Power and energy management of grid/PEMFC/battery/supercapacitor hybrid power sources for UPS applications

This paper presents a hybrid power and energy source supplied by a proton exchange membrane fuel cell (PEMFC) as the main power source in an uninterruptible power supply (UPS) system. To prevent the PEMFC from fuel starvation and degradation and realize their seamless linking in the hybrid UPS system, the power and energy are balanced by the battery and/or supercapacitor (SC) as two alternative auxiliary power sources. Based on the modeling and sizing of hybrid power and energy components, the power and energy management strategies and efficiency measurements of four operating modes in UPS system are proposed. To evaluate the proposed strategies, an experimental setup is implemented by a data acquisition system, a PEMFC generating system, and a UPS system including AC/DC rectifier, DC/AC inverter, DC/DC converter, AC/DC recharger and its intelligent control unit. Experimental results with the characteristics of a 300 W self-humidified air-breathing of PEMFC, 3-cell 12 V/5 Ah of batteries, and two 16-cell 120 F/2.7 V of SCs in parallel corroborate the excellent management strategies in the four operating modes of UPS system, which provides the basis for the optimal design of the UPS system with hybrid PEMFC/battery/SC power sources.     

Control of cyclic fluctuations in an independent microgrid by an SOFC triple combined cycle inertia system

Technology was investigated to control cyclic fluctuations in an independent microgrid powered with unstable renewable energy by use of a solid oxide fuel cell (SOFC, 1 MW) in a triple combined cycle (SOFC-TCC) that included a gas turbine (G/T, 0.8 MW) and a steam turbine (S/T, 0.2 MW). A large-scale solar power system (0.8 MW) and a wind farm (0.8 MW) were interconnected with the electrical power network through an inverter. The cyclic fluctuations ingredient of the network was controlled by a suitably designed inertia system and by governor-free control of the G/T and S/T. The SOFC-TCC’s control block diagram was submitted to MATLAB/Simulink R 2013a, and the deviation of electrical power and frequency in the independent microgrid caused by the SOFC-TCC and renewable energy interconnection was clarified. As a result, a range of suitable inertial constants for G/T and S/T and the electrical output characteristics were determined. Selecting a small inertial constant for the simulation resulted in a large frequency deviation of G/T and S/T, with frequency stabilized for a short time. On the other hand, selecting a large inertial constant resulted in a controlled frequency deviation, although the unstable frequency of the power grid continued for a long time.     

Kirkuk municipal waste to electrical energy

Municipal solid waste (MSW) in Kirkuk city in the north of Iraq poses a serious problem having adverse effects on environment and health of the citizens. Both quantity and volume of MSW have continued to increase with the rapid growth of city population. The population of Kirkuk city, on average, has increased by 3% per annum over the past two decades. The population of Kirkuk city is predicted to increase from 1,050,000 in 2008 to 1,445,556 in 2020. The generation of waste is expected to grow in the future with the rise of city population. The daily waste generation is projected to 1000 tone in 2011. By 2021, the daily waste will amount to 1200 tones. The waste to electricity suggested project in Kirkuk and the choice of electricity generation technology, would lead to improved electricity supply and efficient waste management in the city, and is expected to contribute to technology transfer in this new area. Landfill or Biodigestor technology seems to be the most preferred technology for Kirkuk city to start with. Potential power for a plant sourcing from the MSW mass to be fed into the national grid was estimated at 5 MW.Equivalent CO₂ emission in the absence of waste to electrical energy project and the emission by proposed project were calculated. The reduction in CO₂ emission is 87.4%.     

Effect of varying concentration and temperature on steady and dynamic parameters of low concentration photovoltaic energy system

Low-concentration photovoltaic (LCPV) system has huge potential for further cost reduction of solar photovoltaic (PV) power as compared to flat panel PV. The dependence of steady state and dynamic parameters on concentration and temperature is crucial to extract maximum power from solar photovoltaic system. This article aims to present the effect of varying concentration and temperature on steady state and dynamic parameters of LCPV system under actual test conditions (ATC). The rate of change in I_SC with solar irradiation i.e., dI_SC/dG is found as 0.25 A/W assuming ≈±1 °C change in module temperature. The effect of temperature on inherent material properties responsible for photo-conversion efficiency is studied using impedance spectroscopy technique. A linear response of series resistance of LCPV module is observed with respect to change in module temperature, i.e. dR_S/dT from 297 to 333 K is in the range of 1.15–1.20 Ω with a rate of 1 mΩ/K. From real-time analysis of LCPV system open-circuit voltage found decreasing from 21 to 20.6 V with temperature coefficient of voltage ≈−0.061 V/K. The dynamic resistance has a positive coefficient of module temperature i.e., dr_d/dT given by 0.49 Ω/K.     

