JPH0755077B2 - Inverter device for induction motor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device that controls the rotation speed by changing the voltage and frequency applied to an induction motor.

2. Description of the Related Art An inverter device for controlling the number of revolutions of an induction motor (hereinafter, abbreviated as a motor) is, as shown in FIG. 5, an inverter unit composed of a diode 1, a capacitor 2, a converter unit 3, a transistor 4, and a diode 5. 6, a base drive circuit 7 for supplying the base current of the transistor 4, a control circuit 8 for controlling the whole inverter device and insulatingly supplying the base signal to the base drive circuit 7, and supplying power to the control circuit 8 and the base drive circuit 7. And a power supply circuit 9 for supplying a power supply signal,
And the inverter device 10. The converter unit 3 and the power supply circuit 9 are connected to a three-phase or single-phase power supply 10, the inverter unit 6 is connected to the motor 11, and the rotation speed command 12 is connected to the control circuit 8.

Conventionally, an inverter device stops all operations when a momentary power failure or momentary voltage drop (hereinafter collectively referred to as momentary power failure) occurs for a certain period of time, and restarts from the initial state when the power supply voltage is restored. A method of holding the stopped state is adopted unless it is reset by resetting after being determined as an abnormal state by calling it a “trip”.

It is possible to prevent the voltage supplied from the power supply circuit 9 to the control circuit 8 and the base drive circuit 7 from dropping due to the suspension or shortage of the power supply voltage, thereby preventing malfunction of the microcomputer and the logic IC in the control circuit, and the base drive. This is because when the base current supplied from the circuit 7 to the base of the transistor 4 is insufficient, the transistor 4 enters the active region to prevent the transistor from being destroyed due to the wattage excess.

Problems to be Solved by the Invention Even if it is only for the safety of the device that the inverter stops all operations when a momentary power failure occurs, it is tripped when the power supply voltage is restored and the entire stop is maintained even if it is safe for the equipment. For example, considering a large load of inertia,
Since the rotation speed does not decrease during the instantaneous power failure, when the inverter restarts operation from the initial state when the power supply voltage is restored,
Since the frequency supplied from the inverter to the motor is lower than the rotation speed of the motor, the motor operates as a generator, so-called regenerative state, large current flows through the transistor 4 and diode 5 of the inverter, and regenerative power from the motor causes This is because the voltage of the capacitor 2 rises abnormally, and an overcurrent trip causes an abnormal protection operation called an overvoltage trip.

If the number of revolutions of the motor is observed by a sensor such as a tacho-generator, if a frequency matching the number of revolutions is applied to the motor after a certain period of time when the power supply voltage is restored, a large current will flow or regenerative power will be generated. There is no problem because it does not, but it is not allowed to attach a sensor to the motor in the inverter intended for the operation of a general-purpose motor.

As described above, the conventional inverter has a problem of tripping when an instantaneous blackout occurs. Therefore, it is an object of the present invention to provide an inverter that does not easily trip even when an instantaneous blackout occurs.

Means for Solving the Problems The present invention is a DC-DC converter for making various DC voltages via a high frequency transformer by inputting the DC voltage V _DC of the converter section, and observing the DC voltage V _DC and exceeding a specified value. And a means for suspending the operation of the inverter when the DC voltage V _DC drops below a specified value.

Action According to the above configuration, it is possible to eliminate the occurrence of an unnecessary trip even if an instantaneous blackout occurs.

Example Next, an example of the present invention will be described with reference to FIGS.

In FIG. 1, 13 is a single-phase or three-phase power supply, 14 is a converter section composed of single-phase / three-phase rectifiers and smoothing capacitors 15, 15 is an inverter section composed of transistors and diodes, and 16 is a motor. is there. The control of the entire inverter is performed by the control of the control circuit 17, which insulates the photocoupler and supplies it to the base drive circuit 18, and turns on / off the transistor as the base signal of the transistor of the inverter unit 15.
F

The power supply circuit 19 receives power from the DC voltage V _DC of the converter unit 14 and supplies the power supply voltage to the base drive circuit 18, the control circuit 17, and the DC voltage detection circuit 20. DC voltage detection circuit
20 detects whether the DC voltage V _DC is equal to or higher than a specified value and sends a signal to the control circuit 17.

Next, the power supply circuit 19 will be described. This is a power supply circuit known as a self-excited DC-DC converter by a ringing choke converter system to which a voltage stabilizing circuit is added as shown in FIG. Using this DC-DC converter, output E1
~ E4 as the power supply for the base drive circuit 18 shown in FIG.
Is the power source of the control circuit 17. The power supply current of the base drive circuit 18 is completely in a so-called operating state in which a voltage and a frequency are supplied from the inverter unit 15 to the motor 16 and in a so-called stop state in which the transistor of the inverter unit 15 is OFF and the motor is not supplied with power. On the contrary, in the stop state, the base current of the transistor is unnecessary, so that almost no current flows. In this way, the output voltage of the ringing choke type self-excited DC-DC converter when the load condition is largely divided into two is as shown in Fig. 3 when the DC voltage V _DC is above the point A when the inverter is operating. In contrast, the output voltage can be stabilized up to a low input voltage up to point B, which is lower than point A, while the inverter is stopped.

