JPS61135394A - Operation control system of motor drive voltage type inverter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling the operation of a voltage source inverter for driving a motor during a power outage.

[Conventional technology]

FIG. 2 shows a conventional inverter control circuit. In the figure, 10 is an inverter whose switching element is, for example, a combination of a power transistor 9a and a freewheeling diode 9b, and 7 is provided on the DC input side of this inverter 10, and is a rectifier. A rectifier using a diode 7a, and 8 a smoothing capacitor provided between the inverter 10 and the rectifier 7.

1 in the figure is an inverter control circuit that outputs an ignition signal to the inverter 10 via a pulse amplifier 2, and a protection circuit 3 equipped with a power failure detection section 4 is connected to this circuit. The power transformer 5 connected to the DC power input side of the inverter 10 is used as a detector to receive output from the power transformer 5. 6 in the figure is a constant voltage circuit provided on the output side of the power transformer 5.

In such a circuit, when the power outage detection section 4 detects a power outage, that is, detects that the power supply voltage has become constant and has dropped below the level, as a process in the event of a power outage, a pulse off command is given to the pulse amplifier 2 to turn off the inverter 10 almost instantly. The output was cut off. The reason for doing this is that even if the control power supply is banked up with a capacitor or the like and the motor IM continues to be driven, when power is not supplied from the power supply to the main circuit of the inverter 10, the capacitor 8 of the DC intermediate circuit will This is because the discharge occurs in a very short time and the motor ends up free running.

Furthermore, once the output is cut off, it will not be possible to restart the engine for a while even after power is restored.

This is because the inverter requires startup preparation time such as recharging the DC intermediate capacitor 8, and if the inverter 10 is started at a frequency that is significantly different from that during motor free running, overcurrent due to insufficient back electromotive voltage or overvoltage due to excessive regeneration may occur. This is because there is a risk of invitation.

[Problem that the invention seeks to solve]

In this way, in the conventional method, the inverter output is completely cut off in the event of a power outage, so it takes a considerable amount of time to recover from even a short power outage (or longer than the motor natural stop time if you want reliable startup). This situation may not be acceptable depending on the load.

SUMMARY OF THE INVENTION An object of the present invention is to provide an inverter operation control method that eliminates the disadvantages of the conventional example and allows the inverter to quickly return to normal operation after power is restored.

[Means for solving problems]

In order to achieve the above object, the present invention provides a voltage source inverter having a capacitor in the DC intermediate circuit.When a power outage is detected, the inverter output frequency is lowered to perform regenerative operation, and when the voltage of the capacitor is below a specified value, the inverter is switched off. The gist is to increase the downward slope of the output frequency, thereby maintaining the DC intermediate voltage of the capacitor and continuing the operation of the inverter.

[Effect]

According to the present invention, it is possible to maintain a DC intermediate voltage during a power outage, thereby delaying inverter output cutoff as much as possible, and waiting for power restoration during that time.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a circuit diagram of an inverter operation control circuit used in the method of the present invention, in which the same components as in FIG. 3 showing the conventional example are given the same reference numerals. The inverter 10 generates a pulse width modulated variable voltage/variable frequency output voltage via the control circuit 1. In this case, variable speed operation of the electric motor (for example an induction motor) IM takes place, keeping the voltage/frequency ratio constant, as is well known.

In the present invention, the switch 16 activated by the power outage detection unit 4
is arranged between the speed setting device 12 and the soft start circuit 13, and a DC intermediate voltage section 11 is connected to the capacitor 8, and a deceleration slope setting device 15 is configured to issue an operation command to the soft start circuit 13 to the DC intermediate voltage section. The selector switch 17 was connected.

In the figure, reference numeral 18 indicates a bank-up capacitor provided on the output side of the low voltage circuit 6 which serves as a control power source.

Next, the method of the present invention using such a circuit will be explained based on the time chart of FIG. 2. When a power outage occurs, the power outage detection unit 4 detects it, turns off the switch 16, and sets 12 is disconnected from the soft start circuit 13. As a result, the soft start circuit 13 enters normal deceleration operation, but since sufficient regenerative power cannot be obtained with the normal deceleration slope, the DC intermediate voltage (Voc) of the capacitor 8 decreases (see Figure 2, period T). ). In this way VD
When C reaches the drop detection level, the DC intermediate type pressure portion detection section 11 detects this, and the switch 17 is switched to the rapid deceleration side.

When the soft start circuit 13 commands to perform rapid deceleration, the output frequency of the inverter 10 decreases, and as a result, the regenerated power increases, and '/DC increases (period T1).

When the VOC rises to the recovery level, the switch 17 is switched to the normal deceleration side, returning to the same operation as in period I.

In this way, repeat periods r and ``, decelerate while maintaining VDC, and if the power is restored before stopping, the switch 16 will be turned on and the acceleration operation will begin, and the operation state before the power outage will be interrupted. to return.

Although not shown, in the case of a device with a motor speed detector and a speed feedback loop, control is required to set the output frequency to (actual motor speed) - 1 (slip amount to obtain appropriate regenerative power) in the event of a power outage. All you have to do is switch to .

〔Effect of the invention〕

As described above, the inverter operation control method of the present invention allows the inverter to continue operating as long as possible during a power outage in a voltage source inverter equipped with a capacitor in the DC intermediate circuit. This allows the inverter to return to its operating state before a power outage.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an operation control circuit of an inverter used in the operation control method of the present invention, FIG. 2 is an operation waveform diagram of the same, and FIG. 3 is a circuit diagram showing a conventional example. ■...Inverter control circuit 2...Pulse amplifier 3...Protection circuit 4...
Power failure detection unit 5... Power transformer 6... Constant voltage circuit 7... Rectifier 7a... Rectifier diode 8... Capacitor 9a... Power transistor 9b... Free wheel diode 10... Inverter 11... DC intermediate voltage detection unit 12... Speed setter 13... Soft start circuit 15... Deceleration slope setter 16.17
... Switch 18 ... Bank up capacitor Applicant Fuji Electric Co., Ltd. Figure 2 1 → 1 Kano r? I-base electricity 4-cost electricity f3 diagram

Claims (1)

[Claims] In a voltage source inverter for driving a motor in which a capacitor is provided in a DC intermediate circuit, when a power failure is detected, the inverter output frequency is lowered to perform regenerative operation, thereby maintaining the DC intermediate voltage of the capacitor and continuing operation of the inverter,
An operation control method for a voltage source inverter for driving a motor, characterized in that the capacitor voltage is detected to be lower than a specified value at that time, and the decreasing slope of the inverter output frequency is increased.