Khalid Mohamed Nor

Hydrothermal scheduling based Lagrangian relaxation approach to hydrothermal coordination

This paper presents an improved Lagrangian relaxation based hydrothermal coordination algorithm. By using Lagrangian multipliers to relax system-wide demand and reserve requirements, the problem is decomposed into thermal and hydro subproblems. The thermal subproblem is solved by using dynamic programming without discretizing generation levels. Instead of solving the hydro subproblems independently as done in the standard Lagrangian relaxation formulation, the hydrothermal scheduling is used to solve for the output levels of hydro units. The hydrothermal scheduling uses the commitment status of thermal units obtained from the thermal subproblem. Extensive constraints are considered such as power balance, spinning reserve, minimum up/down time, capacity limits, ramp rate and hydro constraints. Accurate transmission losses are incorporated and nonlinear cost functions are used. Numerical results based on a practical electric utility data show that this new approach consistently provides better schedules than the standard Lagrangian relaxation approach.

Improved three-phase power-flow methods using sequence components

The paper presents the formulation and the solution of the three-phase power-flow problem using sequence components. An improved sequence component transformer model and a decoupled sequence line model were used. As a result, the three sequence admittance matrices are decoupled with three-phase power system features in sequence components. The sequence power-flow algorithm has been formulated such that the single-phase power-flow programs can be called as routines for solving the positive sequence network. The results for the proposed sequence power-flow methods are identical to those obtained from three-phase power-flow programs developed in phase components. The computational efficiency and convergence of the proposed sequence three-phase power-flow methods show that they are as fast and as robust as conventional the Newton-Raphson method.

An efficient method for optimal scheduling of fixed head hydro and thermal plants

An efficient and optimal method for scheduling thermal plants in coordination with fixed-head hydro units is presented. The method linearizes the coordination equation and solves for the water availability constraint separately from unit generation. Once the water constraint Lagrange multiplier is determined, the unit output can be computed easily. Case studies with various systems are presented and discussed. >

Fault Analysis of Multiphase Distribution Systems Using Symmetrical Components

The paper presents a new approach for performing the fault analysis of multiphase distribution networks based on the symmetrical components. The multiphase distribution system is represented by an equivalent three-phase system; hence, the single-phase and two-phase line segments are represented in terms of their sequence values. The proposed technique allows the state of the art short-circuit analysis solvers to analyze unbalanced distribution networks. The fault currents calculated using the proposed technique is compared with the phase components short-circuit analysis solver. The obtained results for the IEEE radial test feeders show that the proposed technique is accurate. Based on the proposed method, the existing commercial grade short-circuit analysis solvers based on sequence networks can be utilized for performing unbalanced distribution systems.

Reusability techniques in load-flow analysis computer program

This paper describes the implementation of reusability aspects in producing load-flow analysis software application. The reusability in the algorithm and codes are obtained by applying matrix partitioning approach for Newton method and sequential approach for Fast Decoupled method. The software is built by using component-based development and object oriented programming methodologies. These methodologies made the developed load-flow analysis software flexible for future enhancement. Adding and changing codes and algorithm of the software can be done without affecting much the existing codes and algorithms. By maximizing the reusability aspects, the cost and time of software maintenance for updating can be reduced.

Development of unbalanced three-phase distribution power flow analysis using sequence and phase components

This paper presents a new power-flow method for analyzing unbalanced distribution networks. In this method, an unbalanced distribution network Is decomposed to: 1) main three-phase network with three-phase line segments and 2) unbalanced laterals with two-phase and single-phase line segments. The proposed method allows solving the main three-phase network based on the decoupled positive-, negative, and zero-sequence networks. The unbalanced laterals are solved using the forward/backward method In phase components. The solution process Involves three main steps. Firstly, In phase components, the backward step Is executed to calculate an equivalent current Injection for each unbalanced lateral. Secondly, the main three-phase network Is solved In sequence components. The standard Newton-Raphson and fast decoupled methods are used for solving the positive-sequence network whereas the negative- and zero-sequence networks are represented by two nodal voltage equations. Finally, In phase components, the forward step Is performed to update the voltages In the unbalanced laterals. The three-steps are repeated till convergence happen. Distribution network characteristics such as line coupling, transformer phase shifts, voltage regulators, PV nodes, capacitor banks, and spot or distributed loads with any type and connection are considered. Solution of unbalanced radial feeders shows that the proposed hybrid algorithm Is accurate.

Lithium-ion battery charger for high energy application

This paper describes the design of microcontroller-based battery charger to charge lithium-ion battery pack with the charging method, balancing technique, charging control algorithm, battery protection, battery management unit and implementation of the battery charger are discussed concisely. Advantages, disadvantages and problems arise are also discussed. In fact, an excellent battery charger offers very fast charge time, full capacity and balanced battery cells, low operating temperature and highly efficient and reliable.

An Approach to Determine a Pair of Power-Flow Solutions Related to the Voltage Stability of Unbalanced Three-Phase Networks

This paper proposes an approach to determine a pair of power-flow solutions associated with the voltage stability of unbalanced three-phase networks. The approach is derived from the observations of the multiple three-phase power-flow solutions of a two-bus network. It is found that there are two pairs of solutions at the load bus. The plot of the voltage magnitude of each pair against the power demand at the load bus shows that two possible PV curves can be constructed for each phase. Each of the two curves is a combination of the two pairs of solutions. One of these curves is associated with the voltage stability of the system whereas the other is associated with the imbalance of the three-phase network. Based on the above observations, a constant impedance load model is utilized to calculate the solution associated with the voltage stability of the study system. Then the equivalent complex power load demand is used to calculate the two pairs of solutions, i.e., the multiple three-phase power-flow solutions. Simulation studies have been carried out for the multiple solutions. The results show that there is a point which is directly proportional to the imbalance in the power demand at the load bus. This point is used to set a criterion to differentiate between the two PV curves. Hence, the PV curve which is related to the voltage stability can be determined without the assumption of the linear load model at the start of the study.

Global and local convergence of a filter line search method for nonlinear programming

A framework for proving global convergence for a class of line search filter-type methods for nonlinear programming is presented without assuming that the Jacobian has full rank everywhere. The underlying method is based on the filter concept where trial points are accepted, provided there is a sufficient decrease in the objective function or constraints violation function. The proposed methods solve a sequence of quadratic programming subproblems via line search techniques to induce global convergence. Under mild conditions, we will also show that the algorithm converges two step superlinearly when the iterates are near to the solution.

Linear generator: design and simulation

A six-slot tubular permanent magnet linear generator is designed, simulated, fabricated and tested. The finite element method is used in calculation and simulation to get the accurate results. Optimization of the translator length is carried out to achieve the minimum cogging force. Tests are conducted to confirm the simulation results. Better performance is achieved in the proposed improved generator prototype.