Energy management system for AC/DC HMGS integrated with interconnected renewable sources and interlinking converter

International Journal of Applied Power Engineering (IJAPE) Vol. 12, No. 1, March 2023, pp. 24~36 ISSN: 2252-8792, DOI: 10.11591/ijape.v12.i1.pp24-36  24 Energy management system for AC/DC HMGS integrated with interconnected renewable sources and interlinking converter Syed Abdul Razzaq, Vairavasamy Jayasankar Department of Electrical and Electronics Engineering, Vel Tech Rangarajan Dr. Sagunthala R and D Institute of Science and Technology, Chennai, India Article Info ABSTRACT Article history: AC/DC hybrid micro grid system (HMGS) is designed with renewable energy sources (RES) and battery energy storage system (BESS) with unique control schemes, interfaced with multi terminal interlinking converters (ILCs). This ILC operates on droop control scheme to guarantee bidirectional power sharing to AC/DC sub grids. The power sources in AC/DC sub grids like PV, Fuel cell, BESS are controlled by advance control methods for maximum power extraction with power quality. A three-level control structure is designed for optimal energy management system (EMS). The first level confirms the power balance in AC/DC sub grid with autonomous bidirectional power transfer via ILC in islanded mode. The second level tracks the batteries state of charge (SoC), based on the minimum and maximum SoC the battery operates for charging and discharging. The third level gives the power redundant capability for critical loads connected in AC/DC sub grid for DC system and single-phase system. Received Oct 23, 2022 Revised Dec 7, 2022 Accepted Dec 23, 2022 Keywords: Battery management system Droop control Energy management system Interlinking converters This is an open access article under the CC BY-SA license. Corresponding Author: Syed Abdul Razzaq Department of Electrical and Electronics Engineering Vel Tech Rangarajan Dr. Sagunthala R and D Institute of Science and Technology No. 42, Avadi-Vel Tech Road Vel Nagar, Avadi, Chennai, Tamil Nadu 600062, India Email: 1. INTRODUCTION Various components in micro grid (MG) are discussed with a conventional droop control for AC/DC hybrid micro grids system (HMGS) with an unique protection system [1]. For renewable energy sources (RES) integrated in HMGS, a strategic model is designed for defining the probabilities for delivering active and reactive power [2]. A review paper discusses in detail about the control techniques for AC/DC HMGS [3]. Small signal model is developed for back to back converters and equally valid for large connected MG [4]. An algorithm is designed with adaptive model and predictive control to maintain the operational costs and improve the system efficiency with a unique energy management system (EMS) [5]. A hierarchical structure is designed for control of DC bus voltage, to increase the reliability and efficiency with primary, secondary and tertiary controls [6]. Improved particle swarm optimization is used to improve the system dynamics with master and slave controls for RES with interlinking converter (ILC) connected to MG [7]. A detailed analysis on DC-MG is elaborated for energy saving in DC distribution system [8]. Stability issues while sharing optimal power through AC/DC grids and restoring the frequency by highlighting the stable and unstable droop gains in root locus are discussed [9]. A dual droop control is suggested with virtual synchronous machine for reducing the impact of circulating currents and the harmonics generated due to connection of anti-parallel diodes is analyzed [10]. The control scheme is derived for battery energy storage system (BESS) and wind energy for optimal usage in MG [11]. A novel scheme is Journal homepage: http://ijape.iaescore.com Int J Appl Power Eng  ISSN: 2252-8792 25 designed for hybrid AC-DC MG for optimal power transfer with six switch AC/DC converter combined with DC/DC unidirectional full bridge converter [12]. Load sharing in MG with parallel connected inverters is discussed with the communication link based control [13]. A decentralized technique is designed for islanded mode of MG for uniformly power sharing and improve the overall power quality [14]. A droop based control scheme is designed to control the frequency and voltage for off-grid MG [15]. In the current trends DC system is also treated as main grid with huge power delivering capacity with an advantage of power injection to load and grid. With the tremendous outcomes of bidirectional power converter for AC/DC grids which is ILC, the use of distributed generation (DG) and energy storage system (ESS) are interconnected with multi-port ILC to form a reliable, robust and efficient MG. ESS performance depends on the state of charge (SoC). Hence, the goals with ESS can set for the performance of MG. Clustering the bidirectional power flow, SoC, maximum power point tracking (MPPT) a hierarchical control scheme can be designed for optimal power flow with robust and redundant power in MG. 2. AC/DC HMGS MODELLING AND CONFIGRATION The proposed AC/DC HMGS is connected with multiple ESS and DG which are interfaced with multi-port ILCs for demand-based power flow in the sub grids. During islanded mode the grid power is disconnected from utility power supply via automatic or static transfer switch (ATS/STS). The proposed control schemes uniformly distribute power with optimal power management. This hierarchical scheme tracks the complete EMS of MG. DC MG can be controlled with DC bus voltage and battery SoC status. The primary, secondary and tertiary control levels are summarized as: − Bidirectional power flow in AC/DC sub grids by voltage and frequency droop controls − Continuous tracking of ESS and DG like batteries, photovoltaic (PV), wind − Universal power sharing in multiple interconnected MG based on load demand The importance of DC distribution system is discussed for household applications is discussed in [16]. Voltage and current control scheme are designed for DC nano grid with different scenarios and the major benefits [17]. The possibility of interconnecting single phase ILC and three phases ILC in HMGS is described in [18]. 2.1. Design of photovoltaic system Load shedding for domestic users is quite common in rural areas, the scheme is developed for load management for PV system for maximum power utilization [19]. Sun irradiance and temperature are the main dependents for maximum PV power output, due to variations in both PV system is considered to be nonlinear. The voltage and current capacity of PV system depends on arrangement of cells in series and parallel. Figure 1 shows the PV system with DC/DC converter and its control. Number of modules connected in series is given by (1). 𝑀𝑠𝑒𝑟𝑖𝑒𝑠 = 0.5 𝑉𝑑𝑐 (1) 𝑉𝑚𝑎𝑥 Where Mseries is modules in series, Vdc is voltage at inverter input, Vmax is maximum voltage from MPPT. The number of modules connected in parallel is given by (2). 𝑀𝑝𝑎𝑟𝑎𝑙𝑙𝑒𝑙 = 0.5 ( 𝑃𝑖𝑛𝑣 𝑃𝑠𝑡𝑟𝑖𝑛𝑔 ) (2) DC link voltage feeding the inverter is given by (3). 𝑉𝑑𝑐 ≥ 2√2 ∗ 𝑉𝑝ℎ𝑎𝑠𝑒 (3) Vphase is RMS (...truncated)