Simultaneous placement of Distributed Generation and D-Statcom in a radial distribution system using Loss Sensitivity Factor

Transcription

1 Simultaneous placement of Distributed Generation and D-Statcom in a radial distribution system using Loss Sensitivity Factor 1 Champa G, 2 Sunita M N University Visvesvaraya college of Engineering Bengaluru, India Abstract Proper location of DGs in power systems is important for obtaining their maximum potential benefits. This paper deals with DG for minimizing active power loss and D-statcom for reactive power loss minimization is considered. The proper siting of DG and D-statcom is a recently developed combination with the aim of reducing line loss in a radial distribution system. Loss Sensitivity Factor (LSF) is used for finding the optimal location of DG and D-statcom A load flow of a 12 bus radial test system is in conducted using Direct Load Flow analysis which uses simple matrix multiplication to obtain a time efficient solution unlike the complex Jacobaian matrix computation. The optimal location is suggested by the LSF for the placement of DG and D-statcom by power loss calculation. Simulation results are given to verify the proposed DLF approach. Keywords Distributed Generation (DG),Distribution Static Compensator (DSTATCOM), Radial Distribution System (RDS), Loss Sensitivity Factor (LSF), Power loss. I. INTRODUCTION In recent years, increase in electricity demand has led to increase in small scale electricity generation commonly known as Distributed generation or DG. If DG is optimally placed in system it reduces greenhouse gas emission, increases the energy security improves power quality and reliability. Distribution losses mainly depends on placement and sizing of DG units. Minimization of losses with better voltage regulation and improved voltage stability in RDS can be achieved. But DG units only control active power economically. Reactive power loss account for a portion of total losses. Reactive power loss can be controlled by placing compensating device across the grid. Compensating devices includes shunt connected capacitor, shunt connected voltage sources such as STATCOM. STACOM have been applied to distribution and transmission system to regulate bus voltage, reactive power and power factor control. STATCOM applied in distribution system is called DSTATCOM. It is capable of providing rapid and uninterruptible capacitive and inductive reactive power supply. In order to minimize distribution losses placement and sizing of both DG and DSTATCOM are important. Hence an efficient and robust load flow method is method fails to meet both requirement and robustness of distribution system. Therefore a novel load flow algorithm for distribution system is desired. In this paper Direct load flow method is proposed for load flow analysis. Advantages of this method is that the only input data used is conventional bus-branch oriented data used by most of the utility. The goal of this paper is to develop for formulation, takes advantages of the topological characteristics of distribution systems, and solve the distribution load flow directly. It means that the time-consuming LU decomposition and forward/backward substitution of the Jacobian matrix or the admittance matrix, required in the traditional Newton Raphson and Gauss implicit Z matrix algorithms, are not necessary. Two developed matrices, the bus-injection to branch-current matrix and the branch-current to bus-voltage matrix, and a simple matrix multiplication are utilized to obtain load flow solutions. This paper focuses mainly on power loss reduction and voltage stability in radial distributed system. Modelling of DSTATCOM is been shown in Section II. Section III presents problem formulation for minimizing losses and the simulation results are shown in section IV. Section V draws the conclusion II D-STATCOM MODELLING In power distribution networks, reactive power is the main cause of increasing distribution system losses and various power quality problems. Voltage Source Converter (VSC) based D-STATCOM achieves voltage regulation in the connected bus by absorbing/supplying the required reactive power. It is basically a converter based distribution flexible AC transmission controller, sharing many similar concepts with that of a Static Compensator (STATCOM) used at the transmission level. At the transmission level, STATCOM handles only fundamental reactive power and provides voltage support, while a DSTATCOM is employed at the distribution level or at the load end for dynamic compensation. Fig shows the model of DSTATCOM, which shows that it is capable of injecting active power in addition to reactive power. required for this purpose. The traditional load flow 131

2 Inequality Constraints: Power constraints: The bus real power is limited to Fig1: schematic of a D-statcom (8) The real power generation at node j by the installation of DG must be equal to the sum of the real power loss at that node to the actual real power demand at that node. The bus reactive compensation power is limited to: Fig 2: D-statcom supplies both real and reactive power The contribution of the DSTATCOM to the load bus voltage equals the injected current times the impedance seen from the device also, that is the source impedance in parallel with the load impedance. Voltage of bus j changes from Vj to Vjnew when DSTATCOM is used. Voltage constraints: Fig 3: phasor diagram of voltage and current of system with D-statcom Injected power by DSTATCOM can be written as III PROBLEM FORMULATION The objective of DG and DSTATCOM placement in the distribution system is to minimize the power loss of the system, subjected to certain working constraints given in Eq. (7). Mathematically, the objective function of the problem is described as: where Vi is the voltage at bus i. To develop the two relationship matrix, a simple Radial Distribution System shown in Fig. 1 is used as an example. Using Eq. (13), the power injections can be converted into equivalent current injection matrix. By applying Kirchhoff s Current Law (KCL) to the distribution network in Fig 4, the relationship between the bus current injections and branch currents is obtained. Some of the examples of branch current are, (7) where PLoss is the total power loss of the RDS. Constraints: Equality Constraint: Angle difference between Vjnew and ID-STATCOM = 90_. To improve the power factor ID-STATCOM must be kept in quadrature with Vjnew. Fig 4: simple radial system 132

