Jiangxi Institute of Engineering
Aiming at the problems of DC bias and frequency variation in weak power grid, an improved inverse Park transform phase-locked loop (IPT-PLL) technology suitable for single-phase grid connected inverter is proposed. Firstly, in the phase detector, α component of Park transformation is used as a reference voltage to solve the problem of DC bias in power grid voltage. The orthogonal component is constructed by the method of 1/4 fundamental periodic delay. Meanwhile, the fractional delay is approximated by Lagrange interpolation polynomial to reduce the delay calculation error caused by frequency change. Secondly, the design method of regulator in PLL is analyzed. The experimental results show that the proposed improved IPT-PLL has frequency adaptability, can significantly suppress the interference of DC bias in the grid voltage. And the dynamic and static performance of the proposed PLL is good.