Jozef Ghijselen

The apparent power concept and the IEEE standard 1459-2000

This paper rigorously considers the concept of apparent power in unbalanced three-phase situations. The analysis shows that there are various related but different concepts that can be associated with the apparent power. In particular two approaches are covered, the one relating to the literature on the single-phase sinusoidal case, the other relating to the recent IEEE Standard 1459-2000. The underlying ideas for each concept are given; the relationship and the differences between them are thoroughly discussed.

Autonomous renewable energy conversion system

This paper briefly reviews the need for renewable power generation and describes a medium-power Autonomous Renewable Energy Conversion System (ARECS), integrating conversion of wind and solar energy sources. The objectives of the paper are to extract maximum power from the proposed wind energy conversion scheme and to transfer this power and the power derived by the photovoltaic system in a high efficiency way to a local isolated load. The wind energy conversion operates at variable shaft speed yielding an improved annual energy production over constant speed systems. An induction generator (IG) has been used because of its reduced cost, robustness, absence of separate DC source for excitation, easier dismounting and maintenance. The maximum energy transfer of the wind energy is assured by a simple and reliable control strategy adjusting the stator frequency of the IG so that the power drawn is equal to the peak power production of the wind turbine at any wind speed. The presented control strategy also provides an optimal efficiency operation of the IG by applying a quadratic dependence between the IG terminal voltage and frequency V∼f2. For improving the total system efficiency, high efficiency converters have been designed and implemented. The modular principle of the proposed DC/DC conversion provides the possibility for modifying the system structure depending on different conditions. The configuration of the presented ARECS and the implementation of the proposed control algorithm for optimal power transfer are fully discussed. The stability and dynamic performance as well as the different operation modes of the proposed control and the operation of the converters are illustrated and verified on an experimental prototype.

Exact voltage unbalance assessment without phase measurements

In this letter, it is shown that the positive- and negative-sequence components of a three-phase, sinusoidal and unbalanced voltage system can be calculated exactly without the application of the Fortescue transformations in the complex plane, while only the root mean square (RMS) line-to-line voltages are required, and without having to measure the phase relationships between these voltages. This results in a convenient procedure to assess voltage unbalance in the field. The phase relationships between the sequence and line components can also be calculated. Moreover, if the RMS values of the line-to-neutral voltages are known, the zero-sequence component can be calculated exactly as well, again, without the application of complex mathematics.

Harmonic mitigation potential of shunt harmonic impedances

Abstract Although complete compensation is only possible using true active filters, shunt harmonic impedances (SHI) have been shown to provide a considerable reduction of the harmonic propagation. In this paper, the mitigation potential of different SHI is investigated, together with their VA-rating. It is shown that a resistive impedance of 1 pu for all harmonics is very effective, especially in the case of power system resonances. To take into account the interaction between harmonics, simulations are performed in the presence of a realistic non-linear load, instead of the common harmonic current source modelling approach.

A Boost PFC Converter With Programmable Harmonic Resistance

Power factor correction converters with low harmonic input resistance are desirable loads to support the reduction of the harmonic distortion on the feeding grid. Therefore, a novel control strategy is proposed. Whereas previously proposed controllers tried to obtain a resistive behavior of the converter with a constant input impedance for all frequencies, including the fundamental, the proposed control strategy allows to set a harmonic input resistance independent of the fundamental input impedance. Consequently, the harmonic input resistance remains low, even when the input power of the converter is decreased. This paper describes the operation of a digitally controlled boost PFC converter with the new control algorithm. Experimental tests on a 1 kW prototype show that a practical realization of the algorithm is possible and that a programmable harmonic input resistance of the converter is obtained

Addendum to the apparent power concept and the IEEE standard 1459-2000

Being involved in the work that led to the IEEE Std. 1459 one of the authors (A. E. Emanuel) feels responsible for the technical and theoretical integrity of the standard. The authors want to make sure that readers do conclude that there is a major flaw in the concept of effective voltage V/sub cB/, that was recommended in IEEE Std. 1459.

Reduction of the voltage distortion with a converter employed as shunt harmonic impedance

The amount of non-linear and unbalanced loads (such as adjustable speed drives and PCs) connected to the electric power system is steadily growing. The power quality i.e. the reliability of the energy supply and the quality of the voltage waveform, may be severely degraded and may cause many unfavourable effects on both the power system and the connected loads. Especially in the case of resonances, severe voltage distortion may result. Although complete compensation is only possible using true active filters, resistive shunt harmonic impedances (SHI) have been shown to provide a considerable reduction of the harmonic propagation. These impedances can be implemented using active power electronic devices and are controlled to synthesize a resistive load. Benefits: no need to measure the polluting load current, effective for all harmonics and different resonance conditions, simple control strategy, and may be implemented as a secondary control function of an active power supply. In this paper, a practical implementation of a resistive SHI is proposed. A new control strategy for a boost power factor correction (PFC) converter has been implemented in order to achieve a programmable resistive input impedance for harmonics, independent of the input impedance for the fundamental component. Furthermore, the potential to damp a resonance in a power distribution system is demonstrated using an experimental setup

Two-phase zero-voltage switching boost converter for medium power applications

A novel two-phase zero-voltage switching boost power converter is proposed. The proposed converter overcomes some limitations of the DC/DC resonant-type converter, such as high circulating energy, limited ZVS load range and complex transformer. The turn-on instant of the switches comes after zero-voltage detection of the voltage across them and there is no load limitation for soft switching. The possibility of using large resonant capacitors results in a considerable turn-off loss reduction. Dividing the power among the two identical 180/spl deg/ shifted phases of the converter contributes to reduced input and output current ripple and results in lower ratings for the switches and passive components. Steady state and dynamic analysis of the power converter are presented for design purposes. The new converter is attractive at medium-power DC/DC applications with output/input voltages ratio between 2 and about 6, where IGBTs are predominantly used as power switches. The principle of operation, features and design considerations of the proposed power converter are described and verified on a 6 kW, IGBT-based experimental circuit.

The influence on harmonic propagation of the resistive shunt harmonic impedance location along a distribution feeder and the influence of distributed capacitors

Although complete compensation is only possible using true active filters, resistive shunt harmonic impedances (SHI) have been shown to provide a considerable reduction of the harmonic propagation. In this work, the harmonic mitigation potential of a resistive SHI is discussed concerning its influence on the voltage distortion profile along a typical distribution feeder, with the location of the SHI along the feeder as a parameter. Although the distortion values are dependent on the SHI location, it is shown that installing the SHI between the middle and the end of the feeder is generally a good choice to locate the SHI, especially when the power system parameters can vary or are unknown. Calculations are performed on a typical radial distribution feeder with distributed capacitors (to model power factor correction capacitors or cable capacitances). In this study, the non-Linear loads are concentrated in single nodes whereas the linear loads are disconnected to obtain the worst case for the voltage distortion.

Optimized loads for damping harmonic propagation

Shunt harmonic impedances have been proposed as an attractive means for mitigating the propagation of harmonic pollution. The effectiveness was shown for linear power systems with current source polluting loads. In this paper, an extension of the concept for a typical nonlinear polluting load (a capacitively smoothed rectifier) is presented. It is shown that the proposed method is especially effective in the case of power system resonances.