Integral control technique for single-phase UPS inverter

This article proposes a reset integral control applied to a single-phase full-bridge DC-AC inverter. The reset integral control, also called one-cycle control, is a nonlinear feed-forward control technique, in which by integrating the filter input-voltage of a buck-type converter, it reaches a reference value in one switching cycle. In this case, the controller design based on a large-signal approach is introduced in order to achieve good transient response and stability in a wide range of parameter variations and high rejection of external disturbances. Besides, in spite of the nonlinear nature of the controller, we obtain a linear average output-voltage dynamic response. On the other hand, in a clear-cut contrast with current mode control, a current sensor is not required. The proposed control provides the following features: fast transient response, "clean" sine-wave output-voltage, fixed switching frequency, and high robustness against load and line step changes. In addition, two PWM pattern generators based on this control scheme are introduced: bipolar and unipolar PWM. The simulation results demonstrate the effectiveness of this control technique for inverters in UPS applications, especially, when nonlinear loads must to be supplied and line has large undesirable harmonic components.