An Improved Direct Voltage Component Extraction Method for Grid Connected Converters

As a consequence of an upward trend in the renewable energy’s share over the last few years, technical specifications for the integration of grid side inverters are becoming more and more harsh. With the aim of satisfying the grid connection requirements, an adequate synchronization algorithm, capable of providing satisfactory performance in the presence of imbalance and harmonics, is essential. In this paper, we introduce a novel algorithm for very fast extraction of the direct voltage component. Using a finite number of grid voltage samples, a system of algebraic equations is solved and sine and cosine factors are obtained. These are further processed by the square root and arctan functions to acquire information about the amplitude and angle of the direct sequence component. An appropriate method for frequency estimation from the direct sequence angle is necessary for the operation of the synchronization algorithm presented in this paper. An all-pass filter (APF) based synchronous reference frame phase locked-loop (SRF PLL) is used as a benchmark for the proposed finite sample count (FSC) algorithm, to evaluate its performance in simulations and experiments. Experimental validation is realized on a standard DSP platform. A grid simulator is used to provide analog grid voltage signals.