电能系统中的增能技术

介绍了直流增能技术的基本原理、先进性和经济性。叙述了最新研发的虚拟六相整流器,通过检测表明,增能增效潜力十分明显,而且实测效率高于三相桥式整流器。随着智能电网、微电网的兴起,特高压直流输电的启运,原先受直流电网发电机转速和频率约束的屏障,有可能被交流增能技术突破,从而进一步提高电能转化效率和提升设备运转效益。也就是说,不管是燃煤发电、水能发电、核能发电还是风能发电,都可以采用交流增能技术或者直流增能技术的不同相关技术,结合现有的发电、变电、输电先进技术产品来提高电力系统的输出功率和效率。     

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.     

On the ability of pem water electrolysers to provide power grid services

Water electrolysis is considered as a cornerstone technology for the large scale storage of energy and for carbon abatements in the frame of the energy transition. The purpose of this research work was to analyze power grid operational constraints, to design specific load profiles of interest for power grid management and then to use these protocols for the characterization and qualification of polymer electrolyte membrane (PEM) water electrolysers in view of grid balancing services. In the first section, management constraints of European power grids are described and analyzed. Using a typical regulation mechanism as an illustrative example, power specifications for primary and secondary reserve management are specified. The economics of such management procedures is also analyzed. In the second section, some key technical characteristics of PEM water electrolysis stacks are described. Test specifications designed for the qualification of water electrolysers to both primary and secondary reserve markets are defined. In the last section, selected test results are reported and the ability of PEM water electrolysis stacks to provide the services of interest is analyzed. In particular, a set of key performance indicators, designed for the characterization of PEM water electrolysers operating in transient power conditions of interest for grid services, are defined. Test results show the ability of PEM water electrolysis stacks to satisfy the most stringent grid constraints, but remaining limitations are identified. The main innovative contributions of this research work were to design test protocols for both primary and secondary power reserves management, and to demonstrate that PEM water electrolysers can be used for such applications.     

Design and implementation of Type-2 fuzzy neural system controller for PWM rectifiers

It is necessary to convert AC to DC for the systems that do not work with AC sources. For this reason, diode and thyristor rectifiers were developed and designed. However, these rectifiers are not well suited for industrial applications requiring high performance. With the advances in power electronics and semiconductor technology, Pulse width modulation (PWM) rectifiers have been successfully employed in various industrial applications including variable-speed drives and uninterruptible power supplies. PWM rectifiers have the advantages of being low input current harmonic, adjustable input power factor, and controllable DC voltage and bidirectional energy flow. Because of all these features of the PWM rectifiers, the control and design of these rectifiers are very important topic. The aim of this paper is to control DC-link voltage of PWM rectifier with type-2 fuzzy neural system (T2FNS) instead of PI controller. For this aim, three-phase PWM rectifier with proposed controller is designed and simulated for four scenarios in this paper. A simulation model of the PWM rectifier is designed in MATLAB/Simulink and the performance of PWM rectifier with proposed controller is analyzed.     

AC/DC power conversion interface for self-excited induction generator

A new AC/DC power conversion interface for the self-excited induction generator (SEIG) is proposed here. The proposed AC/DC conversion interface includes an excitation systemand a diode rectifier connected in parallel.The variable frequency AC power generated by the SEIG is converted into DC power by the diode rectifier.The DC power of the diode rectifier can charge a battery set and supply DC loads or be further converted into fixed-frequency AC power by an inverter for AC loads.The DC voltage is expected to be regulated in the above applications.The excitation system supplies an exciting reactive current to maintain the amplitude of the SEIG output voltage to be a constant value. Moreover, it can also serve as an active power filter to suppress the harmonic current generated by the diode rectifier. The excitation system is composed of an AC power capacitor and a power converter connected in series. The AC power capacitor is adapted to provide a basic reactive power, and it can also reduce the voltage rating and the capacity of the power converter. The salient point of the proposed AC/DC power conversion interface is that the capacity of the power converter in the AC/DC power conversion interface can be minimised, and the power loss of the AC/DC power conversion interface can also be reduced. A prototype is developed and tested to verify the performance of the proposed AC/DC power conversion interface.     

交流励磁用LCL滤波的PWM整流器的研究

提出了采用LCL拓扑的滤波器来减少PWM调制导致的交流电流中的高次谐波的方案,对LCL滤波的三相电压型PWM整流器电路拓扑进行了分析,给出了LCL滤波器及LCL滤波的三相电压型PWM整流器的数学模型.采用了电压电流双闭环控制策略,对电压电流环的设计作了介绍.为了提高系统的稳定性,采取了电容串联电阻的方式.仿真结果表明,LCL滤波的整流器要比纯电感滤波器在滤除高次谐波方面效果好得多.仿真结果验证理论分析的正确性.     

