An improved PWM method for a five-leg inverter supplying two three-phase motors

Component minimized multi-machine drives have recently become an area of much research interest. One such drive comprises two three-phase induction motors supplied by a five-leg voltage source inverter. With only five legs available to supply two three-phase motors one inverter leg is connected to both motors and the drive is controlled in such a way that both machines can operate independently. Many PWM modulation methods have been suggested for such a drive system. However, they all suffer from serious drawbacks that impact negatively on the overall drive performance. This paper presents a new PWM modulation method that overcomes many of the issues experienced using the existing methods. The method effectively utilizes standard three-phase modulators in conjunction with additional logic to generate modulation signals for all five legs of the inverter and enables an arbitrary distribution of the available DC bus voltage between the two machines.