JPS63171181A - Detection lag compensator for ac motor - Google Patents

Abstract

PURPOSE:To compensate for the phase lag of detecting signal along with an AC filter, by adding the product of the output of a coordinate converter by the primary angular frequency of an AC motor, to the output of the coordinate converter. CONSTITUTION:From a speed controlling section 10, the output of current command signal iq* according to a deviation between speed command signal omegar* and speed signal omegar is generated. The current command signal iq* and the speed signal omegar are added to each other, to obtain primary angular frequency omega. In the meantime, primary current iu-iw detected by an AC filter 6 is converted to the current component id1, iq1 of a rotary coordinate system by a coordinate converter 14. Then, the current id1, iq1 and the primary angular frequency omega are applied to multipliers 15, 17 and adders 16, 18, to obtain torque current id, iq. Besides, according to a deviation between the current command signal id*, iq* and the torque current id, iq, voltage command vd*, vq* is applied to a coordinate converter 13, and the voltage command vu*-vw* of a stator coordinate is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a current and voltage detection device for a power converter that drives an AC motor.

[Conventional technology]

Conventional devices detect the current of an AC motor using an AC filter to remove high-frequency noise associated with the switching action of a power converter, as described in Japanese Patent Application Laid-open No. 57-196887, for example. It is commonly used because it is inexpensive.

In this method, it is known that if the noise component is sufficiently removed, the phase of the fundamental wave component lags behind the actual value. This also causes a delay in the response of the current control system. Conventionally, countermeasures to this problem include designing AC filters with low noise removal performance, or correcting them using a current control system simulation circuit as described in Japanese Patent Laid-Open No. 1987-1.95487. It had become. However, when the vehicle is operated over a wide variable speed range, noise components are not removed sufficiently, resulting in insufficient control performance, and the latter has a problem in that the control circuit is complicated.

[Problem that the invention seeks to solve]

When vector I-controlling an AC motor, the fundamental wave component of the detected value of voltage or current of the AC motor is used, but since the detection signal contains high frequency noise components associated with switching of the power converter, an AC filter is used. By removing them, a fundamental wave component detection signal is obtained. Therefore, the detection signal has a phase lag with respect to the actual value. In AC motors that perform vector control, this phase delay causes mutual interference between the detected values of the motor's excitation current component and torque current component, and also causes errors between the command value and the actual value of each of them. .

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 for the phase delay of the fundamental wave component of the detection signal caused by the AC filter in the rotating magnetic field coordinate system.

[Effect]

The phase delay of the fundamental wave component accompanying the detection of 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 accompanying detection is expressed as the amount of mutual interference between the two components in the rotating magnetic field coordinate system.

Therefore, by canceling out the amount of mutual interference, it is possible to compensate for the phase delay of the fundamental wave component accompanying detection. The magnitude of the mutual interference can be found from the product of the output of the coordinate converter mentioned above and the primary angular frequency ω of the AC motor, so this can be applied to the output of the coordinate converter to cancel out the mutual interference mentioned above. By adding , the phase delay can be compensated for.

〔Example〕

An embodiment of a vector control device according to 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 with a variable frequency. The inverter 1 is composed of self-extinguishing elements connected in a Graetz connection and feedback diodes connected in antiparallel to each self-extinguishing element. As the self-extinguishing element, a switching element such as a transistor or a gate turn-off thyristor is used. An induction motor 2 is connected to AC output terminals of each phase U, V, and W of the inverter 1. Primary currents lu, lv+1w (output currents of the inverter 1) of the U-phase, V-phase, and W-phase of the induction motor 2 are detected by current detectors 3 to 5. The detected current 1u+ lvl 1w is converted into primary currents Tτ, T7 . − is converted to

The speed command signal ω- of the speed command circuit 7 is compared with the speed signal ω1 of the speed detector 9 in an adder 8, and the speed control unit 10 adjusts the torque current command signal i of the electric motor 2 according to the deviation.
Output q*. The torque current command signal iq* is multiplied by a predetermined coefficient to calculate a slip frequency command, and an adder 11 outputs a speed signal ω.

The primary angular frequency ω of the electric motor 2 is calculated.

The oscillator 12 outputs a sine wave signal with a constant amplitude and a frequency proportional to this primary angular frequency ω.

This output signal is applied to a coordinate transformer 13.14.

The output signals TτHiv, iw of the AC filter 6 are converted by the coordinate converter 14 into two-phase signals of two current components i++, iq in the rotating magnetic field coordinate system of the electric motor 2. This current T7 is multiplied by the primary angular frequency ω in the multiplier 15,
The adder 16 adds it to iq to calculate torque current iq. The other current T is multiplied by the primary angular frequency ω in the multiplier 17, and added to T7 in the adder 18 to calculate the exciting current i.

