JPS6130996A - Inverter device - Google Patents

Abstract

PURPOSE:To improve torque characteristic obtained by a motor particularly in a low frequency by compensating to increase a terminal voltage in response to the increase in the current of the motor even if the current of the motor increases. CONSTITUTION:When the current I1 of an inverter 10 increases, the value of a signal I1dr1 output from an amplifier 6 increases. Thus, the signal I1dr1+frefK of an adder 7 is increased. Therefore, the average value of signal Pud, Pvd, Pwd output from a drive circuit 9 through a modulator 8 increases to compensate to increase the voltage V1 of the inverter 10. Accordingly, the voltage drop in the primary resistor r1 due to the increase in the current I1 is compensated to compensate the torque decrease of a motor 5.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to an inverter device for driving an electric motor.

[Prior art]

Generally, an induction motor is represented by an equivalent circuit as shown in FIG. In the figure, to=12Fi inductance, rl and r2 are primary resistance and secondary resistance. The following equation holds true for the terminal voltage v1 of the induction motor.

Vl = hrt + 2 rfAO...
・・・・・・・・・・・・・・・・・・・・・(1) However, f is the frequency full, lo ~ 2 is the current, φ is the air gap magnetic flux, and Ll is ignored in the low frequency region. We believe that it is possible. A vector diagram of equation (1) is shown in FIG.

Therefore, as shown in FIG. 3, the terminal voltage v1 and the frequency f
If control is performed to keep the ratio constant, the voltage E1 across the inductance to ideally does not change even if the load changes. However, since there is a -order resistance r1, the voltage E
1 decreases. As a result, the air gap magnetic flux φ decreases and the current I
o will decrease significantly, and the generated torque will become smaller.

If the terminal voltage v1 is increased to compensate for the decrease in torque, the current 1. This results in an inconvenience in which the amount becomes excessive.

In order to solve this problem, p
Proposals have been made to control the secondary magnetic flux or excitation voltage of a single heavy electric machine at a constant level, but such control has the disadvantage of making the inverter device complicated and expensive, and the motor does not require a speed detector or position detector. I needed to equip it.

[Summary of the invention]

This invention was made to eliminate the drawbacks of the conventional ones as described above, and detects the current flowing through the electric motor.
It is an object of the present invention to provide an inverter device that corrects a frequency command according to a detected current and can improve the torque characteristics generated by an electric motor by supplying a drive current that is pulse width modulated based on the corrected frequency command to the electric motor. .

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. Fourth
In the figure, a setter 1 generates a designated voltage Vref having a voltage corresponding to a reference frequency and supplies it to an arithmetic circuit 2.

The arithmetic circuit 2 responds to the designated voltage Vref as shown in FIG. 3 and outputs a signal fref. signal fr
ef is input to the arithmetic circuit 3 and multiplied by a constant K,
The signal becomes “frsfK”.

- 10,000, the current detector 4 indicates the current 1 flowing through the windings of the motor 5.
is detected and outputs a signal 11d having a value proportional to this, which is multiplied by the primary resistance r1 as a constant by the arithmetic circuit 6, resulting in a signal 11 (1'r1).
, 6 signal frefK and signal 11 (1rl) are added,
A signal 11d rl + fr, ef K is generated.

The signal rid rl + fref K is input to the modulation circuit 8 .

The modulation circuit 8 receives a signal 11d rl + f. It has a function of pulse width modulating the carrier signal according to the value of IK, generates a pulse width modulated signal pupV pW, and the signal Pu+Pv+p' is input to the drive circuit 9. The drive circuit 9 amplifies the signal Pu+P'+P'' and generates a signal pud for driving the transistor of the inverter circuit 10.
Outputs pvd and pwd. Inverter circuit 10
supplies a current ■1 that drives the electric motor 5.

Next, the operation will be explained. FIG. 5 is a characteristic diagram of the voltage v1 and current II of the inverter circuit 10 when the load on the motor 5 changes. When the current ■1 of the inverter circuit 10 increases, the signal 11d r output from the amplifier circuit 6
Since the value of l also increases, the signal 11a rl+ of the adder 7
fr. Increase fKO value. Therefore, the signal Pud+Pmaud output from the drive circuit 9 via the modulation circuit 8
, pvd also increases, and compensation is performed to increase the voltage Vl of the inverter circuit 10.

Therefore, as shown in FIG. 1, the voltage drop in the primary resistor ri is compensated for by increasing the current factor 1, and the decrease in torque of the motor 5 is compensated for.

〔Effect of the invention〕

As described above, according to the present invention, even if the current of the motor increases, the terminal voltage is compensated to increase accordingly, so that the torque characteristics obtained by the motor are improved, especially at low frequencies. It has the effect of

[Brief explanation of the drawing]

Fig. 1 is an equivalent circuit diagram of an induction motor, Fig. 2 is a vector diagram of the induction motor, Fig. 3 is a voltage versus frequency characteristic diagram applied to the induction motor, and Fig. 4 is an inverter device according to an embodiment of the present invention. The block diagram in FIG. 5 is a characteristic diagram of the voltage and current applied to the induction motor by the inverter device shown in FIG. 4 and the load. 1... Setting device, 2, 3.6... Arithmetic circuit, 4...
Current detector, 5...Electric motor, T...Adder, 8...
- Modulation circuit, 9... Drive circuit, 10... Inverter circuit. In addition, in the figures, the same reference numerals indicate the same parts.

Claims (1)

[Claims] a detection circuit that detects the current supplied to the induction motor; a first amplifier circuit that gives a detection signal of the detection circuit a gain proportional to the primary resistance of the induction motor; and an output signal of the first amplifier circuit that is proportional to the frequency. a modulation circuit that converts the output signal of the adder into a pulse width modulation signal, and an inverter that generates a current to be supplied to the induction motor in accordance with the pulse width modulation signal. An inverter device equipped with a circuit.