A nonlinear double‐integral sliding mode controller design for hybrid energy storage systems and solar photovoltaic units to enhance the power management in DC microgrids

In this paper, a nonlinear decentralized double‐integral sliding mode controller (DI‐SMC) is designed along with an energy management system (EMS) for the DC microgrid (DCMG). This DCMG includes having a hybrid energy storage system (HESS) that incorporates a battery energy storage system (BESS) and supercapacitor energy storage system (SCESS) while the load demand is met through the power generated from solar photovoltaic (SPV) units. First, dynamical models of each subsystem of DCMGs such as the SPV system, BESS, and SCESS are developed to capture highly nonlinear behaviors of DCMGs under various operating conditions. The proposed nonlinear DI‐SMC is then designed for each power unit in DCMGs to ensure the desired voltage level at the common DC‐bus and appropriate power dispatch of different components to fulfill the load requirement of the DCMG. On the other hand, an energy management system (EMS) is designed to determine the set point for the controller with an aim of ensuring the power balance within DCMGs under various operating conditions where the overall stability is assessed using the Lyapunov theory. Simulation studies along with the processor‐in‐loop validation, including a comparative study with a proportional‐integral (PI) controller, verify the applicability and effectiveness of the EMS‐based DI‐SMC under different operating conditions of the DCMG

Design of Nonlinear Backstepping Double-Integral Sliding Mode Controllers to Stabilize the DC-Bus Voltage for DC–DC Converters Feeding CPLs

This paper proposes a composite nonlinear controller combining backstepping and double-integral sliding mode controllers for DC–DC boost converter (DDBC) feeding by constant power loads (CPLs) to improve the DC-bus voltage stability under large disturbances in DC distribution systems. In this regard, an exact feedback linearization approach is first used to transform the nonlinear dynamical model into a simplified linear system with canonical form so that it becomes suitable for designing the proposed controller. Another important feature of applying the exact feedback linearization approach in this work is to utilize its capability to cancel nonlinearities appearing due to the incremental negative-impedance of CPLs and the non-minimum phase problem related to the DDBC. Second, the proposed backstepping double integral-sliding mode controller (BDI-SMC) is employed on the feedback linearized system to determine the control law. Afterwards, the Lyapunov stability theory is used to analyze the closed-loop stability of the overall system. Finally, a simulation study is conducted under various operating conditions of the system to validate the theoretical analysis of the proposed controller. The simulation results are also compared with existing sliding mode controller (ESMC) and proportional-integral (PI) control schemes to demonstrate the superiority of the proposed BDI-SMC

Nonlinear adaptive backstepping controller design for controlling bidirectional power flow of BESSs in DC microgrids

In this paper, a nonlinear adaptive backstepping controller is designed to control the bidirectional power flow (charging/ discharging) of battery energy storage systems (BESSs) in a DC microgrid under different operating conditions. The controller is designed in such a manner that the BESSs can store the excess energy from the renewable energy sources (RESs) in a DC microgrid after satisfying the load demand and also feeding back the stored energy to the load when RESs are not sufficient. The proposed controller is also designed to maintain a constant voltage at the DC bus, where all components of DC microgrids are connected, while controlling the power flow of BESSs. This paper considers solar photovoltaic (PV) systems as the RES whereas a diesel generator equipped with a rectifier is used as a backup supply to maintain the continuity of power supply in the case of emergency situations. The controller is designed recursively based on the Lyapunov control theory where all parameters within the model of BESSs are assumed to be unknown. These unknown parameters are then estimated through the adaptation laws and whose stability is ensured by formulating suitable control Lyapunov functions (CLFs) at different stages of the design process. Moreover, a scheme is also presented to monitor the state of charge (SOC) of the BESS. Finally, the performance of the proposed controller is verified on a test DC microgrid under various operating conditions. The proposed controller ensures the DC bus voltage regulation within the acceptable limits under different operating conditions