Investigations In High Power Density EMI Filter Solutions For DC-Fed Three Phase Motor Drive Systems

Increasing trend on more-electric transportation requires smaller/lighter power converters, which pushes converter to obtain higher power in smaller volume, with higher switching frequency. This makes the EMI problems worse in these high power density converters. EMI filters are needed here to suppress these noises. Usually EMI filters are made of different kinds of passive components, which is bulky and lossy. EMI filters take a big part in the total system volume and weight. The High density EMI filtering solution becomes a critical factor to the high power density converters. In this dissertation, a series of studies have been done to investigate the EMI problems in DC-fed three phase motor drive systems, focusing on the high density solutions for the conducted EMI reduction in these systems.Common mode (CM) inductor is a big portion in total EMI filter size, the saturation of CM choke is considered to be one of the important limits for further volume reduction of EMI filters. The conventional design for CM choke usually takes DM current and leakage inductance as the main causes of CM choke saturation. In real cases, CM choke still saturates even designed with DM current and leakage inductance constraint, so that the CM choke is usually over designed according to experience to avoid saturation, which makes the CM choke volume is much more than real needs. In this research works, it's proved that CM choke saturation is not only related to the leakage inductance and DM current, but also related to the CM volt-second. A model is proposed in this dissertation to analysis how the CM propagation path parameters, modulation and switching frequency impact on the CM volt-second across the CM choke, which determines the minimum cross-section area of the CM inductor cores. With all these information, the volt-second can be calculated and the minimum volume of the EMI filter can be determined. The model can be a new criterion for CM choke design is proposed in additional of traditional design method.Integration technology provides an effective way to obtain the passive components in a compact space with a good form factor. Furthermore, integration helps on the multi-functional components implementation, which also helps on the total volume reduction. Standardized processes in integration technology give the potential of easier industrial manufacture. Several EMI solutions are studied and compared in this dissertation. In most of previous works, integrated EMI filter stays in the stage of small signal test. In this research work, planar LC integrated EMI filters are fabricated and tested with motor drive system and the parameters are designed with the consideration with in circuit high voltage/ current biases. Some improvements have been validated in the design trying to minimize the total size. By making all these efforts, the version 3 integrated EMI filter size can be pushed to half of the original design. For further size reduction, an attempt of DM capacitor integration using LTCC technology is tried. A large signal test is proposed and finished to study the characteristic of LTCC capacitor under larger signal bias.EMI containment using busbar filters in motor drive systems is also studied in this dissertation. Transmission line busbar filter is firstly proposed in RF area using transmission line effect to suppress the noise signals in system. This concept was extended in power electronics area as an EMI containment solution using power connectors. It provides different paths for currents at different frequencies. It's early in circuit implementation with converters was reported to be in a 500W PFC converter with switching frequency at 400 kHz. It remains unknown if the concept still works in motor drive systems with higher voltage/power ratings and lower switching frequency. To answer all these questions, a baseline busbar filter is fabricated and tested in the motor drive system. Modeling works have been done to find out relationship between the parameters and attenuation. With the knowledge gain from the modeling work, an improved busbar filter is built and tested. The experiment results show good attenuation of this kind of filter.