Depth analysis multimeter test inverter good or bad method

First declare: the multimeter can only roughly test the quality of the main power circuit and output inverter of the inverter, and can not guarantee the accuracy of the test. If the inverter has difficult problems in control, it is best to find the master who is professionally repairing the inverter to do the most secure.

When designing an electronic circuit, it is sure to touch some test and measurement instruments, and the multimeter is one of them. The multimeter generally measures DC current, DC voltage, AC voltage, and the like. The frequency converter is a device that modifies the working power frequency of the motor to realize the control of the alternating current motor. With the popularization of industrialization, the frequency converter is more and more applied to the field of modern electronics. This article will introduce you how to use a multimeter to measure the quality of the inverter.

First, must pay attention to the test before the test

For personal safety, you must ensure that the machine is powered off, wait for its power indicator to go out, remove the inverter input power lines R, S, T and output lines U, V, W, and then operate!

Second, test rectifier module

Test the rectifier circuit to find the P terminal and N terminal of the internal DC power supply of the inverter (Note: The P terminal of the inverter is the positive pole after the rectifier bridge is rectified, the N terminal is the negative pole after rectification, and the PB is the terminal connected to the braking resistor) , the multimeter is adjusted to the diode file, the red bar is connected to the P end, and the black bar is respectively dependent on R, S, T, and should have a resistance of about several tens of ohms, and is basically balanced.

Instead, the black bar is connected to the P terminal, and the red bar is connected to R, S, and T in turn, with a resistance close to infinity (the multimeter shows 1). The red bar is connected to the N-end and the above steps are repeated. The same result should be obtained.

If you have the following results, you can determine that the circuit has an exception:

A, the resistance of the three-phase unbalance, can explain the rectifier bridge failure.

B. When the red bar is connected to the P terminal, the resistance is infinite, and it can be concluded that the rectifier bridge is faulty or the starting resistor is faulty.

Third, test the inverter module

The test inverter circuit connects the red bar to the P terminal, and the black bar is connected to U, V, and W respectively. There should be a resistance of several tens of ohms, and the resistance values ​​of the phases are basically the same, and the inversion should be infinite.

Connect the black bar to the N end, and the red bar to U, V, W respectively. Repeat the above steps to get the same result, otherwise it can be determined that the inverter module is faulty.

Fourth, test the inverter is good or bad

Note: This method requires the inverter to be powered normally.

Use the inverter to drag a power-matched asynchronous motor to run at no load, and adjust its frequency f from 50Hz to the lowest frequency.

Note: The calculation method of the lowest frequency - (synchronous speed - rated speed) × pole log p ÷ 60. For example, a 4-pole motor with a rated speed of 1470 rpm and a minimum frequency = (1500-1470) × 2 ÷ 60 = 1 Hz.

In this process, the current meter is used to detect the no-load current of the motor. If the no-load current is stable during the frequency drop and can be kept basically unchanged, it means that it is a good inverter.