CN100514837C - Integrated method for vector control of induction electromotor frequency conversion under voltage and direct toque control - Google Patents

Abstract

The invention relates to a comprehensive method of vector control and direct torsion control of frequency conversion voltage regulation of induction motors. The invention is primarily to solve the technical difficulty of prior vector control method that time response velocity fails to meet the control requirement of the system. According to the technical proposal of the invention, the comprehensive method comprises the following steps. Firstly, a vector control mathematical model and a difference equation of induction motors are established; expectation values are got through calculation of the difference equation; the difference between the expectation value and the value detected in real time is the control quantity; the control quantity controls a switch of an isolated gate bipolar triode (IGBT) so as to complete combination control of the magnetic field and the torsion. Secondly, a direct torsion control model of induction motors is established; amplitude value of the torsion and size and direction of a rotating magnetic field of an induction motor are calculated in real time; the calculated values are compared with expected torsion and flux to get the difference to adjust the interval controlled and limited by the direct torsion, and to offset lag in response of vector control in nonconstant torsion or nonlinear operation area.

Description

The method of induction motor frequency conversion voltage adjusting vector and direct torque control

Technical field

The present invention relates to the method for a kind of induction motor frequency conversion voltage adjusting vector and direct torque control.

Background technology

As everyone knows, the vector control mode of induction AC motor adopts the control idea with the alternating current machine direct currentization substantially, and the stator current that is about to alternating current machine resolves into the i of the d shaft current of relative static control resultant magnetic field with rotor _d, and the i of the q shaft current of controlling torque _qJust with stator current as control variables.Control resultant flux by control stator current excitation component, control electromagnetic torque by the stator current torque component.For this reason, must carry out in real time the coordinate system of alternating current U, V, the paired direct current d of W system changeover, q system is calculated.Because this vector control method need constantly carry out more loaded down with trivial details coordinate system transformation, this operates in linearity range time response in motor or system is feasible.But when impact load occurring in system, or under the influence of fluctuations of motor transient state, this vector control control method does not reach the control requirement of system on time response velocity fails.

Summary of the invention

The objective of the invention is to solve above-mentioned technological difficulties and a kind of vector control of the induction motor frequency conversion voltage adjusting that vector control and direct torque control are combined and the integrated approach of direct torque control are provided.

The present invention for the technical scheme that solves above-mentioned technological difficulties and adopt is: the method for induction motor frequency conversion voltage adjusting vector and direct torque control, it comprises the following steps:

A) set up induction motor vector control Mathematical Modeling and difference equation, and realize the conversion of stator three-phase U, V, W AC current and voltage, and calculate desired value i the d axle and the controlling torque q axle of resultant magnetic field by following difference equation _{D (t)}, i _{Q (t)}, desired value and the i that detects gained in real time _{1d (t)}, i _{1q (t)}Subtract each other its permissible error value and be pulse width modulation (PWM) adjusting controlled quentity controlled variable, the switch of this controlled quentity controlled variable control insulated gate bipolar triode (IGBT), thus finish at constant torque or detect under the linear operation state that voltage/motor stator frequency (V/f) equals constant Comprehensive Control magnetic field and torque;

$\left[\begin{array}{c}{i}_{d\left(t\right)}\\ i_{q\left(t\right)}\end{array}\right]=\left[\begin{array}{c}\cos {\mathrm{\θ}}_x\cos \left({\mathrm{\ω}}_{s}t\right)+\sin {\mathrm{\θ}}_x\sin \left({\mathrm{\ω}}_{s}t\right)\\ \cos {\mathrm{\θ}}_x\sin \left({\mathrm{\ω}}_{s}t\right)-\sin {\mathrm{\θ}}_x\cos \left({\mathrm{\ω}}_{s}t\right)\end{array}\right]\sqrt{3}{I}_1---\left(1\right)$

