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.

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.

Power Grids' Operation Mode to See Changes from AC to DC or AC/DC Hybrid

1.Development of renewable energies brings challenges to the power grid technologies With the development of power generation technologies for renewable energies,the pattern of clean energy system,in which the renewable energies play the principal role and the electrical power is the main terminal energy,will take shape gradually.In 2012,for example,the global installed capacity with the renewable energies exceeded 1,470 GW(out of which 480 GW was non-hydro renewable energies),achieved a year-on-year increase of 8.5%,accounting for more than 26%of the total global installed capacity,and supplying 21.7%of the electrical power in the globe.The installed capacity of power generation with the solar energy first toppped the 100 GW mark,and the

单级三相谐波电流注入可升降压AC/DC变换器

为适应电动车充电电压宽范围变化需求,本文针对传统充电桩前级整流器拓扑开展研究,提出一种新式单级三相AC/DC变换器。该变换器集成了三相桥式不控整流电路与Cuk模块,为降低输入侧电流谐波分量,选用双向开关管构建谐波电流回馈通路,整体构造成单级式拓扑结构。文章阐述了变换器的电路结构及工作模态,通过建立变换器的等效模型推导出电压增益。变换器通过简单的控制逻辑即可实现正弦输入电流并拥有高功率因数。最后通过搭建变换器数字控制实验平台验证了所提变换器的可行性。

高频链AC-DC矩阵变换器的变控制频率软开关调制策略

针对高频链AC-DC矩阵变换器的高效率要求,提出了一种变控制频率软开关调制策略。该调制策略在基于零矢量嵌入的分段同步控制策略基础上,以单控制周期平均功率不变为原则,通过改变控制周期长度,并调整一个控制周期内的电压矢量排布,优化脉冲宽度,使变换器在换流时全部开关器件的零电压开通成为可能。通过仿真分析和实验证明,采用本文提出的变控制频率调制策略,变换器在整流和逆变模式下,均可实现网侧电流三相平衡正弦,功率因数达到0.981,输出电压纹波小,最高效率达到96.9%,实现了高性能、高效率运行。

Hierarchical Frequency-dependent Chance Constrained Unit Commitment for Bulk AC/DC Hybrid Power Systems with Wind Power Generation

As the steady-state frequency of an actual power system decreases from its nominal value,the composite load of the system generally responds positively to lower power consumption,and vice versa.It is believed that this load frequency damping(LFD)effect will be artificially enhanced,i.e.,sensitivities of loads with respect to operational frequency will increase,in future power systems.Thus,for wind-integrated power systems,this paper proposes a frequency-dependent chance constrained unit commitment(FDCCUC)model that employs the operational frequency as a dispatching variable so that the LFD effect-based load power can act as a supplemental reserve.Because the frequency deviation is safely restricted,this low-cost reserve can be sufficiently exerted to upgrade the wind power accommodation capability of a power system that is normally confined by an inadequate reserve to cope with uncertain wind power forecasting error.Moreover,when the FDCCUC model is applied to a bulk AC/DC hybrid power system consisting of several independently operated regional AC grids interconnected by DC tie-lines,a hierarchically implemented searching algorithm is proposed to protect private scheduling information of the regional AC grids.Simulations on a 2-area 6-bus system and a 3-area 354-bus system verify the effectiveness of the FDCCUC model and hierarchical searching algorithm.

Battery Storage Configuration of AC/DC Hybrid Distribution Networks

The upscaling requirements of energy transition highlight the urgent need for ramping up renewables and boosting system efficiencies.However,the stochastic nature of excessive renewable energy resources has challenged stable and efficient operation of the power system.Battery energy storage systems(BESSs)have been identified as critical to mitigate random fluctuations,unnecessary green energy curtailment and load shedding with rapid response and flexible connection.On the other hand,an AC/DC hybrid distribution system can offer merged benefits in both AC and DC subsystems without additional losses during AC/DC power conversion.Therefore,configuring BESSs on an AC/DC distribution system is wellpositioned to meet challenges brought by carbon reductions in an efficient way.A bi-level optimization model of BESS capacity allocation for AC/DC hybrid distribution systems,considering the flexibility of voltage source converters(VSCs)and power conversion systems(PCSs),has been established in this paper to address the techno-economic issues that hindered wide implementation.The large-scale nonlinear programming problem has been solved utilizing a genetic algorithm combined with second-order cone programming.Rationality and effectiveness of the model have been verified by setting different scenarios through case studies.Simulation results have demonstrated the coordinated operation of BESS and AC/DC hybrid systems can effectively suppress voltage fluctuations and improve the cost-benefit of BESSs from a life cycle angle.

