Robust backstepping global integral terminal sliding mode controller to enhance dynamic stability of hybrid AC/DC microgrids

In this paper,a Backstepping Global Integral Terminal Sliding Mode Controller(BGITSMC)with the view to enhancing the dynamic stability of a hybrid AC/DC microgrid has been presented.The proposed approach controls the switch-ing signals of the inverter,interlinking the DC-bus with the AC-bus in an AC/DC microgrid for a seamless interface and regulation of the output power of renewable energy sources(Solar Photovoltaic unit,PMSG-based wind farm),and Battery Energy Storage System.The proposed control approach guarantees the dynamic stability of a hybrid AC/DC microgrid by regulating the associated states of the microgrid system to their intended values.The dynamic stabil-ity of the microgrid system with the proposed control law has been proved using the Control Lyapunov Function.A simulation analysis was performed on a test hybrid AC/DC microgrid system to demonstrate the performance of the proposed control strategy in terms of maintaining power balance while the system’s operating point changed.Furthermore,the superiority of the proposed approach has been demonstrated by comparing its performance with the existing Sliding Mode Control(SMC)approach for a hybrid AC/DC microgrid.

Control of hybrid AC/DC microgrid under islanding operational conditions

This paper presents control methods for hybrid AC/DC microgrid under islanding operation condition.The control schemes for AC sub-microgrid and DC sub-microgrid are investigated according to the power sharing requirement and operational reliability.In addition,the key control schemes of interlinking converter with DC-link capacitor or energy storage,which will devote to the proper power sharing between AC and DC sub-microgrids to maintain AC and DC side voltage stable,is reviewed.Combining the specific control methods developed for AC and DC sub-microgrids with interlinking converter,the whole hybrid AC/DC microgrid can manage the power flow transferred between sub-microgrids for improving on the operational quality and efficiency.

Double-uncertainty optimal operation of hybrid AC/DC microgrids with high proportion of intermittent energy sources

This paper applies double-uncertainty optimization theory to the operation of AC/DC hybrid microgrids to deal with uncertainties caused by a high proportion of intermittent energy sources.A fuzzy stochastic expectation economic model for day-ahead scheduling based on uncertain optimization theory is proposed to minimize the operational costs of hybrid AC/DC microgrids.The fuzzy stochastic alternating direction multiplier method is proposed to solve the double-uncertainty optimization problem.A real-time intra-day unbalanced power adjustment model is established to minimize real-time adjustment costs.Through comparative analysis of deterministic optimization,stochastic optimization and fuzzy stochastic optimization of day-ahead scheduling and real-time adjustment,the validity of fuzzy stochastic optimization based on a fuzzy stochastic expectation model is proved.

Analysis of the Transition Between Multiple Operational Modes for Hybrid AC/DC Microgrids

There are four basic operational modes for the hybrid AC/DC microgrid,including AC grid-connected while interconnecting,both off-grid while interconnecting,AC gridconnected without connection,and both off-grid without connection.How to achieve a seamless operational mode transition is an urgent technical need to overcome.First,this paper describes the typical structure of the hybrid microgrid,and places a detailed focus on the power balance and transition strategy.Secondly,it takes the master-slave control structure as an example,and designs the transition logic for different operational modes,and then a method for selecting the slack bus and transition time-sequence is proposed.Based on the different roles that the interlinking converter(IC)plays in the process of modes transition,a voltage-power(U-P)control method for a hybrid AC/DC microgrid is proposed,and the exchanged power is calculated based on the voltage deviation between the rating value and measured value.Finally,a control flowchart for the transition between the four operational modes in transition is designed.Using the PSCAD/EMTDC platform,this paper takes a typical seven-point microgrid structure as an example,the proposed transition strategy is carried out,and the results show that the transition method and time sequence can achieve smooth transition between different operational modes.

