并网光伏发电系统暂态特性研究

基于光伏发电系统的物理模型研究,在matlab/simulink中开发了包含光伏阵列模型、光伏阵列的最大功率跟踪（MPPT）模块、DC/DC升压电路和采用电压及电流环控制的逆变系统在内的动态仿真模型,并建立了基于电压型逆变器的暂态数学模型;并通过仿真得到了并网光伏发电系统辐射强度突变和发生短路时的暂态运行特性,为深入研究并网光伏发电系统的暂态特性建立了基础。     

Modeling and simulation of multi‐scale transients for PMSG‐based wind power systems

In a wind energy conversion system (WECS), multiple‐time‐scale transients that cover a wide frequency range from low‐frequency transient stability up to high‐frequency switching events are observed. This paper presents a methodology of modeling diverse transients for a permanent magnet synchronous generator (PMSG)‐based WECS within the same study. Multiple physical areas of the PMSG‐based WECS are given depending on the appearance of carriers contained in the considered waveforms. In order to eliminate different carrier frequencies, the PMSG and generator‐side voltage source converter (VSC) are modeled in the dq0‐reference frame. On the other hand, the grid‐side VSC and utility grid are dealt with in the multi‐scale model of the network in which the shift frequency is available. The switching‐function and average‐value models of the VSC are selected depending on the carrier shifted. In addition, interface between the control and electrical subsystems is redesigned to offset the computation error caused by one time‐step delay. Two test cases are performed to study the wind power fluctuations and faults ride‐through. The results show that the proposed multi‐scale model is able to simulate slow‐changing dynamic responses up to high‐frequency transients accurately while decreasing the simulation burden. In comparison with the results obtained from the EMTP (electromagnetic transients program) type simulators, the effectiveness and accuracy of the multi‐scale model are verified. Copyright © 2017 The Authors Wind Energy Published by John Wiley & Sons Ltd.     

微型电网的并网方式初探

阐述了微型电网的特点和发展现状,提出微型电网并网的几种基本结构,初步比较各自优点得出VSC符合微电网并网要求,着重分析了背靠背VSC简化数学模型,对背靠背VSC采用双闭环控制方法,分析得出具体的功率解耦控制方法。     

光伏电网电压不平衡及跌落补偿控制系统的设计

鉴于非线性冲击负载的影响,光伏电网母线出现电压跌落大、电压不平衡问题。提出一种基于三相VSC的超导储能技术前馈线性化控制方法。利用三相VSC变流器构建数学模型,如果简单地以交轴电流和直流电压来构建控制系统,物理上很难实现。所以文中以直轴和交轴电流来实现电流闭环控制,并在直轴电流环前置电压调节器实现了直流电压的前馈闭环控制。从而推导出三相VSC变流器的逆系统．并构造出伪线性系统。考虑建模误差、系统的快速反应和增强鲁棒性,采用内环PI控制器对伪线性系统进行综合。实现了交轴电流分量和直流电压的解耦,对该闭环控制系统计算机仿真的效果良好。     

A novel strategy based on salp swarm algorithm for extracting the maximum power of proton exchange membrane fuel cell

Cell temperature and water content of the membrane have a significant effect on the performance of fuel cells. The current-power curve of the fuel cell has a maximum power point (MPP) that is needed to be tracked. This study presents a novel strategy based on a salp swarm algorithm (SSA) for extracting the maximum power of proton-exchange membrane fuel cell (PEMFC). At first, a new formula is derived to estimate the optimal voltage of PEMFC corresponding to MPP. Then the error between the estimated voltage at MPP and the actual terminal voltage of the fuel cell is fed to a proportional-integral-derivative controller (PID). The output of the PID controller tunes the duty cycle of a boost converter to maximize the harvested power from the PEMFC. SSA determines the optimal gains of PID. Sensitivity analysis is performed with the operating fuel cell at different cell temperature and water content of the membrane. The obtained results through the proposed strategy are compared with other programmed approaches of incremental resistance method, Fuzzy-Logic, grey antlion optimizer, wolf optimizer, and mine-blast algorithm. The obtained results demonstrated high reliability and efficiency of the proposed strategy in extracting the maximum power of the PEMFC.     

