A linear programming approach to distribution Power Flow

Large-scale distribution systems (DSs) require an efficient power flow algorithm which can explicitly exploit their characteristics. This paper presents a novel power flow algorithm for radial and weakly meshed distribution systems (WMDSs) using a direct method (DM). The paper also develops a novel approach to simulate the voltage-controlled buses which is becoming increasingly important due to the introduction of distributed generations in DSs. The proposed power flow algorithm is constructed based on simple electrical circuit rules so that only a Z matrix expressing common impedances between loads is required for simulation. For WMDSs, only modification is to use the current divider rule to solve meshes. The simulation of PV-buses is presented using the Newton–Raphson solution algorithm. The validation and comparison of results in different systems show the simplicity and low computations of the proposed method which make it time-saving and very efficient for large-scale DSs.

Decentralized saddle-point dynamics solution for optimal power flow of distribution systems with multi-microgrids

This paper develops an injection shift factors for reactive power (QISF) which is dependent on network topology only to achieve a fast linear power flow estimation after multiple loads surges including unexpected large machines inrush and peak hours surges. The proposed approach can estimate power flow subject to surges at an extreme fast speed with acceptable loss of accuracy, which can help system operators modify generator outputs and protect transmission lines from overload. Unlike traditional Newton-Raphson (NR) power flow algorithm and other estimation methods using distribution factors including Jacobian-based distribution factors (JBDFs), the proposed approach is achieved without measurements of system nodal voltages. The proposed approach was tested on IEEE 14 and 30 bus test systems and compared with conventional NR algorithm. The numerical results indicate that with acceptable accuracies, the proposed approach can obtain power flow solutions in significantly short time.

Alternative methods for power flow and fault analysis of single-phase distribution systems are presented. The algorithms for both power flow and fault analysis utilize a generalized approach to network modeling. The generalized admittance matrix, formed using elements of linear graph theory, is an accurate network model for all possible single-phase network configurations. Unlike the standard nodal admittance matrix formulation algorithms, the generalized approach uses generalized component models for the transmission line and transformer. The standard assumption of a common node voltage reference point is not required to construct the generalized admittance matrix. Therefore, truly accurate simulation results can be obtained for networks that cannot be modeled using traditional techniques. >

현재의 배전계통의 전압은 변전소에서 단방향 조류를 고려하여 LDC에 의한 전압조정방법으로 ULTC 변압기의 랩을 변환하여 공급전압을 적정범위 내에서 유지되도록 운전하고 있다. 그러나 현재의 배전계통 운용은 소용량에서 대규모 용량에 이르기까지 다양한 용량의 PV 시스템이 배전계동에 연계되어 운전되는 것을 반영하지 못하고 있는 실정이다. 때문에 다수의 PV 시스템이 계통에 연계되어 양방향 조류가 발생하고 이로 인해 연계점의 전압변동이 발생하여도 이를 효과적으로 조정하지 못하여 계통의 전압이 적정범위 내에서 운용되지 못하는 경우가 발생할 수 있다.<BR> 따라서 본 논문에서는 다수 PV 시스템의 연계에 따른 양방향 조류의 발생을 고려하고 연계점의 전압변동에 따른 계통의 전압을 효과적으로 제어할 수 있도록 실시간 감시가 이루어지는 PV 시스템의 특정을 이용하고 기존의 LDC 전압조정방법을 개선하여 PV 시스템 연계 시에도 변전소에서 계통의 전압을 적정범위 내에서 조정할 수 있는 개선된 전압조정방법을 제안하였다.

This paper focuses on distribution systems featuring renewable energy sources and energy storage devices, and develops an optimal power flow (OPF) approach to optimize the system operation in spite of forecasting errors. The proposed method builds on a chance-constrained multi-period AC OPF formulation, where probabilistic constraints are utilized to enforce voltage regulation with a prescribed probability. To enable a computationally affordable solution approach, a convex reformulation of the OPF task is obtained by resorting to i) suitable linear approximations of the power flow equations, and ii) convex approximations of the chance constraints. Particularly, the approximate chance constraints provide conservative bounds that hold for arbitrary distributions of the forecasting errors. An adaptive optimization strategy is then obtained by embedding the proposed OPF task into a model predictive control framework.

In this paper, a Power Flow (PF) algorithm for a Power Distribution System (DS) derived from the conventional backward-forward sweep method is simulated with the integration of Solar Photovoltaic (SPV) based distributed generation. This integration algorithm is based on the load current injection, where the SPV generation is modeled as a negative load injection at one of the nodes of the DS. In this method, the PF solution is obtained by executing both the sweeps in a single step through a Load Current to Bus Voltage (LCBV) matrix. The SPV system is integrated considering an additional inverter node connected to one of the nodes of DS through the SPV interfacing elements. Based on the control specification at the inverter node, it may operate either in PV or PQ mode. The SPV inverter node voltage is computed using an alternate-iterative method in a separate algorithm. The effectiveness of the modified PF algorithm is verified on the balanced DS, considering diverse test systems (IEEE-33 node, IEEE-69 node DS). The qualitative aspects of the algorithm are analyzed and compared with the existing conventional technique.

