Modeling,control and simulation of a photovoltaic /hydrogen/ supercapacitor hybrid power generation system for grid-connected applications

Hybrid renewable energy systems (HRES) should be designed appropriately with an adequate combination of different renewable sources and various energy storage methods to overcome the problem of intermittency of renewable energy resources. Focusing on the inevitable impact on the grid caused by strong randomicity and apparent intermittency of photovoltaic (PV) generation system, modeling and control strategy of pure green and grid-friendly hybrid power generation system based on hydrogen energy storage and supercapacitor (SC) is proposed in this paper. Aiming at smoothing grid-connected power fluctuations of PV and meeting load demand, the alkaline electrolyzer (AE) and proton exchange membrane fuel cell (PEMFC) and SC are connected to DC bus of photovoltaic grid-connected generation system. Through coordinated control and power management of PV, AE, PEMFC and SC, hybrid power generation system friendliness and active grid-connection are realized. The validity and correctness of modeling and control strategies referred in this paper are verified through simulation results based on PSCAD/EMTDC software platform.     

Dynamic modeling and simulation of a small wind–fuel cell hybrid energy system

This paper describes dynamic modeling and simulation results of a small wind–fuel cell hybrid energy system. The system consists of a 400 W wind turbine, a proton exchange membrane fuel cell (PEMFC), ultracapacitors, an electrolyzer, and a power converter. The output fluctuation of the wind turbine due to wind speed variation is reduced using a fuel cell stack. The load is supplied from the wind turbine with a fuel cell working in parallel. Excess wind energy when available is converted to hydrogen using an electrolyzer for later use in the fuel cell. Ultracapacitors and a power converter unit are proposed to minimize voltage fluctuations in the system and generate AC voltage. Dynamic modeling of various components of this small isolated system is presented. Dynamic aspects of temperature variation and double layer capacitance of the fuel cell are also included. PID type controllers are used to control the fuel cell system. SIMULINK^TM is used for the simulation of this highly nonlinear hybrid energy system. System dynamics are studied to determine the voltage variation throughout the system. Transient responses of the system to step changes in the load current and wind speed in a number of possible situations are presented. Analysis of simulation results and limitations of the wind–fuel cell hybrid energy system are discussed. The voltage variation at the output was found to be within the acceptable range. The proposed system does not need conventional battery storage. It may be used for off-grid power generation in remote communities.     

Application of electrolyzer system to enhance frequency stabilization effect of microturbine in a microgrid system

It is well known that the power output of microturbine can be controlled to compensate for load change and alleviate the system frequency fluctuations. Nevertheless, the microturbine may not adequately compensate rapid load change due to its slow dynamic response. Moreover, when the intermittent power generations from wind power and photovoltaic are integrated into the system, they may cause severe frequency fluctuation. In order to study the fast dynamic response, this paper applies electrolyzer system to absorb these power fluctuations and enhance the frequency control effect of microturbine in the microgrid system. The robust coordinated controller of electrolyzer and microturbine for frequency stabilization is designed based on a fixed-structure H_∞ loop shaping control. Simulation results exhibit the robustness and stabilizing effects of the proposed coordinated electrolyzer and microturbine controllers against system parameters variation and various operating conditions.     

A hybrid power system using alternative energy facilities in isolated island

A hybrid power system uses many wind turbine generators in isolated small islands. The output power of wind turbine generators is mostly fluctuating and has an effect on system frequency. In order to solve this problem, we propose a new power system using renewable energy in small, isolated islands. The system can supply high-quality power using an aqua electrolyzer, fuel cell, renewable energy, and diesel generator. The generated hydrogen by an aqua electrolyzer is used as fuel for a fuel cell. The simulation results are given to demonstrate the availability of the proposed system in this paper.     

