Comments, with reply, on "An algebraic algorithm for microcomputer-based (direct) inverter pulsewidth modulation" by Y.H. Kim and M. Ehsani

The commenter claims the so-called new direct PWM method developed by Y.H. Kim and M. Ehsani (see ibid., vol.23, no.4, p.654-60, July/Aug. 1987) is a reinvention of the conventional regular-sampled PWM technique, which has been widely used for research and industrial applications for over the past 20 years. Moreover, the commenter claims to demonstrate that the results produced by Kim and Ehsani are in error, and therefore the comparisons made with the conventional PWM techniques are incorrect and have the potential for being very misleading. In a reply, Kim and Ehsani point out that Bowes´ insight into the resemblance of the equal area PWM algorithm to the regular-sampled PWM is mostly correct. They claim, however, that the equal-area approach introduces the DC voltage parameter into the real-time PWM algorithm. Therefore, the DC voltage can also vary in time (within limits defined by the carrier frequency) without significantly corrupting the PWM output of the algorithm. This additional degree of freedom is specifically exploited when the direct method is applied to other converters.<>