CN103762923B - The maximum torque control method of asynchronous machine weak magnetic field operation - Google Patents

Abstract

The present invention relates to the maximum torque control method of asynchronous machine weak magnetic field operation, asynchronous machine adopts stator flux orientation vector control, and territory, weak magnetic area, according to voltage limit, current limitation and torque limit, is divided into invariable power region and falls power region; Obtain optimum flux demand in invariable power region according to the restriction of voltage limit and current limitation, obtain optimum flux demand falling the restriction of power region according to voltage limit and torque limit, realize the maximum torque control of asynchronous machine in territory, whole weak magnetic area; This control method, based on stator flux orientation vector control theory, is essentially different with existing rotor flux linkage orientation vector control, and compared with direct torque control, in torque pulsation, steady state controling precision etc., is all better than direct torque control.

Description

The maximum torque control method of asynchronous machine weak magnetic field operation

Technical field

The invention belongs to electric automobile, power electronics and motor-driven technical field, relate to a kind of maximum torque control method of asynchronous machine weak magnetic field operation.

Background technology

Asynchronous machine obtains increasing application due to advantages such as its structure is simple, cheap, reliable operation, easy to maintenance, capacity is large in governing system.When asynchronous machine works in territory, weak magnetic area, often require that it can export breakdown torque.Under maximum voltage, the rated current of motor and the restrictive condition of mechanical property that frequency converter can provide, the size of magnetic flux drastically influence the ability of motor output torque, if magnetic flux is too little, the torque that motor exports diminishes due to the restriction of stator current, if magnetic flux is too large, when high speed, the back electromotive force of motor will become large, thus exceeds the maximum voltage that frequency converter can provide, and the torque that motor exports also can diminish.Therefore, need to select suitable control strategy, make the magnetic flux of motor in territory, weak magnetic area be optimum magnetic flux, Driving Torque is breakdown torque.

When motor speed is less than rated speed, the flux demand of motor is rated flux, and after motor speed is greater than rated speed, motor enters territory, weak magnetic area.In stator flux orientation vector control system, traditional weak magnetics detect strategy is the control strategy that magnetic flux and rotating speed are inversely proportional to, and this control strategy does not consider the maximum voltage that frequency converter can provide, and the torque that motor exports is not breakdown torque.

Summary of the invention

The object of this invention is to provide a kind of maximum torque control method of asynchronous machine weak magnetic field operation, the problem of asynchronous machine in territory, weak magnetic area output breakdown torque cannot be realized to solve existing control technology.

For achieving the above object, the maximum torque control method technical scheme of asynchronous machine weak magnetic field operation of the present invention is as follows: asynchronous machine adopts stator flux orientation vector control, territory, weak magnetic area, according to voltage limit, current limitation and torque limit, is divided into invariable power region and falls power region; Obtain optimum flux demand in invariable power region according to the restriction of voltage limit and current limitation, obtain optimum flux demand falling the restriction of power region according to voltage limit and torque limit, realize the maximum torque control of asynchronous machine in territory, whole weak magnetic area.

The optimum magnetic flux ψ in described invariable power region _{s_P}meet following formula:

$({\mathrm{\ω}}_e^2+\frac{R_s^2{k}^2}{{\mathrm{\σ}}^2{L}_s^4}){\mathrm{\ψ}}_{s\_P}^4-2U_{\max }{\mathrm{\ω}}_e{\mathrm{\ψ}}_{s\_P}^3+(U_{\max }^2-R_s^2{I}_{\max }^2+\frac{2R_s^2{k}^2{I}_{\max }^2}{\mathrm{\σ}{L}_s^2}){\mathrm{\ψ}}_{s\_P}^2+R_s^2{k}^2{I}_{\max }^4=0,$ ω in formula _e: synchronous rotary angular speed; R _s: stator resistance; σ: leakage inductance coefficient; L _s: stator inductance/H; U _max: stator voltage maximum; I _max: stator current maximum;

The described optimum magnetic flux ψ falling power region _{s_P}for ω in formula _e: synchronous rotary angular speed; R _s: stator resistance; σ: leakage inductance coefficient; L _s: stator inductance/H; U _max: stator voltage maximum.

The maximum torque control method of asynchronous machine weak magnetic field operation of the present invention, asynchronous machine adopts stator flux orientation vector control, and territory, weak magnetic area, according to voltage limit, current limitation and torque limit, is divided into invariable power region and falls power region; Obtain optimum flux demand in invariable power region according to the restriction of voltage limit and current limitation, obtain optimum flux demand falling the restriction of power region according to voltage limit and torque limit, realize the maximum torque control of asynchronous machine in territory, whole weak magnetic area; This control method, based on stator flux orientation vector control theory, is essentially different with existing orientation on rotor flux, and compared with direct torque control, in torque pulsation, steady state controling precision etc., is all better than direct torque control.

