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

Modular battery packs are desirable energy storage elements in applications such as DC microgrids and electric vehicles (EVs). Modular battery packs utilize DC/DC converters that are connected in series for high output voltage or connected in parallel for high output currents. An active battery management system (BMS) utilizes the cell state of charge (SOC) to control the cell current. The individual control to input current transfer functions vary with the number of converters in parallel. This paper presents a small-signal model for the parallel converters as a multi-input, multi-output (MIMO) system that shows the interactions among the input current transfer functions. The small-signal model is utilized to design the feedback loop. The paper uses hybrid feedforward control to reduce the interactions between the coupled input-current regulation loops; which simplifies the implementation, increases modularity, and eliminates the need for a central controller. that is generally employed in MIMO systems. The analysis is verified by simulations and by experiments. A 300 W module consisting of three parallel output 100 W boost converters for a cell active balancing management system is used for hardware validation.

Control of Independent-Input, Parallel-Output DC/DC Converters for Modular Battery Building Blocks

A field study of human factors and vehicle performance associated with PHEV adaptation

This paper describes the design of a 6.78 MHz self-oscillating parallel resonant power converter for wireless power transfer applications. By sensing just the polarity of the tank inductor current to generate the switch control signals, the system is able to auto-start and self-oscillate at the desired frequency only by applying power to the input port. Different current sensing techniques, including a current sensing transformer and a series resistor followed by a high-speed differential amplifier, are compared based on bandwidth limitations and noise rejection considerations. Furthermore, delay-compensation networks are included in order to mitigate effects of the propagation delays added by signal processing components in the feedback path. It is shown that the circuit is capable of meeting the A4WP/AirFuel standard specifications for wireless power charging. Both inverter and inverter+rectifier configurations are tested and their performances are verified by simulations and experiments on a 16 W prototype using GaN power devices, showing an efficiency of 98 % and 83 %, respectively.

6.78 MHz self-oscillating parallel resonant converter based on GaN technology

This article presents a new state-of-charge (SOC) balancing method with parallel and series output connected battery power modules (BPMs) in an active battery management system (BMS.) To increase both the battery pack and system-level modularity, the BMS controls the average SOC of the entire battery pack by regulating the input currents of all BPMs to a common reference. A balancing loop introduces input current offsets to regulate all cells SOCs. The BMS functions are distributed between a central controller for battery pack SOC regulation, and a module controller that regulates the input current of the individual BPMs. Experimental results are presented on a 1.5 kWh 1C-rate prototype with five series output connected battery bricks. Each battery brick consists of three parallel output connected BPMs, which employ three battery cells and three 100 W dc/dc converters.

State-of-Charge Balancing With Parallel and Series Output Connected Battery Power Modules

This paper describes a closed-loop regulated dual half-bridge series resonant de-de converter operated at up to 100 MHz switching frequency using GaN half-bridge stages with integrated gate drivers. A digital online efficiency optimization technique together with burst-mode control are developed and applied, to achieve output voltage regulation and efficiency improvements. An experimental prototype is designed and constructed to convert an input de voltage of 20 V to a 12 V output at 100 MHz switching frequency and up to 1.75 W of output power, with up to 82 % efficiency.

Dragan Maksimovic

Papers

Control of Independent-Input, Parallel-Output DC/DC Converters for Modular Battery Building Blocks

A field study of human factors and vehicle performance associated with PHEV adaptation

6.78 MHz self-oscillating parallel resonant converter based on GaN technology

State-of-Charge Balancing With Parallel and Series Output Connected Battery Power Modules

Voltage regulation and efficiency optimization in a 100 MHz series resonant DC-DC converter