Henry Shu-Hung Chung

Adaptive Particle Swarm Optimization

An adaptive particle swarm optimization (APSO) that features better search efficiency than classical particle swarm optimization (PSO) is presented. More importantly, it can perform a global search over the entire search space with faster convergence speed. The APSO consists of two main steps. First, by evaluating the population distribution and particle fitness, a real-time evolutionary state estimation procedure is performed to identify one of the following four defined evolutionary states, including exploration, exploitation, convergence, and jumping out in each generation. It enables the automatic control of inertia weight, acceleration coefficients, and other algorithmic parameters at run time to improve the search efficiency and convergence speed. Then, an elitist learning strategy is performed when the evolutionary state is classified as convergence state. The strategy will act on the globally best particle to jump out of the likely local optima. The APSO has comprehensively been evaluated on 12 unimodal and multimodal benchmark functions. The effects of parameter adaptation and elitist learning will be studied. Results show that APSO substantially enhances the performance of the PSO paradigm in terms of convergence speed, global optimality, solution accuracy, and algorithm reliability. As APSO introduces two new parameters to the PSO paradigm only, it does not introduce an additional design or implementation complexity.

Particle Swarm Optimization With an Aging Leader and Challengers

In nature, almost every organism ages and has a limited lifespan. Aging has been explored by biologists to be an important mechanism for maintaining diversity. In a social animal colony, aging makes the old leader of the colony become weak, providing opportunities for the other individuals to challenge the leadership position. Inspired by this natural phenomenon, this paper transplants the aging mechanism to particle swarm optimization (PSO) and proposes a PSO with an aging leader and challengers (ALC-PSO). ALC-PSO is designed to overcome the problem of premature convergence without significantly impairing the fast-converging feature of PSO. It is characterized by assigning the leader of the swarm with a growing age and a lifespan, and allowing the other individuals to challenge the leadership when the leader becomes aged. The lifespan of the leader is adaptively tuned according to the leaders leading power. If a leader shows strong leading power, it lives longer to attract the swarm toward better positions. Otherwise, if a leader fails to improve the swarm and gets old, new particles emerge to challenge and claim the leadership, which brings in diversity. In this way, the concept “aging” in ALC-PSO actually serves as a challenging mechanism for promoting a suitable leader to lead the swarm. The algorithm is experimentally validated on 17 benchmark functions. Its high performance is confirmed by comparing with eight popular PSO variants.

A Novel Set-Based Particle Swarm Optimization Method for Discrete Optimization Problems

Particle swarm optimization (PSO) is predominately used to find solutions for continuous optimization problems. As the operators of PSO are originally designed in an n-dimensional continuous space, the advancement of using PSO to find solutions in a discrete space is at a slow pace. In this paper, a novel set-based PSO (S-PSO) method for the solutions of some combinatorial optimization problems (COPs) in discrete space is presented. The proposed S-PSO features the following characteristics. First, it is based on using a set-based representation scheme that enables S-PSO to characterize the discrete search space of COPs. Second, the candidate solution and velocity are defined as a crisp set, and a set with possibilities, respectively. All arithmetic operators in the velocity and position updating rules used in the original PSO are replaced by the operators and procedures defined on crisp sets, and sets with possibilities in S-PSO. The S-PSO method can thus follow a similar structure to the original PSO for searching in a discrete space. Based on the proposed S-PSO method, most of the existing PSO variants, such as the global version PSO, the local version PSO with different topologies, and the comprehensive learning PSO (CLPSO), can be extended to their corresponding discrete versions. These discrete PSO versions based on S-PSO are tested on two famous COPs: the traveling salesman problem and the multidimensional knapsack problem. Experimental results show that the discrete version of the CLPSO algorithm based on S-PSO is promising.

Clustering-Based Adaptive Crossover and Mutation Probabilities for Genetic Algorithms

Research into adjusting the probabilities of crossover and mutation pm in genetic algorithms (GAs) is one of the most significant and promising areas in evolutionary computation. px and pm greatly determine whether the algorithm will find a near-optimum solution or whether it will find a solution efficiently. Instead of using fixed values of px and pm , this paper presents the use of fuzzy logic to adaptively adjust the values of px and pm in GA. By applying the K-means algorithm, distribution of the population in the search space is clustered in each generation. A fuzzy system is used to adjust the values of px and pm. It is based on considering the relative size of the cluster containing the best chromosome and the one containing the worst chromosome. The proposed method has been applied to optimize a buck regulator that requires satisfying several static and dynamic operational requirements. The optimized circuit component values, the regulators performance, and the convergence rate in the training are favorably compared with the GA using fixed values of px and pm. The effectiveness of the fuzzy-controlled crossover and mutation probabilities is also demonstrated by optimizing eight multidimensional mathematical functions

A novel maximum power point tracking technique for solar panels using a SEPIC or Cuk converter

