A Multifunctional SiC DC-DC Converter Topology with Normalized Fault Detection Strategy for Electric Vehicle Applications

The automotive industry is experiencing a monumental shift in technology and propulsion strategies. More than ever before, car manufacturers and suppliers are shifting development and funding away from combustion engines in favor of electrified powertrains. One of the main obstacles contributing to customers reluctance to buy EVs is the lack of infrastructure for charging. Traditional 110/220VAC outlets equipped at residential buildings are relatively low power compared to the batteries used in EVs today. These AC chargers, classified as level 1 and level 2, will take approximately 12-24 hours to completely charge a battery, depending on battery size and state-of-charge. Additionally, because this method of charging uses alternating current, vehicles must have chargers on-board to convert the energy from AC to DC to recharge the battery because EV batteries are direct current energy sources. Millions of dollars from the government and private companies are being invested to create an adequate DC fast charging infrastructure. The advantages of DC charging are two-fold, much quicker charging times and the elimination of onboard chargers. However, there is one blatant problem with current investments into a DC charging infrastructure – technological advancement. Most electric vehicles in production have battery pack voltages between 300V and 400V and current DC fast chargers are being developed for the current technology. This will likely change rather quickly; the development of wide-bandgap devices will allow for higher voltage devices. Furthermore, the energy densities of batteries will also likely improve, allowing for higher bus voltages. Higher bus voltages will offer several advantages over current architectures – more power, smaller devices, improved efficiencies, and more. The problem is, once higher bus voltages are achieved and popularized, the current fast charging infrastructure will be deemed obsolete. An intermediate solution needs to be developed to allow higher bus voltage vehicles to continue to utilize the current fast chargers being deployed nation-wide. The proposed DC-DC converter is a practical design that offers multiple purposes when implemented in electric vehicles that utilize permanent magnet synchronous machines (PMSM) and bus voltages of ~800V. It consists of a bi-directional interleaved DC-DC cascaded with an isolated full bridge converter. This configuration provides a 12V source with galvanic isolation during normal propulsion. The interleaved converter can boost in reverse to allow for charging of the 800V bus with current generation DC fast chargers operating at ~400V. Finally, an inverter fault detection methodology has been realized to take advantage of the interleaved DC-DC structure. If an open switch fault is detected on any of the 3-phases driving the PMSM, the appropriate phase-leg is isolated, and a phase-leg from the interleaved DC-DC is used to maintain propulsion. This is realized by monitoring the phase currents of the AC motor and analyzing the difference in value between all three. A threshold value is implemented in C-code, not contingent on the system parameters. A difference of phase currents greater than the threshold value is a clear indication that an open switch fault has occurred. The proposed power conversion structure and the motor inverter fault detection, isolation, and compensation approaches are verified by a PSIM simulation. The simulation results successfully validate the feasibility of proposed electric powertrain structure and inverter switch fault detection and compensation methods.Master of Science in EngineeringEnergy Systems Engineering, College of Engineering & Computer ScienceUniversity of Michigan-Dearbornhttp://deepblue.lib.umich.edu/bitstream/2027.42/156398/1/Brandon Pieniozek Final Thesis.pdfDescription of Brandon Pieniozek Final Thesis.pdf : Thesi