CN1004852B - Inverter-driven induction motor control method - Google Patents

Abstract

An induction motor driven by a voltage-type inverter measures a torque current component by detecting a primary current flowing through the induction motor. The output voltage and frequency of the voltage source converter are controlled based on the measured torque current component. Further, the rotational speed of the induction motor is estimated based on the measured torque current component. The rotation speed of the induction motor is controlled by: that is, the estimated speed signal is made to coincide with the speed command signal.

Description

The control method of converter drive type inductive motor

The present invention relates to a kind of control method of induction motor, be converted to torque current component and excitation current component with the primary current of this method motor, they can be distinguished independently and are controlled, thus the rotating speed of control of induction.

About the control of induction motor, vector control method knows altogether that so far with regard to this method, the primary current of motor is converted to can distinguish controlled independently torque component and excitatory component.Adopt vector control method, the speed control of induction motor can be as realizing with high-speed response in DC motor control situation.

Vector control method as induction motor, usually can be divided into magnetic flux detecting vector control method and slip frequency controlled type vector control method (Slip frequeucy Ceutrol), preceding a kind of control method is disclosed, for example in the corresponding West Germany of United States Patent (USP) № 3824437(publication (DE-OS) № 1941312) in done open, a kind of representational method in back is disclosed among the open communique № 11125/1976 of Japan Patent, with regard to magnetic flux detecting vector control method, in induction motor, the magnetic flux detector must be housed, therefore, such control method can not be used in the designed induction motor of general purpose.In this case, in recent years, slip frequency controlled type vector control method had been caused not only that people noted, and nowadays be used for practical application.

The slip frequency controlled type vector control method that is used for induction motor is based on the output frequency that the rotating speed that relies on motor comes control change device unit.Therefore, need with signal conductor or cable mutual connection between speed detector and power converter cells, and the output of transmission speed detector (or angular position detector).There is the system configuration complexity in this class vector control method as being applied to existing induction motor, shortcoming such as easy break-down in the control procedure.

In order to overcome above-mentioned shortcoming, a kind of so-called speed-less sensor vector control system that is used for induction motor has been proposed.In this system, do not adopt speed detector or senser, and motor current (primary current) and frequency be to control according to the magnetic flux of motor, and magnetic flux be from the terminal voltage of the motor that records by calculate to determine-as Mary's peace people such as (MarianP) at IEEE(1983) being entitled as described in " to a simple control system of the driving induction motor of power pack " article of delivering.

Yet, with regard to the velocity transducer vector control system described in the data of quoting as proof above, still leave over the problem that some wait to solve, for example be used to survey the iron core magnetic saturation phenomenon of the isolating transformer of motor voltage, be used to calculate the problems such as drift of determining magnetic flux and other integrator, particularly under the low-frequency operation state, it is difficulty or even impossible making the calculating of magnetic flux reach satisfied precision, therefore more can not guarantee stable operation.

A kind of control method that the purpose of this invention is to provide induction motor, this method are under without the situation of detector (as speed, the detector of voltage detector and the like) and can improve control precision to the induction motor rotating speed.

Another object of the present invention provides a kind of control method of induction motor, in by the voltage source converter induction motor driven, this method can prevent to cause the decline of control characteristic owing to builtin voltage descends, and can suppress torque appearance fluctuation, thereby guaranteed High Accuracy Control to induction motor.

In view of above-mentioned and other purposes (will become clearer) by following explanation, according to general characteristic of the present invention, propose: the output voltage of converter and frequency are according to being controlled by converter induction motor driven primary current component, this component reference phase with the converter output voltage on phase place is identical, the rotating speed of induction motor or frequency are controlled to consistent with frequency instruction, and this instruction is in turn to be determined by aforesaid current component.

According to another target of the present invention, the voltage drop of converter circuitry is to determine by the calculating to converter output current detection signal, and the output voltage instruction is calibrated according to calculating determined result.

Now accompanying drawing is made brief description:

The circuit diagram of Fig. 1 is represented the structure according to a pulse width modulation (hereinafter to be referred as PWM) the changer system control circuit of the embodiment of the invention.

Fig. 2 a is the general equivalent diagram that shows an induction motor.

Fig. 2 b shows the induction motor equivalent diagram of having eliminated elementary leakage reactance.

Fig. 3 is the performance diagram that concerns between slip frequency and the electric current in the explanation control operation.

Fig. 4 has represented the signal waveforms for the work of explanation pwm converter.

Fig. 5 is a simple circuit diagram, the basic functional principle of expression method of measurement translator internal drop according to the present invention.

Fig. 6 is a performance diagram, and expression converter internal drop and function generator give the relation of putting between the command value.

Fig. 7,8,9,10 and 11 all is circuit diagrams, represents the structure of control circuit in accordance with another embodiment of the present invention respectively.

Figure 12 and 13 is flow charts, represents the performed program of control circuit shown in Figure 11.

Be elaborated referring now to the most preferred embodiment of accompanying drawing to induction motor control method according to the present invention.

Fig. 1 has shown according to one embodiment of the invention, as the PWM(pulse width modulation of induction motor) the type control system.

At first, to the present invention at the basic structure of so-called Speedless sensor type (promptly not having velocity transducer) vector control apparatus be illustrated.

