How to measure the efficiency of variable frequency motors using current sensors and power meters

With the continuous improvement of industrial automation and the national "dual carbon" strategic goal, inverters, as a key part of motor control systems and industrial energy conservation, have high efficiency and energy-saving characteristics and have been widely used in various industries. Therefore, the demand for high-precision testing of motor/inverter power consumption efficiency is also increasing. The variable frequency motor efficiency test system is composed of a power meter, current sensor, speed sensor, etc. As shown in the figure below.

The three-phase sinusoidal AC power supply is input to the converter (i.e., the inverter driver). After being output through the converter, the waveform becomes a pulsating DC waveform, which provides power to the motor, and the motor provides power to the load.

The power provided by the power supply at the input end is tested by the instrument, and the power at the output end of the driver is tested at the same time. The speed and torque are obtained through the speed and torque sensor, and the mechanical efficiency is calculated.

If you want to calculate the efficiency of the drive, you can use the output (position 2) before and after the drive to divide the input (position 1) power to get the conversion efficiency of the inverter drive. Install three current sensors at positions 2 and 1 to accurately measure the current and feed it back to the power meter. If you want to calculate the mechanical efficiency of the motor output, you can use the output (position 3) before and after the speed torque sensor to divide the input (position 2) to calculate the conversion efficiency of the motor's mechanical energy through the formula. By analogy, the efficiency of the entire system can be obtained by the power ratio of the entire system before (position 1) and after (position 3).

We can see that the testing difficulties of the entire system are as follows:

1. High-precision, wide-band measurement

2. Direct input of voltage and current

3. Quickly measure waveforms

4. Simultaneously display input voltage, current power and other parameters

5. Simultaneously measure the torque and speed of the motor

6. Calculate the efficiency by the ratio of input to output at the same time

Easy to make mistakes: Using two meters to test input and output, because the test clocks are not unified, the power is not measured at the same time, which causes huge errors in the results.

To overcome the above difficulties, this test can use a six-channel power analyzer with Hangzhi HIT series wide-band, high-precision current sensors to solve the above test problems at one time.