微电网自适应下垂控制研究

针对微电网并联逆变器采用传统下垂控制方法后输出电压幅值和频率的偏差问题,提出了一种改进的自适应下垂控制方法.该控制方法用渐进性的函数关系代替了传统下垂控制的一次函数,实现了下垂系数的自调整,有效减小了微电网负荷突变等情况下母线电压幅值及频率的波动和偏差.     

孤岛微电网的分布式固定时间二次协调控制

孤岛微电网的下垂控制策略会导致系统稳态的频率和电压偏离额定值.为此,提出一种分布式固定时间二次协调控制策略以实现系统频率和电压的恢复控制,并实现期望的有功功率分配.所提出的控制方法能在固定时间内完成二次控制目标,而不依赖于系统的初始状态.该优势使得根据任务需求来离线预设整定时间成为可能.同时,采用固定时间Lyapunov方法分析二次协调控制系统的稳定性.最后,通过Matlab/Simulink仿真实验验证分布式固定时间二次控制策略的有效性.     

考虑状态受限和一致性的微电网二次控制

为解决交流微电网下垂控制产生的偏差问题, 本文采用二次控制对分布式电源输出电压和频率进行调节. 将微电网看成分布式多智能体系统, 智能体间通过稀疏网络进行通信, 运用多智能体一致性协议, 本文提出一种基 于障碍Lyapunov函数和自适应模糊系统的二次电压和频率控制器. 采用障碍Lyapunov函数设计控制器, 不但能保 持系统的稳定性, 还可使输出的电压和频率限制在预设的范围内. 采用自适应模糊系统可对系统中的一些参变量的 变化进行估计, 提高了控制器的鲁棒性. 本文给出了严格的稳定性证明. 通过对负载变化, 以及拓扑结构改变等的 仿真测试, 验证了所提方案的有效性.     

基于有功功率修正的MMC串联结构微电网相间功率平衡控制策略

针对孤岛不平衡负载下模块化多电平变换器（MMC）串联结构微电网系统中微源输出功率波动,引起的相间功率不平衡及运行不稳定问题,研究了一种基于有功功率修正（Active Power Correction,APC）的相间功率平衡控制策略。基于系统孤岛模式等效电路,对系统输出功率进行了数学建模,并分析了相间功率流动模式。在三相输出电压对称的前提下,根据微源功率及负载功率确定需要修正的功率,设计了环流控制器,对直流环流控制实现相间功率互济。通过仿真验证,该策略能使相间功率自适应动态调节,达到相间功率平衡的目的。     

计划孤岛方式下微电源控制系统的仿真研究

研究微电网控制器优化控制问题,针对微电网运行应满足稳定性要求,在各微电源输出功率分配发生突变时,采用通常控制策略的微电源控制系统常常存在功率调节滞后的缺陷,致使系统频率和母线电压失去稳定.结合微电源的控制,对下垂特性进行优化,提出PQ-Vf控制策略,并设计了控制系统,通过对微电网由联网运行模式向孤岛运行模式切换过程以及孤岛运行模式下进行仿真分析,得到了微网中交流母线的电压和系统频率的动态响应特性曲线,仿真结果表明设计的控制系统能够维持系统稳定,克服了通常控制策略的缺陷.     

矩阵变换器励磁控制的无刷双馈风力发电系统

应用在双馈风力发电系统中的功率变换器必须具有功率双向流动的能力, 交直交循环变流器和交交矩阵变换器都可满足功率的双向流动要求. 而矩阵变换器能同时提供正弦的输入电流和输出电压, 输入电流可调节为超前、滞后或同相于输入电压, 输出电压可实现幅值、频率和网侧功率因数的独立控制. 利用矩阵变换器, 通过控制无刷双馈电机控制绕组的电压幅值、频率, 为风力发电系统提供励磁. 压频比控制器采用模型参考模糊自适应控制策略, 对电机的转速和功率因数进行控制. 采用DSP,CPLD构建了基于四步换流方案的矩阵变换器实验励磁系统, 仿真和实验结果验证了系统设计的正确性、可行性和稳定性, 为矩阵式变换器的实际应用提供了实验基础.     

基于分布式策略的直流微电网下垂控制器设计

本文研究了分布式控制策略下直流微电网的负荷分配和电压平衡问题. 给出一种新的基于分布式策略的下垂控制器设计方法, 能够在统一的框架下实现直流微电网负载共享和电压平衡. 首先,将直流微电网的负载共享和电压平衡问题转化为多目标优化问题, 其性能指标与微源的容量密切相关. 然后, 通过求解多目标优化问题获得实现负载共享和电压平衡的集中式控制策略, 并给出下垂控制器的设计方法. 为了降低系统的通信负担, 给出一种新的只需与邻居节点交换信息的分布式控制策略, 通过理论分析可知该分布式控制策略能够收敛到多目标优化问题的最优解. 最后, 通过对新能源汽车充换电站系统的仿真验证了本文提出的方法的有效性.     

