How to measure the basic parameters of the motor?

When we get a motor in our hands, if we want to tame it, we need to know its basic parameters. These basic parameters will be used in 2, 3, 6, and 10 in the figure below. As for why these parameters are used, we will explain in detail when we start to pull the formula. I have to say that I hate formulas the most, but I can’t do without formulas. What we are discussing in this article is the star connection method of the motor.

Rs phase resistance

The measurement of this parameter is relatively simple. Use a multimeter in your hand to measure the resistance between any two phases, and then divide it by 2 to get the phase resistance Rs of the motor.

Number of pole pairs n

This measurement requires a regulated power supply with current limiting. Apply power to any two phases of the three-phase wiring of the motor in your hand. The current that needs to be limited is 1A, and the voltage that needs to be passed through is V=1*Rs (the parameters measured above). Then turn the rotor by hand, you will feel resistance. If the resistance is not obvious, you can continue to increase the voltage until there is obvious rotation resistance. When the motor rotates one circle, the number of stable positions of the rotor is the number of pole pairs of the motor.

Ls stator inductance

This requires the use of a bridge to test the inductance between any two phases of the stator, and the obtained value is divided by 2 to obtain Ls.

Back EMF Ke

For the FOC control program, these few parameters related to the motor are enough. If matlab simulation is required, a back electromotive force of the motor is also required. This parameter measurement is a little more troublesome. It is necessary to stabilize the motor at n revolutions, and then use an oscilloscope to measure the voltage of the three phases after the motor revolutions are stable, as shown in the figure below:

In the above formula, Vpp is the volt value between the peak and trough of the waveform.

Where Te=60/(n*p), n is the mechanical speed unit rpm, and p is the number of pole pairs. If the motor maintains 1000 revolutions, n is equal to 1000.

Now there is an algorithm called motor parameter identification. This is to use the algorithm to enable the motor controller to have the test function of a multimeter or a bridge, and then it is a matter of measurement and calculation. The parameter identification will be described in detail with reference to relevant formulas later.

Post time: Mar-28-2023