JPH10108499A - Torque controller for induction motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control torque even when a voltage command vector has a magnitude larger than that of a maximum voltage vector by selecting the voltage vector in the rotational direction of an induction motor or a primary angular speed and outputting the voltage vector thus selected as a voltage command for a voltage controlled inverter. SOLUTION: A decision means 11 receives the voltage Vdc of a DC power supply 1 detected through a voltage detector 10, and a voltage command vector V* from a coordinate conversion means 9. A voltage vector selection means 12 receiving an output A from the decision means 11, the voltage command vector V* and a rotational speed ωm from a speed detector 5 selects a voltage vector in the rotation direction which is inputted to an inverter 2. According to the arrangement, torque can be controlled even when the voltage command vector V* has a magnitude larger than that of a maximum voltage vector.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for controlling the torque of an induction motor using an inverter.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram showing an example of a conventional torque control device for an induction motor. In FIG. 2, a current detector 4 detects a primary current vector i of the induction motor 3. The speed detector 5 detects the speed of the rotor of the induction motor 3. From the current detector 4 and the speed detector 5,
The detected current vector i and rotation speed ωm are input, and the calculation means 6 calculates the magnitude T of the torque, the magnitude φ of the magnetic flux vector, and the phase angle θ thereof. An error between the torque T and its command value T * is calculated by a torque error calculating means 71 and amplified by a torque error amplifying means 81 to become a torque component voltage command VT. An error between the magnitude φ of the magnetic flux vector output from the arithmetic means 6 and the command value φ * is obtained by the magnetic flux error arithmetic means 72, and is amplified by the magnetic flux error amplifying means 82 to become the magnetic flux component voltage Vφ.

The torque component voltage command VT and the magnetic flux component voltage Vφ are converted by the coordinate conversion means 9 into a voltage command vector V *, which is represented by the following equation: V * = (Vφ + jVT) exp (jθ) ─── (1) Make the conversion. Where j is-
The imaginary part is represented by the square root of 1. The output from the coordinate conversion means 9 calculated by the equation (1) is a voltage command vector V *, which is input to the voltage control inverter 2. Here, a three-phase voltage corresponding to the voltage command vector V * is applied to the induction motor 3, and power is supplied from the DC power supply 1 to the induction motor 3.
To supply.

[0004]

In the conventional system described above, the torque error amplifying means 81 and the magnetic flux error amplifying means 82 are used.
Is generally constituted by a proportional-integral amplifier. Even if there is no torque error, the output torque voltage command V
T is a value substantially proportional to the rotation speed of the induction motor 3.
When there is no magnetic flux error, the output magnetic flux divided voltage Vφ of the magnetic flux error amplifier 82 has a value of about the voltage drop of the primary resistance of the induction motor 3. Here, the value of the voltage drop of the primary resistance is very small and is ignored.
It can be understood that the magnitude of * is equal to the output torque voltage command VT that is substantially proportional to the rotation speed of the induction motor 3.

[0005] However, if the operating range of the induction motor 3 is to be extended to the high-speed side, the maximum value of the output voltage of the inverter 2 is limited by the voltage of the DC power supply 1, so that the voltage as instructed in the high-speed range is the induction motor. 3 cannot be applied. In this region, the magnitude of the magnetic flux φ can follow the command value φ *, but the magnitude of the torque T cannot be controlled by the conventional control method that is established without any magnetic flux error.

The reason will be described below. First, the magnitude of the output torque component voltage command VT and the output magnetic flux component voltage Vφ when the inverter 2 can output a voltage according to the command value will be described. The relationship between the output voltage vector V of the inverter 2 and the magnetic flux vector ψ is expressed by equation (2), and V = dψ / dt────── (2). However, the voltage drop of the primary resistance of the induction motor 3 is not considered. Here, if ψ = φexp (jθ), Expression (2) is represented by Expression (3), and V = d (φexp (jθ)) / dt + jωφexp (jθ) ─── (3)

Here, ω = dθ / dt. In the conventional method described above, if the voltage control inverter 2 faithfully applies a voltage vector V according to the command value to the induction motor,
Since the voltage command vector V * in the equation (1) becomes equal to the output voltage vector V in the equation (3), the real part and the imaginary part are expressed by the equations (4) and (5), and Vφ = dφ / dt───── (4) VT = ωφ──────── (5) Since the rotational angular velocity ω of the magnetic flux is almost equal to the rotational speed ωm of the induction motor, the output torque voltage command VT is approximately proportional to the speed according to the equation (5), and the output magnetic flux voltage Vφ is the rate of change of the magnetic flux according to the equation (4). It has almost no value because it is equal to. Therefore, it is understood that the magnitude of the voltage command vector V * is determined by the torque voltage command VT proportional to the speed.

