JPH0632592B2 - Induction motor torque control device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a torque control device for an induction motor using a variable voltage variable frequency (VVVF) inverter. In high speed torque control, the operating points of a magnetic flux and torque hysteresis comparator are set. Variable control is used to optimize hysteresis according to load conditions and operating conditions.
It enables reduction of ripples of current and torque, reduction of harmonic loss, reduction of inverter switching frequency, start-up, smooth drive at ultra-low speed operation, and low torque drive.

[Conventional technology]

The basic operation of the torque control system for an induction motor according to the present invention is described in a paper entitled "New High-Speed Torque Control Method for Induction Motor Based on Instantaneous Slip Frequency Control" on page 9 of Vol. ing.

In this paper, the motor magnetic flux is defined as the motor input voltage detected and integrated in the gate circuit. That is,
This is a so-called magnetic flux calculation type control system, which carries an inverter output voltage that follows a magnetic flux command given the length of the magnetic flux vector and draws a circular locus.

Further, the motor-generated torque is calculated as a vector product of the magnetic flux and the motor input current, and an inverter output voltage whose magnitude follows the given torque command is carried. The control is performed so that the instantaneous values of the magnetic flux and the torque are kept within a predetermined error, and the inverter output voltage is updated at high speed every moment.

FIG. 12 shows a torque obtained by applying the output voltage detection method of the PWM inverter proposed by the applicant to the Japanese Patent Application No. 61-99228 (Japanese Patent Laid-Open No. 62-260593) in the control method described in the above paper. 3 is a block diagram of a control system, in which a three-phase PWM inverter 3 is connected from a DC voltage source 1 through a positive bus 1a and a negative bus 1b.
Power is supplied to the three-phase induction motor 6 via. The control circuit 7 processes the command and the detected current and voltage signals, and generates an energization signal for the switching element of the PWM inverter 3.

Although PWM inverter 3 is composed of a transistor and a diode from a reverse parallel connection with six arms comprising respectively three changeover switch S _u as shown in FIG, S _v, can be expressed as S _w.

From each output terminal of the PWM inverter 3, the current detector 5 _u , 5 _v ,
Power is supplied to the three-phase induction motor via 5 _w , and the voltage detector 2 is connected between the positive and negative buses on the DC side. From this, each phase current and each phase voltage can be detected from the detector and the switch state variable described later. ing.

The primary terminal voltage and current of the three-phase squirrel cage induction motor And the secondary current is Then, the voltage equation is However, the symbol Is a vector display of the quantities exchanged on the straight axis, the horizontal axis, that is, the d and q2 axes. Is the d-axis component is v ₁ d and the q-axis component is v ₁ q Indicated by Is similarly defined. In the left side of the equation, both d and q axis components are 0, and in the case of the squirrel cage rotor, the secondary voltage is as follows.

The constant in the equation is R ₁ ; primary winding resistance L ₁₁ ; primary inductance R ₂ ; secondary winding resistance L ₂₂ ; secondary inductance M; mutual inductance m is rotational angular velocity, p is differential operator, j is vector Represents the product.

On the other hand, as the definition of magnetic flux, the primary magnetic flux Is Expand the first line of the expression Substituting expressions and rearranging If you integrate both sides That is, the primary magnetic flux of the electric motor is obtained by the integral calculation of the equation.

The changeover switches S _u , S _v , and S _w may fall to the positive bus line 1a side or to the negative bus line 1b side, and do not take intermediate positions. When the former is the state 1 and the latter is the state 0, the output states of the inverter can all be represented by the switch state variable table shown below.

Here, k is a number indicating the state of the changeover switch, and there are only eight of these. Also, ▲ _d ▼, ▲ _q ▼ are d, q
With the switch state variables expressed by two axis components, the actual d and q axis voltages v _1d and v _1q are the same as the voltage V of the DC voltage source 1. Multiply by Can be expressed as

The switch state variable table is shown in FIG.
The parentheses next to v ₁ indicate the states of the changeover switches S _u , S _v , and S _w , and represent the voltage vector that steps in 60 ° clockwise steps as k increases.

Note that k = 0 and k = 7 are called zero vectors and coincide with the origin in the figure. k = 0 and k = 7 are the outputs of the inverter, respectively, and the changeover switches _Su , S of FIG.
_v, or S _w collapses all positive line 1a side, or of differences fall into negative bus 1b side, but which also zero either the line voltage of the induction motor 6 is a three-phase short circuit mode. Also, u,
The reference axes of the v and w phases are respectively k
= 1, k = 3, k = 5.