In the formula: i _{D (t)}, i _{Q (t)}It is the desired value of calculating gained; I ₁It is stator current; θ _xBe the angular displacement of the leading rotor of rotating magnetic field, by ${\mathrm{\&theta;}}_x\left(t\right)=\&Integral;{\mathrm{\&omega;}}_x\mathrm{dt}=\left(\frac{{\mathrm{\&omega;}}_x\left(t\right)+{\mathrm{\&omega;}}_x(t-1)}{2}\right)\mathrm{\&Delta;t},$ ω _xBe the revolutional slip of the leading rotor of induction machine rotating magnetic field, available following formula is tried to achieve: ${\mathrm{\&omega;}}_x=\frac{{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="C200710139312E00151.png"\; state="\{\{state\}\}">r</figure-callout>}}_2/L_2}{i_{q\left(t\right)}/i_{d\left(t\right)}},$ L ₂=l ₂+ M, l ₂Be the self-induction of rotor, M is the mutual inductance between rotor and stator, r ₂Be the resistance of rotor circuit,

${\mathrm{\&omega;}}_x=\frac{{\mathrm{\&omega;}}_s-{\mathrm{\&omega;}}_r}{{\mathrm{\&omega;}}_s}---\left(2\right)$

In the formula: ω _r=ω _s-ω _sω _x, ω _sBe the speed of rotating magnetic field, ω _s=2 π f are when permanent torque moves, according to ω _sTry to achieve with the proportional relation of voltage; ω _rBe the angular speed of rotor rotation;

B) set up induction motor direct torque control model, calculate the torque T of induction motor by following formula in real time _mAmplitude and rotating magnetic field

Size and Orientation, relatively drawing difference with the torque of expectation and the magnetic flux of expectation is pulse width modulation (PWM) and regulates controlled quentity controlled variable, the switch of this controlled quentity controlled variable control insulated gate bipolar triode (IGBT), thereby finish the interval adjusting that direct torque control limits, remedy the response lag of vector control in non-constant torque or non-linear operation area;

$T_m=\frac{9.55P_r}{n_s}\&times;3---\left(3\right)$

P _r＝E _2NI ₁cosθ _s　　　　　　　　(4)

In the formula: P _rBe the power that stator is transferred to the every phase of rotor; n _sBe the rotating speed of the per minute of rotor, can be when permanent torque moves according to ω _sObtain; E _2NBe by

The voltage of induction; I ₁It is stator current; θ _sBe power of electric motor factor angle, can be by gathering stator voltage E and electric current I in real time ₁Obtain; Voltage E _2NBy measuring E in stator terminal _1NDeduct I then ₁r ₁On voltage drop and obtain E _1NBe the stator terminal measuring voltage, r ₁It is stator resistance;

In the formula:

Be by stator and the common synthetic rotating magnetic field that produces of rotor; ω _rBe the angular speed of rotor rotation, can by ${\mathrm{\&omega;}}_x=\frac{{\mathrm{\&omega;}}_s-{\mathrm{\&omega;}}_r}{{\mathrm{\&omega;}}_s}$ Obtain; E _dBe through the DC power supply before the PWM inversion; K is a constant, depends on the physical structure of motor;

C) distribute and then the adjustment power factor to adjust reactive power by control to insulated gate bipolar triode (IGBT) switch.

Because the present invention has adopted technique scheme, therefore, compares with background technology, has following effect:

(1) control method of the present invention has kept conventional vector control stability, continuity, accuracy and reliability, especially more can show its superior functionality when motor operates under the permanent torque conditions.

By Electrical Motor as can be known, when motor operates in permanent torque conditions following time, the relative velocity of synthetic rotating magnetic field and rotor is a constant, and just the magnetic flux of relative cutting is a constant between rotating magnetic field and the rotor, just

Be constant.We know that the voltage of motor stator is in addition

Wherein, f is system or motor frequency, and N is the every phase number of turn of stator winding, works as magnetic flux

V ∝ f during for constant,

ω is the motor angle frequency, ω=2 π f,

N is a rotary speed of rotator of electric motor. $n=\frac{120f}{p},$ Here p is the N of motor, the S number of poles,

f∝ω∝n.

So stator voltage has v ∝ f ∝ ω ∝ n. when permanent torque moves

(2) because the control method of the present invention technical scheme that adopted direct torque control to combine, so depart from that permanent torque moves or during in non-linear operation, this control method has been avoided the loaded down with trivial details conversion of vector control at motor with vector control.To the relation of any non-linear V/f, can utilize direct controlling torque and magnetic field and rapidly response is made in the variation of motor and system.

