Vector control method for vehicle permanent magnet synchronous motor based on DC power

Abstract

Discloses a vector control method for a vehicle permanent magnet synchronous motor based on a DC power, which comprises a current closed-loop adjuster, a modulation index deviation calculator, a current command angle compensator, a current angle preset, a current command angle limit comparator, a current given amplitude compensator and a current given vector corrector. According to the present disclosure, the adjusting direction is always a flux-weakening direction, and instability caused by repeated adjustment will not occur; according to the present disclosure, by introducing the current for simultaneous correction, the voltage saturation-resistant pressure can be shared to the dq current, so that excessive output torque deviation caused by excessive adjustment of a single-axis current can be avoided; the traditional flux weakening target that the system is controlled without losing stability is ensured, and the accuracy of the torque is ensured.

Claims

1. A vector control method for a vehicle permanent magnet synchronous motor based on a DC power, comprising a current closed-loop adjuster, a modulation index deviation calculator, a current command angle compensator, a current angle preset, a current command angle limit comparator, a current given amplitude compensator and a current given vector corrector; wherein an input of the current closed-loop adjuster is a dq current command output by the current given vector corrector, and after passing through a proportional-integral controller, a dq voltage command is output; an input of the modulation index deviation calculator is the dq voltage command output by the current closed-loop adjuster; after extraction of a sum of squares, an expected modulation index MI.sub.ref is obtained, and then a difference between the expected modulation index and an expected maximum modulation index MI.sub.max of the control system is obtained; after passing through a low-pass filter, a modulation index deviation ΔMI is output; an input of the current angle compensator is the modulation index deviation output by the modulation index deviation calculator, and after passing through a proportional-integral compensator, a correction angle Δθ is output; the current angle preset is used for presetting a current angle θ.sub.pre; the current command angle limit comparator is used for limiting a current angle compensated by the correction angle output by the current command angle compensator to be above the current angle preset by the current angle preset;
θ+Δθ≥θ.sub.pre where θ is the current angle before flux weakening control; an input of the current given amplitude compensator is a difference ΔP between an active power and a real-time power, and a current given amplitude adjustment Δi is output after proportional-integral adjustment; wherein the real-time power P.sub.calcu is:
P.sub.calcu=U.sub.bus×I.sub.bus where U.sub.bus is a sampled value of a bus voltage and I.sub.bus is a sampled value of a bus current; an input of the current given vector corrector is a current |i| compensated by the current given amplitude adjustment output by the current given amplitude compensator, and based on the current angle preset by the current angle preset, the dq current commands i.sub.dref and i.sub.qref after flux weakening control are calculated: $\{\begin{array}{c}{i}_{\mathrm{qref}}=.Math.i.Math.\cos \left(\theta +\mathrm{\Delta \theta }\right)\\ i_{\mathrm{dref}}=-.Math.i.Math.\sin \left(\theta +\mathrm{\Delta \theta }\right)\end{array}\theta +\mathrm{\Delta \theta }>{\theta }_{\mathrm{pre}}\{\begin{array}{c}{i}_{\mathrm{qref}}=.Math.i.Math.\cos \left({\theta }_{\mathrm{pre}}\right)\\ i_{\mathrm{dref}}=-.Math.i.Math.\sin \left({\theta }_{\mathrm{pre}}\right)\end{array}\mathrm{else}.Math.i.Math.={.Math.i.Math.}_{\mathrm{origin}}+\Delta i$ where |i|.sub.origin is a current before flux weakening control.

2. The vector control method for a vehicle permanent magnet synchronous motor based on a DC power according to claim 1, wherein in the current closed-loop adjuster, the dq voltage command is obtained from the dq current commands i.sub.dref and i.sub.qref and the deviation fed back by the dq current through the proportional-integral controller, respectively.

3. The vector control method for a vehicle permanent magnet synchronous motor based on a DC power according to claim 2, wherein in the modulation index deviation calculator, a difference ΔMI.sub.0 between MI.sub.max and MI.sub.ref is: $\Delta {\mathrm{MI}}_0={\mathrm{MI}}_{\mathrm{ref}}-{\mathrm{MI}}_{\max }{\mathrm{MI}}_{\mathrm{ref}}=\frac{\sqrt{3\left(v_{d\_\mathrm{ref}}^2+v_{q\_\mathrm{ref}}^2\right)}}{V_{\mathrm{dc}}}$ where v.sub.d_ref and v.sub.q_ref are dq voltage commands, and V.sub.dc is the bus voltage.

