Robust backstepping global integral terminal sliding mode controller to enhance dynamic stability of hybrid AC/DC microgrids

Roy et al. Protection and Control of Modern Power Systems https://doi.org/10.1186/s41601-023-00281-2 Protection and Control of Modern Power Systems (2023) 8:8 Open Access ORIGINAL RESEARCH Robust backstepping global integral terminal sliding mode controller to enhance dynamic stability of hybrid AC/DC microgrids Tushar Kanti Roy1*, Subarto Kumar Ghosh2 and Sajeeb Saha3 Abstract In this paper, a Backstepping Global Integral Terminal Sliding Mode Controller (BGITSMC) with the view to enhancing the dynamic stability of a hybrid AC/DC microgrid has been presented. The proposed approach controls the switching signals of the inverter, interlinking the DC-bus with the AC-bus in an AC/DC microgrid for a seamless interface and regulation of the output power of renewable energy sources (Solar Photovoltaic unit, PMSG-based wind farm), and Battery Energy Storage System. The proposed control approach guarantees the dynamic stability of a hybrid AC/DC microgrid by regulating the associated states of the microgrid system to their intended values. The dynamic stability of the microgrid system with the proposed control law has been proved using the Control Lyapunov Function. A simulation analysis was performed on a test hybrid AC/DC microgrid system to demonstrate the performance of the proposed control strategy in terms of maintaining power balance while the system’s operating point changed. Furthermore, the superiority of the proposed approach has been demonstrated by comparing its performance with the existing Sliding Mode Control (SMC) approach for a hybrid AC/DC microgrid. Keywords Dynamic stability, Hybrid AC/DC microgrids, Power balance, Robust backstepping controller, Global integral terminal sliding mode controller, Switching control signals 1 Introduction With ever-increasing electricity demand, dwindling fossil fuel reserves, and the Greenhouse Gas (GHG) impact on electrical power systems, green Renewable Energy Source (RES) has emerged as the preferred alternative to nonrenewable energy sources or fossil fuels [1, 2]. The Distributed Generation (DG) concept has played a significant role in the transition from conventional fossil fuelbased energy sources to cleaner RES over the last two *Correspondence: Tushar Kanti Roy ; 1 Department of Electronics & Telecommunication Engineering, Rajshahi University of Engineering and Technology, Rajshahi 6204, Bangladesh 2 Department of Electrical and Electronic Engineering, Rajshahi University of Engineering and Technology, Rajshahi 6204, Bangladesh 3 School of Science, Technology and Engineering, University of the Sunshine Coast, Moreton Bay Campus, Queensland, Australia decades [3]. RES, such as Solar Photovoltaic (PV) and wind energy, are abundant around the world, and they are regarded as the key contributors to improving carbon sustainability [4, 5]. And it is commonly adopted alongside an Energy Storage System (ESS) to form a Microgrid (MG) and serve local electricity demand. The primary benefits of an MG includes to increase dependability, autonomous control, and the flexibility to satisfy local load needs in both islanded (without grid support) and grid-connected modes [6, 7]. However, the intermittencies associated with the RES and the fluctuations in load demands are considered the major issues for MG operators [8, 9]. For example, the generation of wind and solar energy systems, which are the most common RES that features in the MG, depends on the weather conditions (solar irradiation and wind speed). In order to mitigate the intermittencies associated with RES and best utilize their benefits, the Battery © The Author(s) 2023. 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Protection and Control of Modern Power Systems (2023) 8:8 Page 2 of 13 ESS (BESS) has become an indispensable component in an MG system [9]. Solar energy and BESS primarily deal with DC electricity, which can be directly used to power DC loads [10, 11]. This will simplify the control structure because the frequency and reactive power regulation are not required in DC operation [12, 13, 26]. Similarly, RES that generates AC power can be utilized to power the AC loads, obviating the need for rectifiers to power DC loads [14]. As a result, hybrid AC/DC MGs with RESs are quickly increasing and capturing the attention of many researchers [15, 16]. An AC/DC MG combines the advantages of both the AC and DC MGs [17, 18], which can handle both the AC and DC loads without the requirement for further AC-to-DC and DC-to-AC conversions. Furthermore, for a hybrid AC/DC MG, when both AC and DC MG are connected with a Bidirectional Voltage Source Converter (BVSC) reduces the number of conversion steps while simplifying control operations in the MG [13, 19, 26]. However, dealing with intermittencies in RES and fluctuations in loads, and the energy management of diverse components is regarded as a key challenge for the MG operator. Therefore, robust controllers are essential for hybrid AC/DC MGs to provide resiliency against the aforementioned challenges. Different linear and nonlinear controllers for controlling individual DC and AC MGs have been designed and implemented in the existing literature [20–23]. The overall aim of these controllers is to maintain the dynamic stability of a MG regardless of whether they are DC or AC. Liu, et al., [23] and Ma et al., [24], identified that a model free Proportional-Integral (PI) controller can be used to manage the output power of each of the components in hybrid AC/DC MGs where power regulation is achieved by coordinating the actions of individual component controllers. However, the PI controller is not capable to ensure the dynamic stability of hybrid AC/ DC MGs under severe system transients. Sowmmiya and Govindharajan, [25] proposed a similar controller for a hybrid AC/DC MG to manage the grid voltage and frequency. In contrast, a distributed control system is proposed in [26] to coordinate the Multiple Parallel Bidirectional Power Converter (MPBPC) in a hybrid AC/DC MG. However, the dynamical stability of DC-and AC-bus voltages has not been considered in the control approach in [26], though the regulation of these (...truncated)