The Design Of Control Circuit For Low-Voltage Brushless DC Motor Without Position Sensor

There are many advantages on brushless DC motor(BLDCM)system using sensorless control technology,such as miniaturization,high efficiency,high reliability etc.,and it is more and more widely used in electric tools,home appliances and other fields.The detection of the rotor position is important for sensorless control of BLDCM.At present,the back-EMF(BEMF)method is the most popular detection method.The key point of this method is to detect the zerocrossing point(ZCP)of the floating phase BEMF accurately,so it is of great significance to study the detection of the ZCP.Based on the BEMF detection method,the digital integration of control strategy is researched and designed.The following contents are studied mainly:(1)The influence of the spike voltage on the BEMF signal sampling is studied,and the leading edge blanking is achieved through reasonable selection of the sampling window;(2)The freewheeling characteristics of floating phase is studied,and a fixed-time digital filtering method is proposed to eliminate the interference of the freewheeling noise on the ZCP;(3)The hardware integration design of the PI algorithm is studied,and the circuit resource analysis is proposed.The time multiplexing design method effectively reduces the circuit area occupied by the PI algorithm;(4)Design for test of digital integrated circuits is studied,and a circuit structure that can realize pin multiplexing is designed to solve the problem of insufficient circuit’s pins.Finally,based on the FPGA development board and PCB hardware circuit,the designed brushless DC motor control strategy is tested and verified.The results show that the control circuit designed has a steady-state speed regulation range of 100r/min ～ 2500r/min,a start-up time of about 280 ms,and a commutation error of less than 2°.The physical design of the digital circuit is based on the 0.18μm BCD process,and the overall circuit scale is about 10,000 gates.The simulation of the gate level circuit after placement and routing shows that the dynamic power consumption is 402μW,and the scan chain test coverage rate is 99.51%.