Bi-directional real and reactive power control using constant frequency hysteresis control with reduced losses

A simple control technique for the bi-directional real and reactive power flow between dc source and ac grid is presented. A three-phase, three-wire ac grid system is considered. It is shown that for each 60° duration of the line cycle, the three-phase bridge can be considered as dual buck, buck and boost, or dual boost topology depending on the power factor angle of the injected current. Switching tables, for different power factor angles, have been derived corresponding to different circuit topologies. It is shown that to achieve hysteresis control, only two devices need to be controlled at any instant of time. This scheme is simulated with hysteresis control at constant frequency. The injected current magnitude is controlled depending on the dc bus voltage. Power factor of the current injected into the grid can be changed by suitably selecting the switching algorithm. Current distortion is controllable using hysteresis band. Simulation results for different power factors are given as result. Finally, switching loss for different schemes have been analyzed.