Chapter 6 - Maximum output power of wind energy system combined with battery energy storage using rule-based control

Abstract

Maximizing the output power of doubly-fed induction generator (DFIG) driven by a variable speed wind turbine and connected to the utility grid is the main objective of this chapter. Because the rotor excitation voltage affects the output power of a DFIG, detailed expressions for stator power, rotor power, stator loss, rotor loss, and electrical power are derived as functions of the generator speed and the magnitude and phase angle of the rotor excitation voltage. Wind turbine mechanical torque-speed characteristics, as well as generator electromagnetic torque-speed characteristics, are considered in the derivation of the steady-state stability region for the magnitude and phase angle of the rotor excitation voltage. So, the resultant optimal rotor excitation voltage, which gives maximum output power, minimum loss, and satisfying the steady-state stability, is obtained. Integrating a battery energy storage system (BESS) with a wind turbine generator can make these intermittent renewable energy sources more dispatchable. A control strategy is developed for optimal use of the BESS for this purpose. The chapter considers a rule-based control scheme, which is the solution of the optimal control problem defined, to incorporate the operating constraints of the BESS, such as state of charge limits and charge/discharge current limits. The goal of the control is to have the BESS provide as much smoothing as possible so that the renewable resource can be dispatched based on the estimated wind speed data. The effectiveness of this control strategy has been tested by using estimated wind speed data, and it is shown that the BESS can indeed help to cope with variability in wind generation.