The closed-loop stability of power converters with an integrating controller

A theory is developed to predict the stability characteristics of static power converters as a function of the controlled-firing angle for closed-loop systems using an integrating controller. The controlled quantity can be either the output voltage or current. Revealed in the analysis was how the degree of stability is dependent on the operating point, the waveform and pulse number of the supply, the commutating reactance, and the method of modulating the firing angle. The factors that determine stability are related to the step change in the output voltage waveform at the instant of switching. In practical application of the theory, the closed-loop performance can be improved by suitably shaping the modulating function or “firing wave.” It is found that the optimum shape of the firing wave is not the same shape that produces a linear open-loop voltage gain.