基于两级全钒液流电池的风电储能系统的功率优化分配控制

为更好地利用储能系统平抑风电功率波动,采用了两级全钒液流电池(VRB)储能的功率优化分配及控制策略。基于直驱型永磁同步风电系统的工作原理及系统变流器的控制策略,建立了全钒液流电池等效电路模型,采用基于VRB组荷电状态(SOC)的双模式切换的双闭环控制策略,通过比较每级电池组荷电状态值确定优选目标,以VRB组最大充放电功率为电池组安全充放电的约束条件,提出两级VRB组的功率优化分配控制策略,利用Matlab/Simulink仿真平台,在变风速条件下对不同荷电状态的两级VRB储能系统平抑风电功率波动进行仿真,并与功率平均分配策略作对比。结果表明,两级VRB储能系统功率优化分配控制策略能有效平抑风电机组功率波动,同时,还确保了电池组工作于安全运行区域,有效地减少了VRB组的充放电次数,延长了电池组的寿命。     

风力发电系统输出功率随机波动的仿真分析

针对当前风力发电系统输出功率随机波动的问题,以永磁同步风力发电机(PMSG)与直流侧储能系统(钒氧化还原电池)整合的风力发电系统为基础,进行数字仿真建模,采用MATLAB/Simulink软件对固定负载,变化风速工况;固定风速,负荷瞬变工况;风速和负荷同时变化工况;进行了仿真试验和分析。结果表明,对于采用储能技术的风电场并网功率随机波动的平抑控制,可以利用蓄电池的充放电特性,在风速变化以及负荷瞬变时进行功率平衡的调节。     

An inverter design for a new permanent magnet synchronous generator

Design and simulation of a new inverter scheme are reported in the paper. The inverter is especially developed for an axial flux permanent synchronous generator (AFPMSG), which can be used for low power wind energy systems. The system includes a battery charge unit in addition to the inverter. Initially, the permanent magnet synchronous generator (PMSG) model has been created for MATLAB/Simulink environment. Since frequency and amplitude of the waveforms generated by the PMSG strictly depend on the rotation speed, several tests have been performed under different wind speed regimes. Then, an appropriate inverter model has been designed and connected to the output of the PMSG in order to convert the generated voltage from AC to DC. Thereby, stabilizing voltage and frequency has been assured and the charge of the battery unit has been realized for efficient energy storage. The simulations show that the system designed has lower THD on the current signal according to the similar ones presented in recent literature. Furthermore, the THD value has been much improved (i.e. 0.72%) thanks to the design of an additional filter unit. The proposed system can be implemented to low power wind energy systems.     

Dynamic model of wind energy conversion systems with PMSG-based variable-speed wind turbines for power system studies

In order to study the impact of a wind farm on the dynamics of the power system, a significant issue is to develop appropriate equivalent models that allow characterizing the dynamics of all individual wind turbine generators (WTGs) composing the park. In this sense, with the advance of power electronics, direct-driven permanent magnet synchronous generators (PMSGs) have drawn increased interest to wind turbine manufacturers due to their advantages over other variable-speed WTGs. These include the possibility of multi-pole design with a gearless construction that offers slow speed operation and reduced maintenance since no brushes are used, elimination of the excitation system, full controllability for maximum wind power extraction and grid interface, and easiness in accomplishing fault-ride through and grid support. In this way, this paper presents a comprehensive dynamic equivalent model of a wind farm with direct-driven PMSG wind turbines using full-scale converters and its control scheme. The proposed simplified modelling is developed using the state-space averaging technique and is implemented in the MATLAB/Simulink environment. The dynamic performance of the wind farm and its impact on the power system operation is evaluated using the phasor simulation method.     

面向电网稳定性的智能化直流输电控制系统

为了更好地进行能源调配,我国正开始建设坚强智能电网,直流输电控制系统应实现更多系统层的控制功能。智能电网中的直流输电系统的根本控制目标是保障电网整体的自适应和自愈性。为了实现这一目标,需要从直流输电控制的可观测性入手增加控制观测量,引入合理的集控、协调控制理论作为支撑,完善控制输出环节,实现对电网的有效控制。控制的实时性和决策能力是智能化直流输电控制的核心。从可观性、可控性、实时性、自适应性角度分析,提出了面向电网稳定性的多智能体智能化直流输电控制技术框架,为直流输电系统级控制技术的发展提出了思路。     

