Direct coupling photovoltaic power regulator for stand-alone power systems with hydrogen generation

This paper describes a photovoltaic power regulator aimed for photovoltaic stand-alone hydrogen-backup power systems. The main characteristics of the regulator are the following; it employs a modular approach where each power cell has three ports, one input and two outputs, the input port is connected to a photovoltaic source while the two output ports are connected to a battery and to an electrolyser, respectively. A second characteristic is that the proposed regulator is driven sequentially, minimising the regulator losses. The operation and features of the photovoltaic regulator are presented and analyzed. Design guidelines are suggested and experimental validation is also given for a 2 kW prototype.     

Combined maximum power point tracking and output current control for a photovoltaic-electrolyser DC/DC converter

This paper covers the design and the implementation of the control strategy of a DC/DC converter aimed for hydrogen production from photovoltaic sources. This control scheme provides tight control of the injected current to the electrolyser and, if required, maximum power point tracking of the photovoltaic source, by means of two independent external control loops. The two outer loops create a reference signal for an inner control loop, which adjusts the duty cycle of the DC/DC converter and sets the output inductor current to the desired value. Embedded design, which includes analog and digital electronics, has been considered for the practical implementation. Converter and control loop modelling, simulation and experimental validation are discussed in this work.     

Power factor controller used as DC–DC converter for photovoltaic sources

An active power factor controller (PFC) integrated circuit, normally used in AC circuits, has been used for DC-to-DC boost conversion with a stable output voltage for a variable DC input voltage as obtained from photovoltaic (PV) sources. The circuit described here uses a power factor controller MC 34262 to give approximately 400 V_DC output for an input variation from 90 to 280 V_DC. The maximum efficiency achieved was 98% at 450 W. Comparisons between AC and DC operations have been made.     

Implementation of an electrolysis system with DC/DC synchronous buck converter

A synchronous buck DC–DC converter that can be used to produce hydrogen through electrolysis by using the energy generated from renewable energy sources has been designed and implemented. The reason for selecting this topology is that the voltage level at the output of renewable sources, such as solar cells and storage batteries, is about 12 V DC, and the voltage level required for electrolysis is about 2 V DC. Traditional buck converters have low efficiencies at low output voltages since the voltage drops on the components are comparable to the output voltage. The converter has been designed and tested at 25 A output current. Two different electrodes were used for electrolysis and the effect of electrode opening on the operation was observed. In addition, the stability analysis of non-linear electrolysis system load has been performed.     

Energy storage-based power buffering control for photovoltaic power generation system

光伏发电系统输出的最大功率随外界环境变化而波动,无法满足负荷的供电需求,针对该问题,建立了基于储能系统的光伏发电系统结构,介绍了光伏发电系统运行原理,分析了系统功率与直流母线电压的关系,设计了无源式储能系统和有源式储能系统对功率进行缓冲以满足控制目标.仿真结果表明,有源式储能系统较无源式储能系统有更好的功率调节作用,通过双向DC-DC变换器的储放能量自动切换控制,使得光伏发电系统输出的功率与负荷需求功率良好匹配,直流电压稳定.     

A novel hybrid boost converter with extended duty cycles range for tracking the maximum power point in photovoltaic system applications

Nowadays, a large number of power conversion applications is commonly based on DC/DC converters with high voltage boost capability. Different voltage-boosting techniques have been reported in the literature. Each technique has its own merits and demerits depending on the application, cost, complexity, power density, reliability and efficiency. To meet the growing demand for such applications, new power converter topologies are continuously being proposed. This paper focuses on a novel hybrid boost converter, which combines the conventional boost (CB) and the quadratic boost (QB). This new topology allows the extension of the output voltage gain and the duty cycle range regarding to the original topologies. Thus, it ensures high conversion voltage ratio for almost duty cycle values. Consequently, it has two working modes, one as QB mode and the other one as CB mode. In order to verify the performance of the proposed topology, several simulations have been carried out under Matlab/Simulink environment for both QB and CB modes. The well-known P&O algorithm was implemented into a FPGA (Field Programmable Gate Array) board in order to verify experimentally the designed hybrid boost. Experimental results confirm the convenience of the proposed topology for tracking the maximum power point in photovoltaic systems.     

