Parameter measurement method of brushless motor

It is necessary to know the parameters of the motor in hand when developing the motor , The parameters of different brushless motors are different , It's going on FOC Algorithm driven , The correctness of motor parameters is particularly important . Generally, these parameters will be provided by the manufacturer when buying the motor , If the manufacturer does not provide , It can be measured by the following methods .

The following parameters are mainly measured ：

1. The number of poles of the motor .

2. resistance .

3. inductance .

4. Reverse electromotive force .

5. Hall offset angle .

1. Motor resistance （Rs）:

      Phase resistance Rs： Measure the two-phase resistance of the motor with a multimeter RL, You can work out RS=RL/2;

2. Motor inductance (Ls)：

      Phase inductance （LS）： Bridge at 1khz Two phase inductance at frequency LL, You can work out LS=LL/2;

3. Motor pole pairs （P）;

      Clamp one wire of the motor with one wire of the oscilloscope probe , The other one is measured with a probe , Then rotate the motor for one revolution , The corresponding waveform will appear continuously on the oscilloscope , Count the peaks , Divide even values by 2, Is our polar logarithm .

The number of wave peaks in the figure below is 6 individual , So the polar logarithm is 3.

                                    

4. Motor back EMF （Ke）

    The oscilloscope probe is connected to one phase , Ground any one of the other two phases of the motor , Rotate the motor to measure the back EMF waveform , Take the middle waveform , Measure its peak to peak value and frequency .

The calculation formula is as follows ：

                                                                  

1.P Is a polar logarithm

2.Vpp Peak to peak

3.f Is frequency .

                             

5. Motor Hall mounting angle

    Hall sensor is a sensing device that can identify the polarity of rotor magnetic field ; The hall sensor depends on the magnetic pole it faces , Output logic level 0 or 1, Therefore, the hall sensor must be installed on the rotor . 

    Three Hall sensors are usually installed in three-phase permanent magnet motors , Used to feed back rotor position information . They are usually spaced apart 120 Degree or 60 degree .

The following figure shows the interval 60 Degree and 120 Typical waveforms of the output of a degree mounted Hall sensor . It's important to note that , The figure below shows a periodic （ That is, a pair of pole motors rotate for one cycle ）.

                   

                                                              interval 60 Degree and 120 Degree mounted Hall sensor output waveform

      The rotor position measured by Hall sensor is absolute , Rotor pre positioning is not required . However , Special attention should be paid to when the sensor is connected to the input of the microcontroller , Pre positioning is required .

    This software library assumes that the forward rotation is the rotation direction when the positive sequence three-phase supply motor is used . In this case, in order to ensure normal operation . The software library requires an interval 60 Degree and 120 The hall sensors installed at intervals of degrees carry out signal transmission in the sequence shown in the above figure .

    For these reasons , When the permanent magnet motor with Hall sensor is connected to your board, take the following suggestions ：

1. Turn the rotor manually in the assumed direction , And observe the three-phase motor B-emf. So , If the true neutral is not available , The neutral point can be re established by means of three resistors .

2. Connect the motor to the hardware in positive order . Give Way A phase ,B Phase and C Xiang Chengyou TIM1_CH1,TIM1_CH2 and TIM1_CH3 Respective driven motors .

3. Turn the rotor manually in the assumed direction , Observe the three Hall sensor outputs （H1,H2 and H3）, And through the passage 1,2, and 3 Connect with the corresponding timer respectively , Make sure as shown above .