Accompanying drawing explanation

Fig. 1 is the current limitation of motor when invariable power area operation and voltage limit in embodiment;

Fig. 2 be in embodiment motor fall power region run time voltage limit and torque limit;

Fig. 3 is the control block diagram of the maximum torque control method embodiment of asynchronous machine weak magnetic field operation.

Embodiment

Asynchronous machine adopts stator flux orientation vector control, and territory, weak magnetic area Further Division is two regions by voltage limit, current limitation and the torque limit run according to territory, asynchronous machine weak magnetic area, i.e. invariable power region and fall power region.In invariable power region, the torque that motor exports is subject to the restriction of voltage limit and current limitation, according to the relation of voltage limit, current limitation and motor magnetic flux, torque current, can solve the optimum flux demand of motor when invariable power area operation; Falling power region, the torque that motor exports is subject to the restriction of voltage limit and torque limit, according to the relation of voltage limit, torque limit and motor magnetic flux, torque current, can solve the optimum flux demand of motor when falling power region and running.

1) voltage limit

The steady state voltage equation of asynchronous machine stator flux orientation vector control system is as the formula (1):

$\left\{\begin{array}{c}{u}_{\mathrm{sd}}=R_s{i}_{\mathrm{sd}}\\ u_{\mathrm{sq}}=R_s{i}_{\mathrm{sq}}+{\mathrm{\ω}}_e{\mathrm{\ψ}}_s\end{array}\right.---\left(1\right)$

In formula: u _sd, u _sq---d-q axle stator voltage; i _sd, i _sq---d-q axle stator current; R _s---stator resistance; ω _e---synchronous rotary angular speed; ψ _s---stator magnetic flux.

The maximum U of stator voltage _maxby DC voltage U _dcwith pulse-width modulation (PWM) strategy decision, when adopting Using dSPACE of SVPWM strategy (SVPWM), the maximum U of stator voltage _maxfor therefore stator voltage is at the component u of d axle _sdwith the component u of q axle _sqdemand fulfillment formula (2).

$u_{\mathrm{sd}}^2+u_{\mathrm{sq}}^2\≤U_{\max }^2---\left(2\right)$

Therefore the scope of q axle component under voltage limit restriction of stator current is

$i_{\mathrm{sq}}\≤\frac{U_{\max }-{\mathrm{\ω}}_e{\mathrm{\ψ}}_s}{R_s}---\left(3\right)$

2) current limitation

Stator flux orientation vector control system meets following motor equation:

(1+τ _rp)ψ _s＝(1+στ _rp)L _si _sd-ω _slτ _rσL _si _sq（4）

In formula: τ _r---rotor time constant; P---differential operator; L _s---stator inductance; σ---leakage inductance coefficient; L _s---stator inductance; ψ _s---stator magnetic flux; ω _sl---slip.

The stator current of motor can not exceed current limitation, as the formula (5):

$i_{\mathrm{sd}}^2+i_{\mathrm{sq}}^2\≤I_{\max }^2---\left(5\right)$

In formula: I _max---stator current maximum.

Therefore the scope of q axle component under current limitation restriction of stator current is:

$i_{\mathrm{sq}}\≤\sqrt{I_{\max }^2{\left(\frac{{\mathrm{\σL}}_s}{{\mathrm{\ψ}}_{s}1+\mathrm{\σ}}(\frac{{\mathrm{\ψ}}_s^2}{{\mathrm{\σL}}_s^2}+I_{\max }^2)\right)}^2}---\left(6\right)$

3) torque limit

Pull-out torque under asynchronous machine stator flux orientation vector control and torque equation are

$T_e\≤\frac{3(1-\mathrm{\σ})n_p}{{4\mathrm{\σL}}_s}{{\mathrm{\ψ}}_s}^2---\left(7\right)$

$T_e=\frac{3}{2}{n}_p{\mathrm{\ψ}}_s{i}_{\mathrm{sq}}---\left(8\right)$

In formula: n _p---asynchronous machine number of pole-pairs; T _e---electromagnetic torque; ψ _s---stator magnetic flux;

The scope of q axle component under torque limit restriction of stator current is:

$i_{\mathrm{sq}}\≤\frac{(1-\mathrm{\σ}){\mathrm{\ψ}}_s}{{2\mathrm{\σL}}_s}---\left(9\right)$

Asynchronous machine is when invariable power area operation, and the torque that motor exports is subject to the restriction of voltage limit and current limitation, selects different magnetic fluxs, and corresponding q shaft current and the torque of motor will be different.When motor runs under certain frequency, its voltage limit and current limitation can be obtained as shown in Figure 1 according to formula (3) and formula (6).

