Jen-Hao Teng

Distribution system state estimation

A three-phase distribution system state estimation algorithm is proposed in this paper. The normal equation method is used to compute the real-time states of distribution systems modeled by their actual a-b-c phases. A current based formulation is introduced and compared with other formulations. Observability analysis for the proposed distribution system state estimation is discussed. Test results indicate that the normal equation method is applicable to the distribution system state estimation and the current based rectangular form formulation is suitable for this application. >

Development of a smart power meter for AMI based on ZigBee communication

Many governments deploy ubiquitous IT project, which aims to combine the latest wireless network and wide-band technologies etc. to accomplish a ubiquitous wireless communication network. The ubiquitous wireless communication network can be utilized for the Advanced Metering Infrastructure (AMI). Therefore, this paper tries to use the new wireless communication technologies to design and implement a ZigBee-based smart power meter. An outage recording system is also designed and embedded into the smart meter. The microcontroller of Microchip dsPIC30F series is used to develop the proposed smart power meter. A ZigBee system is then deigned and integrated into the proposed power meter, and used to transmit the detailed power consumption data and outage event data to rear-end processing system. The proposed smart power meter cannot only be used for power consumption data collection but also for outage event data recording. The proposed system has great potential to be used to build the area-based AMI. Experimental results demonstrate the validity of the proposed system. Besides, the application of ZigBee communication in power area may, expectedly, lead to make a definite contribution to ubiquitous IT project.

Decentralized Plug-in Electric Vehicle Charging Selection Algorithm in Power Systems

This paper uses a charging selection concept for plug-in electric vehicles (PEVs) to maximize user convenience levels while meeting predefined circuit-level demand limits. The optimal PEV-charging selection problem requires an exhaustive search for all possible combinations of PEVs in a power system, which cannot be solved for the practical number of PEVs. Inspired by the efficiency of the convex relaxation optimization tool in finding close-to-optimal results in huge search spaces, this paper proposes the application of the convex relaxation optimization method to solve the PEV-charging selection problem. Compared with the results of the uncontrolled case, the simulated results indicate that the proposed PEV-charging selection algorithm only slightly reduces user convenience levels, but significantly mitigates the impact of the PEV-charging on the power system. We also develop a distributed optimization algorithm to solve the PEV-charging selection problem in a decentralized manner, i.e., the binary charging decisions (charged or not charged) are made locally by each vehicle. Using the proposed distributed optimization algorithm, each vehicle is only required to report its power demand rather than report several of its private user state information, mitigating the security problems inherent in such problem. The proposed decentralized algorithm only requires low-speed communication capability, making it suitable for real-time implementation.

Optimal Charging/Discharging Scheduling of Battery Storage Systems for Distribution Systems Interconnected With Sizeable PV Generation Systems

Utilizing battery storage systems (BSSs) can reduce the intermittent output of PV generation systems (PVGSs) and make them dispatchable. The aim of this paper is to design an optimal charging/discharging scheduling for BSSs such that the line loss of distribution systems interconnected with sizeable PVGSs can be minimized. A mathematical model for BSSs which can be used to simulate the charging procedures such as the commonly-used constant current to constant voltage (CC-CV) charging method, the discharging procedures and the state of charge (SOC) is proposed first. The minimum line loss problem considering the intermittent output of PVGSs and the scheduling of BSSs is then formulated based on the BSS mathematical model. The optimal charging/discharging scheduling of BSSs can then be obtained by a genetic algorithm (GA) based method. Test results demonstrate the validity of the proposed mathematical model and optimal charging/discharging scheduling for BSSs.

A modified Gauss–Seidel algorithm of three-phase power flow analysis in distribution networks

Abstract This paper introduces a novel approach to solve the three-phase power flow problem for large-scale distribution systems. This method is based on the optimal ordering scheme and triangular factorization of Y -bus matrix, which not only takes advantage of the sparsity of system equations but also is insensitive to network topology. By applying the idea of modified Gauss–Seidel algorithm to the implicit Z -bus Gauss method, a three-phase distribution network can be separated into three single-phase distribution networks and can be solved phase by phase. Comparing to the conventional methods, the memory space requirement is lower and the CPU execution time can be reduced. Test results show that the proposed method has great potential for real-time uses.

