JPH07118953B2 - AC motor detection delay compensation device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a current and voltage detection device for a power converter that drives an AC motor.

[Prior Art] A conventional device detects an electric current of an AC electric motor as described in, for example, Japanese Patent Laid-Open No. 57-196887, and an AC voltage is removed in order to remove high frequency noise caused by a switching action of a power converter. It is generally used because it is cheap to use a filter. In this method, it is known that the phase of the fundamental wave component lags behind the actual value when the noise component is sufficiently removed. Further, this causes a delay in the response of the current control system. Conventionally, as a countermeasure against this problem, the noise removal performance of the AC filter is designed to be low, or correction is performed by using a current control system simulation circuit as described in JP-A-58-195487. It was However, the former has a drawback that the control performance becomes insufficient because the noise component is not sufficiently removed when operating over a wide variable speed range,
The latter has a problem that the control circuit becomes complicated.

[Problems to be solved by the invention]

When performing vector control of the AC motor, the fundamental wave component of the detected value of the voltage or current of the AC motor is used.However, since the detection signal contains a high frequency noise component associated with the switching of the power converter, the AC filter is used. By removing them, the detection signal of the fundamental wave component is obtained. Therefore, the detection signal has a phase delay with respect to the actual value. This phase delay causes mutual interference between the detected values of the exciting current component and the torque current component of the electric motor in the AC motor that performs vector control, and also causes a problem in that there is an error in each command value and actual value. .

An object of the present invention is to detect the fundamental wave component of the voltage or current of an AC motor that performs vector control without phase delay.

[Means for solving problems]

The above object is achieved by compensating the phase delay of the fundamental wave component of the detection signal due to the AC filter in the rotating magnetic field coordinate system.

[Action]

The phase delay of the fundamental wave component due to the detection of the voltage or current in the stator coordinate system of the AC motor is determined by the time constant of the AC filter and the magnitude of the primary angular frequency ω of the AC motor.

In the rotating magnetic field coordinate system, the magnitude of the phase delay of the fundamental wave component due to the detection is expressed as the mutual interference amount of the two components in the rotating magnetic field coordinate system.

Therefore, if the mutual interference amount is canceled, the phase delay of the fundamental wave component due to the detection can be compensated. The magnitude of the mutual interference amount can be obtained from the product of the output of the coordinate converter and the primary angular frequency ω of the AC motor, so that the amount of mutual interference should be canceled by the output of the coordinate converter. , The phase delay can be compensated.

〔Example〕

An embodiment of the vector control device of the present invention will be described below with reference to FIG. First, the overall configuration of the vector control device will be described. In the figure, a PWM inverter 1 converts a DC voltage into an AC voltage having a variable frequency. The inverter 1 is composed of a self-extinguishing element connected by Graet's wire and a feedback diode connected in anti-parallel to each self-extinguishing element. A switching element such as a transistor or a gate turn-off thyristor is used as the self-extinguishing element. An induction motor 2 is connected to the AC output terminals of each phase U, V, W of the inverter 1. Primary currents i _u , i of the U-phase, V-phase and W-phase of the induction motor 2
_v , i _w (output current of the inverter 1) is detected by the current detectors 3-5. The detected currents i _u , i _v , and i _w are primary currents from which high-frequency noise components have been removed via the AC filter 6.
Converted to ▼, ▲ ▼, ▲ ▼.

The speed command signal ω _r * of the speed command circuit 7 is compared with the speed signal ω _r of the speed detector 9 in the adder 8, and the speed control unit 10 determines the torque current command signal i _q of the electric motor 2 according to the deviation.
Output *. The torque current command signal i _q * is multiplied by a predetermined coefficient to calculate a slip frequency command, and is added to the speed signal ω _r in the adder 11 to calculate the primary angular frequency ω of the electric motor 2. The oscillator 12 outputs a sine wave signal having a constant amplitude at a frequency proportional to the primary angular frequency ω. This output signal is applied to the coordinate converters 13 and 14.

Output signal of AC filter 6 ▲ ▼, ▲ ▼, ▲
In the coordinate converter 14, ▼ is converted into a two-phase signal of two current components ▲ ▼ and ▲ ▼ in the rotating magnetic field coordinate system of the electric motor 2. This current ▲ ▼ is multiplied by the primary angular frequency ω in the multiplier 15, and added with ▲ ▼ in the adder 16 to calculate the torque current i _q . The other current ▲ ▼ is multiplied by the primary angular frequency ω in the multiplier 17, and added with ▲ ▼ in the adder 18 to calculate the exciting current i _d .

The exciting current command signal i _d * of the exciting current command circuit 19 is the adder 20.
Is compared with the exciting current i _d, and the exciting current controller 21 outputs the voltage command v _d * of the electric motor 2 according to the deviation. The torque current command i _q * is the torque current in the adder 22.
It is compared with i _q, and the torque current control unit 23 outputs the voltage command v _q * of the electric motor 2 according to the deviation.

The voltage command v _d *, v _q * of the motor 2 is changed from the rotating magnetic field coordinate to the voltage command v _u *, v _v *, v _w * of the stator coordinate based on the sine wave signal of the oscillator 12 in the coordinate converter 13. To be converted. PWM
The inverter 1 converts a DC voltage into an AC voltage based on the voltage commands v _u *, v _v *, v _w *.

Next, a method of compensating for the detected phase delay due to the AC filter will be described. Here, in order to simplify the explanation, the AC filter 6 is a primary delay circuit shown in FIG. The input / output characteristic of this AC filter is expressed by the following equation. As for the U phase, Where T: time constant (= RC), S: Laplace operator (in steady state, S = j _w , ω: angular frequency).

The damping ratio (▲ ▼ / i _u ) and phase delay angle θ (= -tan ^-1 ωT) of this AC filter can be set freely by properly selecting the time constant T of the AC filter as shown in Figs. Can be designed to However, if the phase delay angle θ is sufficiently small with respect to the angular frequency ω (for example, 1 to 300 rad / s) at which the motor operates, there is a problem that a sufficient damping ratio for noise components in the high frequency range cannot be obtained. The phase delay angle θ is allowed 10 to 20 deg.

The influence of the phase delay due to the input / output characteristics of the AC filter is compensated as follows, and the exciting current i _d and torque current i _{q of the} motor are detected.

The relational expression for converting the currents i _u , i _v , i _w in the stator coordinate system of the motor into the currents i _d , i _q in the rotating magnetic field coordinate system is as follows.

Here, [F (ωt)]: coordinate conversion matrix, ω: primary angular frequency of the motor.

By the way, the current detected through the AC filter ▲
▼, ▲ ▼, and ▲ ▼ are expressed by the following expressions from the expression (1).

Therefore, the currents ▲ ▼ and ▲ ▼ in the rotating magnetic field coordinate system detected through the AC filter are given by the following expressions from the expressions (2) and (3).

From equations (2) and (4), it is found through the excitation current i _d , torque current i _{q of} the motor and the AC filter ▲ ▼, ▲ ▼
The relational expression of is obtained as follows.

Where [] ^-1 : [] inverse matrix, Is.

The second term on the right side of the equation (5) is a transient term, and in the steady state, it becomes the following equation.

That is, the excitation current i _d and the torque current i _q that compensate the phase delay due to the AC filter of the electric motor can be detected by performing the calculation of the equation (6) for ▲ ▼ and ▲ ▼ obtained through the AC filter. it can.

In this way, the phase delay and attenuation associated with the AC filter are compensated, so the fundamental wave component of the electric current of the motor can be detected without phase delay, and in the case of vector control, the excitation current component and torque current Since there is no interference between the detected values and the components, there is an effect that stable operation can be performed with high-speed response, which is a feature of vector control.

Although the electric current of the electric motor has been described as the target in the present embodiment, the voltage of the fundamental wave component can be detected in the same manner with respect to the voltage of the electric motor without phase delay. Further, in the present embodiment, an analog circuit is used for easy understanding of the operation description, but it is obvious that the present invention can be applied to a digital control unit using a microprocessor.

〔The invention's effect〕

According to the present invention, even when the fundamental wave component of the voltage or current of the AC motor is detected through the AC filter, it is possible to detect without eliminating the phase delay and attenuation associated with the AC filter, so that the high frequency associated with the switching action of the power converter is achieved. This has the effect of realizing highly accurate vector control that is less affected by noise.

[Brief description of drawings]

FIG. 1 is a control block diagram showing an embodiment of the vector control device of the present invention, FIG. 2 is a circuit diagram showing the circuit configuration of the AC filter of FIG. 1, and FIGS. 3 and 4 are of FIG. It is a characteristic view which shows the damping ratio and phase delay angle of an AC filter. 1 ... PWM inverter, 2 ... induction motor, 3-5 ...
Current detector, 6 ... AC filter, 13,14 ... Coordinate converter, 15, 17 ... Multiplier, 16, 18 ... Adder.

Claims (1)

[Claims] 1. A current detection circuit comprising a current detector of an output current of a power converter for supplying an alternating current of a variable voltage and a variable frequency to an AC electric motor and a filter for removing a noise component, and an output signal of the detection circuit. In a power converter equipped with a coordinate converter that converts two components i _d and i _q of a rotating magnetic field coordinate system that rotates at an angular frequency ω of an AC motor, the outputs i _d and i _{q of the} coordinate converter and the angle A detection delay compensating device for an AC electric motor, comprising an adder for adding a product of frequencies ω to each other of outputs i _d and i _q of the coordinate converter.