Analysis and Design of New Switching Lookup Table for Virtual Flux Direct Power Control of Grid-Connected Three-Phase PWM AC–DC Converter

This paper proposes a comprehensive and systematic approach in developing a new switching lookup table for direct power control (DPC) based on grid virtual flux estimation, implemented in a grid-connected three-phase ac-to-dc converter. The approach provides detailed information regarding the effects of a particular converter voltage space vector to the instantaneous input active and reactive power distributions in the converter system. Thus, the optimal converter switching states are able to be selected by the switching table, allowing the smooth control of the active and the reactive power for each sector. The usage of input ac voltage sensors for synchronization and input power calculation is avoided by applying a virtual flux concept in the control scheme. The grid virtual flux estimation technique is used to extract the grid voltage information from the converter switching states, line currents, and dc-link output voltage. Detailed explanation and analysis regarding the development of virtual flux DPC utilizing the proposed switching lookup table is given in this paper. Finally, the steady-state as well as dynamic performances of the proposed controller is tested both in simulations and laboratory experiments. There exist close agreements between the simulation and experimental results.