Research On Three-phase Unbalanced Phase-locked Loop Method For Photovoltaic Grid LVRT

Low voltage ride through(LVRT) is regarded as one of the biggest challengesin photovoltaic grid equipment’s control technology, which is closely related to thelarge-scale application of photovoltaic power generation. The fast and accurateautomatic phase-locked control is the premise to achieve photovoltaic grid lowvoltage ride through. At present, the traditional phase-locked loop methods onlydetect phase voltage and are designed to adapt the performance requirements ofthree-phase four-wire photovoltaic grid system. Moreover, the traditional methodswill be influenced by voltage offset. Aiming at these shortcomings, this paper takesactual project as the background, and researches a three-phase three-wireunbalanced phase-locked loop method. It provides a technical support forphotovoltaic grid low voltage ride through system.This paper is first to research three-phase four-wire unbalanced phase-lockedloop. Analysis the structure of Single Synchronous Reference Frame forPhase-Locked Loop(SSRF-PLL) and set up its mathematical model. Research thedecoupling equation of Decoupled Double Synchronous Reference Frame forPhase-Locked Loop(DDSRF-PLL). Further research working principle of DualSecond Order Generalized Integral Phase-Locked Loop(DSOGI-PLL). Compare thecomplex frequency domain with DDSRF-PLL. Finally compare advantages anddisadvantages of three phase-locking loops.Based on the research of three-phase four-wire unbalanced phase-locked loop,this paper puts forward a three-phase three-wire unbalanced phase-locked loopmethod. Elaborate working principle of orthogonal signal generator phase-lockedloop, and Put forward improved second order generalized integral orthogonal signalgenerator(SOGI-OSG). It can not only eliminate the influence of voltage offset well,but also be appropriate for DSOGI-PLL. Heron formula and Sine theorem isadopted to calculate the three-phase phase voltage amplitude and phase angle.Then make simulation analysis about grid adaptability of the phase-locked loop.Three-phase four-wire phase-locked loop and three-phase three-wire phase-lockedloop simulation prototypes have been built by employing the MATLB software.Under the different condition of grid, such as voltage imbalance, voltage sag,harmonic interference, voltage offset, this chapter makes simulation analysis andcomparison of a variety of phase-locked loops.At last, a15kW experiment prototype has been designed with TMS320F2812as the central controller, and three-phase three-wire unbalanced phase-locked loopmethod is applied to it. Make the grid adaptability test for this experiment prototype. The experimental results validate the feasibility of the theoretical analysis and theeffectiveness of the proposed strategy.