Impact of PLL and non-PLL vector current control techniques on grid connected inverter

Abstract

In the micro-grids, all the Distributed Power Generation Systems (DPGS) and loads are interconnected across the Point of Common Coupling (PCC). The stability and harmonics of the grid connected inverters are significantly impacted by uncertainties in the renewable energy sources based DPGS. The performance of these grid connected inverters across the PCC depends on the Phase-Locked Loop (PLL) used to track the grid angle and power control structures used to control the power fed to grid. These power control structures can be either PLL based or PLL less systems. The PLL based Vector Current Control Direct Quadrature (VCC DQ) control and PLL less Non-PLL Vector Control (NPVC) techniques are compared along with their controller design and bode plots. Also, the small signal models of grid connected inverter with PLL are presented from which the converter impedance is derived to show the effect of PLL on the system using bode plots. The impact of the PLL based and PLL less control techniques on the grid connected inverter are presented with analytical equations along with simulation and hardware results. A 6 kW grid connected inverter simulation model and 150 W hardware prototype is developed using TI F28379D processor to compare the performance of both with and without PLL control techniques.