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 introduces a fully synthesizable hybrid digital pulse width modulator (DPWM). The DPWM includes a digital delay locked loop around a delay-line with discretely programmable delay cells to achieve constant-frequency clocked operation with the best possible resolution over a range of process or temperature variations. The DPWM module can implement trailing-edge, leading-edge or triangular modulation. It includes two outputs with programmable dead-times, suitable for DC-DC converters with synchronous rectifiers. The DPWM module is well suited for FPGA or custom chip implementation. Experimental results are shown for a 780 KHz, 10-bit FPGA realization

Hybrid DPWM with Digital Delay-Locked Loop

In this paper, second-order sliding-mode (SOSM) control approach is applied to synchronous buck dc–dc converters. The proposed SOSM controller can stabilize synchronous buck dc–dc converters using a simple digital state-machine structure, without requiring current sensing or an integral term in the control loop. The SOSM controller results in fast step-load and start-up transient responses, and is robust against parameter uncertainties. Fast transients and current limitation during start up can be accomplished by adjusting one controller parameter. Furthermore, a hysteresis method is introduced to control the switching frequency. The proposed approach is verified by experimental results on a 1.25-V 10-A prototype.

Second-Order Sliding-Mode Controlled Synchronous Buck DC–DC Converter

General properties that interrelate network complexity, attainable conversion ratios, and switch stresses are derived for pulse-width-modulated (PWM) DC-to-DC converters. The emerging synthesis procedure guarantees that complete classes of converters that satisfy a set of prescribed specifications are generated. The input specifications include the desired DC conversion ratio, nonpulsating terminal currents, possible coupling of inductors, the allowed number of switches, and, in particular, the number of active transistor switches. As a result, a number of novel PWM topologies are uncovered. >

General properties and synthesis of PWM DC-to-DC converters

Historically, electric power system operators have seen photovoltaic (PV) power systems as potential sources of problems due to intermittency and lack of controllability. However, the flexibility of power electronic inverters allows PV to provide grid-friendly features including volt-VAR control, ramp-rate control, high-frequency power curtailment, and event ride-through. These technologies offer power quality improvements and enable wider penetrations of PV systems. Commercially available smart PV inverters can further provide frequency down-regulation by curtailing power, but they are unable to provide true frequency regulation through active power control (APC) because they are unable to increase power on command. The development of inverters capable of APC for primary and secondary frequency regulation without the need for energy storage has the potential to transform the way grid operators view high PV penetration levels. This paper provides a brief tutorial on APC of PV inverters, summarizes state of the art research in the area, and suggests future research directions.

Active power control of photovoltaic power systems

A power supply for providing a single level dc output voltage, with input power factor correction, from a wide range of ac input voltages commonly available worldwide. The power supply rectifier circuit can be configured as a full wave bridge for high line voltage inputs and as a voltage doubler for low voltage inputs. Output voltage regulation and power factor correction are accomplished by a high frequency boost circuit having two inductors connected in parallel for the low input voltage configuration and in series for the high input voltage configuration. The high frequency switching semiconductor components are connected in a series circuit which limits their voltage requirement to one-half the output voltage.

Dragan Maksimovic

Papers

Hybrid DPWM with Digital Delay-Locked Loop

Second-Order Sliding-Mode Controlled Synchronous Buck DC–DC Converter

General properties and synthesis of PWM DC-to-DC converters

Active power control of photovoltaic power systems

High power factor boost rectifier apparatus