With reference to Fig. 1, pwm converter that dc voltage conversion is become the alternating voltage of a changeable frequency of label 1 expression, converter 1 is made up of the self-gravitation element that inside is connected into lattice Ritz (poly phase rectification) connection, each has a feedback diode of reverse parallel connection connection therewith from putting out element, resembles this class solid switch element of transistor or gate-turn-off (GTO) silicon controlled rectifier and can be used as the self-gravitation element.Induction motor 2 is connected the U of converter 1, V and W ac output end mutually.The U of induction motor 2, V and W primary current iu mutually, iv, iw are respectively by current detector 3u, and 3v and 3w detect.

Label 6 expressions are used for producing the speed command circuit of a speed command signal Wr, and this signal is sent to adder 7 and compares with a g Wr from adder 39, the result, and the difference between signal Wr* and the Wr is from adder 7 outputs.According to this difference signal, speed difference amplifier 9 illustrates hereinafter for command signal iq*(of torque current component iq output in the motor current).Command signal iq* is added to adder 11 and coefficient multiplier 29.Adder 11 decision command signal iq* and will be described in more detail below by coordinate converter 32() difference between the torque component signal iq that takes out, be sent to electric current difference amplifier 35 from the difference signal of adder 11 output, this amplifier produces frequency control signal △ ω corresponding to difference signal successively as output signal.Signal △ ω is added to adder 36, in adder, signal △ ω with from the output signal ω r** addition (first command signal ω r** has a time delay with respect to speed command signal ω r*) of first instruction delay circuit 37, thereby, produce a frequency indicator signal ω i* by adder 36.

Oscillator 12 produces the sinusoidal signal of a permanent width of cloth, the frequency of signal and above-mentioned speed command signal ω i* proportional (this signal is as the phase reference signal of converter output voltage).The sinusoidal signal of oscillator 12 outputs is delivered to coordinate conversion circuit 17,18 and 32 respectively.

Current detection signal iu, iv and iw are sent to three-phase/two-phase conversion line 31, and thus, three-phase signal iu, iv and iw are transformed into biphase signaling ia and i signal beta i α and i β and are sent to coordinate conversion circuit 32.Circuit 32 is transformed into the identical component signal iq of phase place to i α and i β respectively according to the sinusoidal signal from oscillator 12.

Signal iq is added to aforesaid adder 11 and function generator 38, and this generator produces a slip frequency signal according to input signal iq Estimated value, the slip frequency signal of this estimation Be added to adder 39, so that from aforesaid frequency command signal ω 1*, deduct this value

, the result is sent to above-mentioned adder 7 immediately from the turn count value ω r of the induction motor 2 of adder 39 outputs.

Excitation current instruction circuit of label 13 expressions, this circuit produces a motor exciting current instruction Id* and exports as it, this signal is sent to and is used to determine that the computing unit 14(of induced electromotive force also is the RMF computing unit) and coefficient multiplier 40, the function of multiplier is that input signal id* be multiply by factor K to export a Kid* signal, and this signal is delivered to adder 28 successively.

Coefficient circuit 29 is used for torque current command signal iq* and COEFFICIENT K are multiplied each other, to produce output signal Kiq*, then this output signal is delivered to adder 30 so that with the output signal Vq* addition of EMF computing unit 14, a voltage command signal Vq** who has revised is delivered to adder 15 immediately as a result, to illustrate that below signal △ Vd* and △ Vq* are sent to adder 15 and 28 respectively.But be noted that here the output signal Vq*** from the output signal Vd*** of adder 28 and adder 15 is added to the input of coordinate conversion circuit 18, this circuit is changed to stator seat mark system (being stator coordinate frame of reference) to the quantitative change of rotating magnetic field coordinate system (being magnetic flux position reference system) according to the sinusoidal signal that oscillator 12 produces, and the result is created in two-phase alternating current signal V α * and V β * the stator seat mark system from the output of coordinate conversion circuit 18.Thereafter signal V α * and V β * are sent to two-phase/three-phase inverter 19, the result produces voltage command signal Vu* by phase conversion device 19, Vv* and Vw*, the frequency of these signals and frequency command signal ω I* are proportional, and mutual phase difference is 120 °, signal Vu*, Vv* and Vw* are added to switching circuit 20.

The output signal of switching circuit 20 is added to comparator 24u respectively, 24v and 24w, compare with CF signal as pulse width modulation, (CF signal is sent here by oscillator 25), thereby, producing pulse width modulation respectively is pwm pulse signal, and this pulse signal is used to open and close the relevant switch block of pwm converter 1.Gate circuit 26 is respectively in response to comparator 24u, and the output pulse signal that 24v and 24w produce provides a gate signal for the switch block of pwm converter 1.So far illustrated circuit structure is about not adopting the vector control of velocity transducer.

To the circuit part of the voltage decline redeeming of appearance in the voltage source converter 1 be illustrated below.

Function generator 4U, 4V and 4W, according to current detector 3U, the amplitude and the polarity of 3V and 3W output signal produce signal △ Vu*, △ Vv* and △ Vw*, the voltage drop of these signal proportions in converter, motor winding and lead.Signal △ Vu*, △ Vv* and △ Vw* are added to three-phase/two phasing commutators 16, be transformed into biphase signaling △ V α * and △ V β *, this biphase signaling is sent to coordinate conversion circuit 17 again, here, the sinusoidal signal according to oscillator 12 produces is transformed into component signal △ Vd* and △ Vq* to signal △ V α * and △ V β *, and lag behind 90 ° respectively, and with the induced electromotive force homophase.From the signal △ Vq* of circuit 17 output be added to adder 15 and with signal Vq** addition from adder 30, thereby produce the voltage command signal Vq*** of a modification by adder 15.On the other hand, another road output signal △ Vd* of coordinate conversion circuit 17 is added to adder 28, so that produce a voltage command signal Vd*** with signal Kid* addition.Above-mentioned line construction is in order to the voltage drop in the compensating converter 1.

