<p>Electronic devices have a non-linear characteristic and emit harmonics into the low voltage grid. Different harmonic studies analyze their impact on the grids based on different types of harmonic models. The most used model is the constant current source. Measurements have shown that the harmonic currents emitted by electronic devices depend on the circuit topology and the existing supply voltage distortion. This paper quantifies the impact of supply voltage distortion on the harmonic current emission of individual devices and the summation of multiple devices. After a classification of the commonly used circuit topologies a time-domain model is developed for each of them. Then the individual and combined impact of voltage harmonics on the harmonic current emission of the modeled devices is analyzed based on simulations. Finally the impact of voltage distortion on the summation of multiple devices is analyzed and the accuracy of constant current source models is evaluated.</p>
Abstract--Network harmonic impedance forms the link between harmonic currents emitted by individual devices and the harmonic voltage levels in the grid. It is essential for the definition of current emission limits in order to ensure Electromagnetic Compatibility between all equipment connected to the grid. Among all electrical equipment in future smart grid electronic devices, like PV inverters, EV chargers or lamps with electronic ballast, will have a dominating share. This is expected to have a considerable impact on the network harmonic impedance characteristic.The paper discusses the frequency-dependent input impedance of different types of modern electronic equipment and its potential impact on the network harmonic impedance. It is shown that the semiconductor switching results in a variation of the impedance within the fundamental cycle. This is not considered by the presently used assessment methods as they assume only passive network elements. Beside a method to measure these variations, several indices are introduced to quantify the level of its impact. The paper aims to provide some impulses for further discussions, particularly about the definition of network harmonic impedance in presence of electronic devices, the necessity to include these variations in realistic harmonic studies and if this has to be considered in the standardization.
This paper presents results of experimental and analytical evaluation of power-dependent harmonic emission of three common types of modern low voltage (LV) power electronic (PE) devices. After a detailed analysis of comprehensive test results, based on both existing and new waveform distortion indices, the development of component-based models of PE devices is discussed. The paper demonstrates the importance of including PE devices' controls for accurate modelling of their characteristics over the entire range of operating powers. Most of the analysed PE devices exhibit strong power-dependent changes of characteristics, additionally influenced by supply voltage conditions, which are important for the analysis of both existing networks and future "smart grids". ).testing of EVBCs, despite the fact that the power during the charging cycle is variable, and will typically reduce during the latter stages. Test procedures for power-generating LV PE devices do consider variable power operation, with [3] and [5] specifying test points at 100% and 50% (and 25% in [3]) of P rated for PVIs. However, the actual output of any PVI can be, and often is lower, dependent on ambient conditions. Across the operating range, the performance of the internal control circuits of a PE device may be compromised, altering the device's characteristics. This may have a negative impact on the supply grid when such equipment is connected in large numbers. This paper presents a detailed experimental-based characterization of a number of SMPS', EVBCs and PVIs across their entire operational ranges and for different supply conditions. Two new indices are introduced for the analysis, which allow separate assessment of the contributions from the low-frequency (LF) harmonics and all other waveform distortions to the device's total operating current. This is of particular importance for the analysis of modern PE devices, for which LF harmonics might not be the most significant part of the total waveform distortion (e.g. [8]). The analysis of measurements is supported by the development of componentbased (circuit-based) models, capable of correctly reproducing the harmonic characteristics over the entire operating range.This paper shows that mostof tested PE devices exhibit distinctive power-dependent performance changes. The impact of realistic supply voltage conditions, i.e. distorted voltage and source impedance, on device characteristics is also considered and is shown to have considerable impact on certain types of equipment. Particular attention is given to the increased distortion in low and very low power operating modes (defined as below 30% and 10% of P rated ), as this issue has received limited attention in literature and is not fully captured by existing indices. When operating in very low power mode, some of the measured PE devices enter unstable operating regions or disconnect (i.e. 'trip' via their internal protection). These effects signify the importance of PE devices' controls when evaluating and modelling power-dependent changes in...
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