Projecting the future cost of PEM and alkaline water electrolysers; a CAPEX model including electrolyser plant size and technology development

The investment costs of water electrolysis represent one key challenge for the realisation of renewable hydrogen-based energy systems. This work presents a technology cost assessment and outlook towards 2030 for alkaline electrolysers (AEL) and PEM electrolysers (PEMEL) in the MW to GW range taking into consideration the effects of plant size and expected technology developments. Critical selected data was fitted to a modified power law to describe the cost of an electrolyser plant based on the overall capacity and a learning/technology development rate to derive cost estimations for different PEMEL and AEL plant capacities towards 2030. The analysis predicts that the CAPEX gap between AEL and PEMEL technologies will decrease significantly towards 2030 with plant size until 1–10 MW range. Beyond this, only marginal cost reductions can be expected with CAPEX values approaching 320–400 $/kW for large scale (greater than 100 MW) plants by 2030 with subsequent cost reductions possible. Learning rates for electrolysers were estimated at 25–30% for both AEL and PEMEL, which are significantly higher than the learning rates reported in previous literature.     

Non-isolated multiphase boost converter for a fuel cell with battery backup power system

This work describes a step-up non-isolated DC/DC converter aimed for fuel cell stand-alone power systems. The proposed converter has the following features: simple structure based on the basic boost topology that reduces the number of components; it uses the interleaving technique in order to reduce the current ripple at the input and output sides, reduction of the inductors size, higher frequency that reduce the output filter capacitor and easier power losses management. In addition, the use of an inner current control loop in the input side assures power sharing and easy module parallelization. The converter feeds a backup battery that maintains a DC voltage level at the main bus. An outer battery-charging loop controls the converter. Experimental validation is given for a four-phases 1 kW prototype at 100 kHz PWM switching frequency connected to a Nexa Ballard (1.2 kW-46 A) PEM fuel cell.     

Apparatus for supplying an isolated DC load from a variable-speedself-excited induction generator

This paper describes the design and laboratory testing of novel generation apparatus for supplying an isolated DC load from a self-excited induction generator operable at variable speed. The variable-speed generating apparatus consists of a self-excited induction machine, a controlled Graetz bridge rectifier, a voltage-boost power converter, and a control system. The induction generator supplies the rectifier. The voltage-boost power converter interfaces the variable output voltage of the rectifier to the fixed DC voltage required for the load. The rectifier is operated at levels of average DC current and voltage which control machine voltage to the rated AC voltage and which also draw the necessary power to supply the DC load. Performance is enhanced with respect to earlier apparatus in that both the DC voltage supplied to the load and the AC voltage on the machine are simultaneously controlled to fixed reference levels over broad operating ranges of load and speed     

Influence of the power supply on the energy efficiency of an alkaline water electrolyser

Electric energy consumption represents the greatest part of the cost of the hydrogen produced by water electrolysis. An effort is being carried out to reduce this electric consumption and improve the global efficiency of commercial electrolysers. Whereas relevant progresses are being achieved in cell stack configurations and electrodes performance, there are practically no studies on the effect of the electric power supply topology on the electrolyser energy efficiency. This paper presents an analysis on the energy consumption and efficiency of a 1 N m³ h⁻¹ commercial alkaline water electrolyser and their dependence on the power supply topology. The different topologies of power supplies are first summarised, analysed and classified into two groups: thyristor-based (ThPS) and transistor-based power supplies (TrPS). An Electrolyser Power Supply Emulator (EPSE) is then designed, developed and satisfactorily validated by means of simulation and experimental tests. With the EPSE, the electrolyser is characterised both obtaining its I–V curves for different temperatures and measuring the useful hydrogen production. The electrolyser is then supplied by means of two different emulated electric profiles that are characteristic of typical ThPS and TrPS. Results show that the cell stack energy consumption is up to 495 W h N m⁻³ lower when it is supplied by the TrPS, which means 10% greater in terms of efficiency.     

Management of excess energy in a photovoltaic/grid system by production of clean hydrogen

