates outside the voltage limit ellipse and is limited by the bus voltage. The AC and DC axis reference currents are calculated respectively. for:

[0029] in

[0030] The maximum output curve of the motor torque is tangent to the current limit circle at point A:

[0031]

[0032] S2.13: Speed ​​range: ω0<ω<ω m

[0033] Depend on Figure 5 It can be seen that when the speed ω0<ω<ω m When , the motor operating point is located at the intersection of the voltage limit ellipse and the current limit circle. As the speed gradually increases, the voltage limit ellipse slowly shrinks and eventually reaches the maximum speed point H.

[0034] The maximum rotational speed can be calculated at the tangent point of the voltage limit ellipse and the current limit circle:

[0035]

[0036] In this interval, the dq-axis current distribution and the maximum torque output expression are exactly the same as those of the above rotational speed ω b < ω < v0 and T * > T i when.

[0037] Advantages: Compared with the prior art, the present invention has the following advantages:

[0038] 1) Compared with the traditional segmented field-weakening control with id = 0, this method improves the torque output ability of the motor in different rotational speed intervals.

[0039] 2) Combining the field-weakening control with the maximum torque current ratio on the basis of segmented field regulation broadens the constant power operation range of the memory motor.

[0040] 3) Under the condition of constant load, this method improves the efficiency of the memory motor in different rotational speed intervals. Description of the Drawings

[0041] Figure 1 is the overall control block diagram

[0042] Figure 2 is the operation region and its boundary of the MTPA control mode under the constant magnetization state in the specific embodiment of the present invention

[0043] Figure 3 is the operation trajectory diagram in the rotational speed interval ω < ω b in the specific embodiment of the present invention

[0044] Figure 4 is the operation trajectory diagram in the rotational speed interval ω b < ω < ω0 in the specific embodiment of the present invention

[0045] Figure 5 is the operation trajectory diagram in the rotational speed interval ω0 < ω < ω m in the specific embodiment of the present invention

[0046] Figure 6 is the schematic diagram of the field regulation strategy in the specific embodiment of the present invention

[0047] Figure 7 is the field-weakening operation trajectory diagram combining magnetization state selection and MTPA in the specific embodiment of the present invention

[0048] Figure 8 is the corresponding relationship diagram of speed - field regulation pulse current - magnetic flux in the specific embodiment of the present invention

[0049] Fig. 9 The constant torque acceleration operation result of the strategy proposed in the specific implementation mode of the present invention is DETAILED DESCRIPTION

[0050] The technical solution of the present invention is further introduced below in conjunction with specific implementation modes and drawings.

[0051] This specific implementation discloses a control method combining the magnetization state selection of a memory motor and the maximum torque current ratio, such as Figure 1 As shown, the specific steps include:

[0052] S1: By analyzing the current limit circle and voltage limit ellipse under the constant magnetization state, the operating area under this magnetization state is obtained as follows Figure 2 As shown, it includes the constant torque area and the constant power area. Three speed points ω are calculated according to the operating area. b ,ω0,ω m , and the boundary line T between constant torque and transverse power i .

[0053] S2: Three speed points ω in the operating area according to the constant magnetization state b ,ω0,ω m , and the boundary line T between constant torque and transverse power i , and discuss the current working conditions of the motor under various operating conditions.

[0054] S2.11: Speed ​​range: ω<ω b

[0055] Depend on Figure 3 It can be seen that when the speed ω<ω b When the motor runs at a relatively low speed, it will not be limited by the bus voltage. At this time, the maximum output torque of the motor is at the intersection A of the MTPA curve and the current limit circle. At this time, the AC and DC axis reference currents are calculated respectively. for:

[0056]

[0057] The maximum torque is:

[0058]

[0059] When point A is within the voltage limit ellipse, as the speed increases, the voltage limit ellipse shrinks, and the maximum torque remains at point A until point A is outside the voltage limit ellipse. At this time, the maximum speed in the constant torque zone ω b for:

[0060]

[0061] S2.12: Speed ​​range: ω b <ω<ω0

[0062] Depend on Figure 4 It can be seen that when the speed ω b When <ω<ω0, as the speed increases, the voltage limit ellipse begins to shrink until it finally passes through the origin, at which point the maximum speed ω0 in this interval is reached:

[0063]

[0064] In this range, for a fixed speed ω, the motor operates at the intersection B of the voltage limit ellipse and the MTPA curve, and the maximum output torque curve T i It also passes through point B. At this time, the AC and DC axis reference currents are calculated respectively. for:

[0065]

[0066] The torque expression on the dividing line between constant torque and constant power is:

[0067]

[0068] In this torque range, for a fixed speed ω:

[0069] When T * <T i When the motor works Figure 4 At point C, the dq current distribution is the same as in equation (5), and the torque output is the same as in equation (6).

