The dc/ac control system for a grid-connected transformerless type photovoltaic generation system

A DC/AC converter control system for a grid-connected transformerless type photovoltaic generation system is provided to secure the stability of an operation of an entire system by using an auxiliary control algorithm for maintaining a proper DC link voltage. A first DQ conversion module is connected to a DC/AC converter and generates synchronous voltage vectors(512,513) required for control by using three-phase distribution voltage(511) and phase angle estimation information(521). A phase synchronous module(520) generates the phase angle estimation information by using the synchronous voltage vectors. A second DQ conversion module generates synchronous current vectors(532,533) by applying the phase angle estimation information to a three-phase current of the DC/AC converter. A current control module(550) generates output voltage vectors(561,562) outputted by the DC/AC converter by comparing an output current reference value(554) with present synchronous current vector information and using generated error information. A DQ inversion module calculates a proper switching time of switching elements constituting the DC/AC converter by using the phase angel estimation information and information of the output voltage vectors. A PWM(Pulse Width Modulation) controls the DC/AC converter by supplying an on and off signal to each of the switching elements according to the switching time calculated by the DQ inversion module. A power control module(540) generates the output current reference value based on output electric energy of a photovoltaic cell array, a voltage(546) of a DC link capacitor, and DC link operation range(547) information.