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

This book, written by two major figures in adaptive control, provides a wealth of material for researchers, practitioners, and students. While some researchers in adaptive control may note the absence of a particular topic, the book‘s scope represents a high-gain instrument. It can be used by designers of control systems to enhance their work through the information on many new theoretical developments, and can be used by mathematical control theory specialists to adapt their research to practical needs. The book is strongly recommended to anyone interested in adaptive control.

Adaptive Control

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

Current-mode control in digitally controlled switched-mode power supplies typically requires analog-to-digital (A/D) conversion of at least two signals, voltage, and current. The complexity of voltage A/D converters can be reduced using window A/D techniques. In conventional current A/D conversion, however, relatively high resolution is required over a wide range of signals, which results in increased complexity, power consumption, and cost of the controller. This paper proposes a very simple feedback sensor capable of high-resolution average inductor current sensing using two analog comparators and an analog low-pass filter. The approach requires very few external components and employs minimal digital hardware resources. A dynamic model and performance of the average inductor current sensor are experimentally verified on a 12-V input, 19-V output, 50-W boost converter prototype. The applicability of the proposed sensor is demonstrated in a digitally controlled 400-W, 400-V output Boost power factor preregulator.

Average Inductor Current Sensor for Digitally Controlled Switched-Mode Power Supplies

This paper introduces an approach to near time- optimal control in DC-DC converters using a simple digital controller realization. The proposed proximate time-optimal digital (PTOD) controller is a combination of a linear PID controller operating near a reference point and a nonlinear switching surface (NSS) controller away from the reference, together with a smooth transition between the two. A capacitor current estimator enables effective switching surface evaluation and eliminates the need for current sensing. The NSS controller, which is implemented as a small Verilog HDL module, can be easily added to an existing digital PWM controller to construct the PTOD controller. In steady state, the converter operates at constant switching frequency. Simulation and experimental results are shown for a 6.5 V-to-1.3 V, 10 A synchronous buck converter.

http://ecee.colorado.edu/~pao/anonftp/Yousefzadeh_EtAl_TPEL.pdf

Proximate Time-Optimal Digital Control for DC-DC Converters

In this paper, nonlinear-carrier (NLC) control is proposed for high-power-factor rectifiers based on flyback, Cuk or Sepic converters operated in the continuous conduction mode. In the NLC controller, the switch duty ratio is determined by comparing a signal proportional to the integral of the switch current with a periodic nonlinear carrier waveform. The shape of the NLC waveform is determined so that the resulting input line current follows the input line voltage, as required for unity-power-factor rectification. A simple exponential carrier waveform generator is described. Using the NLC controller, input line voltage sensing, error amplifier in the current-shaping loop, and the multiplier/divider circuitry in the voltage feedback loop are eliminated. The simple, high-performance controller is well-suited for integrated-circuit implementation. Results of experimental verification on a 150 W flyback rectifier are presented.

Nonlinear-carrier control for high-power-factor rectifiers based on flyback, Cuk or Sepic converters

This paper describes a digital controller chip set for high-frequency DC-DC power converters with galvanic isolation. The secondary-side controller includes an A/D converter and a transmitter that sends a digital error signal as serial data through an opto-coupler. The primary-side controller includes a serial-data receiver, a programmable digital PID regulator, and a high-resolution (10-bit) digital pulse-width modulator. The digital error signal transmission through the isolation boundary eliminates the problem of gain variation when the opto-coupler is used in linear mode. The chip set is tested as a replacement for a conventional analog current-mode controller in a 3.3 V, 20 A, 400 KHz DC power supply. Experimental results with the digital controller show improved dynamic responses compared to the responses obtained with the analog controller.

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Digital controller chip set for isolated DC power supplies

In this paper, we present two DC-DC converters that operate at a microwave frequency. The first converter consists of a class-E switched-mode microwave amplifier, which performs the DC-AC conversion, and two half-wave diode rectifier outputs. The class-E MESFET amplifier has a minimum power-added efficiency of 86%, corresponding drain efficiency of 95%, and 120 mW of output power at 4.5 GHz. The diode rectifier has a maximum conversion efficiency of 98% and an overall efficiency of 83%. The second converter consists of a high-efficiency class-E oscillator and a diode rectifier. The class-E oscillator has a maximum efficiency of 57% and maximum output power of 725 mW. The DC-DC converter is planar and compact, with no magnetic components, and with a maximum overall DC-DC conversion efficiency of 64% for a DC input of 3 V, and the output voltage across a 87-/spl Omega/ load of 2.15 V.

http://ecee.colorado.edu/microwave/docs/publications/1999/MTT_SDdm_99.pdf

Dragan Maksimovic

Papers

Average Inductor Current Sensor for Digitally Controlled Switched-Mode Power Supplies

Proximate Time-Optimal Digital Control for DC-DC Converters

Nonlinear-carrier control for high-power-factor rectifiers based on flyback, Cuk or Sepic converters

Digital controller chip set for isolated DC power supplies

A planar 4.5-GHz DC-DC power converter