Vector flux weakening control system for permanent magnet synchronous motor of electric drive system

Abstract

The present disclosure disclose a vector flux weakening control system for a permanent magnet synchronous motor of an electric drive system, which includes a current closed-loop regulation module, a modulation index deviation calculation module, a current characteristic point setting module, a current compensation vector angle calculation module, a current compensation vector amplitude calculation module, a current compensation vector calculation module and a current instruction correction module. In the present disclosure, the three-phase short-circuit current of the motor is taken as the end point of flux weakening regulation, and when voltage saturation occurs, the motor control system can exit saturation; since an inverter supplies power through a power battery bus at the terminal of the motor, the terminal voltage thereof will not be as low as zero, and there is a large margin to deal with abnormal factors; by introducing a dq current and correcting it at the same time, the pressure of resisting voltage saturation can be distributed to the dq current, thus avoiding excessive deviation of an output torque caused by excessive uniaxial current regulation. According to the present disclosure, the influence of the flux weakening control process on the output torque of the drive system is reduced as much as possible while ensuring the safety of the drive system.

Claims

1. A vector flux weakening control system for a permanent magnet synchronous motor of an electric drive system, for enhancing the robustness of the high-speed operation area of the electric drive control system, comprising a current closed-loop regulation processor, a modulation index deviation calculation processor, a current characteristic point setting processor, a current compensation vector angle calculation processor, a current compensation vector amplitude calculation processor, a current compensation vector calculation processor and a current instruction correction processor, wherein the current closed-loop regulation processor is configured to transmit dq current instructions î.sub.dref and î.sub.qref corrected by the current instruction correction processor to a proportional-integral controller to obtain dq voltage instructions v.sub.dref and V.sub.dref, the modulation index deviation calculation processor is configured to process the dq voltage instructions V.sub.dref and V.sub.dref output by the current closed-loop regulation processor to obtain a desired modulation index MI.sub.ref: ${\mathrm{MI}}_{\mathrm{ref}}=\frac{\sqrt{3\left(v_{\mathrm{dref}}^2+v_{\mathrm{qref}}^2\right)}}{V_{\mathrm{dc}}},$ where V.sub.dc is a bus voltage; then a difference between a maximum modulation index MI.sub.max of a motor control system and the desired modulation index MI.sub.ref is calculated to obtain ΔMI.sub.0, and finally a modulation index deviation ΔMI is obtained through a low-pass filter, the current characteristic point setting processor is configured to set a d-axis bus current i.sub.d_sc when a three-phase terminal of the motor is short-circuited: $i_{d\_\mathrm{sc}}=-\frac{{\phi }_f}{L_d}$ where φ.sub.f is a flux of a rotor permanent magnet and L.sub.d is a d-axis inductance, the current compensation vector amplitude calculation processor is configured to take the output modulation index deviation ΔMI of the modulation index deviation calculation processor as an input, and perform proportional-integral regulation to obtain a current vector compensation amplitude |Δi|: $.Math.\Delta i.Math.=\frac{k_{p}s+k_i}{s}\Delta \mathrm{MI},$ where k.sub.p is a proportional coefficient of the proportional-integral controller and k.sub.i is an integral coefficient of the proportional-integral controller; the current compensation vector angle calculation processor is configured to calculate a current compensation vector angle θ from a current operating point (i.sub.dref, i.sub.qref) to (i.sub.d_sc, 0): $\theta ={\cos }^{-1}\left(\frac{-i_{\mathrm{dref}}{i}_{d\_\mathrm{sc}}}{i_{d\_\mathrm{sc}}\sqrt{i_{\mathrm{dref}}^2+i_{\mathrm{qref}}^2}}\right),$ the current compensation vector calculation processor is configured to calculate dq axis compensation components Δi.sub.dref and Δi.sub.dref according to the current vector compensation amplitude output |Δi| by the current compensation vector amplitude calculation processor and the current compensation vector angle θ output by the current compensation vector angle calculation processor:
Δi.sub.qref=−|Δi| sin θ
Δi.sub.dref=|Δ| COS θ, and the current instruction correction processor is configured to superimpose the output Δi.sub.dref and Δi.sub.dre, of the current compensation vector calculation processor with original dq current instructions i.sub.dref and i.sub.dref to obtain corrected dq current instructions î.sub.dref and î.sub.qref:
î.sub.dref=i.sub.dref+Δi.sub.dref
î.sub.qref=i.sub.qref+Δi.sub.qref.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic diagram of a flux weakening control system in the prior art;

(2) FIG. 2 is a block diagram of the overall topological structure of a flux weakening system of the present disclosure;

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

(4) FIG. 4 is a schematic diagram of current compensation vector angle transformation;

(5) and

(6) FIG. 5 is a schematic diagram of current compensation vector amplitude transformation.