Now, be illustrated at the converter control system principle that constitutes basic conception of the present invention.Fig. 2 a has shown a substitutional connection that induction motor is general, owing to can at random select α, so suitably select the α value, can make elementary leakage reactance reach zero.Thereby produced the equivalent electric circuit shown in Fig. 2 b, this equivalence circuit of now having a talk.

α＝Xl/Xm ……（1）

X′m＝Xl＝Xm+Xl ……（2）

……（3）

Wherein:

The Xm-excitation reactance

X ₁-elementary reactance

X ' _m-excitation reactance (after the equivalent transformation)

X ' ₂-secondary reactance (after the equivalent transformation)

In this case, exciting current I ' ₀, primary current I ₁Given with the relation of torque T by following formula.

……（4）

……（5）

……（6）

E′ ₁＝jx _mI ₀……（7）

In the formula:

The j-imaginary number

The S-revolutional slip

R ' ₂-secondary reactance (behind the equivalent transformation)

ω ₁-elementary angular frequency

R ₁-elementary reactance

The P-number of pole-pairs

Suppose exciting current I ' ₀Be constant, the motor constant is immutable, primary current I ₁With torque T only be the function of slip angular frequency ω s, so slip angular frequency ω s and primary current I ₁Can be as the function of torque T and determined definitely.This means torque T and primary current I ₁Can control according to slip angular frequency ω s.

On the other hand, exciting current I ' ₀Steady state, can by control voltage amplitude | E ' ₁| make itself and angular frequency ₁Proportional reaching.This also can be achieved like this: promptly, and at definite primary voltage V ' ₁The time, the voltage drop R that causes owing to primary impedance ₁i ₁Take into account, this can see in expression formula (6) equally.

According to the top relation of having illustrated, the control operation of controller for transducer shown in Figure 1 now is described, for the purpose of simplifying the description, at first putative signal △ Vd* and △ Vq* are respectively zero.

At first, explanation will keep exciting current | I ' ₀| constant operation.Oscillator 12 produces a sinusoidal signal (for induced electromotive force provides a phase reference), its frequency and frequency command signal ω ₁* proportional.In voltage instruction calculator 42 (its line construction is shown in the frame of broken lines of Fig. 1), frequency instruction ω ₁* multiply by mutually with aforesaid sinusoidal signal and produce an electromotive force instruction e ₁*, amplitude and the frequency and the frequency instruction ω of this electromotive force instruction ₁* proportional.In addition, the voltage drop Rii that produces owing to primary impedance ₁Be from detected current signal i ₁(i _u, i _v, i _w) get, and be added to electromotive force instruction e ₁* in, thus the primary voltage instruction V of generation three-phase sinusoidal signal form ₁* (Vu*, Vv*, Vw*).

More particularly, an axle supposing quadrature rotating magnetic field coordinate system (magnetic flux orientation coordinate system) is called the d axle, simultaneously is called the * axle with the perpendicular axle of d axle, and primary current and the primary voltage component on d axle and q axle is respectively by id, iq and Vd, Vq represents.Oscillator 12 produces the two-phase sinusoidal signal, and the frequency of this sinusoidal signal is with proportional by the frequency command signal of adder 36 outputs.90 ° of the mutual phase phasic differences of this two-phase sinusoidal signal, thereby use COS ω _*T and Sin ω ₁T provides, and the former is as the phase reference signal of U phase excitation component, and the latter is as the phase reference signal of U phase induced electromotive force.

In coordinate conversion line 18, carry out following computing to derive two-phase voltage command signal V α * and V β *.

……（8）

In addition, in phase conversion device 19, three-phase voltage command signal Vu*, Vv* and Vw* draw according to following expression:

……（9）

Voltage command signal Vu*, Vv* and Vw* are drawn by following formula:

ω in the formula ₁Representative is by the angular frequency of the signal of oscillator 12 generations.

By expression formula (8) and (9), voltage command signal Vu* is given by following formula:

Vu＊＝Vd＊＊＊COSω ₁t-Vq＊＊＊Sinω ₁t ……（13）

Following formula (13) also can be rewritten as:

Vu＊＝Vd＊＊＊+jVq＊＊＊ ……（13′）

Expression formula (6) is applied to the V phase.

…（14）

In the formula:

The terminal voltage of Vu-U phase

E ' _uThe induced electromotive force of-U phase

Therefore, obtain by expression formula (13) and (14)

Vd＊＊＊＝KR ₁〔I′ ₀〕

Vq＊＊＊＝K（X′ _m｜I′ ₀｜+R ₁｜Iq｜） …（15）

Wherein K-voltage control gain, simultaneously

Like this, command voltage Vd*** and Vq*** can control according to expression formula (15).

Because the value I ' of id* presentation directives ₀, and the instruction of the value Iq of iq* presentation directives empty Vd*** of electricity and Vq*** are determined by following formula:

Vd＊＊＊＝KR ₁id＊

Vq＊＊＊＝K（X′ _mi _d＊+R ₁i _q＊） ……（16）

I wherein _d*=| I ' ₀| and i _q*=| i _q|

The PWM control circuit (24U, 24V, 24W) in, primary voltage instruction V ₁* compare to realize pulse duration control with CF signal, this technology is in common knowledge for everybody.Thus, the output voltage of pwm converter 1 is controlled like this: the instantaneous value of output voltage and primary voltage instruction V ₁* proportional, in this way, motor voltage by formula (6) is controlled to keep exciting current | I ' ₀| constant.

