CONTROL METHOD FOR VECTOR FLUX WEAKENING FOR VEHICLE PERMANENT MAGNET SYNCHRONOUS MOTOR

Abstract

Disclosed is a vector flux weakening control method for vector flux weakening for a vehicle permanent magnet synchronous motor, which includes a current closed-loop adjuster, a modulation ratio deviation calculator, a current command angle compensator, a current angle preset processor, a current command angle limiting comparator and a current given vector corrector. The adjusting direction of the present disclosure is always a flux weakening direction, and instability caused by repeated adjustment will not occur; by introducing dq current while performing correction, the pressure against voltage saturation can be shared to both d-axis and q-axis current, so as to avoid excessive output torque deviation caused by excessive adjustment of a single-axis current; the influence of the flux weakening control link on the output torque of the drive system can be minimized as much possible while ensuring the safety of the drive system.

Claims

1. A control method for vector flux weakening for a vehicle permanent magnet synchronous motor, comprising a current closed-loop adjuster, a modulation ratio deviation calculator, a current command angle compensator, a current angle preset processor, a current command angle limiting comparator 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 ratio deviation calculator is the dq voltage command output by the current closed-loop adjuster; after an expected modulation ratio MI.sub.ref is obtained by solving a square root of a sum of squares, a difference between the expected modulation ratio and a expected maximum modulation ratio MI.sub.max of a control system is calculated, and after passing through the low-pass filter, a modulation ratio deviation ΔMI is output; an input of the current angle compensation module is the modulation ratio deviation output by the modulation ratio deviation calculator, and after passing through a proportional-integral compensator, a correction angle Δθ is output; the current angle preset processor is configured to preset a current angle θ.sub.pre; the current command angle limiting comparator is configured to limit the 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 processor:
θ+Δθ≥θ.sub.pre where θ is the current angle before flux weakening control; the given current vector correction module is configured to calculate d-axis and q-axis current commands i.sub.dref and i.sub.qref after flux weakening control based on the current angle preset by the current angle preset processor: $\begin{array}{cc}\{\begin{array}{c}{i}_{qref}=.Math.i.Math.\cos \left(\theta +\mathrm{\Delta \theta }\right)\\ i_{\mathrm{dref}}=-.Math.i.Math.\sin \left(\theta +\mathrm{\Delta \theta }\right)\end{array}& \theta +\mathrm{\Delta \theta }>{\theta }_{pre}\\ \{\begin{array}{c}{i}_{qref}=.Math.i.Math.\cos \left({\theta }_{pre}\right)\\ i_{dref}=-.Math.i.Math.\sin \left({\theta }_{pre}\right)\end{array}& \mathrm{else}\end{array}$ where |i| is the current before the flux weakening control.

2. The control method for vector flux weakening for a vehicle permanent magnet synchronous motor according to claim 1, wherein in the current closed-loop adjuster, the dq voltage command is obtained from a deviation of the d-axis and q-axis current commands i.sub.dref, i.sub.qref and a dq current feedback respectively through the proportional-integral controller.

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

4. The control method for vector flux weakening for a vehicle permanent magnet synchronous motor 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 and k.sub.i are proportional coefficient and integral coefficient of the proportional-integral compensator, respectively.

5. The control method for vector flux weakening for a vehicle permanent magnet synchronous motor according to claim 4, wherein the current angle preset processor limits the orientation of a motor by maximum torque per ampere (MTPA) current angle curve plotting, and the current angle θ.sub.pre is preset.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0036] FIG. 1 is a topology block diagram of flux weakening control in the related art.

[0037] FIG. 2 is a block diagram of the overall topology according to the present disclosure.

[0038] FIG. 3 is a schematic diagram of modulation ratio deviation calculation.

[0039] FIG. 4 is a schematic diagram of a current command angle compensator.

[0040] FIG. 5 is a schematic diagram of the current angle preset processor presetting an angle, where the unit of current is A.

