Generalized current control scheme for unity power factor two-level and three-level bi-directional front-end power converters: An approach for multi-level front-end converters

Analysis of two-level and three-level front-end boost-converter employing current error space phasor based hysteresis controller is presented in this paper for various line-side and load-side conditions. Due to the coordination between all the three-phases and selecting only adjacent voltage vectors, the proposed controller is able to overcome limitations of conventional hysteresis current controller; like, limit cycle oscillation, overshoot in current error and random switching of voltage vectors. Generally, current error space phasor based hysteresis controller requires two hysteresis bands and look-up tables for region and sector detection. Because of sector change detection achieved with the help of outer hysteresis band, the current error space phasor moves out of the inner-boundary six-times in a fundamental cycle for two-level and eighteen times in a fundamental cycle for three-level operation, which deteriorates shape of input current waveform. In the proposed work, sector change detection logic is developed without using any outer-hysteresis band and look-up table for two-level converter and the same logic is reported with hardware verification. Transient performance of the proposed controller with two-level and three-level converter is also studied and results are presented depicting good dynamic response and effectiveness of the proposed controller. Front-end converter with conventional hysteresis controller is implemented and hardware results are discussed. Three-level flying capacitor converter with capacitor voltage balancing scheme is analyzed employing the proposed controller for various load side and line side conditions and results are presented. The proposed controller with three-level front-end converter is able to maintain unity power factor and constant dc-link voltage with reduced Total Harmonic Distortion (%THD) at line side as compared to two-level converter.