Comprehensive Control Scheme for an Interlinking Converter in a Hybrid AC/DC Microgrid

This paper presents a comprehensive control scheme for the interlinking converter(ILC)in a hybrid AC/DC microgrid consisting of the outer loop flexible power sharing control and the improved robust inner loop control.The outer loop power control of ILC is presented to achieve flexible power sharing of distributed generations(DGs)in the hybrid microgrid,depending on different power management objectives,which is realized based on the deduced balance state equation,and regulating the frequency and DC voltage at the same time.The improved robust inner loop control of ILC is also presented to suppress external disturbance and system model uncertainties with the improved dynamic response.This improved inner loop control which includes a disturbance observer link,can force the converter current to track the reference value with no steady error and improve the dynamic stability of the microgrid・With the proposed outer loop power sharing control and improved inner loop control,the comprehensive control scheme for the ILC is presented・Simulations cases show the effectiveness and superiority of the proposed comprehensive control scheme.

Multi-objective optimal operation of hybrid AC/DC microgrid considering source-network-load coordination

Taking the consumption rate of renewable energy and the operation cost of hybrid AC/DC microgrid as the optimization objectives,the adjustment of load demand curves is carried out considering the demand side response(DSR)on the load side.The complementary utilization of renewable energy between AC area and DC area is achieved to meet the load demand on the source side.In the network side,the hybrid AC/DC microgrids purchase electricity from the power grid at the time-of-use(TOU)price and sell the surplus power of renewable energy to the power grid for profits.The improved memetic algorithm(IMA)is introduced and applied to solve the established mathematical model.The promotion effect of the proposed source-network-load coordination strategies on the optimal operation of hybrid AC/DC microgrid is verified.

Design and Implementation of a Communication Network and Operating System for an Adaptive Integrated Hybrid AC/DC Microgrid Module

This paper proposes an adaptive integrated hybrid AC/DC microgrid module to accommodate a wide range of distributed renewable energy resources(DRERs),distributed energy storage devices(DESDs)and distributed demand resources(DDRs)into the existing distribution systems.This microgrid module is designed to be portable,scalable,easy to deploy,and simple to operate.The modeling of the proposed microgrid module,based on the IEC 61850 standard,is presented.A novel logical node is introduced,which describes functionalities of the bidirectional interlinking converter(BIC)interfacing AC sub-grid and DC sub-grid in a better way.To achieve the target of plug-and-play functionalities,specific microgrid module communication network(MMCN)and microgrid module operating systems(MMOS)are designed and implemented in the hardware prototype built in the laboratory.Experimental results obtained from the lab prototype clearly validate the effectiveness of the proposed design of the microgrid module,communication network and operating system.

基于NLESO的交直流微电网双向AC/DC换流器改进滑模稳压控制

针对交直流混合微电网中双向AC/DC换流器在外界扰动下出现的直流母线电压波动问题,设计了一种应用于双向AC/DC换流器的非线性扩张状态观测器(nonlinear extended state observer,NLESO),以实现对分布式电源功率波动和负荷投切变化等不确定因素的快速追踪与补偿,保证了在不同扰动下交直流混合微电网的稳定性。进一步提出了基于NLESO的改进积分滑模控制方法,提高了直流母线电压的控制精度。结合非线性光滑函数设计了滑模趋近律,消除了传统滑模控制中的高频抖振现象。通过Lyapunov理论对系统的稳定性进行分析验证,仿真结果表明该控制方法响应速度快、控制精度高、抗扰动能力强并且无抖振现象。

Research on power electronic transformer applied in AC/DC hybrid distribution networks

The AC/DC hybrid distribution network is one of the trends in distribution network development, which poses great challenges to the traditional distribution transformer. In this paper, a new topology suitable for AC/DC hybrid distribution network is put forward according to the demands of power grid, with advantages of accepting DG and DC loads, while clearing DC fault by blocking the clamping double sub-module(CDSM) of input stage. Then, this paper shows the typical structure of AC/DC distribution network that is hand in hand. Based on the new topology, this paper designs the control and modulation strategies of each stage, where the outer loop controller of input stage is emphasized for its twocontrol mode. At last, the rationality of new topology and the validity of control strategies are verified by the steady and dynamic state simulation. At the same time, the simulation results highlight the role of PET in energy regulation.

