直流阻尼调制在大规模交直流电网中的作用

采用一种暂态能量函数,剖析直流阻尼调制抑制低频振荡的机理。基于留数,指出制约直流调制效果的关键因素,对直流调制在交直流电力系统中的运行特性进行分析,认为采用广域信号可以提高直流调制对区间振荡的抑制效果。以我国第1个交直流混合电网——南方电网为背景,验证理论分析的正确性。在此基础上,对直流阻尼调制在大规模交直流电网中的作用进行总结。     

High‐power‐factor single‐switch AC to DC converter for LED lighting

In this paper, we report a novel single‐switch AC to DC step‐down converter suitable for light emitting diodes. The proposed topology has a buck and a buck–boost converter. The circuit is designed to operate in the discontinuous conduction mode in order to improve the power factor. In this topology, a part of the input power is connected to the load directly. This feature of the proposed topology increases the efficiency of power conversion, improves the input power factor, produces less voltage stress on intermediate stages, and reduces the output voltage in the absence of a step‐down transformer. The theoretical analysis, design procedure, and performance of the proposed converter are verified by simulation and experiment. A 36 V, 60 W prototype has been built to demonstrate the merits of this circuit. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A robust power flow model for active power flow control via thyristor‐controlled series compensator

In this paper, a new power flow model for active power flow control through a thyristor‐controlled series compensator (TCSC) in an AC network system is proposed. The proposed power flow model is based on the Newton–Raphson method. In this model, TCSC's admittance effect is included as a state variable into the Jacobian matrix to avoid the divergence problem. Unlike similar studies in the literature, TCSC's admittance is ignored in the bus admittance matrix, and the need for rebuilding the bus admittance matrix in each power flow iteration caused by the change of TCSC's admittance is prevented. So, faster convergence for power flow calculation is achieved. For this aim, new power equations are obtained. Also, in the proposed approach, we need not consider each terminal of TCSC as an individual bus in the power flow calculation. Thus, increasing the Jacobian and bus admittance matrixes sizes caused by the total bus number is prevented. The proposed approach is tested on an IEEE 57‐bus test system. The obtained results prove that this approach provides efficient, reliable, and fast convergence. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A single‐stage integrated bridgeless AC/DC converter for electrolytic capacitor‐less LED lighting applications

In this paper, a single‐stage integrated bridgeless AC/DC converter is proposed. As compared to its counterpart that is composed of totem‐pole boost power factor correction (PFC) cascade fly‐back DC/DC converter, the studied circuit has less components number while overcoming the limits of the totem‐pole type. Thus, it is suitable to the low‐power LED lighting applications. Furthermore, when both PFC inductors L_b and magmatic inductance L_m of the transformer TR1 operate at discontinuous current mode, the bus voltage v_CB can be used to decouple the ac input and constant dc output power. Thus, the approach of increasing bus voltage ripple is employed to eliminate electrolytic capacitors and obtain long operation lifetime. Additionally, it is able to be compatible with our studied twin‐bus configuration for increasing the overall efficiency. A 50‐W hardware prototype has been designed, fabricated, and tested in the laboratory to verify the proposed converter validity. Copyright © 2014 John Wiley & Sons, Ltd.     

A study of an interactive fuzzy multi‐objective optimal power flow

As the necessity of high‐quality electric power supply increases, it has been required to develop sophisticated power system operations in which several requirements stemming from economy, security, and environmental aspects are simultaneously satisfied. In general, a problem of satisfying several noncommensurable criteria is called a multiobjective optimization problem. Although the most powerful means to obtain desirable system operations is optimal power flow (OPF), a straightforward application of the conventional OPF optimizes only one objective and the remaining objectives must be treated as constraints. However, since such objectives are in trade‐off relationships with each other, it is necessary to develop an efficient multiobjective OPF. In this paper, we propose a solution method of multiobjective OPF by means of fuzzy coordination. In the first step, the degree of Decision Maker (DM) satisfaction on each objective would be maximized with a prespecified membership function. The membership function would be updated in accordance with the DM's preference information and target value of the objective function. The degree of satisfaction will be improved step by step by updating the membership functions. Finally, the satisficing solution for the DM would be obtained. The proposed method has been applied to the IEEE 57 and 118 test systems, producing successful results. © 1999 Scripta Technica, Electr Eng Jpn, 130(1): 59–67, 2000     

Short‐circuit current calculation and performance requirement of HVDC breakers for MMC‐MTDC systems