The instantaneous torque T is the primary magnetic flux of the formula And primary current It is calculated by the formula as the vector product of.

Where φ _1d , φ _1q and i _1d , i _1q are the primary magnetic flux, respectively. And primary current Is each component when is decomposed into d and q2 axes.

Block 701 and 703b are changeover switch S _u, and a S _v, the voltage V of the DC voltage source that is detected in the state of S _w and the voltage detector 2 1
Next terminal voltage Is a block for calculating a switch state variable table and an equation.

Block 702 is 3 detected by current detectors 5 _u , 5 _v , 5 _w
This is a block that converts the phase currents iu, iv, and iw into d and q biaxial components by the following equation.

This primary current Is multiplied by the primary winding resistance R ₁ in block 703a, and the product of the primary winding resistance R ₁ and the primary current i ₁ is subtracted from the primary terminal voltage v ₁ in block 704.

The block 705 is a block for integrating the magnetic flux according to the formula The d and q biaxial components φ _1d and φ _1q of
At, the magnetic flux vector length φ ₁ is calculated by the following equation.

Further, in block 710, as shown in the magnetic flux state diagram of FIG. The clockwise rotation angle θ with respect to the d axis of the vector is 30 °, 90 °, 150 °, 210 °, 270 °, 330 ° as the boundary line.
The control flag fθ is generated as follows depending on which region is divided at every 60 °.

−30 ° ≦ θ <30 °; fθ = I 30 ° ≦ θ <90 °; fθ = II 90 ° ≦ θ <150 °; fθ = III 150 ° ≦ θ <210 °; fθ = IV 210 ° ≦ θ < 270 °; fθ = V 270 ° ≦ θ <330 °; fθ = VI FIG. 4 is a state control diagram of the hysteresis comparator. The magnetic flux vector length φ ₁ is the error limit Δφ with respect to the magnetic flux command value ▲ φ ^* ₁ ▼. make use of A control flag fφ for controlling so that That is, the magnetic flux vector length φ ₁ increases and is the upper limit. Control flag fφ = 0 is generated when the magnetic flux vector reaches φ, and the magnetic flux vector length φ ₁ decreases to the lower limit. Control flag fφ = 1 for instructing the magnetization is generated.

Thus, the magnetic flux vector length φ ₁ is controlled so as to draw a limit cycle in the direction of the arrow shown in FIG. 4, but in reality, the magnetic flux vector length φ ₁ calculated by the equation in block 706. Is subtracted from the magnetic flux command value ▲ φ ^* ₁ ▼ in block 708, and the control flag fφ = 1,0 is generated in block 711 according to the state control diagram of FIG.

The limit cycle of the magnetic flux shown in FIG. 4 is the primary magnetic flux as shown in FIG. This corresponds to the fact that the head of the vector is controlled to always exist in the illustrated torus part.

The control flag fφ according to FIG. 4 and the control flag fθ described with reference to FIG. 3 are combined, and, for example, fφ = 1, fθ =
If the I control flag is set, the area is −30 ° ≦
Since it means the magnetization mode at θ <30 °, the primary magnetic flux Primary voltage to be integrated into vector The vector has an outward component of a circle, and it is possible that only k = 1, 2, or 6 is selected from FIG.

Block 707 is a block which calculates the calculated instantaneous torque T a vector product between the output of the block 702, 705 by the equation, by subtracting the instantaneous torque T from the torque command T ^* at block 709, the torque command T ^* and the formula A control flag fr is generated in accordance with the state control diagram of FIG. 5 in block 712 so that the difference from the obtained instantaneous torque T is suppressed within a predetermined error limit.

FIG. 5 is a state control diagram of the three-value hysteresis comparator. The torque deviation T ^* -T is the upper limit value ΔT when the motor is running.
_{When 1} (ΔT ₁ > 0) is reached, the acceleration mode control flag fr
= 1 is generated. When the motor is accelerated and the torque deviation reaches the lower limit value −ΔT ₂ (ΔT ₂ > 0), a zero vector mode control flag fr = 0 is generated, the torque gradually decreases, the deviation increases again, and the upper limit value ΔT ₁ When it reaches to
Draw a limit cycle that goes around the hysteresis loop in the upper half of the figure in the direction of the arrow.

When this is expressed in the time domain, the instantaneous torque T fluctuates as shown in the torque waveform diagram of FIG. 6, and it reciprocates within the band of the upper and lower deviations ΔT ₁ + ΔT ₂ across the torque command T ^* .

