CN103762923A - Control method for maximum flux-weakening operation torque of asynchronous motor - Google Patents

Abstract

The invention relates to a maximum torque control method for asynchronous motor with field-weakening operation. The asynchronous motor adopts stator field-oriented vector control, and the field-weakening area is divided into a constant power area and a reduced power area according to the voltage limit, current limit and torque limit; In the power area, the optimal flux command is obtained according to the limitation of the voltage limit and current limit, and in the power reduction area, the optimal flux command is obtained according to the limitation of the voltage limit and torque limit, so as to realize the maximum torque control of the asynchronous motor in the entire field weakening area ; This control method is based on the theory of stator field-oriented vector control, which is essentially different from the existing rotor flux-oriented vector control, and compared with direct torque control, it is inferior in torque ripple and steady-state control accuracy. 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 has obtained increasing application due to advantages such as it is simple in structure, cheap, reliable operation, easy to maintenance, capacity is large in governing system.When asynchronous machine works in territory, weak magnetic area, often require it can export breakdown torque.Under the restrictive condition of the maximum voltage that can provide at frequency converter, the rated current of motor and mechanical property, the size of magnetic flux is having a strong impact on the ability of motor output torque, if magnetic flux is too little, the torque of motor output is because the restriction of stator current diminishes, if magnetic flux is too large, when high speed, the back electromotive force of motor will become greatly, thereby exceeds the maximum voltage that frequency converter can provide, and the torque of motor output also can diminish.Therefore, need to select suitable control strategy, making motor is optimum magnetic flux at the magnetic flux in territory, weak magnetic area, and output torque is breakdown torque.

When motor speed is less than rated speed, the magnetic flux instruction of motor is specified magnetic flux, and when motor speed is greater than after rated speed, motor enters territory, weak magnetic area.In stator flux orientation vector control system, traditional weak magnetic control strategy is the control strategy that magnetic flux and rotating speed are inversely proportional to, and this control strategy is not considered the maximum voltage that frequency converter can provide, and the torque of motor output 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, to solve existing control technology, cannot realize the problem of asynchronous machine in territory, weak magnetic area output breakdown torque.

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 permanent power region and falls power region; In permanent power region, according to the restriction of voltage limit and current limitation, obtain optimum magnetic flux instruction, according to the restriction of voltage limit and torque limit, obtain optimum magnetic flux instruction falling power region, realize the maximum torque control of asynchronous machine in territory, whole weak magnetic area.

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

$({\mathrm{\&omega;}}_{\mathrm{<figure-callout\; id="2"\; label="e"\; filenames="HDA0000427401360000012.png"\; state="\{\{state\}\}">e</figure-callout>}}^2+\frac{R_s^2{\mathrm{<figure-callout\; id="2"\; label="k"\; filenames="HDA0000427401360000012.png"\; state="\{\{state\}\}">k</figure-callout>}}^2}{{\mathrm{\&sigma;}}^2{L}_s^4}){\mathrm{\&psi;}}_{s\_P}^4-2U_{\max }{\mathrm{\&omega;}}_e{\mathrm{\&psi;}}_{s\_P}^3+(U_{\max }^2-R_s^2{I}_{\max }^2+\frac{2R_s^2{k}^2{I}_{\max }^2}{\mathrm{\&sigma;}{L}_s^2}){\mathrm{\&psi;}}_{s\_\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="HDA0000427401360000012.png"\; state="\{\{state\}\}">P</figure-callout>}}^2+R_s^2{k}^2{I}_{\max }^4=0,$ 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 that falls 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 permanent power region and falls power region; In permanent power region, according to the restriction of voltage limit and current limitation, obtain optimum magnetic flux instruction, according to the restriction of voltage limit and torque limit, obtain optimum magnetic flux instruction falling power region, realize the maximum torque control of asynchronous machine in territory, whole weak magnetic area; This control method, take stator flux orientation vector control theory as basis, is essentially different with existing rotor field-oriented control, and compared with direct torque control, at aspects such as torque pulsation, steady state controling precisions, is all better than direct torque control.

