Load control of a wind-hydrogen stand-alone power system

A new generation of load controllers enable stand-alone power systems (SAPS) to use one or many standard (grid connected) wind turbines. The controllers use fuzzy logic software algorithms. The strategy is to use the control loads to balance the flow of active power in the system and hence control system frequency. The dynamic supply of reactive power by a synchronous compensator maintains the system voltage within the limits specified in EN50160. The resistive controller loads produce a certain amount of heat that is exchanged down to the end user (hot water). It was decided to investigate the implementation of a hydrogen subsystem into the SAPS that can work in parallel with the Distributed Intelligent Load Controller (DILC). The hydrogen subsystem can then function as energy storage on long-term basis and an active load controller on short-term basis.     

Sizing of a stand-alone photovoltaic power system at Dhaka

A stand-alone photovoltaic power system is designed to operate residential appliances such as fluorescent lamp, incandescent light and ceiling fan using standard methods. The total load is estimated for four hours of operation per day. The battery is sized considering different factors that affect battery efficiency to reliably operate the estimated loads during a sequence of below average insolation. The minimum battery size is obtained to be 128Ah @ 100 hr, 24V. The PV array is sized to operate the load on a daily basis based on average weather conditions using monthly average daily values of solar radiation data for 11 years. The array is sized to proper values in order to operate the estimated load reliably in the month of minimum insolation taking into account different types of power losses. The minimum array size is obtained as 6×47W_p.     

Power management strategies for a stand-alone power system using renewable energy sources and hydrogen storage

A stand-alone power system based on a photovoltaic array and wind generators that stores the excessive energy from renewable energy sources (RES) in the form of hydrogen via water electrolysis for future use in a polymer electrolyte membrane (PEM) fuel cell is currently in operation at Neo Olvio of Xanthi, Greece. Efficient power management strategies (PMSs) for the system have been developed. The PMSs have been assessed on their capacity to meet the power load requirements through effective utilization of the electrolyzer and fuel cell under variable energy generation from RES (solar and wind). The evaluation of the PMS has been performed through simulated experiments with anticipated conditions over a typical four-month time period for the region of installation. The key decision factors for the PMSs are the level of the power provided by the RES and the state of charge (SOC) of the accumulator. Therefore, the operating policies for the hydrogen production via water electrolysis and the hydrogen consumption at the fuel cell depend on the excess or shortage of power from the RES and the level of SOC. A parametric sensitivity analysis investigates the influence of major operating variables for the PMSs such as the minimum SOC level and the operating characteristics of the electrolyzer and the fuel cell in the performance of the integrated system.     

Power quality improvement of solar photovoltaic transformer-less grid-connected system with maximum power point tracking control

This paper presents a transformer-less single-stage grid-connected solar photovoltaic (PV) system with active reactive power control. In the absence of active input power, grid-tied voltage source converter (VSC) is operated in the reactive power generation mode, which powers control circuitry and maintains regulated DC voltage. Control scheme has been implemented so that the grid-connected converter continuously serves local load. A data-based maximum power point tracking (MPPT) has been implemented at maximum power which performs power quality control by reducing total harmonic distortion (THD) in grid-injected current under varying environmental conditions. Standards (IEEE-519/1547) stipulates that current with THD greater than 5% cannot be injected into the grid by any distributed generation (DG) source. MPPT tracks actual variable DC link voltage while deriving maximum power from PV array and maintains DC link voltage constant by changing the converter modulation index. Simulation results with the PV model and MPPT technique validations demonstrate effectiveness of the proposed system.     

Economic evaluation of a stand-alone residential photovoltaic power system in Bangladesh

The economics of stand-alone photovoltaic power system is studied to test its feasibility in remote and rural areas of Bangladesh and to compare renewable generators with non-renewable generators. The life cycle cost of these generators are determined using the method of net present value analysis. It is found that the life cycle cost of this experimental PV system is Tk. 43.40/kWh for one family (US $1.00 = Bangladeshi taka Tk.50.00). The life cycle cost for grid electricity is Tk. 20.00/kWh and Tk. 7.75/kWh for generation of fuel costs of Tk. 6.80/kWh and Tk. 0.47/kWh respectively. For a village 1 km away from the distribution line, this cost becomes Tk. 125.00/kWh for a family. For petrol generator life cycle cost is Tk. 50.00/kWh at fuel price of Tk. 22.00 per litre. For diesel generator life cycle cost is found to be Tk. 46.10/kWh at fuel cost of Tk. 15.00 per litre. It is observed that the life cycle cost of one unit of energy from grids that are 1 km away from a village is much higher than the cost of energy from a PV system. Thus, the use of PV system is economically feasible in rural villages and remote areas of Bangladesh, where grid electricity is not available.     