DC/DC converter topologies for electrolyzers: State-of-the-art and remaining key issues

In recent years, the use of electrolyzers to produce cleanly and efficiently hydrogen from renewable energy sources (i.e. wind turbines, photovoltaic) has taken advantage of a growing interest from researchers and industrial. Similarly to fuel cells, DC/DC converters are needed to interface the DC bus with the electrolyzer. Usually, electrolyzers require a low DC voltage to produce hydrogen from water. For this reason, a DC/DC buck converter is generally used for this purpose. However, other DC/DC converter topologies can be used depending on the feature of the electrolyzer and electrical grid as well. The main purpose of this paper is to present the current state-of-the-art of DC/DC converter topologies which can be combined with electrolyzers. The different DC/DC converter topologies are compared in terms of output current ripple reduction, conversion ratio, energy efficiency, and power switch fault-tolerance. Besides, remarks on the state-of-the-art and remaining key issues regarding DC/DC converters are provided.     

A suitable model plant for control of the set fuel cell−DC/DC converter

In this work a state and transfer function model of the set made up of a proton exchange membrane (PEM) fuel cell and a DC/DC converter is developed. The set is modelled as a plant controlled by the converter duty cycle. In addition to allow setting the plant operating point at any point of its characteristic curve (two interesting points are maximum efficiency and maximum power points), this approach also allows the connection of the fuel cell to other energy generation and storage devices, given that, as they all usually share a single DC bus, a thorough control of the interconnected devices is required. First, the state and transfer function models of the fuel cell and the converter are obtained. Then, both models are related in order to achieve the fuel cell+DC/DC converter set (plant) model. The results of the theoretical developments are validated by simulation on a real fuel cell model.     

Field experience study and evaluation for hydrogen production through a photovoltaic system in Ouargla region,Algeria

An experimental study on small-scale for solar hydrogen production system via a Proton Exchange Membrane electrolysis under a desert climatic condition in Ouargla region (South-East of Algeria) has been carried out, the target of this study has been first to evaluate hydrogen production by water analysis and to store the solar energy which has had the form of a hydride-metal hydrogen, after that, to investigate the performance of sophisticated commercial electrolyser (HG-60)powered by photovoltaic panels via the Power Management Unit (PMU) as a power conditioner, this paper has also a mathematical models based on real-time experiments were used to simulate both the photovoltaic system and PEM electrolyser work, along with attempting to direct linking strategy with the same experimental components of photovoltaic panels and commercial electrolyser, it was found through this study, the addition of the number of commercial electrolyser with the bank of four HG-60 stacks in series. More effective considering the improving voltage matching, with power transfer efficiency reach to 99%, also another factor is the photovoltaic panels slope on panel output power and hydrogen productivity are theoretically examined, where the proper selection of optimal tilt angle has an importance for collecting the maximum hydrogen amount, eventually, over the experiment span, the real-amount of hydrogen vented over experiment course is around 92.54l.     

The application of hydrogen and photovoltaic for reactive power optimization

Hydrogen and photovoltaic (PV) are two typical new energies, which are important to sustainable development. Introducing hydrogen or PV into smart grid as distributed generation (DG) becomes a promising approach. These kinds of power generations will help the grid gather more energy and introduce new chances of grid management. In this paper, we will introduce an application of hydrogen and PV in reactive power control. PV is used for hydrogen harvest, and PV is variable and dependent on weather conditions compared with a conventional generator that produces a stable output. Photovoltaic hydrogen fuel cell (PV-${\text{H}}_2$-FC) is introduced as DG, which connects to the grid. Adding hydrogen-based DG would help improve the quality of supply power. A genetic algorithm for DG site selection supporting DG cost optimization is proposed. Reactive power optimization (RPO) is an important function in planning for the future and daily operations of the smart grid system. Implementation of reactive power optimization based on the historical solution matching is also proposed, it considers the PV-${\text{H}}_2$-FC features and grid historical data, which uses Cosine distance for similarity measurement. The proposed RPO algorithm has a great advantage in calculation speed compared with traditional algorithms. The historical load data with the highest similarity are extracted, and its historical RPO scheme is applied to simulate the current RPO scheme. Results show that this method could help to find out an RPO solution effectively. The proposed solution would provide processing purposes for power company information data and further explore the supporting role of information resources in grid operations, which has broad social benefits.     

