Adaptive sliding-mode voltage control for inverter operating in islanded mode in microgrid

Harmonic current caused by nonlinear loads and parametric variations of output filter of inverters make popular proportional–integral–derivative (PID) voltage controller far beyond excellent performance in case of microgrid operating in islanded mode. Motivated by this limitation, this paper proposes an adaptive sliding-mode controller (ASMC) to enhance disturbance-rejection performance of control system of islanded parallel inverters. And adaptive algorithms are designed to observe external disturbances and internal perturbation so as to guarantee the globe robustness of control system of inverter. The switching gain of control input is designed to be a time-varying value which effectively reduces undesirable chattering of control input signal. Simulating and experimental results are presented that the total harmonic distortion, chattering, and steady-state error of output voltage of islanded parallel inverters are effectively reduced and the dynamic performances and the capability of perturbation rejection of control system of inverter are effectively enhanced.     

Nonlinear Decentralized Feedback Linearizing Controller Design for Islanded DC Microgrids

This paper aims to design decentralized controllers for different components in islanded DC microgrids. The major components in the DC microgrid as considered in this paper include a fuel cell, solar photovoltaic (PV) unit, and battery energy storage system (BESS) along with critical and non-critical loads. The main control objective is to maintain the power balance within the DC microgrid through the regulation of the common DC-bus voltage. The controllers are designed based on the dynamical models of the fuel cell, solar PV unit, and BESS. The feedback linearization technique is employed to obtain the control laws, which simplifies the original dynamical models and decouples different components in the form of several subsystems. In this way, the feedback linearization technique allows different components in DC microgrids to achieve the desired control objectives by using only the local information (i.e., in a decentralized manner). The performance of the proposed decentralized controllers for different components is evaluated on a test DC microgrid under different operating conditions. Simulation results demonstrate that the proposed control scheme performs in a much better way as compared to an existing proportional integral controller.     

H‐infinity controller for frequency and voltage regulation in grid‐connected and islanded microgrid

This paper presents a study on a grid‐connected and islanded multiple distributed generation (DG) system for frequency and voltage regulation. The multiple DG system includes solar cells, wind turbine, fuel cell, and battery storage. The H‐infinity controller is used whose weighting parameters are optimized to minimize voltage and frequency deviation. The performance of the system is analyzed under different conditions for both grid‐connected and islanded modes of operation. In case of the load variations, the inner voltage and current loop react based on the H‐ infinity control strategies. The outer power loop uses the droop characteristic controller. The design is simulated using MATLAB/SIMULINK. The simulation results show that the multiple DG system can supply high‐quality power both in grid‐connected and islanded modes. Also, we show that the proposed control methodology will make the system to transit smoothly between the islanded mode and the grid‐connected mode. The results indicate that the frequency and voltage deviations meet the nominal values as per IEEE standard. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

电力系统的电压控制与安全经济运行

本文讲述了电力系统电压控制的必要性、复杂性,以及电压控制与电力系统安全经济运行的关系及如何控制电压和需要注意的问题。     

基于协同强化学习的微电网分布式两级电压优化控制

由于微电网中分布式电源组成复杂,运行模式多样,孤岛微电网的电压恢复控制面临着不确定性干扰的影响。为此,针对不确定性干扰下微电网的二级电压恢复控制问题,提出了一种基于协同强化学习的微电网分布式两级电压优化控制方法,实现孤岛模式下微电网的电压调节控制。首先构建孤岛微电网分布式一致性协同电压控制算法,并建立李雅普诺夫函数稳定性判定方法。其次根据控制器性能与控制器增益参数的关系,求解孤岛微电网电压控制器增益上界,并根据控制器增益参数上界限制强化学习智能体动作集。随后,采用强化学习算法优化二级控制器增益参数,给出相应的强化学习智能体状态集、协同全局奖励函数。最后在Matlab/Simulink上通过仿真实验验证了所提出的控制方法的有效性和适应性。     

