含潮流控制器的改进节点附加注入法潮流计算

通过对常规节点附加注入法和常规牛顿法的剖析比较,得出了常规节点附加注入法收敛性存在问题的主要原因在于等效附加注入项处理得不够全面.在此基础上,提出了改进的节点附加注入法,该方法在潮流方程的节点功率不平衡量中引入新的修正项,使潮流的收敛性得到改善.另外,针对常规节点附加注入PQ分解法的线性收敛特性,应用斯梯芬算法或埃特金δ2加速收敛手续对其进行加速处理,使算法的收敛性在一定程度上也得到了进一步改善,并使计算效率得到比较明显的提高.算例分析结果说明了上述两种方法的良好效果.     

含潮流控制器的改进节点附加注入法潮流计算

通过对常规节点附加注入法和常规牛顿法的剖析比较,得出了常规节点附加注入法收敛性存在问题的主要原因在于等效附加注入项处理得不够全面。在此基础上,提出了改进的节点附加注入法,该方法在潮流方程的节点功率不平衡量中引入新的修正项,使潮流的收敛性得到改善。另外,针对常规节点附加注入PQ分解法的线性收敛特性,应用斯梯芬算法或埃特金δ2加速收敛手续对其进行加速处理,使算法的收敛性在一定程度上也得到了进一步改善,并使计算效率得到比较明显的提高。算例分析结果说明了上述两种方法的良好效果。     

基于回路电流与负荷节点电压方程的配电网潮流计算

将配电网负荷支路与形成环网支路选定为连支,据此将所有回路分为第1类回路及第2类回路,建立配电网的回路电流-负荷节点电压网络方程。方程中含有回路电流和负荷节点电压,网络回路阻抗与节点负荷等效阻抗分离。基于所建方程实现了配电网潮流计算的直接解法和前推回代法。进一步将模型和算法应用于三相不平衡配电网,针对单相负荷为零给直接解法带来的影响提出两种处理方法:将负荷等效为导纳或移除零负荷回路方程。提出的前推回代法直接根据节点负荷和电压计算回路电流,使前推计算得以高效进行,极大地提高了潮流计算速度。     

含分布式电源的阻抗化配电网潮流算法

提出了基于阻抗的改进前推回代法,将负荷等效成阻抗,回代过程中遇到分叉点即返回修正,简化了前推过程.总结了各类分布式电源的能源类型和并网接口形式,建立PQ,PI,PQ(V)和PV四种潮流计算模型.PI,PQ(V)节点在潮流迭代中可以转化为PQ节点,等效为恒阻抗模型,PV节点等效为并联补偿电抗.采用不同的DG接入方案,对31节点算例进行测试,研究各类分布式电源对系统的电压支撑作用以及所提算法的收敛性能.     

修正节点接入导纳潮流算法

针对牛顿–拉夫逊法初值选取不当和PQ分解法受网络RX比例影响造成的计算不收敛问题,提出了一种修正节点接入导纳的潮流算法。理论证明该算法是正确的。算例分析表明,该方法收敛可靠、计算速度快,同时不受RX比例与初值选取的影响。     

求解含小阻抗支路配电网潮流的牛顿法

基于节点导纳矩阵的雅可比矩阵为病态,是采用牛顿法求解含合环支路等小阻抗支路的配电网潮流不易收敛的主要原因。文中以等效负荷支路、合环支路分别为连支建立两类基本回路,潮流方程基于回路电流-负荷节点电压方程建立,合环支路参数不会作为回路矩阵的独立元素存在;采用牛顿法求解时,基于回路导纳矩阵建立良态的雅可比矩阵,使计算收敛性得到保证。多个算例验证了该方法在计算含合环支路和PV节点配电网潮流时的正确性和有效性。     

目标确定下的含FACTS元件统一三相潮流

基于FACTS元件等效电源模型,将FACTS元件对网络的影响以等效三相注入功率表示,可以在不改变原有网络节点导纳矩阵的条件下进行三相潮流计算。将FACTS元件对线路功率的控制目标值引入到节点注入功率平衡方程中,建立含FACTS元件三相潮流模型,此模型结合交替迭代法将节点附加注入功率作为状态变量,保留了传统潮流算法的迭代形式和雅可比矩阵的特点,有利于采用基于序分量—解耦补偿法进行计算。针对3类不同FACTS元件根据其内部约束列出了模型中的差异,并以简单5节点系统进行算例分析,结果表明建立的计算模型具有一定的收敛性,FACTS元件在改善三相不平衡中具有一定的作用。     

PQ分解法潮流计算收敛性的影响因素

形成PQ分解法系数矩阵B’和B”时,可以考虑或忽略对地并联支路导纳、理想变压器非标准变比和支路电阻。探讨了B’和B”不同形式下对PQ分解法收敛特性和收敛速度的影响,详细分析了对他并联支路电纳在形成B'对的作用,并且通过多个系统的潮流计算结果验证了PQ分解法收敛性最佳状态下B’和B”的组成。分析和计算结果表明,形成B’时考虑支路电阻,形成B’对忽略支路电阻,并且将节点与线路并联电纳2倍,PQ分解法收敛速度最快。     