3 Therefore, the relationship between the bus current injections and branch currents can be expressed as current injections and branch currents. The corresponding variations at branch currents, generated by the variations at bus current injections, can be calculated directly by the BIBC matrix. The BCBV matrix represents the relationship between branch currents and bus voltages. The corresponding variations at bus voltages, generated by the variations at branch currents, can be calculated directly by the BCBV matrix. Combining BIBC and BCBV, the relationship between bus current injections and bus voltages can be expressed as: The general form of the equation can be written as, The solution for radial distribution load flow can be obtained by solving the following Eqs. iteratively. where BIBC is the bus-injection to branch-current (BIBC) matrix.the constant BIBC matrix is an upper triangular matrix and contains values of 0 and 1 only. The relationship between branch currents and bus voltages as shown in Fig. 4 can be as follows: For example, the voltages of bus 2, 3, and 4 are: where k is the iteration count and Vo is the initial voltage. Where Vi is the voltage of bus i, and Zij is the line impedance between bus i and bus j. Also the value of voltages V2 and V3 can be substituted into V4 to get the following equation: From above equation, it can be seen that the bus voltage can be expressed as a function of branch currents, line parameters, and the substation voltage. Similar procedures can be performed on other buses; therefore, the relationship between branch currents and bus voltages can be expressed as The above matrix can be re-written in the general form as follows: where BCBV is the branch-current to bus-voltage (BCBV) matrix. The BIBC and BCBV matrices are developed based on the topological structure of distribution systems. The BIBC matrix represents the relationship between bus 133

4 where PRLPM and QREPM are the real and reactive power matrix of the total power system. This makes the calculation fast and easy. In this work, it is taken as the real power is supplied by the DG and the reactive power is compensated by DSTATCOM. Now, both the LSF can be obtained as shown below: LSF for DG placement is, After calculating the LSF, the buses are arranged in descending order according to LSF values. This sequence is stored in a separate matrix B(i). Now the buses having the voltage less than 0.95 is ordered in a sequence and it is stored in V(i). This V(i) decides whether that particular bus listed in B(i) needs DG or DSTATCOM. From this optimal DG and STATCOM location is identified. IV. SIMULATION RESULTS Load flow analysis using direct load flow method was conducted on a 12-bus radial distribution system using MATLAB 15a. The losses obtained were MW at voltage p.u. According to the LSF computed, the optimal position for the placement of DG as well as D-statcom was found to be the 9 th bus of the 12-bus radial system. After the placement of DG and D-statcom at this position shows the reduced losses of MW at p.u V. CONCLUSION In this paper, LSF based DG and DSTATCOM placement in Radial Distribution System is carried out. The study is done with 12 bus radial system. The results are compared. The results show that, DG and DSTATCOM placent reduces the total loss of the test system For the future work the DG and DSTATCOM placement can be done by using LSF and the sizing can be done with PSO, because LSF reduces the processing time. From this research it is concluded that optimizing DG and DSTATCOM location and sizing the total power loss of the Radial Distribution System is reduced with voltage improvement. Also it is suggested that both DG and DSTATCOM placement in same bus has provided the improved voltage profile. REFERENCES [1] Rueda-Medina Augusto C, Franco John F, Rider Marcos J, Padilha-FeltrinAntonio, Romero Rubén. Mixed-integer linear programming approach for optimal type, size and allocation of distributed generation in radial distribution systems. Electr Power Syst Res 2013;97: [2] Moradi MH, Abedini M. A combination of genetic algorithm and particle swarm optimization for optimal DG location and sizing in distribution systems. Electr Power Energy Syst 2012;34: [3] Devi S, Geethanjali M. Application of modified bacterial foraging optimization algorithm for optimal placement and sizing of distributed generation. Expert Syst Appl 2014;41: [4] Ackermann Thomas, Andersson Goran, Soder Lennart. Distributed generation: a definition. Electr Power Syst Res 2001;57: [5] Singh SP, Rao AR. Optimal allocation of capacitors in distribution systems using particle swarm optimization. Electr Power Energy Syst 2012;43: [6] Hamouda Abdellatif, Sayah Samir. Optimal capacitors sizing in distribution feeders using heuristic search based node stability-indices. Electr Power Energy Syst 2013;46: [7] Kaur Damanjeet, Sharma Jaydev. Multiperiod shunt capacitor allocation in radial distribution systems. Electr Power Energy Syst 2013;52: [8] Carpinelli G, Proto D, Noce C, Russo A, Varilone P. Optimal allocation of capacitors in 134

5 unbalanced multi-converter distribution systems: a comparison of some fast techniques based on genetic algorithms. Electr Power Syst Res 2010;80: [9] Tabatabaei SM, Vahidi B. Bacterial foraging solution based fuzzy logic decision for optimal capacitor allocation in radial distribution system. Electr Power Syst Res 2011;81: [10] Abul Wafa Ahmed R. Optimal capacitor allocation in radial distribution systems for loss reduction: a two stage method. Electr Power Syst Res 2013;95: [11] Optimal location and sizing determination of Distributed Generation and DSTATCOM using Particle Swarm Optimization algorithm S. Devi a M. Geethanjali b 135