To evaluate the performance requirement of high‐voltage direct current (HVDC) breakers for modular multilevel converter (MMC)‐MTDC (multi‐terminal high voltage direct current) systems with high efficiency, the equivalent model for calculating the maximum short‐circuit current is presented in this paper. First, the short‐circuit current is decomposed into the steady‐state component and the fault component according to its physical dynamics. Second, the steady‐state component is determined by solving the direct current (DC) network; the fault component is calculated by an equivalent network in which the converters are replaced by a reactance, a resistance, and a capacitance in series. Then, the complete procedure for evaluating the performance requirement of HVDC breakers is described based on short‐circuit current calculation. Verifications have been carried out based on a three‐terminal 800 MW/±400 kV bipolar MMC‐MTDC system. The results show that the proposed methodology is efficient and effective. Lastly, based on the same system, the performance requirement of HVDC breakers and the influence by the sub‐module (SM) capacitance and the smoothing reactor have been studied with the proposed methodology. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

多馈入交直流混联受端电网直流接入能力研究评述

受端电网的直流接入能力是大规模交直流混联电网调度运行部门越来越关注的问题。从直流多馈入交直流混联电网后面临的主要问题出发,分析了影响受端电网直流接入能力的主要因素,对现有直流及新能源接入能力研究方法进行总结。分析了各方法的优缺点,探讨了受端电网直流接入能力的计算方法及未来的研究方向。受端电网直流接入能力是一个多目标优化问题,下一步研究重点是建立系统的优化模型,科学化、实用化地评估受端电网直流接入能力。针对限制受端电网直流接入能力的主要因素,提出了提高电网直流接入能力的相关建议。     

A new arrangement of Z‐source AC–AC converter and its closed‐loop control system

In this study, a Z‐source alternating current‐to‐alternating current (AC–AC) converter with a specific topology, which can provide both buck and boost modes, is investigated. This converter, which can be implemented easily, utilizes only two switches with complemented commands. A comparison between the Z‐source AC–AC converter and a conventional thyristor voltage controlled one is presented here, and it shows that in the most areas, the Z‐source converter provides a faster response and lower total harmonic distortion of the output currents than the conventional one. Moreover, the Z‐source converter is also extended to the multiphase systems. In addition, a new arrangement of this converter is proposed here to remove the isolated single‐phase sources. Furthermore, an open‐loop method is proposed for soft‐starting applications. Finally, a closed‐loop control system is also suggested for a three‐phase Z‐source converter to soft start and control the speed of an induction motor. Computer simulations show the validity and effectiveness of the proposed schemes. Copyright © 2014 John Wiley & Sons, Ltd.     

A high‐voltage gain nonisolated noncoupled inductor based multi‐input DC‐DC topology with reduced number of components for renewable energy systems

This paper proposes a modular nonisolated noncoupled inductor‐based high‐voltage gain multi‐input DC‐DC converter. Despite the high‐voltage gain of the proposed topology, the average of normalized voltage stress (NVS) on its switches/diodes is low. This property leads to less loss and cost of switches/diodes. Using the same number of components, the proposed topology produces higher voltage gains, in comparison with recently presented high step‐up topologies. Also, the proposed topology utilizes less number of components (capacitors, inductors, diodes, and switches) for producing a desired voltage gain, which can reduce the size, mass, cost, complexity, and losses and improve the efficiency of converter. Continuous current of input sources is another main advantage of the proposed topology. All the abovementioned characteristics have made the proposed topology very suitable for renewable energy systems (or even hybrid/electric vehicles). Design considerations of the proposed topology have also been presented. For better evaluation, the proposed topology has been compared with some of recently presented high step‐up structures, from viewpoints of producible voltage gain, number of components, and normalized voltage stress (NVS) on switches/diodes. Finally, the prototype of 2‐input version has been experimentally implemented. Obtained experimental results confirm appropriate performance of the proposed topology.     

计及直流电网线路损耗的直流潮流控制器安装位置选择

多端柔性直流电网内部潮流的分布控制遵循N-1准则,即换流站可独立控制的支路数为换流站个数减去一。当直流电网支路数远多于N-1时会有多条支路不可控,而且换流站功率变化时也会影响到直流电网内部的潮流分布,这时可通过直流潮流控制器增加潮流控制自由度与换流站协调配合,保证支路潮流完全可控。验证了直流潮流控制器及换流站功率改变对电网内部潮流分布的影响,并验证了潮流控制器可以扩大直流系统换流站功率运行区间的作用。最后以四端五节点的直流电网为例,综合考虑各支路的安全裕度和直流系统的线路损耗,对比分析得出直流潮流控制器最优安装位置。     

Constraints violation handling of SSSC with multi‐control modes in Newton–Raphson load flow algorithm