计及发电机无功越限的广域戴维南等值参数在线计算方法

为适应可再生能源大规模接入带来的随机性和波动性,在广域量测条件下,提出基于单一运行状态断面数据的戴维南等值参数在线跟踪计算方法。首先,对负荷节点的负荷进行等效阻抗处理;其次,通过修正原系统节点导纳矩阵得到等效阻抗处理后的系统导纳矩阵;最后,根据修正后导纳阵和节点电压方程,按戴维南等值的定义,计算负荷节点的开路电压作为戴维南等值电势,进而获得负荷节点的戴维南等值全部参数。在该方法基础上,还可以较为准确地计算发电机无功越限即PV转PQ节点情况下的戴维南等值参数。通过仿真算例分析验证了该方法的正确性和有效性,在PV转PQ节点情况下也具有较好的计算精度。     

基于补偿算法改进的隐式Zbus高斯潮流计算方法

隐式Zbus高斯法由于其高效、可靠的特点广泛应用于放射状和弱环状的配电网潮流计算。该方法适合处理PQ节点和P-Q(V)节点,但是当系统中并入PV节点类型的分布式电源时,它存在潮流发散的问题。为了解决这类问题,提出一种基于补偿法改进的隐式Zbus高斯法。其核心思路是在每一次迭代后,通过节点阻抗矩阵和电压不匹配量对PV节点的无功功率进行修正,从而使PV节点的注入无功功率达到真实值,进而求得潮流收敛的解。该方法被应用到IEEE 33节点配电系统中,通过与基于同伦算法改进的隐式Zbus高斯潮流计算方法进行比较,表明提出的方法收敛性更好,收敛速度更快。此外,PV节点的数量对该方法的收敛性和收敛速度影响不大,表明该方法更适合于含PV节点类型配电网潮流计算。     

Improved NR current injection load flow using power mismatch representation of PV bus

This letter presents improvement in the revised current injection mismatch load flow method (NR-RCIM) using new representation of voltage controlled bus (PV bus). In the proposed formulation, the representations of PV buses are based on power mismatches and the other PQ buses based on current mismatches. This combined power and current injection mismatches method (NR-PCIM) decreases the required current injection load flow equations and improves the convergence performance in case of PV buses. Tests and comparisons among different Newton Raphson load flow techniques: conventional Newton Raphson (NR), NR-RCIM and the new NR-PCIM have been held to illustrate the validity and merits of the proposed algorithm.     

An enhanced RCGA for a rapid and reliable load flow solution of electrical power systems

The paper presents a reliable and fast load flow solution by using a real-coded genetic algorithm (RCGA), bus reduction technique and sparsity technique. The proposed load flow solution firstly used reduction technique to eliminate the load buses. Then, the power flow problem is solved for the generator buses only using real-coded GA to calculate the phase angles. Thus, the load flow problem becomes a single objective function, where the voltage magnitudes are specified resulted in reduced computation time for the solution. Once the phase angle has been calculated, the system is restored by calculating the voltages of the load buses in terms of the calculated voltages of the generator buses. A sparsity technique is used to reduce the computation time further as well as the storage requirements. The proposed load flow solution also can efficiently solve the load flow problems for ill-conditioned power systems whereas the conventional RCGA alone fails to solve these systems. The proposed method was demonstrated on 14-bus IEEE, 30-bus IEEE and 300-bus IEEE, and a practical system 362-busbar Iraqi National Grid. The proposed solution has reliable convergence, a highly accurate solution and much less computing time for on-line applications. The method can conveniently be applied for on-line analysis and planning studies of large power systems.     

An operations-oriented formulation and solution to the load flow problem

This paper presents an operations-oriented formulation and solution to the load flow problem. In this approach all the unit real power outputs are assumed specified and the objective is to calculate the bus loads. This fundamental change is useful in some power system problems and is also closer to the actual problem facing a load flow user.Different solution approaches, including a decoupled method, are proposed to solve the above problem. The numerical and analytical properties of this new decoupled load flow approach are similar to those of the conventional decoupled method. The main advantages of this proposed approach are: all the bus generations can be specified, a slack or swing bus need not be defined, and losses are independent of a choice of reference bus.This fundamental change in the load flow formulation has various applications. These include transmission loss evaluation, loss penalty factor calculation, and study applications in energy management systems.     

