CN102098000B - Weak magnetic speed regulating method for induction motor - Google Patents

Abstract

The invention provides a weak magnetic speed regulating method for an induction motor, and belongs to the technical field of alternating current motors and control thereof. The method comprises the following steps of: determining actual given values of exciting current and torque current by using a current control algorithm based on current optimal working trajectory; acquiring space vector pulse width modulation (SVPWM) through a current loop, and obtaining calculation action time of two adjacent non-zero voltage vectors; determining actual action time of the two non-zero voltage vectors through a modulation algorithm so as to acquire a running voltage of the motor; and at the same time, determining a field current calculation given value of the next time through the calculation action time of the two adjacent non-zero voltage vectors. By the method, an operating range of speed constant power of the induction motor is enlarged, a utilization ratio of the voltage and the current of an inverter is increased, and the maximum output torque of the induction motor is improved.

Description

A kind of induction motor weak-magnetic speed-regulating method

Technical field

The invention belongs to alternating current motor and control technology field thereof, be specifically related to a kind of induction motor weak-magnetic speed-regulating method.

Background technology

The ac motor speed control method comprises change slip speed governing, pole changing and frequency control etc.Become the slip speed governing and be divided into energy-dissipating type and feedback type change slip speed governing again, the power consumption during the former speed governing is very big, and operational efficiency is low, and the scope of application is also limited; Slip energy loopback power supply when the latter can be with motor speed adjusting, operational efficiency is high, and like string utmost point speed governing and doubly-fed adjustable speed system, but this method is only applicable to that the asynchronous motor that winds the line and draw is arranged on the rotor, is not suitable for induction motor.Pole changing can not continuous speed adjustment, is of limited application.Frequency control is more a kind of method of using at present, needs use and the motor frequency converter with capacity.Frequency Varying and speed changing method divides open loop V/F control, stator flux orientation control, rotor field-oriented control etc. again.Wherein rotor field-oriented control performance is best, but realizes that difficulty is maximum.

The principle of asynchronous motor rotor field orientation control is: under low speed, generally adopt permanent exciting current control.Along with the increase of torque, exciting current i _dRemain unchanged, and torque current i _qIncrease along with torque is linear, up to arriving the limit that motor or inverter can bear.Because the breakdown torque constant (peak power output is with rotation speed change) of motor output under low speed, so this interval is known as Heng Zhuanjuqu.The back electromotive force of motor increases down at a high speed, and the output voltage of inverter is not enough to satisfy the higher voltage requirement, generally is that exciting current is reduced therefore, air-gap flux is reduced, thereby the back electromotive force of motor is reduced.The maximum output torque of motor diminishes during this period, but exportable maximum power is constant, is called constant-power speed regulation.At last, if also need higher rotating speed, because the restriction of motor stray parameter; Need inverter to keep a constant output voltage; Exciting current and torque current need diminish simultaneously simultaneously, and it is littler that the exportable maximum power of motor also becomes gradually, and this interval is known as the constant voltage speed governing.

Above-mentioned asynchronous motor rotor field orientation control method is to exciting current i _dUsually adopt two kinds of given methods, i.e. open loop control and busbar voltage closed loop method.Open loop control is promptly tabled look-up according to the information of rotating speed, and open loop changes the size of exciting current.The shortcoming of open loop control is to utilize the fan-out capability of inverter according to the variation of busbar voltage to greatest extent, and the breakdown torque of output is not high; The busbar voltage closed loop method busbar voltage of need sampling constantly has higher requirements to sampling precision, implements cumbersome.

The control of asynchronous motor rotor field orientation is except considering above-mentioned exciting current i _dGiven method outside, but also to take the range of operation and the space voltage vector ovennodulation algorithm of electric current into account.But in the range of operation of electric current, confirm to get into proper time the constant voltage district and can improve the operational efficiency of motor in the constant voltage district, but also do not have any scheme to mention the Rule of judgment that gets into the constant voltage district at present.And existing space voltage vector ovennodulation algorithm is comparatively complicated, needs to calculate to keep the angle, in electric current loop, needs to calculate the index of modulation.

