JPH0626079Y2 - Induction motor torque control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a control device for an induction motor using a PWM inverter, and is suitable for applications requiring soft start and gear shift with less shock.

[Conventional technology]

The torque control system to which the present invention is applied is described in a paper entitled "New High Speed Torque Control Method for Induction Motor Based on Instantaneous Slip Frequency Control" on page 9, No. 1, page 106 of the Institute of Electrical Engineers of Japan, Journal B.

In this paper, the motor input voltage is detected and integrated in the control circuit to obtain the motor magnetic flux. That is,
This is a so-called magnetic flux calculation type control method, and selects 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 the inverter output voltage whose magnitude follows the given torque command is selected. 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. 2 shows the control method described in the above-mentioned article, which is proposed in Japanese Patent Laid-Open No. 62-260593, which was previously filed and published by the present applicant.
FIG. 3 is a block diagram of a torque control system that adopts an output voltage system of a WM inverter, and a DC voltage source 1 supplies power to a 3-phase induction motor 6 via a 3-phase PWM inverter 3 via a positive bus 1a and a negative bus 1b. 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 six arms of the switching element and the diode formed by antiparallel connected, such as a transistor, three changeover switches S _u, S
It can be represented as _v , 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 6 via 5 _w , and the voltage detector 2 is connected between the positive and negative buses 1a and 1b on the DC side. From these detectors and the switch state variable table described later, each phase current and each phase voltage are It can be detected.

If the primary terminal voltage and current of the three-phase squirrel cage induction motor are ▲ ▼ and ▲ ▼, respectively, and the secondary current is ▲ ▼, the voltage equation is However, the symbols ▲ ₁ ▼, ▲ ₁ ▼, ▲ ▼ are vector representations of the quantities that have been converted to the direct axis, the horizontal axis, that is, the _d and q 2-axis. _{If it is 1q} , it is shown as ▲ ₁ ▼ ＝ v _1d + jv _iq ……, and ▲ ▼ and ▲ ▼ are defined similarly. The left side of the equation represents the case where both d and q axis components are 0, and the secondary voltage is as follows in the case of the squirrel cage rotor.

The constant in the formula 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 ▲ ▼ = L ₁₁ ▲ ▼ + M ▲ ▼ ...... Expand the first line of the equation ▲ ▼ = (R ₁ + pL ₁₁ ) ▲ ▼ + pM ▲ ▼ Substituting and rearranging ▲ ▼ −R ₁ ▲ ▼ = p ▲ ▼ …… Integrating both sides ▲ ▼ = ∫ (▲ ▼ −R ₁ ▲ ▼) dt …… That is, the primary magnetic flux of the motor is the integral calculation of the formula. Required by.

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 states of the changeover switch.

Further, ▲ ▼ and ▲ ▼ are switch state variables represented by d and q axis components, and 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 changeover switches of FIG. 2 which determine the output of the inverter.
S _u , S _v , S _w all fall to the side of positive bus 1a or negative bus
The line voltage of the induction motor 6 is 0, although there is a difference whether it falls to the 1b side, which is the three-phase short-circuit mode. Also,
The reference axes of the u, v, and w phases respectively correspond to the directions of k = 1, k = 3, and k = 5 by the formulas described later.

The instantaneous torque T is the primary magnetic flux ▲ ▼ and the primary current ▲ in the formula.
It is calculated by the formula as the vector product of ▼.

T = ▲ ▼ × ▲ ▼ = φ _1d × i _1q −φ _1q × i _1d …
Here, φ _1d , φ _1q and i _1d , i _1q are respective components when the primary magnetic flux ▲ ▼ and the primary current ▲ ▼ are decomposed into d and _q axes.

Blocks 701 and 703b are blocks for calculating the primary terminal voltage ▲ ▼ from the states of the changeover switches S _u , S _v , S _w and the voltage V of the DC voltage source 1 detected by the voltage detector 2, and are switch state variables. Calculated from the table and formula.

Block 702 is 3 detected by current detectors 5 _u , 5 _v , 5 _w
This is a block for converting the phase currents i _u , i _v , and i _w into the 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 primary terminal voltage ▲ in block 704.
The product of the primary winding resistance R ₁ and the primary current ▲ ▼ is subtracted from ▼.

A block 705 is a block for performing integral calculation of the magnetic flux according to the formula, and both d and q axis components φ _1d , φ of the primary magnetic flux ▲ ▼
_1q is _{calculated, and the} magnetic flux vector length φ ₁ is _calculated in block 706.

