PERFORMANCE ANALYSIS OF BIDIRECTIONAL SEPIC/ZETA CONVERTER FOR BATTERY ENERGY STORAGE SYSTEM

Abstract

This research is centred on the detailed analysis, control design, and performance enhancement of Zeta converters, which play a crucial role in various applications such as Battery Energy Storage Systems (BESS), motor drives, power factor correction equipment, and solar power systems. A significant portion of the study is dedicated to discussing two prevalent control strategies: Voltage Mode Control (VMC) and Current Mode Control (CMC). These strategies are vital in regulating the output of the Zeta converter. By employing state-space averaging and linearization techniques, the research derives transfer functions that establish the relationship between the converter's input and output parameters. These transfer functions are instrumental in analysing the small-signal behaviour of the converter, which is crucial for designing robust control systems. The control schemes' effectiveness is assessed based on key performance indicators such as steady state error, transient response, and robustness to parameter changes. In addition to the ideal scenarios, the research delves into the complexities introduced by parasitic elements inherent in non-ideal Zeta converters. These parasitic elements, including the resistance in the inductor winding, the equivalent series resistance (ESR) in capacitors, and losses in switches and diodes, significantly impact the converter's operational characteristics, stability, and efficiency. A comprehensive mathematical model is developed to elucidate the interrelationships of these parasitic elements within the context of closed-loop voltage mode control. This model addresses the intricacies added by parasitic components and demonstrates its efficacy through simulations, providing insights into achieving stable and efficient converter performance despite these non idealities. The research extends to the practical implementation of a bidirectional SEPIC/ZETA DC-DC converter, particularly relevant for BESS applications. This converter facilitates bidirectional power flow, enabling battery charging and discharging operations between the battery and the grid or other power sources. The proposed converter design employs a state-space circuit averaged modelling technique to derive the transfer function necessary for managing the switching pulses via a PID controller in both SEPIC and ZETA modes. The tuning process for the PID controller utilizes the classic Ziegler-Nichols method, known for its efficacy in achieving optimal control settings.