(3) because the core of direct torque control control method is controlling torque and magnetic field, thus when low-frequency operation, this control method can be by regulating magnetic field rapidly magnetic field hysteresis problem when compensate for low frequency is moved.Even thereby but make frequency converter also stable operation when frequency goes to zero.

(4) control method of the present invention also changes the distribution of system's reactive power by the control to the adjusting of magnetic flux and switch, and then the continuous power factor of regulating system, makes it satisfy power factor requirement under various load conditions.

(5) because combining of the topological structure of control method of the present invention and switch main circuit makes the sinusoidal waveform of the exportable perfect harmony of frequency converter.This waveform all can reach the requirement of IEEE 519-1992 to overall percent harmonic distortion (THD) index.

(6) by ω _r=ω _s-ω _sω _xFormula can be tried to achieve the angular speed of rotor, so the present invention has adopted the control loop of no speed probe, makes that this control method control rate in control procedure is fast, hardware device is simple and is easy to control.

Description of drawings

Fig. 1 is the frame principle figure of control method of the present invention;

Fig. 2 is the single-phase equivalent circuit diagram of three phase induction motor;

Fig. 3 is the current/voltage vectogram of induction motor stator circuit;

Fig. 4 is the direct voltage E of the random control of PWM _dTo exchanging A, B, C change-over circuit;

Fig. 5 is a magnetic flux

Hexagon motion track figure;

Fig. 6 is that the magnetic flux that the interval and magnetic flux of flux regulator is represented zero point moves schematic diagram;

Fig. 7 is a magnetic flux in the direct torque control method

With torque T _mThe interaction schematic diagram;

Fig. 8 is a PWM technology control IGBT switch to be provided reactive power to produce the capacitive fundamental current and changes the circuit diagram of the current/voltage of power factor to inductive load;

Fig. 9 is a PWM technology control IGBT switch to be provided reactive power to produce the capacitive fundamental current and changes the oscillogram of the current/voltage of power factor to inductive load.

Embodiment

The present invention is described in further detail below in conjunction with drawings and Examples.

As shown in Figure 1, the vector control of the induction motor frequency conversion voltage adjusting in the present embodiment and the integrated approach of direct torque control, it comprises the following steps:

A) set up induction motor vector control Mathematical Modeling and difference equation, and realize the conversion of stator three-phase U, V, W AC current and voltage, and calculate desired value i the d axle and the controlling torque q axle of resultant magnetic field by following difference equation _{D (t)}, i _{Q (t)}, desired value and the i that detects gained in real time _{1d (t)}, i _{1q (t)}Subtract each other its permissible error value and be pulse width modulation (PWM) adjusting controlled quentity controlled variable, the switch of this controlled quentity controlled variable control insulated gate bipolar triode (IGBT), thus finish at constant torque or detect under the linear operation state that voltage/motor stator frequency (V/f) equals constant Comprehensive Control magnetic field and torque;

$\left[\begin{array}{c}{i}_{d\left(t\right)}\\ i_{q\left(t\right)}\end{array}\right]=\left[\begin{array}{c}\cos {\mathrm{\&theta;}}_x\cos \left({\mathrm{\&omega;}}_{s}t\right)+\sin {\mathrm{\&theta;}}_x\sin \left({\mathrm{\&omega;}}_{s}t\right)\\ \cos {\mathrm{\&theta;}}_x\sin \left({\mathrm{\&omega;}}_{s}t\right)-\sin {\mathrm{\&theta;}}_x\cos \left({\mathrm{\&omega;}}_{s}t\right)\end{array}\right]\sqrt{3}{I}_1---\left(1\right)$