In this article, the authors design a new clean storage device for a photovoltaic system (PV) reinforced by the electrical grid. The photovoltaic system supplies power to a DC load. When the power of the photovoltaic source is insufficient, the electrical grid compensates the energy deficit. On the other hand, if the load is satisfied and the PV source is still able of supplying energy, the energy excess is diverted to an own storage unit materialized by an electrolysis which produces gaseous hydrogen by the process of electrolysis of water. The authors show that the quantity of hydrogen produced is proportional to the photovoltaic energy excess and also to the flow of water injected into the electrolysis. In this case, it is a question of designing an electrolysis with specific characteristics, which takes into account the quantity of energy excess and the flow of water injected into it. The authors abandon the idea of controlling the water flow by means of a pumping-electrovalve system, and initiate the idea of replacing the function of the pump by the action of gravity. The work focuses on the development of an electrolysis optimization approach using the water flow control in its alliance with the PV power excess which is also maximized. For an optimized use of the global system (load and electrolysis), the authors present an architecture based on energy-converting structures (DC/DC and AC/DC). In addition, to increase the reliability and safety of the system, the authors finish by developing a power management strategy (PMS) in the designed system. This power management strategy organizes the energy flow and selects the appropriate path of this flow between the two energy sources (PV and electrical grid) and the two possible energy receivers (load and electrolysis). A complete modeling of the system is developed in the Matlab/Simulink environment. The simulation results show that the hybrid system (PV and electrical grid) is able to permanently supplying the load and potentially storing the excess of the PV energy in the form of hydrogen gas.     

A linear quadratic regulator control of a stand-alone PEM fuel cell power plant

This paper introduces a technique based on linear quadratic regulator (LQR) to control the output voltage at the load point versus load variation from a standalone proton exchange membrane (PEM) fuel cell power plant (FCPP) for a group housing use. The controller modifies the optimal gains k _i by minimizing a cost function, and the phase angle of the AC output voltage to control the active and reactive power output from an FCPP to match the terminal load. The control actions are based on feedback signals from the terminal load, output voltage and fuel cell feedback current. The topology chosen for the simulation consists of a 45 kW proton exchange membrane fuel cell (PEMFC), boost type DC/DC converter, a three-phase DC/AC inverter followed by an LC filter. Simulation results show that the proposed control strategy operated at low commutation frequency (2 kHz) offers good performances versus load variations with low total harmonic distortions (THD), which is very useful for high power applications.     

A comprehensive review on PEM water electrolysis

Hydrogen is often considered the best means by which to store energy coming from renewable and intermittent power sources. With the growing capacity of localized renewable energy sources surpassing the gigawatt range, a storage system of equal magnitude is required. PEM electrolysis provides a sustainable solution for the production of hydrogen, and is well suited to couple with energy sources such as wind and solar. However, due to low demand in electrolytic hydrogen in the last century, little research has been done on PEM electrolysis with many challenges still unexplored. The ever increasing desire for green energy has rekindled the interest on PEM electrolysis, thus the compilation and recovery of past research and developments is important and necessary. In this review, PEM water electrolysis is comprehensively highlighted and discussed. The challenges new and old related to electrocatalysts, solid electrolyte, current collectors, separator plates and modeling efforts will also be addressed. The main message is to clearly set the state-of-the-art for the PEM electrolysis technology, be insightful of the research that is already done and the challenges that still exist. This information will provide several future research directions and a road map in order to aid scientists in establishing PEM electrolysis as a commercially viable hydrogen production solution.     

Failure of PEM water electrolysis cells: Case study involving anode dissolution and membrane thinning

Polymer electrolyte membrane (PEM) water electrolysis is an efficient and environmental friendly method that can be used for the production of molecular hydrogen of electrolytic grade using zero-carbon power sources such as renewable and nuclear. However, market applications are asking for cost reduction and performances improvement. This can be achieved by increasing operating current density and lifetime of operation. Concerning performance, safety, reliability and durability issues, the membrane-electrode assembly (MEA) is the weakest cell component. Most performance losses and most accidents occurring during PEM water electrolysis are usually due to the MEA. The purpose of this communication is to report on some specific degradation mechanisms that have been identified as a potential source of performance loss and membrane failure. An accelerated degradation test has been performed on a MEA by applying galvanostatic pulses. Platinum has been used as electrocatalyst at both anode and cathode in order to accelerate degradation rate by maintaining higher cell voltage and higher anodic potential that otherwise would have occurred if conventional Ir/IrO_x catalysts had been used. Experimental evidence of degradation mechanisms have been obtained by post-mortem analysis of the MEA using microscopy and chemical analysis. Details of these degradation processes are presented and discussed.     

A critical review on cathode materials for steam electrolysis in solid oxide electrolysis

The major technologies being considered for the green hydrogen production are polymer electrolyte membrane (PEM) and solid oxide electrolysis (SOE). While PEM electrolysis technology is nearing commercialisation with units now being globally installed at tens of MW scale, SOE technology is still under development with units available only at 100s of kW scale and at much higher costs per kW. SOE due to its high operating temperatures (close to 800 °C) has the potential to reduce the electric energy input by up to 30% for the hydrogen production per tonne by using the low-cost thermal energy input available from the industrial or downstream synthesis processes. The SOE cathode, where steam electrolysis occurs, plays a crucial role in dictating the cell voltage losses and the stability of the cell operation that eventually has a large impact on the SOE efficiency and lifetime. The current state-of-the-art cathode materials based on Ni-YSZ pose many challenges. There is, therefore, a global effort to find alternative cathode materials suitable for steam electrolysis in SOE. This review critically reviews novel nanoengineered cathode materials and points to the fact that such materials synthesized using infiltration and exsolution techniques, in combination with advanced materials characterisation like high-temperature scanning probe microscopy and in situ Raman spectroscopy can be a right approach to find the suitable cathode materials for steam electrolysis in SOE. This, however, may need to be combined with a techno-economic analysis to provide the technical and economic viability of these materials for the SOE commercialisation.     