Comparison of oscillation damping capability in three power control strategies for PMSG‐based WECS

With the aid of small signal analysis and digital simulations, this paper compares the mechanical and power oscillation damping performances of three power control strategies for the multi‐pole permanent magnetic synchronous generator (PMSG)‐based direct driven wind energy conversion system (WECS). Maximal power point tracking (MPPT) control implemented in the generator side has inherent abilities on the oscillation damping. For the smoothed or constant power requirements, power oscillations are hard to damp, and additional active damping controller is required. Active damping can be achieved with power control on the generator or grid side and DC link voltage control on the generator side. With additional compensator in the power or DC link voltage control loop, a damping torque is produced to suppress the oscillations. An improved control structure, which has inherent oscillation damping capability, is proposed for the power control of WECS. Combined with different power control strategies, this structure can be applied to achieve different power outputs. The validation of the proposed control structure is verified by the simulations. Copyright © 2010 John Wiley & Sons, Ltd.     

Maximum power point tracker of wind energy conversion system

In this paper, a simple control strategy for an optimal extraction of output power from grid connected variable speed wind energy conversion system (WECS) is presented. The system consists of a variable speed wind turbine coupled to a permanent magnet synchronous generator (PMSG) through a gear box, a diode bridge rectifier, a dc-to-dc boost converter and a current controlled voltage source inverter. The maximum power point tracker (MPPT) extracts maximum power from the wind turbine from cut-in to rated wind velocity by sensing only dc link power. The MPPT step and search algorithm in addition to the DC–DC and DC–AC converters PWM controllers are simulated using MATLAB-SIMULINK software. The obtained simulation results show that the objectives of extracting maximum power from the wind and delivering it correctly to the grid are reached.     

Combined operation of DC isolated distribution and PV systems for supplying unbalanced AC loads

This paper describes a DC isolated network which is fed by distributed generation (DG) from photovoltaic (PV) renewable sources to supply unbalanced AC loads. The battery energy storage bank has been connected to the DC network via DC/DC converter called storage converter to control the network voltage and optimize the operation of the PV generation units. The PV units are connected to the DC network via its own DC/DC converter called PV converter to ensure the required power flow. The unbalanced AC loads are connected to the DC network via its own DC/AC converter called load converter without transformer. This paper proposes a novel control strategy for storage converter which has a DC voltage droop regulator. Also a novel control system based on Clarke and Park rotating frame has been proposed for load converters. In this paper, the proposed operation method is demonstrated by simulation of power transfer between PV units, unbalanced AC loads and battery units. The simulation results based on PSCAD/EMTDC software show that DC isolated distribution system including PV units can provide the balanced voltages to supply unbalanced AC loads.     

Distributed control of a user-on-demand renewable-energy power-source system using battery and hydrogen hybrid energy-storage devices

A user-on-demand power source based on renewable energy requires storage devices to balance power sources and power demands because of the fluctuation of power sources like solar cells or wind power generators. The role of the control system is defined as two different tasks: allowing a power-flow imbalance between demand and power sources; and balancing the power flow inside the system. Since this control is complicated, many control methods using precise calculation of the power balance have been proposed. An analogue-like distributed control method - named “modified DC-bus signalling” - for controlling a renewable-energy power source without the need for a central processing unit is proposed. The modified DC bus signalling method discussed in this paper is composed of a DC-bus line connected with a battery, water-splitting electrochemical cell, and a fuel cell for hydrogen-energy storage via converters. The proposed control method was demonstrated to be able to control step-like and random changes in input and output power. The battery compensated high-frequency fluctuations in power demand, and the electrochemical cell and fuel cell handled the remaining low-frequency ones, which were matched to their response speeds.     

Investigation of maximum wind power extraction using adaptive virtual lookup‐table approach

With the advance of power electronic technology, direct‐driven permanent magnet synchronous generators (PMSG) have increasingly drawn interests to wind turbine manufacturers. Unlike a fixed‐speed wind turbine, the maximum power extraction of a PMSG wind turbine is affected by (1) electrical characteristics of the generator, (2) aerodynamic characteristics of the turbine blades, and (3) maximum power extraction strategies. In an environment integrating all the three characteristics, it is found in this paper that the existing commercial lookup‐table maximum power extraction mechanism suitable to a DFIG wind turbine is not suitable to a PMSG wind turbine. Through the integrative study of all the three characteristics, this paper proposes a novel PMSG maximum power extraction design. The special features of the proposed strategy include (i) an adaptive virtual lookup‐table approach for PMSG maximum power extraction and (ii) an implementation of the peak power‐tracking scheme based on a novel direct‐current vector control configuration. The proposed maximum power extraction mechanism with a nested speed‐ and current‐loop control structure is built by using MatLab SimPowerSystems. Simulation studies demonstrate that the proposed PMSG peak power‐tracking strategy has superior performance in various aspects under both stable and gust wind conditions. Copyright © 2010 John Wiley & Sons, Ltd.     

