JP2000166259A - Control method for inverter device for drive of motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control method for an inverter device in which an inverter circuit is made modular and which is optimum when a semiconductor is used. SOLUTION: In this control method, the voltage/frequency(F/V) ratio of a V/F converter is set to be larger than the V/F ratio in the acceleration or constant-speed state of a motor 3. The V/F ratio is changed over by a changeover circuit 21b on the basis of the operating state of the motor 3. As a result the current of diodes constituting an inverter circuit 15 is reduced, and the inverter circuit 15 is made easily modular so as to be made low-cost.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling an inverter for driving a motor.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram showing a conventional example of an inverter device for driving a motor of this type, wherein 1 is an AC power source such as a commercial power source, and 2 is an inverter device for driving a motor (hereinafter simply referred to as an inverter device). Reference numeral 3 denotes an electric motor such as an induction motor driven by the inverter device 2.

This inverter device 2 includes a diode rectifier circuit 11, a capacitor 12 composed of an electrolytic capacitor or the like for smoothing the output of the diode rectifier circuit 11, a voltage detector 13 for detecting a voltage across the capacitor 12, a resistor 14a, A discharge resistor circuit 14 comprising a semiconductor switch 14b; an inverter circuit 15 comprising a bridge connection of a plurality of anti-parallel circuits of a self-extinguishing element such as an IGBT and a diode; a semiconductor switch 14b and an inverter circuit 1
5 includes a control circuit 16 formed by a well-known technique in each of the control elements described below.

That is, the control circuit 16 has an inverter circuit.
The frequency of the alternating current output from the road 15 is^*age
Frequency setting device 16a that outputs a predetermined acceleration / deceleration
And finally the frequency set value F^*Matches
Frequency command value F^**And an acceleration / deceleration calculator 16b that outputs
The value V via the filter 16c is added to the value detected by the pressure detector 13. ₁
And frequency command value F^**And a predetermined voltage
/ Sine-wave-shaped voltage command value V resulting in frequency ratio^*Output
V / F converter 16d and voltage command value V^*Filter 16
e and the carrier signal from the carrier generator 16f.
And perform a PWM operation using the
Circuit 1 for turning on / off each IGBT
6g and the V₁That is, the voltage across the capacitor 12 is
Voltage V of reference power supply 16h_TwoSemiconductor switch
And a comparator 16j for turning the switch 14b on.
You.

[0005]

In the above-described conventional inverter device 2, an IG constituting the inverter circuit 15 is provided.
As the BT and the diode, those in which the upper and lower arms are modularized as shown in FIG. 4 or those in which the entire three-phase bridge is modularized are generally used.

However, in this modularized inverter circuit 15, the rated current value of the IGBT is
In many cases, the rated current value of the diode is, for example, 60% to 70% or less. As a result, the rated output of the inverter device 2 set from the rated capacity of the motor 3 and the acceleration / deceleration time, that is, the rated output of the inverter circuit 15, In some cases, the above-described module is selected based on the rated current value of the diode. In this case, there is a problem that the inverter circuit 15 becomes large and expensive, and naturally, the entire inverter device 2 becomes large and expensive. An object of the present invention is to provide a control method of an inverter device for driving a motor, which solves the above problems.

[0007]

SUMMARY OF THE INVENTION The present invention provides a diode rectifier circuit for rectifying a voltage of an AC power supply, a capacitor for smoothing the output of the rectifier circuit, a discharge resistor circuit connected to both ends of the capacitor, and An inverter circuit for converting a voltage between both ends of the capacitor into an alternating current having a desired voltage and frequency, wherein the motor has a variable speed controlled by an output of the inverter circuit. The voltage / frequency ratio at the time of deceleration operation of the electric motor is set to be large in advance with respect to the AC voltage / frequency ratio output by the inverter circuit at the time of operation, so that the electric motor enters a deceleration operation state and both ends of the capacitor When the voltage becomes higher than a preset voltage, the discharge resistor circuit is operated to suppress an increase in the voltage across the capacitor. While being characterized by slowing operated electric motor.

According to the present invention, the AC voltage /
The voltage ratio at the time of deceleration operation of the electric motor is compared with the frequency ratio.
By setting the frequency ratio large in advance, it is possible to reduce the current of the diode of the module used in the inverter circuit as described later.

[0009]

FIG. 1 is a circuit diagram of an inverter device for driving a motor according to an embodiment of the present invention.
1 having the same functions as those of the conventional circuit shown in FIG.

