Control method for sensorless motors with energy recovery ability

A method for controlling a sensorless motor with energy recovery ability, the method comprising the steps of:

• (a) selecting a comparing voltage from a first or a second voltage by setting a duty cycle of a duty-cycle setting unit;
• (b) comparing a terminal voltage of the motor in the non-excited phase with the comparing voltage, so as to determine the occurrence of a zero-crossing of the back EMF in the motor;
• (c) shifting a phase angle required to start the motor after the occurrence of the zero-crossing, so as to perform phase commutation in the motor;
• (d) transmitting a trigger signal to set the operation of the motor in a normal operating mode or in an energy-recovery mode, according to the commutation period, a triangular wave provided by a triangular waveform generator, and the duty cycle of the duty-cycle setting unit;
• (e) producing the comparing voltage and detecting the terminal voltage of the motor in the non-excited phase, so as to measure the back EMF in the motor, at the time either when a time counter of the triangular waveform generator is reset to zero or when the counting period ends;
• (f) setting the first voltage as the comparing voltage if the turn-on duration of a lower-arm switch in the control phase of chopped wave which is used to control turning-on or off between two phases is larger than the duty cycle;
• otherwise, setting the second voltage as the comparing voltage;
• (g) comparing the back EMF to the comparing voltage, if no zero-crossing occurred, the operation of the motor is maintained;
• otherwise, commutation in the motor is performed by shifting a phase angle required to start the motor;
• and
• (h) detecting a zero-crossing signal of the back EMF according to the duty cycle, and switching a three-phase VFD sequentially, so that a current from one of the multiple-phase windings of the stator of the motor flows into a DC power supply.