The excitation current command signal id* of the excitation current command circuit 19 is compared with the excitation current id in an adder 20, and the excitation current control unit 21 sets the voltage command vd* of the motor 2 according to the deviation.
Output. Further, the torque current command i1 is compared with the torque current iq in the adder 22, and the torque current control unit 23 outputs the voltage command vq* of the electric motor 2 according to the deviation.

Voltage command Vdt of electric motor 2, vq*i coordinate converter 1
3, based on the sine wave signal of the oscillator 12, voltage command Vu"IVv"IV from the rotating magnetic field coordinates to the stator coordinates.
− is converted to PWM inverter 1 uses this voltage command V
u*I Vv'', converts DC type voltage to AC voltage based on V-.

Next, a method of compensating for the detection phase delay caused by the AC filter will be described. Here, to simplify the explanation, the AC filter 6 is assumed to be a first-order lag circuit shown in FIG. The input/output characteristics of this AC filter are expressed by the following equation. Regarding the U phase, 1=...(1)
1+TS Here, T2 time constant (=RC), S nira plus operator (in steady state S=j.2.U:V:]-2ω: angular frequency).

The damping ratio (i1/i-) and phase delay angle 0 (=-tan-'ωT) of this AC filter are the third. As shown in FIG. 4, the AC filter can be freely designed by appropriately selecting the time constant T. However, if the phase delay angle 0 is made sufficiently small relative to the angular frequency ω (for example, 1 to 300 rad/s) at which the motor is operated, there is a problem that a sufficient damping ratio for noise components in the high frequency range cannot be obtained. A phase delay angle θ of 10 to 20 degrees is allowed.

The influence of phase delay due to the input/output characteristics of this AC filter is compensated as follows, and the exciting current of the motor], d+
Torque current iq is detected.

The relational expression for converting the currents iu, iv, iw in the stator coordinate system of the motor into the currents id, iq in the rotating magnetic field coordinate system is as follows.

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

By the way, the current 1uy detected through the AC filter
iv and iw are expressed by the following equations from equation (1).

Therefore, the current T7. of the rotating magnetic field coordinate system detected through the AC filter. From equations (2) and (3), τ is the following equation.

From equations (2) and (4), the exciting current of the motor ]-dl
1", which is determined through the l"lux current iq and the AC filter.
The relational expression for ゜iq is found as follows.

...(5) Here, []-E: Inverse matrix of [], S-□ t10) It is.

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

That is, the excitation current id and torque current iq that have compensated for the phase delay caused by the AC filter of the motor can be detected by performing the calculation of equation (6) on ia and iq determined through the AC filter.

In this way, the phase delay and attenuation associated with the AC filter are compensated, so the fundamental wave component of the motor current can be detected without phase delay, and when performing vector control, the excitation current component and torque current component can be detected without phase delay. Since there is no interference between detected values and components, stable operation can be achieved with fast response, which is a feature of vector control.

Although the present embodiment has been described with reference to the current of the motor, the voltage of the fundamental wave component can be similarly detected with respect to the voltage of the motor without phase delay. Further, in this embodiment, an analog circuit is used to explain the operation in order to make it easier to understand, but it is obvious that the present invention can also be applied to a digital control unit using a microprocessor.

〔Effect of the invention〕

According to the present invention, even when detecting the fundamental wave component of the voltage or current of an AC motor via an AC filter, it can be detected without phase delay and attenuation associated with the AC filter, so high frequency components associated with the switching action of the power converter can be detected. This has the effect of realizing highly accurate vector control with less influence of noise.

[Brief explanation of the drawing]

FIG. 1 is a control configuration diagram showing one embodiment of the vector control device of the present invention, FIG. 2 is a circuit diagram showing the circuit configuration of the AC filter in FIG. 1, and FIGS. FIG. 3 is a characteristic diagram showing the attenuation ratio and phase delay angle of an AC filter. 1...PWM inverter, 2...induction motor, 3~
5... Current detector, 6... AC filter, 13.1
4... Coordinate converter, 15.17... Multiplier, 16.
18... Adder.

Claims (1)

[Claims] 1. A current detection circuit consisting of a current detector for the output current of a power converter that supplies alternating current of variable voltage and variable frequency to the alternating current motor and a filter that removes noise components; In a power converter equipped with a coordinate converter that converts a rotating magnetic field coordinate system rotating at an angular frequency ω into two components i_d and i_q, the product of the outputs i_d and i_q of the coordinate converter and the angular frequency ω is converted into the coordinate 1. A detection delay compensation device for an AC motor, characterized in that an adder is provided for mutually adding outputs i_d and i_q of a converter.