The static synchronous series compensator (SSSC ) is an important component of flexible AC transmission systems (FACTS ) devices. SSSC can be used to control the active and reactive power flow in transmission lines. This paper presents a simplified model for SSSC in Newton–Raphson (NR ) load flow algorithm. It also presents strategies for handling the operating constraints of SSSC including the series‐injected voltage and current passing through this device. The presented strategies are based on modifying the specified active and reactive powers with the maximum limits of the operating constraints. However, the SSSC is simply implemented in NR load flow algorithm based on the power injection approach. In this model, the SSSC is represented as injected loads as a function of the desired power flow through the transmission line. The main advantages of this model are avoiding the modification of Jacobin matrix and reducing the complexities of incorporating SSSC in the load flow algorithm. Moreover, the resistance of SSSC is considered in this model. Standard IEEE 14‐bus and 30‐bus test systems are used to verify the performance of the developed model and strategies handling the constraints of the SSSC model. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A distributed autonomous approach for bulk power system restoration by means of multi‐agent system

In recent years, the electric utility industry worldwide has been facing pressure to be deregulated. Also, the risk of blackout in large areas will increase. Actually, it is still vivid in our memory that the northeastern United States and southern Canada suffered the worst blackout in history. Consequently, a method to find the optimal solution rapidly is needed all the more. In this paper, we propose a new multi‐agent method for a bulk power system restoration. In order to demonstrate the capability of the proposed multi‐agent system, it has been applied to a model bulk power system, which consists of three local areas including 12 generating units and 12 loads, and three remote areas with 12 loads. A large number of simulations are carried out on this model network with changing conditions. The simulation results show that the proposed multi‐agent approach is effective and promising. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(1): 69–76, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20485     

A switch‐mode boost DC–DC converter for IR‐drop compensation of charging cable

A switch‐mode boost DC–DC converter has been developed to compensate for the IR‐drop because of the finite resistance of a charging cable. The boost ratio of the DC–DC converter is adaptively controlled by an IR‐drop sensing circuit to provide the required voltage level to a battery charger regardless of the cable resistance. Implemented in a 0.18 µm BCDMOS process, the IR‐drop compensating switch‐mode boost DC–DC converter occupies 6.2 mm² active area and shows the 93.2% peak efficiency. The proposed IR‐drop compensating boost converter can be applied to compensate for the IR‐drop of any type of charging cables. Copyright © 2014 John Wiley & Sons, Ltd.     

Impact of HVDC line on the convergence property of AC/DC power flow calculation

This paper explores the impact of HVDC line on the convergence property of AC/DC power flow calculation. Firstly, the model of AC/DC power flow computation is constructed, including unified method and alternate iterative method. Then, an improved Levenberg–Marquardt (LM) method with line search technique is developed to solve the nonlinear equations of AC/DC power flow. To test the convergence property of the proposed method, LM method with trust region technique and Newton method are also employed. The researches on the impact of heavy DC transmission power and multiple HVDC lines on the convergence property of AC/DC power flow calculation are made on a modified IEEE 118-bus AC/DC hybrid test system. Simulation results show that the developed method under the model of alternate iterative method is superior to other methods under different models in convergence property. For the influence of heavy DC transmission power on the convergence property, it is improved by the new parameter configuration of DC transmission line firstly and adding proper new shunt capacitor on the weak nodes secondly; for the influence of multiple DC transmission lines on the convergence property, it can also be improved by the change of control mode firstly and adding new shunt capacitor secondly, which are based on the least square solution obtained by proposed method under the model of alternate iterative method.     

Non‐isolated single‐switch DC–DC converters with extended duty cycle for high step‐down voltage applications

Several new topologies of single‐switch non‐isolated DC–DC converters with wide conversion gain and reduced semiconductor voltage stress are proposed in this paper. Most of the proposed topologies are derived from the conventional inverse of SEPIC (Zeta) converter. The proposed topologies can operate with larger switch duty cycles compared with the existing single switch topologies, hence, making them well suitable for high step‐down voltage conversion applications. With extended duty cycle, the current stress in the active power switch is reduced, leading to a significant improvement of the system losses. Moreover, the active power switch in some of the proposed topologies is utilized much better compared to the conventional Zeta and quadratic‐buck converters. The principle of operation, theoretical analysis, and comparison of circuit performances with other step‐down converters are discussed regarding voltage and current stress and switch silicon utilization. Finally, simulation and experimental results for a design example of a 50 W/5 V at 42‐V input voltage operating at 50 kHz will be provided to evaluate the performance of the proposed converters. Copyright © 2014 John Wiley & Sons, Ltd.     