Modelling and simulation of a heaving wave energy converter based PEM hydrogen generation and storage system

The research on wave energy systems has been ongoing for decades. However, there are not many operational wave energy converters in use. The hydrogen energy systems also have a great potential. The proposed solution is to combine wave energy system with hydrogen energy system. The study provides details of simulation models and related simulation results. It is environmentally friendly, safe, feasible and effective. The results indicate that the proposed system model has a very high potential. With the use of low to medium energy density sea states, it is appears to be possible to generate (for DS1, DS2 and DS3, m_H2 = 350.8 kg, 623.9 kg and 2124 kg, respectively) a considerable amount of hydrogen in 20-min. The presented results include WEC motion properties, instantaneous and moving average value of other system parameters. The future promising simulations results indicate that next generation wave energy converter systems could be accompanied by hydrogen generation and storage systems.     

Steady-state and dynamic performance analysis of PV supplied DC motors fed from intermediate power converter

The steady-state and transient performance of PM and series motors coupled to centrifugal pump supplied from Photovoltaic source through intermediate buck-boost converter is analyzed. The effect of duty ratio selection based on maximum power operation of PV source and maximum daily gross mechanical power is investigated on the solar cell array operating point, motor armature voltage, armature current and motor efficiency variation. Studies are carried out by formulating the mathematical models for photovoltaic source, DC motors, power converter and load. Starting torque variation, Torque magnification factors expressions are derived and their variations plotted for the above two cases. Simulation software is developed for the transient and steady-state analysis of PV supplied DC motors for different duty ratios of power converter and solar insolations. Steady-state and transient performance characteristics are presented. The performance of PM DC motor is compared with the series motor operating under identical conditions.     

直流模块式光伏发电系统前级DC/DC变换研究

针对传统集中式光伏发电系统结构存在的问题,介绍了直流模块式光伏发电结构,并利用反激变换器作为直流模块式光伏发电系统的前级直流模块,采用变步长的滞环比较法实现光伏电池的最大功率跟踪控制,采用带有输入电压前馈控制的电压闭环控制策略实现直流母线的稳压控制。试验结果表明,该方案可行。     

Design and experimental validation of a high voltage ratio DC/DC converter for proton exchange membrane electrolyzer applications

This paper deals with hydrogen production via water electrolysis, which is considered the most attractive and promising solution. Specifically, the use of renewable energy sources, such as wind electric power generators, is hypothesized for supplying the electrolyzer, aiming to strongly reduce the environmental impact. In particular, micro-wind energy conversion systems (μWECSs) are attractive for their low cost and easy installation. In order to interface the μWECS and the electrolyzer, suitable power conditioning systems such as step-down DC-DC converters are mandatory. However, due to the requested high conversion ratio between the DC bus grid, i.e. the output of a three-phase diode rectifier connected to the output of the electric generator, and the rated supply voltage of the electrolyzer, the classic buck converter alone is not suitable. Therefore, a converter is proposed and designed, consisting of a buck converter, a full-bridge IGBT converter, a single-phase transformer, and a diode bridge rectifier; LC filters are also included between buck and full-bridge converters, and at the output of the diode bridge rectifier with the aim of reducing the ripple on currents and voltages. The components of the described physical system from the output of the three-phase rectifier up to the electrolyzer are then modeled assuming the transformer as ideal, and the model is employed for designing a PI-type controller. Experimental results are provided in order to demonstrate the effectiveness of the developed converter and its control for these applications.     

Performance analysis of a 3 kW grid-connected photovoltaic plant

In this paper, the grid-connected photovoltaic plant of the University of Calabria is presented. The photovoltaic plant has a peak power of 2.7 kW, and has been projected and built near the Building Energy Research Laboratory of the Department of Mechanical Engineering at the University of Calabria.The plant is suitably monitored for the experimental validation of the models and of the simulation codes that allow the evaluation of the performance of the single components and of the overall plant. In this paper, some experimental results of the efficiencies of the photovoltaic field and of the inverter are presented, as well as other plant data.     

Techno-economic optimisation of hydrogen production by PV - electrolysis: “RenHydrogen” simulation program

The work concerns the optimisation of hydrogen production by electrolysis using renewable energy resources. To achieve this aim, the techno-economic analysis was dedicated to a system composed of PV panels and an electrolyser, including all associated technology such as the chopper circuit¹. The first step was to complete a LabVIEW simulation program which was able to reproduce a photovoltaic (PV) plant connected to the alkaline electrolyser. The virtual instrument was developed on the basis of the models of incident radiation, PV cells and electrolyser. After the indication of PV cell type and number, tilt of all panels, number of strings², latitude and main characteristics of the electrolyser (e.g. nominal power, number of electrolytic cells, working temperature and pressure), the program computes the hydrogen produced, the electrolyser running hours and other data, for a chosen period of the year.Differently tilted photovoltaic panels were considered either directly coupled with the electrolyser or connected via a DC converter between the two systems.The simulation program, called “RenHydrogen”, provides a qualitative calculation of the hydrogen production during the whole year, comparing different technological options and leading to the techno-economic optimisation of the PV-electrolysis system.     

