JPH09247990A - Inverter device and method for continuing operation at instantaneous break - Google Patents

Abstract

PROBLEM TO BE SOLVED: To continue the operation even in a system with large load inertia by realizing the PI control of the value multiplied by two kinds of deceleration rates to control the deceleration time, and stopping the deceleration if the voltage reaches the value before detecting the power failure, or the DC intermediate voltage is boosted during the deceleration. SOLUTION: A PI controller 16 operates the deceleration rate 1 by the target value of the DC intermediate voltage and the detected value so that an AC motor is smoothly decelerated in a short transmission interruption, and operates the deceleration rate 2 by the change of rate of the DC intermediate voltage, and realizes the PI control by the value multiplied by these two deceleration rates. The rotational speed of an AC motor is smoothly reduced. When a voltage boosting detection circuit 17 detects the boosting of the DC intermediate voltage, or the boosting of the voltage over the voltage before detecting the power failure is detected by a voltage detection circuit 18, a deceleration stopping means 19 is operated to stop the deceleration. The dropping/boosting ratio of the DC intermediate voltage is reduced to continue the operation irrespective of the size of the load inertia.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for continuing operation of an inverter device for driving an electric motor during an instantaneous power failure.

[0002]

2. Description of the Related Art A rectifier circuit for an AC power supply voltage, a smoothing capacitor for smoothing a rectified voltage and a DC intermediate circuit of an inverter, and an inverter section for DC / AC conversion are main circuit components. In a voltage source inverter that uses an AC motor as its load, the following method has been conventionally used as a method for continuing operation during an instantaneous power failure. In the method disclosed in Japanese Patent Laid-Open No. 6-165579, when the terminal voltage (intermediate voltage) of the smoothing capacitor drops to level 1 or lower, the AC motor is decelerated, and the intermediate voltage rises to level 2 or higher due to regenerative power accompanying deceleration. If it rises, the AC motor is sped up, and thereafter the acceleration / deceleration control is repeated according to the increase / decrease of the intermediate voltage to reduce the drop rate of the intermediate voltage.

In the method disclosed in Japanese Patent Laid-Open No. 4-91696, a deceleration command for slightly lowering the speed command of the inverter circuit is sent by the operation of the power failure detection circuit at the time of a momentary power failure to regenerate the electric motor. By doing so, the reduction of the inverter circuit voltage is prevented. Further, Japanese Unexamined Patent Publication No.
The method disclosed in Japanese Patent No. 308781 reduces the power loss during continuous operation by setting the torque command to the AC electric motor to zero by the power failure detection signal and reducing the magnetic flux command, and instantaneously using the energy stored in the smoothing capacitor. It is designed to continue driving when stopped.

[0004]

However, in the prior art, it is difficult to set the deceleration time to an allowable speed in a system in which the load changes depending on the application. If the deceleration time is set slowly, an abnormally low voltage will result. If the deceleration time is set too short, deceleration and acceleration will be repeated, causing a problem of vibration of the motor. Especially when applied to a system with a large load inertia, there is a problem in that control cannot be performed due to a sharp change in the drop and rise of the DC bus voltage (VPN), and the operation cannot be continued because the overvoltage or low voltage protection operates. In view of the problems of the prior art, it is therefore an object of the present invention to allow a system having a large load inertia to continue operation without operating overvoltage or low voltage protection during an instantaneous power failure.

[0005]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention relates to a continuous operation method for coping with a momentary power failure of an AC power source in a PWM inverter device having an AC motor as a load. , So that the DC intermediate voltage is constant during deceleration,
The deceleration rate 1 is calculated from the target value and the detected value of the DC intermediate voltage, the deceleration rate 2 is calculated from the change rate of the DC intermediate voltage, and the value obtained by multiplying the two deceleration rates is PI controlled so that the motor decelerates smoothly. Thus, the deceleration time is controlled, and the deceleration is stopped when the voltage reaches the voltage before the power failure is detected or the DC intermediate voltage rises during the deceleration. Also,
In a PWM inverter device using an AC motor as a load, a power failure detection unit that detects an instantaneous power failure of an AC power supply, and a power failure detection output from the power failure detection unit causes the inverter to decelerate the AC motor, and the DC intermediate voltage is constant during deceleration. So that the deceleration rate 1 is calculated from the target value and the detected value of the DC intermediate voltage, the deceleration rate 2 is calculated from the change rate of the DC intermediate voltage, and the motor smoothly decelerates the value obtained by multiplying the two deceleration rates. The deceleration time is controlled by performing PI control so that the deceleration time control circuit stops the deceleration when the voltage before detection of a power failure or the DC intermediate voltage rises during deceleration.

According to such a configuration of the present invention, when a momentary power failure of the AC power source occurs, the inverter operation command to the load motor is decelerated and decelerated and stopped by using the degree of decrease / increase of the DC intermediate voltage as a parameter. By using together, the drop / increase rate of the DC intermediate voltage can be reduced and the operation can be continued. Further, if the voltage reaches the voltage before the power failure is detected or the DC intermediate voltage rises during deceleration, deceleration by PI control is stopped.