Accompanying drawing explanation

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

Fig. 2 is voltage limit and the torque limit of motor when falling power region operation in embodiment;

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, according to voltage limit, current limitation and the torque limit of the operation of territory, asynchronous machine weak magnetic area, by territory, weak magnetic area Further Division, is two regions, i.e. permanent power region and fall power region.In permanent power region, the torque of motor output 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 magnetic flux instruction of motor when permanent power region operation; Falling power region, the torque of motor output 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 magnetic flux instruction of motor when falling power region operation.

1) voltage limit

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

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

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 _dcand pulse-width modulation (PWM) strategy decision, while 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 _sdcomponent u with q axle _sqneed to meet formula (2).

${\mathrm{<figure-callout\; id="2"\; label="u\; sd"\; filenames="HDA0000427401360000012.png"\; state="\{\{state\}\}">u</figure-callout>}}_{\mathrm{sd}}^{}+u_{\mathrm{<figure-callout\; id="2"\; label="sq"\; filenames="HDA0000427401360000012.png"\; state="\{\{state\}\}">sq</figure-callout>}}^2\&le;U_{\max }^2---\left(2\right)$

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

$i_{\mathrm{sq}}\&le;\frac{U_{\max }-{\mathrm{\&omega;}}_e{\mathrm{\&psi;}}_s}{R_s}---\left(3\right)$

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):

$i_{\mathrm{<figure-callout\; id="2"\; label="sd"\; filenames="HDA0000427401360000012.png"\; state="\{\{state\}\}">sd</figure-callout>}}^2+i_{\mathrm{sq}}^2\&le;I_{\max }^2---\left(5\right)$

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

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

$i_{\mathrm{sq}}\&le;\sqrt{I_{\max }^2{\left(\frac{{\mathrm{\&sigma;L}}_s}{{\mathrm{\&psi;}}_{s}1+\mathrm{\&sigma;}}(\frac{{\mathrm{\&psi;}}_{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="HDA0000427401360000012.png"\; state="\{\{state\}\}">s</figure-callout>}}^2}{{\mathrm{\&sigma;<figure-callout\; id="2"\; label="L\; s"\; filenames="HDA0000427401360000012.png"\; state="\{\{state\}\}">L</figure-callout>}}_s^{}}+I_{\max }^2)\right)}^2}---\left(6\right)$

3) torque limit

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

$T_e\&le;\frac{3(1-\mathrm{\&sigma;})n_p}{{4\mathrm{\&sigma;L}}_s}{{\mathrm{\&psi;}}_s}^2---\left(7\right)$

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

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

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

$i_{\mathrm{sq}}\&le;\frac{(1-\mathrm{\&sigma;}){\mathrm{\&psi;}}_s}{{2\mathrm{\&sigma;L}}_s}---\left(9\right)$

Asynchronous machine is when permanent power region operation, and the torque of motor output 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 moves under certain frequency, according to formula (3) and formula (6), can obtain its voltage limit and current limitation as shown in Figure 1.

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

$({\mathrm{\&omega;}}_{\mathrm{<figure-callout\; id="2"\; label="e"\; filenames="HDA0000427401360000012.png"\; state="\{\{state\}\}">e</figure-callout>}}^2+\frac{R_s^2{\mathrm{<figure-callout\; id="2"\; label="k"\; filenames="HDA0000427401360000012.png"\; state="\{\{state\}\}">k</figure-callout>}}^2}{{\mathrm{\&sigma;}}^2{L}_s^4}){\mathrm{\&psi;}}_{s\_P}^4-2U_{\max }{\mathrm{\&omega;}}_e{\mathrm{\&psi;}}_{s\_P}^3+(U_{\max }^2-R_s^2{I}_{\max }^2+\frac{2R_s^2{k}^2{I}_{\max }^2}{\mathrm{\&sigma;}{L}_s^2}){\mathrm{\&psi;}}_{s\_\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="HDA0000427401360000012.png"\; state="\{\{state\}\}">P</figure-callout>}}^2+R_s^2{k}^2{I}_{\max }^4=0,---\left(10\right)$

