A Sliding Mode Control in a New Reference Frame for Three-Phase UPFR With Extended Control Range

This article presents a new switching strategy for a unity power factor rectifier (UPFR) using sliding-mode control (SMC). The traditional SMC in the natural frame suffers from a cross-coupling problem among controllers due to the neutral point voltage. To address this issue, a nonlinear transformation is applied to obtain the voltages and currents in a new 2-D reference frame. Based on the transformed variables, a nonlinear model is derived, and two different sliding-mode surfaces are designed using hysteresis band comparators. The nonlinear transformation is based on a switching strategy that not only avoids the cross-coupling problem but also injects a third harmonic in the control signal, providing an extended control range. As a result, a SMC is designed, providing relevant properties such as output voltage robustness, fast transient response against sudden load changes, and grid-voltage sags. Experimental results are provided to validate the theoretical contributions of this article.