http://ieeexplore.ieee.org/iel5/5610941/5624686/05624745.pdf

Power electronics

The aim of this paper is to present a review of current control techniques for three-phase voltage-source pulsewidth modulated converters. Various techniques, different in concept, have been described in two main groups: linear and nonlinear. The first includes proportional integral (stationary and synchronous) and state feedback controllers, and predictive techniques with constant switching frequency. The second comprises bang-bang (hysteresis, delta modulation) controllers and predictive controllers with on-line optimization. New trends in current control-neural networks and fuzzy-logic-based controllers-are discussed, as well. Selected oscillograms accompany the presentation in order to illustrate properties of the described controller groups.

Current control techniques for three-phase voltage-source PWM converters: a survey

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.

/pdf/a-review-of-single-phase-improved-power-quality-ac-dc-2pm6h4zjxq.pdf

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

The authors discuss high-voltage power conversion. Conventional series connection and three-level voltage source inverter techniques are reviewed and compared. A novel versatile multilevel commutation cell is introduced: it is shown that this topology is safer and more simple to control, and delivers purer output waveforms. The authors show how this technique can be applied to either choppers or voltage-source inverters and generalized to any number of switches.<<ETX>>

Multi-level conversion : high voltage choppers and voltage-source inverters

With rapid development of wind power technologies and significant growth of wind power capacity installed worldwide, various wind turbine concepts have been developed. The wind energy conversion system is demanded to be more cost-competitive, so that comparisons of different wind generator systems are necessary. An overview of different wind generator systems and their comparisons are presented. First, the contemporary wind turbines are classified with respect to both their control features and drive train types, and their strengths and weaknesses are described. The promising permanent magnet generator types are also investigated. Then, the quantitative comparison and market penetration of different wind generator systems are presented. Finally, the developing trends of wind generator systems and appropriate comparison criteria are discussed. It is shown that variable speed concepts with power electronics will continue to dominate and be very promising technologies for large wind farms. The future success of different wind turbine concepts may strongly depend on their ability of complying with both market expectations and the requirements of grid utility companies.

Overview of different wind generator systems and their comparisons

The interaction between the natural oscillatory characteristic of a nonlinear system with a periodic driving source gives rise to oscillations whose frequency depends on the amplitude of the oscillation. The existence of combination tones (both harmonic and subharmonic) in such systems, gives rise to complicated oscillatory behaviour induced by either the occurrence of the saturation of transformer cores or by system conditions leading to the reduction in the magnitude of damping. By studying the frequency characteristics (Bode plot) of single phase nonlinear power networks, the possible oscillatory modes that may be excited can be anticipated. This aspect is then extended to three phase power networks to include the influence of mutual coupling between phases and unbalance due to non-transposition of transmission lines. The Frequency Scan feature in the Alternative Transients Program (ATP) is used for that purpose.

Determining the frequency characteristics of power networks using atp

This paper presents an improved in-line uninterruptible power supply system, which has voltage sag compensation and power factor improvement. The system employs a voltage-source voltage-controlled converter with battery storage. The converter voltage is synchronised to the grid voltage and a link inductor is inserted between the converter and the grid. The load is connected directly to the converter output voltage. The magnitude of the converter voltage is maintained constant through the sinusoidal PWM signal that provides stabilisation from any voltage sags and large fluctuation of the mains voltage. The power factor correction is controlled through the power flow of the system. The inverter is maintained to supply the reactive power to the load, therefore, the grid supplies the active power. Results from simulation using PSCAD/EMTDC and laboratory tests are included.

An improved in-line uninterruptible power supply system

This paper presents the complete system modelling, designing and controlling of an islanded minigrid power supply to the town of Carnarvon, Western Australia. Carnarvon power system is an isolated network supplying power to approximately 5000 people via 205km of distribution lines. The existing power system is supplied by a number of large centralized 21MW Diesel Generators. The objective of this paper is to report the design, development and installation of a Photovoltaic (PV) diesel hybrid-power system such that the operating cost can be minimized and the load on the aging generators could be significantly reduced. The proposal includes the installation of two 25kW DC variable speed diesel generators and a suitably sized advanced battery bank at each suburban transformer to ensure hundred percent penetration of solar power by residential customers in the local area. This method of control is modelled and simulated in HOMER, PSpice and Matlab. The different modes of control used to integrate maximum solar energy, reduce diesel consumption and also the methodology imposed to store excess renewable energy for operation during the night. Keywords— Hybrid system, Renewable energy, Variable speed generator, remote, Carnarvon, Ultrabattery.

/pdf/design-and-modeling-of-a-hundred-percent-renewable-energy-42kerifmru.pdf

Design and Modeling of a Hundred Percent Renewable Energy Based Suburban Utility

This paper analyses a wave-shaping controller (WSC) in detail and examines the effect of different parameters, their advantages and limitations on the stability of a single-phase voltage controlled voltage source inverter (VCVSI) without incorporating additional hardware and/or extra complex control techniques It is shown that the proposed improved WSC can maintain power quality in the presence of non-linear loads and abnormalities Discussions of the concepts, mathematical modelling, computer simulations and experimental results for a 2 kVA inverter are presented

A Sinusoidal VSI Wave-shaping Controller for Non-linear Loads

Design and optimization of a hybrid power system is site specific. It depends mainly on the available of renewable sources and the load demand. Sizing of the components has significant influence on the system performance. Due to the weather dependant nature of renewable energy sources, a fossil fuel based constant-speed generator is an essential component in traditional hybrid power systems. However, the efficiency of this generator especially at light loads can be significantly improved by adopting a variable-speed operation. This paper presents a combined sizing and operation control programme that can be used with both traditional constant-speed generators as well as novel variable-speed generators. The programme uses the polynomial curve fitting for the fuel consumption characteristics of variable-speed generators. The accuracy of the calculations is verified by comparing with a well known renewable energy optimization package.

C.V. Nayar

Papers

Determining the frequency characteristics of power networks using atp

An improved in-line uninterruptible power supply system

Design and Modeling of a Hundred Percent Renewable Energy Based Suburban Utility

A Sinusoidal VSI Wave-shaping Controller for Non-linear Loads

Simulation and components sizing of a stand-alone hybrid power system with variable speed generator