可再生能源交流孤网转并网运行中的电压控制策略

柔性直流远距离输送有仅通过直流送出模式和交直流混联送出模式。两种送出模式下,系统的运行点存在较大差异,直接切换会对电网产生较大冲击。文章首先分析了两种送出模式下系统的调压控制特点,指出并网点电压幅值偏差是切换过程的关键点,设计了以可再生能源集群并网点电压偏差最小为主目标,换流站综合无功裕度最大为次目标的柔性切换策略。最后,基于某柔直电网可再生能源送端规划系统进行仿真,验证了所提策略的有效性。     

Research and application of a power-flow-calculation method in multiterminal VSC-HVDC power grid

For demonstrating a multiterminal voltage-source converter (VSC)-based high-voltage DC (HVDC) (VSC- HVDC) project, this study puts forward a technical route for calculating the power flow in a 500-kV VSC-HVDC power grid in comparison with that of an AC power grid. The Jacobian matrix used in the power-flow calculation was deduced through methods such as Newton-Laphson iteration and Taylor series expansion. Further, the operation effect of power- flow calculation on a true bipolar VSC-HVDC power grid was analyzed briefly. The elements of the Jacobian matrix corresponding to VSC were studied under the mode of droop control and the control strategy of VSC-HVDC power grid was analyzed in detail. The power-flow calculation model for VSC-HVDC power grid of the master-slave control mode was simplified using the PQ decomposition method of the power-flow calculation of an AC power grid. Moreover, a four-terminal model of the Zhangbei VSC-HVDC demonstration project was established and tested on MATLAB. The simulation results under two kinds of operating conditions were analyzed and compared to the results of BPA; the deviation between the power-flow results was studied. The results show that the proposed calculation method can provide a feasible support for calculating the power flow in VSC-HVDC grids.     

Synchronverter assessment for the frequency regulation of control areas encompassing Renewable Distributed Generation

The efforts to reduce the impact of the electric power generation from fossil fuels have been conducted to increase renewable energy sources and the trend to implement a decentralised scheme by distributed generation systems. However, small power plants' use does not contribute to the frequency regulation in the electrical power system due to the lack of the inertia and damping properties of synchronous generators used conventionally. This condition can produce unpredictable and unstable operational conditions of multi-area power systems. Hence, this paper aims to assess a voltage source converter (VSC) controlled by a synchronverter to help in frequency regulation in power networks that contain an actual number of renewable sources connected. The contribution lies in using the synchronverter as a control element capable of interacting correctly in a power network with a distributed generation system integrated with synchronous generators and renewable energy sources. Under this scenario, a hardware-in-the-loop (HIL) strategy of a photovoltaic-fuel cell-battery power generation system demonstrates that the VSC controlled by a synchronverter can react adequately under frequency deviations. A three power plants' performance, a conventional one and two photovoltaic (P.V.) farms handled by a synchronverter tied through a transmission link, is studied to demonstrate that the frequency viewpoint's behaviour and control purposes are satisfied. The results show the viability of the synchronverter as a frequency control strategy in electrical networks.     

混合直流输电系统中柔性直流单元的作用和控制优化

常规直流和柔性直流并联构成的混合直流输电系统,可发挥常规直流大功率输电和柔性直流有功/无功快速解耦控制的优势,尤其针对落点极弱交流系统有较好的经济技术性能。结合云南电网与南网主网背靠背异步联网工程实例,分析了混合直流中柔直单元对于系统稳态运行和故障恢复特性的改善作用及效果,并进一步提出了柔直单元的功率优化控制策略。仿真分析结果表明,柔直单元对于合理配置无功小组、提高弱系统强度、改善故障后常规直流恢复特性效果明显,验证了功率优化控制策略的有效性。     

核电稳压器内模PID优化控制

针对核电站稳压器非线性、时变和多扰动的特点,基于内模控制理论设计了内模PID控制系统,为进行内模PID控制器参数整定,提出了一种高速收敛的量子粒子群算法,经典型函数测试验证了算法的有效性并应用于参数寻优.仿真结果表明：所提出的内模PID控制系统的控制效果优于常规PID控制系统,在对象模型特性改变或模型具有扰动的情况下,内模PID控制器仍能取得较好的控制效果,在鲁棒性和抗干扰能力方面均具有较强优势.     