一种基于VSG技术的混合微电网控制策略

针对混合微电网易受负荷和电源波动影响的问题,提出一种基于虚拟同步发电机技术的混合微电网控制策略,增强混合微电网的惯性能够平抑频率和电压突变,同时,联络换流器(interfacing converter,IC)根据2个子网的需要进行功率交换。建立IC控制的小信号模型,推导负荷及电源变化与传输功率之间的传递函数。分析系统的动态性能,确定控制参数的选取方法。最后,仿真与实验验证所提算法能够改善混合微电网的动态性能,增强电网的稳定性。     

Technico-economic analysis of off grid solar PV/Fuel cell energy system for residential community in desert region

A technico-economic analysis based on integrated modeling, simulation, and optimization approach is used in this study to design an off grid hybrid solar PV/Fuel Cell power system. The main objective is to optimize the design and develop dispatch control strategies of the standalone hybrid renewable power system to meet the desired electric load of a residential community located in a desert region. The effects of temperature and dust accumulation on the solar PV panels on the design and performance of the hybrid power system in a desert region is investigated. The goal of the proposed off-grid hybrid renewable energy system is to increase the penetration of renewable energy in the energy mix, reduce the greenhouse gas emissions from fossil fuel combustion, and lower the cost of energy from the power systems. Simulation, modeling, optimization and dispatch control strategies were used in this study to determine the performance and the cost of the proposed hybrid renewable power system. The simulation results show that the distributed power generation using solar PV and Fuel Cell energy systems integrated with an electrolyzer for hydrogen production and using cycle charging dispatch control strategy (the fuel cell will operate to meet the AC primary load and the surplus of electrical power is used to run the electrolyzer) offers the best performance. The hybrid power system was designed to meet the energy demand of 4500 kWh/day of the residential community (150 houses). The total power production from the distributed hybrid energy system was 52% from the solar PV, and 48% from the fuel cell. From the total electricity generated from the photovoltaic hydrogen fuel cell hybrid system, 80.70% is used to meet all the AC load of the residential community with negligible unmet AC primary load (0.08%), 14.08% is the input DC power for the electrolyzer for hydrogen production, 3.30% are the losses in the DC/AC inverter, and 1.84% is the excess power (dumped energy). The proposed off-grid hybrid renewable power system has 40.2% renewable fraction, is economically viable with a levelized cost of energy of 145 $/MWh and is environmentally friendly (zero carbon dioxide emissions during the electricity generation from the solar PV and Fuel Cell hybrid power system).     

Continuous operation in an electric and hydrogen hybrid energy storage system for renewable power generation and autonomous emergency power supply

Under the background of extensive improvement of renewable resources and demand for reliable emergency power supply, we proposed a hybrid energy storage system including an electric double-layer capacitor bank and a hydrogen system which is composed of fuel cell, electrolyzer, gas tank and metal hydride tank. Through its integration with photovoltaic power sources in a local direct current grid, we expect to obtain both of stable energy source at ordinary times and long-time reliable autonomous emergency power supply when outages happen. A three-day demonstration of the proposed system was performed. The fluctuation compensation performance of the components and the long-time stable power supply obtained by the entire system were evaluated at first, hence the configuration and the management methods of the proposed system were verified in the autonomous emergency power supply application. Meanwhile, the performance of the hybrid use of the gas tank and the metal hydride tank in the system was preliminarily evaluated, for its effectiveness verification on reducing auxiliary power for temperature condition of the metal hydride tank. Moreover, we investigated the distribution characteristics of the power and energy loss in the electric double-layer capacitor, electrolyzer and fuel cell, and their correlation to the efficiency characteristics under different conditions during the operation. The investigation results showed that the continual low-load-ratio state of the electrolyzer and fuel cell led to the low efficiency, the rare high-power occurrence of the electrolyzer and fuel cell led their demanded excessive power capacity. Thus, we proposed a solution method of shifting the electrolyzer and fuel cell's load to the EDLC, when the electrolyzer and fuel cell are in low-load-ratio and excessive high-power state, in order for efficiency increase and facility capacity reduction.     

Simulation of a solar-hydrogen-fuel cell system: results for different locations in Mexico

The authors report the results obtained from the simulation of a PV-hydrogen-fuel-cell (PVHFC) hybrid system for different locations in Mexico. The hybrid system consists of photovoltaic arrays coupled with an electrolyzer to produce hydrogen, a fuel cell which converts chemical energy (H₂) to electricity, a hydrogen storage, a battery storage system, and the load. In this kind of system, all components can be connected electrically in parallel. The voltage of the PV arrays the fuel cell must be high enough to charge the battery, and the voltage of the electrolyzer must be low enough for the battery to power it during periods of low insolation. The simulation is based on the electrical component models and variable insolation data depending on the location.     