Performance of printable supercapacitors in an RF energy harvesting circuit

We report the fabrication of a supercapacitor on a plastic substrate with mass-production-compatible methods and its characterisation using galvanostatic and voltammetric methods. The supercapacitor is prepared in ambient conditions using activated carbon and an aqueous, non-acidic electrolyte. The obtained capacitances are 0.45 F and 0.21 F for device sizes of 4 cm² and 2 cm², respectively. Additionally, we demonstrate the utilisation of the supercapacitor in an autonomous energy harvesting and storage system. The RF energy harvester comprises a printed loop antenna and a half-wave organic diode rectifier operating at 13.56 MHz frequency. The harvested energy is stored in two supercapacitors connected in series to increase the maximum operating voltage. In order to power a device such as a sensor or a small indicator display, voltage regulation is needed. A voltage regulator, implemented as an application specific integrated circuit (ASIC), was designed for this purpose, and fabricated commercially. We demonstrate the ability of the harvester storage unit to power the regulator for hours with a constant regulator output voltage and power. The effect of supercapacitor charging time on the actual supercapacitor charging state is also discussed, as a slower charging rate is found to have a significant effect on the output of the supercapacitor.     

Nonlinear intelligent DC grid stabilization for fuel cell vehicle applications with a supercapacitor storage device

This paper presents an intelligent DC link control using a fuzzy logic controller based on the differential flatness control theory for hybrid vehicle applications supplied by a fuel cell (FC) (main source) and a supercapacitor (auxiliary source). The energy in the system is balanced by dc bus energy stabilization (or indirect voltage regulation). A supercapacitor module functions by supplying energy to regulate the dc bus energy. The FC, as a slow dynamic source in this system, supplies energy to the supercapacitor module to maintain its charge. The FC converter combines four-phase parallel boost converters with interleaving, and the supercapacitor converter employs four-phase parallel bidirectional converters with interleaving. These two converters are called a multi-segment converter for high power applications. Because the model of the power switching converters is nonlinear, it is preferable to apply model-based nonlinear control strategies that directly compensate for the nonlinearity of the system without requiring a linear approximation. Using the intelligent fuzzy control law based on the flatness property, we propose straightforward solutions to hybrid energy management and to the dynamic and regulation problems. To validate the proposed method, a hardware system is developed with analogue circuits, and a numerical calculation is generated with a dSPACE controller DS1104. Experimental results for a small-scale power plant (a polymer electrolyte membrane FC (PEMFC) of 1200 W and 46 A with a supercapacitor module of 100 F, 500 A, and 32 V) in the laboratory corroborate the excellent performance of this control scheme during vehicle motor drive cycles.     

System wide MV distribution network technical losses estimation based on reference feeder and energy flow model

This paper presents an integrated analytical approach to estimate technical losses (TL) of medium voltage (MV) distribution network. The concept of energy flow in a radial MV distribution network is modelled using representative feeders (RF) characterized by feeder peak power demand, feeder length, load distribution, and load factor to develop the generic analytical TL equations. The TL estimation approach is applied to typical utility MV distribution network equipped with energy meters at transmission/distribution interface substation (TDIS) which register monthly inflow energy and peak power demand to the distribution networks. Additional input parameters for the TL estimation are from the feeder ammeters of the outgoing primary and secondary MV feeders. The developed models have been demonstrated through case study performed on a utility MV distribution network supplied from grid source through a TDIS with a registered total maximum demand of 44.9 MW, connected to four (4) 33 kV feeders, four (4) 33/11 kV 30 MVA transformers, and twelve (12) 11 kV feeders. The result shows close agreement with TL provided by the local power utility company. With RF, the approach could be extended and applied to estimate TL of any radial MV distribution network of different sizes and demography.     