[0070] When T * >T i When the motor works Figure 4 Point D is shown. At this time, the motor operates outside the voltage limit ellipse and is limited by the bus voltage. The AC and DC axis reference currents are calculated respectively. for:

[0071]

[0072] The maximum output curve of the motor torque is tangent to the current limit circle at point A:

[0073]

[0074] S2.13: Speed ​​range: ω0<ω<ω m

[0075] Depend on Figure 5 It can be seen that when the speed ω0<ω<ω mWhen , the motor operating point is located at the intersection of the voltage limit ellipse and the current limit circle. As the speed gradually increases, the voltage limit ellipse slowly shrinks and eventually reaches the maximum speed point H.

[0076] The maximum speed is calculated from the tangent point of the voltage limit ellipse and the current limit circle:

[0077]

[0078] In this range, the dq axis current distribution and maximum torque output expression are consistent with the above speed ω b <ω<ω0 and T * >T i Exactly the same when.

[0079] S3: According to the different magnetization states of the permanent magnets of the motor during the charging and demagnetization process, two magnetization states are selected and recorded as MS1 and MS2, and the flux linkage is recorded as ψ pm (i f1 ),ψ pm (i f2 ), and ψ pm (i f1 )>ψ pm (i f2 ), the operating area boundaries under the two magnetization states can be obtained by analyzing steps S1-S2 as follows Figure 6 As shown, the turning speed and the corresponding magnetic flux of the motor under each magnetization state are stored in the speed-magnetic flux table, and the current of the magnetization and demagnetization is corresponding to the magnetic flux-magnetization and demagnetization current table. The corresponding relationship is as follows Figure 8 shown.

[0080] S4: Figure 6 As shown, combined with steps S1-S3, assuming that the motor is at point A in the MS1 magnetization state at the beginning, at this time, according to the speed-flux linkage-charge and demagnetization current correspondence, by applying appropriate charge and demagnetization current, the permanent magnet flux linkage is ψ pm (i f1 ); When the speed needs to be increased to point B, due to the limitation of the MS1 operating area, a reverse demagnetization current i must be applied to the permanent magnet first f2 , so that the motor is in MS2 state. On the contrary, when the speed is reduced, the magnetizing current is applied to increase the load capacity in the low speed area.

[0081] S5: Combined with steps S1-S4, the magnetization state selection and the motion trajectory of the maximum torque current ratio of the motor under constant torque are analyzed, such as Figure 7As shown. The motor starts to work in the MS1 magnetization state, accelerates with a constant torque, and the motor working point stabilizes at the intersection A of the torque curve and the MTPA curve. As the speed increases, the voltage limit ellipse shrinks. When the speed reaches n1, the voltage limit ellipse passes through point A. At this time, the maximum output torque of the motor is limited by the DC bus voltage, and the magnetization state of the motor needs to be changed. According to the magnetic modulation strategy proposed above, a demagnetization pulse current is applied to the motor. At this time, the motor working point is located at the intersection B of the MTPA curve and the torque curve in this magnetization state. According to the voltage limit ellipse expression, it can be seen that in this magnetization state, the voltage limit ellipse expands, and the motor works stably at point B and maintains torque output. As the speed further increases, the voltage limit ellipse shrinks again to pass through point B. When the speed increases again, in order to maintain the torque output, the motor working point continues to work on the torque curve as the speed increases. At this time, the dq axis currents change until the motor works at the intersection C of the current limit circle and the torque curve. Afterwards, the motor operates at the change point D along the intersection of the current limit circle and the voltage limit ellipse. At this time, the torque output cannot be maintained and decreases as the speed n2 increases.

[0082] The relationship between the dq axis currents in various states can be analyzed and obtained in step S2.

