Research On Single-phase Quasi-Z Source Grid-connected Inverter

Photovoltaic (PV) grid inverter is the bridge between solar panels and thegrid, which plays an irreplaceable role. This paper based on a single phasequasi-Z source inverter topology, analyzes its advantages and disadvantages, putsforward the corresponding control strategy, and sets up the hardware platform.Experiments show that it can capture the maximum power point of the solarpanels, inject a sinusoidal current to the grid with unit power factor, and has thefunction of island protection.Firstly, after analyzing all the working states of the quasi-Z souse inverter,the values of the inductances and capacitors of the main topology have beenoptimally designed. Meanwhile, according to the requirements of the outputcurrent, the filter has also been designed. And then set up the hardware platformof the inverter.Secondly, the whole control strategy is analyzed in detail. According tosimple boost control method in a single polarity SPWM modulation way, insertthe expected shoot-through state and realize boosting the input voltage. Putforward a method, which directly control the shoot-through duty based onperturb and observe (P&O) method, completing the MPPT function. The voltageand current dual-loop control strategy is used to control the active duty, makingthe inverter inject current to the grid with unit power factor.Then, after analyzing several phase locked loop(PLL) techniques,combining with the advantages and disadvantages of the single-phase andthree-phase synchronization phase lock loop techniques, put forward a virtualthree-phase synchronization phase lock loop method, set up its loop model,analyze its stability, and design the parameters of the controller. Some simulationand practical operation waveforms are presented to prove that the phase lockedloop has good work performance.At last, according to quasi-Z source inverter, the over/under voltage andover/under frequency passive island protection method and the active frequencydrift active island protection method are combined, realizing the function ofisland protection.