JPH0797911B2 - Inverter device power failure detection method - Google Patents

Description

The present invention relates to a power failure detection method for an inverter device.

[Conventional technology]

 FIG. 2 is a block diagram showing a conventional technique.

In FIG. 2, 8 is a constant-voltage / constant-frequency three-phase AC power source, 5 is a rectifier circuit as a DC power source that rectifies the AC power from the three-phase AC power source, and 6 is an intermediate that smoothes the output of the rectifier circuit 5. A smoothing capacitor as a DC part, 7 is an inverter transistor as a conversion output part for converting the output of the smoothing capacitor 6 into AC power of variable voltage / variable frequency and supplying power to a load 9 such as an electric motor, 2 is an inverter transistor 7 1 is a DC-DC converter that supplies the DC power required by the control circuit from both terminals of the smoothing capacitor 6. Further, 3 is a low voltage detection circuit that monitors the terminal voltage of the smoothing capacitor 6, and 4 is an instantaneous power failure detection circuit that monitors the voltage of each phase of the three-phase AC power supply 8.

Generally, in the inverter device, the control method is different between the instantaneous power failure and the normal power failure or the power interruption, so it is necessary to detect which of the above-mentioned power failures of the input side AC power source. Therefore, in the above-described inverter device, when the low voltage detection circuit 3 that monitors the terminal voltage of the capacitor 6 detects that the voltage has dropped to a predetermined undervoltage level, the control circuit 2 detects the output of the instantaneous power failure detection circuit 4. It is determined whether the power failure of the input side AC power supply is due to a momentary power failure of the AC power supply 8, or a normal power failure or a power interruption, and if the result is due to an instantaneous power failure, an instantaneous power failure. Control is performed, and if it is due to a normal power failure or power interruption, the operation of the inverter device is stopped to protect the inverter device.

[Problems to be Solved by the Invention]

However, in the conventional power failure detection circuit of the inverter device, a low voltage that monitors the voltage between the terminals of the capacitor 6 in order to reliably determine whether the power failure is an instantaneous power failure, a normal power failure or a power interruption. Instantaneous power failure detection circuit 4 that monitors the voltage of each phase of detection circuit 3 and input AC power supply 8
And must be provided separately. For this reason, the circuit configuration of the inverter device becomes complicated, and it also causes a cost increase.

An object of the present invention is to eliminate the above-mentioned drawbacks of a conventional inverter device in which a power failure detection circuit for monitoring an input AC power supply and a low voltage detection circuit for monitoring an intermediate DC part are separately provided, and a circuit of the inverter device is eliminated. The purpose is to simplify the structure.

[Means for Solving the Problems]

To achieve the above object, the present invention provides a DC power supply unit, an intermediate DC unit, a conversion output unit, a control circuit for the conversion output unit, and power from the intermediate DC unit to the control circuit.
A DC-DC converter and a low voltage detection circuit for detecting the voltage of the intermediate DC section, when the low voltage detection circuit detects that the intermediate DC section voltage has dropped to a predetermined undervoltage level. The control circuit determines that an instantaneous power failure occurs if the intermediate DC part voltage recovers to a predetermined voltage level while power is being supplied from the DC-DC converter to the control circuit. When the control circuit is no longer supplied with a predetermined amount of power, the control circuit determines that a normal power failure or power cutoff occurs.

[Action]

According to the above means, when the low voltage detection circuit detects that the intermediate DC part voltage has dropped to a predetermined undervoltage level,
The control circuit determines that an instantaneous power failure occurs if the intermediate DC part voltage recovers to a predetermined voltage level while power is being supplied from the DC-DC converter to the control circuit. If power is no longer supplied, it is judged as a normal power failure or power interruption, and only the low voltage detection circuit and control circuit that monitors the voltage of the intermediate DC part,
It is possible to reliably determine whether there is an instantaneous power failure, a normal power failure, or a power interruption, and protect the inverter device.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of the present invention.
The figure is a characteristic curve diagram for explaining the operation of the embodiment of the present invention.

