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 presents transformerless stacked active bridge (TSAB) converters derived from N-to-1 ladder switched capacitor (SC) converters by addition of small ac inductors. The ladder-TSAB (L-TSAB) converters feature soft charging of all flying capacitors and zero-voltage switching of all switches. The use of small ac inductors and low voltage devices is enabled by low volt-seconds applied to inductors and low device voltage stresses equal to 1/N of the supply voltage. Output regulation and flying capacitor voltage balancing can be achieved through phase-shift control. Experimental results are presented for a 3-to-1 L-TSAB prototype in two application scenarios: 12-to-4 V, 10 A, and 36-to-12 V, 15 A. In the 12-to-4 V prototype, the peak measured efficiency is 98.7%, while the full load efficiency is 92.4%. In the 36-to-12 V case, the peak efficiency is 98.7% and the full-load efficiency is 96.3%.

Ladder Transformerless Stacked Active Bridge Converters

This paper presents a resonant dc-dc converter capable of providing load-independent output current without the need for active current control. This converter comprises an LC3L resonant tank, with inductance and capacitance values selected based on a new design methodology that achieves two objectives: 1) the converter’s output current is independent of its output voltage, and 2) the resonant tank losses are minimized. The design methodology is based on minimizing inductive energy storage to improve the power conversion efficiency. This design methodology makes the converter suitable for applications that require constant current over a wide range of output voltages, such as USB-C power delivery (PD) based battery charging. An efficiency-optimized current-source LC3L converter prototype operating from 20-V input and delivering 6 A current with USB-C PD output voltages in the range from 5 V to 15 V is designed, built and tested. The prototype achieves a peak efficiency of 92%, maintains >87% efficiency over the entire output voltage range, and is also shown to have >10% lower losses compared to a conventionally designed prototype. A loss breakdown demonstrates how reduced inductive energy storage results in lower system losses.

Efficiency-Optimized Current-Source Resonant Converter for USB-C Power Delivery

This paper presents a practical injection-based method for continuous monitoring of the crossover frequency and phase margin in digitally controlled switched-mode power supplies (SMPS). The proposed approach is based on Middlebrook's loop-gain measurement technique, adapted to digital controller implementation. A digital square-wave signal is injected in the loop, and the injection signal frequency is adjusted while monitoring loop signals to obtain the system crossover frequency and phase margin online, i.e., during normal SMPS operation. The approach does not require open loop or steady-state SMPS operation and is capable of convergence in the presence of load transients or other disturbances. Experimental results are presented for various power stage configurations demonstrating close matches between monitored and expected crossover frequencies and phase margins.

An online phase margin monitor for digitally controlled switched-mode power supplies

This paper describes a very simple Digital Pulse Width Modulator (DPWM), with under 100 picoseconds resolution capability in low-cost field-programmable gate arrays (FPGA). The DPWM implementation is based on internal carry chains and internal logic resources which are present in most FPGA families. The proposed approach does not require manual routing or placement, consumes few hardware resources, and does not rely on specialized phase locked loop or clock management resources. The DPWM is capable of supporting high switching frequencies for digitally controlled switched-mode power converters. A 50 MHz switching frequency DPWM with 60 picoseconds resolution and a 1 MHz switching frequency DPWM with 90 picoseconds resolution are experimentally demonstrated, with monotonicity and excellent linearity.

Simple Digital Pulse Width Modulator with 60 picoseconds resolution using a low-cost FPGA

This paper presents a modular control architecture for a composite dc-dc converter topology. A composite converter comprises multiple dissimilar partial-power converter modules arranged and operated to minimize stresses and improve system efficiency over a wide range of operating points. This requires transitioning to different operating modes for different operating conditions. A control strategy is required to determine the optimal mode, and to achieve smooth mode transitions and fast closed-loop system dynamic responses. A modular control architecture capable of meeting these objectives is described. In this architecture, low-level module controls are decoupled from system-level operations. The resulting hierarchical control strategy is relatively simple, and highly scalable in nature. The approach is developed and validated on a controller hardware-inthe-loop (CHIL) platform. A frequency scaling strategy is applied to allow validations of high-switching frequency converters on bandwidth-limited CHIL platforms.

Dragan Maksimovic

Papers

Ladder Transformerless Stacked Active Bridge Converters

Efficiency-Optimized Current-Source Resonant Converter for USB-C Power Delivery

An online phase margin monitor for digitally controlled switched-mode power supplies

Simple Digital Pulse Width Modulator with 60 picoseconds resolution using a low-cost FPGA

Controller Hardware-in-the-Loop Validation of a Modular Control Architecture for a Composite DC-DC Converter