Hybrid PV/fuel cell system design and simulation

In this paper, a hybrid Photovoltaic (PV)-fuel cell generation system employing an electrolyzer for hydrogen generation is designed and simulated. The system is applicable for remote areas or isolated loads. Fuzzy regression model (FRM) is applied for maximum power point tracking to extract maximum available solar power from PV arrays under variable insolation conditions. The system incorporates a controller designed to achieve permanent power supply to the load via the PV array or the fuel cell, or both according to the power available from the sun. Also, to prevent corrosion of the electrolyzer electrodes after sunset, i.e. when its current drops to zero, the electric storage device is designed so as to isolate the electrolyte from the electrolysis cell.     

Control analysis of renewable energy system with hydrogen storage for residential applications

The combination of an electrolyzer and a fuel cell can provide peak power control in a decentralized/distributed power system. The electrolyzer produces hydrogen and oxygen from off-peak electricity generated by the renewable energy sources (wind turbine and photovoltaic array), for later use in the fuel cell to produce on-peak electricity. An issue related to this system is the control of the hydrogen loop (electrolyzer, tank, fuel cell). A number of control algorithms were developed to decide when to produce hydrogen and when to convert it back to electricity, most of them assuming that the electrolyzer and the fuel cell run alternatively to provide nominal power (full power). This paper presents a complete model of a stand-alone renewable energy system with hydrogen storage controlled by a dynamic fuzzy logic controller (FLC). In this system, batteries are used as energy buffers and for short time storage. To study the behavior of such a system, a complete model is developed by integrating the individual sub-models of the fuel cell, the electrolyzer, the power conditioning units, the hydrogen storage system, and the batteries. An analysis of the performances of the dynamic fuzzy logic controller is then presented. This model is useful for building efficient peak power control.     

Modeling of a hybrid marine current-hydrogen active power generation system

This paper presents the modeling and the simulation of a hybrid marine current-hydrogen power generation system. The marine current power generation system consists of a fixed pitch marine current turbine directly coupled to a permanent magnet synchronous generator (PMSG). The generator is connected to a DC link capacitor via a controlled rectifier, which has two modes of operation. The first mode is the maximum power point tracking (MPPT) by using torque control when the generator runs below the rated speed. The second mode is the power limitation (at the rated value) when the generator runs above the nominal speed. The generated power is transferred from the DC-link to the load via an inverter to run the system in a stand-alone operation mode. An energy storage system must cover the difference between the generation and the consumption for this scheme. The hydrogen, compared with the different energy storage systems, exhibits characteristics more applicable for marine current power generation systems. When the generated power is higher than the load requirements, a Megawatt-scale proton exchange membrane (PEM) electrolyzer consumes the surplus energy for hydrogen generation. The generated hydrogen is stored in tanks to feed a PEM fuel cell system to generate power in case of shortage. Based on this topology and operation procedure, the overall system is called an active power generation system. The MW scale PEM electrolyzer model is presented based on state of the art and the literature of different scales PEM electrolyzer system modeling.     

Dynamic modeling,design and simulation of a wind/fuel cell/ultra-capacitor-based hybrid power generation system

Recent research and development of alternative energy sources have shown excellent potential as a form of contribution to conventional power generation systems. In order to meet sustained load demands during varying natural conditions, different energy sources and converters need to be integrated with each other for extended usage of alternative energy. The paper focuses on the combination of wind, fuel cell (FC) and ultra-capacitor (UC) systems for sustained power generation. As the wind turbine output power varies with the wind speed: an FC system with a UC bank can be integrated with the wind turbine to ensure that the system performs under all conditions. We propose herein a dynamic model, design and simulation of a wind/FC/UC hybrid power generation system with power flow controllers. In the proposed system, when the wind speed is sufficient, the wind turbine can meet the load demand while feeding the electrolyzer. If the available power from the wind turbine cannot satisfy the load demand, the FC system can meet the excess power demand, while the UC can meet the load demand above the maximum power available from the FC system for short durations. Furthermore, this system can tolerate the rapid changes in wind speed and suppress the effects of these fluctuations on the equipment side voltage in a novel topology.     