Adaptive fuzzy control with an optimization by using genetic algorithms for grid connected a hybrid photovoltaic–hydrogen generation system

The integration of significant amounts of renewable-storage hybrid power generation systems to the electric grid poses a unique set of challenges to utilities and system operators. This article deals with the designing methodology of an intelligent control based grid-connected a hybrid system composed of renewable energy source (RES) and storage system (SS). RES is a photovoltaic (PV) source and SS is a process of hydrogen transformation system (H₂TS) which composed of alkaline water electrolysis (AWE) for decomposition water by using the PV power, a tank used for gas storage and a proton exchange membrane (PEM) fuel cell (FC) to transform the H₂ to the electrical energy. The interconnection of the grid with the power generation system (PGS) is ensured through using a DC/AC hysteresis converter and it can synchronize current with the grid voltage among an independent control of active (P) and reactive (Q) power through a possibility of the Q compensation. In the proposed system, three algorithms are applied; two used inside generation and the third is used inside the grid. Perturb and observe (P&O) maximum power point tracking (MPPT) control algorithm always finds optimal power in the PV generator. A simple cascade controls loop of DC-DC boost converter and operate the FC generator to ensure maximum power and to regulate the DC Bus voltage. In addition, adaptive fuzzy logic control (FLC) unit is developed to control the DC/AC inverter, with adopting an off-line optimization based on genetic algorithms (GAs) applauded for tune different issues as scaling factors of the FLC and PIDs gains of the PV and the H₂TS control loops. Simulated results prove a big success of the proposed controls of the grid connected the hybrid PV-H₂TS with good performance.     

PWM整流器在变速恒频风力发电系统中的应用

变速恒频风力发电系统要求励磁电源有良好的输入、输出特性和能量双向流动的能力.交-直-交双PWM变频器是理想的励磁电源,而PWM整流器是其中一项关键技术.文章从三相电压型PWM整流器主电路拓扑结构出发,建立了基于三相静止坐标系和两相同步旋转坐标系的数学模型.阐述了电压、电流双闭环控制的基本原理和空间矢量脉宽调制技术在三相PWM整流器中的应用.在Matlab/Simulink环境下,对其进行了单位功率因数整流和逆变的仿真研究.结果证明,该整流器是满足交流励磁需要的理想整流电源.     

Simplified model for evaluating ripple effects on commercial PEM fuel cell

In this paper a simple model for evaluating current ripple effects on commercial PEM fuel cells is presented. The model is formulated starting from the Randles equivalent circuit and extending it assuming a dielectric relaxation of the material to represent dynamic processes in the frequency range typical of inverter current ripple. The proposed equivalent circuit is experimentally validated on a 14 kW commercial Morphic PEM fuel cell at the frequencies of interest. Finally the effects of current ripple on losses and fuel cell efficiency are discussed.     

考虑风电不确定性的交直流混联系统同质化能量函数模型

交直流混联电网是电网发展的新形态,如何有效保障交直流混联系统安稳运行是重大而紧迫的国家需求。文章针对含大规模风电的交直流混联系统稳定性问题,提出考虑风电波动不确定性的交直流混联弱送端系统同质化能量函数模型。首先,研究含大规模风电的交直流混联弱送端系统潮流方程;其次,建立含风电的交直流混联系统支路暂态势能函数模型,研究交直流混联系统功角稳定机理,建立基于同质化能量函数模型;在此基础上,提出基于同质化能量函数的电力系统稳定性评估模型,并推导交直流混联系统稳定性判据;最后,以北方某区域交直流混联系统为仿真算例,验证所提模型的有效性,为含大规模新能源的交直流混联系统的稳定性控制提供理论依据。     

浮式风电制氢装置设计研究

对浮式风电制氢装置工程化进行了研究,并基于8～10 MW的浮式风电平台,设计了3MW独立式风电制氢装置,制定了利用风机发电提供的能源,提取海水进行纯化和电解水制氢的技术路线,提出了关键设备的技术要求,并进行了系统的布置及初步的安全性和经济性分析。结果表明,由于经济性差,海工应用还不成熟,目前海上浮式制氢的工程化还需要一个过程,进行工程试验是大规模工程化的前提。