Pieter Vermeyen

The Feasibility of Small-Scale Residential DC Distribution Systems

The application of DC distribution of electrical power has been suggested as an efficient method of power delivery. This concept is inspired by the absence of reactive power, the possibility of efficient integration of small distributed generation units and the fact that, internally, many appliances operate using a DC voltage. A suitable choice of rectifier facilitates the improvement of the power quality as well as the power factor at the utility grid interface. Stand-by losses can be largely reduced. However, because of the inherent danger associated with DC voltages and currents, it is imperative that a considerable amount of design effort is allocated for risk analysis and the conception of protective devices and schemes, in order to guarantee personal and material (especially fire) safety. This paper consists of the following topics: topological design, buffering of the DC bus, interfacing distributed generators, efficiency analysis and safety measures. The conclusion of this work is that (at the moment) it is generally not efficient to implement a DC distribution system exclusively at the level of the end-user. Rather, further research should focus on the extension of DC power delivery to higher levels of the electricity grid

Protection Issues in Microgrids with Multiple Distributed Generation Units

The application of local generators in distribution grids has consequences for the protection system. In this paper, protection issues concerning distributed generation are discussed, followed by a discussion of the results of simulations. These simulations concern the effect of local induction generators on protection selectivity in a system with parallel distribution feeders and the effect on fault detection. It is found that local induction generator can pose a selectivity problem in a system with parallel feeders when a line-to-line fault or a double line-to-ground fault occurs. Regarding the fault current detected at the beginning of a feeder, detected current is lowest when a line-to-line fault or a line-to-ground fault occurs. Depending on the relay settings, this can result in a detection problem.

State estimation in distribution grids

Problems and techniques for estimating the state of an observable distribution grid are investigated. A distribution grid is observable if the state of the grid can be fully determined. For the simulations, the modified 34-bus IEEE test feeder is used. The measurements needed for the state estimation are generated by the ladder iterative technique. Two methods for the state estimation are analyzed: weighted least squares and extended Kalman filter. Both estimators try to find the most probable state based on the available measurements. The result is that the Kalman filter mostly needs less iterations and calculation time. The disadvantage of the Kalman filter is that it needs some foreknowlegde about the state.

Numerical observability analysis of distribution systems

Observability analysis is a very important tool in state estimation. For a given set of measurements and their geographical location in the system, it determines whether the state of the whole system can be estimated. In this paper a numerical observability analysis, applicable to distribution systems is discussed and applied to the IEEE 34 bus test feeder. The method is based on the inverse function theory and the Jacobian matrix of the system. By calculating the dependent columns of the Jacobian matrix it is possible to determine the unobservable branches in the system. This also gives an indication of how many linearly independent pseudo-measurements are required to make the distribution system observable. Because the R=X ratio is not negligible in the distribution lines, a transformation has been used to simplify the observability analysis.