In the formula: i _{D (t)}, i _{Q (t)}It is the desired value of calculating gained; I ₁It is stator current; θ _xBe the angular displacement of the leading rotor of rotating magnetic field, by ${\mathrm{\&theta;}}_x\left(t\right)=\&Integral;{\mathrm{\&omega;}}_x\mathrm{dt}=\left(\frac{{\mathrm{\&omega;}}_x\left(t\right)+{\mathrm{\&omega;}}_x(t-1)}{2}\right)\mathrm{\&Delta;t};$ ω _xBe the revolutional slip of the leading rotor of induction machine rotating magnetic field, available following formula is tried to achieve: ${\mathrm{\&omega;}}_x=\frac{{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="C200710139312E00151.png"\; state="\{\{state\}\}">r</figure-callout>}}_2/L_2}{i_{q\left(t\right)}/i_{d\left(t\right)}},$ L ₂=l ₂+ M, l ₂Be the self-induction of rotor, M is the mutual inductance between rotor and stator, r ₂Be the resistance of rotor circuit,

${\mathrm{\&omega;}}_x=\frac{{\mathrm{\&omega;}}_s-{\mathrm{\&omega;}}_r}{{\mathrm{\&omega;}}_s}---\left(2\right)$

In the formula: ω _r=ω _s-ω _sω _x, ω _sBe the speed of rotating magnetic field, ω _s=2 π f are when permanent torque moves, according to ω _sTry to achieve with the proportional relation of voltage; ω _rBe the angular speed of rotor rotation;

Among Fig. 1

Be the flux compensation ring.Because when flux change, even allow i _dChange, can not follow flux change at once,, must increase the d shaft current component i that is directly proportional with the flux change rate in order to compensate this lagging component _d

B) set up induction motor direct torque control model, calculate the torque T of induction motor by following formula in real time _mAmplitude and rotating magnetic field

Size and Orientation, relatively drawing difference with the torque of expectation and the magnetic flux of expectation is pulse width modulation (PWM) and regulates controlled quentity controlled variable, the switch of this controlled quentity controlled variable control insulated gate bipolar triode (IGBT), thereby finish the interval adjusting that direct torque control limits, remedy the response lag of vector control in non-constant torque or non-linear operation area;

$T_m=\frac{9.55P_r}{n_s}\&times;3---\left(3\right)$

P _r＝E _2NI ₁cosθ _s　　　　　　　　(4)

In the formula: P _rBe the power that stator is transferred to the every phase of rotor; n _sBe the rotating speed of the per minute of rotor, can be when permanent torque moves according to ω _sObtain; E _2NBe by

The voltage of induction; I ₁It is stator current; θ _sBe power of electric motor factor angle, can be by gathering stator voltage E and electric current I in real time ₁Obtain; Voltage E _2NBy measuring E in stator terminal _1NDeduct I then ₁r ₁On voltage drop and obtain;

In the formula:

Be by stator and the common synthetic rotating magnetic field that produces of rotor; ω _rBe the angular speed of rotor rotation, can by ${\mathrm{\&omega;}}_x=\frac{{\mathrm{\&omega;}}_s-{\mathrm{\&omega;}}_r}{{\mathrm{\&omega;}}_s}$ Obtain; E _dBe through the DC power supply before the PWM inversion; K is a constant, depends on the physical structure of motor;

C) distribute and then the adjustment power factor to adjust reactive power by control to insulated gate bipolar triode (IGBT) switch.

As shown in Figure 2, each element is expressed as stator resistance r respectively among Fig. 2 ₁, stator leakage flux

Mutual flux between stator and rotor

Leakage-flux of rotor

With resistance r ₂/ s (its expression rotor on absorbed the active power that transmits from stator), wherein S is a revolutional slip, can by ${\mathrm{\&omega;}}_x=\frac{{\mathrm{\&omega;}}_s-{\mathrm{\&omega;}}_r}{{\mathrm{\&omega;}}_s}$ Try to achieve.

R among Fig. 2 ₁, x ₁(stator resistance, reactance), r ₂, x ₂(rotor resistance, reactance), x _m(excitation winding reactance).

By Electrical Motor as can be known, the total magnetic flux among Fig. 3

Equal With

Vector and.Promptly be:

In like manner, can be expressed from the next by the represented total torque of three phase power:

$T_m=\frac{9.55P_r}{n_s}\&times;3---\left(3\right)$

According to Electrical Motor as can be known, in the formula (3), n _sBe the rotating speed of the per minute of rotor, can be when permanent torque moves according to ω _sObtain.And ω _sBe the speed of rotating magnetic field as previously mentioned, when permanent torque moves, according to ω _sTry to achieve with the proportional relation of voltage.

