JPH07327398A - System for restarting voltage inverter device - Google Patents

Abstract

PURPOSE:To restart safely a voltage inverter device, by limiting the discharge current during a predetermined term from a DC capacitor to an AC motor when making the inverter device restart in a short term after its stopping and making the speed of the AC motor recover. CONSTITUTION:After an instantaneous service interruption or a fault recovery, the functions of a converter 10 and an inverter 13 are restarted. Then, by the voltage difference between a capacitor 12 and a motor 14, a discharge current flows quickly from the capacitor 12 to the motor 14, and a current limiting command signal is generated from a comparator 28 when the output current of the inverter 13 exceeds the value set by a setting device 27. Subsequently, the inverter 13 is brought into OFF-state by its pulse distributing circuit, and a rush current flowing from the capacitor 12 to the motor 14 is reduced. The inverter 13 is returned to ON-state after the current limiting command is made off and a predetermined time elapses therefrom. When the inverter 13 is again brought into ON-state and the discharge current exceeds the limiting value, the current limiting signal is generated, and this operation is repeated. Thereby, the inverter 13 can be restarted safely without any protecting operation from its overcurrent.

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 device, and more particularly to a restart system for a PAM controlled voltage type inverter device.

[0002]

2. Description of the Related Art As a control device for an AC motor such as an induction motor which is controlled at a variable speed, a PAM control type voltage source inverter device shown in FIG. 3 is known. As shown in the figure, the voltage source inverter device is composed of a converter 10, a DC reactor 11, a DC capacitor 12, and an inverter 13, and supplies AC power of variable frequency and variable voltage to an AC motor 14. The inverter 13 is composed of 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 this voltage source inverter device will be briefly described. SPre set by the frequency setting device 15
The f signal is input to the rate-of-change limiting circuit 16, and the frequency reference Fre
f is generated and the frequency reference Fref is input to the voltage / frequency function generating circuit 17 to generate the 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 the phase control circuit 20 controls the converter 10.

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

Inverters used in important facilities such as power plants are often troubled if they stop due to a momentary power failure or a transient overcurrent protection operation. Or, the function to automatically reset and restart the failure is required.

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

First, the RUN signal, which is the operation signal of the inverter, is turned off due to momentary power failure or failure, 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 change rate limiting circuit 16 is switched from the reference input SPref from the frequency setter 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 changed. The frequency reference Fref is controlled so as to be zero, and the motor voltage phase is controlled to follow. At this time, the function of the change rate limiting circuit 16 is turned off to prioritize frequency tracking.

Next, when the operation signal RUN is turned on due to power recovery after a momentary power failure or automatic resetting of a failure, the inverter 1 is operated at a frequency and voltage phase that match the motor frequency and voltage phase.
3 control and converter 10 control are started, and the motor 14
The operating frequency of is slowly returned to the value of the frequency setter 15 by the change rate limiting circuit 16.

[0009]

In the conventional device shown in FIG. 3, restarting is performed by momentary power failure or failure automatic resetting. There is such a problem. This will be described with reference to FIG.

FIG. 4 shows the movements 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. Therefore, the motor voltage Vmot is lower than the frequency reference Fref. Falls fast.

On the other hand, the DC capacitor voltage Vfc holds the voltage at the time of the stop because the inverter stops 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 to the motor as shown in FIG. 4, and an excessive motor current Imot flows, The inverter could not be restarted safely. Also,
Frequency reference Fref even after the capacitor voltage is discharged
Since the motor voltage Vmot has decreased with respect to the voltage reference Vref determined by the above, the output of the voltage control increases in an attempt to increase the motor voltage Vmot, and the excessive motor current I
There was a problem that mot flowed.

[0012] Generally, a restarting device is a device used for important equipment that must continue to operate as much as possible, and it is not allowed to fail restarting.
An inverter device that can be safely restarted 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 for a voltage source inverter device that can be restarted safely.

[0014]

In order to achieve the above object, the first aspect of the present invention provides a voltage source of a PAM control system in which a converter controls a voltage of a DC capacitor and an inverter controls a frequency. In a restart method of an inverter device, when restarting the inverter in a short time after stopping the inverter to restore the speed of the AC motor, the discharge current from the DC capacitor to the AC motor at restart is limited. It is characterized in that it is provided with a current limiting means for operating the inverter output current limitation for a predetermined period.

