Improved frequency decoupled energy management technique by using cascaded controllers in multi-renewables integrated hybrid energy storage systems
Pranati Rani Purohit, Arnab Ghosh, Pravat Kumar RayPurpose
The purpose of this paper is to meet load demand and reduce the impact of renewable energy sources’ intermittency, microgrids (MGs) rely on the coordinated operation of photovoltaic (PV), wind and hybrid renewable energy sources (HRSS). A hybrid energy storage system (HESS) integrates both long-term energy storage in batteries and short-term energy compensation in supercapacitors. To keep direct current (DC) MGs stable, manage power sharing and regulate DC bus voltage, which indicates a supply–demand imbalance, power electronic converters and good management procedures are necessary. To guarantee dependable operation of a low-voltage direct current (LVDC) MG in dynamic environments, robust power management is crucial.
Design/methodology/approach
Maintaining a constant DC bus voltage is essential for reliable LVDC MG operation and proper HESS charging/discharging under varying generation and load. To achieve this, a dynamic frequency-decoupled energy management strategy (DFD-EMS) is proposed, which uses a hierarchical structure to separate low-frequency (steady-state) and high-frequency (dynamic) power components, enabling coordinated power sharing among PV, wind, battery and supercapacitor units. The architecture uses cascaded PI-LagLead (PILL) controllers in outer voltage and inner current loops, as shown in Figure 3, enabling hierarchical coordination for stable and efficient power management.
Findings
This paper presented a robust control and energy management framework for LVDC MGs with hybrid renewable sources and hybrid energy storage. A dynamic frequency-decoupled EMS enabled coordinated power sharing between batteries and supercapacitors, with a novel cascaded PILL controller implemented in both voltage and current loops to enhance stability, transient response and noise rejection. The performance of the proposed PILL-based controller was systematically compared with four conventional cascaded control configurations using proportional–integral (PI) and lag-lead controllers. Comparative simulation and real-time hardware-in-the-loop (HIL) results across seven operating scenarios demonstrated superior DC-bus voltage regulation, reduced overshoot and faster settling times compared to conventional controllers. Quantitative analysis confirmed low overshoot (<4%) and fast settling times of less than 0.008 s under generation and load disturbances, validating the robustness and practical applicability of the proposed approach. The simplicity and real-time feasibility of the classical PILL-based framework make it well-suited for practical LVDC MG applications. Future work will focus on experimental validation using full-scale hardware prototypes and the extension of the proposed framework to grid-interactive DC MG architectures.
Originality/value
This work suggests a comprehensive control and power management framework for LVDC MGs integrating HRES and HESS. The significant contributions of this work are as follows: A novel cascaded control structure using phase-compensated PILL controllers in both the outer DC-bus voltage loop and the inner current loop is proposed. A dynamic frequency-decoupled EMS is proposed to enable coordinated power sharing among PV, wind, battery and supercapacitor sources. Comparative evaluation of five cascaded control configurations for HRES using HESS, including the proposed controller and four conventional control strategies designed and analysed for performance assessment: Outer PI–Inner PI, Outer LagLead–Inner LagLead, Outer PI–Inner LagLead, Outer LagLead–Inner PI and Outer PILL–Inner PILL (Proposed). A unified classical control framework with stability analysis is developed with the proposed cascaded PILL controller, which outperforms other classical configurations under diverse operating conditions. Although non-linear control strategies can provide enhanced dynamic performance, their practical implementation may require increased computational resources, accurate system modelling and higher tuning effort. For moderate-power 48 V LVDC MG applications rated at 1.2 kW, the proposed PILL-based controller offers an attractive trade-off between control performance, implementation simplicity and cost-effectiveness. The effectiveness and robustness of the proposed PILL-based DFD-EMS are validated through real-time HIL experiments under seven distinct operating scenarios involving independent and simultaneous variations in PV power, wind power and load demand. These results confirm reliable operation under multi-timescale disturbances and demonstrate the practical applicability of the proposed strategy for LVDC MGs.