Sensorless BLDC Motor Controller

Traditional brushless DC (BLDC) motor systems rely on Hall-effect sensors embedded within the motor stator to determine rotor position for electronic commutation. In harsh operational environments involving high ambient temperatures, heavy mechanical vibration, and moisture, Hall sensors frequently degrade, leading to commutation misalignment or drive failure. Developing a robust sensorless control topology eliminates vulnerable physical sensors while reducing manufacturing cabling and unit cost.

Lead Hardware and Firmware Developer. Designed the three-phase power inverter stage, calculated gate charge requirements and bootstrap circuit parameters, developed analog back-EMF filtering stages, and programmed the embedded commutation state machine.

A discrete three-phase bridge composed of six N-channel IRFZ44N power MOSFETs driven by IR2104 high- and low-side gate drivers with bootstrap capacitors. At each commutation state in six-step trapezoidal control, two phases conduct current while the third remains floating. The floating phase develops an induced back-EMF voltage. By comparing this floating phase voltage against an analog virtual-neutral reference, the zero-crossing instant is detected, which indicates that the rotor has reached 30 electrical degrees prior to the next commutation step.

Engineered an analog resistor divider and low-pass filter network to eliminate high-frequency PWM switching ripple while preserving back-EMF zero-crossing phase fidelity. Programmed a multi-stage startup sequence: rotor alignment into a known detent position, open-loop frequency acceleration ramping, and seamless handover into closed-loop back-EMF commutation once sufficient generator voltage is reached. Regulated motor torque and speed by modulating PWM duty cycle on high-side switches.

Demonstrated dependable open-loop rotor spin-up and steady synchronization into closed-loop back-EMF tracking. Inverter bridge maintained thermal and switching stability across variable speed targets.