Next, when the electric motor is performing regenerative braking, a hysteresis loop in the lower half of FIG. 5 is drawn, and when the torque deviation reaches the negative lower limit value ΔT ₁ (ΔT ₁ > 0), the deceleration mode The control flag fr = -1 is generated. After that, the limit cycle in the direction of the arrow is repeated as in the case of power running. Thus, block 712 outputs the control flags fr = 1,0, -1.

Block 713 is output from blocks 710, 711, 712 3
This is a block for determining the most suitable inverter output voltage for each combination of the individual control flags fθ, fφ, fr, and the primary magnetic flux described in FIG. Of the vector length and rotation direction of these three control flags f
θ, fφ, fr are controlled.

For example, when the control flags fφ = 1 and fθ = I as described above, the voltage vector is set according to k in the switch state variable table. If k = 1, 2, or 6 may be selected as the voltage vector, then if the control flag fr = 1 at this time, the vector K having a component that rotates in the clockwise direction is used. = 2, that is, the output voltage vector Is selected. If fr = -1 Zero vector when fr = 0, Or Is selected.

The following switching table shows three control flags f
The values of the number k of the output voltage vector are shown for all combinations of φ, fθ, fr. By referring to this switching table in block 713 for each operation cycle, the switching signal is sent to the inverter 3 and the magnetic flux And instantaneous control of torque is performed.

The inverter frequency is the primary magnetic flux in Fig. 3. It can be considered as the rotational speed of the vector, but this is not given from the outside but occurs as a result of integrating the voltage vector by the formula.

[Problems to be solved by the invention]

The new space vector method which solves many drawbacks of the conventional vector control of the induction motor has been described in detail, and the summary is as follows.

Primary terminal voltage And primary current To the primary magnetic flux And the instantaneous torque T are calculated, and the calculated primary magnetic flux The magnitude of the vector is controlled by the magnetic flux hysteresis comparator according to the magnetic flux command value ▲ φ ^* ₁ ▼ and the error limit Δφ. The instantaneous torque T is controlled by the three-value torque hysteresis comparator with respect to the torque deviation T ^* -T from the torque command T ^* .

Conventionally, the operating point values at which these hysteresis comparators operate, namely, the magnetic flux error limit Δφ, the upper limit value ΔT ₁ of the torque deviation, and the lower limit value −ΔT ₂ are fixed values irrespective of the load condition and the operating condition. Was set.

Therefore, under special operating conditions, the primary terminal voltage of the induction motor Primary current There is a tendency that the generated instantaneous torque T or the like changes sharply before and after the operating point of hysteresis, and the running operation lacks smoothness.

[Means for solving problems]

In order to perform a smooth motion operation with less shock in the entire operating region of the induction motor, the operating points of the magnetic flux hysteresis comparator and the torque hysteresis comparator are variably controlled in response to the load and operating conditions.

First, the case where the operating point of the magnetic flux hysteresis comparator is variable will be described. Based on the magnetic flux command value ▲ φ ^* ₁ ▼ and the error limit Δφ Primary magnetic flux controlled to be The vector is controlled by a binary hysteresis comparator so that when the magnetic flux vector length φ ₁ exceeds the upper limit, it demagnetizes, and when it falls below the lower limit, it increases.

When starting up or driving at an ultra-low speed, the magnetic flux command value ▲ φ ^* ₁ ▼
The primary magnetic flux in the induction motor When is a weak field, the generated torque is small. This is also clear from the equation.

After the smooth start-up, the magnetic flux command value is gradually increased and changed to a predetermined operating point, so that the magnetic flux command value ▲ φ
^* ₁ Compared to the starting operation with the ▼ fixed at the specified operating point, the primary terminals of the induction motor ▲ ₁ ▼, primary current The change in the instantaneous torque T becomes smooth and stable.

Therefore, in order to operate the magnetic flux hysteresis comparator stably in the entire operating range, the magnetic flux command value ▲ φ ^* ₁ ▼ which is almost proportional to the rotation speed of the induction motor is given, and the error limit Δφ is proportional to the operation interval of the hysteresis comparator. Therefore, it may be set to a value close to the limit of the switching frequency of the inverter.

Next, a case where the operating point of the torque hysteresis comparator is made variable will be described. In the three-value hysteresis comparator, the operation mode is controlled by the upper limit value ΔT ₁ and the lower limit value −ΔT ₂ , and the control flag fr is generated. With the hysteresis operating points ΔT ₁ and ΔT ₂ fixed, the operation frequency of the hysteresis comparator is low at light load,
The ratio of the generated torque ripple increases. On the contrary, when the load is heavy, the ratio of the power running mode becomes large and the normal hysteresis operation cannot be performed.

