Design, Analysis and Coordinated Control of PV-Wind Energy fed LVDC Microgrid with Hybrid Energy Storage System

Abstract

Due to the escalating global population and accelerating technological advancements, worldwide energy demand is increasing at an unprecedented rate. It significantly strains the energy infrastructure, environment, economy, and society. To address these multifaceted issues, the adoption of renewable energy sources (RES) is prioritized in conjunction with improving energy efficiency and conservation practices. Government, industries, and individuals are working together to reduce the carbon footprint by transitioning to cleaner sources of energy (i.e. roof-top photovoltaic (PV)/wind energy-fed homes or buildings), adopting sustainable lifestyles (i.e. electric vehicles, more usage of public transportation) and supporting the development of low-carbon technologies. In this context, the development of microgrids can help in bringing a synergistic balance between energy generation and load demand. A microgrid is a small-scale, self-contained power network that can operate independently or in conjunction with the utility grid. It typically includes small-scale multiple power generation sources (i.e. PV systems, wind turbines, biomass, fuel cells etc.), energy storage systems (ESS), power converters and a variety of loads. DC microgrid (DCMG) offers the advantage of having relatively simpler control and power management, allowing them to overcome various challenges commonly encountered in AC microgrids such as reactive power compensation, phase synchronization, and high inrush current etc. The complementary characteristics of battery and supercapacitor (SC) in terms of energy and power density are combined to form hybrid energy storage systems (HESS). In recent times, low-voltage direct current (LVDC) microgrid has emerged as a new trend and smart solution for the seamless integration of RES and HESS. However, the energy output of RES is susceptible to fluctuations caused by weather patterns and diurnal variations. Consequently, the output power becomes unreliable and intermittent posing a challenge in providing a stable power to the load. This voltage fluctuation can be easily suppressed by interfacing a hybrid energy storage system comprising battery-SC as storage elements. Therefore, a hybrid RES along with appropriate HESS and proper control mechanism can be considered a reliable option for residential application/remote locations, future DC homes, commercial buildings, spacecraft and shipboard power systems due to its improved efficiency, reliability and controllability. This research work delineates a coordinated control and power management of an LVDC microgrid equipped with a parallel active configured HESS and its comprehensive design, development, and implementation. The system comprises a PV system, battery-SC with bidirectional interfacing converter forming the HESS, a wind power generation system (WPGS), and loads. All these distributed energy resources are connected to the DC bus through appropriate power electronic converters. The PV system consists of a PV array and a buck converter to extract maximum power integrated to the DC bus. The WPGS uses a DC motor coupled self-excited induction generator (SEIG)-based wind system interfaced with the same DC bus through a 3-phase rectifier and a buck converter. The intermittent nature of RES and the unpredictable variations in load demand necessitates the integration of both high-power and high-energy density storage systems in a DCMG. In this context, an actively configured battery and SC based HESS is linked to the 48 V LVDC bus via dedicated bidirectional DC-DC converters. The central idea of hybridization is to mitigate the instantaneous surge current demand and alleviate the charge/discharge stress of the battery during transients, enhancing the cycle life of the battery. By incorporating the battery-supercapacitor (SC) based HESS, the scheme effectively handles sudden and gradual power surges, leading to swift regulation of the DC bus voltage, effective power balance, and reduced current stress on the battery. The PV-wind fed 48 V LVDC microgrid integrated with HESS is designed and implemented with a proposed coordinated power management scheme (CPMS) operating in different modes. The CPMS enhances the dynamic response of the system, enabling it to quickly adapt to changing conditions such as fluctuations in RES generation and load demand. Furthermore, constraints like %SOC of both battery and SC are considered to safeguard the HESS while ensuring smooth transitions between different operating modes without disrupting the system stability. The individual systems are designed, developed, tested and finally, integrated forming the LVDC microgrid executed with proposed CPMS. The developed power management scheme is tested using a DS1103 digital platform, confirming effective mode transition and power sharing among all RES and loads. The experimental results demonstrate that the CPMS efficiently manages power among PV system, WPGS, HESS, and load under various environmental and load disturbances. The developed 48 V LVDC microgrid can be a promising solution for powering consumer electronics in homes/office spaces or other small-scale applications. However, it is important to carefully evaluate the specific needs and requirements of the loads being served.