Towards a nearly optimal synthesis of power bridge commands in the driving of ac motors

The synthesis of low depth command streams for power bridges is considered, with regards to drives for ac motors. Focus is on the exploitation of the degrees of freedom still available once the command rate is set. Using a nonlinear motor model, different options are evaluated up to the mechanical output. Options such as Delta Sigma Modulation (DSM) and Pulse Width Modulation (PWM) are associated to tuples of merit factors defining points in a performance space. Standard DSM is shown to favor perceived drive quality, while PWM helps keeping the switching rate low. Interpreting both PWM and DSM as heuristics for Pulse Density Modulation (PDM), it is shown that DSM may offer some commonly unexploited forms of tuning and may lead to a more flexible choice of placement on the performance space.