[0007]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram showing the entire inverter device of the present invention, FIG. 2 is a block diagram of a sequence circuit for selecting a deceleration time and a frequency command during power failure detection, and FIG.
Is a block diagram of the deceleration time control circuit that controls the deceleration time so that the DC voltage is constant during PI detection during power failure detection, and stops deceleration when the DC voltage rises during deceleration or reaches the voltage before the power failure was detected. Figure 4 shows the time chart when a power failure occurs. In FIG. 1, the main circuit unit includes a rectifier 1 for converting AC power from an AC power supply into DC power, a smoothing capacitor 2 for smoothing the DC power from the rectifier 1, and a DC power sent via the smoothing capacitor. It is composed of a PWM inverter circuit 3 for converting to an arbitrary frequency. Further, 4 is an electromagnetic contactor on the side of the AC power source, and 5 is an AC electric motor whose drive is controlled by the output of the PWM inverter circuit 3.

The control section connected to the main circuit section, as shown in FIG. 1, includes a frequency setter 6 for setting the output frequency,
Acceleration / deceleration time setter 7 for setting the acceleration / deceleration time of the electric motor 5
A voltage detection circuit 8 for detecting a DC voltage of the smoothing capacitor 2, a sequence circuit 9 for detecting a power failure and setting a deceleration time and a frequency command during the power failure detection, and a DC voltage constant by PI control during the power failure detection. The deceleration time control circuit 10 that controls the deceleration time so that the soft starter 11 performs the acceleration / deceleration of the output frequency within the set acceleration / deceleration time, and the inverter circuit 3 based on the output signal from the soft starter 11.
And a base control circuit 13 for driving the transistors of the inverter circuit 3 based on the output signal from the PWM control circuit 12. As shown in FIG. 2, the sequence circuit 9 includes switch means 21 and 22 for selecting a frequency command and deceleration time at the time of a power failure based on the low voltage detection output from the voltage detection circuit 8 or the power failure detection output from the outside. Have.

Further, as shown in FIG. 3, the deceleration time control circuit is roughly divided into two parts. One is a deceleration time control based on a deviation between a DC voltage command and a detected value for deceleration time control. And a deceleration rate control circuit 15 for controlling the deceleration time based on the change rate of the DC voltage.
And the PI controller 16, the other one is a circuit 1 for detecting an increase in DC voltage in order to stop deceleration during a power failure.
7, a circuit 18 that detects whether the DC voltage is higher than the voltage before the power failure is detected, and whether a DC voltage increase is detected,
Alternatively, it is composed of a circuit 19 that stops deceleration when the DC voltage rises above the voltage before the power failure is detected. Next, the operation continuation control method during the power failure detection in the inverter device of the present embodiment will be described. FIG. 4 is a time chart when a power failure occurs in this inverter device. (A) shows the AC power supply ON / OFF state, (b) shows the power failure detection contact open / close state,
(C) shows the state of the operation command, (d) shows the change of the intermediate voltage VPN, and (f) shows the output frequency of the inverter.

Now, when an instantaneous power failure of the AC power source occurs,
The electromagnetic contactor 4 (FIG. 1) is opened, or the DC voltage of the smoothing capacitor 2 falls below the low voltage detection level, and the voltage detection circuit 8 for detecting the DC voltage detects a power failure. When a power failure is detected, the signal during power failure detection is "1" as shown in Fig. 2.
Therefore, the sequence circuit 9 switches the frequency command to 0 by the switch means 21 and 22 by this signal "1" or the detection output of the voltage detection circuit 8 and switches the deceleration time to the set deceleration time during the power failure detection. When the inverter 3 that controls the driving of the AC motor 5 is changed from the operating state to the deceleration mode, the rotational energy corresponding to the deceleration amount of the AC motor becomes regenerative electric power that passes through the inverter unit to form the DC intermediate circuit. The smoothing capacitor 2 is charged and its terminal voltage is increased.