Power switch failures tolerance and remedial strategies of a 4-leg floating interleaved DC/DC boost converter for photovoltaic/fuel cell applications

In recent years, many researchers have proposed new DC/DC converters in order to meet the fuel cell requirements. The reliability of these DC/DC converters is crucial in order to guarantee the availability of fuel cell systems. In these converters, power switches ranked the most fragile components. In order to enhance the reliability of DC/DC converters, fuel cell systems have to include fault-tolerant topologies. Usually, dynamic redundancy is employed to make a fault-tolerant converter. Despite this kind of converter allows ensuring a continuity of service in case of faults, the use of dynamic redundancy gets back to increase the complexity of the converter. In order to cope with reliability expectations in DC/DC converters, floating interleaved boost converters seem to be the best solution. Indeed, they have much to offer for fuel cells and DC renewable energy sources (i.e. photovoltaic system), including reduced input current ripple and reliability in case of faults. Despite the offered benefits of this topology, operating degraded modes lead up to undesirable effects such as electrical overstress on components and input current ripple increasing. The aim of this paper is to carry out a thorough analysis of these undesirable effects and to propose remedial strategies to minimize them.     

Distributed generation from renewable sources in an isolated DC network

This article describes a direct current (DC) isolated network that is infed with distributed generation from renewable sources and cogeneration units. The sources are connected to the network via DC/DC converters to keep the voltage within a defined range and to ensure the required power flow. The consumption is directly connected to the DC network, without any DC/DC converter. The storage is located at a single point in the network. A simulation analysis based on a DC-network model shows that it is possible to operate a DC network with standard elements used for the generation side as well as for the consumption side. The key elements are the DC/DC converters, which control the voltage of the network and optimize the operation of the sources.     

A high efficiency photovoltaic module integrated converter with the asymmetrical half-bridge flyback converter

A module integrated converter (MIC) for a photovoltaic (PV) cell is important part of power conditioning system (PCS). It performs maximum power point tracking of a PV cell to generate the power as much as possible from solar energy. There are several methods for connection between the PV modules and the MICs. In order to avoid partial shading effects, converter-per-module approach was proposed. The MIC that performs maximum power point tracking (MPPT), if it is low efficiency, is no use. The MIC whose output is connected to the output of PV module was proposed for high efficiency. However, there are some problems. In this study, an asymmetrical half-bridge flyback converter is proposed instead of the original flyback converter with same method to solve the problems. The proposed MIC was built to verify the performance. The new topology using soft switching technique showed good performance for the efficiency. At the higher power, the efficiency of the proposed converter is higher than existing converter.     

High-efficiency grid-connected photovoltaic module integrated converter system with high-speed communication interfaces for small-scale distribution power generation

This paper presents a high-efficiency grid-connected photovoltaic (PV) module integrated converter (MIC) system with reduced PV current variation. The proposed PV MIC system consists of a high-efficiency step-up DC-DC converter and a single-phase full-bridge DC-AC inverter. An active-clamping flyback converter with a voltage-doubler rectifier is proposed for the step-up DC-DC converter. The proposed step-up DC-DC converter reduces the switching losses by eliminating the reverse-recovery current of the output rectifying diodes. To reduce the PV current variation introduced by the grid-connected inverter, a PV current variation reduction method is also suggested. The suggested PV current variation reduction method reduces the PV current variation without any additional components. Moreover, for centralized power control of distributed PV MIC systems, a PV power control scheme with both a central control level and a local control level is presented. The central PV power control level controls the whole power production by sending out reference power signals to each individual PV MIC system. The proposed step-up DC-DC converter achieves a high-efficiency of 97.5% at 260 W output power to generate the DC-link voltage of 350 V from the PV voltage of 36.1 V. The PV MIC system including the DC-DC converter and the DC-AC inverter achieves a high-efficiency of 95% with the PV current ripple less than 3% variation of the rated PV current.