Two-stage Optimal Dispatching of AC/DC Hybrid Active Distribution Systems Considering Network Flexibility

The increasing flexibility of active distribution systems(ADSs)coupled with the high penetration of renewable distributed generators(RDGs)leads to the increase of the complexity.It is of practical significance to achieve the largest amount of RDG penetration in ADSs and maintain the optimal operation.This study establishes an alternating current(AC)/direct current(DC)hybrid ADS model that considers the dynamic thermal rating,soft open point,and distribution network reconfiguration(DNR).Moreover,it transforms the optimal dispatching into a second-order cone programming problem.Considering the different control time scales of dispatchable resources,the following two-stage dispatching framework is proposed.d dispatch uses hourly input data with the goal(1)The day-ahea of minimizing the grid loss and RDG dropout.It obtains the optimal 24-hour schedule to determine the dispatching plans for DNR and the energy storage system.(2)The intraday dispatch uses 15-min input data for 1-hour rolling-plan dispatch but only executes the first 15 min of dispatching.To eliminate error between the actual operation and dispatching plan,the first 15 min is divided into three 5-min step-by-step executions.The goal of each step is to trace the tie-line power of the intraday rolling-plan dispatch to the greatest extent at the minimum cost.The measured data are used as feedback input for the rolling-plan dispatch after each step is executed.A case study shows that the comprehensive cooperative ADS model can release the line capacity,reduce losses,and improve the penetration rate of RDGs.Further,the two-stage dispatching framework can handle source-load fluctuations and enhance system stability.

隔离型双向AC-DC矩阵变换器闭环控制方法研究

根据隔离型双向AC-DC矩阵变换器(Isolated AC-DC Matrix Converter,IAMC)没有中间电容缓冲环节,输入和输出变换器控制之间存在耦合,研究提出了IAMC两级功率变换器的控制方法。通过对全桥变换器进行闭环控制进而实现对直流侧输出电流和功率的直接控制;三相-单相矩阵变换器实现对有功和无功功率的独立控制,以满足网侧功率因数的高精度控制。所提控制策略有效降低了两级变换器的耦合强度,保证了系统的良好性能。在MATLAB中进行仿真,结果表明,所提出的控制方法在使系统电能质量得到提高的同时,可以实现单位功率因数可调,验证了所提控制策略的正确性和有效性。

V2G车网互联的双向AC/DC变换器直流阻抗模型及特性分析

双向AC/DC变换器的控制及直流输出阻抗是电动汽车充电桩并网运行及稳定性分析的关键。首先,提出含直流下垂环节的虚拟同步电机(VSM)控制策略,并利用上层功率指令实现双向AC/DC变换器直流电压的无差调节。然后,建立VSM功率控制环小信号模型,分析有功功率传输、有功功率指令与直流电压间的交互作用及影响。接着,建立双向AC/DC变换器在直流下垂VSM控制策略下的直流输出阻抗模型,详细分析阻尼系数、惯性系数、直流侧电容、传输功率、直流下垂系数等关键参数对直流输出阻抗的影响。最后,通过仿真及阻抗测量验证了所提直流下垂VSM控制策略的有效性和阻抗模型的正确性。

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.

一种适用于电动汽车的无电解电容单级双向AC/DC变换器

针对电动汽车充电电源额外热量产生影响电池使用寿命的问题,提出一种无电解电容隔离式单级双向AC/DC变换器。该变换器能有效阻止低频功率纹波注入电池单元,减少了额外热量的产生;同时电解电容的消除也大大提高了系统的可靠性。控制策略方面,提出的一种四相控制器,不仅能使所有开关管实现零电压开关(Zero Voltage Switch,ZVS),并在导通损耗进行了性能优化。最后,通过PSIM仿真软件和实验样机,验证了理论分析的正确性和可行性。

Optimal power flow calculation in AC/DC hybrid power system based on adaptive simplified human learning optimization algorithm

This paper employs an efficacious analytical tool,adaptive simplified human learning optimization(ASHLO)algorithm,to solve optimal power flow(OPF)problem in AC/DC hybrid power system,considering valve-point loading effects of generators,carbon tax,and prohibited operating zones of generators,respectively.ASHLO algorithm,involves random learning operator,individual learning operator,social learning operator and adaptive strategies.To compare and analyze the computation performance of the ASHLO method,the proposed ASHLO method and other heuristic intelligent optimization methods are employed to solve OPF problem on the modified IEEE 30-bus and 118-bus AC/DC hybrid test system.Numerical results indicate that the ASHLO method has good convergent property and robustness.Meanwhile,the impacts of wind speeds and locations of HVDC transmission line integrated into the AC network on the OPF results are systematically analyzed.

