Control scheme evaluation for Class-D amplifiers in a power-ultrasonic system

Power-converters or amplifiers are required to drive high-power piezoelectric transducers and attached processing equipment, at the optimum resonance mode for best processing efficacy, while under varying loading conditions. The driving power converter must synthesize relatively low-distortion sinusoidal output current to prevent harmonic- current excitation of neighbouring, less-productive or desirable resonant modes. Continuously-variable output-voltage capability is required to maintain output power at a level which optimises processing. Three output synthesis methods have been reviewed in this paper for the Class-D amplifier constituting the transducer driver. Typical output-waveform quality is assessed, and PSPICE simulation and laboratory results are presented to illustrate performance.