Implementation of d-q decoupling and feed-forward current controller for grid connected three phase voltage source converter

This paper presents a vector current controller scheme, which operates according to grid virtual flux orientation for the three phase, 3-wire pulse-width modulated voltage source converter (VSC). The usage of voltage sensors to determine the grid voltage angle for synchronization and the grid voltage magnitude for the controller operation are avoided by applying a virtual flux concept in the proposed control scheme. The virtual flux concept is utilized to obtain the input power equations, which will be used to calculate the reference d (direct) and q (quadrature) axis currents. The estimated grid virtual flux provides a new approach in developing the proposed control structure of three phase VSC by including the d-q axes decoupling and the feed-forward components to enhance the performance of front-end VSC during load and supply voltage disturbances. Computer simulation and laboratory experiment are conducted to verify the operation and performances of the VSC under steady-state and transient conditions. The results indicate VSC utilizing the proposed virtual flux oriented control (VFOC) is able to produce unity power factor operation, low harmonic distortion of input line current, adjustable dc output voltage and fixed switching frequency.