3-Phase 4-leg unified series–parallel active filter system with ultracapacitor energy storage for unbalanced voltage sag mitigation

This paper presents the analysis and design of a 3-phase 4-leg (3P4L) unified series–parallel active filter (USPAF) with ultracapacitor energy storage (UCES) for improving the power quality in three-phase four-wire (3P4W) distribution system. The series and parallel active filter (AF) of 3P4L USPAF system are realized by four-leg voltage source inverters (VSIs) to a common dc-link capacitor. Due to its high power density, the UCES is well-suited to supply high power for short period of time. The objective of this paper is to enhance the unbalanced voltage sag mitigating capability of the 3P4L USPAF system by adding UCES, directly connected in the dc-link. This is achieved by injecting energy from the UCES to maintain the dc-link voltage constant. Thus, the proposed system is capable of mitigating unbalanced voltage sag with zero-sequence component in the source voltage and compensating harmonic, reactive power and unbalanced current of the load in 3P4W distribution systems. The proposed scheme is validated by an experimental prototype with a 1.93 F UCES bank and using dSPACE DS1103 real-time control platform in the laboratory. The experimental results show that the combined system offer improved performance to maintain the load voltage constant at its rated value during unbalanced voltage sag in the supply voltage.     

Integration of compressed air energy storage systems co-located with wind resources in the ERCOT transmission system

In this paper, we investigate optimal locations and capacity for integrating storage systems in the electric transmission grid to improve wind power production. The impacts on wind power production and conventional thermal generation due to operation of utility-scale storage systems are simulated. A compressed air energy storage (CAES) is chosen as an utility-scale storage technology, which can provide several hundred MWs of electric power. A mixed integer programming (MIP) is implemented for the mathematical formulation. The Electric Reliability Council of Texas (ERCOT) wind, load data and its simplified transmission system are used for a case study. To mandate wind power production, we apply 20% goal for renewable portfolio standard (RPS). Operation of 1350 MW CAESs improves wind power production and RPS target achievements, however, thermal generation does not significantly decrease under the given simulation condition.     

Improving power quality of wind energy conversion system with unconventional power electronic interface

The increasing interest to utilize wind energy as a power source prompted more researches to be dedicated to the unconventional integration of this power source into the current grid. In this paper, one avenue to achieve this efficient utilization, through the use of integrated wind energy conversion system (WECS) using doubly fed induction generator (DFIG) is presented. Wind grid integration brings the problems of voltage fluctuation and harmonic distortion. This paper presents an Unconventional Power Electronic Interface (UPEI) to reduce the total harmonic distortion (THD) and enhance power quality during disturbances. The models used in the paper includes a pitch-angled controlled wind turbine model, a DFIG model, power system model and an UPEI having controlled converters. A phase to phase fault is simulated on 132 kV bus and the measured results obtained from grid connection of the wind generation system are presented. The results have demonstrated the ability of UPEI to regulate pitch angle, VAR and to reduce THD. The proposed system increases the effectiveness of the utilization of wind energy.     

Energy management strategy for fuel cell/battery/ultracapacitor hybrid vehicle based on fuzzy logic

In order to enhance the fuel economy of hybrid vehicle and increase the mileage of continuation of journey, a fuzzy logic control is utilized to design energy management strategies for fuel cell/battery (FC + B) hybrid vehicle and fuel cell/battery/ultra-capacitor (FC + B + UC) hybrid vehicle. The models of hybrid vehicle for FC + B and FC + B + UC structure are developed by electric vehicle simulation software ADVISOR which uses a hybrid backward/forward approach. The results demonstrate that the proposed control strategy can satisfy the power requirement for four standard driving cycles and achieve the power distribution among various power sources. The comprehensive comparisons with the power tracking control strategy which is wide adopted in ADVISOR verify that the proposed control strategy has better rationality and validity in terms of fuel economy and dynamic property in four standard driving cycles. Therefore, the proposed strategy will provide a novel approach for the advanced energy management system of hybrid vehicle.     