基于线性自抗扰和变分模态分解的混合储能控制策略

风力发电具有随机性和波动性的特点,可通过引入储能技术减少其直接并网对电力系统造成的影响,因此基于超导磁储能和蓄电池储能系统之间的互补关系,提出一种基于线性自抗扰和变分模态分解的混合储能控制策略。针对传统混合储能变流器多变量、非线性及强耦合的特点,在装置层建立了混合储能系统的数学模型,基于跟踪微分器、线性扩张状态观测器及线性误差反馈律三部分,设计了混合储能系统的交、直流侧线性自抗扰控制器;其次,为了更加合理地平抑风电功率波动,避免经验模态分解时出现的模态混叠问题,在系统层提出了变分模态分解的功率分配方法;最后通过仿真验证了方法的可行性。     

A fuzzy control strategy for power smoothing and grid dynamic response enrichment of a grid‐connected wind energy conversion system

This paper concentrates on the output power smoothing and the grid dynamic response enhancement of a grid‐interactive MW‐class permanent magnet synchronous generator‐based wind energy conversion system (WECS). A simple fuzzy controller method is applied to improve the overall performance of the WECS. The proposed method can retrieve the storing kinetic energy from the inertia of a wind turbine, perfectly. As a result, it can ensure a proficient power smoothing of the variable speed WECS. On the other hand, the grid side inverter is controlled by the fuzzy controller. This approach can reduce the fluctuation of DC link voltage and can deliver a smooth power to the power grid. The proposed method is compared with two other methods such as the maximum power point tracking control method and the without fuzzy controller method. A simple shunt circuit also includes in the DC link circuit. Therefore, during the system fault condition, the WECS can perform a stable operation. Effectiveness of the proposed method is verified by numerical simulations. Copyright © 2013 John Wiley & Sons, Ltd.     

基于双电池不平衡状态优化的风功率平滑控制

在双电池平滑风功率过程中,改善双电池充放电不平衡状态可以提高充放电深度,减少充放电状态切换次数.文章分析了双电池风功率平滑系统的充放电不平衡状态及其产生的原因,提出了一种改进控制策略,该策略可根据双电池荷电状态调整风功率平抑目标功率,以此改善双电池不平衡状态.基于Matlab/Simulink分析了风速湍流强度以及风功...     

具有模式激活的储能双向DC-DC变换器的有限集模型预测控制方法

针对直流微电网中分布式发电机组输出功率不确定及负荷波动导致系统功率不平衡和直流母线电压不稳定的问题,提出了一种双向DC-DC变换器的模式激活有限集模型预测控制方法,预设了直流母线电压允许波动范围的上下限,利用范围比较器,根据母线电压实际值自动选择储能系统的工作模式,并实现其在不同模式之间的自由切换。仿真结果表明,提出的控制策略在三种模式切换的过程中,能够快速地稳定母线电压值,提高系统的电能质量并延长蓄电池的使用寿命。研究成果可用于指导工程实践。     

基于MMC-PET的直流微电网综合控制策略

为提升智能配电网电能质量,提出一种基于模块化多电平型电力电子变压器的直流微网构架及其综合控制策略,对分布式电源并网方式进行简化,设计MMC-PET及风光储系统的控制器,对智能配电网中电压深度跌落、三相不平衡等电能质量问题进行治理。在PSCAD/EMTDC平台搭建基于MMC-PET的直流微网风光储系统仿真模型,进行仿真分析总结,结果表明该方法很大程度地提高了新能源接入适应性,具备更快的动态响应速度和更强的鲁棒性,能有效改善智能配电网电能质量。     

Multi-pole permanent magnet synchronous generator wind turbines' grid support capability in uninterrupted operation during grid faults

Emphasis in this paper is on the fault ride-through and grid support capabilities of multi-pole permanent magnet synchronous generator (PMSG) wind turbines with a full-scale frequency converter. These wind turbines are announced to be very attractive, especially for large offshore wind farms. A control strategy is presented, which enhances the fault ride-through and voltage support capability of such wind turbines during grid faults. Its design has special focus on power converters' protection and voltage control aspects. The performance of the presented control strategy is assessed and discussed by means of simulations with the use of a transmission power system generic model developed and delivered by the Danish Transmission System Operator Energinet.dk. The simulation results show how a PMSG wind farm equipped with an additional voltage control can help a nearby active stall wind farm to ride through a grid fault, without implementation of any additional ride-through control strategy in the active stall wind farm.     

