Importance

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Abstract

Systems and methods for controlling a polyphase brushless direct current (DC) motor (12) are described. One system includes a meter (14) coupled to a motor terminal (A, B, C) and adapted to produce a range of digital output values (44) representative of a motor terminal signal from which a back EMF signal is derivable. The system (10) also may include a controller (16) that is coupled to the meter (14, 42) and is operable to monitor the range of meter output values and to compute a motor commutation time based upon a monitored local minimum meter output value and a monitored local maximum meter output value. A pulse width modulation (PWM) circuit (26) may be provided, and the meter (14, 42) may be synchronized with the PWM circuit (26). Zero crossings in the back EMF signals are identified based upon direct measurements of the signals at the motor terminals (A, B, C). In this way, sensors and complex circuitry, such as an ASIC or a plurality of comparators, that typically are used to determine when zero crossings occur are avoided. Furthermore, because the local maximum values and the local minimum values may be measured periodically (e.g., once every driving cycle), the invention readily accommodates component drifts and temperature variations.

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First Claim