JP3251769B2 - Restart method of voltage source inverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a restart system for a voltage-type inverter, and more particularly to a restart system for a PAM-controlled voltage-type inverter.

[0002]

2. Description of the Related Art As a control device of an AC motor such as an induction motor controlled at a variable speed, a voltage type inverter device of a PAM control system shown in FIG. 3 is known. As shown in FIG. 1, the voltage source inverter device includes a converter 10, a DC reactor 11, a DC capacitor 12, and an inverter 13, and supplies an AC motor 14 with variable frequency and variable voltage AC power. The inverter 13 is constituted by a device having a self-extinguishing ability, such as a gate turn-off thyristor or a transistor, and converts the voltage of the DC capacitor 12 into AC by switching.

Next, the operation of the voltage source inverter device will be briefly described.
The f signal is input to the rate-of-change limiting circuit 16, and the frequency reference Fre is
f, and a frequency reference Fref is input to a voltage / frequency function generator 17 to generate a voltage reference Vref. The voltage control circuit 18 compares the voltage reference Vref with the voltage of the DC capacitor 12 detected by the voltage detector 19, outputs the phase reference of the converter 10, and controls the converter 10 by the phase control circuit 20.

On the other hand, the frequency reference Fref is converted to an integrator 21.
To generate an inverter output voltage phase θref. The pulse distribution circuit 22 controls the inverter 13 to supply an AC voltage to the motor 14. The inverter 13 controls the voltage of the DC capacitor 12 by the converter 10, determines the amplitude of the output AC voltage, and varies the frequency under the control of the inverter 13, and is called a PAM control method.

[0005] Inverters used in important facilities such as power plants are often troublesome to stop due to momentary power failure or transient overcurrent protection operation. Or a function to automatically reset a failure and restart it.

A method of restarting by this instantaneous power failure or automatic failure reset will be described.

First, due to a momentary power failure or failure, the RUN signal, which is the operation signal of the inverter, is turned off, and the control of the converter 10 and the inverter 13 is stopped. Further, the motor voltage detected by the AC voltage detector 23 and the inverter output voltage phase signal θref are input to the PLL circuit 24. When the operation signal RUN is turned off, the input of the rate-of-change limiting circuit 16 is switched from the reference input SPref from the frequency setting device 15 to the output of the PLL circuit 24, and the difference between the inverter output voltage phase and the detected motor voltage phase is calculated. The frequency reference Fref is controlled so as to become zero so as to follow the motor voltage phase. At this time, the function of the change rate limiting circuit 16 is turned off to give priority to the following of the frequency.

Next, when the operation signal RUN is turned on due to an instantaneous power failure recovery or automatic reset of a failure, the inverter 1 operates at a frequency and a voltage phase that match the motor frequency and the voltage phase.
3 and control of the converter 10 are started.
Is slowly returned to the value of the frequency setting device 15 by the change rate limiting circuit 16.

[0009]

In the conventional apparatus shown in FIG. 3, in order to perform a restart due to an instantaneous power failure or a failure automatic reset, when the operation signal RUN is once turned off and then turned on again to restart, the following operation is performed. There is such a problem. This will be described with reference to FIG.

FIG. 4 shows the movement of the DC capacitor voltage Vfc, the motor frequency Fref, and the motor voltage Vmot. Before the operation signal RUN is turned off, that is, until time t1, Vfc, Fref, and Vmot are all set to 100%.
Next, when the operation signal RUN is turned off at time t1 and the inverter is stopped, the motor frequency, that is, the rotation speed is reduced as shown in FIG. 4 and the magnetic flux of the motor is also reduced, so that the motor voltage Vmot is higher than the frequency reference Fref. Declines fast.

On the other hand, the DC capacitor voltage Vfc holds the voltage at the time of the stop because the inverter is stopped and there is no special discharge circuit. Therefore, when the inverter is started at time t2, the voltage difference between the motor voltage and the capacitor voltage is large, so that the capacitor is rapidly discharged from the capacitor to the motor as shown in FIG. 4, and an excessive motor current Imot flows. The inverter could not be restarted safely. Also,
After the capacitor voltage is discharged, the frequency reference Fref
Since the motor voltage Vmot decreases with respect to the voltage reference Vref determined from the above, the output of the voltage control increases in an attempt to increase the motor voltage Vmot, and the excessive motor current Imot
There was a problem that mot flowed.

In general, a device for restarting is a device used for important equipment which must continue operation as much as possible, and it is not permissible to fail restart.
An inverter device that can be restarted safely has been desired.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a restart method of a voltage-type inverter device that can safely restart.

[0014]

In order to achieve the above object, a first aspect of the present invention is a PAM control type voltage source in which the voltage of a DC capacitor is controlled by a converter and the frequency is varied by controlling an inverter. In the restarting method of the inverter device, the DC capacitor is stopped after the inverter stops.
When the inverter is restarted within a short time in which the voltage of the sensor remains and the speed of the AC motor is restored, an inverter output current limit for limiting a discharge current from the DC capacitor to the AC motor at the time of restarting For a predetermined period of time.

According to a second aspect of the present invention, in a restart method of a PAM control type voltage type inverter device in which a voltage of a DC capacitor is controlled by a converter and a frequency is varied by controlling an inverter , straight
When the inverter is restarted within a short time in which the voltage of the current capacitor remains to restore the speed of the AC motor, the voltage reference at the time of restart is gradually reduced from a value reduced according to the AC motor voltage. A voltage limiting means for returning to a value determined by the frequency is provided.

According to a third aspect of the present invention, in the restarting method of the voltage type inverter device according to the second aspect, a first-order lag filter is used as the voltage limiting means.