Modeling of hydrogen production with a stand-alone renewable hybrid power system

Hydrocarbon resources adequately meet today’s energy demands. Due to the environmental impacts, renewable energy sources are high in the agenda. As an energy carrier, hydrogen is considered one of the most promising fuels for its high energy density as compared to hydrocarbon fuels. Therefore, hydrogen has a significant and future use as a sustainable energy system. Conventional methods of hydrogen extraction require heat or electrical energy. The main source of hydrogen is water, but hydrogen extraction from water requires electrical energy. Electricity produced from renewable energy sources has a potential for hydrogen production systems. In this study, an electrolyzer using the electrical energy from the renewable energy system is used to describe a model, which is based on fundamental thermodynamics and empirical electrochemical relationships. In this study, hydrogen production capacity of a stand-alone renewable hybrid power system is evaluated. Results of the proposed model are calculated and compared with experimental data. The MATLAB/Simscape^® model is applied to a stand-alone photovoltaic-wind power system sited in Istanbul, Turkey.     

Power quality compensation using universal power quality conditioning system

The aim of this letter is to present a universal power quality conditioning system (UPQS) named after a unified power quality conditioner (UPQC), which is extended by adding a shunt active filter at the load side. Its main purpose is to compensate for supply voltage and load current imperfections, such as sags, swells, interruptions, imbalance, flicker, harmonics, reactive currents, and current unbalance. Converter and control analysis is presented together with results showing the UPQS modes of operation.     

A systems approach for sizing a stand-alone residential PEMFC power system

Polymer electrolyte membrane fuel cells (PEMFCs) show great promise in portable, automotive, and stationary applications. They have reached the test and demonstration phase in automotive and power markets today. This paper is focused on a stand-alone residential PEMFC power system that provides the electricity needs of the house. A novel stochastic sizing methodology is developed that considers both fuel cell system dynamics and residential load dynamics in overall system sizing for the stand-alone residential fuel cell power system. Understanding the nature of demand side is critical in stand-alone system sizing. Thus, experimental measurements have been completed to capture the load side dynamics in detail. No such data is found in the current literature. The Threshold Bootstrap method is used to model the residential load demand and to produce many realistic load profiles. Matlab/Simulink is used to run system simulations to determine system sizes based on parameters defined through a designed experiment. Comparison between the proposed sizing method and a possible worst case scenario sizing is given. The new sizing methodology can be used together with sophisticated demand analysis programs to obtain customized sizing for each user as stand-alone power systems become more viable.     

Techno-economic analysis of a stand-alone hybrid photovoltaic-diesel–battery-fuel cell power system

The main objective of this work is to model a renewable energy system that meets a known electric load with the combination of a photovoltaic (PV) array, a diesel generator and batteries. The replacement of conventional technologies with hydrogen technologies is examined. The analysis utilizes the power load data from an electric machinery laboratory located in Kavala town, Greece. The modeling, optimization and simulation of the proposed system were performed using HOMER software. Different combinations of PV, generators, and batteries sizes were selected in order to determine the optimal combination of the system on the basis of the Net Present Cost (NPC) method.     

The effect of the hysteresis band on power management strategies in a stand-alone power system

A stand-alone power system that consists of a photovoltaic array and wind generators for the exploitation of renewable energy sources (RES), and that is capable of storing excessive energy in the form of hydrogen via water electrolysis for subsequent use in a polymer electrolyte membrane (PEM) fuel cell is currently being installed at Neo Olvio of Xanthi in Greece. The performance of two power management strategies (PMSs) that utilize a hysteresis band in the operation of the integrated system over a typical 4-month period is assessed. The state-of-charge (SOC) level of the accumulator is the main parameter that governs the operation of the electrolyzer and the fuel cell. The introduction of a hysteresis band in the boundary limits of the SOC of the accumulator provides larger flexibility in the operation of the electrolyzer, the fuel cell, and the accumulator. In this way, the units can be protected from heavy and unnecessary utilization or irregular operation (reduction of frequent start-ups and shut-downs). The simulated results for the implemented PMSs revealed important information about the reliability of the load satisfaction, the total operation time that each subsystem undergoes, as well as about the hydrogen inventory in the integrated system. The study also identified the effect of variation of hysteresis band size on the system performance as an important feature for the development of an integrated control strategy.     

