Solid-state switch-mode rectification converters have reached a matured level for improving power quality in terms of power-factor correction (PFC), reduced total harmonic distortion at input AC mains and precisely regulated DC output in buck, boost, buck-boost and multilevel modes with unidirectional and bidirectional power flow. This paper deals with a comprehensive review of improved power quality converters (IPQCs) configurations, control approaches, design features, selection of components, other related considerations, and their suitability and selection for specific applications. It is targeted to provide a wide spectrum on the status of IPQC technology to researchers, designers and application engineers working on switched-mode AC-DC converters. A classified list of more than 450 research publications on the state of art of IPQC is also given for a quick reference.

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A review of single-phase improved power quality AC-DC converters

With the fast-paced changing technologies in the power industry, new power references addressing new technologies are coming to the market. So there is an urgent need to keep track of international experiences and activities taking place in the field of modern unit-commitment (UC) problem. This paper gives a bibliographical survey, mathematical formulations, and general backgrounds of research and developments in the field of UC problem for past 35 years based on more than 150 published articles. The collected literature has been divided into many sections, so that new researchers do not face any difficulty in carrying out research in the area of next-generation UC problem under both the regulated and deregulated power industry.

Unit commitment-a bibliographical survey

Evolutionary algorithms are heuristic methods that have yielded promising results for solving nonlinear, nondifferentiable, and multi-modal optimization problems in the power systems area. The differential evolution (DE) algorithm is an evolutionary algorithm that uses a rather greedy and less stochastic approach to problem solving than do classical evolutionary algorithms, such as genetic algorithms, evolutionary programming, and evolution strategies. DE also incorporates an efficient way of self-adapting mutation using small populations. The potentialities of DE are its simple structure, easy use, convergence property, quality of solution, and robustness. This paper proposes a new approach for solving economic load dispatch problems with valve-point effect. The proposed method combines the DE algorithm with the generator of chaos sequences and sequential quadratic programming (SQP) technique to optimize the performance of economic dispatch problems. The DE with chaos sequences is the global optimizer, and the SQP is used to fine-tune the DE run in a sequential manner. The combined methodology and its variants are validated for two test systems consisting of 13 and 40 thermal units whose incremental fuel cost function takes into account the valve-point loading effects. The proposed combined method outperforms other state-of-the-art algorithms in solving load dispatch problems with the valve-point effect.

Correction to "Combining of Chaotic Differential Evolution and Quadratic Programming for Economic Dispatch Optimization with Valve-Point Effect"

This paper presents a new genetic approach for solving the economic dispatch problem in large-scale power systems. A new encoding technique is developed. The chromosome contains only an encoding of the normalized system incremental cost in this encoding technique. Therefore, the total number of bits of chromosome is entirely independent of the number of units. The salient feature makes the proposed genetic approach attractive in large and complex systems which other methodologies may fail to achieve. Moreover, the approach can take network losses, ramp rate limits, and prohibited zone avoidance into account because of genetic algorithm's flexibility. Numerical results on an actual utility system of up to 40 units show that the proposed approach is faster and more robust than the well-known lambda-iteration method in large-scale systems.

Large-scale economic dispatch by genetic algorithm

The growing costs of fuel and operation of power generating units warrant improvement of optimization methodologies for economic dispatch (ED) problems. The practical ED problems have non-convex objective functions with equality and inequality constraints that make it much harder to find the global optimum using any mathematical algorithms. Modern optimization algorithms are often meta-heuristic, and they are very promising in solving nonlinear programming problems. This paper presents a novel approach to determining the feasible optimal solution of the ED problems using the recently developed Firefly Algorithm (FA). Many nonlinear characteristics of power generators, and their operational constraints, such as generation limitations, prohibited operating zones, ramp rate limits, transmission loss, and nonlinear cost functions, were all contemplated for practical operation. To demonstrate the efficiency and applicability of the proposed method, we study four ED test systems having non-convex solution spaces and compared with some of the most recently published ED solution methods. The results of this study show that the proposed FA is able to find more economical loads than those determined by other methods. This algorithm is considered to be a promising alternative algorithm for solving the ED problems in practical power systems.