Therefore, if the upper limit value ΔT ₁ and the lower limit value −ΔT ₂ of the torque deviation T ^* −T between the instantaneous torque T of the induction motor and the torque command T ^* are set substantially in proportion to the magnitude of the torque command T ^* , then Hysteresis operation according to the torque command T ^* becomes possible in the motion region.

However, if the torque hysteresis width ΔT ₁ + ΔT ₂ is made too narrow, the switching frequency of the inverter becomes high, so it may be set narrow within the switching frequency limit of the switching elements forming the inverter.

[Action]

The operation of the magnetic flux hysteresis comparator and the torque hysteresis comparator will be specifically described.

The state diagram of the magnetic flux hysteresis comparator is as shown in Fig. 4, but in order to make it easier to understand its operation, the horizontal axis is left unchanged from the primary magnetic flux length φ ₁ of the motor. Rewrite. In these figures, the magnetic flux command value ▲ φ ^* ₁ ▼ is the distance from the center of the error limit Δφ = φmax−φmin to the magnetic flux zero, and the error limit Δφ, which is the difference between the maximum magnetic flux φmax and the minimum magnetic flux φmin, is the operation of the hysteresis comparator. Indicates the hysteresis width.

There is little back electromotive force due to speed, such as during startup and ultra-low speed, and the primary magnetic flux If is small, as shown in Fig. 8, the magnetic flux command value ▲ φ
^* ₁ ▼ is reduced and the error limit Δφ is set to the magnetic flux command value ▲
Reduce it as the primary function of φ ^* ₁ ▼. Note that the function form of Δφ is a linear function of ▲ φ ^* ₁ for simplicity, but it is possible to use a curve other than linear to make the change in characteristics smooth.

As the speed gradually increases after startup, the magnetic flux command value ▲ φ ^* ₁
By approaching ▼ and the error limit Δφ to a predetermined value as shown in FIG. 7, the operating range of the hysteresis of the magnetic flux can be effectively used, and the switching characteristics of the switching element of the inverter system can be used to the maximum. be able to.

Next, the operation of the torque hysteresis comparator will be described. The state diagram of the torque hysteresis comparator is as shown in Fig. 5, but in order to make it easier to understand its operation, the horizontal axis is the instantaneous torque T of the electric motor.
Rewrite to 10.

In these figures, the torque command T ^* is the distance from the center of the hysteresis loop to the torque zero point, and the torque deviation T ^* -
The operation of the ternary hysteresis comparator is determined by the upper limit value ΔT ₁ and the lower limit value ΔT ₂ of T. As shown in FIG. 9, when the torque command T ^* is large, the upper limit value ΔT ₁ and the lower limit value ΔT ₂
Both set large, the upper limit value [Delta] T ₁ when a small torque command T ^* as shown in 10 in the opposite, the lower limit value [Delta] T ₂ so that both smaller, the upper limit value [Delta] T _1, the lower limit value [Delta] T ₂ together the torque command T ^* The operating point is changed as a first-order function of. ΔT _{1 and} ΔT ₂ are linear functions of T ^* for the sake of simplicity, but it is possible to use curves other than linear to smooth the change in characteristics.

By doing so, the operating range of the torque hysteresis can be effectively used, and the inverter switching frequency characteristic can be used to the maximum capacity. Furthermore, it is possible to reduce the ripple of the torque generated by the induction motor,
The effect of the improvement is greater than that of the conventional method.

In the above explanation, the hysteresis of the magnetic flux and the torque was separately performed, but since this motor drive system is originally controlled at the same time, the torque ripple, the current ripple, and the harmonic are controlled while controlling both the magnetic flux and the torque. Reduction of wave loss, further start, smooth drive at ultra low speed,
A low torque stable drive is possible.

〔Example〕

FIG. 1 is a block diagram of a torque control system by a torque control device for an induction motor according to the present invention. The same symbols as those in the twelfth denote the same parts, and different parts are blocks 711 and 712.
This means that the blocks are changed to 1a and 712a and blocks 710a and 710b are added.

That is, although the conventional blocks 711 and 712 are both hysteresis comparators having a constant allowable deviation, the magnetic flux hysteresis comparator of the block 711a in this embodiment is the magnetic flux command value ▲ φ corrected in the block 710b.
^* ₁ ▼ is also input, as explained in Fig. 7 and Fig. 8,
As a first-order function of this modified magnetic flux command ▲ φ ^* ₁ ▼ ′, the error limit Δφ is increased / decreased.