[0083] The process of observing the permanent magnetic flux linkage by the above-mentioned permanent magnetic flux linkage observer is as follows:

[0084] The super-helical sliding film flux observer is used, and its control algorithm is shown as follows:

[0085]

[0086] Among them, x1, x2 and They represent the state variables and their estimated values ​​respectively, ρ1(x1,t) and ρ2(x2,t) are the system disturbances, and k1 and k2 are the control switching gains.

[0087] To ensure that the system converges to the sliding surface within a finite time, the following requirements must be met:

[0088]

[0089] It can be seen from the motor state equation that the permanent magnet flux only appears in the q-axis equation expression, so the q-axis expression is written as follows:

[0090]

[0091] Where A = -R / L q , B=1 / L q , u=u q -L d ωi d , k e=-1 / L q , e q =ωψ pm (i f ), e q It is the component of the permanent magnet magnetic flux rotation electromotive force on the q axis.

[0092] Based on the q-axis equation (12), the following sliding film observer is designed:

[0093]

[0094] in, is the q-axis current observation value, is the estimated value of the current error of the q axis,

[0095] Select the synovial hyperplane function Corresponding to formula (10), we can get:

[0096]

[0097] When σ>>0:

[0098]

[0099] When equation (14) and inequality (15) are satisfied, it is guaranteed that the system can converge to the synovial hyperplane within a certain period of time. Subtracting equation (12) from equation (13) yields:

[0100]

[0101] When the actual value i q With observed value When they are equal, it can be considered that the system has reached the synovial hyperplane. At this time:

[0102]

[0103] S6: Set the direct axis current given value obtained in step S5 and the quadrature axis current given value With the direct axis current i d and the quadrature axis current i q After comparison, the direct axis voltage u is obtained through the current regulator d and the quadrature axis voltage u q .

[0104] S7: The direct axis voltage u d and the quadrature axis voltage u q The α-axis voltage u under two-phase stationary coordinates is obtained by dq / αβ transformation α and β-axis voltage u β , will u α and uβ and DC bus voltage U dc The SVPWM is input into the space vector pulse modulation unit (SVPWM), and the six pulse modulation signals output by the operation drive the power tubes in the three-phase inverter; at the same time, the magnetic modulation pulse current i f With the magnetic modulation pulse given value Together they are input into the PWM module to generate a PWM signal to drive the H-bridge converter used in the modulated magnetic converter.

[0105] The motor starts to work at 0.24Wb (MS1) magnetization state, accelerating at a constant torque of 2Nm. When the speed reaches 1024rmp, Figure 7 At point A, the maximum output torque of the motor is limited by the DC bus voltage, and the magnetization state of the motor needs to be changed. According to the magnetic adjustment strategy proposed above, a demagnetization pulse current of -40A is applied to the motor to make the motor work in the magnetization state of 0.14Wb (MS2). As the speed increases further, when the speed increases to about 1400rpm, Figure 7 At point B, the motor operating point starts to work on the 2Nm curve. At this time, both the dq axis currents change. As the speed further increases to 2100rpm, Figure 7 At point D, the torque output cannot be maintained and decreases as the speed increases.

[0106] In this process, the analysis of the motor operating point is as follows: Figure 7 As shown; the motor speed, torque, dq axis current are as follows Fig. 9 shown.

