DESIRE: A Power Quality Prediction System

This paper describes a system for estimating the parameters of a simple model of an electric utility outlet using a transient measurement. Parameters of the utility model are estimated using data collected by the prototype. Nonlinear, frequency dependent eeects observed in previous work in this area are accounted for with a physically based model. The performance of the entire system is demonstrated by comparison of measured and predicted line voltage distortion during current transients created by a laser printer. From a service outlet, the electrical utility can be modeled as a sinusoidal voltage source in series with an inductor and a resistor. In a commercial or industrial building , impedances seen at the \user interface" arise predominantly from an upstream transformer, protection circuitry, and cabling. Harmonic currents generated by loads ow through these impedances, creating voltage drops that result in a distorted voltage waveform at the service outlet. In 1], the authors present an ingenious technique for determining the local apparent impedance of the electrical utility service. The impedance is identiied by brieey closing a capacitor across the electrical service at a precise point in the line voltage waveform. The shape and decay of the transient capacitor current in the resulting RLC circuit can be used to estimate the line impedance. In this paper, the technique is reformulated in the DESIRE (Determination of Electrical Supply Inductance and Resistance) system for characterizing a local electrical service. This new system ooers several advantages. The hardware features a power-level, digitally programmable test capacitor, a precision switch with a programmable ring angle, and a data collection interface. The exibility of the DESIRE hardware, in particular its digital control, allows it to collect the data required to accurately characterize the local electrical service. The software uses methods we describe here to estimate the parameters of the local distribution service, given the transient test data generated by the DESIRE hardware. The estimation method is particularly attractive because it does not require calibration of the parasitics introduced by the DESIRE hardware. This paper also develops a model, motivated by theory, to account for the measured increase in utility resistance with increasing test frequency observed in 1]. The model is used to predict the characteristics of the service impedance over a wide range of frequencies, given a limited number of test measurements. In 2] and 3], a transient event detector for nonintrusive load monitoring was introduced, which can …