When the power failure detection signal becomes "1", as shown in FIG. 3, the DC voltage level is set so that the DC voltage detected by the voltage detection circuit 8 becomes the input voltage set value × 1.35. And the deceleration rate PI while watching the change rate of the DC voltage
Control. In FIG. 3, K of the deceleration rate control circuit 14
l is a coefficient for controlling the deceleration time according to the level of the DC voltage (when the deceleration rate K1 = 1.0, deceleration is performed at the set deceleration time, and when K1> 1.0, the deceleration time becomes shorter,
When 1 <1.0, the deceleration time becomes long), and K2 of the deceleration rate control circuit 15 is a coefficient for controlling the deceleration time according to the rate of change of the DC voltage. Deceleration rate control circuit 1
No. 4 compares the target value of the DC voltage with the feedback value during deceleration, and when the feedback value is higher than the target value, the coefficient of the deceleration rate becomes a value smaller than 1.0 and the deceleration time becomes long. When the feedback value is lower than the target value, the deceleration rate coefficient becomes a value larger than 1.0, and the deceleration time becomes short. When the deceleration time becomes short, the regenerative energy returns to the smoothing capacitor and the DC voltage rises. Further, the deceleration rate control circuit 15 checks the rate of change of the DC voltage during deceleration, and if the DC voltage is decreasing, sets the deceleration rate to 1.0 and decelerates for the set deceleration time. When the DC voltage is increasing, the deceleration rate becomes a value smaller than 1.0, and deceleration is performed for a time longer than the set deceleration time. When the deceleration time becomes long, the regenerative energy is not returned to the smoothing capacitor and the DC voltage does not rise.

The PI controller 16 determines the deceleration rate by multiplying the deceleration rate calculated from the target value of the DC voltage and the feedback value by the deceleration rate calculated from the change rate of the DC voltage so that the motor decelerates smoothly. Perform PI control. In this way, the rotation speed of the AC electric motor does not decrease sharply but only gradually decreases, and the electric motor continues to operate during an instantaneous power failure. When the load inertia is large and the deceleration time is short, the DC voltage rises sharply and an overvoltage occurs. Therefore, the voltage rise detection circuit 17 detects an increase in the DC voltage, or the DC voltage detects a power failure. When the voltage detection circuit 18 detects that the voltage has risen above the previous voltage, the deceleration stop means 19 operates to stop deceleration, so the subtracted frequency (frequency decelerated in a certain fixed time) of the circuit in FIG. 3 is set to 0. Stop the deceleration during a power failure.

When the momentary power failure of the AC power source of the inverter is restored, the electromagnetic contactor is closed and the DC voltage becomes higher than the low voltage detection level, and the power failure detection signal of FIG. The drive control for accelerating or decelerating to the frequency set value during the acceleration / deceleration time is executed.

[0014]

As described above, according to the present invention, as a control method for coping with a momentary power failure of an AC power source in a PWM inverter having an AC motor as a load, a decrease / increase of a DC intermediate voltage of the inverter can be achieved. Depending on the degree, by using the operation command to the inverter in combination with the deceleration mode and the deceleration stop mode by PI control, the rate of decrease / increase of the DC intermediate voltage can be reduced, regardless of the magnitude of the load inertia. It is possible to continue the operation, and it is possible to improve the reliability of the operation of the line equipment and the like in which the AC motor is a main component.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an entire inverter device of the present invention.

[Fig. 2] Block diagram of sequence circuit for selecting deceleration time and frequency command during power failure detection

FIG. 3 is a deceleration time control circuit that controls the deceleration time so that the DC voltage is constant during PI detection during power failure detection, and stops deceleration when the DC voltage rises during deceleration or reaches the voltage before power failure detection. Block diagram

[Figure 4] Time chart when a power failure occurs

[Explanation of symbols]

 1 rectifier 2 smoothing capacitor 3 PWM inverter 4 electromagnetic contactor 5 AC motor 6 frequency setting device 7 acceleration / deceleration time setting device 8 voltage detection circuit 9 sequence circuit 10 deceleration time control circuit 11 soft start 12 PWM control circuit 13 base drive circuit 14 deceleration Rate control circuit 15 Deceleration rate control circuit 16 PI controller 17 Voltage rise detection circuit 18 Pre-power failure voltage detection circuit 19 Deceleration stop means 21, 22 Switch means

Claims (2)

[Claims] 1. A method of continuing operation for coping with a momentary power failure of an AC power source in a PWM inverter device using an AC electric motor as a load, wherein the inverter starts deceleration by a power failure detection signal, and a DC intermediate voltage becomes constant during deceleration. To
The deceleration rate 1 is calculated from the target value and the detected value of the DC intermediate voltage, the deceleration rate 2 is calculated from the change rate of the DC intermediate voltage, and the deceleration time is controlled by PI controlling the value obtained by multiplying the two deceleration rates. A method for continuing operation during an instantaneous power failure of an inverter, characterized in that the deceleration is stopped when the voltage reaches the level before a power failure is detected or the DC intermediate voltage rises during deceleration. 2. In a PWM inverter device using an AC motor as a load, a power failure detecting means for detecting a momentary power failure of an AC power source, and a power failure detecting output from the power failure detecting means is used to decelerate the AC electric motor, and during deceleration. The deceleration rate 1 is calculated from the target value and the detected value of the DC intermediate voltage so that the DC intermediate voltage is constant, the deceleration rate 2 is calculated from the change rate of the DC intermediate voltage, and the value obtained by multiplying the two deceleration rates is calculated. By controlling the deceleration time by PI control, if the voltage before the power failure is detected or the DC intermediate voltage rises during deceleration,
An inverter device comprising a deceleration time control circuit for stopping the deceleration.