Power P in the formula _rBe the active power that absorbs between point 4 and N, this power is and flows into active power unanimity between point 2 and the N.Because idle original paper X ₁, X _mDo not consume active power, therefore can get following formula:

P _r＝E _2NI ₁cosθ _s　　　　　　　　　　(4)

In the formula:

P _rBe the power that stator is transferred to the every phase of rotor.

E _2NBe by

The voltage of induction.

I ₁It is stator current.

θ _sBe power of electric motor factor angle, can be by gathering stator voltage E and electric current I in real time ₁Obtain.

Voltage E _2NCan not directly measure, but its numerical value is to calculate easily, by measuring E in stator terminal _1NDeduct I then ₁r ₁On voltage drop and obtain.

Magnetic flux in Fig. 3

Be and voltage E _2NBe directly proportional and backward its 90 °, Fig. 3 vectogram has marked stator current voltage and I ₁r ₁Between relation.Can gather stator current I in real time ₁Determine power factor cos θ with voltage E _s(ignore I herein ₁r ₁).Thereby can obtain formula (3) and formula (4), also i.e. important parameter T in the direct torque control method _mObtained solution.

Another important parameter in the direct torque control method

Available following formula is asked for:

As shown in Figure 1:

By stator and the common synthetic rotating magnetic field that produces of rotor.

ω _rBe the angular speed of rotor rotation.By preceding described, can by ${\mathrm{\&omega;}}_x=\frac{{\mathrm{\&omega;}}_s-{\mathrm{\&omega;}}_r}{{\mathrm{\&omega;}}_s}$ Obtain.Just when motor operates in lower frequency or loads thereby weak magnetic area, electric moter voltage and the rotational speed omega that fluctuation causes departing from permanent torque appears this moment _sBecome non-linear relation, but in minimum time interval, still can handle, thereby reach quick estimation ω by linear relationship _sAnd ω _rPurpose.

E _dBe through the DC power supply before the PWM inversion.

K is a constant, depends on the physical structure of motor.As motor type and the every N of stator, the number of turn that the S electrode had etc.

Because Be vector, and try to achieve by formula (7)

Value is a scalar, for ease of real-time tracing in the direct torque control method

Direction, can in the vectogram of Fig. 3, incite somebody to action

The direction of any time is obtained.

As shown in Figure 4, this be one by direct voltage Ed by random PWM method with direct voltage E _dChange into three-phase A, B, C alternating voltage circuit.Can go to the position of control switch 1,2,3,4,5,6 at any time by control PWM.Thereby produce the magnetic flux that constantly changes With torque T _m

Magnetic flux

Can be controlled in

The interval in.In like manner, torque T _mCan be controlled in T _B＜T _m＜T _AThe interval in.

According to the converter of Fig. 4 six pulses, can obtain different magnetic directions by different switch combinations.For example:, be by winding A is connected to DC power supply E for the acquisition of the magnetic direction of A (+) _dPositive terminal.And B, C winding are connected to E _dNegative pole end.The rest may be inferred for other.

As shown in Figure 5, three phase induction motor resultant magnetic field at any time

Be to control direct voltage E with the PWM conversion by switch with shown in Figure 4 _dThe magnetic flux that generation three-phase alternating current A, B, C winding are produced after inversion is corresponding.By winding and E _dDifferent connected modes can produce the magnetic flux of six direction, A (+), A (-), B (+), B (-), C (+), C (-).The stator magnetic flux of supposing three phase electric machine is limited within the dashed circle, and the magnetic flux of each direction is exactly to point to a definite direction from centre of figure so.Wanting to finish magnetic flux rotates a circle and needs the direction of six magnetic fluxs of conversion at least.

Suppose that prime direction at magnetic flux is is A (+) by vectorial 0-1.By being applied in 1 this combination of going up stack C (+), magnetic flux

To advance from 1 o'clock to 2 o'clock.Magnetic flux just

Move on to 2 points from 1.After arriving at 2, continue stack combinations again, then magnetic flux with A (-)

To continue to advance to 3.After arriving at 3, continue to use the combination of B (+) magnetic flux, with magnetic flux

Move on to a little 4, the rest may be inferred.

