How is the inverter performance? You can tell by testing it with a multimeter

As we all know, frequency converters have many protection functions, such as overcurrent, overvoltage, overload protection, etc. With the continuous improvement of industrial automation, frequency converters have also been widely used. This article will explain to you how to use a multimeter to measure the quality of frequency converters.

It should be noted that for personal safety, the machine must be powered off and the inverter input power lines R, S, T and output lines U, V, W must be removed before operation! First, set the multimeter to the "diode" position, and then use the red and black test pens of the multimeter to detect according to the following steps:

The black test lead touches the negative pole P(+) of the DC bus, and the red test lead touches R, S, and T in turn, and records the displayed value on the multimeter. Then touch the red test lead to N(-), and the black test lead to R, S, and T in turn, and record the displayed value on the multimeter. If the six displayed values ​​are basically balanced, it means that there is no problem with the inverter diode rectification or soft-start resistor. Otherwise, the rectifier module or soft-start resistor at the corresponding position is damaged, and the phenomenon is: no display.

The red test lead touches the negative pole P(+) of the DC bus, and the black test lead touches U, V, and W in turn, and records the displayed value on the multimeter. Then touch the black test lead to N(-), and the red test lead to U, V, and W in turn, and record the displayed value on the multimeter. If the six displayed values ​​are basically balanced, it means that there is no problem with the inverter IGBT inverter module. Otherwise, the IGBT inverter module at the corresponding position is damaged, and the phenomenon is: no output or fault reporting.

Use a frequency converter to drive an asynchronous motor with matching power to run at no-load, and adjust the frequency f from 50Hz to the lowest frequency.

During this process, an ammeter is used to detect the no-load current of the motor. If the no-load current is very stable during the frequency reduction process and can remain basically unchanged, then it is a good inverter.

The minimum frequency can be calculated as follows: (synchronous speed - rated speed) × number of pole pairs p ÷ 60. For example, a 4-pole motor with a rated speed of 1470 rpm has a minimum frequency = (1500-1470) × 2 ÷ 60 = 1 Hz.

There is no problem with the soft-start resistor. Otherwise, the rectifier module or soft-start resistor at the corresponding position is damaged. Phenomenon: no display.

The red test lead touches the negative pole P(+) of the DC bus, and the black test lead touches U, V, and W in turn, and records the displayed value on the multimeter. Then touch the black test lead to N(-), and the red test lead to U, V, and W in turn, and record the displayed value on the multimeter. If the six displayed values ​​are basically balanced, it means that there is no problem with the inverter IGBT inverter module. Otherwise, the IGBT inverter module at the corresponding position is damaged, and the phenomenon is: no output or fault reporting.

Use a frequency converter to drive an asynchronous motor with matching power to run at no-load, and adjust the frequency f from 50Hz to the lowest frequency.

During this process, an ammeter is used to detect the no-load current of the motor. If the no-load current is very stable during the frequency reduction process and can remain basically unchanged, then it is a good inverter.

The minimum frequency can be calculated as follows: (synchronous speed - rated speed) × number of pole pairs p ÷ 60. For example, a 4-pole motor with a rated speed of 1470 rpm has a minimum frequency = (1500-1470) × 2 ÷ 60 = 1 Hz.

Distinguishing between AC and DC solid-state relays: Usually, the input and output terminals of the DC solid-state relay housing are marked with "+" and "-", and the words "Dc input" and "DC output". However, the AC solid-state relay can only be marked with "+" and "-" on the input terminal, and the output terminal has no positive or negative distinction.

Identification of input and output terminals: For unmarked solid-state relays, use the multimeter R×10k range to identify the input and output terminals by measuring the forward and reverse resistance values ​​of each pin. When the forward resistance of two pins is small and the reverse resistance is infinite, these two pins are the input terminals, and the remaining two pins are the output terminals. In a measurement with a small resistance value, the black test pen is connected to the positive input terminal, and the red test pen is connected to the negative input terminal.

If the forward and reverse resistances of two pins are both 0, it means that the solid-state relay has been broken down. If the forward and reverse resistances of each pin of the solid-state relay are infinite, it means that the solid-state relay has been open-circuited and damaged.