System and method for determining harmonic contributions from nonlinear loads in power systems.

摘要

The objective of this research is to introduce a neural network based solution for the problem of measuring the actual amount of harmonic current injected into a power network by an individual nonlinear load.;In electrical networks, harmonic currents are injected into the network by nonlinear loads such as power electronic equipment, arc furnaces, saturating inductances, and so on. When such loads are supplied from a sinusoidal voltage, their injected harmonic currents are referred to as contributions from the customer. Harmonic currents which flow in any network, cause harmonic volt drops, so that the supply voltage at the customer is no longer sinusoidal. Any other customers, even with linear loads, connected to the terminals (called the Point of Common Coupling, or PCC) of the first customer, will have harmonic currents injected into them by the distorted network voltage at the PCC. Such currents are referred to as contributions from the power system, or supply harmonics. Currently no method exists which can reliably distinguish between load harmonics and supply harmonics. The proposed load modeling method addresses this issue. The theoretical aspect of load modeling is explained. The scheme is verified on a number of different power electronic circuits. It is shown that there is a difference in the current distortion of a load depending on whether the load is served by a clean voltage supply or a distorted voltage supply. To quantify this difference, a new parameter em is introduced. The utility is responsible for ensuring there are no resonance conditions created by their use of capacitors on the system. However, if a significant amount of voltage distortion exists on a circuit, customer loads can have an increased level of current harmonics as a result of the voltage distortion. So, it can be difficult to determine whether a customer is within IEEE519 compliance or not. The proposed load modeling concept is also able to identify the amount of customer injected harmonic current regardless of whether a resonant condition exists on the utility power system.;All loads supplied by the utility are designed and optimized to operate at the supply frequency (60 Hz or 50 Hz, depending on the geographical region of operation). However, the voltage at the PCC is rarely a pure sinusoid and hence loads do not get a clean 60 Hz supply. If several loads are connected to a PCC, another important parameter of interest is to monitor the change in the voltage distortion level at the PCC, if a nonlinear load were to filter out its harmonics. The proposed source modeling scheme addresses this issue. The scheme is verified in simulation as well as on actual field data. The source modeling scheme aids the implementation of IEEE 519 by predicting whether or not the voltage distortion limit at the PCC is restored if corrective action is taken by a nonlinear load in terms of reducing its current harmonics.;The intellectual property of this research is protected. This would help the commercialization of the proposed methods. The main advantages of the proposed schemes are that only waveforms of voltages and currents are required for their operation and they are applicable to both single and three phase systems. Both the schemes are designed as software tools and can be integrated into any existing power quality instrument. This could also be fabricated into a commercial standalone instrument that could be installed in substations of large customer loads, or used as a hand-held clip on instrument.