Scheduling and control framework for distribution-level systems containing multiple energy carrier systems: Theoretical approach and illustrative example

Traditional optimization and control techniques are no longer suitable to account for the interactions introduced by new technologies like combined heat and power units (CHP) and renewable sources. In this paper a general optimization framework and a hierarchical control architecture are presented for systems with multiple energy carriers, i.e. electricity, heat, gas, etc. The proposed framework is based on the energy hub approach and is an extension of previous research done in this field.Two-level architectures can be adjusted to fulfill the needs of future power systems, where there will be a higher participation of decentralized generation. Nevertheless, the papers generally focus exclusively on electricity flows, even when they include cogeneration units like fuel cells. For this reason the contribution of this paper is to propose a two-level control strategy that can be applied in systems with multiple energy carriers and to provide an illustrative example in which the results of using the strategy can be observed. The complete framework presented in this paper consists of an optimization algorithm and a real-time control algorithm. The optimization algorithm indicates when to turn on and turn off a generation unit and how much power it should deliver at a certain time period. The optimization is done for a forecasted period of 24 h and the real-time control strategy runs continuously to compensate for the mismatches between the scheduled load and the real load by means of control actions.     

太阳能电源热源一体化系统的设计与开发

从外观结构、能量流向及控制电路等方面设计了太阳能电源热源一体化系统。本系统具有可移动性,配备了滚轮且模拟光源可拆卸,可以在室外工作,在没有任何外接电源的情况下进行太阳能的相关应用。本系统结合了太阳能发电和太阳能发热两方面的技术,其中太阳能电源部分用于为自身供电并可对外输出电能,太阳能热源部分用于产生热能。通过实验测试结果可知,本系统每年可产生691kWh的电能和3047.8kWh的热能。本系统由于可移动且不需外接电源等特点,可满足偏远地区或孤岛等无电网地区的日常生活对热水与电力的需求,也可用于太阳能方面的实验测试。     

Experimental analysis of a solar PV/diesel hybrid system without storage: Focus on its dynamic behavior

Integration of solar photovoltaic systems with diesel generators for the electrification of remote and rural areas would assist in expanding the electricity access in the sub-Saharan Africa region. In fact, countries of this region are well endowed in solar resource: their mean daily solar radiation exceeds 5.5 kWh/m²/day. They are, therefore, good locations for PV systems. This paper deals with an experimental study of the dynamic behavior of a hybrid system prototype (based on “flexy-energy” concept) set up at Kamboinsé, located at 15 km far from Ouagadougou (12, 22° N and 1, 31° W) in Burkina Faso. The prototype is composed of a 2.85 kWp PV array, a 3.3 kW single phase inverter and a diesel generator rated at 9.2 kW. Two resistive load banks of about 4 kW each are used to simulate the load profiles. Experimental results show that the PV generation leads the distribution feeder to shift toward higher voltages. The voltage rise is exacerbated when the PV generation is at its highest and the demand at its lowest. Care should then be taken to ensure that for a hybrid PV/diesel system, the PV rated power connected to each phase of the diesel generator is as equal as possible. The present study also points out that “well designed” inverters generate very small voltage harmonics and current distortions, even when high PV penetration systems are considered.     

A new optimal unified power flow controller placement and load shedding coordination approach using the Hybrid Imperialist Competitive Algorithm-Pattern Search method for voltage collapse prevention in power system

As power systems become more complex and heavily loaded, voltage collapse has become one of the most destructive events in modern power systems leading to blackouts in electric utilities worldwide. Voltage collapse is mainly caused by operating power systems at lower stability margins due to a surge in electric power demand. This paper presents an optimal unified power flow controller (UPFC) placement and load shedding coordination approach for voltage collapse prevention in N − K (K = 1, 2 and 3) contingency condition using Hybrid Imperialist Competitive Algorithm-Pattern Search (HICA-PS). ICA is the main optimizer of the proposed algorithm while pattern search is applied to further fine tune the results of the ICA. To show the effectiveness of the proposed approach in preventing voltage collapse in complex power systems, we implemented it on the New-England 39 bus power system. Its performance was also compared to that of some classical optimization techniques. Decrease in load shedding amounts, continuity of energy supply and voltage collapse prevention is the main positive features of the proposed approach.     

Design and control of LCL filter interfaced grid connected solar photovoltaic (SPV) system using power balance theory

In this paper solar photovoltaic (SPV) system connected to the utility grid is designed and simulated. The utility grid and SPV system are coupled with current controlled voltage source converter (VSC) and LCL filter. The design of LCL filter, MPPT algorithm and power quality improvements are discussed and simulation results are shown for the performance analysis of grid-coupled PV system under different load condition. The system is controlled through power balance theory method. The principle behind the control implementation is to evacuate the solar power generated during the daytime and the reactive power demand for the load should be supplied by the PV. The grid coupled system consists of SPV system, dc–dc boost converter, maximum power point tracking (MPPT), voltage source converter (VSC), LCL filter, different loads and three phase utility grid. This system is capable of eliminating harmonic and load balancing by supplying unbalanced current from the PV as a compensator. The system is simulated with 10 kW SPV array using indirect current control scheme.     