A microcontroller-based stand-alone photovoltaic power system for residential appliances

In this study, a stand-alone photovoltaic power system was designed and implemented to operate residential ac-powered appliances such as fluorescent lambs, fans etc. Sun-tracker is implemented for improved efficiency of the system by keeping the solar module perpendicular to the sun's incoming rays. The charge method is realized with closed-loop current control of buck-boost dc–dc converter. The proposed system also uses a voltage source type PWM inverter to convert DC voltage from battery storage to supply AC loads. In the PWM method used, selected harmonics are eliminated with the smallest number of switching and an improvement in the system efficiency by reducing switching losses and providing ease of filtering on the inverter output is obtained. Charge controller and PWM inverter systems have been realized by using PIC16F873 microcontrollers. An experimental system was implemented to demonstrate the effectiveness of the proposed system. Simulation and experimental results are given to verify the system's efficiency.     

Testing of a small-scale stand-alone power system based on solar energy and hydrogen

An experimental small-scale stand-alone power system based on hydrogen and solar energy has been tested. The system performance and operational experience are reported. Future expansion of the test-facility is taken into consideration using solutions with wide working ranges. The test-facility is designed for testing of individual components, for subsystems, and for complete power system operation. The complete power system in this study consists of a 4.8 kW programmable power supply, 1.5 kW electrolyser, a hydrogen purification unit (99.999% H₂ quality), a 14 Nm³ H₂ metal hydride storage, a 0.5 kW fuel cell, a 300 Ah lead-acid battery, and a 0.6 kW programmable load. Possible applications for such small-scale power systems are mountain cabins, remote islands, and telecommunication stations, among others. The basic idea in this particular power system configuration was to make it as simple as possible; the fuel cell and the metal hydride unit were air-cooled, and the components were connected in parallel without DC/DC converters. The only control action possible in the power system (presented in this study) was to switch the components either ON or OFF. However, connecting the components electrically in parallel without DC/DC converters gives no degrees of freedom regarding the ability to regulate power and voltage levels of the different components. Air-cooled metal hydrides might fail to deliver hydrogen due to poor heat transfer.     

Costing of a stand-alone photovoltaic system

We have used a life-cycle cost analysis for a stand-alone photovoltaic system with and without an auxiliary engine generator. Because of different published cost calculations, we apply average values or new estimates in the analysis based on examinations of component lifetimes, maintenance operations, fuel consumption, components costs, percentage of installation completed, and discount rates.     

风能-太阳能互补独立发电系统设计优化与分析

提出了一种风能-太阳能互补发电系统的优化设计方法.在经济技术性能分析过程中引入了Pareto最优的概念来确定最优系统方案.实例计算表明:使用该优化设计方法可以获得系统经济技术性能与系统配置的关系和大量的Pareto最优解,从而可以得到最满意的系统方案.风能发电和太阳能发电具有互补性,风能-太阳能互补发电系统的经济技术性能优于单一的风能发电或太阳能发电系统.     

Distributed generation system with PEM fuel cell for electrical power quality improvement

In this paper, a physical model for a distributed generation (DG) system with power quality improvement capability is presented. The generating system consists of a 5 kW PEM fuel cell, a natural gas reformer, hydrogen storage bottles and a bank of ultra-capacitors. Additional power quality functions are implemented with a vector-controlled electronic converter for regulating the injected power.     

Performance improvement of PEM fuel cell power system using fuzzy logic controller-based MPPT technique to extract the maximum power under various conditions

Power generation of a fuel cell (FC) is mostly dependent upon operational variables such as cell temperature and membrane water content. There is an individual maximum power point (MPP) on the P-I curve of the FC. The location of the MPP varies with respect to the MPP position. Thus, an MPP tracking (MPPT) system should exist to guarantee that the FC works at the MPP in order to maximize the functionality. Due to their straightforward structure, prevalent MPPT methods had strong functionality. However, their primary limitations include fluctuations around the MPP and inefficiency under abrupt variations of operating conditions. The primary objective of this paper is to maintain the PEMFCs operation at an efficient power point. To this purpose, the efficiency of PEM-FC is tested and enhanced using a variety of MPPT-based smart controller techniques. To determine the appropriate MPPT controller parameters, the modified fluid search optimization (MFSO) approach and fuzzy logic controller (FLC) are employed. Furthermore, the MFSO method is deployed to adjust the membership functions (MFs) of the FLC. The MFSO is an excellent approach for coping with the stochastic behavior of the PEM-FC system when the temperature and water content of the membrane change. In terms of improved dynamic behavior, better convergence rate, reduced oscillations, and better tracking of the MPP, the results obtained by employing the suggested strategy demonstrate the superior functionality of the system compared to case using other methods. Moreover, the power generated by the PEMFC system is less than the nominal capacity for the temperature's rated capacity. Therefore, the deficit in power would be covered by transacting power with the grid.     

