The Delay Margin of Dead-time Compensators

Dead-time compensators (DTCs) are frequently regarded as being excessively sensitive to uncertainty in the loop delay. This claim, however, is based mostly on empirical studies rather than on any rigorous analysis. In particular, despite existing literature on the calculation of the delay margin, μd, there appears to be no study of the underlying reasons of such a sensitivity. In this paper we address the latter issue. By applying Nyquist criterion arguments, we show that μd of DTCs may be discontinuous as a function of system parameters. We demonstrate that a substantial deterioration of μd is caused by the multiplication of the crossover frequencies, which is enforced by the controller. Some ways to avoid this phenomenon are discussed.