Consideration of Electromagnetic Noise During Design of Inverter for Transportation Applications

Abstract

One of the main goals in modern power electronics lies in the increase of power density. This trend is mostly provoked by the electrification in the transportation (electric/hybrid vehicles and aircraft). The increase of power density should be resolved keeping the other parameters of power converters such as cost and degree of complexity on the adequate level. Moreover, all environmental conditions should be also fulfilled regarding the application. The power converters were improved from the topology and control point of view since the invention of silicon (Si) insulated gate bipolar transistors (IGBT) at the beginning of the '80s. However, the development and appearance on the market of the new power switches took the most attention of engineers in the last decade. Such semiconductor materials as silicon carbide (SiC) and gallium nitride (GaN) introduce a new class of power switches with reduced switching and conduction losses. At the first view, it seems that it is possible to improve the existing power converters only by the replacement of the conventional Si power switches. It is often assumed that such a simple approach reduces the size of the cooling system and/or the size of the passive components due to the increased switching frequency. However, low switching losses are also associated with short commutation times (rise/fall times of voltages and currents) and with high voltage slew rate (du/dt). The increased switching frequency and high values of du/dt introduces new limitations in the design of power converters, which were underestimated or neglected in the power electronics based on the semiconductors with low commutation speed. Several problems of high-speed commutation can be indicated in the literature: high overvoltages and oscillations during the commutation due to the presence of stray inductance, influence on the isolation, the increased bearing currents in the electrical drives and additional problems of electromagnetic interference (EMI). The last problem can be crucial for the application of the new power switches because it can require the installation of additional filters. The additional EMI filters can lead to the decrease of the power density of the whole system including power converter itself and all passive components. This thesis discusses the problem of EMI generated by the inverter of an electrical drive in the transportation systems. The work considers the aerospace application, where power density plays the most important role, but the requirements for the EMI are very strict. The nature of the conducted noise in the AC drives is considered in the details. The thesis presents also the various methods applied for the reduction of emissions generated by the power converter. The research work considers the application of conventional EMI filters and different inverter design techniques (topology, modulation techniques and hardware). This research was carried out to build an approach for including the high-frequency EMI effects in the design stage of the inverter utilizing the appropriate simulation. Whereas the most existing research works are concentrated on the EMI filter design and its optimization, this work presents a new frequency domain model, which is capable to consider different noise reduction techniques in the AC drive including the EMI filters and the inverter design methods. Moreover, the most existing models do not take coupling between common mode and differential mode into account. However, it is shown theoretically and experimentally, that the mixed-mode (MM) noise can be observed in the system where EMI is measured according to the aerospace standards. The proposed frequency domain models can be used to analyse the MM noise. The model keeps the simple frequency domain behaviour with low computational effort that makes it suitable for the application in the optimization procedure. The prototype of an inverter based on SiC metal-oxide-semiconductor field-effect transistors (MOSFET) was built within the research work to implement the AC drive system for the EMI measurements. It is used to conduct the experimental investigation of different noise reduction techniques as well as to validate the developed model. The results show that the EMI in the AC drives has a very complex nature. The particular noise reduction techniques are efficient only under the certain conditions. The proposed model can be used to analyse these conditions.