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.

A Discrete State Event Driven Simulation based Losses Analysis for Multi-terminal Megawatt Power Electronic Transformer

At present,power electronic transformers(PETs)have been widely used in power systems.With the increase of PET capacity to the megawatt level.the problem of increased losses need to be taken seriously.As an important indicator of power electronic device designing,losses have always been the focus of attention.At present,the losses are generally measured through experiments,but it takes a lot of time and is difficult to quantitatively analyze the internal distribution of PET losses.To solve the above problems,this article first qualitatively analyzes the losses of power electronic devices and proposes a loss calculation method based on pure simulation.This method uses the Discrete State Event Driven(DSED)modeling method to solve the problem of slow simulation speed of large-capacity power electronic devices and uses a loss calculation method that considers the operating conditions of the device to improve the calculation accuracy.For the PET prototype in this article,a losses model of the PET is established.The comparison of experimental and simulation results verifies the feasibility of the losses model.Then the losses composition of PET was analyzed to provide reference opinions for actual operation.It can help pre-analyze the losses distribution of PET,thereby providing a potential method for improving system efficiency.

Structured Microgrids (SμGs) and Flexible Electronic Large Power Transformers (FeLPTs)

Structured microgrids(SμGs)and Flexible electronic large power transformers(FeLPTs)are emerging as two essential technologies for renewable energy integration,flexible power transmission,and active control.SμGs provide the integration of renewable energy and storage to balance the energy demand and supply as needed for a given system design.FeLPT’s flexibility for processing,control,and re-configurability offers the capability for flexible transmission for effective flow control and enable SμGs connectivity while still keeping multiscale system level control.Early adaptors for combined heat and power have demonstrated significant economic benefits while reducing environmental foot prints.They bring tremendous benefits to utility companies also.With storage and active control capabilities,a 300-percent increase in bulk transmission and distribution lines are possible without having to increase capacity.SμGs and FeLPTs will also enable the utility industry to be better prepared for the emerging large increase in base load demand from electric transportation and data centers.This is a win-win-win situation for the consumer,the utilities(grid operators),and the environment.SμGs and FeLPTs provide value in power substation,energy surety,reliability,resiliency,and security.It is also shown that the initial cost associated with SμG and FeLPTs deployment can be easily offset with reduced operating cost,which in turn reduces the total life-cycle cost by 33%to 67%.

New Progress of Power Electronic On-Load Tap Changing Distributing Transformer

At present, the widely applied mechanical on-load tap-changer is not suitable for the 10 kV power distribution network. Along with the development of power electronic technology, there has the report on on-load tap changing （OLTC） distributing transformer based on the power electronic technology. In this paper, the analysis on the characteristic of several kinds of non-contacts OLTC distributing transformer was carried on. The result indicates that OLTC distributing transformer based on the solid state relay has the broad applied prospect in the 10 kV medium distribution network.

Dual-Timescale Control for Power Electronic Zigzag Transformer

Power electronic zigzag transformer is an attractive solution for the flexible interconnection of smart distribution networks.It is constituted by slow-response and low-precision thyristor converters and fast-response and high-accuracy voltage source converters.This paper models its primary circuit and addresses its basic operation mechanism.Then a dual-timescale control scheme is investigated to realize the coordinated regulation of both types of converter.A simulation case is established in PSCAD containing interconnected mid-voltage distribution networks.Simulations with poor-and well-matched control timescales are both carried out.And accordingly,the power flow controllability under these conditions is compared.When the shorter control timescale is no more than tenth of the longer one,the power electronic zigzag transformer will operate with satisfying performances.

Optical fiber-based power and data delivery system for high voltage electronic current transformer

This paper describes a prototype power delivery system developed for high voltage electronic current transformer （ECT） that uses laser light to transfer power to and communicates with the primary converter. The design is based on optical-to-electrical power converters, solid-state diode lasers and optical fibers. Command signals are transmitted via the same up-fiber used to send power from secondary power supply to primary converter. The upward data transmission is completed during the brief interruption of power delivery without affecting steady power-supply. A simple comparator added to the primary converter can take the command data. Experimental results show that the fibers can provide reliable up-link for data transmission at 200 kb/s from the secondary to the primary converter. Based on the delivery system, the secondary converter can control three auxiliary channels to provide additional information. These monitoring channels are used in a time-multiplexing mode to provide information about the operation temperature, voltage and current at the remote unit for monitoring the ECT. This preventive maintenance or built-in test can increase reliability by giving early warning for necessary maintenance request.

