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Contribution a la caracterisation et a la commande rapprochee de composants a grand gap moyenne tension pour onduleur de tension
Abstract and Figures
In an economic and political climate that promotes the use of electric vehicles, since 2011 Renault offers a range of EVs. The powerful models are based on an electrical architecture of 60 kW to 70 kW traction inverters and a 400V DC BUS. The static converters used, as in every embedded power system, must have high energetic yield, high robustness and high reliability during every operating phase of the vehicle. At the same time, the power electronics field is currently undergoing a technical revolution. New wideband gap power devices, such as Silicon Carbide (SiC, in the range of 600V, 1200V and 1700V) and Gallium Nitride (up to 600V), are available on the market. Those components are characterized by both voltage (dv/dt) and current (di/dt) high speed switching, and also by operating temperatures above than 175°C. These characteristics not only offer the prospect of achieving better performance converters, obtaining a significant gain on the autonomy of electric vehicles, but also more compact converters, facilitating their integration into the vehicle. However, these extreme switching are sources of issues, especially in the inverter topologies. Thus, based on a partnership between the LAPLACE Laboratory in Toulouse and RENAULT Technocentre in Guyancourt, three main problematic areas were addressed by this PhD research. First of all, there was a detailed analysis of the switching phenomena in an inverter switching cell. This work enabled the establishment of simple analytical models. These models allow, from the principal physical and linearized quantities of the components and from the functional parameters of the driver, direct predetermination of dv/dt and di/dt across the inverter operating range. The second topic deals with the characterization of these new power devices. A 1200V Cree SiC MOSFET and a first generation GaN HEMT power module from the prototype chain of CEA-LETI in Grenoble have been characterized in static and dynamic operation in both reverse and direct conduction mode. The results allowed the development of a static and dynamic behavioral model, using PSPICE type circuit elements, dedicated to the use of GaN HEMT transistors in a voltage inverter. The advantage of this model is its ability to emulate the reverse conduction in both gate bias cases (VGS>VGTH and VGS<VGTH) as per the operating conditions of an inverter leg. The third topic related to the gate drive operation of these components was based on the analytical modeling of the switching process. The work includes the proposal and test optimization of active or passive gate drive strategies. Two passive adjustment approaches could thus be compared in terms of dv/dt - Switching Energies trade-off, one overall and classic by the gate driver resistance ; another more selective by including a capacitor between the gate and drain of the components. This second method, for a specified dv/dt, may cause a switching energy loss saving of up to 18%. A final active method has been studied and tested via simulation. In principle, the proposed circuit consists of a limitation of di/dt, without influencing the dv/dt. The control loop uses the voltage that appears across the source inductance during switching of the current to activate an auxiliary transistor which brings or takes electric charges to and from the power transistor gate in order to ultimately obtain a di/dt real-time control.
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