光伏DG接入配电网及微电网的过电压自动调节方法研究

针对光伏DG接入配电网因过电压而导致渗透率低的问题、微电网离网运行期间过电压问题,以及微电网在非计划孤岛状态下并网转离网暂态过电压问题,提出一种P/U下垂调节方法。当光伏DG接入配电网,该方法能避免光伏DG因过电压而退出运行。当光伏DG接入离网运行微电网,因负荷减少、DG出力增加等因素而导致过电压时,该方法可以实现无通信互连线的稳态离网能量平衡。当含光伏DG的微电网在并网转离网期间,该方法能够解决暂态过电压问题。首先推导电压偏差公式并分析过电压产生机理。其次介绍P-U下垂调节方法原理。最后为验证方法可行性,以光伏DG接入配电网为算例分析对象,搭建Matlab/Simulink仿真模型,并在逆变器样机上进行试验验证。结果表明P-U下垂调节方法可行有效。     

云广直流孤岛运行的稳定特性研究

根据云广直流孤岛运行的实际情况,提出了适用于孤岛运行的稳定判据;对孤岛运行的静态电压稳定问题进行了分析,提出了适用于孤岛运行的静态电压稳定裕度指标,计算了典型方式的稳定极限和稳定裕度;对线路、机组等元件N?1、N?2和多重严重故障下系统的响应进行了分析,掌握了孤岛系统暂态电压稳定和频率稳定的规律;提出了提高孤岛系统稳定性的措施建议。     

Integration of a hybrid fuel cell-battery system to a distribution grid

In order to integrate a proton exchange membrane type (PEM) fuel cell system (FCS) combined with a battery bank to a distribution grid; this paper proposes a local controller based on fuzzy logic. The proposed system provides primary frequency control and local bus voltage support to the local grid. This opposes the passive distributed generation of the present that do not provide auxiliary services, such as back-up power, voltage support and reliability of supply as they operate under constant power factor equal to 1 at all times. During network disturbances, the distributed generations of the present are disconnected until normal operation is reestablished. When the distributed generation penetration is high this may lead to system instability. The microgrid concept is the effective solution for the control and quality improvement of grids with high level of DG penetration. So, the proposed system, also, can be an active controllable microsource of a microgrid in the future that cooperates with other microsources in order to cover the local load demands for active and reactive power either under grid-connected mode or under islanding operating mode. In cases where the distribution grid (working as microgrid) is forced to operate in islanded mode, the hybrid system provides the demanded active and reactive power. The FCS is connected to a weak distribution grid so that the system performance is studied under the worst conditions. The simulation results are obtained using MATLAB software under a severe step load change where the grid is still connected and under islanded operation. In both cases the system presents a good performance.     

面向单相微电网的双模式并联逆变器协调控制方法

微电网中的接口变流器往往采用电压控制方法或电流控制方法。对于电压控制方法,其优点是可以应用在并网/孤岛两种模式下,然而缺点是功率控制动态响应慢。电流控制方法的优点是动态响应快,但是不能应用在孤岛模式。采用分布式电源通过两个并联逆变器接入电网的结构,与传统方法不同的是,其中一个逆变器采用电压控制,另一个逆变器采用电流控制。这种方式可以同时发挥两种控制方法的优势。与此同时,加入功率耦合环节,提高电压控制逆变器和整个系统的动态特性。单相双逆变器的仿真和实验结果证实了所提出的结构与控制方法的有效性。     

基于分布式内模设计的微电网协调二次控制策略

研究基于多代理系统的孤岛型微电网二次电压和频率控制策略。首先建立孤岛型微电网电压和频率控制数学模型,利用状态反馈得到输入-输出线性化模型;然后简要介绍所需的基本图论原理,并利用内模设计原理设计分布式协调二次控制器,避免了集中控制结构下对中央控制器的依赖。基于多代理系统的分布式二次控制器通过一定的有向通信网络连接,每个代理只需本地及相邻节点信息。最后在PSCAD/EMTDC中建立孤岛微网的测试系统,通过仿真对所提控制策略的有效性进行验证,结果表明所提策略能够使频率和电压恢复额定值,同时保证有功功率分配的准确性。