PLL-Less One-Cycle Controlled Modified Load Compensator for Wide Range of Loads

Load compensators utilizing the principle of STATCOM are becoming more and more popular. Among the direct and indirect current control techniques, direct current control techniques are more popular as they offer better transient response and higher current control bandwidth. However, the aforementioned techniques require the service of a PLL to generate the current reference template. Presence of the PLL reduces the robustness of the controller. Although schemes based on instantaneous reactive power theory do not require the service of a PLL, they fail to perform if the utility voltages are distorted and/or unbalanced. As a result schemes based on one-cycle control are becoming more and more popular. These schemes do not require the service of reference current template and hence the PLL which makes them robust so far as the presence of distortions in the utility voltages are concerned. However, these schemes give rise to instability problem in current control if the real component of the load current falls below a certain level or if the nature of the load is regenerative. In this paper a modified one-cycle controlled load compensator is proposed which significantly improves the stability margin of its operation so that it can negotiate loads having low real current component as well as regenerative loads. The compensator has been developed for both single phase as well as three phase applications. The viability of the scheme is ascertained through detailed simulation studies