Method and device for controlling the speed of the brushless DC motor provided for an electric vehicle

A device for controlling a speed of a brushless DC motor for driving an electric vehicle, the brushless DC motor being rotatable in bidirection and having a plurality of phases to generate back electromotive force (EMF) waves from a respective winding of said motor when in rotation, said device comprising:

• A phase inverter for inverting an input speed command
• a plurality of differential amplifiers, through which the back EMF waves are taken from input terminals of the motor to obtain valid level voltages and low-pass filtered waves:
• a back EMF analog multiplexer for synthesizing the back EMF signals taken from the rising and falling regions of the back EMF waves of each phase;
• a phase detecting circuit for controlling the operating time of the back EMF analog multiplexer based on control signals responsive to each phase generated by inputting commutation signals of a magnetic pole sensor;
• an absolute value circuit for full-wave rectification of an AC signal taken from the back EMF analog multiplexer;
• a low-pass filter for low-pass filtering the output of the absolute value circuit to a smooth positive DC voltage which is proportional to the rotation speed of the motor;
• and
• a motor rotating direction detecting circuit for detecting a rotating direction of the motor by checking the phase relationship of the commutation signals from the magnetic pole sensors;
• a feedback signal polarity analog multiplexer for generating a positive or negative analog voltage, which is to be used as a speed feedback signal, based on the positive analog voltage output from the low-pass filter according to the rotating direction of the motor detected by the motor rotating direction detecting circuit;
• and
• a speed compensator, which is a proportional amplifier, for controlling the voltage supplied to the brushless DC motor by amplifying a voltage difference between the inverted speed command and the feedback signal in a proportional manner.