[0041] FIG. 6 is a schematic diagram of current angle correction in a weak magnetic region.

[0042] FIG. 7 is a schematic diagram of the change trend of a current angle before and after correction, 1 is before correction and 2 is after correction.

[0043] FIG. 8 is a comparison chart of current angles before and after correction.

DESCRIPTION OF EMBODIMENTS

[0044] As shown in FIG. 2, the control method for vector flux weakening for a vehicle permanent magnet synchronous motor according to the present disclosure includes:

[0045] 1. A current closed-loop adjuster: this part is the dependent module of the present disclosure, and its function is to obtain a dq voltage command v.sub.dqref from a deviation of the dq current commands i.sub.dref, i.sub.qref and a dq current feedback respectively through the proportional-integral controller.

[0046] 2. A modulation ratio deviation calculator: as shown in FIG. 3, MI.sub.ref is obtained by solving the square root of the sum of squares of dq voltage commands output by the current closed-loop adjuster:

[00005]${\mathrm{MI}}_{ref}=\frac{\sqrt{3\left(v_{\mathrm{d\_ref}}^2+v_{\mathrm{q\_ref}}^2\right)}}{V_{dc}}$

where v.sub.d_ref and v.sub.q_ref are d-axis and q-axis components of v.sub.dqref, and V.sub.dc is the bus voltage; then ΔMI.sub.0 is obtained by the difference between the expected maximum modulation ratio MI.sub.max of the control system and the expected modulation ratio MI.sub.ref.

ΔMI.sub.0=MI.sub.ref−MI.sub.max

[0047] The modulation ratio deviation ΔMI is obtained through 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 regulating module, so that the output flux weakening control device can smooth the output current correction and prevent the motor torque from fluctuating greatly.

[0048] 3. A current command angle compensator: as shown in FIG. 4, the output of the modulation ratio deviation calculator ΔMI is used as the input, and after passing through PI compensator, the output is the correction angle Δθ:

[00006]$\mathrm{\Delta \theta }=\frac{k_{p}s+k_i}{s}\Delta \mathrm{MI}$

where k.sub.p and k.sub.i are the proportional coefficient and integral coefficient of the PI compensator.

[0049] 4. A current angle preset processor: as shown in FIG. 5, the orientation of the standard motor is limited by maximum torque per ampere (MTPA) current angle curve plotting, a value is assigned at the MTPA (1000 rpm) of the dq current curve, and the current angle is preset as θ.sub.pre.

[0050] 5. A current command angle limiting 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 processor, θ+Δ θ≥θ pre; where θ is the angle of a current vector before flux weakening.

[0051] 6. A current given vector corrector (sin/cos): combining with the current angle preset module, the current i.sub.dref and i.sub.qref of d-axis and q-axis after flux weakening are calculated as follows:

[00007]$\begin{array}{cc}\{\begin{array}{c}{i}_{qref}=.Math.i.Math.\cos \left(\theta +\mathrm{\Delta \theta }\right)\\ i_{\mathrm{dref}}=-.Math.i.Math.\sin \left(\theta +\mathrm{\Delta \theta }\right)\end{array}& \theta +\mathrm{\Delta \theta }>{\theta }_{pre}\\ \{\begin{array}{c}{i}_{qref}=.Math.i.Math.\cos \left({\theta }_{pre}\right)\\ i_{dref}=-.Math.i.Math.\sin \left({\theta }_{pre}\right)\end{array}& \mathrm{else}\end{array}$

where |i| is the magnitude of a current vector before flux weakening. As shown in FIG. 6, from the flux weakening inflection point indicated by the arrow, the current command angle limiting comparator and the current given vector corrector start to function, and the dq current running curve changes correspondingly. As shown in FIG. 7, the current angle is automatically corrected in the weak magnetic field. As shown in FIG. 8, 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, and the current given vector corrector corrects the angle after 120°, and the circle shows the correction effect.