由于柔性直流输电系统通常采用架空线进行直流输电,其故障发生率较高。当系统发生单极短路接地故障后,通过真双极接线方式可将故障极不平衡功率转带给非故障极。根据换流站的功率裕度将不平衡功率分为自消纳和协同消纳情况,针对自消纳情况,通过送端双极换流站间的功率转带即可实现故障穿越;针对协同消纳情况,设计换流站及耗能电阻间的协调控制策略,考虑到耗能电阻投入时长有限,采用后续风机切机的方式减少直流系统内不平衡功率。最后,通过PSCAD验证了所提控制策略的有效性。仿真结果表明,该策略能有效避免故障范围的扩大,确保系统的安全运行。

Because DC system usually adopts overhead line for DC transmission, its failure rate is high. When a single-pole short-circuit grounding fault occurs in the system, the unbalanced power of the fault pole can be transferred to the non-fault pole through the real-bipolar wiring mode. The unbalanced power can be divided into self-absorption and collaborative absorption according to the power margin of the converter station. For the self-absorption situation, fault ride-through can be realized by power transfer between sending end bipolar converter stations. For the situation of collaborative absorption, the coordinated control strategies between converter station and energy dissipation resistance are designed. Considering the limited input time of energy dissipation resistance, unbalanced power in DC System is reduced by sub-sequent generator cutting. Finally, the effectiveness of the proposed control strategy is verified in PSCAD. The simulation results show that the strategy can effectively avoid the expansion of fault range and ensure the safe operation of the system.

电解水制氢(power-to-hydrogen,PtH)装置耦合海上风电运行,在促进风电消纳的同时可以制备绿色氢能,推进工业领域的无碳化进程,因而备受关注。文章开展海上风电制氢微网的实时能量管理策略研究。首先,构建海上风电制氢微网的实时能量管理模型,包含海上风电、电制氢装置以及储氢罐等元件。然后,提出基于近似动态规划(approximate dynamic programming,ADP)的微网实时能量管理策略,采用分段线性函数近似状态值函数以应对不确定性因素。最后,通过算例验证所提策略的有效性和优越性。在所提策略下,海上风电通过电制氢装置就地消纳,实现氢气的提前制备和存储。以具备精准预测技术的理想算例为基准,所提策略在满足正态分布的实时测试场景下,优化准确率平均值大于99%。

Introducing power-to-hydrogen (PtH) into offshore wind farms can assist the integration of wind power and produce green hydrogen, which accelerates decarbonization in industrial sectors and has attracted attention worldwide. In these circumstances, this paper studies the real-time energy management strategy of the offshore wind PtH microgrid. First, the real-time energy management model of the offshore wind PtH microgrid is proposed, including offshore wind farms, PtH devices and hydrogen storage tanks. Then, real-time energy management strategy based on approximate dynamic programming (ADP) is proposed. The value function is approximated by piece-wise linear functions (PLFs) to cope with uncertainties in the microgrid. Finally, the effectiveness and superiority of the proposed strategy is verified by case studies. Under the proposed strategy, offshore wind power can be consumed by PtH, achieving production and storage of hydrogen in advance. On the basis of the ideal case with perfect forecasting, the proposed strategy has an average optimization accuracy of more than 99% in real-time test scenarios with normal distribution.

混合级联型海上风电直流外送系统具有高压、大容量、投资成本低等优势,但其并网稳定性问题一直备受关注,而系统阻抗建模是分析稳定性的基础。基于电压源型换流器(voltage-source converter,VSC)与二极管整流器(diode rectifier units,DRU)的混合级联型海上风电直流外送系统,建立了VSC-DRU混合级联换流站的详细数学模型;为实现直流外送系统中有功功率主动分配和交流集电系统电压稳定,研究了含滤波电容电流反馈的VSC功率-电压调节控制策略;采用小信号扰动方法,考虑锁相环输出相角调节、有源阻尼控制及功率控制影响,推导并分析了闭环控制下VSC-DRU混合级联换流站的详细阻抗模型,为研究系统稳定性提供了依据。最后,在PSCAD/EMTDC中进行仿真验证,结果表明所提控制策略具有良好的功率-电压调节性能,并通过频率扫描法验证了所建详细阻抗模型的正确性。

Offshore wind power integration system applying hybrid cascaded DC transmission has the advantages of high voltage, large capacity and low investment cost, but its stability has gained many concerns. And the system impedance modeling is the basis for analyzing stability. In this paper, a detailed mathematical model of VSC-DRU hybrid cascaded valve station is established. In order to realize active power distribution and AC voltage control of the DC transmission system, the power-voltage control strategy of VSC with filter capacitor current feedback is studied. Considering the influence of output phase-angle adjustment of phase-locked loop, active damping control and power control, the detailed impedance model of VSC-DRU hybrid cascaded valve station is derived and analyzed by using small-signal disturbance method, which provides a basis for studying stability. Finally, the simulation results in PSCAD/EMTDC show that the proposed control has good performance of power-voltage regulation. And the correctness of the established detailed impedance model is verified by the frequency-scanning method.

We prove that testing feasibility for an AC power flow system is a strongly NP-hard problem. (C) 2019 Elsevier B.V.

本文针对煤炭码头卸车调度问题,提出了相应的多约束多目标优化模型,并设计了采用仿真推演策略解码的遗传算法求解。首先,本文考虑列车、煤种、场存、设备、翻堆线和卸车作业过程等约束条件,以卸车效率最大和列车在港时间最短为目标,构建了煤炭码头卸车调度问题多目标数学模型。然后,综合运筹学、遗传算法以及仿真技术,给出了煤炭码头卸车调度问题遗传算法详细设计,包括组合式编码和仿真推演解码方法,染色体生成算法,适应度函数设计,以及采用多种策略的遗传操作及修正等,并列出了算法步骤。实例测试表明,本算法的执行效率高而且优化效果好,结果适用。

This paper puts forward a multi-objective constrained optimization model on unloading scheduling problem of coal terminal and the design of the genetic algorithm in which a simulation strategy is used to decode. First, the optimization model on unloading job scheduling problem is established with the multi-objective concerning maximizing the rate of unloading and minimizing the total time of train in port and some constraints including trains, coals, stocks, equipment, dumping lines and unloading processes. On the basis of summing up operations research, genetic algorithm and simulation, the genetic algorithm is designed including the improved coding and decoding with the simulation and deduction method, the way of chromosome generation, the design of fitness, genetic operation and correction using multiple strategies. Besides, the paper lists the steps of the genetic algorithm. Finally, the actual numerical experiment and the successful application have shown that the solution has a high execution efficiency and satisfactory effect.