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

Asynchronous machine is when falling power region operation, 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 ${\mathrm{\&psi;}}_{s\_P}=\frac{2{\mathrm{\&sigma;L}}_s{U}_{\max }}{R_s(1-\mathrm{\&sigma;})+2\mathrm{\&sigma;}{L}_s{\mathrm{\&omega;}}_e}---\left(11\right)$

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

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

As shown in Figure 3, the threephase stator electric current collecting is tied to the rotation transformation of two-phase rotating coordinate system by three phase static coordinate, realizes the independent of torque current and exciting current and control.

The outer shroud of torque current is der Geschwindigkeitkreis, and the output of motor speed ring is carried out to 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 magnetic flux instruction of motor is specified magnetic flux, and when motor speed is greater than after rated speed, motor enters territory, weak magnetic area.Enter behind territory, weak magnetic area, motor obtains optimum magnetic flux instruction in permanent power region by the method for tabling look-up, and obtains optimum magnetic flux instruction falling power region through type (11), realizes the maximum torque control of asynchronous machine in territory, whole weak magnetic area; This control algolithm is take asynchronous machine stator flux orientation vector control as basis, traditional weak magnetic control is made as the control strategy that magnetic flux and rotating speed are inversely proportional to, if this method base speed is chosen as rated speed, magnetic flux instruction is less than normal, stator current is operated in current limitation, stator voltage but can not be operated in voltage limit, and the torque of motor output is not breakdown torque; If base speed is selected to be greater than rated speed, magnetic flux instruction 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 of motor output is not breakdown torque.

Claims (3)

1. The maximum torque control method for the field-weakening operation of the asynchronous motor, which is characterized in that the asynchronous motor adopts stator field-oriented vector control, and the field-weakening area is divided into a constant power area and a power reduction area according to the voltage limit, current limit and torque limit ; In the constant power area, the optimal flux command is obtained according to the limit of the voltage limit and the current limit; Torque control. 2. The maximum torque control method for asynchronous motor field weakening operation according to claim 1, characterized in that, the optimal magnetic flux ψ _{s_P} in the constant power region satisfies the following formula: $({\mathrm{\&omega;}}_e^2+\frac{R_{\mathrm{the\; s}}^2{k}^2}{{\mathrm{\&sigma;}}^2{L}_{\mathrm{the\; s}}^4}){\mathrm{\&psi;}}_{\mathrm{the\; s}\_P}^4-2u_{\max }{\mathrm{\&omega;}}_e{\mathrm{\&psi;}}_{\mathrm{the\; s}\_P}^3+(u_{\max }^2-R_{\mathrm{the\; s}}^2{I}_{\max }^2+\frac{2R_{\mathrm{the\; s}}^2{k}^2{I}_{\max }^2}{\mathrm{\&sigma;}{L}_{\mathrm{the\; s}}^2}){\mathrm{\&psi;}}_{\mathrm{the\; s}\_P}^2+R_{\mathrm{the\; s}}^2{k}^2{I}_{\max }^4=0,$ Where ω _e : synchronous rotation angular velocity; R _s : stator resistance; σ: leakage inductance; L _s : stator inductance/H; U _max : maximum value of stator voltage; I _max : maximum value of stator current;

3. The maximum torque control method of the magnetic field weakening operation of the asynchronous motor according to claim 1 or 2, characterized in that, the optimal magnetic flux ψ _{s_P} in the power reduction region is Where ω _e : synchronous rotation angular velocity; R _s : stator resistance; σ: leakage inductance; L _s : stator inductance/H; U _max : maximum value of stator voltage.

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