In the calculation of the corrected magnetic flux command value ▲ φ ^* ₁ ▼ ', the time required for one calculation loop is constant in the case of a digital system, and therefore the calculation required for the primary magnetic flux ▲ ₁ ▼ vector to rotate _once in block 710a. The frequency f of the magnetic flux is roughly estimated by counting and storing the number of loops and calculating the reciprocal thereof.

The magnetic flux command value ▲ φ ^* ₁ ▼ and the frequency of the magnetic flux are input to the block 710b. As shown in the modified magnetic flux command value-magnetic flux frequency characteristic diagram of FIG. 11, the magnetic flux frequency f is set at a predetermined magnetic flux frequency f ₀ . With the decrease, the magnetic flux command value ▲ φ ^* ₁ ▼ is decreased in a predetermined pattern, and the corrected magnetic flux command value ▲ φ ^* ₁ ▼ 'is output.

Further, the torque hysteresis comparator of the block 712a in the present embodiment operates as a three-value hysteresis comparator for the torque command T ^* -T as in the conventional example, but the torque command T ^* is also input and
Figure, as described in FIG. 10, the torque command T ^* 1
As the next function, the upper limit value ΔT ₁ and the lower limit value ΔT ₂ are increased or decreased.

〔The invention's effect〕

When the operating point of the magnetic flux and torque hysteresis comparator is constant as in the past, control is performed at the same operating point during high speed and high torque during low speed and low torque. There was a problem such as torque shock.

According to the torque control device for an induction motor of the present invention,
By making the operating point of the hysteresis comparator of the magnetic flux and torque variable in response to the load and the operating state, the torque control of the induction motor becomes smooth and the shock is small.

In particular, shockless operation at start-up or ultra-low speed, reduction of torque ripple, etc. are more effective than conventional control with a constant operating point. Further, the same effect can be expected for the operations up to deceleration and stop.

In addition, the chopping frequency of the inverter can be controlled by making the operating point of the hysteresis comparator variable, and it is possible to prevent increase or decrease of the wasteful chopping frequency, and also it is possible to smoothly control the torque according to the load and the operating state. Therefore, the technical effect is extremely large.

[Brief description of drawings]

FIG. 1 is a block diagram of a torque control system by a torque control device for an induction motor according to the present invention, FIG. 2 is an output voltage vector diagram of an inverter by a switch state variable, and FIG. 3 is an instantaneous control of a primary magnetic flux vector of an electric motor. FIG. 4 is a state control diagram of a magnetic flux hysteresis comparator, FIG. 5 is a state control diagram of a torque three-value hysteresis comparator, and FIG. 6 is a torque waveform diagram of an electric motor. , Fig. 8 is an operation explanatory diagram of the magnetic flux hysteresis comparator, Figs. 9 and 10 are operational explanatory diagrams of the torque hysteresis comparator, and Fig. 11 is a corrected magnetic flux command value-
FIG. 12 is a block diagram of a torque control system based on the conventional torque control method. 1 ... DC voltage source, 2 ... voltage detector, 3 ... PWM inverter, 5u, 5v, 5w ... current detector, 6 ... induction motor, 7 ... control circuit.

Claims (1)

[Claims] 1. An instantaneous value of a magnetic flux vector and torque is calculated from voltage and current vector component signals in a stationary coordinate system, and when the deviation between the calculated magnetic flux value and its command value exceeds a predetermined allowable range, the magnetic flux increases. Alternatively, a binary hysteresis comparator that generates a first control flag for instructing a magnetic flux reduction, and a deviation between the calculated torque value and the command value exceed a predetermined allowable range or fall within a predetermined allowable range. Depending on the case, a three-value hysteresis comparator that generates a second control flag for instructing torque increase / decrease or current status maintenance, and which arc area the current circle is divided from based on the magnitude and sign of the magnetic flux vector component And a magnetic flux position detecting means for generating a third control flag indicating whether or not there is present, and a combination of these three control flag values. By designating the switching state of the inverter that generates the voltage vector that optimizes the torque response, the torque generated by the induction motor is controlled to follow the command value and the magnetic flux vector is controlled to draw an approximate circular locus. In the above, the operating point of the binary hysteresis comparator is variably controlled so that the upper and lower limits of the magnetic flux deviation are large when the magnetic flux command value is large, and the upper and lower limits of the magnetic flux deviation are small when the magnetic flux command value is small, and the torque command is large. A torque control device for an induction motor, wherein the operating point of the three-value hysteresis comparator is variably controlled so that the upper and lower limits of the torque deviation are large when the torque command is small and the upper and lower limits of the torque deviation are small when the torque command is small.