Improved PLL structures for single-phase grid inverters

Abstract — Phase, amplitude and frequency of the utility grid are critical information for the operation of the grid-connected power conditioning equipments. In such applications, an accurate and fast detection of the phase angle of the utility voltage is essential to assure a correct generation of the reference signals. This paper presents two improved phase-locked-loop (PLL) methods for single-phase grid connected systems. The investigated PLL methods are based on a transport delay method and an inverse Park transformation method. The improvements in the case of using the delay-based PLL are: non-frequency dependent and better filtering of the harmonics. For the other investigated PLL method based on inverse Park transformation the improvement consists of better filtering of the harmonics. Experimental results validate the effectiveness of the two proposed methods.