Strategic distributed generator placements for service reliability improvements

The values of distributed generators (DGs) are very dependent on their type, size and location as they are installed in distribution feeders. In order to enhance the reliability and obtain the benefits for DG placement, a strategic DG placement method is proposed in this paper. The proposed method tries to find the best balance between the costs and benefits of DG placement. The main aim is to find the optimal types of DG and their corresponding locations and sizes in distribution feeders. Test results have shown that with proper types, sizes and installation site selection, DG can be used to improve service reliability, reduce the customer interruption costs and save the power cost. The most important is that the electric utilities can often obtain the maximal economical benefits.

Three-phase distribution network fast-decoupled power flow solutions

Abstract An efficient power flow solution is introduced in this paper. This solution is a current-injection based Newton–Raphson method in rectangular coordinates. The Jacobian matrix of the proposed method could be decoupled into two identical sub-Jacobian matrices. The G-matrix is used to execute load flow. The “Fast-Decoupled” idea is incorporated into the distribution network analysis the for first time. Using the rectangular-coordinate system, the matrix symmetry is retained and the memory requirement of the traditional fast-decoupled load flow is reduced to half. This method is significantly faster than any other method developed so far. Tests have shown that this method has great potential for on-line operations.

A highly efficient algorithm in treating current measurements for the branch-current-based distribution state estimation

A highly-linear branch-current-based state estimation model for a distribution system is proposed in this paper. This algorithm is based on the concepts presented by Baran and Kelley (see IEE Trans. on Power Systems, vol.10, no.1, p.483-91, 1995). Baran and Kelley proposed a novel branch-current-based approach to solve distribution state estimation. However, the treatment of current magnitude measurements and the complicated gain matrix by Baran and Kelley greatly degrades its value in real-world applications. The approach presented in this paper substantially revised the original method. A new algorithm with constant gain matrix and a decoupled form was developed. Tests have shown that the proposed method is robust, efficient and needs minimal storage requirement. The new algorithm provides a very good theoretical foundation for developing more applications and research in this area.

A novel and fast three-phase load flow for unbalanced radial distribution systems

A novel and fast three-phase load flow algorithm for unbalanced radial distribution systems is proposed in this paper. The proposed method uses branch voltages as state variables and employs the Newton-Raphson algorithm to solve the load flow problem. By utilizing branch voltages as state variables, a constant Jacobian matrix can be obtained and a building algorithm for Jacobian matrix is then developed from the observation of the constant Jacobian matrix. A solution technique, which takes the network structure into account to avoid the time-consuming LU factorization, is also developed. Since the factorization procedure can be avoided, the proposed method can save computation time. For any power system equipment, if its equivalent current injection or admittance matrix can be obtained, it can be integrated into the proposed method. Test results demonstrate that by integrating the Jacobian building algorithm and efficient solution technique, the proposed method is an effective three-phase load flow method and has great potential for real-time use.

Three-phase unbalanced distribution power flow solutions with minimum data preparation

An exact three-phase fast decoupled power flow solution is introduced in this paper. This method uses traditional Newton-Raphson algorithm in a rectangular coordinate system. The Jacobian matrix of the proposed method can be decoupled both on phases as well as on real and imaginary parts. In addition, the memory requirement of the traditional fast decoupled load flow can be reduced to only one-sixth. The need of the complicated mutual coupling terms can be avoided. It is even possible to solve the distribution system with line conductances only. That is, an exact three-phase distribution load-flow program can be executed with minimum data preparation to substantially offload the burden of distribution engineers. Tests have shown 10 to 100 times performance than other methods for test systems with 45 to 270 buses.