Below, at motor current, the operation of torque and rotating speed (angular speed) (or saying control) describes.

Primary current | i ₁|, perpendicular to excitation current component i ' ₀(I ' here ₀≡ i _d) primary current i ₁Component i _q(here | i _q| ≡ i _q) (promptly this component is with respect to exciting current i ' ₀90 ° of phase differences are arranged, thus with induced electromotive force E ' homophase) torque T and exciting current i _dBetween amplitude relation by following various given.

At exciting current i _dThe situation of constant amplitude under, above-listed various given various values just (R ' ₂/ ω s) function, thereby make control depend on slip frequency ω s, in addition, torque T and current component i _qThere is proportionate relationship, so can think current component i _qBe equivalent to torque.Current component i _qDetect by current component detection line (this circuit is represented by frame of broken lines 43 in Fig. 1).This be according to:

i _q＝eα·iα+eβ·iβ ……（20）

Wherein:

iα＝iu

Iu, iv, iw are the instantaneous value of U, V and W phase current.

E α=eu=-Siu ω ₁T and

In above-listed expression formula, eu, ev and ew be respectively U mutually, the phase reference signal of the induced electromotive force of V phase, W phase, constant amplitude not only, and with the electromotive force homophase, what should be mentioned in that is: in voltage instruction calculator 45, with these signals and frequency instruction ω ₁* multiply each other, for each prepares an electromotive force instruction e* mutually.

With this detected current component i _q, in adder 11 with torque instruction T*(∞ i _q*) compare, deviate total in adder is adjusted slip angular frequency (output frequency of converter) ω s according to frequency control signal △ ω, and △ ω depends on this deviate, thereby, according to torque instruction T* controlling torque pro rata.At (i _q-ω *) control circuit gains when enough high, and torque can be subjected to and this control, so that removes to follow the torque instruction T* with high response speed.

On the other hand, slip angular frequency ω s have by expression formula (18) given relation to current component iq, therefore, slip angular frequency ω t can measure according to current component iq, this mensuration is finished by function generator 38, and the example of a typical ω s-iq characteristic is shown in Fig. 3.Do not surpassing in the scope of nominal torque, current component iq is approximate proportional with slip angular frequency ω s.So, can be without function generator 38, Fig. 3 further illustrates primary current | i ₁| with respect to the characteristic of slip angular frequency ω s.With regard on the occasion of scope, current component iq approx with primary current | i ₁| overlap, so just might be according to primary current | i ₁| also can determine to estimate slip frequency signal ω s.Needless to say, primary current | i ₁| can be by primary current detection signal i ₁Amplitude decide.

Estimation rotating speed (calculated value) ω r can calculate according to following formula:

ωr＝K（ω ₁＊-ωs） ……（21）

In the formula: K represents proportionality constant.

Above-mentioned calculating realizes in adder point 39.

Speed difference amplifier 9 produces torque instruction signal T*(∞ i _q*), this signal depends on the difference between speed command signal ω r* and its calculated value ω r, and here, torque is according to torque instruction T* Be Controlled pro rata, to finish speed control.Illustrated as the front, because the estimated value ω r of rotating speed is from elementary frequencies omega ₁Deduct that slip angular frequency ω s calculates, when rotating speed reduces owing to the peculiar skew of induction motor, can obtain through overcompensation proofreading and correct.Therefore, compare with known so far V/F control technology, this method can realize speed control with higher precision.

The effect of first instruction delay circuit 37 is that the variation of following speed command ω r* removes to change frequency instruction ω ₁*, so that aforesaid frequency control signal △ ω becomes one to stablizing the significant instruction of slip angular frequency ω s.

From the narration of front, can understand: according to the embodiments of the invention figure explanation that is situated between, speed control as induction motor, under portion need not pack the situation of speed detector and motor voltage detector within it, have high response speed and improved control precision.

Yet, must be pointed out that a problem still awaits solving, more particularly, because voltage instruction Vu*, the relation between Vv* and V ω * and the corresponding actual output voltage is non-linear (as for its reason, explanation below), the voltage of motor can not be as a linear function of voltage instruction and is controlled, this itself means again, and motor current can not be controlled as a linear function of command value, thereby makes the vector control operation become unreliable.Like this, just be provided with obstacle in the stable operation that induction motor is realized high response speed, and the stable operation of this high response speed one of the advantage of vector control just.

Now, explain why between voltage instruction and the realization output voltage be non-linear reason.

