Sensorless motor applications will be very popular. In order to sense the rotor position of the brushless DC motor (BLDC) and permanent magnet synchronous motor (PMSM), the motor system must be placed with a magnetic sensor to feedback the rotor position information to the controller and output corresponding signals to drive the motor. Although this design method is simple, the failure rate is high. Therefore, in order to reduce the cost of the sensor and related wires and prolong the service life of the motor, sensorless motor design has been paid more and more attention.
Li Xinzhou, director of the motor marketing department of Nuvoton Technology, said that motor manufacturers are increasingly demanding sensorless BLDC/PMSM solutions in order to reduce manufacturing costs and maintenance costs.
Li Xinzhou, Director of Motor Marketing Department of Xintang Technology
Li Xinzhou said that the current operation mode of BLDC and PMSM can be divided into Hall Effect Sensor or Sensor-less scheme; sensorless scheme has higher requirements on microcontroller (MCU) specifications and is not widely used in the past. For use; in recent years, motor developers have increased their demand for sensorless BLDC/PMSM solutions to reduce manufacturing and maintenance costs.
In fact, the Hall sensor is a magnetic field sensor based on the Hall effect. It can determine important parameters such as conductivity type, carrier concentration and carrier mobility of semiconductor materials. It is widely used in industrial automation technology and detection technology. etc. In the BLDC and PMSM motors, the Hall sensor's task is to sense the rotor position of the magnetic component and return the position parameter to the MCU. The MCU then outputs the corresponding control signal according to the rotor position to drive the motor.
Li Xinzhou pointed out that the Hall sensor senses the rotor position and drives the motor. Although the system design is simple, the disadvantage is that the repair rate is high. He further explained that because the Hall sensor is close to the moving and rotating rotor, the components themselves are inevitably damaged for a long time. When the Hall sensor fails, the whole body will be moved and the motor will not operate normally. On the other hand, the design of some motors is not suitable for Hall sensors. For example, air conditioning systems, washing machines or refrigerators must be installed in the compressor in a sealed manner, which will limit the application of Hall sensors.
Conversely, the sensorless solution eliminates the need for additional mechanical components and sensor wiring, which not only reduces material costs and reliability, but also reduces the chance of motor failure due to Hall sensor wear.
Li Xinzhou said that the sensorless solution is to obtain rotor position information by detecting the back-EMF (Back-EMF) voltage difference. The back electromotive force depends on the angular velocity of the rotor, the magnetic field generated by the rotor magnet and the number of turns of the stator winding. Therefore, the MCU of the sensorless design must contain components such as a digital analog converter (ADC) and a comparator, so that the algorithm of the MCU can analyze the rotor. The back EMF waveform, which in turn outputs a control signal.
According to the application requirements of the product, the motor can be controlled by square wave and sine wave, as well as sensor and sensorless design. Therefore, the MCU can be roughly divided into four types, namely square wave Hall sensor scheme, square wave sensorless scheme, and string. Wave Hall sensor solution, sine wave sensorless solution.
It is worth noting that in order to meet the application requirements of both sensor and sensorless solutions, MCU vendors have also begun to introduce dual-mode solutions. Li Xinzhou said that even if the Hall sensor of the forward is faulty, the MCU can immediately start the algorithm to analyze the back electromotive voltage difference and obtain the rotor position parameters to let the motor run as usual.
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