How to choose a position sensor for a brushless DC motor?
The most commonly used position sensor for brushless DC motors is the Hall sensor. The selection precautions are as follows:
1. Adopting a switch type Hall integrated circuit with latch type or near latch type (with symmetrical characteristics), its output waveform duty cycle is close to 1:1, and the output is symmetrical at the S and N poles, without causing additional torque fluctuations.
2. Select the Hall sensor with a maximum working temperature higher than the maximum winding temperature based on the maximum working temperature of the winding.
3. In welding, in order to ensure that the Hall sensor is not locally overheated and damaged, a temperature controlled soldering iron is used, low-temperature soldering is performed, and the welding time is less than 3 seconds with a temperature below 300 ℃.
4. Try to avoid bending the pins as much as possible. If bending is necessary, it should be chosen at a distance of 3mm from the root of the lead.
5. The installation position of the Hall sensor chip should be controlled within 10 ° of the theoretical position, which has a small impact on the performance of the DC brushless motor and is acceptable.
6. Directly installing the Hall sensor chip on the stator makes it susceptible to strong magnetic field interference. For long-distance transmission, a decoupling capacitor can be connected between the switch output and ground to eliminate interference pulses.
The minimum number of position sensors should be equal to the number of motor phases. For three-phase motors, three position sensors should be installed.
There are two installation methods for Hall sensors:
(1) Installed together with the motor body. Install the Hall chip directly into the slot of the stator core or the groove on the tooth top. It can save space, but it is easily affected and interfered by changes in the armature reaction magnetic field, and the temperature of the winding will be transmitted to the chip.
(2) Split installation. A Hall sensor consists of a stator and a rotor. The motor rotor can be directly used as the rotor of the sensor. Several Hall plates (3 for 3-phase motors) and some resistance and capacitance components are soldered onto a printed circuit board, which is installed on the stator bracket or end cover. Split installation is convenient for adjusting the position of the sensor stator, or for adjusting the initial angle to conduct in advance and achieve better operating results.
Regardless of the form of integer slot, fractional slot winding, stacked winding, concentric winding, full distance or short distance, the position of the Hall sensor can be unified under one pair of poles, coinciding with the axis position of the three-phase magnetic potential. At the same time, the mirror position of the axial magnetic force is also the correct position of the Hall sensor. HC corresponds to FA, HA corresponds to FB, and HB corresponds to FC.