Each switch element of forming converter 1 essential part only just can be opened or turn-off under (promptly postponing) the certain hour situation that lags behind.Therefore, between the both positive and negative polarity brachium pontis short circuit appears, the gate signal relevant with pwm pulse be at Fig. 4 (b) and (c) dotted line represented open a delay time t _dIn time, provide, and this opens a delay time t _dUsually be decided to be bigger one or two times than the turn-off time of this switch element.Suppose line the voltage (=E between U phase and V are mutually now _u-N-E _v-N) be to open a delay time t disregarding _dMeasure under the situation, the waveform of this line voltage is shown in Fig. 4 (d) solid line, and now, let us is determined to take into account opens a delay time t _dU phase under the situation and the line voltage between the V phase.Suppose the output current of converter 1, promptly the electric current that flows into induction motor 2 from converter is a positive polarity, and hypothesis is when the U phase current is positive pole and the V phase current is a negative polarity simultaneously.The U phase current will flow through some diodes like this: they and the switch element parallel connected in reverse phase that is negative arm in opening a delay cycle.Therefore, in opening a delay cycle, U phase current potential is negative (-), on the other hand, the V phase current of negative polarity, to flow through and the diode that in opening a delay cycle, is the parallel connected in reverse phase of positive arm, therefore, in opening a delay cycle, V phase current potential is just (+), like this, open under the situation of a delay time in consideration, U and V phase voltage present (l) and waveform (f) among Fig. 4 respectively, therefore, the waveform of the line voltage (Vu-N-Vv-N) between U and the V phase is shown in the dotted line shadow region of (d) among Fig. 4, and it is significantly less than hypothesis and ignores out the solid line waveform that a delay time draws.

In common knowledge as the present technique field, switch element changes its turn-off time according to the current amplitude (being the output current of converter 1) that flows through switch element.Therefore, in opening a delay cycle, turn-off the switch element of positive and negative arm simultaneously, the time of shutoff is as a function of the output current amplitude of converter 1 and change.In other words, the amplitude (considered and opened a delay time) of dash area changes with converter 1 output current amplitude in the waveform that dotted line is represented among Fig. 4 (d).

As can recognizing, in the cycle, open time-delay phenomenon, that is: a delay that when switch element " is opened ", relates to owing to exist in each ON/OFF of switch element by above-mentioned analysis) and voltage drop appears.When the PWM switching frequency is compared with the output frequency of converter when enough high, the output current homophase of voltage drop (fundametal compoment) and converter.With regard to this point, the voltage drop of being considered has the voltage drop character that is produced on an Ohmic resistance.

On the other hand, the amplitude of voltage drop and converter output current have non-linear relation, and this specific character can record with following method.

Now suppose phase voltage directive signal Vu*, Vv* and Vw* are set at Vu*=Vac*, Vv=Vdc* and Vw*=O, and Fig. 5 represents an equivalent electric circuit.Wherein, motor receives the direct current from converter.In the figure, aforesaid voltage drop in the E representation transformation device, R represents the resistance of interconnecting conductor between motor winding resistance and converter and the motor or lead, and under these all given situations, the relation between voltage instruction Vde* and the converter average anode current idc is provided by following formula:

Vde＊＝R·id＊+E（idc） ……（22）

Can see that voltage drop E and Ridc can determine according to voltage instruction Vde*.When resistance R is given when knowing earlier, the internal pressure drops E of converter can be handled by the voltage drop Ride that the resistance of motor winding and bonding conductor causes respectively.Fig. 6 shows the example of this measurement result, and the relation of the amplitude of voltage drop and output current is non-linear as we can see from the figure.Therefore be that voltage drop includes harmonic component under the situation about exchanging at the converter output current.

For overcoming the above problems, give the pressure drop Ri that the internal pressure drops E of first measurement translator and motor winding and conductor resistance cause, here be stored in respectively and be inserted in function generator 4U by measuring determined performance data, in the memory in 4V and the 4W, so that according to converter output current sense data, be used for compensating electric step-down E and the Ri relevant respectively with output current.The compensation of voltage drop can be by function generator 4U, 4V and 4W, and three-phase/two phasing commutators 16, coordinate conversion circuit 17 and adder 15 and 28 circuits of being formed are finished.More precisely, voltage drop signal △ Vu*, △ Vv* and △ Vw* are transformed into biphase signaling △ V α *, △ V β *, are converted into the amount △ V of rotating magnetic field coordinate system then again ^* _dWith △ V ^* _g, then be sent to adder 15 and 28, so that voltage command signal Vd* and Vq* are modified to Vd*** and this signal of Vq***-is the voltage instruction of having revised for voltage drop is compensated.By said process, by the above-mentioned corresponding estimator of having stored, actual voltage-drop is compensated, the induction electric potential energy of induction motor is controlled to voltage instruction V α * and V β * consistent.

In this connection, it should be noted that, as converter internal pressure drops E with because the summation of the pressure drop Ri that winding and conductor resistance cause is when importing an output characteristic and be provided with as function generator, two voltage drops of E and Ri can be compensated, yet, the DC component that occurs in the converter output current is impossible suppress, and this DC component causes owing to imbalance between the converter switches element positive and negative terminal causes producing in the converter output voltage DC component.In view of this, it may be the most effective removing compensated voltage drop according to the summation of E and Ri.Therefrom, relevant with converter output current amount has been given first being deducted.As an example.The function generator 4U that packs into, the content of 4V and 4W can be set like this so that satisfy following condition:

The i+E of the output of function generator=(R-K) ... (23)

The Ki representative amount relevant in the formula with above-mentioned output current, however should be noted that the amount in the consideration is not necessarily proportional with current i, but any other relation can be arranged with the latter, and play a part similar.

Below, the method that the function generator content is set automatically is described.

Though aforesaid voltage drop E is intrinsic to converter, voltage drop Ri can change according to the resistance of the motor that is physically connected to converter and the lead that uses.Set function generator 4U, during the content of 4V and 4W, should consider that constant voltage falls E and consider that again Ri falls in variable voltage.Yet this step bothers very much, in this case, to measure these voltage drops automatically and automatically function generator is provided with in perhaps pack into the method for data describe.

Above-mentioned method can be by means of comprising direct voltage command link 21, coefficient multiplier 22U, and 22V and 22W, Circuits System such as switching circuit 20 and ammeter 5 realize.