Further, in block 710, as shown in the magnetic flux state diagram of FIG. 4, the rotation angle θ in the clockwise direction with respect to the d axis of the primary magnetic flux vector is 30 °, 90 °, 150 ° as boundaries.
The control flag fθ is generated in the following manner depending on which region is divided every 60 ° of 210 °, 210 °, 270 ° and 330 °.

−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. 6 is a state control diagram of the hysteresis comparator. The magnetic flux vector length φ ₁ is the error limit (hysteresis value) with respect to the magnetic flux command value φ ₁ ^*. Using Δφ A control flag fφ for controlling so that That is, the magnetic flux vector length φ ₁ increases and is the upper limit. When it reaches, a control flag fφ = 0 for instructing demagnetization is generated,
In addition, the magnetic flux vector length φ ₁ decreases and is the lower limit. When it reaches, a 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. 6, but in reality, the magnetic flux vector length φ calculated by the equation in block 706. ₁ is subtracted from the magnetic flux command value φ ₁ ^* in block 708, and the sixth value is subtracted in block 711.
A control flag fφ = 1, 0 is generated according to the state control diagram of the figure.

The magnetic flux limit cycle shown in FIG. 6 corresponds to the fact that the head of the primary magnetic flux vector is controlled so that it always exists in the illustrated annular portion with respect to FIG.

A combination of the control flag fφ according to FIG. 6 and the control flag fθ described with reference to FIG. 4, for example, fφ = 1, fθ =
If the control flag of I is set, the area is -30 ° ≤
Since it means the magnetization mode at θ <30 °, the primary voltage ▲ ▼ vector to be integrated into the primary magnetic flux ▲ ▼ vector has an outward component of a circle, and k = 1, from FIG. Either 2, 6 may be selected.

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, determined by the torque command T ^* and the formula In order to suppress the difference from the instantaneous torque T within a predetermined error limit, a control flag fτ is generated in block 712 according to the state control diagram of FIG.

FIG. 7 is a state control diagram of the three-value hysteresis comparator. When the motor is running, the torque deviation T ^* -T is the upper limit value ΔT.
_{When 1} (ΔT ₁ > 0) is reached, the acceleration mode control flag f
Generate τ = 1. 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 fτ = 0 is generated, the torque is gradually decreased, and the deviation is increased again, and the upper limit value ΔT ₁ When it reaches
The limit cycle in which the hysteresis loop in the upper half part of FIG. 7 orbits in the direction of the arrow is drawn.

When this is expressed in the time domain, the instantaneous torque T fluctuates as shown in the torque waveform diagram of FIG. 5, and the allowable error (hysteresis, which is the sum ΔT ₂ + ΔT ₂ of the upper and lower deviations across the torque command T ^*). It reciprocates within the band of (value) ΔT with the maximum value T ₁ and the minimum value T ₂ .

Next, when the motor is performing regenerative braking, a hysteresis loop in the lower half of FIG. 7 is drawn, and when the torque deviation reaches the negative lower limit value ΔT ₁ (ΔT ₁ > 0), the deceleration mode A control flag fτ = -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 flag fτ = 1, 0, −1.

A block 713 is a block for determining the most suitable inverter output voltage for each combination of the three control flags fθ, fφ, fτ output from the blocks 710, 711, 712, and the vector length of the primary magnetic flux ▲ ▼ described in FIG. And the rotation direction and speed, these three control flags fθ, fφ, f
τ controls.

For example, when the control flags fφ = 1 and fθ = I as described above, if the voltage vector is represented by ▲ ▼ (k) according to k in the switch state variable table, there is a possibility that k may be selected as the voltage vector. = 1, 2 or 6, but if the control flag fτ = 1 at this time, the vector k = 2 having the component rotating clockwise, that is, the output voltage vector ▲ ▼ (2) is selected. If fτ = -1, it is (6), and if fτ = 0, it is a zero vector.
▼ (0) or ▲ ▼ (7) is selected.

The following switching table shows three control flags f
The values of the output voltage vector number k are shown for all combinations of φ, fθ, and fτ.

By referring to this switching table in block 713 for each operation cycle, a switching signal is sent to the inverter 3 and instantaneous control of magnetic flux and torque is performed.

The inverter frequency can be considered as the rotational speed of the primary magnetic flux vector ( _{1) in} FIG. 4, but it is not given from the outside but is generated as a result of integrating the voltage vector by the equation.

[Problems to be solved by the invention]

In the high-speed torque control method using the instantaneous space vector as described above, since the torque is controlled by the hysteresis comparator, the control cannot be performed when the torque command is smaller than the hysteresis value of the hysteresis comparator.

