Sensorless control technology has been an important research direction for brushless DC motors ( BLDC ) in the past decade. The core of sensorless control research is the rotor position signal detection circuit, software filtering and anti-high pulse interference during commutation. These are the prerequisites for reliable and stable operation of brushless DC motors (BLDC) . At present, there are many rotor position detection modes. The most mature and reliable is the back-EMF rotor position detection, which is generally a nine-resistance method. It can work stably with the corresponding filter capacitor. However, at high speeds of tens of thousands of rpm, the filter capacitor will produce a phase delay, which will cause a backward shift in the rotor position and requires software correction filtering. A large number of experiments have verified that the back-EMF method can extract and stably detect the rotor position signal in both the powered phase and the non-powered phase. Extracting a stable rotor position signal is the cornerstone of the implementation of a sensorless BLDC controller. The selection of MCU is very important. Not all single-chip MCUs can be used. It is necessary to select a high anti-interference and non-free machine crash, otherwise it will cause the drive logic to be confused, the FET smoke module and the MCU to be damaged during the six-step commutation .
The following is a description of the startup and operation sequence : 1. Startup: The brushless DC motor starts in a synchronous manner and the speed reaches more than 1000. After the back electromotive force is stably generated, the MCU takes over the rotor position detection and performs closed-loop control. After taking over, the performance is: the shaft loading speed decreases but there is no loss of steps. 2. Speed closed loop: The brushless DC motor is driven in six steps. Every two steps are a sub-unit, accounting for 1/3 of a circle ( 120 degrees ) . The MCU built-in counter starts counting at the beginning of 120 degrees and stops counting at the end. 3 sampling counts are performed per circle. This value is the motor speed value. The start and end of 120 degrees are related to the rotor position signal. After comparing the speed value stored in the MCU unit with this value, the duty cycle of the PWM wave is controlled to adjust and stabilize the speed. After the speed closed loop takes over, the performance is: the shaft loading speed does not decrease and the PWM duty cycle changes within the range of 5-+10 turns. The MCU chip selected in this case that has passed the test can work stably without connecting a large capacitor.
Software / circuit hardware supports 200,000+ rpm , working voltage 12.5V ----25V working current 30A maximum 55A protection 75A . There are under-voltage and over-temperature protection, etc. The circuit board size of the whole system is 40mm long , 40mm wide and 6MM high , excluding the heat dissipation shell. The software is written in assembly to improve the speed of timing and the stability of the system. If you need to communicate about circuit debugging and related tests and physical circuit samples, please use QQ.
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1579653499 / SMS within the station. The development of this BLDCcontroller is aimed at low-voltage12---25Vsmall and medium-power3-75Aspeed adjustable high-speed1500-200000rpm low-cost miniaturized high-speed tools/drones/etc. application scenarios. Through the adjustment of the power input position andFET, theBLDCcan work normallyat a minimum3V
The circuit testwaveform is as follows:
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