Before the motor actual motion, at first will E and Ri fall with following method measuring voltage.Promptly, direct voltage instruction Vdc* is produced by direct voltage command link 21, set three-phase voltage instruction Vu* then respectively, Vv* and Vw* are respectively by coefficient multiplier 22U, 22V and 22W set Vu '=Vdc*, Vv*=-Vdc* and Ww*=θ, at that time, switching circuit 20 is switched to the indicated position by a, in this state, direct current id* will flow out from converter.By reading direct voltage instruction Vdc* corresponding to direct current id*, can obtain one and resemble the characteristic shown in Fig. 6, this specific character is at function generator 4U, sets among 4V and the 4W.

When in case motor begins actual motion, switching circuit 20 is switched to the represented position by b, thereby make the output signal Vu* of output voltage according to two-phase/three-phase inverter 19, Vv* and Vw* and be controlled, therefore, illustrated that part of voltage drop was passed through from function generator 4U as top, the signal △ Vu* of 4V and 4W output, △ Vv* and △ Vw* are compensated.In addition, in order to suppress the DC component in the converter output current, deducted the amount relevant among the result of planar survey in the past, so that can put into the performance data that is more suitable in the function generator with the latter.

Fig. 7 has expressed an alternative embodiment of the invention, and it and system's difference shown in Figure 1 are, detect exciting current i, so that remove control change device output voltage according to the difference between detected exciting current id and the house-keeping instruction value id*.As previously mentioned, exciting current id can pass through control | Ei|/ω ₁Ratio constant and keep constant.Yet in actual applications, when in acceleration suddenly or deceleration, exciting current may be subjected to instantaneous variation.Therefore, proposed detection exciting current id according to an embodiment of the present invention, and proposed correctly to control the amplitude of primary voltage instruction Vi* so that exciting current id presents a constant predetermined value.

In Fig. 7, excitation current component detector of label 43 expressions, be used to detect the component id of exciting current, this id differs from 90 ° with the reference phase of converter output voltage (induced electromotive force) on phase place, 33 represent adders or say summing point, be used to provide the difference between detected excitation current component id and the relevant command value id*, exciting current difference amplifier of 34 expressions is used for amplified differences.Multiplier of 42 expressions is used for the output signal of amplifier 34 and frequency instruction ω 1* are multiplied each other, and is used to be provided with primary voltage instruction V to export one ₁* the signal of amplitude.Other with Fig. 1 in identical or equivalent line unit represent with same label, and omitted further specifying to these unit.

In the operation, the part that with dashed lines surrounds among current component detector 43(Fig. 7 is represented), detect excitation current component id according to id=l β i α-l α i β.L α in the formula, e β, i α and i β represent the fixed amount in front.

Then, deviation (being difference) between excitation current instruction value id* and the detected exciting current id, amplify and then multiply each other by exciting current deviation amplifier 34, thereby be that primary voltage is instructed V with the value that roughly is shown in the frequency calculator of frame of broken lines 42 among Fig. 7 ₁* prepare an amplitude signalization.Voltage instruction calculator 42 is full of device 12(for producing induced electromotive force with the amplitude signalization with coming self-vibration) phase reference signal multiply each other, be respectively U, V produces voltage instruction V mutually with W ₁*.Other operations in Fig. 7 system are identical with the front in conjunction with the explanation of Fig. 1.Because exciting current id always with excitation current instruction value id* Be Controlled as one man, be to suppress the skew of exciting current id or fluctuation with this method.

Fig. 8 represents the another kind of embodiment of the present invention, and the difference of it and Fig. 7 is: the d axle component of converter output voltage is to control according to the difference (or saying deviation) between detected exciting current i α and the house-keeping instruction value id*.As described above, by correctly controlling primary current instruction V ₁* amplitude, exciting current id is sure keep constant so that the exciting current id that is detected is fixed in predetermined value.Yet in actual applications, this thing happens for possibility, and promptly exciting current id and torque current iq are fluctuateed in response to the variation of load, and caused phase mutual interference tends to reduce control performance.

As described below, according to the embodiment of top structure shown in Figure 8, its detected exciting current id is controlled in a constant predetermined value.

With reference to Fig. 8, excitation current instruction circuit 13 is motor output excitation current instruction id*, and this signal id* is sent to induced electromotive force (EMF) computing unit 14, adder 33 and coefficient multiplier 40.Deviate between adder 33 output excitation current instruction id* and the detected exciting current id, this difference signal is sent to electric current difference amplifier 34, and this amplifier is according to above-mentioned difference between current output voltage instruction signal Vd* successively.Signal Vd* is sent to adder 41 then.On the other hand, coefficient multiplier 40 multiplies each other command signal id* and COEFFICIENT K.The output signal Kid* of coefficient multiplier 40 is sent to adder 41, at this, and the output signal Vd* addition of this signal and electric current difference amplifier 34, the result exports this signal of voltage command signal Vd**-that is corrected and is sent to adder 28 again.

Difference between excitation current instruction id* that is provided by command link 13 and the exciting current id that has measured is amplified by amplifier 34, thereby is obtained voltage instruction Vd*.D shaft voltage component Vd(is promptly perpendicular to the component of voltage of induced electromotive force) as the function of voltage instruction Vd* and be controlled, so that the exciting current id that has recorded is consistent with excitation current instruction id*.

