Original article
Renewable sources based DC microgrid using hydrogen energy storage: Modelling and experimental analysis

https://doi.org/10.1016/j.seta.2020.100840Get rights and content

Highlights

  • Metal hydride is used as hydrogen storage medium.

  • Mathematical modelling of DC microgrid in MATLAB Simulation has been done.

  • Power management strategy is described using the simulation.

  • Experimental results validates the proposed power management strategy.

Abstract

A microgrid (µG) system can be operated in DC or AC modes using suitable power electronics interface which interconnect power generators, loads and energy storage mediums. It can be interesting to analyze the potential advantages of hydrogen storage-based DC µG system. In this study, a mathematical model is developed for the theoretical prediction of the performance in terms of energy analysis of overall system and charging/discharging characteristics of hydrogen storage unit in the µG. It is found that DC mode of operation of the µG significantly increases the performance and energy efficiency of overall system. A power management system (PMS) is designed which addresses the issues related to the integration of renewable power sources, stability of DC bus voltage, demand–supply balance, and load dynamics involved in the system. The designed PMS working shows that integration of the PV, FC, electrolyzer, and battery is suitable to meet the load demand in the transient operating conditions such as low and high PV power generation; and abrupt increase and decrease in the load demand. After simulation realization, a hardware prototype of PMS is designed and developed which validates its working.

Introduction

Hydrogen (H2) storage has shown a suitable choice as energy storage medium (ESM) in distributed energy system such as microgrid (µG) [1]. In µG system, H2 can be generated on-site using the surplus electricity of the renewable power generators (RPG) during the low load demand [2]. This generated H2 can be stored in H2 cylinder which can be utilized by fuel cell (FC) to generate the electricity during high load demand or unavailability of RPG [3]. Water electrolysis has shown suitable application for H2 generation in µG [4]. For H2 storage, metal hydride (MH) i.e. LaNi5 offers various advantages such as it stores H2 at lower pressure and temperature in solid form which is safer as compared to high-pressure storage [5]. Due to fast operating response and suitable application at lower temperature, proton exchange membrane fuel cell (PEMFC) can be a suitable power back-up generator with photovoltaic (PV) system [6]. PV, FC, battery, and electrolyzer (EL) are integral parts of the H2 storage-based µG system. Some previous works were based on the analysis of operational performance, energy efficiency, and demonstration of the H2 storage-based µG/hybrid system technology [7], [8], [9], [10], [11], [12]. Ghosh et al. [13] have provided an analysis on performance, operation, and safety concerns of the PV-FC hybrid system. The energy efficiencies of the PV, FC, and EL were 12%, 60% and 55%, respectively. Valverde et al. [14] have introduced some useful key parameters which can be very helpful in evaluation of the effectiveness and energy efficiency of the PV-FC µG system in different operating conditions. Gonzatti at el. [15] have attempted to provide a theoretical model for the PV-FC-EL hybrid system. They aimed to identify the correction factors in coefficients used in modelling of the system components to validate the theoretical results with experimental observations. Valverde et al. [16] have worked on the mathematical modelling of the PV-FC µG system. The proposed modelling of the system components was validated with experimental results. Caliskan et al. [17] have performed the energy analysis of wind-PV-FC hybrid system. According to the modelling results, overall energy efficiency (round-trip efficiency of H2 generation and utilization) of system was found to be 3.44%. Calderon et al. [18] have performed a study on energy analysis of wind-PV-FC standalone hybrid system. The energy efficiencies of PV system, and combination of EL and FC system have been reported to be 8.41% and 26.67%, respectively. Kumar et al. [19] have worked on the MH application in µG in AC domain and its energy analysis. The main contribution of study is to considering the losses in MH storage for evaluating the round-trip efficiency in the H2 cycle in µG. The round-trip efficiency of PV-H2 generation to utilization is found to be 2.3%. In another study, Kumar et al. [20] worked on the energy efficiency analysis of FC + MH system in µG application. PEMFC and LaNi5 were considered as auxiliary power generator and MH storage, respectively in the system. The energy efficiency was found to be 37% for FC + MH system. Barthels et al. [21] demonstrated an autonomous PV-FC hybrid power plant. They studied the plant performance at larger power scale, the total peak load consumption ≈15 kW, alkaline EL ≈26 kW, PEMFC ≈ 6.5 kW and compressed H2 storage tank ≈ 350 Nm3. However, no critical attention was devoted to MH storage in the system.

Some studies were focused on designing of the PV-FC hybrid system in simulation domain [22], [23], [24], [25], [26]. Major focus was given on the control and operation strategies to integrate the PV-FC hybrid system. Control and operation of the H2 storage-based µG system have been a subject of extensive research in recent years. Ipsakis et al. [27] studied the performance of PV-FC hybrid system in different operating modes. They found that hysteresis band approach was more suitable for prolong and safe operation of the EL and FC components. Dursun et al. [28] studied different control strategies for PV-FC hybrid system for improving operating life of PEMFC and its continuous utilization. They also used battery state of charge (SOC) for controlling the operation of EL and FC. It was found that by controlling FC operation according to SOC of battery, overall utilization and number of turn on/off of FC can be controlled which was helpful for improving FC lifespan. Valverde et al. [29] have worked on the control, planning and operation of the H2 storage-based µG in AC mode. They worked on the model predictive control (MPC) approach for energy management of the H2-based µG. It was found that MPC was more effective in control and operation of H2 based µG as compared to hysteresis band control strategy. Konstantinopoulos et al. [30] performed a simulation study on energy management and reserve rescheduling for PV-FC-wind µG system. The main aim was to prove the use of H2 storage system in effective uncertainty balancing.

