A novel control strategy for a hybrid energy storage system in a grid-independent hybrid renewable energy system

摘要

In this paper, a novel control strategy is proposed for a hybrid energy storage system (HESS), as a part of the grid-independent hybrid renewable energy system (HRES), to maintain active power balance among different constituents of HRES. The considered HRES includes a wind energy conversion system (WECS), a photovoltaic (PV) system, the HESS comprising the battery energy storage system (BESS) and supercapacitor energy storage system (SCESS), dump load, and a set of critical and noncritical loads. The proposed control strategy is executed into two parts: In the first part, the HESS controller maintains the active power balance among different constituents of HRES under variable operating conditions (viz, wind speed, solar irradiance, and load). The low-frequency components of imbalance power are diverted to BESS for its smooth charging/discharging while the high-frequency components are diverted to the SCESS, thereby reducing the stress on BESS. Further, the state of charge of the HESS is maintained within the limits and hence increasing its operating life. In the second part, the three-phase inverter controller, based on vector control technique, regulates the three-phase AC voltage magnitude and frequency within limits against any perturbation. The novelty of the proposed control strategy lies also in the fact that some portion of the power, which remains uncompensated by BESS when using conventional low pass filter (LPF) scheme, is compensated by SCESS by generating reference current corresponding to this uncompensated power. Further, the synergetic use of the typical HRES-PV system and WECS-and the typical HESS-BESS and SCESS-is also a new proposition. Simulations are carried out in MATLAB/Simulink and the results demonstrate the effectiveness of the control strategy in terms of active power balance of HRES, regulation of DC link voltage (V-DC), three-phase AC voltage and frequency, and maintaining SoC constraints of HESS in transient as well as steady state conditions.