On the other hand, utilize motor torque, slip frequency and torque current component iq to be in this fact of ratio, slip frequency ω s can be estimated in adder 39 that the slip signal ω s that deducts estimation from frequency command signal ω * is to detect g ω r by slip calculator 38 according to signal iq.Difference between the rate signal ω r of speed command signal ω r* and estimation is amplified by amplifier 9, thereby obtains torque current instruction iq*.Deviate between torque current instruction iq* and the torque current iq that recorded is amplified by amplifier 35 in addition, thereby obtains frequency instruction ω according to the difference signal △ ω of amplifier 35 outputs ₁*.When the torque current iq that records instructs iq* less than torque current, then increase frequency instruction ω ₁, the variation of slip frequency on the increase direction as a result causes the increase of torque current.Ruuning situation is in contrast the time, and above-mentioned explanation is correct equally.In this way, the control that is subjected to of torque current iq makes itself and torque current instruction iq* consistent.In addition, signal ω ₁* provide voltage instruction Vq* through multiplying each other with id, this voltage instruction for control q shaft voltage component Vq(promptly with the component of voltage of induced electromotive force homophase) provide the foundation, as a result, the ratio of induced electromotive force and frequency is controlled as constant (being that magnetic flux is constant).

In this way, the control of induction motor can be finished in the such identical mode of DC motor, promptly according to excitation current instruction id*, magnetic flux by the control motor gives the value of setting earlier to reach one, simultaneously, slip frequency and torque are controlled according to torque current instruction iq*.

Fig. 9 shows an alternative embodiment of the invention, and among the figure, the part identical with Fig. 8 represent with identical label, and repeated description no longer.Embodiment shown in Figure 9 and difference embodiment illustrated in fig. 8 are: function generator 4U, the output of 4V and 4W is added to alternating voltage command signal Vu* respectively, on Vv* and the Vw*.

More particularly, two-phase/three-phase inverter 19 output voltage instruction signal Vu*, Vv* and Vw*, the frequency of these signals and frequency command signal ω ₁* proportional, and phase difference each other is 120 °.These voltage command signals Vu*, Vv* and Vw* are delivered to adder 40U respectively, 40V and 40W, by adder, voltage command signal Vu*, Vv* and Vw* and function generator 4U, the output signal △ Vu* of 4V and 4W, △ Vv* and △ Vw* with the polarity shown in scheming respectively according to vector addition, thereby produce voltage command signal Vu**, Vv** and Vw**, and be sent to switching circuit 20.

Embodiment shown in Figure 9 has the same effect embodiment illustrated in fig. 8 except guaranteeing, also has additional advantage, thereby promptly can save converter required in the system shown in Figure 8 16 and 17 and simplified system configuration.

Figure 10 shows an alternative embodiment of the invention, among the figure, represents with same numeral with Fig. 9 same section, and omits its explanation.The difference of system shown in Figure 10 and system shown in Figure 9 is: adopt current command signal iu*, iv* and iw* be respectively as function generator 4U, the input signal of 4V and 4W.

More particularly, the effect of coordinate conversion circuit 44 is that the sinusoidal signal that produced according to oscillator 12 is two amounts in the output signal iq*(rotating magnetic field orientation diagram of the output signal id* of excitation current instruction circuit 13 and velocity deviation amplifier 9) convert mark on a map amount in (coordinate system) of stator seat to, thereby, produce two-phase alternating current signal i α * and i β *, these two signals are sent to two-phase/three-phase inverter 45, and the result obtains current command signal i _u*, i _v* and i _w*, their frequency and frequency command signal ω ₁* proportional, and mutual phase difference is 120.Yet these signals are delivered to function generator 4U, 4V and 4W respectively.

System shown in Figure 10 not only can guarantee identical effect embodiment illustrated in fig. 9, also has additional advantage, promptly because only comprise fundametal compoment in the current-order, the influence of the harmonic noise that so current-order iu*, iv* and iw* are not subjected in the motor current to be comprised.

The front for the explanation that simplifies the operation, is used in combination the exemplary embodiments of analog line, and the invention has been described.Yet obviously, the present invention goes for adopting the numerical control system based on microprocessor equally.

Figure 11 shows the another kind of embodiment that the present invention is applied to numerical control system.

With reference to Figure 11, the U phase of induction motor 2, V phase and W primary current iu mutually, the output current of iv and iw(converter 1) respectively by current detector 3U, 3V and 3W measure, and are added to mould-number (A/D) converter 46 respectively.

Numerical calculation circuit 56 comprises the processor 55 that is used to carry out calculating process, a program storage device 54 of storing control program, an archival memory 53 of storing data, I/O port 49 and 51, calculator 50 and the address/data bus 52 that is connected these parts.Before induction motor 2 computings, processor 55 makes converter 1 supply with direct current to induction motor 2 according to the processing procedure that is stored in the control program in the memory 54, so that measure the characteristic relation (curve is the characteristic shown in Fig. 6) between direct voltage instruction and the direct current, the result of measurement packs in the data memory 53.In service at induction motor 2, processor 55 according to be stored in control program in the memory 54 given processing procedure, value via bus 52 taking-up counters 50, this counter is used for the output signal of recording voltage-frequency changer (V/F) 47, thereby calculate the voltage instruction Vu*, Vv* and the Vw* that determine as the induced electromotive force of induction motor 2.In addition, processor 55 takes out the output current of converters 1 by I/O port 51, and via bus 52 from data memory 53 read-out voltages instruction △ Vu*, △ Vv* and △ Vw*, they have as compensated voltage drop required amplitude and polarity.These voltage instruction values △ Vu*, △ Vv* and △ Vw* respectively with give (as above-mentioned) the exemplary voltages command signal Vu* that measures earlier, Vv* and Vw* addition, the result who adds exports number-Mo (D/A) transducer 48 from I/O port 49 to through bus 52.

