Controller design for a Hybrid Energy Storage System enabling longer battery life in wind turbine generators

The permanent magnet synchronous generator (PMSG) based variable speed wind turbine is connected to the power grid via a full-scale converter. The full-scale converter presented in this paper consists of an active rectifier, an inverter and DC-DC converter for Energy Storage System (ESS). The rectifier controller uses the rotor flux oriented control (FOC) system and achieves Maximum Power Point Tracking (MPPT) which is necessary for the wind turbine to obtain maximum power conversion. The grid side controller uses a voltage oriented control system to regulate the active and reactive power dispatched to the power grid. The employed voltage source inverter (VSI) regulates the output power at desired reference value (in our case 1 pu) while keeping the output voltage in a sinusoidal waveform. The output electrical power from the PMSG is fluctuating, which is unacceptable from the standpoint of power system operation. An energy storage system (ESS) can help accommodate the difference between fluctuating wind power and that dispatched to the grid. The ESS absorbs the extra energy from the DC-link (via charging) and releases the stored energy to the DC-link when required (via discharging). The presented ESS for this paper is a Hybrid Energy Storage System (HESS) consisting of high power density supercapacitors and high energy density batteries. The HESS controller is designed to smooth and regulate the output power while help increase the battery´s life. In the control system of DC-DC controller some logic gates are employed to appropriately disconnect the battery from DC-link. The system is modeled and simulated in PSCAD software.