Development of hybrid photovoltaic-fuel cell system for stand-alone application

In this paper we present firstly the different hybrid systems with fuel cell. Then, the study is given with a hybrid fuel cell–photovoltaic generator. The role of this system is the production of electricity without interruption in remote areas. It consists generally of a photovoltaic generator (PV), an alkaline water electrolyzer, a storage gas tank, a proton exchange membrane fuel cell (PEMFC), and power conditioning units (PCU) to manage the system operation of the hybrid system. Different topologies are competing for an optimal design of the hybrid photovoltaic–electrolyzer–fuel cell system. The studied system is proposed. PV subsystem work as a primary source, converting solar irradiation into electricity that is given to a DC bus. The second working subsystem is the electrolyzer which produces hydrogen and oxygen from water as a result of an electrochemical process. When there is an excess of solar generation available, the electrolyzer is turned on to begin producing hydrogen which is sent to a storage tank. The produced hydrogen is used by the third working subsystem (the fuel cell stack) which produces electrical energy to supply the DC bus. The modelisation of the global system is given and the obtained results are presented and discussed.     

Optimal shifting of Photovoltaic and load fluctuations from fuel cell and electrolyzer to lead acid battery in a Photovoltaic/hydrogen standalone power system for improved performance and life time

Cost reduction is very critical in the pursuit of realizing more competitive clean and sustainable energy systems. In line with this goal a control method that enables minimization of the cost associated with performance and life time degradation of fuel cell and electrolyzer, and cost of battery replacement in PV/hydrogen standalone power systems is developed. The method uses the advantage of existing peak shaving battery to suppress short-term PV and load fluctuations while reducing impact on the cycle life of the battery itself. This is realized by diverting short-term cyclic charge/discharge events induced by PV/load power fluctuations to the upper band of the battery state of charge regime while operating the fuel cell and electrolyzer systems along stable (smooth) power curves. Comparative studies of the developed method with two other reference cases demonstrate that the proposed method fares better with respect to defined performance indices as fluctuation suppression rate and mean state of charge. Modeling of power electronics and design of controllers used in the study are also briefly discussed in Appendix A.     

Determination of the optimum hybrid renewable power generating systems for Kavakli campus of Kirklareli University,Turkey

This study is to search for possibilities of supplying the load demand of Kavakli campus of Kirklareli University with solar energy and the fuel cell power generating system (electrolyzer/hydrogen tank/fuel cell) by using the HOMER software due to the fact that hybrid power systems with renewables can significantly reduce emissions which are caused by utilization of non-renewable power sources. In this study, various hybrid systems will be examined and compared among themselves considering cost of energy (COE), renewable fraction, total net present cost (NPC) and hydrogen production. Additionally, this study will seek whether a fuel cell can be integrated into the hybrid systems. According to the study results, the grid connected systems appear cost-effective as expected. Although the grid-connected photovoltaic (PV) hybrid system has the lowest COE and NPC, the grid-connected PV/fuel cell hybrid system with COE, 0.294$/kWh has a slightly higher cost than the optimum one. It is strongly believed that this system may be chosen because it is a cleaner system and its emissions are fairly low.     

Dynamic modeling of a photovoltaic hydrogen fuel cell hybrid system

The objective of this paper is to mathematically model a stand-alone renewable power system, referred to as “Photovoltaic–Fuel Cell (PVFC) hybrid system”, which maximizes the use of a renewable energy source. It comprises a photovoltaic generator (PV), a water electrolyzer, a hydrogen tank, and a proton exchange membrane (PEM) fuel cell generator. A multi-domain simulation platform Simplorer is employed to model the PVFC hybrid systems. Electrical power from the PV generator meets the user loads when there is sufficient solar radiation. The excess power from the PV generator is then used for water electrolysis to produce hydrogen. The fuel cell generator works as a backup generator to supplement the load demands when the PV energy is deficient during a period of low solar radiation, which keeps the system's reliability at the same level as for the conventional system. Case studies using the present model have shown that the present hybrid system has successfully tracked the daily power consumption in a typical family. It also verifies the effectiveness of the proposed management approach for operation of a stand-alone hybrid system, which is essential for determining a control strategy to ensure efficient and reliable operation of each part of the hybrid system. The present model scheme can be helpful in the design and performance analysis of a complex hybrid-power system prior to practical realization.     