[0017]

According to the present invention, the current limiting means prevents the inverter from being stopped when the inverter is restarted, and the inverter can be restarted safely and smoothly.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. The same elements as those in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted. In this embodiment, the components added to the conventional device of FIG.
6, a bias setting unit 27, a comparator 28, a one-shot timer 29, and a first-order lag filter 30.

Next, the operation of this embodiment will be described with reference to the operation waveform diagram of FIG. Now, at time t1, the operation signal RUN is temporarily turned off due to an instantaneous power failure or a failure, the functions of the inverter 13 and the converter 10 are stopped, and the motor current I
mot becomes zero. Until the restart is started at time t2, the motor 14 detects that the speed decreases according to the load and inertia by the PLL circuit 24 to which the motor voltage is input, and causes the frequency reference Fref to follow the speed. Further, since the magnetic flux of the motor is also reduced, the motor voltage Vmot is significantly lower than the frequency. On the other hand, the capacitor voltage Vfc holds the value at the time t1 because there is no circuit to discharge.

At time t2, converter 10 and inverter 1
Restart the function of 3. First, due to the difference between the capacitor voltage and the motor voltage, the DC
The discharge current starts flowing toward. When the output current of the inverter exceeds the value Ilmt set by the setter 27, the comparator 28 generates a current limit command limit signal. The current limit command limit signal is transmitted to the inverter pulse distribution circuit 22. The pulse distribution circuit 22 turns off the inverter 13 and reduces the rush current from the capacitor to the motor.
The inverter 13 is turned on a predetermined time after the current limit command is turned off. When the inverter 13 is turned on again and the discharge current increases and reaches the limit value, a current limit signal is generated again and this operation is repeated.

The above-described current limiting operation is performed by the RUN
It is operated for a certain period determined by the time width of the one-shot timer 29 from the rise of the signal. Therefore, the discharge current Imot from the capacitor 12 to the motor 14 can be limited to the value of Ilmt, as shown in FIG.

Next, the motor voltage V decreased at time t2 by voltage limiting means such as a first-order lag filter circuit 30.
Starting from mot, the voltage reference Vref is gradually increased. Therefore, the output of the voltage control circuit 18 does not rise sharply, and the exciting current of the motor does not flow excessively. When the delay time of the first-order lag filter 30 affects the frequency change rate limiting circuit 16 during normal operation,
The effect can be eliminated by setting the delay time of the first-order lag filter 30 to zero except for a fixed time from the rise of the operation signal RUN.

As described above, according to this embodiment, after the inverter is restarted, the inverter output current is operated for a predetermined period of time, so that the DC capacitor voltage is reduced to the motor voltage while limiting the discharge current of the DC capacitor. Can be matched. Furthermore, by starting the operation based on the voltage reference in consideration of the amount of decrease in the magnetic flux of the motor and gradually increasing the voltage reference, it is possible to prevent a sharp increase in the voltage control output and suppress an excessive current from flowing through the motor.

[0024]

As described above, according to the present invention,
When restarting due to a momentary power failure or automatic reset of a failure in a PAM control type voltage-type inverter, the DC capacitor voltage remains and the motor voltage drops, causing a sudden discharge from the capacitor and restart of the voltage control output. It is possible to suppress the overcurrent of the motor from flowing due to a rapid rise, to operate the overcurrent protection and to safely restart without stopping the inverter device, and to continue the operation. Also,
Even if a difference occurs between the DC capacitor and the motor voltage, a simple PA can be used without using a complicated PWM method for adjusting the pulse width.
There is an advantage that it can be realized by the M control method.

[Brief description of the drawings]

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

FIG. 2 is a waveform chart for explaining the operation of FIG.

FIG. 3 is a circuit configuration diagram of a conventional voltage source inverter device.

FIG. 4 is a waveform chart for explaining the operation of FIG. 3;

[Explanation of symbols]

10: thyristor converter, 11: DC reactor,
12 ... DC capacitor, 13 ... Inverter, 14 ... AC motor, 15 ... Frequency setting device, 16 ... Change rate limiting circuit,
17 voltage / frequency function generation circuit, 18 voltage control circuit, 19 voltage detector, 20 phase control circuit, 21 integrator, 22 pulse distribution circuit, 23 AC voltage detector
24 PLL circuit, 25 current transformer, 26 rectifier circuit, 2
7: bias setting circuit, 28: comparator, 29: one-shot timer, 30: first-order lag filter, 31: subtractor, 32: multiplier.

Claims (3)

(57) [Claims] 1. A PA that controls the voltage of a DC capacitor with a converter and changes the frequency by controlling an inverter.
In the restarting method of the voltage control type inverter device of the M control type, the voltage of the DC capacitor after stopping the inverter.
When the inverter is restarted within a short time in which the AC motor remains to restore the speed of the AC motor, an inverter output current limit for limiting a discharge current from the DC capacitor to the AC motor at the time of restart is set for a predetermined period. A restart method for a voltage type inverter device, comprising a current limiting means for operating. 2. A PA that controls the voltage of a DC capacitor with a converter and further varies the frequency with the control of an inverter.
In the restarting method of the voltage control type inverter device of the M control type, the voltage of the DC capacitor after stopping the inverter.
When the inverter is restarted and the AC motor speed is restored within a short time in which the AC motor voltage remains , the voltage reference at the time of restart is gradually determined by the frequency from a value reduced according to the AC motor voltage. A restart method for a voltage-type inverter device, comprising voltage limiting means for returning the value to a value. 3. The restarting method of the voltage-type inverter device according to claim 2, wherein a first-order lag filter is used as the voltage limiting means.