In the figure, 8 is a three-phase AC power source, 5 is a rectifier circuit that rectifies the AC power from the three-phase AC power source, 6 is a smoothing capacitor that smoothes the output of the rectifier circuit 5, and 7 is the output of the smoothing capacitor 6, which is the desired AC voltage. An inverter transistor for converting the electric power to supply electric power to a load 9 such as an electric motor, 2 is a control circuit for controlling the inverter transistor 7, and 1 is a DC power required by the control circuit from both terminals of the smoothing capacitor 6. Is a DC-DC converter that
A low voltage detection circuit 3 for monitoring the terminal voltage of is connected between the terminals of the smoothing capacitor 6.

In such an inverter device, when the input-side three-phase AC power supply 8 is momentarily or normally interrupted or the power is cut off, the smoothing capacitor 6 in the intermediate DC part is discharged and its terminal voltage is lowered to a predetermined level. First, the low voltage detection circuit 3 detects that the voltage level has dropped to the undervoltage level.

At that time, the terminal voltage of the smoothing capacitor 6 continues to drop thereafter, but the DC-DC converter 1 fed from the smoothing capacitor 6 still has a control circuit for a short period after the terminal voltage becomes equal to or lower than the undervoltage level. The power supply to 2 can be continued.

Then, in the control circuit 2 of the present invention, the terminal voltage E _DC of the smoothing capacitor 6 is insufficient while the power is being supplied from the DC-DC converter 1 to the control circuit 2, as shown at point A in FIG. When the voltage exceeds the voltage level and returns to the predetermined voltage value, this power failure is determined to be an instantaneous power failure, control is performed at the time of the predetermined instantaneous power failure, and the operation of the inverter device is continued as it is.

On the other hand, as shown at point B in FIG. 3, the terminal voltage of the smoothing capacitor 6 still exceeds the undervoltage even after the period in which the output of the DC-DC converter 1 can be supplied to the control circuit 2 has passed, and the predetermined voltage value If the DC-DC converter 1 does not supply a predetermined amount of power to the control circuit 2, the control circuit 2 determines that a normal power failure or power cutoff has occurred, Stop the operation of the inverter and protect it.

〔The invention's effect〕

INDUSTRIAL APPLICABILITY As described above, the present invention is a DC power supply unit, an intermediate DC unit, a conversion output unit, a control circuit for the conversion output unit, and a DC-DC that supplies power from the intermediate DC unit to the control circuit.
A converter, and a low voltage detection circuit for detecting the voltage of the intermediate DC portion, when the low voltage detection circuit detects that the intermediate DC portion voltage has dropped to a predetermined undervoltage level, the DC -While the power is being supplied from the DC converter to the control circuit, the control circuit determines that an instantaneous power failure has occurred if the intermediate DC section voltage recovers to a predetermined voltage level, and the DC-DC converter transfers the control circuit to the control circuit. If the control circuit determines that the predetermined power is no longer supplied to the normal power failure or power interruption, the low-voltage detection circuit and the control circuit alone, is a momentary power failure of the input side AC power supply, Since it is possible to protect the inverter device by determining whether it is a normal power failure or power interruption, separately monitor the input AC power supply like the power failure detection circuit of the conventional inverter device. There is no need to provide an instantaneous power failure detection circuit for, to simplify the circuit configuration of the inverter device, and allows the cost of the device.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing a conventional technique, and FIG. 3 is a characteristic curve diagram for explaining the operation of the embodiment of the present invention. 1: DC-DC converter, 2: Control circuit, 3: Low voltage detection circuit,
5: Rectifier, 6: Smoothing capacitor, 7: Inverter transistor, 8: Three-phase AC power supply, 9: Load.

Claims (1)

[Claims] 1. A DC power supply section, an intermediate DC section, a conversion output section, a control circuit for the conversion output section, a DC-DC converter for supplying electric power from the intermediate DC section to the control circuit, and the intermediate section. It has a low voltage detection circuit for detecting the voltage of the DC part,
When the low voltage detection circuit detects that the intermediate DC part voltage has dropped to a predetermined undervoltage level, the DC-DC
If the intermediate DC voltage recovers to a predetermined voltage level while power is being supplied from the converter to the control circuit, the control circuit determines that there is an instantaneous power failure, and the DC-DC converter outputs a predetermined voltage to the control circuit. A method for detecting a power failure in an inverter device, wherein the control circuit determines that a power failure or normal power failure occurs when power is no longer supplied.