Dynamic characteristics of a PEM fuel cell system for individual houses

The method of determination of the control variables for a system controller, which controls the electric power output of a solid‐polymer‐membrane (PEM) fuel cell system during electric power load fluctuations, was considered. The operation was clarified for the response characteristics of electric power generation for setting the control variables of proportional action and integral action considered to be the optimal for the system controller. The power load pattern of an individual house consists of loads usually moved up and down rapidly for a short time. Until now, there have been no examples showing the characteristics of the power generation efficiency of a system that follows a load pattern that moves up and down rapidly. Therefore, this paper investigates the relation of the control variables and power generation efficiency when adding change that simulates the load of a house to PEM fuel cell cogeneration. As a result, it was shown that an operation, minimally influenced by load fluctuations, can be performed by changing the control variables using the value of the electric power load of a system. Copyright © 2006 John Wiley & Sons, Ltd.     

Electrolytic hydrogen based renewable energy system with oxygen recovery and re-utilization

The Hydrogen Research Institute (HRI) has developed a stand-alone renewable energy (RE) system based on energy storage in the form of hydrogen. When the input devices (wind generator and photovoltaic array) produce more energy than is required by the load, the excess energy is converted by an electrolyzer to electrolytic hydrogen, which is then stored after stages of compression, purification and filtration. Conversely, during a time of input energy deficit, this process is reversed and the hydrogen produced earlier is reconverted to electrical energy through a fuel cell. The oxygen which has been produced by the electrolyzer during the hydrogen production is also stored at high pressure, after having gone through a purification and drying process. This stored oxygen can be re-utilized as oxidant in place of compressed air in the fuel cell. The modifications of the electrolyzer for oxygen storage and re-utilization of it as oxidant for the fuel cell are presented. Furthermore, the HRI has designed and developed the control system with power conditioning devices for effective energy management and automatic operation of the RE system. The experimental results show that a reliable autonomous RE system can be realized for such seasonal energy sources, using stored hydrogen as the long-term energy buffer, and that utilizing the electrolyzer oxygen by-product as oxidant in the fuel cell increases system performance significantly.     

Load response characteristics of a fuel cell micro-grid with control of number of units

The dynamic characteristics and generation efficiency of a micro-grid structured from 17 houses were examined. A gas engine generator with a power generation capacity of 3 kW installed in a house is made to correspond to the base load, and a solid-polymer-membrane-type fuel cell with a power generation capacity of 1 kW is installed in 16 houses. Moreover, when changing the load of a micro-grid, the correspondence takes place by controlling the number of fuel cells. Using numerical analysis, the characteristics of the power quality of a fuel cell micro-grid, and the generation efficiency of the fuel cell were examined. As a result, the relationship between the parameter of the controller and power quality and a fall in generation efficiency by a partial load was clarified.     

Multi-loop nonlinear predictive control scheme for a simplistic hybrid energy system

A simplistic hybrid energy system is composed of the wind turbine, electrolyzer, and PEM fuel cell stack. In view of the high current demand and fast load changes, the hybrid dynamic simulation shows that the fuel cell may be in risk of oxygen starvation and overheating problems. Regarding the safe operation as well as long lifetime of the fuel cell, the effective control manner is expected to regulate both the stack temperature and oxygen excess ratio in the cathode at the desired level. Under the multi-loop nonlinear predictive control framework, the controlled output variables are specified independently by manipulating air (oxygen) and water flowrates, respectively. The dynamic modeling and control implementation are realized in the Matlab–Simulink? environment.