Claims

1. A control method combining magnetization state selection of a memory motor and maximum torque current ratio, characterized in that: The following steps are involved: S1: By analyzing the current limit circle and voltage limit ellipse under the constant magnetization state, the operating area under this magnetization state is obtained as shown in Figure 2, including the constant torque area and the constant power area. Three speed points ω are calculated according to the operating area. b ,ω0,ω m , and the boundary line T between constant torque and transverse power i . S2: Three speed points ω in the operating area according to the constant magnetization state b ,ω0,ω m , and the boundary line T between constant torque and transverse power i , and discuss the current working conditions of the motor under various operating conditions. S3: According to the different magnetization states of the permanent magnets of the motor during the charging and demagnetization process, two magnetization states are selected and recorded as MS1 and MS2 respectively, and the flux linkage is recorded as ψ pm (i f1 ),ψ pm (i f2 ), and ψ pm (i f1 )>ψ pm (i f2 ), the operating area boundaries under the two magnetization states can be obtained by analyzing step S1-S2 as shown in Figure 6, and then the turning speed under each magnetization state and the corresponding flux of the motor are stored in the speed-flux table, and the charging and demagnetization current is corresponding to the flux-charging and demagnetization current table. The corresponding relationship is shown in Figure 8. S4: As shown in FIG6, combined with steps S1-S3, assuming that the motor is at point A in the MS1 magnetization state at the beginning, at this time, according to the speed-flux linkage-charge and demagnetization current correspondence, by applying appropriate charge and demagnetization current, the permanent magnet flux linkage is ψ pm (i f1 ); When the speed needs to be increased to point B, due to the limitation of the MS1 operating area, a reverse demagnetization current i must be applied to the permanent magnet first f2 , so that the motor is in MS2 state. Conversely, when the speed decreases, a magnetizing current is applied to increase the load capacity in the low speed area. S5: Combined with steps S1-S4, the magnetization state selection and the motion trajectory of the maximum torque current ratio of the motor under constant torque are analyzed, as shown in Figure 7. The motor starts to work in the MS1 magnetization state, accelerates with a constant torque, and the motor operating point stabilizes at the intersection A of the torque curve and the MTPA curve. As the speed increases, the voltage limit ellipse shrinks, and when the speed reaches n1, the voltage limit ellipse passes through point A. At this time, the maximum output torque of the motor is limited by the DC bus voltage, and the magnetization state of the motor needs to be changed. According to the magnetic modulation strategy proposed above, a demagnetization pulse current is applied to the motor. At this time, the motor operating point is located at the intersection B of the MTPA curve and the torque curve under this magnetization state. According to the voltage limit ellipse expression, in this magnetization state, the voltage limit ellipse expands, and the motor works stably at point B and maintains torque output. As the speed increases further, the voltage limit ellipse shrinks again to pass through point B. When the speed increases again, in order to maintain the torque output, the motor working point continues to work on the torque curve as the speed increases. At this time, the dq axis currents change until the motor works at the intersection C of the current limit circle and the torque curve. After that, the motor works at the change point D along the intersection of the current limit circle and the voltage limit ellipse. At this time, the torque output cannot be maintained and decreases with the increase of the speed n2. The relationship between the dq axis currents in various states can be analyzed and obtained in step S2.

2. The control method combining the magnetization state selection and the maximum torque current ratio of the memory motor according to claim 1 is characterized in that: The step S2 specifically includes the following steps: S2.11: Speed ​​range: ω<ω b As shown in Figure 3, when the speed ω<ω b When the motor runs at a relatively low speed, it will not be limited by the bus voltage. At this time, the maximum output torque of the motor is at the intersection A of the MTPA curve and the current limit circle. At this time, the AC and DC axis reference currents are calculated respectively. for: The maximum torque is: When point A is within the voltage limit ellipse, as the speed increases, the voltage limit ellipse shrinks, and the maximum torque remains at point A until point A is outside the voltage limit ellipse. At this time, the maximum speed in the constant torque zone ω b for: S2.12: Speed ​​range: ω b <ω<ω0 As shown in Figure 4, when the speed ω b When <ω<ω0, as the speed increases, the voltage limit ellipse begins to shrink until it finally passes through the origin, at which point the maximum speed ω0 in this interval is reached: In this range, for a fixed speed ω, the motor operates at the intersection B of the voltage limit ellipse and the MTPA curve, and the maximum output torque curve T i It also passes through point B. At this time, the AC and DC axis reference currents are calculated respectively. for: The torque expression on the dividing line between constant torque and constant power is: In this torque range, for a fixed speed ω: When T * <T i When , the motor works at point C as shown in Figure 4. At this time, the dq current distribution is the same as that of equation (5). The torque output is the same as that of equation (6). When T * >T i When the motor works at point D as shown in Figure 4, the motor works outside the voltage limit ellipse and is limited by the bus voltage. The AC and DC axis reference currents are calculated respectively. for: The maximum output curve of the motor torque is tangent to the current limit circle at point A: S2.13: Speed ​​range: ω0<ω<ω m As shown in Figure 5, when the speed ω0<ω<ω m When , the motor operating point is located at the intersection of the voltage limit ellipse and the current limit circle. As the speed gradually increases, the voltage limit ellipse slowly shrinks and eventually reaches the maximum speed point H. The maximum speed is calculated from the tangent point of the voltage limit ellipse and the current limit circle: In this range, the dq axis current distribution and maximum torque output expression are consistent with the above speed ω b <ω<ω0 and T * >T i Exactly the same when.

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