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。

交直流微电网AC/DC双向功率变换器控制策略

为了实现交直流混合微电网的可靠并网,基于微电网中AC/DC双向功率变换器下垂控制策略和预同步工作原理,提出一种适用于混合微电网中连接交直流子网的AC/DC双向功率变换器的控制策略。孤岛/并网模式时采用双向下垂控制实现双向功率流动。在由孤岛模式转为并网模式时,利用消除dq轴电压偏差实现幅值与相位同步,无需通过锁相环获取相位信息,实现平滑并网。同时,针对微电网中由于不平衡负载导致的三相不平衡工况,采用正负序分别控制的方法实现了非理想工况下微电网的同步互联。仿真结果验证了该方案的可行性。

孤立交直流混合微电网双向AC/DC换流器功率控制与电压波动抑制策略

在孤立交直流混合微电网中,对双向AC/DC换流器进行合理控制可以有效实现微网功率的协调分配并提高系统的抗外界干扰能力。将孤立混合微电网中的交流微网和直流微网等效为整合电源,分别给出双向AC/DC换流器交流侧和直流侧的有功功率下垂控制方程,进而提出基于全网功率成比例分配原则的双向AC/DC换流器外环功率控制策略,实现孤立混合微电网的功率平衡和自主分配;同时针对常规比例-积分(proportionalintegral,PI)内环控制无法获得理想的电压动态响应的问题,在对双向AC/DC换流器进行电压波动分析的基础上,提出一种抑制电压波动的双向AC/DC换流器改进内环控制策略,实现换流器电压对参考信号的无静差跟踪,提高下垂控制微电网系统的鲁棒稳定性。仿真结果验证了该控制策略的正确性和有效性。

基于扰动观测器的孤立交直流混合微电网双向AC/DC换流器电压波动控制策略研究

针对孤立交直流混合微电网中双向AC/DC换流器在外界扰动下出现电压波动的问题,设计了一种应用于双向AC/DC换流器的母线电压扰动观测器,以实现在分布式电源出力和负荷功率变化等外界扰动情况下对系统扰动量的快速跟踪,且无需增加额外的电压或电流传感器,保证了交直流混合微电网内分布式电源和负荷的即插即用功能。进一步地提出了基于扰动观测器的孤立交直流混合微电网双向AC/DC换流器电压波动控制策略,以有效抑制暂态电压波动和冲击,提高了孤立混合微电网在不同扰动下的动态响应性能和鲁棒稳定性。在PSCAD/EMTDC平台上搭建了孤立交直流混合微电网仿真模型,通过在不同暂态过程下的仿真测试验证了所提方法的有效性和正确性。

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。

基于前馈解耦的交直流混合微电网双向AC-DC变换器控制策略研究

作为交直流混合微电网的重要器件,双向AC-DC变换器能够实现能量的双向流动,满足混合微电网中负载波动对电能的需求,可平衡交直流母线电压。但双向AC-DC变换器的控制系统具有时变性,且非线性和耦合性较强,控制复杂,需要解决控制量间的耦合问题。本文针对这一问题展开研究,首先介绍混合微电网系统的结构,并建立双向AC-DC变换器数学模型;然后针对双向AC-DC变换器,采用交流侧电压前馈解耦方案,设计控制器并分析比例积分(PI)控制策略的稳定性;最后基于Matlab/Simulink建立系统仿真模型,以验证所提控制策略的可行性。仿真结果表明,前馈解耦控制策略下的双向AC-DC变换器具有快速的动态响应和良好的抗负载扰动性能。

Transient Characteristics and Accommodative Current Limiting Strategy for Bidirectional Interlinking Converters in Hybrid AC/DC Microgrids

Bidirectional interlinking converter(BIC)is the core equipment in a hybrid AC/DC microgrid connected between AC and DC sub-grids.However,the variety of control modes and flexible bidirectional power flow complicate the influence of AC faults on BIC itself and on DC sub-grid,which potentially threaten both converter safety and system reliability.This study first investigates AC fault influence on the BIC and DC bus voltage under different BIC control modes and different pre-fault operation states,by developing a mathematical model and equivalent sequence network.Second,based on the analysis results,a general accommodative current limiting strategy is proposed for BIC without limitations to specific mode or operation condition.Current amplitude is predicted and constrained according to the critical requirements to protect the BIC and relieving the AC fault influence on the DC bus voltage.Compared with conventional methods,potential current limit failure and distortions under asymmetric faults can also be avoided.Finally,experiments verify feasibility of the proposed method.