Power flow control for transmission networks with implicit modeling of static synchronous series compensator

This paper presents an implicit modeling of Static Synchronous Series Compensator (SSSC) in Newton–Raphson load flow method. The algorithm of load flow is based on the revised current injection formulation. The developed model of SSSC is depended on the current injection approach. In this model, the voltage source representation of SSSC is transformed to current source, and then this current is injected at the sending and auxiliary buses. These injected currents at the terminals of SSSC are a function of the required line flow and voltage of buses. These currents can be included easily to the original mismatches at the terminal buses of SSSC. The developed model can be used to control active and reactive line flow together or individually. The implicit modeling of SSSC device decreases the complexity of load flow code, the modification of Jacobian matrix is avoided, the change only will be in the mismatches vector. Finally, this modeling solves the problem that happens when the SSSC is only connected between two areas. Numerical examples on the WSCC 9-bus, IEEE 30-bus system, and IEEE 118-bus system are used to illustrate the feasibility of the developed SSSC model and performance of the Newton–Raphson current injection load flow algorithm.     

大电网可靠性影响分析的潮流跟踪方法

提出了大电网可靠性评估中削减负荷的潮流跟踪模型, 建立了节点和系统可靠性对元件的分配计算模型,基于此易于分析系统的薄弱环节。在负荷削减的潮流跟踪模型中,按负荷对发电机和线路利用系数的大小顺序削减负荷。基于潮流跟踪削减负荷能建立故障元件与削减负荷节点间的映射关系,该模型的核心在于找出所有元件中对削减负荷节点利用系数最大的元件。算例结果证明了所提出方法的有效性。     

配网三相潮流的常雅可比牛顿算法

根据牛顿法的基本原理,本文基于配电网的特点,提出了一种新的适用于不对称配电网的三相常雅可比潮流算法.该算法引入内节点来处理平衡节点处的三相电压不平衡,同时对负荷节点进行了合理的假设,最终得到的雅可比矩阵为常数矩阵,在迭代过程中保持不变;同时算法不解耦,不受大的R/X的影响;该算法对有环配网也同样适用.文中通过对算例进行仿真,表明该算法有可靠的稳定性和好的收敛速度.     

广义快速分解潮流计算方法

快速分解潮流(FDLF)算法在当今的国内外电网调度控制中心和规划部门得到了广泛应用。在大部分情况下FDLF算法具有很高的计算效率,但对于高阻抗比的输电网和配电网,FDLF法的数学基础不再成立,其收敛性和计算效率均变差,因而FDLF无法适用于高阻抗比的输电网和配电网。针对以上问题,文中通过对节点注入有功功率/无功功率进行变换,进而得到类有功注入功率/类无功注入功率,两者具有更好的解耦特性,且这种解耦特性与阻抗比的值无关;在此基础上提出一种广义快速分解潮流(GFDLF)算法。GFDLF算法只需基于一个前提条件,而传统的FDLF算法则需要3个前提条件,因此GFDLF算法对输电网和配电网(包括高阻抗比网络)均具有良好的适应性。算例仿真验证了所提方法具有良好的收敛性和较高的计算效率。     

MODELING AND ELIMINATION OF LOAD BUSES IN OPTIMAL POWER FLOW SOLUTIONS

ABSTRACT

This paper presents a method to solve the optimal power flow problem after eliminating load buses from the system. Loads are first modeled and reflected in the admittance matrix and then their respective buses are eliminated. The obtained model is a reduced model of the original system. The admittance matrix is of the same order as the number of voltage-controlled buses in the system. The variables of the reduced model are the voltage-controlled buses voltages, angles and active power generations. Newton Raphson method is used to calculate the variables of the reduced model while minimizing an objective function. Voltages and angles of the original system are then calculated by a direct method. These voltages are required to update load models and to check for voltage and line current violations at the eliminated portions of the network. The simulation is carried out on two systems, IEEE 118 bus test system and a 131 bus actual system. It is shown that solution time is significantly reduced when compared to the conventional optimal power flow Newton Raphson method using the original system.     

A simple implementation of power mismatch STATCOM model into current injection Newton–Raphson power-flow method

This paper presents a simple implementation of Static Shunt Compensator (STATCOM) into Newton–Raphson current injection load flow method. The controlled STATCOM bus in the network is represented by voltage-controlled bus with zero active power generation at the required voltage magnitudes. The power mismatch equation of the connected STATCOM bus is included in Newton–Raphson current injection load flow algorithm, while the other PQ buses are represented by current mismatch equations. Moreover, the parameters of STATCOM can be calculated during iterative process and the final value will be updated after the convergence is achieved. This representation of generator buses reduces the number of required equations with respect to the classical and improved versions of the current injection methods. In addition of that the developed model reduces the complexities of the computer program codes and enhances the reusability by avoiding modifications in the Jacobian matrix. The performance of the developed STATCOM model has been tested using standard IEEE systems.     

大型输电系统运行可靠性分析的实用技术

为使输电系统运行的可靠性分析进入实用阶段,本文采用时序模拟法模拟系统实际运行状态,采用下次事件推进法调整模拟时钟。采用交流潮流对系统分析,其结果作为线路过负荷和节点电压越限的判据。用灵敏度法调整发电机出力和削减负荷量。采用简化搜索法进行网络结构辩识,并提出了适用于工程实际的解列处理措施。在系统不同的调度运行方式下考虑了多重故障、母线及变压器的相关故障等。依据算法编制的软件可计算系统及各节点的可靠性