JPH04331475A - Inverter current detecting method - Google Patents

Abstract

PURPOSE:To obtain a correct inverter output current value subjected to error correction by employing the output from an A/D converter, under a state where the inverter current is zero, as a reference. CONSTITUTION:A CPU connected with an A/D converter 4 reads out the output from the A/D converter 4 as a current detection value and makes a decision whether an inverter IN is not operating at that time. If it is not operating, a decision is made whether the inverter IN stopped for the first time and if the answer is affirmative, the read out current detection value is stored as a correction data. If the answer is negative, a stored correction data is subtracted from the read out current detection data to produce a data detection value. According to the invention, a correct inverter current value subjected to error correction can be outputted without requiring difficult regulation of offset voltage.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting current in a voltage source inverter. When operating a voltage type inverter, the operating status of the inverter is displayed on the operation panel, and one of the operating statuses is to detect and display the inverter current (inverter load current). will be held. The present invention relates to a method for detecting current in a voltage source inverter, which is carried out in response to such a need.

0002

2. Description of the Related Art FIG. 2 is a circuit diagram showing a conventional current detection method for a voltage source inverter. In the same figure, P
is the power supply, CON is the converter section, IN is the inverter section,
M is a load, 1 is a shunt resistor, 2 is an operational amplifier, 3 is an isolation amplifier, and 4 is an A/D converter.

That is, as shown in FIG. 2, a shunt resistor 1 is inserted and connected to the DC intermediate bus of a voltage source inverter consisting of a converter section CON and an inverter section IN, and the voltage drop due to the inverter current flowing through the resistor 1 is reduced. It is taken out from both ends, amplified by an operational amplifier 2, then inputted to an A/D converter 4 via an isolation amplifier 3, where analog/digital conversion is performed and digitized as a detected value of the inverter current (for example, a CPU etc.) was used.

In the conventional current detection method as described above, the voltage drop taken out from both ends of the shunt resistor is a low value on the order of mmV, so this is amplified by an operational amplifier and converted into an A/D on the order of V. I am trying to input it to a converter. In such a case, if the inverter current is small, the voltage taken out from both ends of the shunt resistor will also be very small, and the operational amplifier (op-amp) that is the amplification means will
Since it is at the same level as the offset voltage of , the actually detected value (the sum of the actual inverter current value and the offset voltage of the operational amplifier) contains a large error. Therefore, in order to correct such errors, conventionally, a resistor bridge for adjusting the offset voltage has been connected to the operational amplifier circuit.

[0005]

[Problems to be Solved by the Invention] However, the method of connecting a resistor bridge for offset voltage adjustment has the problem that the offset voltage is a minute voltage, so precision is required for resistance adjustment, making it difficult to adjust. . SUMMARY OF THE INVENTION An object of the present invention is to overcome the problems in the prior art and provide an inverter current detection method that can accurately detect an inverter current value without adjusting the offset voltage.

[0006]

[Means for Solving the Problems] In order to achieve the above object, in the present invention, a shunt resistor is inserted and connected to the DC intermediate bus of a voltage source inverter, and the voltage drop due to the inverter current flowing through the resistor is extracted and amplified by an operational amplifier. After that,
In an inverter current detection method in which the inverter current is digitized by an A/D converter and output as a detected value of the inverter current, the A when the inverter current is set to zero;
The digital output value from the A/D converter was determined and stored as a detection error, and the detection error was corrected by subtracting the detection error from the digital output value from the A/D converter when the inverter current was flowing. The correct detection value is now output.

[0007]

[Operation] In this way, it has become possible to output a correct inverter current value with errors corrected without adjusting the offset voltage.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a flowchart showing an embodiment of the present invention. The circuit configuration as hardware is the same as that shown in FIG.

Refer to FIGS. 1 and 2. In step S1, the CPU connected to the A/D converter 4 reads the output data of the A/D converter 4 as a current detection value. At that time, it is determined in step S2 whether or not the inverter is stopped.
Judgment shall be made.

If it is stopped (because the current flowing through the DC intermediate bus is zero), the process proceeds to step S3, where it is determined whether or not it is the first time.If it is the first time, in step S4,
The current detection value read in step S1 is stored as correction data.

[0011] In step S2, when it is determined that the inverter is not stopped, the process proceeds to step S5, and the correction data stored in step S4 is subtracted from the current detection value read in step S1 to obtain a data detection value. ,finish.

0012

[Effects of the Invention] As explained above, according to the present invention,
In the inverter current detection method of voltage source inverter,
This has the advantage that a correct inverter current value with errors corrected can be output without the need for difficult offset voltage adjustment.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing one embodiment of the present invention.

FIG. 2 is a circuit diagram showing a current detection circuit of a voltage source inverter.

[Explanation of symbols]

1...Resistor, 2...Operation amplifier, 3...Isolation amplifier, 4...A/
D converter

Claims (1)

[Claims] Claim 1: A shunt resistor is inserted and connected to the DC intermediate bus of a voltage source inverter, and the voltage drop due to the inverter current flowing through the resistor is extracted, amplified by an operational amplifier, and then digitized by an A/D converter to obtain the inverter current. The inverter current detection method includes the step of determining and storing a digital output value from the A/D converter when the inverter current is in a zero state as a detection error; An inverter current detection method comprising the step of subtracting the detection error from the digital output value from the A/D converter when the current is flowing, and outputting a corrected value as a current detection value.