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.

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.

Reverse Droop Control-based Smooth Transfer Strategy for Interface Converters in Hybrid AC/DC Distribution Networks

Hybrid AC/DC distribution networks are promising candidates for future applications due to their rapid advancement in power electronics technology.They use interface converters(IFCs)to link DC and AC distribution networks.However,the networks possess drawbacks with AC voltage and frequency offsets when transferring from grid-tied to islanding modes.To address these problems,this paper proposes a simple but effective strategy based on the reverse droop method.Initially,the power balance equation of the distribution system is derived,which reveals that the cause of voltage and frequency offsets is the mismatch between the IFC output power and the rated load power.Then,the reverse droop control is introduced into the IFC controller.By using a voltage-active power/frequency-reactive power(U-P/f-Q)reverse droop loop,the IFC output power enables adaptive tracking of the rated load power.Therefore,the AC voltage offset and frequency offset are suppressed during the transfer process of operational modes.In addition,the universal parameter design method is discussed based on the stability limitations of the control system and the voltage quality requirements of AC critical loads.Finally,simulation and experimental results clearly validate the proposed control strategy and parameter design method.

计及混合通信组网的信息物理主动配电系统协调规划

为充分提高配电系统调度和控制的灵活性,建设和落实以智能化和主动化为导向,以信息通信技术为支撑的信息物理主动配电系统(cyber-physical active distribution system,CPADS)显得至关重要。基于此,提出计及混合通信组网的CPADS协调规划方法。首先,将信息域混合通信组网策略和物理域主动配电系统时空运行策略有机统一,建立旨在最小化投资–运行总成本的CPADS协调规划模型。具体而言,综合考虑主动控制设备投资成本、有线/无线组网投资成本、网损成本、弃光成本、失负荷成本、电压偏差优化成本等建立多维度投资运行目标函数。然后,综合考虑物理域主动控制设备的选址或选型、信息域有线组网和无线组网的差异性构建投资约束;充分考虑设备主动控制策略、电压偏差等构建CPADS时空运行约束。最后,综合考虑场景概率分布不确定性置信度集合的1-范数和∞-范数约束,将所提规划模型重构为一个数据驱动下的分布鲁棒协调规划框架,并利用列与约束生成(columnandconstraintgeneration,CCG)算法迭代求解。

50 GHz optical true time delay beamforming in hybrid optical/mm-wave access networks with multi-core optical fiber distribution

We propose and experimentally validate an optical true time delay beamforming scheme with straightforward integration into hybrid optical/millimeter（mm）-wave access networks. In the proposed approach, the most complex functions, including the beamforming network, are implemented in a central office, reducing the complexity and cost of remote antenna units. Different cores in a multi-core fiber are used to distribute the modulated signals to high-speed photodetectors acting as heterodyne mixers. The mm-wave carrier frequency is fixed to 50 GHz（VBand）, thereby imposing a progressive delay between antenna elements of a few picoseconds. That true time delay is achieved with an accuracy lower than 1 ps and low phase noise.

考虑风电不确定性的交直流混合配电网分布式优化运行

未来交直流混合配电网表现出显著的分区特性,且不断渗入的分布式电源(如风电等)具有较强的不确定性。基于此,该文提出考虑风电不确定性的交直流混合配电网分布式优化模型。该模型以最小化上级电网购电成本(交流子区域电网)与交直流子区域间购售电成本、弃风成本、微型燃气轮机发电成本等为优化目标,利用1-范数和∞-范数对筛选获得的典型场景概率分布不确定性进行约束,构建基于数据驱动的两阶段分布鲁棒模型,并采用列与约束生成算法进行求解。而交直流混合配电网分布式优化则以电压源型换流器为耦合元件,通过功率一致性约束对各子区域配电网进行协调,并利用交替方向乘子进行全局协调与迭代求解,实现整个交直流混合配电网各子区域间功率平衡。最后,算例验证了所提分布式优化和分布鲁棒方法的有效性。