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。

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.

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.

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.

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.

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.

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.

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.

交直流混合微电网DC-DC变换器的改进VSG控制策略

针对交直流混合微网惯量低、交流频率和母线电压易受功率波动的影响,在混合微电网接口变换器虚拟同步电机(VSG)控制和交流微电网下垂控制的基础上,通过分析交流微电网的VSG控制策略,改进了适用于混合微网直流层储能DC-DC双向变换器的VSG控制。结果表明:在逆变模式下,系统的响应速度约为0.5 s,直流电压的波动最大约为1 V;在整流模式下,系统的响应速度约为0.5 s,直流电压的波动最大约为2 V。改进的交直流混合电网VSG协调控制策略,有效抑制了交直流混合微电网交流频率和直流电压的突变,均衡了混合微电网的功率传输,证明了所提控制策略的有效性。

Bi-objective optimal active and reactive power flow management in grid-connected AC/DC hybrid microgrids using metaheuristic-PSO

In the context of evolving energy needs and environmental concerns,efficient management of distributed energy resources within microgrids has gained prominence.This paper addresses the optimization of power flow management in a hybrid AC/DC microgrid through an energy management system driven by particle swarm optimization.Unlike traditional approaches that focus solely on active power distribution,our energy management system optimizes both active and reactive power allocation among sources.By leveraging 24-hour-ahead forecasting data encompassing load predictions,tariff rates and weather conditions,our strategy ensures an economically and environmentally optimized microgrid operation.Our proposed energy management system has dual objectives:minimizing costs and reducing greenhouse gas emissions.Through optimized operation of polluting sources and efficient utilization of the energy storage system,our approach achieved significant cost savings of~15%compared with the genetic algorithm coun-terpart.This was largely attributed to the streamlined operation of the gas turbine system,which reduced fuel consumption and associated expenses.Moreover,particle swarm optimization maintained the efficiency of the gas turbine by operating at~80%of its nominal power,effectively lowering greenhouse gas emissions.The effectiveness of our proposed strategy is validated through simu-lations conducted using the MATLAB®software environment.

基于混合储能的交直流混联微电网功率分级协调控制策略

针对交直流混联微电网孤岛运行时,仅靠互联变流器协调网间功率无法有效缓解系统频率与电压波动,且单一蓄电池储能难以适用多场景功率需求的问题,提出利用超级电容和蓄电池混合储能的交直流混联微电网功率协调控制策略。将混合储能作为储能子网连接在直流母线上,优先采用超级电容平抑交直流子网内功率波动,提出以储能荷电状态来划分五种工作模式的改进混合储能控制策略。兼顾超级电容快速响应特性和减少互联变流器的频繁起动,根据直流子网电压和交流子网频率波动程度,提出功率自治和功率互济工况的两级分层协调控制策略。通过设计混合储能处于不同工作模式的网间功率互济场景,仿真证明了所提混合储能和互联变流器协调控制策略能够平抑各子网负荷功率波动。

基于线性化方法的交直流混合配电系统网架规划

随着配电系统中直流设备的大量接入,交直流混合配电系统得到越来越广泛的应用。为适应交直流混合配电系统中不同交直流(AC/DC)类型的负荷或电源的接入,提出一种新的交直流混合配电系统网架结构规划方法,该方法考虑了网架交直流配置的所有可能性。首先以二进制网络矩阵描述配电系统的网架结构;其次建立网架单层规划模型,将规划变量和运行变量同时进行优化以提升全局寻优能力;最后将单层规划模型进行线性化处理,转换为混合整数线性规划问题以提升求解效率。仿真结果表明,所提方法能够为配电系统中不同交直流类型的负荷和电源的接入提供最佳的网架配置方案,相比于传统的纯交流规划方案具有更好的经济性和供电能力,在算法上与经典遗传算法求解的双层规划方法相比,具有更好的全局寻优能力和计算效率。