Narrow pulse elimination PWM for multilevel digital audio power amplifiers using two cascaded H-bridges as a nine-level converter

This paper presents a methodology to reduce total harmonic distortion (THD) in digital audio power amplifiers, using two new approaches: 1) a multilevel converter made of two cascaded full-bridges, with suitable power supplies to operate as a nine-level hybrid type converter and 2) a new pulsewidth modulation (PWM) technique called narrow pulse elimination (NPE) PWM. The proposed nine-level converter uses only eight MOSFETs. Unlike conventional PWM, the NPE PWM does not generate excessively narrow pulses, so that power semiconductors nonideal delays and switching times are still negligible. Therefore, the nine-level output voltage THD, mostly introduced in the power stage, is strongly reduced. With the NPE technique, the resolution of the generated PWM is no longer limited by the switching speed of the output switches, but only by the frequency of digital processing circuit. Simulation and experimental results from a laboratory prototype are presented in order to show the effectiveness of the proposed approaches.