Multilevel digital sonar power amplifier with modified unipolar SPWM

Sonar projectors are resonant transducers that are operated around the resonance frequency and the power amplifiers of sonar transmitters are designed to drive a non linear, frequency dependent load. The input electrical admittance of these projectors varies rapidly in the frequency band of operation. So the limits of load offered to a power amplifier for a wide bandwidth projector has to be maximized. For limited bandwidth operation, the existing digital power amplifiers will do their best for limited range of load variation, but for wide bandwidth operation other concepts should be explored and evaluated. This paper discusses a multilevel power amplifier in shared leg concept with modified unipolar switching in order to take-care the increased load limits with reduced voltage stress on the switching devices.