Summary of the invention

The objective of the invention is to propose a kind of induction motor weak-magnetic speed-regulating method, improved the electric current and voltage utilance of inverter, increased the range of operation of motor.

A kind of induction motor weak-magnetic speed-regulating method may further comprise the steps:

(1), and combines the exciting current calculated for given value

of current time motor and actual set-point of exciting current

and the actual set-point of torque current

that torque current calculated for given value calculates the current time motor according to the optimum work of electric current track

The optimum work of said electric current track comprises Heng Zhuanjuqu, Heng Gongshuaiqu and constant voltage district, and exciting current is constant in the permanent torque district, and torque current increases with load, and the limit of bearing up to arriving motor or inverter gets into Heng Gongshuaiqu; The peak power output of permanent power district built-in motor is constant, and along with rotating speed raises, magnetoelectricity stream reduces, and torque current increases, when the ratio of exciting current and torque current absolute value during smaller or equal to the motor magnetic leakage factor, and entering constant voltage district; Exciting current and torque current reduce simultaneously and keep that ratio is permanent to be magnetic leakage factor in the constant voltage district, reach the exciting current lower limit up to exciting current;

(2) according to step (a) in? and?

OK two adjacent non-zero voltage vector is calculated action time?

and?

(3) obtain according to step (2)

With

Confirm the practical function time of two nonzero voltage space vectors, thereby obtain the operation required voltage of motor, confirm next exciting current calculated for given value constantly

T _sBe switch periods, t is a time variable, and α is weak magnetic coefficient.

Said step (3) is confirmed the practical function time of two adjacent nonzero voltage space vectors as follows:

With the O point is vector startpoint, and first nonzero voltage space vector is positioned on the OC direction, and second nonzero voltage space vector is positioned on the OI direction, and A, B, C point be the amplitude of corresponding first nonzero voltage space vector respectively 2U _Dc/ 3 draws

Straight line OF is the angular bisector between OC and the OI, and the OD segment length on the straight line OF does

The OF segment length does

U _DcBe DC bus-bar voltage; According in the step (1)

With

Confirm synthesized voltage vector calculated for given value

Its amplitude is U ^*, the practical function time of first and second nonzero voltage space vector is expressed as T respectively ₁And T ₂,

When $U^{*}\&le;U_{\mathrm{Dc}}/\sqrt{3},$ ${\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="110127141417.png,DEST\_PATH\_110322143209.png"\; state="\{\{state\}\}">T</figure-callout>}}_1={\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="110127141417.png,DEST\_PATH\_110322143209.png"\; state="\{\{state\}\}">T</figure-callout>}}_1^{*},$ ${\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="DEST\_PATH\_110322143229.png"\; state="\{\{state\}\}">T</figure-callout>}}_2={\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="DEST\_PATH\_110322143229.png"\; state="\{\{state\}\}">T</figure-callout>}}_2^{*};$

When If

Be positioned at triangle OBD, then

Otherwise

0＜k＜1 is by T ₁And T ₂The synthesized voltage vector terminal point that effect obtains is positioned on the BD section;

When

If

Be positioned at triangle OBF, then

0＜k%＜1 is by T ₁And T ₂The synthesized voltage vector terminal point that effect obtains is positioned on the BD section, otherwise T ₁=T _s, T ₂=0.