一种面向储能系统的双向隔离型AC-DC矩阵变换器控制策略

为了满足网侧高电能质量以及储能元件安全可靠和长使用寿命的需求,本文针对双向隔离型AC-DC矩阵变换器提出了一套系统的控制策略,包括对系统的双闭环控制和变换器的后级单重移相调制方法。其中双闭环控制包含网侧电流内环控制和直流侧电流外环控制,调制方法中保持前后级电路间协调同步,前级电路采用双线电压调制方式,后级电路采用等比例移相调制方式。仿真和实验结果显示,变换器的网侧功率因数可达0.99,直流侧电压纹波在0.15%以内。直流侧电流指令突变时,电流跟踪速度快且无超调。因此,采用所提出的控制策略可以保证网侧电能质量高、直流侧具有良好的动静态特性。

Characteristic Analysis of UHVAC/DC Hybrid Power Grids and Construction of Power System Protection

Strong DC coupling with weak AC and large-scale renewable energy integration are the two significant characteristics of ultra-high-voltage AC/DC(UHVAC/DC)hybrid power grids in China.Strong coupling between AC and DC grids and the different integration performance of renewable energy sources have profoundly changed the stability characteristics of the power system.The traditional stability control system is inadequate for the stability control of UHVAC/DC power grids.This paper analyzes the requirements for constructing an integrated defense system in a UHVAC/DC hybrid power grid(i.e.power system protection).The definition,connotation,and designing principles of power system protection are put forward.The relationship between the power system protection and the traditional three-defense lines is investigated.The design principles,general hardware structure and main functions of a power system protection are presented.Key problems and technologies are specified in the construction of the power system protection.

一种高效率半桥LLC型的AC/DC变换器设计

AC/DC开关电源是电力系统的主要动力来源,其发展趋势是:容量大、功率密度大、效率高、功率因数低、谐波含量低。但现有的数字电源仍存在着一些普遍问题:抗干扰能力差、结构功能简单、无法满足电厂和变电站等相关场所使用需求。设计了一种基于芯片控制的半桥开关电源,对其主电路进行了理论分析,并对EMI整流滤波电路、PFC功率因数校正电路、LLC半桥电路等电路进行了详细的设计。实验测试结果表明,该设计合理,具有大容量、高效率、高功率因数、低纹波等特点,能够充分满足目前的市场需求。

基于扩展移相的隔离型AC-DC变换器零矢量PWM调制策略

传统隔离型双向AC-DC变换器多为两级式结构,变换器效率低、控制系统复杂,现有的单级式解决方案通常依赖大量实时计算,难以兼具低电流应力、宽软开关范围和高功率传输能力特性。为此,该文设计基于双有源全桥的新型单级隔离型双向AC-DC谐振变换器,提出一种含有零矢量的复合频率调制策略。从高频开关周期入手,利用数学推导,证明所提方案在实现自动功率因数校正功能的同时,可降低开关器件的开关频率,免除附加吸收电路,实现交直流全桥的软开关,且几乎无功率回流,从而有效提升变换器的功率传输能力,所提单变量调节方法简化控制系统设计。最后,搭建额定功率为450W的仿真和实验平台,证明理论分析的正确性和调制策略的可行性。

一种面向高频链AC-DC矩阵变换器的高频变压器绕组优化设计方法

针对高频链AC-DC矩阵变换器中高频变压器绕组损耗大的问题,提出了一种高频变压器绕组优化设计方法,该方法首先建立了漏感模型和绕组损耗模型,并基于模型合理选择关键参数作为优化参数,应用有约束的多目标遗传优化算法对关键参数进行寻优,最后得到一套高频变压器绕组的优化设计方案。仿真和实验结果表明,该方法与传统面积乘积法(AP)法相比,绕组损耗可降低10%以上,变换器整机效率最高提升了1.07%,由此证明,该变压器绕组优化设计方法可以通过降低高频变压器的绕组损耗,达到降低高频链AC-DC矩阵变换器损耗、提升变换器整体效率的目的。

新能源汽车DC/AC变换电路教学模型设计

DC/AC变换电路作为新能源汽车上的核心电路之一,在实车上,由于集成度高、高电压等特性,非常不利于初学者进行学习。本文中设计的DC/AC变换电路教学模型,学生不仅能直观认识其主电路和控制电路的结构,而且还能通过预留的接线端子进行电路再次搭建和测量其关键信号线上的电路参数,进而快速掌握DC/AC变换电路的基本结构和工作原理,为后续实车故障诊断打下较好的基础。

隔离型AC-DC矩阵变换器最小电流应力控制方法

针对隔离型AC-DC矩阵变换器降低功率器件成本、提高效率和抑制电磁干扰等需求,提出了一种基于零矢量嵌入的移相策略的最小电流应力控制方法。基于移相策略深入研究了影响变换器电流应力的关键因素。建立了三维(3D)功率模型,从中求取等功率分布线,通过引入功率约束条件以及移相角范围,对电流应力在限定条件下采用序列二次寻优方法进行最小化寻优,得到使电流应力最小的最优移相比。仿真和实验结果表明,基于零矢量调制的移相调制策略可以实现前后级电路的协调控制,功率因数在0.96左右,直流侧输出电压和电流稳定且纹波小。因此,采用所提控制方法,在保证网侧和直流侧的基本性能的同时,实现了对变换器电流应力的最小化。