D. PWM control principle
In the EMB system, the key of achieving brake is that,
according to the pedal brake signals, ECU can control the
motor to produce the corresponding braking torque, so as to
make the EMB output the corresponding brake power. The
brake pedal model receives the driver’s commands via
angular speed sensor, and converts it into digital signals to
ECU. ECU converts the digital signals into the braking
signal of the brushless DC motor. Then according to the
three-phase rotor position signals, current signals and the
torque feedback signals and so on, ECU analysis and
processes the braking signal to control the torque and
turning of the motor.ECU is a core part of motor control. To
adjust speed, the ECU changes the average voltage of the
brushless DC motor through adjusting the PWM duty cycle,
using PWM pulse width modulation.
The average voltage of the motor armature windings can
be expressed as follows: