Electromagnetic Interference Analysis of Fast-Switching-Speed Semiconductors Applied to Power Electronics Converters

With new semiconductor technologies of outstanding performance each day more accessible, higher power density converters are being developed and introduced into the market, taking advantage of the potential increase of the switching frequency offered by such devices while keeping the same overall efficiency. As the switching frequency enters a range covered by EMI standards, unwanted and even neglected issues may arise, as the increase of the differential mode (DM) noise. Along with that, also the common mode (CM) noise source is affected, specially by the high dv/dt from faster switching events. For designing an EMI filter, the first step is to understand which and how the noise sources are. In this work, various aspects of the noise source are analysed: types of coupling, categorization of emissions, DC-DC and DC-AC converters mostly used on solar applications, and in uence of semiconductors switching events. Because of the PV cell output characteristics, a voltage regulation/boost is usually necessary and it is usually performed by a DC-DC stage. Therefore, the noise source of step-down, step-up and a multi-cell step-up converters are analysed. Moreover, typical non-isolated inverters as full-bridge, H5, HERIC and 3-level NPC are also assessed in terms of their generated noise. The semiconductors switching waveforms also influence the frequency spectrum, therefore the most relevant non-ideal effects are investigated in detail: rise and fall times, overvoltage, oscillations and soft-switching. Fourier series analysis of those cases are performed, enabling the understanding their effects on the spectrum. Application requirements and properties of inductors and capacitors are also presented. At first suitable materials and properties of magnetic core and windings are described. Following that, capacitors types and materials are described and compared, with focus given to capacitors for EMI filters. Additionally, a review of methods for minimizing the series stray inductance of these capacitors is presented, with a practical example also shown. Finally, some aspects of EMI filter design are investigated, based on a one-phase grid-connected 2.3 kW full-bridge PV inverter operating with bipolar modulation. At first the system requirements are analysed. Following that, the noise source is described. Based on that, the power and EMI filter can be designed. Finally, a prediction of the filter performance is achieved by extracting the parasitic elements of its single components. Based on the simulation and experimental results, a very strong influence of the components self-resonance and coupling effects is observed, as the response was even worse with filter at higher frequencies. Therefore, it is shown that the minimization of coupling effects and parasitic elements of the filter components is essential to achieve best filter responses on the frequencies of interest.