Braham Ferreira

A Novel Distributed Direct-Voltage Control Strategy for Grid Integration of Offshore Wind Energy Systems Through MTDC Network

Although HVDC transmission systems have been available since mid-1950s, almost all installations worldwide are point-to-point systems. In the past, the lower reliability and higher costs of power electronic converters, together with complex controls and need for fast telecommunication links, may have prevented the construction of multiterminal DC (MTDC) networks. The introduction of voltage-source converters for transmission purposes has renewed the interest in the development of supergrids for integration of remote renewable sources, such as offshore wind. The main focus of the present work is on the control and operation of MTDC networks for integration of offshore wind energy systems. After a brief introduction, this paper proposes a classification of MTDC networks. The most utilized control structures for VSC-HVDC are presented, since it is currently recognized as the best candidate for the development of supergrids, followed by a discussion of the merits and shortcomings of available DC voltage control methods. Subsequently, a novel control strategy-with distributed slack nodes-is proposed by means of a DC optimal power flow. The distributed voltage control (DVC) strategy is numerically illustrated by loss minimization in an MTDC network. Finally, dynamic simulations are performed to demonstrate the benefits of the DVC strategy.

DPFC control during shunt converter failure

Distributed Power Flow Controller (DPFC) is a new device within the family of FACTS. The DPFC has the same control capability as the UPFC, however at much lower cost and with a higher reliability. The reliability of the DPFC is given by the redundancy of multiple series converters. The shunt converter is the bottleneck for remaining reliability, because there is only one shunt converter in a DPFC system. During the shunt converter failure, the DPFC continues to work as controlled impedance, and only control the active power flow through the line. This paper presents a control of the DPFC, which keeps the DPFC system stable during the shunt converter failure. Adapted control schemes are employed to every series converters, which can automatically switch the series converter between the full-control mode and limited-control mode.With the adapted control, the reliability of the whole DFPC system is further improved. The adapted control scheme is verified both by simulation and experiment.

A New FACTS component — Distributed Power Flow Controller (DPFC)

This paper presents a new concept for power flow control by distributed UPFC. The system, called distributed power flow controller (DPFC), consists of several low-power series converters and one shunt large-power converter without common dc link. Also new is that the power exchange between the shunt and series parts is through the existing transmission line at a harmonic frequency. This solution enables the DPFC to fully control all power system parameters, and it reduces the cost and increases the reliability of device at the same time.

Utilizing Distributed Power Flow Controller (DPFC) for power oscillation damping

Because of the power industry moving toward marketoriented, the power tends to be transmitted over longer distances. However, the capability of long, inter-regional power transmission is usually limited, and one of the limitations is caused by low-frequency power oscillations. One of the critical oscillation, known as Inter-area oscillation, is observed when a group of generates in one region swings against group in another region [1]. The traditional solution is to use power system stabilizers (PSSs) on generator excitation control systems [2]. However, PSSs are usually designed for local oscillation damping, and in large multi-area power systems it might be difficult to tune all the PSSs parameters. FACTS devices can be employed for inter-area power oscillation damping (POD), and they are proved to be effective [3], [4], [5].

Thermally enhanced SMT power components

The paper introduces new x-dimension (x-dim) components that allow for high components packaging density and automated manufacturing of power converters. The x-dim components are double sided SMT passives, having uniform height (x) and enhanced thermal properties. With stacked converter construction and the x-dim components soldered to two sides, the heat removal from the systems can be significantly improved. This publication presents various methods to manufacture thermally enhanced x-dim components. The thermal behaviour of x-dim components is improved by integrating heat extractors, removing packaging materials and filling the air gaps by potting compounds. In the stacked construction, thermal enhancement of one component improves heat removal from other components, placed in adjacent stack layers. Thermal performance of x-dim components in both standard and stacked converter constructions is evaluated by FEM and analytical simulations. New x-dim components employed in stacked construction play a key role in overcoming current power density limits.

Thermal modeling of the module integrated DC-DC converter for thin-film PV modules

This paper presents an investigation into the thermal behavior of a DC-DC converter integrated on the back side of a thin-film photovoltaic (PV) module. Analytical thermal models of the converter and the PV module are made and the results obtained from the models are compared to the results obtained by computational fluid dynamics (CFD) simulations.

Design of a flexible very low profile high step-up PV module integrated converter

Recently, improved PV system architectures were proposed with more granular power processing by means of distributed maximum power point tracking (DMPPT). This is achieved by connecting an MPPT unit to each PV module in the PV array. This paper presents a step further in the distributed power tracking approach, with the optimized, very low profile, high step-up, high frequency power converter suitable for integration into a low cost flexible PV module. Additional problems arise in this approach, specifically in the magnetic design and thermal management, due to the tight thermal coupling and specific mechanical requirements for a flexible converter design. Overcoming these limitations presents a challenge, but can lead to a cost effective, reliable solution for PV systems with improved integration level and power density.

New system integration concept for high power density drives

Current construction technology and design methods of power converters have reached power density limits that can only be surpassed by changing the way we design and build converters. This paper presents a system integration approach that allows for achieving high power densities. The key issues of the approach, namely hybrid integration in the form of integrated power electronics modules (IPEMs) and integrated thermal and spatial design with optimized air flow are presented in the paper. The spatial and thermal concept of a case study 2.2 kW converter for ac drives is presented and the technologies for implementing the IPEMs are listed. The complete system and the experimental results thereof are presented. The converter has a power density of 3.8 kW/1, which is almost four times larger than that of commercially available drives. The approach is not restricted to this application and can be applied to any converter in the medium power range.

Hierarchical EMC analysis approach for power electronics applications

In this paper, a novel method for EMI (electromagnetic interference) level prediction is proposed. The method is based on the hierarchical structure of the generation of EMI. That is, the determination of EMI level can be divided into three levels, namely the functional level, the transient level and propagation level. The lower level provides parameter values for the higher level. That makes the analysis to be a single direction chain. In functional level, the working points are obtained. Through transient level analysis, the exact noise sources are determined. In propagation level, the high frequency characteristics in the propagation path are expressed including the variation of parasitic parameters. Frequency analysis can be used to get the EMI level measured in the receiver side rapidly. Because this approach is a straight forward method, the impact of any components can be evaluated immediately instead of doing the simulation from begin to end.

Thermal and spatial design of a high power density drive

Industrial drives, like many other power electronics applications are experiencing an ever increasing demand for high power densities. Only through a system integration approach which involves an integrated thermal and spatial design and using integration technologies can this goal be achieved. Hybrid integration in the form of integrated power electronics modules (IPEMs) is one of the key elements of this approach. Advanced thermal management with optimised air flow and a special heat sink structure is the other key element. In this paper a thermal management concept for high power density drives is investigated and a novel method, i.e. the integrated I-Housing, is utilized to implement the heat removal system. The complex thermal management structure consisting of an impingement cooled pin fin heatsink and heat exhaust paths, which significantly reduce the amount of air required for cooling, are modelled. The model presented in this paper is experimentally verified with a thermal dummy. The model is ultimately to be used to design the thermal management for a fully functional 2.2 kW inverter with a total volume of 500 cm3 - four times smaller than the current state of the art.