Power quality improvement for 20 MW PEM water electrolysis system

Hydrogen is an important alternative as a clean fuel for industry and power-to-gas energy storage. The water electrolysis process is a promising technology in green hydrogen production where proton exchange membrane (PEM) technology has been keenly interested. Industrial large-scale PEM electrolyzers need a high current power supply. When connected to an alternating current (AC) source, high current power rectifiers are used to convert AC to DC. Currently, the most commonly used topology in large-scale PEM electrolysis systems is the thyristor-based topology due to its technology maturity and low cost. However, this topology presents several drawbacks in terms of power quality and consequently leads to higher stack-specific energy consumption (SEC) and additional losses. In the present research, we demonstrate the potential power quality improvement for a 20 MW PEM water electrolysis system by rectifier topology upgrade. Rather than traditional thyristor-based topology, a 3-phase interleaved buck rectifier topology is proposed. The new topology presents advantages on both AC and DC sides via a validated simulation model, which is built using MATLAB/Simulink and then validated with experimental data from an industrial 20 MW PEM water electrolyzer at Air Liquide's Bécancour plant. Results show a great improvement in terms of power factor, Total Harmonic Distortion (THD), and DC-current ripple reducing the total losses and the SEC of the PEM stack, especially under partial load. Towards a higher power efficiency, the proposed rectifier topology may be considered in the construction of future large-scale PEM systems.     

An insight into power quality disturbances using wavelet multiresolution analysis

The wavelet transform is beginning to be used widely in power engineering. Its effectiveness for analyzing transients with time localized information is now well known. Multiresolution analysis is especially suitable for feature enhancement of transients and thus makes it possible for power disturbances to be classified. In addition, the wavelet transform works well where the Fourier transform fails. A graphical insight is demonstrated in this letter.     

独立光伏电源系统设计方法

近年来通信行业的迅猛发展,对通信电源的要求也越来越高,所以稳定可靠的太阳能电源正被广泛应用于通信领域。而如何根据各地区太阳能辐射条件,来设计出既经济而又可靠的光伏电源系统,是需要大家关注的问题。笔者发现有些设计仅考虑了蓄电池的自维持时间（即最长连续阴雨天）,而没有考虑到亏电后的蓄电池最短恢复时间（即两组近似最长连续阴雨天之间的最短间隔天数）。这个问题在我国南方地区应引起高度重视,因为我国南方地区阴雨天既长又多,而对于方便适用的独立光伏电源系统,由于没有应急的其他保护电源备用,必须在设计中考虑这个…     

Automation infrastructure and operation control strategy in a stand-alone power system based on renewable energy sources

The design of the automation system and the implemented operation control strategy in a stand-alone power system in Greece are fully analyzed in the present study. A photovoltaic array and three wind generators serve as the system main power sources and meet a predefined load demand. A lead-acid accumulator is used to compensate the inherent power fluctuations (excess or shortage) and to regulate the overall system operation, based on a developed power management strategy. Hydrogen is produced by using system excess power in a proton exchange membrane (PEM) electrolyzer and is further stored in pressurized cylinders for subsequent use in a PEM fuel cell in cases of power shortage. A diesel generator complements the integrated system and is employed only in emergency cases, such as subsystems failure. The performance of the automatic control system is evaluated through the real-time operation of the power system where data from the various subsystems are recorded and analyzed using a supervised data acquisition unit. Various network protocols were used to integrate the system devices into one central control system managing in this way to compensate for the differences between chemical and electrical subunits. One of the main advantages is the ability of process monitoring from distance where users can perform changes to system principal variables. Furthermore, the performance of the implemented power management strategy is evaluated through simulated scenarios by including a case study analysis on system abilities to meet higher than expected electrical load demands.