A µG can be configured in the DC, AC and hybrid AC-DC modes according to the load requirement [31]. Lotfi et al. [32] have presented a review on the comparison between AC and DC µGs. They concluded that DC µG is more advantageous due to safe operation, high energy efficiency and no requirement of reactive power control. Anand et al. [33] have studied different voltage levels DC µG application to meet the load demand. They found that DC µG offers advantages as compared to AC µG due to the simple control and operation, and reduction in the energy conversion stages in the power electronic interface devices.

Some research activities were solely focused on energy management system (EMS) of the H2 energy storage-based µG system [34], [35], [36]. Karami et al. [37] have worked on the EMS in the PV-FC hybrid system using the DC bus signalling (DBS) approach. It was found that DBS is simple, economical, and effective for decentralized control and operation of µG. Thounthong et al. [38] have worked on the stabilization of DC bus voltage of µG having the battery and FC generators using the flatness methodology. In another study, Martin et al. [39] have provided a study on energy management between supercapacitor and battery storages for µG application. A modelling and experimental validation was given using the four FC generators (1.2 kW each) and three supercapacitors (83.3F each). Mokrani et al. [40] have proposed an energy management strategy for effective utilization of excess FC power in hybrid vehicle applications. Zaouche et al. [41] have demonstrated the supervisory control and operation strategy for hybrid PV-battery system.

Significant research work has been already done on H2 storage applications in AC µG domain considering their performance, energy efficiency, and control strategy etc. Fewer studies are focused on energy management issues in DC µG using H2 storage. However, there are still scope to analyse the effect of the DC mode on energy flow in µG and performance of the system components. H2 storage application in µG is a complex and interdisciplinary system which requires detail understanding of the individual components and their operational characteristics during their coordinated operations. Renewable sources, EL (H2 generation using the renewable power sources), FC (H2 into electricity converter), and MH (H2 storage) along its auxiliary systems (cooling/heating) components are involved in the H2 storage-based µG system. These components are integrated with each other using suitable power electronics interfaces. There are energy losses associated with energy conversion stages in system components and power electronic interfaces. Therefore, energy conversion losses can significantly affect the operation, efficiency, and effectiveness of such type of storage application in µG. DC mode application of µG using the DC-DC power electronic interfaces can significantly improve the energy efficiency of µG system. H2 storage-based µG system in DC mode is motivation of present study, therefore, a modelling and experimental study is carried out in present study to address the energy efficiency analysis, operational characteristics, control and operation of such system.

A mathematical modelling is done in the MATLAB simulation tool for the theoretical prediction of performance for such DC system. Most of previous studies were focused on the high-pressure H2 storage in µG system and only fewer studies attempted MH application in µG. Proposed mathematical modelling of µG system also incorporates the MH storage modelling along with PV, FC, EL, and battery systems. A control methodology is developed and analyzed in the simulation model to operate such H2 storage-based µG system. In designed control methodology, battery storage works as energy buffer and helps in control the operations of H2 system units (EL, FC, and MH). This theoretical model is also helpful for estimation of energy flow in µG, energy losses in system components levels, and its effect on overall energy efficiency of the system. An attempt is also made for the comparison between DC and AC µG having such ESM. However, such complex system requires proper controlling system for the stable and effective operation during transient operating conditions such as sudden increase and decrease in PV generator power, abrupt load variation, and SOC status of MH and battery etc. A dynamic control methodology is realized in the simulation using the MATLAB Simulink by designing a power management system (PMS). This addresses the issues related to power sharing between the power generators (PV and FC) and ESM (battery). PMS also controls the energy flow in the ESMs such as MH and battery as per the availability of the renewable power generation, SOCs of battery and MH tank, and load demand. The working of the control methodology is verified by designing the hardware prototype of PMS.

Section snippets

System description

In this study, a DC µG is studied to meet the laboratory load demand. The load demand is primarily met by the electricity of PV generator. Two ESMs, battery and H2 are used in the µG. In case of surplus PV electricity, EL generates the H2 which is stored in the MH tank. Cooling and heating requirements are provided to MH tank during the H2 charging and discharging, respectively. Battery storage is used to support the H2 storage system and works as energy buffer for improving the transient

Simulation results

This section describes the effect of the DC and AC modes on the performance of H2 storage-based µG system. Fig. 7a shows the load profile for given time duration. Fig. 7b shows the comparison between the power output of PV system in the AC and DC µGs. The power output of the PV system is higher in case of the DC µG which is justified as the losses in the AC-DC conversion stage are avoided in the DC µG. It may be noted that PV system is operated at maximum power point for extracting maximum

Conclusions

In this study, a mathematical modelling is provided for the operational behaviour of individual components along with overall integrated system for H2 storage-based DC µG. A control algorithm is developed for the coordinated operation of H2 storage in-conjunction with the battery storage in the µG. A comparative performance analysis between the AC and DC µGs shows that the performance of the DC µG increases significantly in terms of H2 production, FC power saving, reduction in H2 consumption

CRediT authorship contribution statement

Mohd Alam: Conceptualization, Methodology, Modelling, Experimental, Manuscript writing. Kuldeep Kumar: Methodology, Modelling, Experimental, Manuscript reviewing and editing. Saket Verma: Modelling, Manuscript editing. Viresh Dutta: Visualization, Investigation, Supervision.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

Authors express thanks to Dr. A. K. Mukherjee for his continuous guidance for the hardware development of PV-FC microgrid in the laboratory. Gas Authority of India limited (GAIL), New Delhi, India funded for the fuel cell-electrolyzer system under the Project ID: RP2526.

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