JPH06233587A - Inverter device - Google Patents

Abstract

PURPOSE:To suppress the torque vibration by slip frequency and torque ripple by getting the modified voltage command value being obtained by subtracting torque computing element output from voltage command value output. CONSTITUTION:This device is provided, on output side of a voltage type inverter 1, with a current detector 15, and is provided with a torque computing element 16, which receives the output of a current detector 15 and the output of a magnetic flux computing element 4, and is additionally provided with a computing element 7 which outputs a voltage command value Vr', receiving the output of an adder 13 and the output of the computing element 16. And, if toad torque increases, the torque tau of the output of the torque computing element 16 increases, and the voltage command value proportionate to the inverter frequency becomes small by the subtracter 17, and if the inverter frequency is developed, the slip frequency of a motor decreases, so load torque decreases, and the increase of load torque by torque ripple is suppressed. Conversely, even if load torque decreases by torque ripple, the decrease of load torque is suppressed. As a result, the load torque becomes stable, and the abnormal vibration of the motor can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage source inverter for driving a three-phase induction motor, and more particularly to an inverter device capable of suppressing abnormal vibration of the motor.

[0002]

2. Description of the Related Art A conventional inverter device is shown in FIG. That is, the inverter device inputs the magnetic flux command value φ * and the angular frequency command value ω * as command values, and the voltage of the electric motor as detection values, respectively, and outputs the three-phase voltage command Vu.
It is a device that obtains *, Vv *, Vw * and controls the motor voltage.

In FIG. 2, a voltage source inverter 1 takes in voltage command values Vu *, Vv *, Vw * and drives a three-phase induction motor (hereinafter simply referred to as an electric motor) 2. The voltage detector 3 detects three phases of the motor line voltage, and Vd and Vq obtained through (three-phase to two-phase) conversion are input to the magnetic flux calculator 4.

Then, the magnetic flux calculator 4 having the transfer function shown in the following equation obtains the calculated magnetic flux vectors φd and φq.
T is a time constant. φd = {T / (1 + ST)} ・ Vd φq = {T / (1 + ST)} ・ Vq ‥‥‥‥‥‥‥‥‥‥ (1)

On the other hand, the phase angle θ obtained by integrating the angular frequency command value ω * by the integrator 9 is input to the function generator 10, and (sin
θ), (cos θ). In the phase difference calculator 11, φd,
Using φq, sin θ, cos θ, the phase error ε is obtained from ε = φd · sin θ−φq · cos θ ······· (2).

A value obtained by amplifying the phase error ε via an operational amplifier 12 for proportional and integral amplification and a value obtained by multiplying two values of an angular frequency command value ω * and a magnetic flux command value φ * by a multiplier 8 are added. In addition to the device 13, the voltage command value Vr is obtained.

On the other hand, the absolute value of the magnetic flux φ obtained by the absolute value calculator 5 from φd and φq is subtracted from the magnetic flux command value φ * using the subtracter 6. The value is amplified by the operational amplifier 7 that performs the proportional-plus-integral operation, and the voltage command value Vφ is obtained. The obtained voltage command values Vr, Vφ are converted by the voltage converter 14 into three-phase voltage command values Vu *, Vv *, Vw *.

The conversion formula is as follows. First, the voltage command values Vr, Vφ are converted into voltage command values Vd, Vq in the d, q coordinate system. Vd = Vφ · cos θ−Vr · sin θ Vq = Vφ · sin θ + Vr · cos θ ‥‥‥‥‥‥‥‥‥‥‥‥‥ (3)

Next, three-phase voltage command values Vu *, Vv *, Vw * are obtained by converting Vd, Vq into two-phase / three-phase conversion. Vu * = √ (2/3) · Vd Vv * = √ (2/3) · {(− 1/2) Vd + (√3 / 2) Vq} Vw * = √ (2/3) · {(− 1/2) Vd- (√3 / 2) Vq} ‥‥‥‥‥‥‥‥‥‥ (4)

[0010]

In the prior art, torque ripple occurs in the electric motor due to the influence of slot harmonics generated in the induction machine. The torque ripple changes the motor speed, and the inverter frequency is constant, so the slip frequency changes. Then, the torque changes and the speed changes accordingly. The fluctuation of the speed further causes the fluctuation of the slip frequency and the torque, and finally the oscillation occurs. In particular, this oscillation phenomenon is likely to occur when the system is operated with a small moment of inertia.

[0011]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a current detector for detecting an output current of a voltage source inverter, an output of the current detector and an electric motor. At least a torque calculator that calculates the amount corresponding to torque using the output of the magnetic flux calculator that calculates the calculated magnetic flux vector from the voltage, and a corrected voltage command value that is obtained by subtracting this torque calculator output from the voltage command value output It is configured to obtain.