Unbalanced Load Simulation of Electronic Power Transformer in Distribution System

A control scheme of electronic power transformer (EPT) in a three-phase four-wire distribution system, which included an input section, an isolating section and an output section, was researched under unbalanced loads. The simple and appropriate control scheme was developed through analyzing the system requirements of the primary side and the load requirements of the secondary side. In the input section, a dual-loop control in synchronous rotating d-q coordinates was introduced, and in the output section, a dual-loop control based on instantaneous output voltage was used. Load characteristics of EPT were investigated by using Matlab/Simulink software. Simulation results showed that, with the proposed control scheme, the EPT has good performances and the sinusoidal input current and constant output voltage can be realized under both balanced and unbalanced loads.

Towards a (More) Electronic Transmission and Distribution (eT&D)

The challenges and the path towards a(more)electronic transmission and distribution(eT&D)is presented in this paper.The challenges are first identified together with key stakeholders in the drive for grid modernization.A fundamental question is then asked about the investment priority.Six basic characteristics are reviewed,leading to the composition of structured microgrids as the basic functional cell of a modern grid.One example of fractal radial structure and one fractal meshed structure are presented.The likely evolution path is then proposed together with basic technology sets.Specific foundation technologies are discussed in detail,including adiabatic power conversion,3MC technology,medium voltage conversion,distribution-level electronic power transformer and FACTs hardware integration,and back-to-back converters as a universal interconnect element.The rapidly emerging on-wire sensing technology is also discussed.It is pointed out that the distribution-level large electronic power transformer will provide a key component to enable hybrid ac/dc grid flow control and ancillary support for a flexible electronic transmission and distribution(eT&D)systems.

电力电子变压器参与配电网调压调频的应用研究

为提升配电网的稳定性,该文提出利用配电网电力电子变压器对配电网的电压和频率进行调节。通过电力电子变压器输入级进行配电网无功功率调节,利用母线电压下垂特性提出无功调节方法,并引入无功电流反馈以提高配电网电压质量和稳定性;同时,通过电力电子变压器输出级控制负载电压以调节配网有功功率,作为一次调频储备负载,从而在频率暂态期间减小频率偏差。通过对基于配电网电力电子变压器的调压调频控制方法进行实验验证,所提控制策略能改善配电网电压和频率质量,有效提升配电网的稳定性。

“光储直柔”建筑配电系统应用研究

以某项目为例分析“光储直柔”在建筑物中的应用,并对“光储直柔”系统的应用场景、建筑直流配电系统的关注点及“光储直柔”系统关键设备进行阐述。

Power electronic transformer with adaptive PLL technique for voltage-disturbance ride through

The power electronic transformer(PET) has recently emerged as a type of power converter. It features the basic functions of power conversion and isolation as well as additional functions related to power quality control. A novel PET for a distribution grid called a flexible power distribution unit is proposed in this paper, and the energy exchange mechanism between the network and the load is revealed. A 30 kW 600 VAC/220 VAC/110 VDC medium-frequency isolated prototype is developed and demonstrated. This paper also presents key control strategies of the PET for electrical distribution grid applications,especially under grid voltage disturbance conditions.Moreover, stability issues related to the grid-connected three-phase PET are discussed and verified with an impedance-based analysis. The PET prototype is tested, and it passes the voltage-disturbance ride-through function. The experimental results verify the power quality control abilities of the PET.

A novel low voltage ride through strategy for cascaded power electronic transformer

In view of the operating characteristics for voltage sags of AC side of the power electronic transformer(PET),a low-voltage ride through(LVRT)strategy adapted to bidirectional power exchange of PET is proposed for the purposes of maintaining the system stability,assisting the system voltage recovery and protecting PET safety.During the asymmetric voltage sag,the negative sequence current of PET is eliminated to ensure the symmetry of the injected current.According to the degree of positive sequence voltage sag,the reactive current injection is provided to assist in voltage recovery.According to the PET active power condition before the voltage sag,the level and direction of which are maintained as far as possible without exceeding the limit,for which the disturbance to the AC and DC grids is reduced.Finally,the effectiveness of the proposed LVRT strategy is verified by simulation model.