That is, the inverter device 20 shown in FIG.
The control circuit 21 includes a frequency setting unit 16a, an acceleration / deceleration computing unit 16b, a filter 16c, a filter 16e, a PWM circuit 16g, a reference power supply 16h, and a comparator 16j.
It has a V / F converter 21a replacing the / F converter 16d and a switching circuit 21b. The control method of the inverter device 20 is described in a flowchart shown in FIG.
This will be described below with reference to the / F characteristic diagram.

In the switching circuit 21b, first, an acceleration / deceleration computing unit
16b output frequency command value F ^**Load (Figure
2, step S1), this read value is the previous read
If the value is larger than the acceleration, the motor 3 accelerates.
State (FIG. 2, step S2, branch Y), and
Operates with the powering V / F ratio (see FIG. 3) for the / F converter 21a
(FIG. 2, step S3).

If the current read value in step S1 is smaller than the previous read value, it is determined that the motor 3 is decelerating, that is, the motor 3 is in a decelerating state (step S4, branch Y), and V / F conversion is performed. A command is issued to the heater 21a to operate at the regenerative V / F ratio (see FIG. 3) (FIG. 2, step S5).

Furthermore, when read value by the current step S1 is equal to the read value of the previous (Figure 2, step S4, the branch N), it reads the output of the filter 16c, i.e., the voltage across V ₁ of the capacitor 12 ( FIG.
Step S6), and compares the voltage V ₂ corresponding value of a preset reference power 16h in the V ₁ and the switching circuit 21b, V ₁
> If V _2, since the electric motor 3 is in the deceleration ends just before (FIG. 2, step S7, branch Y), the step S5
If V ₁ ≦ V ₂ , the motor 3 is operating at a constant speed (FIG. 2, step S7, branch N), and the process proceeds to step S3.

That is, as shown in FIG. 3, since the regenerative V / F ratio is set to be larger than the powering V / F ratio, the output voltage of the inverter circuit 15 for the same output frequency becomes higher. With respect to the regenerative power from the power supply = (voltage (voltage of capacitor 12)) × (regenerative current), it is possible to reduce the current of the diode constituting the inverter circuit 15 by an amount higher than that of the conventional circuit. it can.

Note that, even if the output frequency of the inverter device 20 shown in FIG. 3 is increased or the output voltage is constant (= the constant output region of the electric motor 3), the regenerative V / F ratio is maintained at the powering V / F ratio.
By setting the value to be higher than the F, the current of the diode constituting the inverter circuit 15 can be reduced by an amount corresponding to the increase in the voltage as compared with the conventional circuit.

[0016]

According to the present invention, the voltage / frequency ratio at the time of deceleration operation of the motor is compared with the AC voltage / frequency ratio output by the motor drive inverter device at the time of acceleration and constant speed operation of the motor. By setting a large value in advance,
The current of the diode of the module used in the inverter circuit can be reduced, and as a result, it is possible to contribute to downsizing and cost reduction of the entire inverter device.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart for explaining the operation of FIG. 1;

FIG. 3 is a characteristic diagram for explaining the operation of FIG. 1;

FIG. 4 is a circuit configuration diagram showing a conventional example.

[Explanation of symbols]

1. AC power supply 2. Inverter device for driving electric motor 3.
Motor, 11: diode rectifier circuit, 12: capacitor, 13: voltage detector, 14: discharge resistance circuit, 14a ...
Resistance, 14b Semiconductor switch, 15 Inverter circuit, 16 Control circuit, 16a Frequency setting device, 16b
Acceleration / deceleration calculator, 16c: filter, 16d: V / F converter, 16e: filter, 16f: carrier generator, 16
g: PWM circuit, 16h: reference power supply, 16j: comparator,
20: an inverter device for driving a motor, 21: a control circuit,
21a: V / F converter, 21b: switching circuit.

Claims (1)

[Claims] 1. A diode rectifier circuit for rectifying a voltage of an AC power supply, a capacitor for smoothing an output of the rectifier circuit, a discharge resistor circuit connected to both ends of the capacitor, and a voltage between both ends of the capacitor being a desired voltage. An inverter circuit for converting a frequency into an alternating current, wherein the inverter drives the motor at a variable speed based on the output of the inverter circuit; an AC voltage output by the inverter circuit during acceleration and constant speed operation of the motor; The frequency / frequency ratio at the time of decelerating operation of the motor is set to be larger in advance than the / frequency ratio. When the motor enters a decelerating operation state and the voltage across the capacitor becomes higher than a preset voltage. Operating the electric motor to decelerate the motor while suppressing an increase in the voltage across the capacitor by operating the discharge resistor circuit. The method of the motor driving inverter apparatus according to claim.