Sjoerd W. H. de Haan

Electrochemical reactions and electrode corrosion in pulsed electric field (PEF) treatment chambers

Abstract In Pulsed Electric Field systems for preservation of liquid food, electrochemical reactions can occur in the treatment chamber. This may result in partial electrolysis of the solution, in corrosion of the electrode and in introduction of small particles of electrode material in the liquid. This contribution will describe the phenomena that occur at the electrodes. The ultimate objective is to be able to adapt the design and the pulse waveform such that these phenomena are minimised. After revisiting the basic theory on electrochemical reactions, an equivalent circuit is presented that can be used to model an electrochemical cell. Based on these models it is shown that electrode corrosion can be limited with short enough pulses. The theory has been verified by experiments. The results of these experiments are presented in this contribution.

Basic Operation Principles and Electrical Conversion Systems of Wind Turbines

Abstract This paper gives an overview of electrical conversion systems for wind turbines. First, the basics of wind energy conversion with wind turbines are reviewed and requirements with respect to the electric system are considered. Next, the three classical conversion systems are described with their strengths and weaknesses: constant speed, variable speed with doubly-fed induction generator and variable speed with direct-drive generator. The applied power electronic converters are shortly addressed. Finally alternative generator systems and trends are discussed. There is a clear trend towards variable speed systems. Doubly-fed induction generator systems are increasingly equipped with grid fault ride through capabilities. For direct-drive turbines, the radial flux permanent-magnet synchronous generator is cheaper and more efficient than the electrically excited synchronous generator. It is expected that the voltage level of generators will increase up to values in the order of 5 kV.

A FACTS Device: Distributed Power-Flow Controller (DPFC)

This paper presents a new component within the flexible ac-transmission system (FACTS) family, called distributed power-flow controller (DPFC). The DPFC is derived from the unified power-flow controller (UPFC). The DPFC can be considered as a UPFC with an eliminated common dc link. The active power exchange between the shunt and series converters, which is through the common dc link in the UPFC, is now through the transmission lines at the third-harmonic frequency. The DPFC employs the distributed FACTS (D-FACTS) concept, which is to use multiple small-size single-phase converters instead of the one large-size three-phase series converter in the UPFC. The large number of series converters provides redundancy, thereby increasing the system reliability. As the D-FACTS converters are single-phase and floating with respect to the ground, there is no high-voltage isolation required between the phases. Accordingly, the cost of the DPFC system is lower than the UPFC. The DPFC has the same control capability as the UPFC, which comprises the adjustment of the line impedance, the transmission angle, and the bus voltage. The principle and analysis of the DPFC are presented in this paper and the corresponding experimental results that are carried out on a scaled prototype are also shown.

Real time simulation of a power system with VSG hardware in the loop

The method to investigate the interaction between a Virtual Synchronous Generator (VSG) and a power system is presented here. A VSG is a power-electronics based device that emulates the rotational inertia of synchronous generators. The development of such a device started in a pure simulation environment and extends to the practical realization of a VSG. Investigating the interaction between a VSG and a power system is a problem, as a power system cannot be manipulated without disturbing customers. By replacing the power system with a real time simulated one, this problem can be solved. The VSG then interacts with the simulated power system through a power interface. The advantages of such a laboratory test-setup are numerous and should prove beneficial to the further development of the VSG concept.

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.

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].

Analysis of the Effect of Source Voltage Fluctuations on the Power Factor in Three-Phase Controlled Rectifiers

The effect of source voltage fluctuations on the harmonics and the power factor is analyzed for a six-pulse line-commutated converter. Exact expressions are derived for currents in the filter network and the ac supply lines as a function of the size of a series inductor in the LC type low-pass filter connected to a resistive load. The harmonics are calculated according to a method which is unorthodox in power engineering and which is based on the convolution theorem. Switching functions required for the discontinuous conduction mode are derived from time-domain analysis. The method is applicable to a wide class of switching networks.

A New Integral Pulse Module for the Series-Resonant Converter

A method to apply the principle of integral pulse modulation to the series-resonant converter is proposed, analyzed, and tested. The proposed control module facilitates combining the favorable properties of the series-resonant power converter (reliability, low weight, high efficiency) with those of the pulse integral control system (accuracy, fast response).

Conductive Carbon Loaded Polymer Film Electrodes for Pulsed-Power Applications. Part I: Determination of the Film Properties

Abstract Electrically conductive polymer composites consisting of a nonconductive polymer matrix and conductive fillers, such as carbon black, are widely used. This contribution describes the specific electrical properties of polymer composite films for pulsed conditions in the microsecond (10−6 s) range. Investigation of an industrially available volume conductive polymer film (Carbostat) showed that the electrical properties of this material, which can be considered for electrodes in pulsed power applications, are quite different from the properties for DC conditions.

Winding Losses in High-Current, High-Frequency Transformer Foil Windings with Leakage Layer

High-frequency, high-power transformers are becoming of increasing importance. Such transformers often use foil windings because of their superior thermal properties. Transformers in resonant converters require a specific leakage inductance. The specific leakage inductance value can be obtained by implementation of so called leakage layer. The leakage layer might not influence only the leakage inductance value but also the losses in winding foils. The influence of the leakage layer geometry on the winding losses is discussed in this paper. FEM simulations are used to analyse the influence of several leakage layer configurations and the results are compared with the performance of transformer prototypes. The investigation showed that the leakage layer spanning the whole width of the winding window gives the best results with a relatively simple shape of the layer.