An Optimum Tuning Method for DC Bus Voltage Regulation in Double Stage Off-Grid PV Systems

This paper presents an optimum control strategy to regulate DC bus voltage in Off-Grid PV systems. The topology of the Off-Grid PV systems chosen in this work is double- stage PV system. The DC bus voltage regulation is achieved by controlling a bidirectional DC-DC converter which is connected between PV and energy storage systems. Internally, the DC bus voltage regulation controller is composed from a current feedback controller which is cascaded with a voltage regulation system. Both controllers are conventional Proportional-Integral (PI) controllers. The PI control parameters for the inner current loop are determined by pole placement technique, whereas for the outer voltage regulation loop, the PI control parameters are determined by using symmetrical optimum (SO) method. From the simulation result it is showed that the stability of the DC bus voltage highly depends on the tuning parameter well known as symmetrical distance of the SO. The greater the symmetrical distance, the relative stability of the system will increase, but on the other hand the speed of response to disturbances will be slower.

I. Introduction

Nowadays, the harvesting of green energy is commonly found worldwide. The main reason behind this fact is the increasing of the global energy consumption and the depletion of fossil energy which happen in every year. One of the renewable energy sources that is widely used is solar - based energy sources [1]–[2]. By using PV panels, the solar energy is converted into electrical energy which then inj ected to the grid (on-grid PV system) or used directly (off -grid PV systems).