Sascha Muller

Characterization of small photovoltaic inverters for harmonic modeling

Some commercially available photovoltaic (PV) inverters with rated current below 16 A are systematically characterized in terms of harmonic emission by laboratory measurements. The test stand allows the analysis of a large number of test states by using an fully automated test procedure. It is shown that the current emission of inverters can be strongly dependent on the existing voltage harmonics. In order to quantify this influence a sensitivity index is introduced. The paper shows furthermore that the network impedance at the connection point can also impact the harmonic emission. The results of the study give a first more detailed overview of the harmonic characteristics of small PV inverters and form the basis for the development of accurate and reliable models.

Characterisation of harmonic interactions between electric vehicle battery chargers and PV inverters

This paper presents and discusses some initial results of the measurement and assessment of the harmonic characteristics of electric vehicle (EV) chargers and photovoltaic (PV) inverters, which are tested individually and when connected in different combinations to the same phase of a programmable three-phase LV supply in the laboratory. The range of possible harmonic interactions is assessed for three source impedance values and three characteristic supply voltage waveforms. The presented results can help in understanding how the exchange of energy between the grid, power electronic loads (EV chargers) and inverter-interfaced distributed generation (PV inverters) could be assessed in terms of the anticipated “smart grid” transformation of electricity networks.

Component-based modelling of EV battery chargers

This paper reviews typical circuit topologies and control algorithms for on-board unidirectional single-phase electric vehicle battery chargers (EVBCs) and provides simple yet reasonably accurate component-based models for their representation for power system analysis. The accuracy of the developed models is validated against measurements of actual EVBCs, for both ideal voltage supply conditions and typically distorted voltage supply waveforms. The paper also provides exponential and polynomial EVBC model interpretations, as well as some discussion of the further use of the presented models for the analysis of existing networks and future smart grids with high penetration levels of EVBCs.

Stochastic harmonic load model of residential users based on measurements

Realistic modeling of residential users is important to achieve accurate and reliable results in harmonic studies of public LV grids. This modeling is complex, because multiple factors influence the emission and propagation of harmonics through the network, like time-variation of number and types of connected devices, the supply voltage distortion and the network impedance. This paper discusses the advantages and disadvantages of state of the art modeling methodologies and it describes a novel modeling approach based on measurement of harmonic emission of individual residential users and aggregates of residential users. The developed model can represent the stochastic variation of harmonic currents and is useful e.g. to analyze the impact of new equipment technologies (like EV chargers) on the summation and propagation of harmonic currents in public LV grids.

Comparison of methods for modelling electric vehicle chargers for harmonic studies

As a significant increase of electric vehicles (EV) is expected in the future, studies of the impact of this new technology on the harmonic levels in distribution grids are very important. Realistic simulation results require reliable and accurate models of EV chargers, which generally utilize complex circuits including control algorithms for the active PFC. As part of a research project on the impact of high EV penetrations on the harmonic levels in public low voltage networks, a time-domain and a frequency-domain approach for the design of such models have been studied and compared in terms of difficulty, development effort and accuracy. The paper discusses in detail the methodology for the development of both types of models and summarizes their specific advantages and drawbacks, for both assessing performance of individual devices and for analyzing their interactions in network simulations. Based on different objectives, the conclusions provide guidance on the preferred modelling approaches for efficient and reliable network simulations.

Harmonic interaction of electric vehicle chargers in a central charging infrastructure

The operation of electric vehicles (EVs) in a central charging infrastructure represents an important future scenario for network operators. As EV chargers contain power electronics, such a scenario needs to be evaluated also with regard to Power Quality (PQ), in particular harmonics. Therefore, a field study has been carried out in a low voltage (LV) network with mainly commercial users and five three-phase EVs connected to one terminal. A large heat pump and some further loads were connected to the same terminal, which allows an assessment of the total harmonic emission for different combinations of the above mentioned devices. The emission of the combined operation is characterized by different cancellation effects between all devices as well as by the mutual influence between the voltage distortion and the harmonic currents. Particularly, the heat pump strongly influences the existing voltage distortion, which in turn affects the harmonic current emission of the EVs. To explain these harmonic interactions, the concept of primary and secondary cancellation is applied. The results of this field study are finally used for the validation of existing harmonic EV models. A comparison between measured and simulated harmonic currents has shown a good match.

Evaluation of hybrid harmonic modelling techniques: Case study of harmonic interactions of EVs and CFLs

Continuous increase of numbers of various modern power electronic (PE) devices requires careful investigation of their impact on both operation of distribution networks and other connected equipment. This paper discusses typical harmonic models and modelling techniques, using as examples electric vehicle battery charger (EVBC) and compact fluorescent lamp (CFL). Different models and modelling techniques are compared and their performance is evaluated for the analysis of harmonic emissions and interactions of EVBCs and CFLs in a simple network case study. Particular attention is given to the combined implementation of the frequency-domain and timedomain models in hybrid harmonic modelling approaches.