Technique effect of the present invention is embodied in: adopt a kind of improvement exciting current i _dThe given method of closed loop has not only improved the electric current and voltage utilance of inverter, and has realized simple than existing voltage close loop method than open-loop method; According to the optimal trajectory work of electric current, can improve the range of operation of motor and improve the output torque in the gamut; Further, propose a kind of new space voltage vector ovennodulation algorithm, this algorithm is simple and practical, need not calculate to keep the angle, when there is electric current loop in system, need not calculate the index of modulation.In whole modulation range, promptly from linear zone up to six ladder patterns, algorithm can Unified Treatment, need not distinguish voltage vector and be in which kind of ovennodulation district, output voltage can change continuously.Adopt algorithm according to the invention can enlarge the speed adjustable range of motor and improve the output torque in the whole service scope.

Description of drawings

Fig. 1 always schemes for said asynchronous motor weak-magnetic speed-regulating method.

Fig. 2 is exciting current i _dThe control method sketch map, wherein Fig. 2 (a) is exciting current i _dThe given method schematic diagram of voltage close loop, Fig. 2 (b) are modified model exciting current i _dThe given method schematic diagram of closed loop.

Fig. 3 is each voltage vector sketch map action time of space voltage vector modulator approach SVPWM algorithm.

Fig. 4 is the vector running orbit figure (sixth figure) under the ovennodulation algorithm of the present invention.

Fig. 5 is current phasor (RHP) and voltage vector (left half-plane) trajectory diagram of having considered the optimum work of electric current track.

Embodiment

Fig. 6 is embodiment experimental waveform figure.

Said asynchronous motor weak-magnetic speed-regulating method is always schemed like Fig. 1.Whole weak magnetic control system algorithm increases or has improved closed loop field weakening control method, optimum three parts such as track and ovennodulation Processing Algorithm of working of electric current on the basis of rotor field-oriented vector control algorithm.Idiographic flow is: according to the optimum work of electric current track, combined the current time exciting current calculated for given value that a last moment calculates

The torque current calculated for given value that calculates with current time

Obtain the actual set-point of the final exciting current of current time With the actual set-point of torque current Wherein, right

When carrying out current limliting, be limited to I on it _QMAX, and satisfy:

Under be limited to-I _QMAX, σ is the motor magnetic leakage factor, I _MaxBe controller output current amplitude; Utilization

Calculate the calculating action time of two adjacent nonzero voltage space vectors of SVPWM through current closed-loop

With

Utilization improves the closed loop field weakening control method, will

With switch periods T _sRelatively, its difference is carried out integration and promptly get next exciting current calculated for given value constantly

Simultaneously according to calculating action time

With Adopt ovennodulation Processing Algorithm of the present invention to confirm current time two nonzero voltage space vector practical function time T ₁, T ₂In order to control.

Wherein, closed loop field weakening control method principle is seen Fig. 2.Existing exciting current closed loop control method principle is: suppose that the inverter DC bus-bar voltage is U _Dc, then the maximal phase voltage magnitude that can export of inverter does

The voltage U that system need be exported ^*With

Compare, when

The time, not much of that with regard to illustrative system voltage fan-out capability, at this moment will reduce exciting current i _dOtherwise, then increase i gradually _d, with reference to figure 2 (a).Because sampling U _DcCumbersome, the present invention combines the SVPWM algorithm to propose modified model exciting current closed loop control method, like Fig. 2 (b).

Improved excitation current loop control principle of the method is: first through the current loop to calculate the current needed to control the current two nonzero voltage vector calculating duration of action?

and? When?

without weakening and over-modulation processing; when?

voltage vector can be considered output has been unable to reach the limit, then you need to be weakening.Therefore can design weak magnetic algorithm is:

$\mathrm{\&Delta;}=T_s-({\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="110127141417.png,DEST\_PATH\_110322143209.png"\; state="\{\{state\}\}">T</figure-callout>}}_1^{*}+{\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="DEST\_PATH\_110322143229.png"\; state="\{\{state\}\}">T</figure-callout>}}_2^{*}),$ $i_d^{*}=\mathrm{\&alpha;}\&Integral;\mathrm{\&Delta;dt}$

α is a weak magnetic constant coefficient in the formula, can and confirm that its size has determined i by the systematic function requirement _dCommand value

The speed that changes, α value generally satisfy to be made The increment of phase weekly be 1/5000～1/1000 of motor rated current.

