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

Multilevel converters have been under research and development for more than three decades and have found successful industrial application. However, this is still a technology under development, and many new contributions and new commercial topologies have been reported in the last few years. The aim of this paper is to group and review these recent contributions, in order to establish the current state of the art and trends of the technology, to provide readers with a comprehensive and insightful review of where multilevel converter technology stands and is heading. This paper first presents a brief overview of well-established multilevel converters strongly oriented to their current state in industrial applications to then center the discussion on the new converters that have made their way into the industry. In addition, new promising topologies are discussed. Recent advances made in modulation and control of multilevel converters are also addressed. A great part of this paper is devoted to show nontraditional applications powered by multilevel converters and how multilevel converters are becoming an enabling technology in many industrial sectors. Finally, some future trends and challenges in the further development of this technology are discussed to motivate future contributions that address open problems and explore new possibilities.

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Recent Advances and Industrial Applications of Multilevel Converters

This paper presents a new multilevel converter topology suitable for very high voltage applications, especially network interties in power generation and transmission. The fundamental concept and the applied control scheme is introduced. Simulation results of a 36 MW-network intertie illustrate the efficient operating characteristics. A suitable structure of the converter-control is proposed.

An innovative modular multilevel converter topology suitable for a wide power range

Overview of current development in electrical energy storage technologies and the application potential in power system operation

Active filtering of electric power has now become a mature technology for harmonic and reactive power compensation in two-wire (single phase), three-wire (three phase without neutral), and four-wire (three phase with neutral) AC power networks with nonlinear loads. This paper presents a comprehensive review of active filter (AF) configurations, control strategies, selection of components, other related economic and technical considerations, and their selection for specific applications. It is aimed at providing a broad perspective on the status of AF technology to researchers and application engineers dealing with power quality issues. A list of more than 200 research publications on the subject is also appended for a quick reference.

A review of active filters for power quality improvement

Pulse width modulated (PWM) rectifiers allow the elimination of low order harmonics. Filtering requirements for PWM current-source rectifiers are usually satisfied through the use of low-pass LC input filters. The design of LC filters involves the positioning of the resonant frequency to meet the harmonic attenuation requirements (THD), and the introduction of damping at the resonant frequency to avoid amplification of residual harmonics. The systematic approach proposed is focused on PWM rectifiers but can be extended to other classes of converters. Practical design considerations are detailed and design equations are derived. Simulated results are presented to validate the design approach. >

http://faculty.mu.edu.sa/public/uploads/1338674793.8365lc_filter%20design_complete.pdf

Input filter design for PWM current-source rectifiers

Force-commutated multiconverter systems have been proposed and recently implemented for high power applications, particularly high-voltage direct current (HVDC) transmission and flexible ac transmission systems (FACTS) devices, including STAtic var COMpensators (STATCOM). This paper demonstrates that pulse-width modulation (PWM) based on space vector modulation (SVM), and using low switching frequencies (a few hundred Hertz) can be implemented in multimodule power converter systems. The proposed scheme is based on a delayed sampling technique and allows output voltage control and minimization of harmonic components. Pattern generation options are analyzed and system waveforms are presented for different switching frequencies and number of modules. Results are validated by simulation and confirmed by experiments on a 5-kVA prototype unit.

Low switching frequency space vector modulators for high power multimodule converters

Wind energy is fluctuating. However, in wind turbine generators (WTGs), by allowing a certain amount of variations of the voltage on the bus, a dc bus capacitor is able to offer a power shaping ability, and can function as an energy storage system (ESS). This paper proposes a power fluctuation filtering algorithm, applied to the ESS to selectively and adequately attenuate the medium frequency wind power fluctuations. A medium-sized ESS produces a fairly smooth wind power output and ensures the WTG stability under severe wind fluctuations. The proposed algorithm is applied to a 2 MW permanent magnet synchronous machine (PMSM) WTG, simulated in an electromagnetic transients program. The fluctuations of both pre- and post-filtered wind powers are presented, and quantified in the different frequency regions. Simulation results confirm the effectiveness and robustness of the control algorithm.

Attenuation of Wind Power Fluctuations in Wind Turbine Generators using a DC Bus Capacitor Based Filtering Control Scheme

Solid State Transformer (SST) is a new type of power transformer based on power electronic converters and high frequency transformers. The SST realizes voltage transformation, galvanic isolation, and power quality improvements in a single device. In the literature, a number of topologies have been introduced for the SST. In this work, employing a modular multilevel converter, a new SST topology is introduced which provides not only high-voltage AC (HVAC), low-voltage AC (LVAC) and low-voltage DC (LVDC) ports, but also high-voltage DC (HVDC) port. Besides, the proposed topology is easily scalable to higher voltage levels.

A topology for three-stage Solid State Transformer

Integration of an energy storage system (ESS) improves wind energy system performance. Due to its simplicity and robustness, the bidirectional IGBT buck/boost converter is often selected to interface the supercapacitor or battery ESS with the DC voltage bus. For conventional single-unit topologies, the converter has discontinuous current on the high voltage side and other limitations. This paper proposes a parallel structure of bidirectional buck/boost converters and its power-tracking control scheme for wind ESS applications. The converter performance is studied and compared to the single-unit topologies. The proposed converter has smooth currents and fast dynamics which allow reduction of converter switching frequency and DC filtering capacitor. Other advantages of this topology include reduction of switching losses, improved reliability and flexibility.

Geza Joos

Papers

Input filter design for PWM current-source rectifiers

Low switching frequency space vector modulators for high power multimodule converters

Attenuation of Wind Power Fluctuations in Wind Turbine Generators using a DC Bus Capacitor Based Filtering Control Scheme

A topology for three-stage Solid State Transformer

A Parallel Bidirectional DC/DC Converter Topology for Energy Storage Systems in Wind Applications