面向低压大容量直流供电的混合型AC/DC接口变流器解耦控制

为解决传统基于电流源型整流器(currentsourcerectifier,CSR)的两级式高降压比电力电子变换设备中存在的多控制目标之间的耦合问题,在所提出的相控电流源型整流器和输入串联输出并联LLC-DC/DC变换器相结合的混合型拓扑结构基础上,通过建立考虑系统直流环节电感电容的小信号模型,提出了一种在较低自由度下可同时实现交流侧功率因数和输出直流电压调节的解耦控制方法。通过绘制系统的根轨迹,分析了系统解耦前后控制参数对系统稳定性的影响。最后,通过RT-Lab半实物仿真验证了所提方法的有效性。

基于改进MFAC的交直流微电网分布式二次控制

针对现有交直流微电网分布式二次控制(distributed secondarycontrol,DSC)受分布式电源一次控制参数影响较大、通信拓扑结构复杂、二次控制参数难以整定等问题,提出基于改进MFAC的交直流微电网DSC(MFAC-DSC),利用分布式电源的历史采样数据在线估计其动态线性化参数,解决了传统方法受一次控制参数影响较大的问题;通过优化DSC的通信结构和控制策略,避免了互联变流器参与二次控制通信,解决了互联变流器通信失效影响DSC的问题;推导了MFAC-DSC系统收敛性,给出了稳定收敛条件。基于交直流微电网实验平台在多种工况下验证了MFAC-DSC的可行性,与传统的DSC策略的对比结果表明:MFAC-DSC方法有效减少分布式电源下垂系数变化带来的功率波动,保证下垂系数有更大的调节范围,同时解决了互联变流器通信失效造成的控制失效和母线电压偏移等问题。

混合微网中双向AC/DC变换器研究与设计

在交直流混合电网中,AC/DC变换器既要实现直流微网与上级交流电网的连接,也要成为风力发电、燃气轮机发电等交流型分布式能源的并网接口。基于此,首先建立交直流混合微网中AC/DC变换器模型;其次采用PID闭环控制,实现配电系统的稳定,并在系统中增设可控出力的蓄电池双向功率变换环节,实现功率平衡;最后采用SVPWM进行逆变控制策略,降低谐波畸变率,进一步保证系统稳定性。

Performance Analysis of Grid Connected and Islanded Modes of AC/DC Microgrid for Residential Home Cluster

This paper presents performance analysis on hybrid AC/DC microgrid networks for residential home cluster. The design of the proposed microgrid includes comprehensive types of Distributed Generators (DGs) as hybrid power sources (wind, Photovoltaic (PV) solar cell, battery, fuel cell). Details about each DG dynamic modeling are presented and discussed. The customers in home cluster can be connected in both of the operating modes: islanded to the microgrid or connected to utility grid. Each DG has appended control system with its modeling that will be discussed to control DG performance. The wind turbine will be controlled by AC control system within three sub-control systems: 1) speed regulator and pitch control, 2) rotor side converter control, and 3) grid side converter control. The AC control structure is based on PLL, current regulator and voltage booster converter with using of photovoltaic Voltage Source Converter (VSC) and inverters to connect to the grid. The DC control system is mainly based on Maximum Power Point Tracking (MPPT) controller and boost converter connected to the PV array block and in order to control the system. The case study is used to analyze the performance of the proposed microgrid. The buses voltages, active power and reactive power responses are presented in both of grid-connected and islanded modes. In addition, the power factor, Total Harmonic Distortion (THD) and modulation index are calculated.

基于改进过压限制器和ACDTS的混联半波长系统故障保护策略

交直流混联半波长输电系统的暂态特性与常规的混联系统存在着很大差异。当混联系统半波长沿线发生不对称故障时,直流系统会受到沿线工频过电压和过电流的冲击。文章详细分析了混联系统半波长沿线故障的传播过程,研究了故障传播耦合机理。针对直流侧过电压问题,提出了在直流母线侧加装改进过压限制器,增设辅助限压通道,分级抑制直流侧过电压,并降低单个通道的电流值,提高了系统保护的限压水平;另一方面,对于直流侧过电流问题,提出了在换流站接口端并联接入双向晶闸管,实现交流系统等效三相短接,隔离交流侧母线馈入的故障过电流,确保换流站设备及线路的安全性。最后利用仿真验证了两种保护策略的可行性。

Practice and Prospect of AC/DC Hybrid Power Grid in Southern China

China Southern Power Grid is a unique EHV AC/DC hybrid transmission network that operates in China. In its service area, the distribution of energy resources and the development of economy are extremely unbalanced, so long-distance and bulk power transmission are needed; besides, the geography and climate conditions are serious, rains, fogs, lightning and typhoon as well as high temperature are common all the year round. Facing these challenges, the power grid enhanced stability control, improved the equipment and strengthen the network structure. In the future, the power grid plans to optimize the disposition of power sources and build digitalized power system.