Next, the DC voltage detection circuit 20 will be described. This is the output voltage V _DC of the converter section (14 in Fig. 1) directly or V / F, F
It has a function of judging whether or not the voltage obtained by insulation with a / V converter or the like is equal to or higher than the voltage indicated by point A in FIG. 4 and transmitting it to the control circuit.

Next, the overall control content will be described based on the time chart of FIG.

When the power supply 13 shown in FIG. 1 experiences an instantaneous power failure of T ₁ width from time t ₀ , the output voltage V _DC of the converter unit 14 stops at an inclination determined by the load of the motor. When the power supply is restored at t ₁ , the DC voltage V _DC rises again, but at that time t ₁ , the DC voltage V _DC
2 is equal to or higher than the voltage at the point A in FIG. 2, the power supply voltage of the control circuit 17 and the base drive circuit 18 is stable.
There is no malfunction of the IC or transistor breakdown due to insufficient base current of the transistor. Therefore, although the voltage V ₀ applied to the motor of the inverter decreases, it is not necessary to suspend or stop the operation of the inverter such as trip.

Then V _DC at the time t ₂ is longer than the time width T _A down to point A of FIG. 3, the DC voltage V _DC is instantaneous short T ₂ width than the time width T _B down to point B of FIG. 3 DC voltage when a stop occurs
The inverter is operated until time t ₃ when V _DC becomes the voltage at point A, and at time t ₃ , the base supplied from the base drive circuit (18 in FIG. 1) to the transistor of the inverter unit (15 in FIG. 1). Stop the current, turn off the transistor, and put it in the dormant state. Then, as shown in FIG. 4, the power supply voltage of the control circuit is stable until the DC voltage V _DC drops to the point B, and the malfunction of the microcomputer or logic IC does not occur.

When at time t ₄ instantaneous blackout is completed by detecting a DC voltage V _DC is equal to or greater than point A inverter is operated again. At that time, the frequency is the frequency at time t ₃ . It is often better to apply a slightly lower frequency to the motor due to the inertia of the load. As shown in the figure, when the output voltage is raised to a predetermined voltage with a constant gradient, a large current does not flow in the motor, and a current trip of the inverter does not occur.

Therefore, the inverter is completely stopped when the DC voltage V _DC becomes a voltage lower than the point B in FIG. 3, and as shown in FIG. 4, a long instantaneous blackout of time duration T _B or more has come. Only in time.

In addition, the DC voltage V _DC from time t ₃ to time t ₄ in FIG.
The slope of the decrease in voltage is determined by the capacity of the capacitor in the converter unit 14 in FIG. 1 and the output capacity of the secondary side output E ₅ (shown in FIG. 2) for the control circuit 17 in the power supply circuit 19. Even if a power failure occurs, if it is desired to extend the idle state, it is possible to simply increase the capacity of the capacitor in the converter unit 14.

In addition, the operating frequency when the input voltage is restored is to be operated at the frequency immediately before entering the rest state or at a frequency 3 to 10 Hz lower than the frequency immediately before.

EFFECTS OF THE INVENTION As described above, the inverter device of the present invention is an inverter that does not trip easily because abnormal operation does not occur even if an instantaneous blackout occurs.

[Brief description of drawings]

FIG. 1 is a block diagram of an inverter of an embodiment of the present invention, FIG. 2 is a circuit diagram of a power supply circuit used in the present invention, and FIG. 3 is an input / output characteristic diagram of the power supply circuit of FIG. FIG. 4 is a time chart diagram of an embodiment of the present invention, and FIG. 5 is a block diagram of an inverter used conventionally. 14 …… Converter section, 15 …… Inverter section, 16 …… Motor, 17 …… Control circuit, 19 …… Power supply circuit, 20 …… DC voltage detection circuit.

Claims (1)

[Claims] 1. A control power supply circuit comprising a self-excited DC-DC converter by a ringing choke converter system, to which a voltage stabilizing circuit provided on the DC side of an inverter is added, and the voltage of the DC-DC converter is detected. A detection circuit that compares with a specified value, and based on the signal from this detection circuit, the inverter is in the operating state and voltage stabilization does not work.The input voltage causes the inverter to enter the dormant state, and when the input voltage is restored, the dormant state is entered. An inverter device for an induction motor, comprising: a control circuit for returning operation at a frequency immediately before or a frequency slightly lower than the frequency immediately before.