Loss minimization by the predictor–corrector modified barrier approach

This paper presents a new approach, predictor–corrector modified barrier approach (PCMBA), to minimize the active losses in power system planning studies. In the PCMBA, the inequality constraints are transformed into equalities by introducing positive auxiliary variables, which are perturbed by the barrier parameter, and treated by the modified barrier method. The first-order necessary conditions of the Lagrangian function are solved by predictor–corrector Newton's method. The perturbation of the auxiliary variables results in an expansion of the feasible set of the original problem, reaching the limits of the inequality constraints. The feasibility of the proposed approach is demonstrated using various IEEE test systems and a realistic power system of 2256-bus corresponding to the Brazilian South-Southeastern interconnected system. The results show that the utilization of the predictor–corrector method with the pure modified barrier approach accelerates the convergence of the problem in terms of the number of iterations and computational time.     

“Deglorifying” the Maximum Power Transfer Theorem and Factors in Impedance Selection

The limited usefulness of the maximum power transfer theorem in practice is argued. Inappropriately, the utility and value of the maximum power transfer theorem are often elevated to be religious icons of electrical engineering. While the theorem appears to be useful, often in real circuits the load impedance is not set equal to the complex conjugate of the equivalent impedance of the connecting source. When the load impedance happens to be equal to the complex conjugate of the source impedance, other practical reasons for this type of impedance matching exists, other than effecting maximum power transfer. Some reasons are discussed in a straightforward fashion.     

电力系统电压稳定性分析的实用算法

阐述了用于电压稳定性分析的一种实用计算方法。这种方法通过参数变换,解决了最大负荷点处病态潮流方程不收敛的问题,从而可以获得精确的电压稳定极限,并且通过引进预估校正技术更好地考虑了发电机无功越限及系统其它限制因素的影响。算法计算简单快捷,结果更具有理论依据。     

三倍频变压器的物理试验研究

提出了通过开路试验和短路试验确定倍频变压器等值漏感抗的方法,为倍频变压器等值参数的仿真计算提供了验证的基础。试验结果表明,根据等值内阻抗确定的匹配负载电阻,可得到最大输出功率。采用变截面铁心结构,可提高三倍频变压器的效率和热稳定性。研制了日字形三倍频变顺输出功率6kW,效率已达92.5%。     

独立光伏发电系统最大功率点跟踪原理分析及仿真研究

为有效地利用太阳能,必须进行最大功率点跟踪.分析了光伏电池特性,推导出Boost电路阻抗变换关系,给出了光伏发电系统最大功率点跟踪方案,即改变Boost占空比使得负载的等效阻抗与光伏电池阵列内部阻抗相匹配.利用Matlab软什对光伏电池、Boost电路进行建模,仿真结果验证了理论分析的正确性与方案设计的可行性.     

计及负荷电压静态特性的电力系统最小负荷裕度的快速评估

负荷裕度是静态电压稳定性最重要指标之一,定义了非线性复变电力系统的最小负荷裕度。利用非线性电路动态等值方法,引入功率参变量,构造拉格朗日函数。证明非线性电力网络负荷节点获取极大有功功率的必要条件：负荷静态等值阻抗模等于负荷节点看进系统的动态等值阻抗模,然后提出评估电压稳定性的阻抗模裕度指标。同一扰动下,阻抗模裕度越小,电压稳定性越薄弱,节点负荷裕度越小,只需计算最薄弱节点的最大负荷裕度,即系统最小负荷裕度。通过阻抗模裕度最先到达零来确定最薄弱节点获取的极大有功功率,计算其最大负荷裕度。计及负荷功率扰动方式与负荷电压静态特性,通过对IEEE30节点系统的仿真表明：单节点负荷功率扰动方式及恒定阻抗与恒定电流负荷比例的增加,提高了系统的最小负荷裕度。     

基于实时数字仿真系统的同群光伏系统等值建模研究

研究了同群光伏系统等值建模的原理和特点,针对倍乘等值方法的不足,提出一种基于变流器输入阻抗不变的聚合等值方法。以某典型光伏系统为例,在实时数字仿真系统(real time digital simulation system,RTDS)中分别搭建了30台参数相同的1 MW光伏多机参考模型、1台30 MW光伏倍乘模型和1台30 MW光伏聚合模型。通过仿真试验,比对这3个模型在光伏系统公共并网点(point of common coupling,PCC)的故障穿越、有功阶跃、频率偏移等暂态特性及阻抗频率特性。结果表明,3个模型的暂态特性基本相同,倍乘模型与参考模型的阻抗频率特性有明显差异,而聚合模型与参考模型的阻抗频率特性高度一致。     

磁耦合谐振式无线电能传输系统阻抗分析与匹配电路设计方法

针对无线电能传输系统中阻抗失配引起的效率低和烧毁射频功放等问题,综合考虑耦合因数、电源和线圈内阻,利用互感耦合理论对四线圈结构的磁耦合谐振式无线电能传输系统中射频功放的负载阻抗进行等效分析;并针对通过改变系统互感系数来调整阻抗难以达到理想效果的缺陷,提出和设计阻抗匹配电路方法来调整阻抗。根据阻抗特性设计了π型结构的阻抗匹配电路,给出了系统器件参数的计算方法和结果。最后设计了基于磁耦合谐振技术的无线电能传输装置,并进行了阻抗匹配实验,实验结果与理论分析具有较好的一致性,证明了理论分析的正确性。也为进一步研究自适应阻抗匹配,提高无线电能传输功率和效率提供了有益的参考。     

一种无通信的无线电能传输阻抗匹配方法

磁耦合谐振式无线电能传输系统由于线圈两侧的电气隔离,通常使用无线通信来实时获取原副边的电压电流信息并对其进行控制。在一些特殊应用场合比如航天器,由于频率管制等原因无法使用通信电路。为了解决该问题同时使得系统的传输效率最优,提出了一种无通信的阻抗匹配方法。该方法选用Buck电路作为阻抗匹配网络,在负载电压变化时采用线性拟合的方法对整流输出电压进行控制,进而实现对系统最大效率的跟踪。建立了系统的等效电路模型,在不同负载下对系统的效率曲线进行了分析,给出了系统的控制策略。仿真与实验表明,在10 cm的传输距离下系统的效率保持87%以上,验证了无通信阻抗匹配方法的可行性。     

Adjusted optimal power flow solutions via parameterized formulation

This work proposes a parameterized formulation of the optimal power flow (OPF) problem, which is aimed at preventing the divergence of the OPF iterative process. A parameter, whose function is to adjust the power demand and/or operational limits in case of absence of feasible solutions, is added to the objective function of the original optimization problem. This modified problem is solved through the nonlinear version of the predictor–corrector interior point method. Besides indicating the potential reasons for non-convergence of the iterative process, the proposed methodology also provides the possible actions that could be taken to determine an operational solution. Numerical results obtained with test systems of different sizes illustrate the application of the proposed strategy.