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Harmonic Estimation and Source Identification in Power Distribution Systems Using Observers

Ujile, Awajiokiche

[Thesis]. Manchester, UK: The University of Manchester; 2015.

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Abstract

With advances in technology and the increasing use of power electronic components in the design of household and industrial equipment, harmonic distortion has become one of the major power quality problems in power systems. Identifying the harmonic sources and quantifying the contributions of these harmonic sources provides utility companies with the information they require to effectively mitigate harmonics in the system. This thesis proposes the use of observers for harmonic estimation and harmonic source identification. An iterative observer algorithm is designed for performing harmonic estimation in measured voltage or current signals taken from a power distribution system. The algorithm is based on previous observer designs for estimating the power system states at the fundamental frequency. Harmonic estimation is only carried out when the total harmonic distortion (THD) exceeds a specified threshold. In addition, estimation can be performed on multiple measurements simultaneously. Simulations are carried out on an IEEE distribution test feeder. A number of scenarios such as changes in harmonic injections with time, variations in fundamental frequency and measurement noise are simulated to verify the validity and robustness of the proposed iterative observer algorithm.Furthermore, an observer-based algorithm is proposed for identifying the harmonic sources in power distribution systems. The observer is developed to estimate the system states for a combination of suspicious nodes and the estimation error is analysed to verify the existence of harmonic sources in the specified node combinations. This method is applied to the identification of both single and multiple harmonic sources. The response of the observer-based algorithm to time varying load parameters and variations in harmonic injections with time is investigated and the results show that the proposed harmonic source identification algorithm is able to adapt to these changes. In addition, the presence of time delay in power distribution system measurements is taken into consideration when identifying harmonic sources. An observer is designed to estimate the system states for the case of a single time delay as well as multiple delays in the measurements. This observer is then incorporated into the observer-based harmonic source identification algorithm to identify harmonic sources in the presence of delayed measurements. Simulation results show that irrespective of the time delay in the measurements, the algorithm accurately identifies the harmonic sources in the power distribution system.