A Critical Topology Review of Power Electronic Transformers:In View of Efficiency

Design of power electronic transformers is a hot research topic and its efficiency improvement is a critical problem all over the world.It is also the largest barrier hindering the application of power electronic transformers in industry.In this paper,the state of power electronic transformers is fully presented in terms of efficiency improvements.It is followed by the efficiency modeling of several typical topologies,and their detailed analysis and comparisons.Then,the corresponding industrial application scope of these topologies is presented,providing theoretical guidance for their industrial applications.

单相电力电子变压器整流级复合无源控制

针对单相级联H桥型电力电子变压器整流级易受输入电压、负载电阻等参数影响,及传统PI双闭环控制性能较差的问题,提出一种电流内环的复合控制策略。在无源控制(PBC)的基础上加入扩张状态观测器(ESO)作为扰动观测,并进行补偿。通过MATLAB/Simulink软件搭建三级型电力电子变压器整流级模型,将结合扩张状态观测器的无源控制与传统PI控制、无源控制进行对比。结果表明:提出的控制策略能有效降低交流侧电流谐波量,且系统动态响应速度快、鲁棒性更好。

A Three-phase Integrated Power Electronic Transformer with the Capability of DC Fault Clearance

This paper presents a three-phase integrated power electronic transformer(PET)topology with the capability of DC fault clearance based on the investigation of PET topology.The proposed PET has three ports of high-voltage AC,high-voltage DC and low-voltage DC,which can achieve the flexible access of distributed energy resources・The power unit of the PET adopts a three-phase integrated topology,and the single-phase fluctuating power in the DC-link capacitor is reduced by a 4-port DC/DC converter,thereby reducing the capacitance of the DC-link capacitor;Meanwhile,the power unit uses the clamp double sub-module(CDSM)to allow for self-clearing of the short-circuit fault on the high-voltage DC side.Finally,this paper verifies the proposed PET through an EMT simulation and experimental prototype.

基于数字孪生技术的新型电力系统数字化

随着“双碳”目标的提出,大规模的清洁能源、电力电子设备和新型负荷将接入电力系统,传统的电力系统管理控制模式难以应对双侧随机性、波动性增强等问题,电力系统的安全稳定运行迎来巨大挑战。数字孪生技术作为重要的数字化手段,成为电力系统转型升级新方法。针对新型电力系统内在机理发生的深刻复杂变化,综述了数字孪生的发展历程以及其在电力系统领域的研究现状,并从新型电力系统数字化需求、数字建模方法、数字化平台建设3个层面研究了电力系统数字化转型进程。最终,提出了以数字孪生技术为核心的新型电力系统建模方法和框架。

基于等效励磁电感的SiC串联器件型中压双有源桥变换器的软开关技术

基于SiC串联器件的双有源桥变换器因具有开关损耗小、功率密度高、能量控制简单等优势,有望成为中压变换场景中实现高频隔离的优选方案。为保证SiC串联器件的可靠均压,各器件上并联大容值缓冲电容,然而该设计使变换器在传输功率较低时难以实现零电压开通,严重影响变换器的整体效率和串联器件的可靠运行。该文通过构建SiC串联器件型中压双有源桥变换器多模态运行模型并深入分析其运行特性,提出一种基于等效励磁电感的无源软开关技术。所提技术可通过优化外接传输电感位置的方式实现中压侧等效励磁电感参数调节,从而在无额外控制前提下实现SiC串联器件的软开关范围扩展。最后,设计了4 kV/1 kV实验样机,实现了100 kW下运行。实验结果显示,所提出的软开关技术能显著地扩展变换器中SiC串联器件的软开关范围,在保证SiC串联器件均压稳定性的同时能够大幅降低变换器在轻载运行时的功耗。

0.2~2.0GHz100W超宽带GaN功率放大器

设计并实现了一款基于0.25μm GaN高电子迁移率晶体管(HEMT)工艺的100 W超宽带功率放大器。基于SiC无源工艺设计了集成无源器件(IPD)输入预匹配电路芯片;设计了基于陶瓷基片的T型集成输出预匹配电路;基于建立的传输线变压器(TLT)的精确模型,设计了宽带阻抗变换器,在超宽频带内将50Ω的端口阻抗变换至约12.5Ω,再通过多节微带电路与预匹配后的GaN HEMT芯片实现阻抗匹配。最终,以较小的电路尺寸实现了功率放大器的超宽带性能指标。测试结果表明,功率放大器在0.2~2.0 GHz频带内,在漏极电压36 V、输入功率9 W、连续波的工作条件下,输出功率大于103 W,漏极效率大于50%,输入电压驻波比(VSWR)≤2.5。