Patent ID: 8134327

Claim:
A method for sampling data for each phase of a three-phase inverter driving a motor, the three-phase inverter being controlled by three pulse width modulated (PWM) drive signals, each PWM drive signal having a respective duty cycle, the duty cycles being set by a controller for corresponding phase windings of the motor, the sampling being based upon a common direct current (DC)-link current resistor, the method comprising: computing an index of modulation for each of the three PWM drive signals for a current demand voltage vector set by a motor controller and comparing it with a threshold value; if the respective duty cycle of one of the three PWM drive signals differs from the duty cycle of the other two PWM drive signals by less than a minimum value, thereby impeding sampling of the DC-link current of at least two of the three PWM drive signals and if so, then determining which of the following three conditions is true a) the duty cycles of at least two of the PWM drive signals differ by less than the minimum value and the duty cycle of the third PWM drive signal is greater than the duty cycles of the other two, b) the duty cycles of at least two of the PWM drive signals differ by less than the minimum value and the duty cycle of the third PWM drive signal is smaller than the duty cycles of the other two, or c) the duty cycles of the three PWM drive signals differ among each other by less than the minimum value; and when at least one of the conditions a), b), and c) is true, then creating sampling windows for sampling at least two phase currents by performing at least one of inverting and complementing at least one of the PWM drive signals, and inserting a fixed time active vector in null sub-intervals of at least one of the PWM drive signals and maintaining a compound duty cycle over every PWM period of the affected signal, the inserting being based upon the comparison of the index of modulation with the threshold value and true condition.