This paper presents an optimal Short-term Distribution System Planning (S-DSP) problem, with a particular focus on the load transfer ability project. Section 2 formulates the problem as a Mixed-Integer Linear Programming (MILP) optimization, considering the objective function of minimizing investment costs and non-switchable capacity, along with constraints like distribution system power flow, line capacity, and bus voltage. Section 3 extends the optimization problem into a multi-objective function-based approach using the Epsilon constraint method. In Section 4, we introduce a method for estimating the Pareto-front set and outline the decision-making process for selecting the optimal alternative. The proposed method's effectiveness is demonstrated through in-depth case studies, first with a 36-bus test system and then with a practical application to Korea's distribution system, which features 2056 buses and 2082 lines (Section 5 and Section 6). This research based on the empirical study underscores the practical applicability of the proposed S-DSP approach to the advance distribution management system (ADMS) in Korea.

This paper presents a novel m ethod for evaluating Power flow in a radial distribution networks. Conventionally power flow algorithms used consider real and reactive power to be independent of node voltage which is not always true in case of distribution systems. Voltage sensitive nature of load imparts a considerable amount of influence over actual amount of power flowing in the system. A forward backward sweep based load flow technique that takes into consideration changes in amount of real and reactive power being consumed by loads is developed. Precise loss estimation based on newly developed power flow technique is performed.

Large-scale integration of Wind Generators (WGs) with distribution systems is underway right across the globe in a drive to harness green energy. The Doubly Fed Induction Generator (DFIG) is an important type of WG due to its robustness and versatility. Its accurate and efficient modeling is very important in distribution systems planning and analysis studies, as the older approximate representation method (the constant PQ model) is no longer sufficient given the scale of integration of WGs. This thesis proposes a new three-phase model for the DFIG, compatible with unbalanced three-phase distribution systems, by deriving an analytical representation of its three major components, namely the wind turbine, the voltage source converter, and the wound-rotor induction machine. The proposed model has a set of nonlinear equations that yields the total three-phase active and reactive powers injected into the grid by the DFIG as a function of the grid voltage and wind turbine parameters. This proposed model is integrated with a three-phased unbalanced power flow method and reported in this thesis. The proposed method opens up a new way to conduct power flow studies on unbalanced distribution systems with WGs. The proposed DFIG model is verified using Matlab-Simulink. IEEE 37-bus test system data from the IEEE Distribution System sub-committee is used to benchmark the results of the power flow method.

Power flow is the most fundamental computation in power system analysis. Traditionally, the linear solution in power flow is solved by a direct method like LU decomposition on a CPU platform. However, direct methods may suffer scalability issues in parallel computing when the scale of the system increases. In contrast, iterative solvers, as an alternative to direct solvers, are generally more scalable with better parallelism. This work presents a fast decouple power flow (FDPF) algorithm with a graphic processing unit (GPU)-based preconditioned conjugate gradient (CG) iterative solver. In addition, the inexact Newton method is integrated to further improve the GPU-based parallel computing performance for solving FDPF. The results show that the GPU-based FDPF maintains the same precision and convergence as the original CPU-based FDPF, while providing considerable performance improvement for several large-scale systems. The proposed GPU-based FDPF with inexact Newton method gives a speedup of 2.86 times for a system with over 10,000 buses if compared with traditional FDPF, both implemented based on Matlab. This demonstrates the promising potential of the proposed FDPF computation using a preconditioned iterative solver under GPU architecture.

A generalized power flow analysis for distribution systems with high penetration of distributed generation

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper extends the conventional power flow formulation in order to enable the solution of networks modeled at the bus section level. The proposed extension is centered on a methodology to represent zero impedance branches successfully employed in state estimation studies. Accordingly, the active and reactive power flows through switches and circuit breakers are treated as new state variables along with the complex voltage at the network nodes. Information regarding device statuses is included into the power flow problem as new (and linear) equations, producing a solvable non-redundant set of algebraic equations. Applications of the proposed modifications in connection with the power flow solution via Newton-Raphson's method are presented and discussed. The proposed approach provides an efficient tool to directly determine the power flow distribution over selected substations of the network, avoiding unreliable artifices and tedious post-processing procedures required when a conventional power flow formulation is applied. The IEEE 24-bus and IEEE 30-bus test systems are employed to illustrate and evaluate the proposed approach, considering distinct substation layouts. </para>

Distributed generation (DG), which is interlinked with distribution system, will inevitably have an impact to system. In the paper, a reliability evaluation method is proposed, which is based on the analysis to the structure and power flow of distribution system with distributed generation. First, a new concept, the smallest unit, is put forward for improving the fault traversal networks times. The authors use the depth-first search in data structure to divide distribution system into several the smallest units, and propose the islanding operation mode to increase the reliability of the system. Distribution system will be automatically turned into the islanding operation mode once faults occur. To evaluate quantitatively the reliability of distribution system, Monte Carlo simulation method is used by simulating the running status of distribution system. At last, the calculation results of actual case show that the proposed method is available to evaluate the reliability of distribution system with distributed generation.

The access of distributed generation to changes the structure, power flow and failure modes of traditional power distribution systems, which may lead to the decrease of sensitivity, malfunction and reclosing of traditional three-stage current protection.etc. Aiming at this problem, this paper based on analyzes the influence of distributed power supply on the relay protection of distribution network, and puts forward the protection scheme of circuit breaker, direction module and inverse time overcurrent protection. Finally, the PSCAD/EMTDC is used to simulate a 10 KV distribution system with distributed generation to verify the effectiveness of the proposed protection scheme.