DESCRIPTION OF EMBODIMENTS

(7) As shown in FIG. 2, the vector flux weakening control system for a permanent magnet synchronous motor in an electric drive system of the present disclosure includes a current closed-loop regulation module, a modulation index deviation calculation module, a current characteristic point setting module, a current compensation vector angle calculation module, a current compensation vector amplitude calculation module, a current compensation vector calculation module and a current instruction correction module; specifically:

(8) (1) The current closed-loop regulation module transmits the dq current instructions î.sub.dref and î.sub.qref corrected by the current instruction correction module to the PI controller to obtain dq voltage instructions v.sub.dref and v.sub.dref.

(9) $v_{\mathrm{dref}}=\frac{K_{\mathrm{pd}}s+K_{\mathrm{id}}}{s}\left({\hat{i}}_{\mathrm{dref}}-i_d\right)$

(10) $v_{\mathrm{qref}}=\frac{K_{\mathrm{pq}}s+K_{\mathrm{iq}}}{s}\left({\hat{i}}_{\mathrm{qref}}-i_q\right)$

(11) in which, K.sub.pd and K.sub.pq are d-axis proportional coefficient and q-axis proportional coefficient of the PI controller respectively, K.sub.id and K.sub.iq are d-axis integral coefficient and q-axis integral coefficient of the PI controller respectively, and i.sub.d and i.sub.q are dq-axis feedback currents collected in real time during the operation of the PI controller.

(12) (2) As shown in FIG. 3, the modulation index deviation calculation module calculates a sum of squares of the dq voltage instructions v.sub.dref and v.sub.dref output by the current closed-loop regulation module, and then extracts a root, which is multiplied by √{square root over (3)} and divided by the bus V.sub.dc to obtain the desired modulation index MI.sub.ref:

(13) ${\mathrm{MI}}_{\mathrm{ref}}=\frac{\sqrt{3\left(v_{\mathrm{dref}}^2+v_{\mathrm{qref}}^2\right)}}{V_{\mathrm{dc}}};$

(14) A difference between the maximum modulation index MI.sub.max of the motor control system and the expected modulation index MI.sub.ref is calculated, wherein MI.sub.max can be set and its theoretical limit is 0.635; ΔMI.sub.0=MI.sub.ref−MI.sub.max is made to pass through a low-pass filter (LPF) to obtain a modulation index deviation ΔMI, wherein the function of the low-pass filter is to remove the high-frequency noise in a dq current regulator, so that the output flux weakening control system smoothly outputs a current correction, thus preventing great fluctuation of the motor torque.

(15) (3) The current characteristic point setting module: i.sub.d_sc is a d-axis bus current when the three-phase terminal of the motor is short-circuited, and the output voltage of the motor at this moment is 0, which is the flux weakening limit point of the motor, the theoretical value of which is:

(16) $i_{d\_\mathrm{sc}}=-\frac{{\phi }_f}{L_d},$

(17) in which φ.sub.f is the flux of a rotor permanent magnet and L.sub.d is a d-axis inductance. Because of the saturation effect, i.sub.d_sc will change due to the change of the d-axis inductance, but in the high-speed operation area of the motor, i.sub.d_sc is basically a fixed value in a steady state; it should be pointed out that i.sub.d_sc may be larger than the maximum current allowed by the motor drive system, and the scenario used in this application is that the short-circuit current is smaller than the maximum current, which is also a common feature of the high-speed IPMSM motor for vehicles.

(18) (4) As shown in FIG. 4, the current compensation vector amplitude calculation module takes the modulation index deviation ΔMI as an input, and adjusts the following PI regulation to obtain the current vector compensation amplitude |Δi|:

(19) 0$.Math.\Delta i.Math.=\frac{k_{p}s+k_i}{s}\Delta \mathrm{MI}$

(20) in which k.sub.p is a proportional coefficient of the PI controller and k.sub.i is an integral coefficient of the PI controller.

(21) (5) As shown in FIG. 5, the current compensation vector angle calculation module calculates the current compensation vector angle θ from current operating point (i.sub.dref, i.sub.qref) to (i.sub.d_sc, 0):

(22) $\theta ={\cos }^{-1}\left(\frac{-i_{\mathrm{dref}}{i}_{d\_\mathrm{sc}}}{i_{d\_\mathrm{sc}}\sqrt{i_{\mathrm{dref}}^2+i_{\mathrm{qref}}^2}}\right).$

(23) (6) The current compensation vector calculation module calculates dq axis compensation components Δi.sub.dref and Δi.sub.dref as follows according to the current vector compensation amplitude |Δi| output by the current compensation vector amplitude calculation module and the current compensation vector angle θ output by the current compensation vector angle calculation module:
Δi.sub.qref=−|Δi| sin θ
Δi.sub.dref=|Δi| cos θ.

(24) (7) The current instruction correction module superimposes the output Δi.sub.dref and Δi.sub.dre of the current compensation vector calculation module with original dq current instructions i.sub.dref and I.sub.dref to obtain corrected dq current instructions î.sub.dref and î.sub.qref:
î.sub.dref=i.sub.dref+Δi.sub.dref
î.sub.qref=i.sub.qref+Δi.sub.qref.