基于电压源换流器的光伏并网系统暂态特性研究

在分析VSC基本原理的基础上建立了采用SPWM控制的基于VSC的光伏并网系统暂态数学模型,分析了其开关特性和暂态运行机理;并通过仿真得到了光伏并网系统输送功率突变和发生短时故障时的暂态运行特性,为进行基于VSC的光伏并网系统深入暂态分析建立了基础。     

Effect of intermittent voltage source converter faults on the overall performance of wind energy conversion system

The doubly fed induction generator (DFIG) is interfaced to the AC network through voltage source converters (VSCs) which are considered to be the core of the DFIG system. This paper investigates the impact of different intermittent VSC faults on the overall performance of a DFIG-based wind energy conversion system (WECS). The fault ride through capability of the DFIG under various VSC faults is also investigated. Faults such as open circuit and short circuit across the switches, when they occur within the grid side converter (GSC) and rotor side converter (RSC), are considered and compared in this paper. Short circuit and open circuit across the DC-link capacitor are also considered in this study as common VSC problems. Simulation results indicate that the short circuit faults have a severe impact on the overall performance of the DFIG, especially when they occur within the GSC. This is attributed to the fact that the GSC directly regulates the point of common coupling voltage. The open circuit faults have less impact on the performance of the DFIG-based WECS. A proper controller along with flexible AC transmission device should be available to compensate the required active and reactive power during these faults. A protection technique is necessary to detect these faults in advance to protect the VSC switches and the machine winding from any catastrophic failure.     

Variable Speed Wind Turbines for Power System Stability Enhancement

This paper investigates possible improvements in grid voltage stability and transient stability with wind energy converter units using modified P/Q control. The voltage source converter (VSC) in modern variable speed wind turbines is utilized to achieve this enhancement. The findings show that using only available hardware for variable-speed turbines improvements could be obtained in all cases. Moreover, it was found that power system stability improvement is often larger when the control is modified for a given variable speed wind turbine rather than when standard variable speed turbines are used instead of fixed speed turbines. To demonstrate that the suggested modifications can be incorporated in real installations, a real situation is presented where short-term voltage stability is improved as an additional feature of an existing VSC high voltage direct current (HVDC) installation     

基于反推方法的滑模自适应励磁控制

针对电力系统参数摄动和外界干扰等因素对励磁系统的影响,经过对传统模型状态变量的变换,建立了励磁控制系统模型,设计了基于backstepping方法的模糊滑模励磁控制器。该方法通过逐步构造Lyapunov函数和设计切换函数．从而得到了最终的控制规律。最后对所设计的算法进行了仿真研究,与常规PID＋PSS控制方法相比,系统在动静态响应性能上均优于PID＋PSS控制。通过仿真表明这种控制方法不仅有效而且还能达到比较满意的控制效果。     

Development and simulation of systematic of Micro-SMES for operating at high-temperature regions

近年来第Ⅱ代YBCO高温超导涂层导体的制备工艺取得巨大的进展,其优越于第Ⅰ代BSCCO高温超导体的性能使它在电力领域的应用受到广泛重视.本文考虑到YBCO涂层导体磁场下各向异性载流特性,在确保储能容量的基础上最大限度地减少导体用量获得超导磁储能(SMES)磁体的优化;依据磁体损耗和引线漏热分析进行过冷液氮低温系统的整体设计;采用斩波器和电压型变换器实现SMES与系统间的能量/功率传递;通过仿真建模探索其在电力系统中的作用和影响,并对应用的可行性进行了探讨.     

水轮机调速器液压随动系统精细化建模研究

本文分析了当前电力系统仿真所采用的液压随动系统模型的不足,通过对其电液转换单元、液压放大单元、执行机构的内部结构分析,以及试验测试,获得了各环节的传递函数和准确参数.并通过MATLAB Simulink建立了随动系统的准确模型.然后接入PID控制器和各环节反馈进行了闭环测试,通过大、小两种阶跃扰动,开展了实际物理设备的...     

