Patent ID: 9496716
Filing Date: 2016-11-15
CPC Classification: H02J

Claim Text:
1. An islanding detection apparatus for parallel distributed generations, comprising: an inverter configured to convert a DC voltage supplied from a renewable energy source into an AC voltage; a three-phase/two-phase converter configured to convert an output of the inverter into a three-phase/two-phase stationary reference frame; a phase locked loop (PLL) configured to calculate the phase and frequency of a grid voltage of a grid connected to the inverter using a two-phase voltage outputted from the three-phase/two-phase converter; a filter configured to pass a half cycle of one cycle of a signal outputted from the three-phase/two-phase converter or the PLL; a phase controller configured to generate a current phase reference value for controlling an output phase of the inverter, using the frequency of the output voltage of the PLL and a current amplitude reference value applied from outside; a half cycle passer configured to perform an AND operation on the current phase reference value outputted from the phase controller and an output of the filter and output a current phase reference value for islanding detection; a current reference frame converter configured to convert the current amplitude reference value of a synchronous reference frame and the current phase reference value of the synchronous reference frame, outputted from the half cycle passer, into a current amplitude reference value and a current phase reference value of a two-phase stationary reference frame, using a phase angle outputted from the PLL; a current phase calculator configured to subtract the phase of the inverter output current outputted from the current two-phase converter from the current phase reference value of the two-phase stationary reference frame, outputted from the current reference frame converter, and output a current phase control value; a current amplitude calculator configured to subtract the amplitude of the inverter output current, outputted from the current two-phase converter, from the current amplitude reference value of the two-phase stationary reference frame, outputted from the current reference frame converter, and output a current amplitude control value; a current controller configured to generate a current control signal using the calculated current phase and the calculated current amplitude; an output three-phase converter configured to convert the current control signal of the two-phase stationary reference frame, outputted from the current controller, frame into a current control signal of a three-phase stationary reference frame; and a PWM controller configured to output a PWM control signal to the inverter using the current control signal of the three-phase stationary reference frame, outputted from the output three-phase converter.