That is, for example, when starting, the torque command T ^* is
When it is smaller than the hysteresis value ΔT ₁ shown in the figure, the torque deviation T ^* -T input to the block 712 does not exceed the upper limit value ΔT ₁ , so the control flag fτ = 1 in the acceleration mode cannot be generated. , Can not enter the operating state. At the time of starting, the torque command T ^* must be greater than or equal to the upper limit value ΔT ₁ shown in FIG. 7, resulting in torque shock at the time of starting.

This applies not only to the phenomenon at the time of starting, but also to the case where it is desired to shift gears during operation with no load.

[Means for solving problems]

The torque control device for an induction motor according to the present invention uses an instantaneous primary magnetic flux vector from the primary terminal voltage and current of a three-phase induction motor in order to avoid a torque shock that occurs in a conventional high-speed torque control method using an instantaneous space vector. And means for calculating an instantaneous torque, and a first hysteresis comparator means for generating a magnetizing or demagnetizing command so that the length of the primary magnetic flux vector follows a magnetic flux command value given within a predetermined error. Corresponding to the phase of the primary magnetic flux vector and second hysteresis comparator means for generating a command to advance or stop the phase of the primary magnetic flux vector so as to follow the given torque command within a predetermined error. Optimal for the output commands of the first and second hysteresis comparator means and means for determining the output voltage vector of the inverter. In the torque control device for an induction motor, when a torque command lower than the hysteresis value of the second hysteresis comparator means is given, the pulse width modulating means for converting the torque command into an on / off pulse train having an amplitude equal to the hysteresis value. It is characterized by having.

[Action]

In the state control diagram of the second hysteresis comparator in the conventional torque control device shown in FIG. 7, when the value of the torque deviation T ^* -T exceeds the upper limit value ΔT ₁ , the acceleration mode control flag fτ = 1 is generated. , Then torque deviation T due to acceleration
^* -T is adapted to generate a control flag fτ = 0 for if the lower limit value -.DELTA.T ₂ zero vector mode decreases.

In the torque control device for the induction motor according to the present invention, the upper limit value ΔT ₁ of the second hysteresis comparator is set.
When the following small torque command T ^* is given, the value when the torque command T ^* is on is ΔT ₁ and the value when it is off is −T ^.
Input to block 709 as an improved torque command T ^** and pulse width modulated by on-off pulse train changes [Delta] T _2, by sending to the block 712 calculates the difference between the modified torque command T ^** and instantaneous torque T , Equivalently second
The torque control can be performed by following the torque command smaller than the upper limit value ΔT ₁ of the hysteresis comparator means.

〔Example〕

FIG. 1 is a block diagram of an embodiment of a torque control device for an induction motor according to the present invention. The same reference numerals as those in FIG. 2 indicate the parts having the same functions, and those different from FIG. Only the ^* is input and the output of the saw-tooth wave generator 714 pulse-modulates this, and the modulator 715 sent to the block 709 as the improved torque command T ^** is followed.

FIG. 8 is a graph for explaining the operation of the modulator,
In both (a) and (b), the horizontal axis represents time, (a) is an output waveform diagram of the sawtooth wave generator, and (b) is an output waveform diagram of the modulator.

The output sawtooth of the sawtooth generator 714 has a period of t _p ,
The maximum value has an upper right-hand waveform that is equal to the upper hysteresis limit value ΔT ₁ of the second hysteresis comparator of block 712 and the minimum value is also equal to the lower hysteresis limit value −ΔT ₂ .

The period t _p may be arbitrary, but 5 to 10 msec is desirable, and 100 to 2
A frequency of 00Hz is recommended. This waveform can be expressed by the following equation when N is a natural number of 1 or more and the output is y.

The sawtooth wave generated by the sawtooth wave generator 714 is sent to the modulator 715, and the modulator 715 also outputs a torque command T ^*.
When the torque command T ^* is larger, a value equal to the upper limit value ΔT ₁ of the second hysteresis comparator is set, and when the torque command T ^* is smaller, the second command is input. Lower limit of hysteresis comparator of −ΔT ₂
The value equal to is set as the improved torque command T ^** in block 709.
Send to.

FIG. 8B shows the waveform of the improved torque command T ^{**. When} the torque command T ^* is larger than the upper limit value ΔT ₁ of the second hysteresis comparator, the improved torque command T ^** is equal to the torque command T ^*. but when the torque command T ^* when there is positive smaller than the upper limit value [Delta] T ₁ of the second hysteresis comparator compares the sawtooth wave of the instantaneous value and the torque command T ^*, is larger torque command T ^* Is a high-level output ΔT ₁ , and when the torque command T ^* is smaller, the pulse train having the low-level output −ΔT ₂ becomes the improved torque command T ^** . The period of this pulse train is t _p , which is the same as the period of the sawtooth wave.

