Renewable energy sources like wind, sun, and hydro are seen as a reliable alternative to the traditional energy sources such as oil, natural gas, or coal. Distributed power generation systems (DPGSs) based on renewable energy sources experience a large development worldwide, with Germany, Denmark, Japan, and USA as leaders in the development in this field. Due to the increasing number of DPGSs connected to the utility network, new and stricter standards in respect to power quality, safe running, and islanding protection are issued. As a consequence, the control of distributed generation systems should be improved to meet the requirements for grid interconnection. This paper gives an overview of the structures for the DPGS based on fuel cell, photovoltaic, and wind turbines. In addition, control structures of the grid-side converter are presented, and the possibility of compensation for low-order harmonics is also discussed. Moreover, control strategies when running on grid faults are treated. This paper ends up with an overview of synchronization methods and a discussion about their importance in the control

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Overview of Control and Grid Synchronization for Distributed Power Generation Systems

The use of distributed energy resources is increasingly being pursued as a supplement and an alternative to large conventional central power stations. The specification of a power-electronic interface is subject to requirements related not only to the renewable energy source itself but also to its effects on the power-system operation, especially where the intermittent energy source constitutes a significant part of the total system capacity. In this paper, new trends in power electronics for the integration of wind and photovoltaic (PV) power generators are presented. A review of the appropriate storage-system technology used for the integration of intermittent renewable energy sources is also introduced. Discussions about common and future trends in renewable energy systems based on reliability and maturity of each technology are presented

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Power-Electronic Systems for the Grid Integration of Renewable Energy Sources: A Survey

This review focuses on inverter technologies for connecting photovoltaic (PV) modules to a single-phase grid. The inverters are categorized into four classifications: 1) the number of power processing stages in cascade; 2) the type of power decoupling between the PV module(s) and the single-phase grid; 3) whether they utilizes a transformer (either line or high frequency) or not; and 4) the type of grid-connected power stage. Various inverter topologies are presented, compared, and evaluated against demands, lifetime, component ratings, and cost. Finally, some of the topologies are pointed out as the best candidates for either single PV module or multiple PV module applications.

A review of single-phase grid-connected inverters for photovoltaic modules

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

Predictive control is a very wide class of controllers that have found rather recent application in the control of power converters. Research on this topic has been increased in the last years due to the possibilities of today's microprocessors used for the control. This paper presents the application of different predictive control methods to power electronics and drives. A simple classification of the most important types of predictive control is introduced, and each one of them is explained including some application examples. Predictive control presents several advantages that make it suitable for the control of power converters and drives. The different control schemes and applications presented in this paper illustrate the effectiveness and flexibility of predictive control.

Predictive Control in Power Electronics and Drives

Preface. 1. Introduction. I: Converters in Equilibrium. 2. Principles of Steady State Converter Analysis. 3. Steady-State Equivalent Circuit Modeling, Losses, and Efficiency. 4. Switch Realization. 5. The Discontinuous Conduction Mode. 6. Converter Circuits. II: Converter Dynamics and Control. 7. AC Equivalent Circuit Modeling. 8. Converter Transfer Functions. 9. Controller Design. 10. Input Filter Design. 11. AC and DC Equivalent Circuit Modeling of the Discontinuous Conduction Mode. 12. Current Programmed Control. III: Magnetics. 13. Basic Magnetics Theory. 14. Inductor Design. 15. Transformer Design. IV: Modern Rectifiers and Power System Harmonics. 16. Power and Harmonics in Nonsinusoidal Systems. 17. Line-Commutated Rectifiers. 18. Pulse-Width Modulated Rectifiers. V: Resonant Converters. 19. Resonant Conversion. 20. Soft Switching. Appendices: A. RMS Values of Commonly-Observed Converter Waveforms. B. Simulation of Converters. C. Middlebrook's Extra Element Theorem. D. Magnetics Design Tables. Index.

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Fundamentals of Power Electronics

This paper explores predictive digital current programmed control for valley, peak or average current. The control laws are derived for the three basic converters: buck, boost, and buck-boost. It is found that for each variable of interest (valley, peak or average current) there is a choice of the appropriate pulse-width modulation method to achieve predictive digital current control without oscillation problems. The proposed digital control techniques can be used in a range of power conversion applications, including rectifiers with power factor correction (PFC). Very low current distortion meeting strict avionics requirements (400-800 Hz line frequency) is experimentally demonstrated on a digitally controlled boost PFC employing predictive average current programmed control.

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Predictive digital current programmed control

An equivalent circuit model for the discontinuous conduction mode flyback converter based on the loss-free resistor concept is presented. This simple model correctly describes the basic power processing properties of the converter, including input port resistor emulation, output port power source characteristics, and control characteristics. Based on this model, steady-state design equations are described and are used in a design example. Design of the slow output voltage feedback loop is also considered. A small-signal AC model is developed for both the resistive load and the DC-DC converter-voltage regulator load cases. In addition, a simple first-order approximation for the line current distortion and phase shift caused by 120 Hz duty cycle variations is derived. >

Design of a simple high-power-factor rectifier based on the flyback converter

A family of AC-to-DC converters which integrate the functions of low harmonic rectification, low frequency energy storage, and wide bandwidth output voltage control into a single converter containing one, two, or four active switches is presented. These converters utilize a discontinuous conduction mode input inductor, an internal energy storage capacitor, and transformer secondary circuits which resemble the bridge, forward, flyback, or Cuk DC-DC converters. A large-signal equivalent circuit model for this family which uses the loss-free resistor concept is presented. Design strategies and experimental results are given. High performance regulation with satisfactory line current harmonics is demonstrated with conventional duty ratio control. Further improvements in line current are possible by simultaneous duty ratio and switching frequency control. >

Integrated high quality rectifier-regulators

This paper describes the complete design and implementation of a digital controller for a high-frequency switching power supply Guidelines for the minimum required resolution of the analog-to-digital converter, the pulse-width modulator, and the fixed-point computational unit are derived A design example based on a buck converter operating at the switching frequency of 1 MHz is presented The controller design is based on direct digital design approach and standard root-locus techniques Experimental results are shown to validate the design approach and the allocation of resources (resolution) in the implementation

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Robert W. Erickson

Papers

Fundamentals of Power Electronics

Predictive digital current programmed control

Design of a simple high-power-factor rectifier based on the flyback converter

Integrated high quality rectifier-regulators

Design and implementation of a digital PWM controller for a high-frequency switching DC-DC power converter