Next, the reason why the inverter 2 can output a voltage according to the command value and the reason why it cannot be output will be described. The instantaneous voltage vectors that can be output from the inverter 2 are composed of seven types of voltage vectors including a zero vector. The center of a regular hexagon is a zero vector having a size of zero, and the six vertices are composed of the remaining six types of voltage vectors. And the voltage command vector (V
*) Is the voltage command vector (V *), which is the sum of the products of three types of voltage vectors (Vo, Va, Vb) including the zero vector (Vo) close to the respective output times (To, Ta, Tb). And three types of voltage vectors (Vo, Va, Va) so as to be equal to the product of the sum of the output times (Ts).
Vb) is sequentially output to each output time (To, Ta, Tb)
By outputting, a voltage vector V equal to the voltage command vector V * can be output. That is, it is necessary to satisfy the condition of the following expression (6). V * · Ts = Vo · To + Va · Ta + Vb · Tb─── (6)

However, if the voltage command vector V * is larger than the regular hexagon, the voltage vector V equal to the command value cannot be output. Moreover, it is the torque component voltage command VT that determines the magnitude of the voltage command vector V *, and the output torque component voltage command VT of the torque error amplifier 81 is determined by the error between the magnitude T of the torque and the command value T *. As the voltage increases, the voltage command vector V * tends to become larger and larger from the equation (1), the difference between the voltage command vector V * and the voltage vector V actually applied to the induction motor also increases, and the torque T cannot follow the command value. Become.

When the magnetic flux component voltage Vφ is amplified due to an error between the magnitude of the magnetic flux φ and the command value φ *, the magnetic flux component voltage Vφ is a vector perpendicular to the torque component voltage command VT according to equation (1). Since Vφ is sufficiently smaller than VT, V *
There is almost no increase in the direction of the magnitude, and it appears as a change in the phase angle direction of V *. Even if V * is larger than the size of the regular hexagon and the inverter cannot output a voltage vector having a magnitude equal to the command value, the magnitude of the magnetic flux φ follows the command value φ * because it can cope with a change in the phase direction. I do.

Thus, conventionally, the voltage command vector V
When the magnitude of * is larger than the magnitude of the maximum voltage vector V limited by the input DC voltage of the inverter, there is a problem that torque cannot be controlled. The present invention has been made in view of the above points, and an object of the present invention is to provide a torque control device for an induction motor that solves these drawbacks.

[0012]

Means for achieving the object is to determine whether or not the voltage control inverter can output a voltage equivalent to a command value from a voltage command and a voltage of an input power supply of the voltage control inverter. Determination means for determining whether the output of the induction motor and the rotation direction of the induction motor or the rotation direction of the primary angular velocity are input, and if it is determined that the output is impossible by the determination means, A voltage vector selecting means for selecting a voltage vector in the rotating direction and outputting it as a voltage command of the voltage control inverter; and a case where the magnetic flux error amplifying means is a proportional-integral amplifier, and when it is determined that the output is impossible by the determining means Is provided by providing a magnetic flux error integral value fixing means which does not update the output of the integrator of the magnetic flux error amplifying means.

The voltage command vector V * is determined by the determination means.
Is outside the regular hexagon, the inverter cannot output a voltage equivalent to the voltage command vector V *. Then, a voltage vector V ** in the rotation direction is selected by the voltage vector selection means (one of the vertices of a regular hexagon).
When the voltage command vector V * is replaced, the magnitude of the magnetic flux φ becomes smaller without following the command value φ * by the magnetic flux error integral value fixing means, and the magnitude T of the torque almost follows the command value T *. it can. Therefore, torque can be controlled. The reason is described below.

If the voltage command vector V * is outside the voltage range (regular hexagon) that the inverter can output, the magnitude of the magnetic flux φ is determined by selecting the voltage vector in the rotation direction of the magnetic flux vector by the voltage vector selection means. It can be smaller than the command value φ *.