[0012]

With this solution, the torque calculator calculates an amount that is substantially proportional to the torque of the motor from the current value detected by the current detector and the calculated magnetic flux vectors φd and φq, and the torque τ corresponding to the calculated amount is subtracted by the subtractor. By feeding back to the voltage command value Vr, torque vibration can be suppressed.

That is, when torque ripple is generated due to the influence of slot harmonics and the speed of the motor decreases, the slip frequency increases because the inverter frequency is constant, and the voltage command value proportional to the inverter frequency decreases due to the subtractor. The inverter frequency decreases. Then, the slip frequency of the electric motor decreases, so the load torque decreases, and the increase in load torque due to torque ripple is suppressed. vice versa,
Even if the load torque decreases due to the torque ripple, the decrease of the load torque can be suppressed in the same manner. Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the essential structure of an embodiment of the present invention represented in a manner similar to FIG. 2, in which 15 is a current detector, 16 is a torque calculator, and 17 is a subtractor. In the figure, the parts having the same reference numerals as those in FIG. 2 indicate the parts having the same functions. That is, in FIG. 2, a current detector 15 is provided on the output side of the voltage source inverter 1, a torque calculator 16 having the output of the current detector 15 and the output of the magnetic flux calculator 4 is provided, and an output of the adder 13 is provided. The configuration is such that a subtractor 17 that receives the output of the torque calculator 16 and outputs the voltage command value Vr 'is additionally provided.

In FIG. 1, the current detector 15 detects three phases of the winding current of the motor 2 and performs (three-phase-two-phase) conversion,
The current values Id and Iq are output. This current value Id, Iq and the calculated magnetic flux vector φd, φq obtained from the magnetic flux calculator 4.
Are input to the torque calculator 16 to calculate the torque τ.

Τ = K (φd · Iq−φq · Id) (5) Here, K is a gain constant.

Further, the torque τ is subtracted from the conventional voltage command value Vr by using the subtracter 17 to obtain a new voltage command value Vr 'of the output. This corrected voltage command value is applied to the voltage converter 14
To give to.

In this embodiment, when the load torque increases, the torque τ output from the torque calculator 16 increases, and the subtractor
By 17, the voltage command value proportional to the inverter frequency becomes smaller, and the inverter frequency decreases. Then, the slip frequency of the electric motor decreases, so the load torque decreases, and the increase in load torque due to torque ripple is suppressed. On the contrary, even if the load torque decreases due to the torque ripple, the decrease of the load torque can be suppressed in the same manner.

[0019]

As described above, according to the present invention, it is possible to provide a device having a simple structure capable of stabilizing the load torque and suppressing the abnormal vibration of the electric motor in response to the increase and decrease of the load torque due to the torque ripple.

[Brief description of drawings]

FIG. 1 is a system block diagram showing a main part configuration of an embodiment of the present invention.

FIG. 2 is a system block diagram showing a conventional example.

[Explanation of symbols]

 1 voltage type inverter 2 three-phase induction motor (motor) 3 voltage detector 4 magnetic flux calculator 5 absolute value calculator 6 subtractor 7 operational amplifier 8 multiplier 9 integrator 10 function generator 11 phase difference calculator 12 operational amplifier 13 Adder 14 Voltage converter 15 Current detector 16 Torque calculator 17 Subtractor ω * Angular frequency command value φ * Flux command value

Claims (1)

[Claims] 1. A voltage source inverter for inputting a voltage command value to drive an induction motor, a voltage detector for detecting the voltage of the induction motor, a magnetic flux calculator for calculating a calculation magnetic flux vector from the output of the voltage detector, and an angular frequency. An integrator that integrates a command value to output a phase angle, a function generator that generates a trigonometric function from the integrator output, a phase difference calculator that calculates a phase difference error from the magnetic flux calculator and the function generator output, A first operational amplifier that outputs a phase control amount by proportionally and integrally amplifying the output of the phase difference calculator; a multiplier that outputs a voltage amplitude value from the angular frequency command value and the magnetic flux command value; and a first operational amplifier output. An adder that adds a multiplier output, an absolute value calculator that calculates the absolute value of the magnetic flux calculator output, a first subtractor that subtracts the absolute value output from the magnetic flux command value, and a proportional output of the first subtractor Magnetic flux control by integral amplification In an inverter device including a second operational amplifier that outputs a quantity and a voltage converter that calculates a voltage command value by inputting the adder output and the second operational amplifier output, the output current of the voltage source inverter is detected. Current detector, a torque calculator that calculates a torque equivalent amount using the current detector output and the magnetic flux calculator output, and a corrected voltage command value obtained by subtracting the torque calculator output from the adder output An inverter device comprising: a second subtractor provided to the converter.