4. The vector control method for a vehicle permanent magnet synchronous motor based on a DC power according to claim 3, wherein in the current command angle compensator, the correction angle Δθ is: $\mathrm{\Delta \theta }=\frac{k_{p}s+k_i}{s}\Delta \mathrm{MI}$ where k.sub.p is a proportional coefficient of the proportional-integral compensator and k.sub.i is an integral coefficient of the proportional-integral compensator; ΔMI is a modulation index deviation.

5. The vector control method for a vehicle permanent magnet synchronous motor based on a DC power according to claim 4, wherein the current angle preset limits an orientation of the motor by depicting a current angle curve of a maximum toque per ampere MTPA, and presets the current angle as θ.sub.pre.

6. The vector control method for a vehicle permanent magnet synchronous motor based on a DC power according to claim 5, wherein in the current given amplitude compensator, the current given amplitude adjustment ΔI is: $\Delta i=\frac{k_{\mathrm{pP}}s+k_{\mathrm{iP}}}{s}\Delta P\Delta P=P_{\mathrm{tab}}-P_{\mathrm{calcu}}$ where P.sub.tab is an active power; k.sub.pP and k.sub.iP are proportional coefficient and integral coefficient of proportional integration in the current given amplitude compensator.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a topology block diagram of a prior art of flux weakening control;

(2) FIG. 2 is a block diagram of the overall topology of the present disclosure;

(3) FIG. 3 is a schematic diagram of modulation index deviation calculation;

(4) FIG. 4 is a schematic diagram of a current command angle compensator;

(5) FIG. 5 is a schematic diagram of the preset angle set by the current angle preset; where the unit of current is A;

(6) FIG. 6 is a schematic diagram of a current compensator with a given amplitude;

(7) FIG. 7 is a schematic diagram of current angle correction in weak magnetic region; Where the unit of current is A;

(8) FIG. 8 is a schematic diagram of the change trend of current angle before and after correction; where, the unit of current is A, 1 is before correction and 2 is after correction;

(9) FIG. 9 is a comparison diagram of current angles before and after correction;

(10) FIG. 10 is a comparison diagram of measured current-torque curves of electric drive systems M1 and M2; the unit of the torque is Nm, and the unit of the current is A;

(11) FIG. 11 is a comparison diagram of measured current-torque curves of electric drive systems M1 and M3; the unit of the torque is Nm, and the unit of the current is A.

DESCRIPTION OF EMBODIMENTS

(12) The present disclosure ensures the safety of the drive system, and at the same time, reduces the influence of the flux weakening control link on the output torque of the drive system as much as possible. To achieve the above purpose, as shown in FIG. 2, the vector control method for a vehicle permanent magnet synchronous motor based on a DC power of the present disclosure includes:

(13) 1. Current closed-loop adjuster: this part is a dependent module of the present disclosure, and its function is to obtain a dq voltage command v.sub.dqref from the dq current commands i.sub.dref and i.sub.qref and the deviation fed back by the dq current respectively through the proportional-integral PI controller.

(14) 2. Modulation index deviation calculator: As shown in FIG. 3, MI.sub.ref is obtained from the extraction of the sum of squares of the dq voltage command output by the current closed loop adjuster:

(15) ${\mathrm{MI}}_{\mathrm{ref}}=\frac{\sqrt{3\left(v_{d\_\mathrm{ref}}^2+v_{q\_\mathrm{ref}}^2\right)}}{V_{\mathrm{dc}}}$

(16) where v.sub.d_ref and v.sub.q_ref are dq components of v.sub.dqref, and V.sub.dc is a bus voltage; then Δ MI.sub.0 is obtained by the difference between the expected maximum modulation index MI.sub.max of the control system and the expected modulation index MI.sub.ref:
ΔMI.sub.0=MI.sub.ref−MI.sub.max

(17) a modulation index deviation ΔMI is obtained by a low-pass filter (LPF); the function of the low-pass filter is to remove the high-frequency noise in the dq current closed-loop adjuster, so that the output flux weakening control device can smooth the output current correction and prevent the motor torque from fluctuating greatly.

(18) 3. Current command angle compensator: As shown in FIG. 4, the output of THE modulation index deviation calculator ΔMI is used as the input, and after passing through proportional-integral PI compensator, the output is the correction angle Δθ:

(19) $\mathrm{\Delta \theta }=\frac{k_{p}s+k_i}{s}\Delta \mathrm{MI}$

(20) where k.sub.p and k.sub.i are the proportional coefficient and integral coefficient of the proportional-integral compensator.