基于切换模型的双向AC-DC变换器控制策略

双向AC-DC变换器作为交直流混合微电网的重要组成部分,对系统的稳定运行和功率的协调分配有着重要作用。本文基于切换系统理论,提出一种双向AC-DC切换控制方法。该方法首先建立双向AC-DC切换动态模型,选取系统的储能函数作为共同Lyapunov函数。基于此,设计了系统最优切换律并分析了该切换律条件下系统在切换平衡点处的稳定性。为了便于控制器数字化实现,建立了切换系统单步预测模型并对切换策略离散化。仿真和实验结果验证了本文所采用的建模方法和控制策略的有效性。

交直流混合微电网中AC/DC双向功率变流器的新控制策略

交直流混合微电网中的AC/DC双向变流器,对系统的稳定运行和功率的协调分配有着重要作用。为了使直流微电网部分作为一个电压功率可控的单元接入交流母线,提出了一种新的AC/DC双向变流器控制策略,用于平衡交直流微电网间的功率流动并提高系统联网和孤岛运行的稳定性及可控性。在联网模式时,新方法基于dq坐标系,通过直流侧电压外环给定内环直轴电流参考值,进而控制功率流动和联网运行。孤岛模式时,新方法以交直流母线的电压差值作为外环,控制功率在交直流母线间的流动,使其互为支撑,提高系统稳定性。与传统的并网控制不同,新方法在电压控制的基础上引入有功功率控制项,很好地解决了并网时功率流动的问题。通过对双向变流器及其控制策略的分析研究,给出新方法的状态方程及控制框图。仿真结果证明了该方法的可行性和有效性。

基于双向DC/AC变换器的混合储能系统动态控制策略

针对风电和光伏并网发电系统的功率波动问题,研究了一种基于双向DC/AC变换器的混合储能系统的动态控制策略。对含有超级电容器与蓄电池组的混合储能系统,通过双闭环控制器对变换器内部的电压电流进行控制,把波动变化较快的电流分量分配给超级电容器,由蓄电池来响应波动变化较慢的电流分量。同时,控制系统将超级电容器的电压稳定在预设范围内。基于扩展卡尔曼滤波(Extended Kalman Filter,EKF)对蓄电池的荷电状态(State of Charge,SOC)进行控制,使其SOC值稳定在安全范围内并延长了蓄电池的使用寿命。通过仿真实验,验证了控制方法的有效性。

AC/DC混合输电系统分散协调控制

针对电压源型高压直流输电(VSC-HVDC)在应用中带来的AC/DC交直流输电系统的协调控制问题,建立了AC/DC数学模型,并对AC/DC提出了一种新的分散最优协调控制模式。在该模式中,逆系统线性化理论被应用于直流输电系统的控制。文中为了与交流电网相配合,将标幺制引入了直流输电系统,并以Lyapunov间接法证明了该闭环非线性系统的稳定性。AC/DC混合输电系统的数值仿真结果表明了该控制策略的有效性和鲁棒性。

直流微电网双向AC/DC变换器并联系统控制策略仿真研究

为了便于扩展直流微电网的容量与增强系统可靠性,采用双向AC/DC变换器并联系统来实现直流微电网与大电网之间的能量交互。提出了一种直流微电网双向AC/DC变换器并联系统的低电压偏移功率均分控制策略,通过反馈直流线路的平均电流作为全局变量,并引入积分环节,实现了各变换器的功率精确分配而不受线路参数的影响。通过引入平均输出电压比例积分控制,减小了直流母线电压的偏移。探讨了二次纹波电流对并联系统功率控制的影响,引入带阻滤波器,抑制二次纹波电流和电压对并网电流畸变率的影响。分析了变换器并联系统的稳定性,给出了合适的控制参数。最后,仿真验证了所提出的控制策略的有效性。