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

/pdf/overview-of-control-and-grid-synchronization-for-distributed-2nx31ovpe9.pdf

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

/pdf/power-electronic-systems-for-the-grid-integration-of-4s5cxjhatl.pdf

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.

/pdf/a-review-of-single-phase-improved-power-quality-ac-dc-2pm6h4zjxq.pdf

A review of single-phase improved power quality AC-DC converters

The paper describes a DC-DC power converter for use with low voltage microprocessor loads. The control method is a hysteretic current-mode control in the continuous conduction mode which has fast transient response. At light loads, the power converter operates in the discontinuous conduction mode using a peak current control method which causes the switching frequency to be proportional to load current, thus maintaining high efficiency in a very wide range of loads. The control method implementation, transient response and output inductor design equations, and equations for designing an input filter to reduce input current di/dt are provided. An inductor current estimator which provides higher efficiency, good transient response, and current limiting, is presented. Experimental results for a 5.0 V input, 3.1 V output, 13 A DC-DC converter are included to verify the theoretical information.

DC-DC converter with fast transient response and high efficiency for low-voltage microprocessor loads

Zero-voltage-switching, quasi-square-wave (ZVS-QSW) power converters with controllable rectifiers feature constant-frequency, PWM-like operation with low voltage and relatively low current stresses on active devices. New closed-form analytic results are derived and applied to construct a detailed design procedure for the ZVS-QSW switch. Starting with usual design constraints, resonant elements are selected so that zero-voltage switching is achieved under all operating conditions, with favorable tradeoff between switching and conduction losses. Results are derived in a form applicable to a wide variety of ZVS-QSW power converter topologies. The design procedure is illustrated on a flyback power converter example and is supported by simulation results. >

Design of the zero-voltage-switching quasi-square-wave resonant switch

This paper introduces a single-phase digital power-factor correction (PFC) control approach that requires no input voltage sensing or explicit current-loop compensation, yet results in low-harmonic operation over a universal input voltage range and loads ranging from high-power operation in continuous conduction mode down to the near-zero load. The controller is based on low-resolution A/D converters and digital pulsewidth modulator, requires no microcontroller or DSP programming, and is well suited for a simple, low-cost integrated-circuit realization, or as a hardware description language core suitable for integration with other power control and power management functions. Experimental verification results are shown for a 300-W boost PFC rectifier.

A Simple Digital Power-Factor Correction Rectifier Controller

The paper describes a closed-loop controller for adaptive voltage scaling (AVS) where the supply voltage to a standard-cell ASIC is dynamically adjusted to the minimum value required for the desired system speed. The controller includes a clock generator that provides a low-jitter clock to the ASIC at all steady-state operating points and through transients. To speed up the voltage transient response to step changes in clock frequency, the controller is based on a multiple-tap resettable delay line. A chip including the AVS controller and a dual 16-bit MAC application has been fabricated in a standard 0.5 /spl mu/ CMOS process. The area taken by the AVS controller is 0.12 mm/sup 2/. Experimental results demonstrate operation over the application clock frequency range from 80 kHz to 20 MHz, and a 38 /spl mu/s transient response for a step change in speed from standby to maximum throughput operation.

/pdf/closed-loop-adaptive-voltage-scaling-controller-for-standard-twckwu4r8o.pdf

Closed-loop adaptive voltage scaling controller for standard-cell ASICs

Recent work has shown the feasibility of integrating nonparametric frequency-domain system identification functionality into digital controllers for switched-mode pulse-width modulated (PWM) dc-dc power converters. The resulting discrete-time frequency response can be used for design, diagnostic, or self-tuning purposes. The success of these applications depends on the fidelity of the identified frequency responses and the degree to which the process is automated, as well as the costs, in terms of gate count, time duration of identification, and effect on output voltage, incurred to obtain these benefits. This paper demonstrates the feasibility of incorporating fully automated frequency response measurement capabilities in digital PWM controllers at relatively low additional cost. In particular, it is shown that relatively accurate and smooth frequency response data can be obtained using a Verilog-coded implementation with low tens of thousands of logic gates and about 10 kB of memory. The identification process can be accomplished in several hundred milliseconds and the output voltage can be kept within specified bounds during the entire process. Experimental results are provided for four different PWM dc-dc converters, including a synchronous buck with two different filter capacitors, a boost operating in continuous conduction mode (CCM), and a boost operating in discontinuous conduction mode (DCM).

Dragan Maksimovic

Papers

DC-DC converter with fast transient response and high efficiency for low-voltage microprocessor loads

Design of the zero-voltage-switching quasi-square-wave resonant switch

A Simple Digital Power-Factor Correction Rectifier Controller

Closed-loop adaptive voltage scaling controller for standard-cell ASICs

Integration of Frequency Response Measurement Capabilities in Digital Controllers for DC–DC Converters