Switching Transition Control of Insulated-Gate Power Semiconductor Devices
thesisposted on 17.02.2016, 00:00 by Hossein Riazmontazer
As the industry demands move toward more compact and high-power-density applications, it is desirable to increase the switching frequency of the power semiconductor devices (PSDs) to reduce the size and cost of the passive elements. On the other hand, increasing the switching frequency results in higher switching loss in PSDs. Therefore, voltage and current slopes during the switching transitions need to be increased to decrease the duration of the switching transition and switching loss. However, adverse current and voltage slopes during the switching transitions are the main sources of the noise, EMI issues and switching stress such as over current and overvoltage. Consequently, a solution to empower one to gain an optimal performance in terms of switching loss, device stress and EMI is desirable. Several EMI and stress reduction techniques have been introduced in the literature to mitigate the undesirable affect of high di/dt and dv/dt. Those approaches include but not limited to: Active and passive clamps, snubber circuits, Active and passive EMI filters and soft switching techniques. The main drawbacks of the above-mentioned approaches are adding additional bulky and expensive passive and/or active devices to the power circuit, modification of the original topology and complexity of the control. Active and passive gate drive (or switching transition control) techniques are used to control EMI, device stress and switching losses by shaping the current and voltage slopes of the switching transitions of a PSD. In contrast to previously mentioned EMI and stress reduction techniques, switching transition controllers are placed in the control and gate drive stages and do not need any change in the original topology of the power circuit. Active gate drive circuits are controlling the di/dt and/or dv/dt of turn-off and/or turn on switching transitions of PSDs to gain the optimal performance regarding EMI, device stress and switching losses. The main limitations of the state of the art switching transition controllers are lack or limited adjustability of di/dt and dv/dt, and lack or limited ability to independently control di/dt, dv/dt and delay to gain an optimal performance in terms of loss, device stress and EMI. This dissertation outlines novel optical-based and electrical-based switching transition controllers for insulated gate power semiconductor devices such Si and SiC MOSFETs and IGBTs. The main advantage of the proposed controllers is unified independent control of di/dt and dv/dt of turn-on and turn-off switching transition. This feature gives more degree freedom to designer in different applications to gain an optimal performance regarding the switching loss, device stress and EMI noise. The other unique feature of the optical-based controllers is using optical beam to trigger and control the switching transition of PSDs that reduces the susceptibility to the external noise. Initially an optical-based two level switching transition controller is outlined. This controller is able to independently control the turn-off di/dt and dv/dt of the power MOSFETs by adjusting the optical intensity in each region of control. Independent controllability of turn-off dv/dt and di/dt is guaranteed by predicting the onset of transition between the regions of control considering the optical-to-electrical and circuit propagation delays. Subsequently, an electrical switching transition controller is presented for high speed SiC MOSFETs. This controller adjusts the di/dt and dv/dt of the turn-off switching transition by closed-loop control of the gate current. It independently control the very fast di/dt and dv/dts of the SiC MOSFET by predicting the onset of transition between dv/dt and di/dt control regions. Finally, an optical-based four-level switching transition controller is outlined that is able to independently control the delay, di/dt, dv/dt and voltage tail of the turn-on transition of the IGBTs. This controller comprises of three control blocks that predict the onset of transition between the four control regions. Each control parameter can be controlled individually by adjusting the optical intensity in that region.