Firefly Algorithm for solving non-convex economic dispatch problems with valve loading effect

A branch-and-bound method for scheduling thermal generating units is presented. The decision variables are the start and stop times and the generation levels of the units. A simple rule is defined to compute the lower bound of each candidate schedule for interim computation usage, and the branching process takes place on the subschedule with the lowest lower bound. The heap data storage structure and space saving encoded data representations for partially fulfilled unit commitment schedules are utilized to facilitate the branch-and-bound procedure. By successive branching and bounding, the unit commitment schedule with the minimum cost can be obtained. Two examples, a 10 unit, 24 h and a 20 unit, 36 h case, are shown to illustrate the effectiveness of the proposed algorithm. >

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Branch-and-bound scheduling for thermal generating units

The traditional frequency-shift methods for islanding detection of grid connected PV inverters (the active frequency-drift method and the slip mode frequency-shift method) become ineffective under certain paralleled RLC loads. The automatic phase-shift method is proposed in this paper to alleviate this problem. The method is based on the phase shift of the sinusoidal inverter output current. When the utility malfunctions, the phase-shift algorithm keeps the frequency of the inverter terminal voltage deviating until the protection circuit is triggered. Simulation and experiments are performed for verification.

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Automatic phase-shift method for islanding detection of grid-connected photovoltaic inverters

This paper proposes a novel single-stage ac-to-dc light-emitting-diode (LED) driver circuit. A buck-boost power factor (PF) corrector is integrated with a flyback converter. A recycling path is built to recover the inductive leakage energy. In this way, the presented circuit can provide not only high PF and low total harmonic distortion but also high conversion efficiency and low switching voltage spikes. Above 0.95 PF and 90% efficiency are obtained from an 8-W LED lamp driver prototype.

A Novel Single-Stage High-Power-Factor AC-to-DC LED Driving Circuit With Leakage Inductance Energy Recycling

An active snubber cell is proposed to contrive zero-voltage-transition (ZVT) pulsewidth-modulated (ZVT-PWM) converters. Except for the auxiliary switch, all active and passive semiconductor devices in a ZVT-PWM converter operate at zero-voltage-switching (ZVS) turn on and turn off. The auxiliary switch operates at ZVS turn off and near zero current-switching (ZCS) turn on. An analytical study on a boost ZVT-PWM converter with the proposed active snubber cell is presented in detail. A 750 W 80 kHz prototype of the boost ZVT-PWM converter has been built in the laboratory to experimentally verify the analysis. Six basic ZVT-PWM converters can be easily created by attaching the proposed active snubber cells to conventional PWM converters. A detailed design procedure of the proposed active snubber cell is also presented in this paper.

Novel ZVT-PWM converters with active snubbers

Analysis and design of a single-stage LLC resonant converter are proposed. A single-stage converter uses only one control signal to drive two power converters, a power factor corrector (PFC) converter and a dc/dc converter, for reducing the cost of the system. However, this simplicity induces power imbalance between two converters, and then, the bus voltage between two converters drifts and becomes unpredictable. To ensure that the bus capacitor voltage can be kept in a tolerable region, the characteristics of a PFC converter and an LLC tank are investigated, and then, a design procedure is proposed correspondingly. Finally, a single-stage LLC resonant converter is implemented to verify the analysis.

Chern-Lin Chen

Papers

Branch-and-bound scheduling for thermal generating units

Automatic phase-shift method for islanding detection of grid-connected photovoltaic inverters

A Novel Single-Stage High-Power-Factor AC-to-DC LED Driving Circuit With Leakage Inductance Energy Recycling

Novel ZVT-PWM converters with active snubbers

Analysis and Design of Single-Stage AC/DC $LLC$ Resonant Converter