As shown in Figure 6, a flux regulator interval is set and controls magnetic flux

Adjustable range.The adjustable range of magnetic flux is 1.0-1.1PU among this figure, and the black matrix point among the figure shows that magnetic flux is at a time frozen in the air or become zero point that just when that moment, the speed of magnetic flux operation is zero.The immediate cause that causes this result is the three-phase alternating current winding coil short circuit that at a time DC power supply Ed is connected.Obviously, in the one-period of magnetic flux operation, chill point is many more, and magnetic flux speed is slow more, otherwise then fast more.

As shown in Figure 7, in this figure, be provided with the flux regulator zone

And torque control area T _A, T _BSuppose magnetic flux

At a time move position shown in the figure.Obviously

Than minimum magnetic flux

Little.For making

Enter the flux regulator zone, must be to DC power supply E _dControl with the connected mode of AC Windings.As previously mentioned, there are seven kinds of modes to remove to control the running orbit of magnetic flux, i.e. A (+), A (-), B (+), B (-), C (+), C (-) and particular point, zero point.Like this, select A (+) will produce a magnetic flux that points to horizontal right side, and select C (+) can produce one from the horizontal by 120 ° magnetic flux, and instantaneous with threephase stator winding and DC power supply E _dThe short circuit meeting produces a zero point, and the rest may be inferred.The track that importantly how to determine the magnetic flux operation below is to reach the purpose of controlling magnetic flux and torque simultaneously.Obviously, in the position shown in the figure, A (-), B (+) and zero point are not suitable selections, because they can make magnetic flux

Remain unchanged, perhaps become littler.Further analyze, be easy to notice that A (+), B (-), C (+), C (-) are possible selections.But how to determine best selection, this just depends on this moment torque T _mThe position.If T _m＜T _B, just select C (+), because it can be to magnetic flux

Producing one has moving of important directions, and this moves the torque that can increase motor.But, if T _mT _A, just select A (+).This selection at first is that magnetic flux has entered adjustable range, and it also produces braking action to motor torque simultaneously.At last, if T _mJust in time be in T _AAnd T _BBetween, B (-) is exactly a best choice so.Because it not only makes magnetic flux enter control interval, also motor has been produced the small torque along direction of rotation.If T _mObviously greater than T _A, just select C (-), thereby produce strong torque braking.If the slippage S of motor is bigger, also can select zero point to dwindle slippage at this moment, make it to level off in the expectation interval.No matter magnetic flux

Operate on any position of flux path circle, above control method all is suitable for.

As seen, T _m,

Be real-time measurement values, and T _A, T _B,

Desired value for control method.Its both permissible error value is the controlled quentity controlled variable of the corresponding IGBT switch of Fig. 1.

As shown in Figure 8, for example adjust to adjust power factor by perception or capacitive load to various loads for this circuit.IGBT electronic power switch shown in Fig. 8 behind voltage zero-cross preceding half period conducting and disconnect in later half cycle.Like this, just can utilize switching characteristic to carry reactive power to inductive load ZL, this also just is equivalent to and has been connected in series power capacitor in circuit.Distribute thereby changed the reactive power on the load, and then regulated the power factor of load.Use the same method, half period IGBT disconnects before also can utilizing the capacitive load circuit, and the notion of later half cycle conducting is regulated power factor.Like this, though load operation under perception or capacitive load state, control method of the present invention all has the function of powerful adjusting power factor.Said process is all monitored load character in real time by this control method and then is sent the PWM trigger impulse by controller and remove to operate corresponding IGBT switch and realize.