That is, the torque component voltage command VT is given by the following equation (5).
As shown in (4), when the value is sufficiently large with respect to the magnetic flux component voltage command, the voltage vector V * in the rotation direction with respect to V *.
Is present in a minus direction with respect to Vφ shown in the equation (1), and by outputting V *, the negative Vφ is forced.
Is output. Then, from the equation (4), it can be seen that the magnitude φ of the magnetic flux decreases regardless of the command value φ *. It can be seen from equation (5) that VT also decreases as the magnitude φ of the magnetic flux decreases.

When the magnitude of the magnetic flux φ becomes smaller than the command value φ *, Vφ increases in the plus direction by the magnetic flux error amplifying means, but the magnetic flux error integral value fixing means prevents the increase due to the error integration of Vφ. It is simply the sum of a value proportional to the error between the magnitude φ of the magnetic flux and the command value φ * and a fixed integral value.

When V * exceeds the voltage range that the inverter can output due to the above operation, a voltage vector V ** in the rotating direction is applied to the induction motor in response to the voltage command vector V *, and the operation of the magnetic flux integrator is performed. By stopping V
To reduce the VT without causing the magnitude of the magnetic flux φ to follow the command value φ * while preventing the increase in φ, and to make the torque T follow the command value T * by preventing the error between V * and V ** from diverging. Is possible. Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0018]

FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, the same parts as those in the prior art shown in FIG. Only the part within the dotted line) will be described. In FIG. 1, a discriminating unit 11 receives a voltage Vdc of the DC power supply 1 detected by a detector 10 and a voltage command vector V * output from a coordinate transforming unit 9, and outputs an output time satisfying the equation (6). When the sum of Ta and Tb is larger than the sum Ts, A = 1 is output, and when it is smaller, A = 0 is output. The voltage vector selection means 12 inputs the output A of the determination means 11, the voltage command vector V *, and the rotation speed ωm of the detector 5, and if A = 0, V ** = V *, and if A = 1, ωm The voltage vectors Va and V of the equation (6) according to the polarity
Select the voltage vector in the rotation direction from b, and V ** = V
a or V ** = Vb is output and input to the inverter 2.

The magnetic flux error integrated value fixing means 13 receives the output A of the discriminating means 11 and does not update the value of the integrator of the magnetic flux error amplifying means 821 when A = 1.

[0020]

As described above, conventionally, when the magnitude of voltage command vector V * is greater than the magnitude of maximum voltage vector V limited by the input DC voltage of the inverter, torque cannot be controlled. However, according to the present invention, the torque can be controlled even when the magnitude of the voltage command vector V * is larger than the magnitude of the maximum voltage vector V limited by the input DC voltage of the inverter.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a block diagram showing an example of the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC power supply 2 Voltage control inverter 3 Induction motor 4 Current detector 5 Speed detector 6 Calculation means 71 Torque error calculation means 72 Flux error calculation means 81 Torque error amplification means 82 Flux error amplification means 821 Flux error amplification means 9 Coordinate conversion means DESCRIPTION OF SYMBOLS 10 Voltage detector 11 Judgment means 12 Voltage vector selection means 13 Magnetic flux error integral value fixing means

Claims (2)

[Claims] 1. A calculating means for calculating a magnetic flux vector and a torque of a three-phase induction motor, and a torque error calculating means for comparing a magnitude of a magnetic flux vector and a torque output from the calculating means with a command value of the magnetic flux vector and a torque. And a magnetic flux error calculating means, a torque error amplifying means and a magnetic flux error amplifying means for amplifying the output of these error calculating means, It comprises a coordinate conversion means for converting, and a voltage control inverter for applying a three-phase voltage to the induction motor through a voltage vector selection means for inputting an output of the coordinate conversion means as a voltage command and converting the output into a voltage waveform. In the torque control device for an induction motor, the voltage control inverter transmits a command based on the voltage command and a voltage of an input power supply of the voltage control inverter. A determination unit that determines that a voltage cannot be output, and an output of the determination unit and a rotation direction of the induction motor or a rotation direction of the primary angular velocity, and the determination unit that indicates that the voltage is in a limited state. A voltage vector selecting means for selecting a voltage vector in the rotation direction of the induction motor or the primary angular velocity in accordance with an output, and outputting the selected voltage vector as a voltage command of the voltage-controlled inverter. Torque control device. 2. When the magnetic flux error amplifying means is a proportional-integral amplifier, the output of an integrator of the magnetic flux error amplifying means is not updated when the output of the magnetic flux error amplifying means is determined to be impossible. The torque control device for an induction motor according to claim 1, further comprising means.