The improved torque command T ^** is expressed as follows.

When T ^* ≥ ΔT ₁ When T ^** = T ^* ΔT ₁ > T ^* > 0, N is a natural number of 1 or more. Thus, when the torque command T ^* is smaller than the upper limit value ΔT ₁ of the second hysteresis comparator, the block 70
ΔT ₁ and −ΔT ₂ are alternately sent to 9 at a cycle t _p .
The cycle t _p is a relatively long cycle of 5 to 10 msec. Therefore, the period in which ΔT ₁ is sent is also longer than the calculation cycle of 50 to 100 μsec.

Considering the case where the torque command T ^* given at the time of starting is smaller than ΔT _{1, the} improved torque command T from the modulator 715 is considered.
^When ΔT ₁ is output as ^** , the block 712 outputs the control flag fτ = 1 in the acceleration mode while the instantaneous torque T is small, and the instantaneous torque can be obtained by combining the other control flags fφ and fθ for each calculation cycle. The primary voltage vector ▲ ▼ is selected and accelerated so that T increases.

When the instantaneous torque T increases and reaches the magnitude of ΔT ₁ + ΔT ₂ ,
Since the input of the block 702 reaches −ΔT ₂ , its output changes to the control flag fτ = 0 in the zero vector mode, and the zero vector is set as the primary voltage vector ▲ ▼ regardless of the other control flags fφ and fθ. Is selected, the instantaneous torque T gradually decreases and the acceleration speed decreases. Even if the output of the modulator 715 changes to −ΔT ₂ while the instantaneous torque T is decreasing, the control flag fτ
= 0 does not change.

If the output of the modulator 715 changes from ΔT ₁ to −ΔT ₂ before the increase rate of the instantaneous torque T is slow and reaches ΔT ₁ + ΔT ₂ ,
The output of the block 702 is changed to the control flag fτ = 0 in the zero vector mode at that time, and the other control flags fφ and fθ are set.
, The zero vector is selected as the primary voltage vector ▲ ▼.

As described above, even if the torque command T ^* that is smaller than the upper limit value ΔT ₁ of the second hysteresis comparator is given, it is converted into the improved torque command T ^** to follow the torque control. You can

[Effect of device]

As described in detail with reference to the embodiments above, according to the torque control device for an induction motor of the present invention, it is possible to easily perform a soft start and a gear shift with less shock, which are difficult with the conventional high-speed torque control method using the instantaneous space vector. This is possible only by adding such a device, and is particularly suitable for applications that require software activation.

[Brief description of drawings]

FIG. 1 is a block diagram of a torque control device for an induction motor according to the present invention, FIG. 2 is a block diagram of a conventional torque control system, FIG. 3 is an output voltage vector diagram of an inverter based on a switch state variable table, and FIG. Is a magnetic flux state diagram showing the instantaneous control method of the primary magnetic flux vector of the motor, FIG. 5 is a torque waveform diagram, FIG. 6 is a state control diagram of the magnetic flux hysteresis comparator, and FIG. 7 is a state of the torque three-value hysteresis comparator. FIG. 8 is a control diagram, and FIG. 8 is a graph for explaining the operation of the modulator used in the embodiment of the present invention.
[Fig. 3] is an output waveform diagram of the sawtooth wave generator, and (b) is an output waveform diagram of the modulator. 1 ... DC voltage source, 2 ... voltage detector, 3 ... PWM inverter, 5u, 5v, 5w ... current detector, 6 ... induction motor, 7 ... control circuit, 714 ... sawtooth wave generation Bowl, 715 ……
Modulator.

Claims (1)

[Scope of utility model registration request] 1. A means for calculating an instantaneous primary magnetic flux vector and an instantaneous torque from primary terminal voltage and current of a three-phase induction motor, and a magnetic flux command in which the length of the primary magnetic flux vector is given within a predetermined error. First hysteresis comparator means for generating a magnetizing command or a demagnetizing command so as to follow the value, and a phase advance of the primary magnetic flux vector so as to follow the given torque command within a predetermined error, Second hysteresis comparator means for generating a stop command and first and second corresponding to the phase of the primary magnetic flux vector
And a means for determining an output voltage vector of the inverter most suitable for the output command of the hysteresis comparator means, the torque controller for the induction motor is provided with a torque command lower than the hysteresis value of the second hysteresis comparator means. The torque control device for an induction motor according to claim 1, further comprising pulse width modulation means for converting the torque command into an on / off pulse train having an amplitude equal to the hysteresis value.