飞轮安装偏差的过驱动航天器有限时间姿态控制

针对反作用飞轮安装存在偏差的过驱动航天器姿态跟踪问题, 提出一种有限时间姿态补偿控制策略. 通过设计自适应滑模控制器保证实现对不确定性转动惯量与外部干扰的鲁棒控制, 同时实现对飞轮安装偏差的补偿控制, 并应用Lyapunov 稳定性理论证明了该控制器能够在有限时间内实现姿态跟踪控制. 最后, 将该控制器应用于某型航天器的姿态跟踪控制, 仿真结果验证了所提出方法的有效性.     

不平衡电网中三相脉冲调宽整流器的控制

在常规的三相整流器控制器设计中,一般均假设三相电网电压平衡,然而当实际电网不平衡时,传统双闭环控制策略将使直流侧出现严重的二次谐波功率从而严重影响整流器输出品质.鉴于此,本文在分析PWM整流器数学模型和电网不平衡条件的基础上,电压外环采用模糊PI控制,提高直流侧电压动态响应速度,电流内环采用无需进行正负序分解的正、负序电流独立控制策略,实现了不平衡电网下对三相PWM整流器的双闭环控制.仿真结果表明:所设计的控制方法保证了在不平衡条件下直流侧电压快速地稳定,有效抑制了直流侧二次谐波,提高了整流器的运行性能.     

基于链式SVG三相不平衡负荷的平衡补偿方法的仿真分析

本文对链式静止无功发生器的工作原理进行了分析,在深入研究三相不平衡负荷的平衡化补偿原理的基础上,提出了一种基于链式静止无功发生器在不平衡补偿时的分相补偿控制方法.该方法是通过对静止无功发生器各相输出电压与电网电压的相角差δ进行调节来控制各相输出电流,从而可以有效地对三相负载不平衡的系统进行平衡补偿.对所提出的补偿方法进行了仿真研究,仿真结果表明运用分相控制方法补偿三相不平衡负载,具有比较好的稳态补偿效果,补偿后电网电流三相平衡,各相电流与电压基本同相位并且幅值成相同的比例,达到了负载功率平衡和无功补偿的目的.     

Selective compensation of voltage harmonics in grid-connected microgrids

In this paper, a novel approach is proposed for selective compensation of main voltage harmonics in a grid-connected microgrid. The aim of compensation is to provide a high voltage quality at the point of common coupling (PCC). PCC voltage quality is of great importance due to sensitive loads that may be connected. It is assumed that the voltage harmonics are originated from distortion in grid voltage as well as the harmonic current of the nonlinear loads. Harmonic compensation is achieved through proper control of distributed generators (DGs) interface converters. The compensation effort of each harmonic is shared considering the respective current harmonic supplied by the DGs. The control system of each DG comprises harmonic compensator, fundamental power controllers, voltage and current proportional-resonant controller and virtual impedance loop. Virtual impedance is considered at fundamental frequency to enhance power control and also at harmonic frequencies to improve the nonlinear load sharing among DGs. The control system design is discussed in detail. The presented simulation results demonstrate the effectiveness of the proposed method in compensation of the voltage harmonics to an acceptable level.     

Multi-objective voltage and frequency regulation in autonomous microgrids using Pareto-based Big Bang-Big Crunch algorithm

Voltage and frequency regulation is one of the most vital issues in autonomous microgrids to ensure an acceptable electric power quality supply to customers. In this paper, a real-time control structure including power, voltage, and current control loops is proposed for microgrid inverters to restore voltage and frequency of the system after the initiation and load changes. The Proportional-Integral (PI) gains of the voltage controller are optimized in a real-time basis after a perturbation in the microgrid to have a fast and smooth response and a more stable system. The current controller produces Space Vector Pulse Width Modulation command signals to be fed into the three-leg inverter. The multi-objective optimization problem has objective functions of voltage overshoot/undershoot, rise time, settling time, and Integral Time Absolute Error (ITAE). The modified Multi-Objective Hybrid Big Bang-Bing Crunch (MOHBB-BC) algorithm is employed as one of efficient evolutionary algorithms in order to solve the optimization problem. The MOHBB-BC method obtains a set of Pareto optimal solutions; a fuzzy decision maker is used to pick up the most preferred Pareto solution as the final solution of the problem. Results from testing the control strategy on a case study are discussed and compared with previous works; according to them, the proposed method is able to obtain dynamic PI regulator gains to have a more appropriate response.     

