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 demonstrates the feasibility of detecting an onset of instability by monitoring the pattern of the output voltage error signal, and adaptively changing the compensator parameters in a digitally controlled switched-mode power supply. The techniques are verified on an experimental 90 W, 50 V-to-15 V forward converter where an abrupt change in operating conditions that leads to instability is emulated by removing the input filter damping. It is shown that the system can regain stability and return to regulation. The proposed techniques have potential applications in decentralized active stability control of power management and distribution systems typical for aerospace applications

Detection of instability and adaptive compensation of digitally controlled switched-mode power supplies

A hybrid digital pulse width modulator (DPWM) with digital delay-locked loops (DLLs) is provided. In this implementation, the digital pulse-width-modulator is synthesizable and includes a digital delay-locked loop around a delay-line to achieve constant frequency clocked operation. In this implementation, the resolution of the modulator is consistent over a wide range of process or temperature variations. The DPWM may implement trailing-edge, leading-edge, triangular, or phase-shift modulation. In an implementation suitable for DC-DC converters with synchronous rectifiers, for example, the DPWM may include two or more outputs for programmable dead-times. In another implementation, a digital pulse-width-modulator with a digital phase-locked loop is also provided.

Digital Pulse-Width-Modulator with Discretely Adjustable Delay Line

Cascaded dc-ac converters with interleaved carriers are commonly used in applications where elevated voltages and low-distortion multilevel waveforms are needed. Example applications include modular multilevel converters and solid-state transformers. In such systems, carrier interleaving is generally achieved via communication among the stacked converters or a centralized controller. Due to the large number of converters in such a system, existing approaches entail significant wiring complexity and communication may limit resilience to failures. In this paper, we introduce a control strategy which achieves communication-free carrier interleaving among series-connected converters. The proposed controller is embedded within each converter control loop and only requires measurements available at each set of converter terminals. We formulate a dynamic system model and show that the system converges to the interleaved condition irrespective of the number of converters in the stack. After outlining a practical method for digital implementation, experiments are shown on a hardware-in-the-loop setup.

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Decentralized Carrier Interleaving in Cascaded Multilevel DC-AC Converters

In this paper we present design and implementation of a 16-phase digitally controlled converter with 1.56 MHz per-phase switching frequency, 25 MHz sampling rate, and the closed-loop bandwidth of approximately 1 MHz. The experimental system includes 16 buck converters, a digital multi-phase modulator and a digital controller implemented on an FPGA. Direct digital design of the compensator is based on a multi-level converter model. A preorder arrangement of phases is used to minimize the output ripple. A zero-error-bin approach addresses the effects of phase-mismatches and sub-harmonic ripples on the stability of the wide-bandwidth controller. Simulation and experimental results show that very wide bandwidth operation and very fast transient responses are feasible even in the presence of significant phase mismatches

Design and Implementation of a Wide-bandwidth Digitally Controlled 16-phase Converter

This paper presents a cell-level simulation model of photovoltaic (PV) systems that is capable of reproducing partial-shading and other mismatch effects at high granularity. The nonlinear diode voltage-current characteristic is stored in a piecewise-linear model, and the stored values are employed to compute the Jacobian matrices very efficiently. As a result, the model can be solved with low computational effort, so that simulations at cell-level granularity and over long time spans can be carried out efficiently. The model is well suited for evaluations of energy capture, including the effects of partial shading or other mismatches, in large PV systems over long periods of time. Comparisons of simulation and experimental results are provided for three representative PV systems.

Dragan Maksimovic

Papers

Detection of instability and adaptive compensation of digitally controlled switched-mode power supplies

Digital Pulse-Width-Modulator with Discretely Adjustable Delay Line

Decentralized Carrier Interleaving in Cascaded Multilevel DC-AC Converters

Design and Implementation of a Wide-bandwidth Digitally Controlled 16-phase Converter

A cell-level photovoltaic model for high-granularity simulations