Ronald G. Harley

Particle Swarm Optimization: Basic Concepts, Variants and Applications in Power Systems

Many areas in power systems require solving one or more nonlinear optimization problems. While analytical methods might suffer from slow convergence and the curse of dimensionality, heuristics-based swarm intelligence can be an efficient alternative. Particle swarm optimization (PSO), part of the swarm intelligence family, is known to effectively solve large-scale nonlinear optimization problems. This paper presents a detailed overview of the basic concepts of PSO and its variants. Also, it provides a comprehensive survey on the power system applications that have benefited from the powerful nature of PSO as an optimization technique. For each application, technical details that are required for applying PSO, such as its type, particle formulation (solution representation), and the most efficient fitness functions are also discussed.

Harmonic and Unbalance Compensation Based on Direct Power Control for Electric Railway Systems

This paper presents a general filtering and unbalance compensation scheme for electric traction systems using a direct power control-based algorithm. For a balanced three-phase three-wire system, the proposed method is able to control the power flow exchange between the grid and the load so that the instantaneous complex power is maintained constant. As a consequence, any nonlinear unbalanced load is seen by the three-phase supply as a balanced linear load. The proposed filter is evaluated on power substations with open delta (V-V) and Scott transformer feeders, and for two-level and dual-converter in the power stage. The scheme has been simulated and experimentally validated. The results from experimental and simulation tests show the controller advantages and the applicability of the proposed method in railway systems.

Multiple STATCOM Allocation and Sizing Using Particle Swarm Optimization

This study shows step by step the application of the particle swarm optimization (PSO) method to solve the problem of optimal allocation and sizing of multiple static compensators (STATCOM) in a medium size power network (45 bus system, part of the Brazilian power network). The PSO is proposed as an alternative methodology for traditional heuristic approaches and complicated mixed integer linear and non linear programming methods. Simulation results show the suitability of the PSO technique in finding multiple optimal solutions to the problem (Pareto front) with reasonable computational effort. As a part of this study, the optimal setting of PSO parameters is investigated and different power system load conditions are tested to determine the impact over the location and size of each STATCOM unit

Swarm Intelligence for Transmission System Control

Many areas related to power system transmission require solving one or more nonlinear optimization problems. While analytical methods might suffer from slow convergence and the curse of dimensionality, heuristics based swarm intelligence can be an efficient alternative. This paper highlights the application of swam intelligence techniques for solving some of the transmission system control problems.

An improved nearest-level modulation method for the modular multilevel converter

This paper proposes an improved nearest-level modulation (NLM) method for the modular multilevel converter (MMC). By injecting an optimal common-mode voltage, the proposed method enables optimal capacitor-voltage balancing and circulating-current control of the MMC. A general approach to determine the optimal common-mode voltage is introduced in detail in this paper. In the proposed method, the level number of the output phase voltage of the MMC reaches the maximum (i.e., 2n+1, where n is the number of submodules in the upper or lower arm of each phase), which leads to reduced harmonics. Both of these advantages are not provided by earlier NLM methods. Furthermore, the proposed method is simple to implement and generally applicable to multiphase systems. Simulation results verify the effectiveness and performance of the proposed method.

Calculating the unsaturated inductance of 4/2 switched reluctance motors at arbitrary rotor positions based on partial differential equations of magnetic potentials

Phase inductance is a key parameter in switched reluctance motor (SRM) design because torque and the dynamics of phase voltages and currents are directly related to inductance. Therefore, accurate calculation of the inductance at arbitrary rotor positions is important in determining the SRM behavior. Contrary to the popular but time-consuming approach to determine the flux linkage and inductance of a SRM with finite element analysis (FEA), this paper proposes a novel analytical solution based on the partial differential equations of magnetic potentials to calculate the inductance profile of a 4/2 SRM with respect to rotor position, which makes the inductance prediction more time-efficient. The accuracy of this method is validated by comparing its estimated inductance profile to the inductance obtained by FEA.

Optimal utilization of STATCOM devices in a power system with high penetration of wind generation

As wind generation penetration increases in older power networks, a system becomes more vulnerable due to intermittency of the wind. It is desired to replace more conventional power with wind generation, but this may lead to overloaded lines as well as low voltage buses. In certain cases the power system may even collapses (i.e., no valid load flow solution exists). Static synchronous compensator (STATCOM) devices can provide significant reactive power to ensure the voltage stability, but they should be optimally designed, for both their ratings and locations, because of their high costs of installation. Based on a particle swarm optimization (PSO) algorithm, this paper introduces a general approach to determine the optimal location and sizing of the STATCOM devices for the power system with low-voltage buses or no valid load flow solution. Simulation results demonstrate that the voltage stability of the power system is achieved after the STATCOM devices are optimally placed, for all the potential stochastic output powers of the wind plants.

An optimized control strategy for the modular multilevel converter based on space vector modulation

This paper proposes an optimized control strategy for any modular multilevel converter (MMC), based on a generalized space vector modulation (SVM) method. By fully utilizing the flexibility of the SVM method, i.e., the redundant switching sequences and adjustable duty cycles, this optimized control strategy enables optimal capacitor-voltage and circulating-current control of the MMC. The proposed control strategy can also be implemented with other pulse width modulation methods, e.g., the carrier-based modulation and the nearest-level modulation, though sophisticated selection of the common-mode voltage injection may be required. This paper therefore also demonstrates that for the MMC, the SVM is more flexible than other modulation methods. Typical case studies are given to validate the analysis.