Investigation of supercapacitor energy storage for network integration of renewable energy

Abstract

The fast growth of inexhaustible renewable energy systems such as wind energy has led to increasing research on utilization of the wind energy in the most efficient manner. Due to the intermittent nature of the wind output power, this dissertation focuses on integration of supercapacitor energy storage in order to reduce the fluctuations in the net power fed into the grid. This dissertation focuses on the derivation of the supercapacitor parameters and its software model which is based on a commercial supercapacitor module. The energy storage system consisting of the supercapacitor and bidirectional DC-DC converter, is interfaced with the wind energy conversion system to smoothen the fluctuations in the grid. The energy storage can be connected with the wind energy conversion system in different ways, and in this work it was connected to the DC link. To allow power flow in both directions such that the supercapacitor stores energy or supplies energy to the grid, the bidirectional DC-DC converter control strategies were implemented. The controllers consists of a cascaded control system consisting of an outer power loop and an inner current loop. The interleaved converter was implemented in simulation were the current ripple was significantly reduced and hence allows the use of lower switching frequencies. Integration of the energy storage system to the grid side converter was achieved to smoothen the fluctuations in the DC link power. Testing of the performance of the energy storage system was done by emulating a turbulent wind profile. The results obtained show that the fluctuations in the wind power were heavily attenuated, leading to a smooth net power flow to the grid.