Distributed Secondary Control and Optimal Power Sharing in Microgrids

We address the control problem of microgrids and present a fully distributed control system which consists of primary controller, secondary controller, and optimal active power sharing controller. Different from the existing control structure in microgrids, all these controllers are implemented as local controllers at each distributed generator. Thus, the requirement for a central controller is obviated. The performance analysis of the proposed control systems is provided, and the finite-time convergence properties for distributed secondary frequency and voltage controllers are achieved. Moreover, the distributed control system possesses the optimal active power sharing property. In the end, a microgrid test system is investigated to validate the effectiveness of the proposed control strategies.      

孤岛微电网异构电池储能系统的分布式有限时间次级控制

针对孤岛微电网异构电池储能系统频率、电压以及电池能量的一致性问题,考虑初级下垂控制,提出一种新的分布式有限时间次级控制策略.采用所提出的控制方案能够在有限时间内实现系统频率、电压恢复一致到额定值,并获得电池能量等级的均衡一致和期望的有功功率分配.该控制方法的优势在于整定时间的上界独立于系统的任意初始条件,能够保证微电网...     

A backstepping high-order sliding mode voltage control strategy for an islanded microgrid with harmonic/interharmonic loads

This paper presents a new nonlinear voltage control strategy based on backstepping control and a high-order sliding mode differentiator for an islanded microgrid. The microgrid consists of multiple distributed generation (DG) units with an arbitrary configuration that can be parametrically uncertain or topologically unknown. The proposed controller robustly regulates the microgrid voltages in the presence of parametric uncertainties, unmodeled dynamics, load imbalances, and nonlinear loads with harmonic/interharmonic currents. In contrast to existing methods, the controller does not need to know the frequency of harmonic and interharmonic current of microgrid loads that lead to the reduction of the steady-state error of the voltage controller in the frequency of unknown harmonics and interharmonics. The MATLAB/SimPowerSystems toolbox has verified the proposed control strategy's performance.     

Distributed generation system control strategies with PV and fuel cell in microgrid operation

Control strategies of distributed generation (DG) are investigated for different combination of DG and storage units in a microgrid. In this paper the authors proposed a microgrid structure which consists of a detailed photovoltaic (PV) array model, a solid oxide fuel cell (SOFC) and various loads. Real and reactive power (PQ) control and droop control are developed for microgrid operation. In grid-connected mode, PQ control is developed by controlling the active and reactive power output of DGs in accordance with assigned references. Two PI controllers were used in the PQ controller, and a novel heuristic method, artificial bee colony (ABC), was adopted to tune the PI parameters. DGs can be controlled by droop control both under grid-connected and islanded modes. Droop control implements power reallocation between DGs based on predefined droop characteristics whenever load changes or the microgrid is connected/disconnected to the grid, while the microgrid voltage and frequency is maintained at appropriate levels. Through voltage, frequency, and power characteristics in the simulation under different scenarios, the proposed control strategies have demonstrated to work properly and effectively. The simulation results also show the effectiveness of tuning PI parameters by the ABC.     

基于FPGA的九区图控制策略优化设计

电站电压无功控制（VQC）装置控制的主要目标是保证电压合格和无功基本平衡,是提高电能质量的重要保障,可以达到降损节能的效果,从而获得较好的经济效益。目前VQC的控制策略主要采用九区图控制策略,该控制策略控制简单、方便．但实际使用时某些区域对控制结果容易产生振荡现象以及装置频繁动作的问题,因此文中采用优化的九区图控制策略进行VQC系统设计,用Handel-C语言对VQC系统进行描述,最终在FPGA上实现其控制功能,弥补了装置频繁动作和振荡的缺陷,减少了变压器分接头调节和并联补偿电容器组投切次数,提高了电压稳定性和无功补偿的有效性。     

基于电网电压定向的光伏并网逆变器系统研究

针对传统的光伏并网系统逆变控制策略存在控制复杂、谐波含量多的问题,提出了一种基于电网电压定向的光伏并网逆变器直接电流控制方法,给出了以TMS320F2812为主控制器的三相光伏并网逆变器系统的硬件及软件设计。该逆变器直接电流控制方法采用过零检测电路测量电网电压的过零点时刻,得出过零点时刻的电网电压的旋转角度,从而得到逆变器输出电压的幅值和相位;采用SVPWM技术控制IPM的开断,使逆变器输出上述幅值和相位的电压,从而实现单位功率因数并网发电功能。实验结果表明,该逆变器直接电流控制方法简单,逆变器输出电流与电网电压基本保持相同的频率和相位,并网发电功率因数接近于1。