Evaluation model for multi‐microgrid with autonomous DC energy exchange

This paper proposes an evaluation model to analyze the impact of microgrid topologies on self‐sufficiency for a given size of batteries and photovoltaic (PV) panels (resources). Three topologies are evaluated for a community of 19 houses: centralized resources (ideal case), stand‐alone resources, and a multi‐microgrid topology with autonomous exchange. Depending on the ratio of PV and battery size, the topology with stand‐alone resources has a clear disadvantage in terms of self‐sufficiency compared to the centralized, ideal topology. To counteract this, we propose a hybrid topology: households are interconnected so that they can exchange energy between each other based on an autonomous energy exchange algorithm we developed. We show that for a well‐chosen ratio of batteries and PV, the interconnected system can improve the stand‐alone design by up to 10% without requiring any additional resources. This topology can approach performance similar to that of a centralized microgrid but its design is more flexible and resilient to failures or accidents. The evaluation model computes the self‐sufficiency ratio (SSR) for the three topologies for 0–20 kWh batteries and 1–14 kWp PV sizes. Furthermore, seasonal differences in SSR per topology are analyzed for an actual community with real resources. We also calculate the savings in PV and battery due to the interconnected topology. Finally, the third topology's feasibility is demonstrated on a full‐scale platform in Okinawa on which the autonomous energy exchange software was tested for over a year in a community of 19 houses. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

An improved fast decoupled power flow model considering static power–frequency characteristic of power systems with large‐scale wind power

Large‐scale wind power (LSWP) integration may cause significant impact on power system frequency, so it is necessary to take frequency regulation issues into account in power system steady‐state operation analysis. An improved fast decoupled power flow model considering static power–frequency characteristic of power systems with LSWP is proposed in this paper. In this scheme, the active power of generators and loads are presented with their static power–frequency characteristics. The slack bus degenerates to the nodal voltage phase angle reference bus of the system, and all the generators with frequency regulation capability participate in unbalanced power regulation. The power flow calculation results can reveal the impact to the system frequency of operation mode change and load variation, and present the output adjustment of the generators. The proposed model can be solved conveniently by the block solving technology based on the fast decoupled power flow algorithm. The scheme presented in this paper has been tested on the IEEE standard 30‐bus test system by simulating basic operation and primary and secondary frequency regulation of the generators, which demonstrated the validity by the method. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

非并联运行AC/DC系统中直流变流器的非线性附加控制器设计

针对交直流联合输电系统中直流线路与交流线路非并联运行的情况,本文为HVDC换流站设计了附加控制器以阻尼交流系统中区域间的功率振荡.文中将直流线路功率调节作用等效为一阶惯性环节,将交直流联合的多机系统等值为两机两区域系统,由此建立了综合考虑机电振荡的三阶模型;然后运用反馈线性化方法设计了交直流系统非线性稳定控制器.仿真结果证明了该文所提出的控制器能有效地阻尼区域间功率振荡,提高系统的暂态稳定性.但同时也引入了其它一些问题.需要进一步研究的内容在最后进行了讨论.     

一种求解交直流互联电网分布式最优潮流的同步ADMM方法

对于具有多个调度中心的大规模多区域交直流互联电网,对最优潮流计算进行分布式求解更符合信息的保密性和安全性需求。通过将联络线复制同时放到相邻分区中和引入边界变量一致性约束的方法建立交直流互联电网分布式最优潮流模型,并提出了一种完全分布式的不需要任何协调中心的同步交替方向乘子法(Synchronous Alternating Direction Method of Multipliers,SADMM)求解最优潮流模型。对于交直流系统直流部分的网络分区,提出将换流站保留在各自区域中只将中间直流线路复制的直流联络线处理方法。SADMM通过对高斯赛德尔型ADMM(GS-ADMM)进行改进,将当前迭代得到的相邻区域边界节点电压值的加权平均作为下一次迭代的固定参考值,实现不同区域间的并行同步计算。并根据优化问题的特点,确定算法中惩罚因子的合理取值,以加快算法的收敛性。以某一实际大规模交直流互联电网和两个修改的IEEE交直流系统为例,通过与集中式最优潮流计算比较,验证了所提算法的正确有效性。     

Transient analysis of multi‐state dc–dc converters using system energy characteristics

The study of multi‐state dc–dc power conversion techniques is restricted by the complicated inner switching behaviors. This paper presents a general and unified transient analysis for various sorts of multi‐state dc–dc converters from a viewpoint of their system energy characteristics. With the applications to the boost converters, the proposed analytical method has indicated its advantages of high convenience and practicability to the multi‐state converters. The generalized concepts of system energy parameters of dc–dc converters are introduced and applied to the transient analysis. Consequently, the expressions of system model parameters of multi‐state dc–dc converters are deduced. The new 2nd order transfer functions are obtained to describe the large‐ and small‐signal mathematical models accurately. The model simulation and experimental results are provided to support the theoretical analysis. Copyright © 2007 John Wiley & Sons, Ltd.