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

This paper proposes a digital output voltage sensing method for power factor correction (PFC) rectifiers that requires only a single analog comparator and a small amount of digital hardware Using this method a digital estimation of the output error voltage can be obtained at a rate of twice the line frequency (2f line ) without the use of a traditional analog to digital converter (A/D) The proposed method effectively implements a windowed A/D around the output reference voltage with a window range equal to the magnitude of the ac output voltage ripple When used in combination with a nonlinear-carrier (NLC) current controller, a power feedforward function is inherently embedded in the operation of the single-comparator A/D (SCA/D), which simplifies the voltage loop design and reduces voltage loop gain variation due to operating power level Experimental results are reported comparing load transient responses using the SCA/D or a traditional A/D in a digitally controlled 300W boost PFC

Single comparator based A/D converter for output voltage sensing in power factor correction rectifiers

This paper describes a distributed master-slave multiphase DC-DC converter architecture and related digital control and communication techniques. In the distributed master-slave architecture, all converter modules are identical, but one module operates as the master. The master module communicates its voltage error and current data over a single-wire serial bus to remove the voltage sensing mismatch and to accomplish active current sharing among the modules. Experimental results are shown for a 5 V-to-12 V input, 1.3 V, 20 A output two-phase synchronous buck converter.

Digitally controlled distributed multiphase DC-DC converters

This paper presents a boost dc-dc converter design that maximizes drive-cycle weighted efficiency based on the CAFE standard. A drive-cycle simplification approach is introduced to enable faster yet accurate CAFE-based optimization. The optimization is based on calibrated loss models, including soft switching operation in boundary conduction mode (BCM) using a compact planar inductor. An enhanced thermal management strategy based on additional thermally-conductive layers is proposed to address design limitations related to the planar inductor realization. The design approaches are verified on an experimental 400 V, 11 kW SiC boost converter prototype, which achieves 99% measured efficiency over a wide operating range, and a CAFE-weighted efficiency of 99.1%.

Drive-Cycle Optimized 99% Efficient SiC Boost Converter Using Planar Inductor with Enhanced Thermal Management

This paper discusses the linearity of a class-E X-band PA in a digital polar transmitter. The PA is nonlinear since it is compressed by 2.2 dB when achieving a 59% PAE at 10 GHz. Load-pull is performed under a two-tone test and the resulting optimal efficiency impedance is found to be over 30% different from the single-tone load-pull. In addition standard two-tone load-pull measurements indicate that the impedance for max Pout coincide with worst nonlinearity (IMD). Surprisingly, in the two-tone polar load-pull, impedance for max Pout differs significantly from the impedance corresponding to worst IMD. Therefore, under polar modulation a different matching circuit should be designed for optimal linearity and efficiency. The PA is part of a digital polar transmitter which enables linearization including phase predistortion, with IMD levels over 11 dB lower than in the standard two-tone test. Load-pull performed on the polar class-E PA shows that the level of intermodulation products varies for different signals input into the PA.

Linearity of X-band Class-E Power Amplifiers in a Digital Polar Transmitter

The paper presents a second-order sliding-mode (SOSM) control approach for synchronous buck dc-dc converters. The SOSM controller is implemented digitally, using a simple state machine, which does not require current sensing or an integral term. A hysteresis is introduced to control the switching frequency. The SOSM controller results in fast transient responses without overshoots, and is robust against parameter uncertainties. The proposed approach is verified by experimental results on a 1.25 V, 10 A prototype.

Dragan Maksimovic

Papers

Single comparator based A/D converter for output voltage sensing in power factor correction rectifiers

Digitally controlled distributed multiphase DC-DC converters

Drive-Cycle Optimized 99% Efficient SiC Boost Converter Using Planar Inductor with Enhanced Thermal Management

Linearity of X-band Class-E Power Amplifiers in a Digital Polar Transmitter

State-machine realization of second-order sliding-mode control for synchronous buck DC-DC converters