Power quality investigation of a solar PV transformer-less grid-connected system fed DVR

This paper presents a single stage transformer-less grid-connected solar photovoltaic (PV) system with an active and reactive power control. In the absence of active input power, the grid-tied voltage source converter (VSC) is operated in a reactive power generation mode, which powers the control circuitry, and maintains a regulated DC voltage to the VSC. A data-based maximum power point tracking (MPPT) control scheme which performs power quality control at a maximum power by reducing the total harmonic distortion (THD) in grid injected current as per IEEE-519/1547 standards is implemented. A proportional-integral (PI) controller based dynamic voltage restorer (DVR) control scheme is implemented which controls the grid side converter during single-phase to ground fault. The analysis includes the grid current THD along with the corresponding variation of the active and reactive power during the fault condition. The MPPT tracks the actual variable DC link voltage while deriving the maximum power from the solar PV array, and maintains the DC link voltage constant by changing the modulation index of the VSC. Simulation results using Matlab/Simulink are presented to demonstrate the feasibility and validations of the proposed novel MPPT and DVR control systems under different environmental conditions.     

Flexible HVDC Transformer for Next Generation Renewable Energy Industry

The growing demand on non-fossil fuel energy has escalated the desire for mega-scale renewable energy power generation, which can no longer be satisfied solely by relying on onshore renewable energy power plants. Outcomes from a recent project funded by the Sixth European Union Framework Programme （FP6）, Project ＂Upwind＂ concluded that larger offshore wind turbines （i.e., 〉 10 MW） are feasible and cost effective. It will be beneficial for such future large scale renewable energy power generators （i.e., large offshore turbines） and plant （i.e., large offshore wind farms） to have a dedicated high efficiency, robust, flexible and low cost power collection, transmission and distribution technology. Proposed in this paper is a compact and effective hybrid HVDC （high voltage direct current） transformer that allows realisation of a highly robust and financially rewarding next generation multi-terminal HVDC system for future offshore renewable energy power plant. This concept, potentially, allows the elimination or minimisation of the need for a centralised local offshore HVDC platform or substation in each wind farm, solar farm, or tidal farm. This paper discusses the study outcome of the proposed hybrid HVDC transformer and the application of a multi-terminal HVDC system in the renewable energy industry, compared to the existing HVAC and VSC （voltage source converters） type HVDC systems.     

VSC-based direct torque and reactive power control of doubly fed induction generator

This paper proposes a novel direct torque and reactive power control (DTC) for grid-connected doubly fed induction generators (DFIGs) in the wind power generation applications. The proposed DTC strategy employs a variable structure control (VSC) scheme to calculate the required rotor control voltage directly and to eliminate the instantaneous errors of active and reactive powers without involving any synchronous coordinate transformations, which essentially enhances the transient performance. Constant switching frequency is achieved as well by using space vector modulation (SVM), which eases the designs of power converter and ac harmonic filters. Simulated results on a 2 MW grid-connected DFIG system are presented and compared with those of the classic voltage-oriented vector control (VC) and traditional look-up-table (LUT) direct power control (DPC). The proposed VSC DTC maintains enhanced transient performance similar to the LUT DPC and keeps the steady-state harmonic spectra at the identical level as the VC strategy when the network is strictly balanced. Besides, the VSC DTC strategy is capable of fully eliminating the double-frequency pulsations in both the electromagnetic torque and the stator reactive power during network voltage unbalance.     

超临界机组协调系统的模糊增益调度预测控制

针对火电厂超临界机组多变量锅炉-汽机协调系统在大工况范围内运行具有强非线性的特点,提出了一种基于模糊增益调度的预测控制方法.通过现场试验获取多个工况点处的协调系统传递函数模型,结合增益调度和模糊逻辑推理方法建立全局自适应模糊模型,利用预测控制技术确保控制系统全局优化品质.基于模糊增益调度的预测控制方法设计火电厂超临界机...