(21) 4. Current angle preset: as shown in FIG. 5, the orientation of the standard motor is limited by depicting the current angle curve of the maximum toque per ampere (MTPA), and the current angle is preset as θ.sub.pre according to the dq current curve in MTPA (1000 rpm).

(22) 5. Current command angle limit comparator: the angle compensated by the current command angle compensator is limited to be above the preset angle θ.sub.pre of the current angle preset, θ+Δθ.sub.pre; where θ is the angle of a current vector before flux weakening.

(23) 6. Current given amplitude compensator: after the current command angle compensator completes the angle compensation, it is considered that the system has met the stability requirements of flux weakening, and then its output is corrected.

(24) A real-time calculation power P.sub.calcu:
P.sub.calcu=U.sub.bus×I.sub.bus

(25) where U.sub.bus is a sampled value of a bus voltage V.sub.dcc, and I.sub.bus is a sampled value of a bus current I.sub.dc.

(26) A difference between a DC power P.sub.tab that should be operated at this time and the power P.sub.calcu calculated in real time is obtained:
ΔP=P.sub.tab−P.sub.calcu

(27) where, the direct current power P.sub.tab is obtained by looking up the table.

(28) ΔP is used as the input of the current given amplitude compensator, as shown in FIG. 6, and then the adjustment of the current given amplitude Δi is adjusted by the proportional integral PI:

(29) $\Delta i=\frac{k_{\mathrm{pP}}s+k_{\mathrm{iP}}}{s}\Delta P$

(30) where k.sub.pP and k.sub.iP are proportional coefficient and integral coefficient of proportional integration in the current given amplitude compensator.

(31) 7. Current given vector corrector (sin/cos): the current angle preset and the current given amplitude compensator are integrated to calculate the currenti.sub.dref and i.sub.qref of the dq axis after flux weakening as follows:

(32) $\{\begin{array}{c}{i}_{\mathrm{qref}}=.Math.i.Math.\cos \left(\theta +\mathrm{\Delta \theta }\right)\\ i_{\mathrm{dref}}=-.Math.i.Math.\sin \left(\theta +\mathrm{\Delta \theta }\right)\end{array}\theta +\mathrm{\Delta \theta }>{\theta }_{\mathrm{pre}}\{\begin{array}{c}{i}_{\mathrm{qref}}=.Math.i.Math.\cos \left({\theta }_{\mathrm{pre}}\right)\\ i_{\mathrm{dref}}=-.Math.i.Math.\sin \left({\theta }_{\mathrm{pre}}\right)\end{array}\mathrm{else}.Math.i.Math.={.Math.i.Math.}_{\mathrm{origin}}+\Delta i$

(33) where |i|.sub.origin is the magnitude of a current vector before flux weakening, and |i∥ is the magnitude of the current vector after Δi compensation.

(34) In this embodiment, the electric drive system M1 is constructed based on all the above modules, and the test data under the same electric drive system M1 are obtained as shown in FIGS. 7 to 9, which proves the effectiveness of the current angle preset, the current command angle limit comparator and the current given vector corrector. As shown in FIG. 7, starting from the flux weakening inflection point indicated by the arrow, the current command angle limit comparator and the current given vector corrector start to function, and the dq current running curve changes correspondingly. As shown in FIG. 8, the current angle is automatically corrected in the flux-weakening region. As shown in FIG. 9, when the slope of the curve in the figure is not 1, it means that the actual angle is larger than the preset angle θ.sub.pre. After 120°, the current given vector corrector corrects the angle, and the circle shows the correction effect.

(35) The current given amplitude compensator in the electric drive system M1 is removed to obtain another electric drive system M2, and the current sampling gain of M2 to be higher than M1, with the floating ratio of 3%; as shown in FIG. 10, the current sampling gain of the electric drive system M2 is greater than M1, resulting in the actual torque of M2 being less than M1. A current given amplitude compensator is added to the electric drive system M2 to obtain a electric drive system M3, and the current sampling gains of M2 and M3 are the same. As shown in FIG. 11, the torque of the electric drive system M3 using the current given amplitude compensator is basically the same as that of M1. To sum up, FIGS. 10-11 prove the effectiveness of the current given amplitude compensator.