Claims (1)

1, the method for a kind of induction motor frequency conversion voltage adjusting vector and direct torque control is characterized in that: comprise the following steps:

A) set up induction motor vector control Mathematical Modeling and difference equation, and realize the conversion of stator three-phase U, V, W AC current and voltage, and calculate desired value i the d axle and the controlling torque q axle of resultant magnetic field by following difference equation _{D (t)}, i _{Q (t)}, desired value and the i that detects gained in real time _{1d (t)}, i _{1q (t)}Subtract each other its permissible error value and be pulse width modulation (PWM) adjusting controlled quentity controlled variable, the switch of this controlled quentity controlled variable control insulated gate bipolar triode (IGBT), thus finish at constant torque or detect under the linear operation state that voltage/motor stator frequency (V/f) equals constant Comprehensive Control magnetic field and torque;

$\left[\begin{array}{c}{i}_{d\left(t\right)}\\ i_{q\left(t\right)}\end{array}\right]=\left[\begin{array}{c}\cos {\mathrm{\&theta;}}_x\cos \left({\mathrm{\&omega;}}_{s}t\right)+\sin {\mathrm{\&theta;}}_x\sin \left({\mathrm{\&omega;}}_{s}t\right)\\ \cos {\mathrm{\&theta;}}_x\sin \left({\mathrm{\&omega;}}_{s}t\right)-\sin {\mathrm{\&theta;}}_x\cos \left({\mathrm{\&omega;}}_{s}t\right)\end{array}\right]\sqrt{3}{I}_1---\left(1\right)$

In the formula: i _{D (t)}, i _{Q (t)}It is the desired value of calculating gained; I ₁It is stator current; θ _xBe the angular displacement of the leading rotor of rotating magnetic field, by ${\mathrm{\&theta;}}_x\left(t\right)=\&Integral;{\mathrm{\&omega;}}_x\mathrm{dt}=\left(\frac{{\mathrm{\&omega;}}_x\left(t\right)+{\mathrm{\&omega;}}_x(t-1)}{2}\right)\mathrm{\&Delta;t},$ ω _xBe the revolutional slip of the leading rotor of induction machine rotating magnetic field, available following formula is tried to achieve: ${\mathrm{\&omega;}}_x=\frac{r_2/L_2}{i_{q\left(t\right)}/i_{d\left(t\right)}},$ L ₂=l ₂+ M, l ₂Be the self-induction of rotor, M is the mutual inductance between rotor and stator, r ₂Be the resistance of rotor circuit,

${\mathrm{\&omega;}}_x=\frac{{\mathrm{\&omega;}}_s-{\mathrm{\&omega;}}_r}{{\mathrm{\&omega;}}_s}---\left(2\right)$

In the formula: ω _r=ω _s-ω _sω _x, ω _sBe the speed of rotating magnetic field, ω _s=2 π f are when permanent torque moves, according to ω _sTry to achieve with the proportional relation of voltage; ω _rBe the angular speed of rotor rotation;

B) set up induction motor direct torque control model, calculate the torque T of induction motor by following formula in real time _mAmplitude and rotating magnetic field

Size and Orientation, relatively drawing difference with the torque of expectation and the magnetic flux of expectation is pulse width modulation (PWM) and regulates controlled quentity controlled variable, the switch of this controlled quentity controlled variable control insulated gate bipolar triode (IGBT), thereby finish the interval adjusting that direct torque control limits, remedy the response lag of vector control in non-constant torque or non-linear operation area;

$T_m=\frac{9055P_r}{n_s}\&times;3---\left(3\right)$

P _r＝E _2NI ₁cosθ _s　　　　　　　(4)

In the formula: P _rBe the power that stator is transferred to the every phase of rotor; n _sBe the rotating speed of the per minute of rotor, can be when permanent torque moves according to ω _sObtain; E _2NBe by

The voltage of induction; I ₁It is stator current; θ _sBe power of electric motor factor angle, can be by gathering stator voltage E and electric current I in real time ₁Obtain; Voltage E _2NBy measuring E in stator terminal _1NDeduct I then ₁r ₁On voltage drop and obtain E _1NBe the stator terminal measuring voltage, r ₁It is stator resistance;

In the formula:

Be by stator and the common synthetic rotating magnetic field that produces of rotor; ω _rBe the angular speed of rotor rotation, can by ${\mathrm{\&omega;}}_x=\frac{{\mathrm{\&omega;}}_s-{\mathrm{\&omega;}}_r}{{\mathrm{\&omega;}}_s}$ Obtain; E _dBe through the DC power supply before the PWM inversion; K is a constant, depends on the physical structure of motor;

C) distribute and then the adjustment power factor to adjust reactive power by control to insulated gate bipolar triode (IGBT) switch.

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