Three-leg four-wire voltage source inverters for hybrid standalone system feeding unbalanced load

Abstract

This paper presents a new design and control for HWDBS (Hybrid Wind-Diesel-Battery System) feeding three-phase four-wire local loads. The proposed system consists of two energy sources connected to the dc bus; a WT (Wind Turbine) and a DE (Diesel Engine) based on variable speed generators. The system utilizes two back-to-back connected converters and uncontrolled three-phase converter connected in cascade with dc-dc SEPIC converter. The system uses BESS (Battery Energy Storage System) placed at the dc bus to manage the exchange of power between the energy sources and the loads. The VSC (Voltage Source Converter) of WT side is controlled in order to achieve maximum power tracking by varying the rotor speed of the SCIG (Squirrel Cage Induction Generator). In order to improve the control performance and to reduce the cost of SCIG, the MRAS (Model Reference Adaptive System) speed observer based on stator voltage and currents is adopted. The DE is controlled in order to balance the power of the system by changing its speed according to the load power demand and to minimise the fuel consumption. DE is switch off when the WT power is greater than the load power demand. The main objective of the interfacing load side VSC is to achieve a constant voltage and frequency and to compensate unbalance using symmetrical components of the load currents. The proposed system is studied for various types of linear, nonlinear and dynamic loads and under varying wind speed conditions. The dynamic behavior of the proposed system is verified using MATLAB/SIMULINK.