According to a second aspect of the present invention, in a restart method of a voltage type inverter device of a PAM control system in which a converter controls a voltage of a DC capacitor and a frequency is controlled by controlling an inverter, a short time after the inverter is stopped. When restarting the inverter to restore the speed of the AC motor, voltage limiting means for gradually returning the voltage reference at the time of restart from a value lowered according to the AC motor voltage to a value determined by the frequency is provided. It is characterized by having.

According to a third aspect of the present invention, in the restart system 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, it is possible to prevent the inverter device from being stopped by the current limiting means when the inverter device is restarted, and to restart the inverter device safely and smoothly.

[0018]

EXAMPLE An example of the present invention will be described below with reference to FIG. The same elements as those in FIG. 3 are designated by the same reference numerals and the description thereof will be omitted. In this embodiment, components added to the conventional device of FIG. 3 are a current transformer 25 and a rectifier circuit 2.
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. At time t1, the operation signal RUN is once turned off due to a momentary power failure or 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 due 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 greatly reduced below the frequency. On the other hand, the capacitor voltage Vfc holds the value at time t1 because there is no circuit for discharging.

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 capacitor 12 to the motor 14 is rapidly changed.
Discharge current starts to flow 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, and the pulse distribution circuit 22 turns off the inverter 13 to reduce the inrush current from the capacitor to the motor.
The inverter 13 is turned back on after a predetermined time has passed since the current limit command was 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 current limiting operation is performed by the RUN at restart.
The one-shot timer 29 is operated for a fixed period from the rise of the signal, which is determined by the time width of the one-shot timer 29. 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 the voltage limiting means such as the first-order lag filter circuit 30.
The voltage reference Vref is gradually increased starting from mot. 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 has an influence as compared with the frequency change rate limiting circuit 16 during normal operation,
The influence can be removed by setting the delay time of the first-order delay filter 30 to zero except for a certain time from the rise of the operation signal RUN.

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

[0024]

As described above, according to the present invention,
When a PAM-controlled voltage-type inverter restarts due to a momentary power failure or automatic failure reset, the DC capacitor voltage remains and the motor voltage drops, causing a sudden discharge from the capacitor and a voltage control output. It is possible to prevent the overcurrent of the motor from flowing due to a sudden rise, safely restart the inverter device without stopping the inverter device, and continue the operation. Also,
Even if there is a difference between the DC capacitor and the motor voltage, a simple PA can be used without using the 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 drawings]

FIG. 1 is a circuit configuration 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 diagram for explaining the operation of FIG.

[Explanation of symbols]

10 ... Thyristor converter, 11 ... DC reactor,
12 ... DC capacitor, 13 ... Inverter, 14 ... AC motor, 15 ... Frequency setter, 16 ... Change rate limiting circuit,
17 ... Voltage / frequency function generating 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 ... Divider, 32 ... Multiplier.

Claims (3)

[Claims] 1. A PA in which a converter controls a voltage of a DC capacitor and an inverter controls a frequency.
In the restart method of the voltage-controlled inverter device of the M control method, when the speed of the AC motor is restored by restarting the inverter in a short time after the inverter is stopped, the DC capacitor at the time of restart to the AC motor. Is a restarting method for a voltage source inverter device, which is provided with a current limiting means for operating an inverter output current limitation for limiting a discharge current of the inverter for a predetermined period. 2. A PA in which the voltage of a DC capacitor is controlled by a converter and the frequency is varied by the control of an inverter.
In the restart method of the voltage-controlled inverter device of the M control method, when the speed of the AC motor is restored by restarting the inverter in a short time after stopping the inverter, the voltage reference at the time of restart is set to the AC motor voltage. A restart method for a voltage source inverter device, comprising a voltage limiting means for gradually returning the value from a value that is lowered accordingly to a value that is determined by the frequency. 3. The restart system for a voltage-source inverter device according to claim 2, wherein a first-order lag filter is used as the voltage limiting means.