JPH04355669A - Control circuit for inverter - Google Patents

Abstract

PURPOSE:To protect an inverter by preventing an output from exceeding a rated value to an excess. CONSTITUTION:In addition to a PI regulator 7 for detecting a current corresponding to an apparent power from an output current of an inverter 2 and so controlling it as to become equal to a set value, a PI regulator 10 for detecting a current corresponding to an effective power and so controlling it as to become equal to the set value, is provided to prevent both the apparent power and the effective power from exceeding rated values, thereby protecting the inverter.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter control circuit.

0002

2. Description of the Related Art FIG. 2 shows a conventional circuit of this type. In the same figure, 1 is a DC power supply, 2 is a switching element T1 to T
3 is a current transformer, 4 is a filter, 5 is a current detection circuit, 6 is a setting device, and 7 is a PI regulator. That is, a current equivalent to the apparent power is detected via the current transformer 3 and the current detection circuit 5, and each switching of the inverter circuit 2 is adjusted so that the current corresponds to the setting value from the setting device 6 using the PI controller 7. By driving the elements T1 to T4, the output load (apparent power) is controlled so as not to exceed the rated value.

0003

[Problem to be Solved by the Invention] However, since such a circuit detects and controls a current equivalent to the apparent power, when the power factor of the load increases,
There is a problem in that even though the apparent power does not exceed the rating, the effective power exceeds the rating. Therefore, the object of the present invention is to protect the inverter circuit by preventing both the apparent power and the active power from exceeding the ratings, regardless of the power factor of the load.

0004

[Means for Solving the Problems] In order to solve the above problems, the present invention detects the output current of an inverter device having two ratings of apparent power and active power, and sets the apparent power component to a constant value. A first current control circuit that controls the active power component so as to have a constant value, and a second current control circuit that similarly controls the active power component to a constant value are provided, and control is performed so that both the apparent power and the active power do not exceed the rated values. It is characterized by

[0005]

[Operation] By providing the first and second current control circuits,
Regardless of the power factor, both the apparent power and the active power should not exceed the rated values to protect the inverter circuit.

[0006]

Embodiment FIG. 1 shows an embodiment of the present invention. As is clear from the same figure, this embodiment has the following differences from the one shown in FIG.
It is characterized by the addition of a current detection circuit 8 and a PI regulator 10. Note that 9 is a setting device. That is, the current detection circuit 8 detects a current equivalent to the active power, and the PI controller 10 controls this so that it matches the setting value set by the setting device 9, so that the active power does not exceed the rating. It is intended to do so. By extracting the outputs of the PI regulators 7 and 10 via diodes 11 and 12, when the output load becomes excessive and the apparent power exceeds the rating, the output of the PI regulator 7 is extracted via the diode 11. When the active power exceeds the rated value, the output of the PI regulator 10 is taken out via the diode 12, and the switching element T1 of the inverter circuit 2 is
By driving T4, both the apparent power and the active power are prevented from exceeding the ratings, thereby ensuring the safety of the inverter circuit. Note that the diodes 11 and 12 form an OR circuit, and the PI regulators 7 and 1
The smaller output of 0 will be taken out with priority.

[0007]

[Effects of the Invention] According to the present invention, both the apparent power and the active power are controlled so as not to exceed the ratings regardless of the power factor of the load, so that the output capacity is prevented from exceeding the ratings. This provides the advantage of being able to prevent this and ensure the safety of the inverter.

[Brief explanation of drawings]

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

FIG. 2 is a circuit diagram showing a conventional example.

[Explanation of symbols]

1 DC power supply 2 Inverter circuit 3 Current transformer 4 Filter 5 Current detection circuit 6 Setting device 7 PI controller 8 Current detection circuit 9 Setting device 10 PI controller 11 Diode 12 Diode

Claims (1)

[Claims] 1. A first current control circuit that detects the output current of an inverter device having two ratings of apparent power and active power and controls the apparent power component to a constant value;
An inverter control circuit comprising: a second current control circuit that also controls the active power component to a constant value, and controls the apparent power and the active power so that they do not exceed rated values.