Below, with reference to Figure 12 and 13, the compensating operation of converter internal drop is described.

At first, be illustrated as the induced electromotive force of compensated induction motor 2 and prepare the method for data as the difference between the exemplary voltages command signal of converter 1, and this data storage of determining like this in memory 53.For reaching this purpose, according to the same principle of explanation that combines system shown in Figure 1 with the front, induction motor 2 is coupled with the direct current idc from converter 1 before practical operation.

With reference to Figure 12, at square or step 12a the output frequency instruction f* that supplies with converter being set is zero (being direct current), the Vdc* of direct voltage instruction simultaneously is zero, at step 12b, the direct current idc that makes converter 1 is from zero increment size △ Vdc* and the above-mentioned data storage leading address M among data memory 53 that changes to the direct voltage instruction Vdc* of load current value then.At step 12c, the content of data memory 51 is cleared.At step 12d, the voltage instruction V*u* that the U phase is set is dc*, and the voltage instruction V*u* that the V phase is set is zero for-Vdc* and voltage instruction V ω * * that the W phase is set.These voltage instructions are by I/O port 49 outputs then.

At step 12e, record and deliver to A/D converter 46 by current detector 3u corresponding to the output current iu of the converter 1 of direct voltage instruction Vdc*.From the digital signal I of A/D converter 46 outputs, export via bus 52 by I/O port 51.At step 12f, judge the output current I(digital quantity of converter 1) whether reached rated value, when output current I is lower than load current value,, be written among the address M+1 of data memory 53 via bus 52 according to the result of (direct voltage instruction Vdc*-KI) computing at step 12g.In the superincumbent expression formula, K is identical with the constant that appears at expression formula (23).

At step 12h, direct voltage instruction Vdc* is increased an increment △ Vdc*, so that draw the direct voltage instruction Vdc* that has upgraded, gets back to step 12d then, and repeated execution of steps 12d is to 12h.

When step 12f judges that the output current I of converter 1 is not less than rated value, by judge the content on the address that does not have data in the memory 53 with interpolation technique, via bus 52 this content is write data memory then at step 12i.In addition, in order to prepare the content of data memory for the negative polarity electric current, read as the data of positive polarity electric current via bus 52, write data memory 53 via bus 52 again behind the figure shift at step 12j.

Like this, the processing before induction motor 2 operations just is through with, subsequent, induction electric is confidential to have brought into operation.

Now, operation in conjunction with induction motor 2 illustrates, with reference to Figure 13, output pulse signal at step 13a ' V/F converter 47 takes out by counter 50 countings (this converter is transformed into a series of pulses to the output signal of speed command circuit 6) and via bus 52, so that calculate voltage instruction type signal Vu*, the range value of Vv* and Vw* as the induced electromotive force of induction motor 2.

At step 13b, the output current iu of converter 1, iu and iw are respectively by current detector 3u, and 3v and 3w record, and are sent to A/D converter 46, export iu, iv and iw through the numeral that bus 52 is sent by I/O port 51.At step 13c, according to IU, the amplitude of IV and IW and polarity, the content of sense data memory 53.These contents are respectively by △ Vu*, △ Vv* and △ Vw* representative.

At step 13d, by the voltage instruction type signal Vu* that step 13a determines, △ Vu*, △ Vv* and △ Vw* addition that Vv* and Vw* read with step 13* respectively.At step 13d, through the result of bus 52 by I/O port 49 output step 13d additions.

The included program of step 13b to 13e is repetition, and in the explanation in front, the content of tentation data memory 53 also is under motoring, reads by processor 55.This point is understandable, if the output of A/D converter 46 is the addresses-at once that are configured to data memory 53, the content of data memory 53 can directly be read (the leading address M as the data memory is set to zero) by I/O port through bus.

The present embodiment decapacitation guarantees that the front is in conjunction with outside the mentioned advantageous effect of Fig. 9, start preceding set-up procedure from induction motor and can also realize continuous processing to its whole service process, because this excellent characteristic, even when the combination and variation of converter and induction motor, still can keep aforesaid advantageous effect in conjunction with Fig. 9.

Can figure out from the explanation of front, according to technology instruction of the present invention, not adopt such as speed, under the situation of detectors such as voltage, it is possible removing the rotating speed of control of induction with the precision of height.In addition, can avoid effectively, thereby improve the control precision and the reliability of motor widely because the decline of the caused control performance of fluctuation appears in voltage source converter internal pressure drops and torque.

Claims (8)

1. A control method for an induction motor driven by a voltage-type converter, the converter comprising: a plurality of arms each having first and second switching elements connected in series with each other; An "open" gate signal provided to the above-mentioned one switching element is delayed for a predetermined time (open-delay time) after the "close" gate signal is provided to the other switching element, The output voltage of a voltage source converter is controlled based on a torque current command and an excitation current command independently of each other to adjust the frequency and magnitude of the primary current supplied to the induction motor. It is characterized by the following steps: Detect the primary current supplied to the induction motor and generate a current detection signal; generating a non-linear compensation signal corresponding to the current sense signal to compensate for the on-delay voltage drop and the resistor voltage drop; and The output voltage of the voltage source converter is compensated in response to the nonlinear compensation signal.

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