Measurement and acquisition of permanent magnet motor parameters (inductance, resistance, pole number, flux linkage constant)

Recently, I sorted out the measurement and calculation methods of several parameters most commonly used in permanent magnet synchronous motor , Share the record .

1. resistance 、 Inductance measurement
2. Polar logarithm measurement
3. Calculation of flux linkage constant

1、 resistance 、 Inductance measurement ：
Before measuring, you need to know whether the motor is star connected or triangle connected , As we all know, there are ：
Line current = Phase current
Line resistance = 2 * Phase resistance
Line voltage = √3 * Phase voltage

For triangle connection, there are ：
Line resistance = 2/3 * Phase resistance
√3 * Line current = Phase current
Line voltage = Phase voltage

The obvious difference between star connected and triangle connected motors is that the load is different , The withstand voltage is also different . From the above relationship, it can be seen that the star connection method is helpful to reduce the voltage borne by the winding 、 Starting current 、 Insulation grade . Delta connection motor helps to improve motor power , But the starting current is also large …

Cough , sorry , Off topic .

Here is only for star connected motor measurement .

Go on, ha ~

In the case of digital bridge ：

Clamp both ends of the digital bridge between any two phases for measurement , Then change the order. , Three sets of values are measured , The result after the average is divided by 2.
Inductance is the same , But the inductance of any two phases is related to the position of the rotor , Rotate the rotor in the same direction 180 In the case of kilowatt hour electric angle, it presents a similar sine wave signal .

La la la ~ So the inductance and resistance are measured .
Without digital bridge ：
This can be referred to as http://t.csdn.cn/uxcJw
Of course , In addition to the above two methods, software can also be used for offline parameter identification .
Here is also a brief introduction ：

Stator resistance identification method ：
Because there is a permanent magnet synchronous motor in ABC Stator voltage equation of shaft West ：

us： Stator voltage space vector
Ls： Equivalent synchronous inductance
When a low DC voltage is applied to the three-phase winding of a permanent magnet synchronous motor , There is no alternating current on the stator side of the motor , No rotating magnetic field , Therefore, the motor rotor will not rotate , There is no back EMF , At this time, the generated three-phase stator current will soon reach a stable value . Because the current is a stable value , The motor does not rotate , So in the steady state, the voltage equation can be almost equal to ：
us =Rs * is
Because the applied voltage is known , Equivalent diagram

Then we can see from the figure -ia /2 = ib = ic
The stator resistance is calculated from the known quantity Rs = 2/3 * UA/ia
There are many methods to identify stator inductance , For example, high frequency injection 、 Pulse voltage method and so on , This will be described in detail later .

Next is the measurement of polar logarithm .

2、 Measurement method of polar logarithm

The first is to use only DC regulated power supply .

The method is to set the voltage to 0, The limiting current of the power supply is set at... Of the rated current of the motor 5％~10％;
Then connect the positive and negative poles to any two phase lines , Turn on the power output . Rotate the motor by hand , Feel whether the motor has obvious impedance force , Otherwise, increase the current
Then rotate the motor , Record the number of times the motor gets stuck in one circle , Polar logarithm = The number of stops .

This is very simple .

The second one only uses oscilloscope

The method is to clamp a phase line of the motor with the ground wire of the oscilloscope , Any other phase line is connected to the probe , Then rotate the motor for one revolution （ shortcoming ： It's not easy to control. It's just a lap ）, Intercept waveform , Count the number of peaks , Divide the even value by 2, Is the number of poles of the motor .

It can be seen from the above picture that 6 Peaks , Namely 3 Polar logarithm

3、 Calculation of flux linkage constant

Flux linkage is actually the integration of voltage and time , On the contrary, the back EMF of the motor is the differential of the flux linkage , The flux linkage constant can be obtained by measuring the back EMF .
Ah ha ha , That is, as long as the back EMF is determined, the flux linkage can be calculated .

Copy only one paragraph ：https://www.zhihu.com/question/360666988/answer/933930161
The force acting on the electrified conductor in the magnetic field , This will produce a magnetic field . The rotor is the so-called energized conductor , In the applied magnetic field, there will be a force . The rotor will also generate a magnetic field due to energization , Cutting the stator coil will also generate an electromotive force , This electromotive force is called back electromotive force , Because the direction of its electromotive force is opposite to the direction of the electromotive force we apply to the stator to generate the magnetic field . This process is also called armature reaction , Therefore, the voltage balance equation of the motor can generally be written ：
u=R*i+v
This v It's back EMF .

Because the winding current is small when the motor is unloaded , So in this case, the error of back EMF is naturally small . Therefore, the back electromotive force at no-load should be used for calculation .

So how to measure the back EMF ？ Opposite drag
But I usually get a motor , It will take us half a day to get the result , It's too troublesome .
Generally, we just need to determine a stable electrical cycle , Don't you think it's over if you find a way to make the motor rotate stably for a few rounds ？！（ Lazy people do ）

Pictured above , I casually wrote a rough value of the cycle , I forgot to take the screenshot .
Formula I summarized three calculations , In fact, the simplification is the same , Ah ha ha .

Calculation 1 I'll simplify it , As long as you measure the periodic value （ Company ：s）, And the peak and peak values of line voltage can be directly formulated ：

example ： As shown in the figure above, the peak value I measured is 88.4V, cycle 4ms = 0.004s
Then the flux constant is equal to 0.0162649.

Calculation 2 And calculation 3 It's the same .

Bye-bye , Do so much first ~~