Autonomous renewable energy conversion system

This paper briefly reviews the need for renewable power generation and describes a medium-power Autonomous Renewable Energy Conversion System (ARECS), integrating conversion of wind and solar energy sources. The objectives of the paper are to extract maximum power from the proposed wind energy conversion scheme and to transfer this power and the power derived by the photovoltaic system in a high efficiency way to a local isolated load. The wind energy conversion operates at variable shaft speed yielding an improved annual energy production over constant speed systems. An induction generator (IG) has been used because of its reduced cost, robustness, absence of separate DC source for excitation, easier dismounting and maintenance. The maximum energy transfer of the wind energy is assured by a simple and reliable control strategy adjusting the stator frequency of the IG so that the power drawn is equal to the peak power production of the wind turbine at any wind speed. The presented control strategy also provides an optimal efficiency operation of the IG by applying a quadratic dependence between the IG terminal voltage and frequency V∼f². For improving the total system efficiency, high efficiency converters have been designed and implemented. The modular principle of the proposed DC/DC conversion provides the possibility for modifying the system structure depending on different conditions. The configuration of the presented ARECS and the implementation of the proposed control algorithm for optimal power transfer are fully discussed. The stability and dynamic performance as well as the different operation modes of the proposed control and the operation of the converters are illustrated and verified on an experimental prototype.     

Two-level energy management strategy for PV-Fuel cell-battery-based DC microgrid

With the fast development of DC Microgrid (MG) technology, its operating economy and reliability are getting more and more concern. The traditional distributed control method is aimed at power balance and system stability, and is difficult to meet the requirement of energy management system for multi-source hybrid DC MG. This paper provides a two-level energy management strategy for PV-fuel cell-battery-based DC MG, which is divided into device control level and system control level. At the device control level, the distributed control methods based on MPPT-droop dual-mode control and droop control are proposed to enhance system reliability; at the system control level, the equivalent consumption minimization strategy (ECMS) is used to distribute system net power between battery pack and fuel cell system. A lab-scale DC microgrid platform is developed to verify the proposed energy management strategy in this paper. Moreover, the analysis and compare of the results show that the proposed two-level energy management strategy can achieve lower equivalent hydrogen consumption than classical PI control and state machine control method.     

基于DSVPWM的PMSG并联型GS-NSC研究

为提高九开关变换器直流侧电压利用率,减少开关损耗,采用一种不连续空间矢量脉宽调制（DSVPWM）,同时将九开关变换器用于直驱式永磁同步风力发电机（PMSG）网侧构成并联型网侧九开关变换器（GS-NSC）。在对并联型GS-NSC控制策略、故障穿越方案进行理论分析的基础上,建立PMSG并联型GS-NSC仿真模型,设计多种电网电压故障工况对其进行仿真研究。结果表明,在电网电压正常工况下,并联型GS-NSC可维持电网电流的正弦波特性。在电网电压跌落工况下,并联型GS-NSC可向电网注入无功电流辅助电网电压的恢复,并通过提升并网电流幅值减少卸荷电路的功率损耗,降低PMSG散热负担。在电网电压骤升工况下,并联型GS-NSC可动态分配直流母线电压,避免因直流侧过压而导致PMSG退出运行。     

Operating capability as a PQ/PV node of a direct-drive wind turbine based on a permanent magnet synchronous generator

This paper describes the modelling and control system of a direct-drive PMSG wind turbine for effective active and reactive power generation control and voltage control at the grid connection point. This study focuses on the maximum power capability of the wind turbine, which is limited by its generator and power converter. The ability of this model and control strategy are assessed by means of simulations and discussed at length. The results of our study show that a PMSG wind turbine is able to actively participate in grid operation because it can independently control active and reactive power production (operating as a PQ node) or the active power and voltage at the connection node (operating as a PV node).