As can be seen from Figure 1, magnetic flux is chosen as ψ _{s_P}time corresponding electromagnetic torque be breakdown torque, now machine operation is at voltage limit and current limitation, optimum magnetic flux ψ _{s_P}meet following formula

$({\mathrm{\ω}}_e^2+\frac{R_s^2{k}^2}{{\mathrm{\σ}}^2{L}_s^4}){\mathrm{\ψ}}_{s\_P}^4-2U_{\max }{\mathrm{\ω}}_e{\mathrm{\ψ}}_{s\_P}^3+(U_{\max }^2-R_s^2{I}_{\max }^2+\frac{2R_s^2{k}^2{I}_{\max }^2}{\mathrm{\σ}{L}_s^2}){\mathrm{\ψ}}_{s\_P}^2+R_s^2{k}^2{I}_{\max }^4=0,---\left(10\right)$

Asynchronous machine is when falling power region and running, and the torque that motor exports, by the restriction of voltage limit and torque limit, can obtain its voltage limit and torque limit as shown in Figure 2 according to formula (3) and formula (9).

Asynchronous machine is when falling power region and running, and optimum magnetic flux is chosen as ψ _{s_P}time corresponding electromagnetic torque be breakdown torque, now machine operation is in voltage limit and torque limit, magnetic flux ψ _{s_P}for ${\mathrm{\ψ}}_{s\_P}=\frac{2{\mathrm{\σL}}_s{U}_{\max }}{R_s(1-\mathrm{\σ})+2\mathrm{\σ}{L}_s{\mathrm{\ω}}_e}---\left(11\right)$

Below in conjunction with Fig. 3, the maximum torque control method of asynchronous machine weak magnetic field operation is further described.

Whole device is made up of three-phase voltage source type frequency converter back-to-back, and wherein net side converter is used for stable DC side voltage, and pusher side current transformer is for controlling the magnetic flux of motor, rotating speed and torque.

As shown in Figure 3, by the threephase stator electric current that collects by three-phase static coordinate system to the rotation transformation of two-phase rotating coordinate system, the independence realizing torque current and exciting current controls.

The outer shroud of torque current is der Geschwindigkeitkreis, the output of motor speed ring is carried out amplitude limiting processing by voltage limit, current limitation and torque limit, and then obtains torque current instruction.The outer shroud of exciting current is flux ring, and when motor speed is less than rated speed, the flux demand of motor is rated flux, and after motor speed is greater than rated speed, motor enters territory, weak magnetic area.After entering territory, weak magnetic area, motor obtains optimum flux demand in invariable power region by the method for tabling look-up, and obtains optimum flux demand falling power region through type (11), realizes the maximum torque control of asynchronous machine in territory, whole weak magnetic area; This control algolithm is based on asynchronous machine stator flux orientation vector control, traditional weak magnetics detect is the control strategy that magnetic flux and rotating speed are inversely proportional to, if this method base speed is chosen as rated speed, then flux demand is less than normal, stator current is operated in current limitation, stator voltage but can not be operated in voltage limit, and the torque that motor exports is not breakdown torque; If base speed is selected to be greater than rated speed, then flux demand is bigger than normal, and stator voltage is operated in voltage limit, but torque current can not trace command, and stator current can not be operated in current limitation, and the torque that motor exports is not breakdown torque.

Claims (1)

1. the maximum torque control method of asynchronous machine weak magnetic field operation, is characterized in that, asynchronous machine adopts stator flux orientation vector control, and territory, weak magnetic area, according to voltage limit, current limitation and torque limit, is divided into invariable power region and falls power region; Obtain optimum flux demand in invariable power region according to the restriction of voltage limit and current limitation, obtain optimum flux demand falling the restriction of power region according to voltage limit and torque limit, realize the maximum torque control of asynchronous machine in territory, whole weak magnetic area;

The optimum magnetic flux ψ in described invariable power region _{s_P}meet following formula: $\left({\mathrm{\ω}}_e^2+\frac{R_s^2{k}^2}{{\mathrm{\σ}}^2{L}_s^4}\right){\mathrm{\ψ}}_{s\_P}^4-2U_{\max }{\mathrm{\ω}}_e{\mathrm{\ψ}}_{s\_P}^3+\left(U_{\max }^2-R_s^2{I}_{\max }^2+\frac{2R_s^2{k}^2{I}_{\max }^2}{{\mathrm{\σL}}_s^2}\right){\mathrm{\ψ}}_{s\_P}^2+R_s^2{k}^2{I}_{\max }^4=0,$ ω in formula _e: synchronous rotary angular speed; R _s: stator resistance; σ: leakage inductance coefficient; L _s: stator inductance/H; U _max: stator voltage maximum; I _max: stator current maximum;

The described optimum magnetic flux ψ falling power region _{s_P}for ω in formula _e: synchronous rotary angular speed; R _s: stator resistance; σ: leakage inductance coefficient; L _s: stator inductance/H; U _max: stator voltage maximum.