A novel technique for efficiently extracting the maximum output power from a solar panel under varying meteorological conditions is presented. The methodology is based on connecting a pulse-width-modulated (PWM) DC/DC SEPIC or Cuk converter between a solar panel and a load or battery bus. The converter operates in discontinuous capacitor voltage mode whilst its input current is continuous. By modulating a small-signal sinusoidal perturbation into the duty cycle of the main switch and comparing the maximum variation in the input voltage and the voltage stress of the main switch, the maximum power point (MPP) of the panel can be located. The nominal duty cycle of the main switch in the converter is adjusted to a value, so that the input resistance of the converter is equal to the equivalent output resistance of the solar panel at the MPP. This approach ensures maximum power transfer under all conditions without using microprocessors for calculation. Detailed mathematical derivations of the MPP tracking technique are included. The tracking capability of the proposed technique has been verified experimentally with a 10-W solar panel at different insolation (incident solar radiation) levels and under large-signal insolation level changes.

Inductorless DC-to-DC converter with high power density

A new type of switching-mode power supply containing no inductors or transformers is proposed. The controlled transfer of energy from a unregulated DC source to a regulated output voltage is realized through a switched-capacitor (SC) circuit. A duty-cycle control is used; the driving signals of the transistors in the SC circuit are determined by the feedback circuit. The absence of magnetic devices makes possible the realization of power converters of small size, low weight and high power density, able to be manufactured in IC technology. High efficiency, small output voltage ripple and good regulation for large changes in the input voltage and/or load values are other positive features of the new type of DC-to-DC power converter. The input-to-output voltage conversion ratio is flexible; the same converter structure can provide a large range of constant desired values of the output voltage for a given input voltage, by predetermining the steady-state conversion ratio. The frequency response shows good stability of the designed converter. The experimental results obtained by using a prototype of a step-down SC-based DC-to-DC converter confirmed the theoretical expectations and the computer simulation results. >

Evaluation of the shielding effects on printed-circuit-board transformers using ferrite plates and copper sheets

This paper presents an effective shielding technique and a simple structure for printed-circuit-board (PCB) transformers. The performance of PCB transformers using the proposed shielding technique is evaluated using thin ferrite plates and copper sheets. Without affecting the transformer energy efficiency, the shielding method under investigation can achieve 28 dB shielding effectiveness (SE), which is much higher than the SE (about 4 dB) obtained by shielding the transformer windings with only two ferrite plates. The proposed PCB transformer structure is very simple and has high energy efficiency (>90%) for Megahertz operation.

A novel maximum power point tracker for PV panels using switching frequency modulation

A novel technique for efficiently extracting maximum power from photovoltaic (PV) panels is presented. The power conversion stage, which is connected between a PV panel and a load or bus, is a SEPIC or Cuk converter or their derived circuits operating in discontinuous inductor-current or capacitor-voltage mode. A method of locating the maximum power point (MPP) is based on injecting a small-signal sinusoidal perturbation into the switching frequency and comparing the AC component and the average value of the panel terminal voltage. Apart from not requiring any sophisticated digital computation of the panel power, the proposed technique does not approximate the panel characteristics and can globally locate the MPP under wide insolation conditions. The tracking capability has been verified experimentally with a 10 W solar panel under a controlled experimental setup. Performances under the steady state and in the large-signal change of the insolation level will are given.

Constant-Frequency Hysteresis Current Control of Grid-Connected VSI Without Bandwidth Control

The theory, design, and implementation of a constant-frequency hysteresis current control for grid-connected voltage source inverter (VSI) is presented. The proposed control technique retains the benefit of the hysteresis control having fast dynamic response and tackles the drawback of the standard hysteresis control having variable switching frequency. The concept is based on predicting the current reference, system dynamic behavior and past time to formulate the switching function for dictating the switching times of the switches in the inverter within a pre-defined switching period. Of particular importance, no hysteresis bandwidth (a challenge in the practical implementation) is needed in the entire control method. The operating principles of proposed technique and mathematical derivation of the switching functions will be given. The proposed method is successfully applied to a 300W, 110V, 60Hz grid-connected VSI prototype with the controller implemented by a simple analog circuit. The steady-state and large-signal dynamic response of the VSI are studied. Experimental results show that the inverter can reach the steady-state in two switching actions after the inverter is subject to large-signal input and output disturbances.

Circuit-level comparison of STATCOM technologies

This paper performs a comprehensive circuit-level evaluation of four modern STATCOM systems, namely true-48-pulse and quasi-48-pulse STATCOMs, cascade multilevel and binary multilevel inverters. The comparison is based on a number of factors including circuit topology, harmonic distortion, system losses, GTO quantities, their specific applications, and other considerations. The theoretical results are verified by simulation with the use of MATLAB-Simulink Power System Blockset.