Grid integration of single stage SPV-STATCOM using cascaded 7-level VSC

A multi-functional single-stage grid-tied solar photovoltaic (SPV) system with STATCOM (Static Compensator) capabilities using a cascaded three phase seven level voltage source converter (VSC) is presented in this paper. PS-PWM (Phase Shifted Pulse Width Modulation) technique with a low switching frequency (450 Hz) is used to operate the VSC. The proposed SPV-STATCOM system works in three modes i.e. in Mode-1, only active power is supplied to the grid; in Mode-2, both active and reactive powers are supplied to the grid and in Mode-3, only reactive power is supplied to the grid thereby utilizing the proposed system to its fullest capacity in 24 h of a day. To extract the maximum power from the SPV array, the incremental conductance maximum power point tracking scheme is utilized. To synchronize the SPV-STATCOM power to the grid and to maintain power factor close to unity, a decoupled current controller, feed-forward term and positive sequence detector dq phase locked loop (PSD-dqPLL) control approach are used. Lower switching losses, harmonic distortions, high output voltage and power are some of the advantages of using a single-stage 7-level cascaded H-bridges. The design and the control scheme performances in all modes are simulated in MATLAB and validated through real time hardware in loop (HIL) system.     

Robust predictive dual-loop control method based on Lyapunov function stability and energy equilibrium though double-core processors for active power filter

In this paper, a robust predictive dual-loop control method based on Lyapunov function stability and energy equilibrium for active power filter (APF) is proposed to improve the anti-interference performance and self-adaptive capability of system. The proposed control method mainly includes robust predictive current control based on Lyapunov function stability (RPCC-LFS) in the inner current loop and energy equilibrium proportional-integrator (PI) control in the outer dc-link voltage loop. The RPCC-LFS is proposed to enhance self-adaptive capability when the output filter inductors vary, speed up the dynamic response, and improve the tracking accuracy when the loads fluctuate. The energy equilibrium PI controller is proposed to maintain the dc-link voltage stable and suppress the transient impulse. The stability and dynamic response of the proposed control system are analyzed in detail, and the proper control parameters are selected. A specific hardware and software design program based on double-core processors DSP + FPGA is thoroughly given out. Finally, the comparative simulations and experiments verified the validity of the proposed method.     

减碳中多阶段的煤电机组退役与新能源、储能规划协同

规划现役煤电机组的有序退役是电力系统低碳化转型中的关键问题:煤电机组退役会造成发电量缺额和系统灵活性不足的问题,尤其是在新能源占比逐渐增大的条件下,而储能是平衡电力供需、提升供电灵活性的有效技术途径.故应将电力系统规划与未来较长时间内煤电机组逐步退役一同考虑.为此,采用多阶段模型,在电力系统减碳背景下将煤电机组退役协同于新能源和储能规划.基于IEEE 39节点系统验证所提模型的有效性,从机组退役和电力系统减碳2个角度分析规划结果,结果表明通过合理规划新能源和储能能够辅助煤电机组退役的进程,从而实现电力系统低碳化转型.     

Collaborative distributed sun-tracking control system for building integration with minimal plant area and maximum energy-conversion efficiency

This paper presents a collaborative distributed sun-tracking control system for a novel Fixed Mirror Solar Concentrator (FMSC) structure, which increases the energy-conversion efficiency of the FMSC and reduces the space between solar collectors units, a positive aspect for in-building integration. The improved FMSC uses solar concentration collectors suited for mid-range thermal applications (90–200 °C) and is designed for easy installation in buildings because of its relatively small extension. The proposed solar orientation system (ORSYS) relies on a two-step algorithm to increase the energy captured by the receiver, which provides tolerance to common logical and mechanical errors in the estimation of the receiver position. ORSYS is implemented as a CAN-based distributed system, extended with web-interface features for supervision and configuration of the overall system. ORSYS also includes a coordination algorithm that allows adjacent collectors to share the physical space between them, thus reducing the total plant area. Experimental evaluation has been performed using an industrial-scale solar collector prototype, showing its feasibility and efficiency in terms of energy conversion in real environments.