Said ovennodulation Processing Algorithm is as shown in Figure 3.

When adopting SVPWM method output voltage, space voltage vector end points scope of activities is in the hexagon that constitutes of the specific vector of six non-zeros.This hexagon is made up of six sectors.Space voltage vector can resolve into two adjacent nonzero voltage space vectors in each sector, its T action time separately ₁, T ₂Sum must be less than switch periods T _s, i.e. T ₁+ T ₂≤T _s

After executing the weak magnetic algorithm of exciting current control, adopt the ovennodulation algorithm to T ₁, T ₂Carry out amplitude limiting processing so that last output.Existing ovennodulation algorithm all can use, the modified model ovennodulation algorithm of recommending preferred the present invention to propose, and the end points track of ovennodulation algorithm synthesized voltage vector of the present invention is as shown in Figure 3.

The present invention proposes a kind of improved ovennodulation algorithm, can reduce:

1) when the amplitude

of synthesized voltage vector,

2)

The time, if

Be positioned at triangle OBD, then

Otherwise 0＜k＜1 is by T ₁And T ₂The synthesized voltage vector terminal point that effect obtains is positioned on the BD section;

3)

The time, if

Be positioned at triangle OBF, then

0＜k%＜1 is by T ₁And T ₂The synthesized voltage vector terminal point that effect obtains is positioned on the BD section, otherwise T ₁=T _s, T ₂=0.

The optimum work of said electric current track is as shown in Figure 4.

Under the stable state, the voltage equation of induction motor under synchronous coordinate system is (not considering the stator resistance pressure drop):

u _d＝-ω ₁σL _si _q，u _q＝ω ₁L _si _d

The electromagnetic torque of motor is relevant with voltage: T _e=K _vu _qu _dIt is thus clear that work as σ | i _q|=i _dThe time, two components of synthesized voltage vector in synchronous coordinate system equate.This is explanation just, works as σ | i _q| and i _dSatisfy σ | i _q|＞i _d, expression needs to get into the constant voltage output area.Answer the angle between sustaining voltage and the current phasor constant in the constant voltage output area, to realize breakdown torque/volt control.

The running orbit in three intervals of motor is described below.Shown in 4, wherein, I ₁, I ₂Be respectively the lower limit and the higher limit of exciting current, I _Max, U _MaxBe respectively controller output current amplitude and voltage magnitude, ADEF is an electric current optimized operation curve, and OGH is a voltage optimized operation curve.

1) Heng Zhuanjuqu.Current phasor end points track should be walked along the AD straight line among Fig. 4 under the low speed.

2) Heng Gongshuaiqu.After rotating speed reached a high some rotating speed, voltage end was named a person for a particular job and is positioned on the GH camber line at the D point.If will continue to increase rotating speed, obviously have only through reducing i _dJust can obtain.After the amplitude of voltage and current vector all reached maximum, because the restriction of inverter capacity, the amplitude of electric current and voltage vector can not continue to increase, and therefore can only make rotating speed continue to rise through changing its phase angle.Current locus will be walked the point up to E along the DE circular arc line this moment, and voltage trace is walked the point up to H along the GH circular arc line simultaneously.Since during this period the size of voltage, current phasor and between angle constant basically, the maximum power of motor output is also constant basically, so this interval is called as Heng Gongshuaiqu.

3) constant voltage output area.After voltage trace reaches the H point; If continue to increase rotating speed, in order to utilize the voltage fan-out capability of inverter to greatest extent, it is constant after this should to make voltage trace maintain the H point; Promptly control, so this interval is called the constant voltage output area by the every voltage of breakdown torque (MTPV).And current locus should be walked along the EF straight line, arrives F point (minimum value that exciting current allows) at last.Because the amplitude of current phasor constantly reduces, and the power of inverter output will constantly reduce, motor has not been an output-constant operation in this process.Along with rotating speed raises, the output torque of motor will descend rapidly.

The practical implementation example: to a rated power 5.5KW, the asynchronous motor of rated speed 1500r/min has carried out weak magnetic control system.Simulation waveform is as shown in Figure 5, and Fig. 5 is that motor is from static rotational speed and torque and the current waveform that starts to the 8000rpm process.Experimental waveform is as shown in Figure 6, and Fig. 6 is the current waveform of full load under the twice rated speed.Can find out from emulation and experimental result; Adopt the weak magnetic control system strategy of induction machine according to the invention; Not only can enlarge the speed adjustable range of motor and improve the output torque in the whole service scope, and be easy to practical implementation, be applicable to numerous industrial occasions such as main shaft drives, electric automobile.

Claims (2)

1. induction motor weak-magnetic speed-regulating method may further comprise the steps:

(1), and combines the exciting current calculated for given value

of current time motor and actual set-point of exciting current

and the actual set-point of torque current that torque current calculated for given value

calculates the current time motor according to the optimum work of electric current track

The optimum work of said electric current track comprises Heng Zhuanjuqu, Heng Gongshuaiqu and constant voltage district, and exciting current is constant in the permanent torque district, and torque current increases with load, and the limit of bearing up to arriving motor or inverter gets into Heng Gongshuaiqu; The peak power output of permanent power district built-in motor is constant, and along with rotating speed raises, exciting current reduces, and torque current increases, when the ratio of exciting current and torque current absolute value during smaller or equal to the motor magnetic leakage factor, and entering constant voltage district; Exciting current and torque current reduce simultaneously and keep that ratio is permanent to be magnetic leakage factor in the constant voltage district, reach the exciting current lower limit up to exciting current;

(2) according to step (a) in the

and

OK two adjacent non-zero voltage vector is calculated duration of action

and

(3) obtain according to step (2)

With

Confirm the practical function time of two adjacent nonzero voltage space vectors, thereby obtain the operation required voltage of motor, confirm next exciting current calculated for given value constantly

T _sBe switch periods, t is a time variable, and α is weak magnetic coefficient.

2. induction motor weak-magnetic speed-regulating method according to claim 1 is characterized in that, said step (3) is confirmed the practical function time of two adjacent nonzero voltage space vectors as follows:

With the O point is vector startpoint, and ray OC representes the first nonzero voltage space vector direction, and ray OI representes the second nonzero voltage space vector direction, and the line segment OA on the ray OC, OB and OC length are respectively

2U _Dc/ 3 draws Ray OF is the angular bisector between ray OC and the ray OI, and the OD segment length on the ray OF does

The OF segment length does

U _DcBe DC bus-bar voltage; According in the step (1)

With

Confirm synthesized voltage vector calculated for given value

Its amplitude is U ^*, the practical function time of first and second nonzero voltage space vector is expressed as T respectively ₁And T ₂,

When $U^{*}\&le;U_{\mathrm{Dc}}/\sqrt{3},$ $T_1=T_1^{*},T_2=T_2^{*};$

When $U_{\mathrm{Dc}}/\sqrt{3}<U^{*}\&le;{2U}_{\mathrm{Dc}}/3,$ If

Be positioned at triangle OBD, then

Otherwise

0＜k＜1 is by T ₁And T ₂The synthesized voltage vector terminal point that effect obtains is positioned on the BD section;

When ${2U}_{\mathrm{Dc}}/3<U^{*}\&le;{4U}_{\mathrm{Dc}}/3\sqrt{3},$ If Be positioned at triangle OBF, then

0＜k ^%＜1, by T ₁And T ₂The synthesized voltage vector terminal point that effect obtains is positioned on the BD section, otherwise T ₁=T _s, T ₂=0.

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