Michael Bosch

Zusammenfassung

With its low parasitic capacitances, gallium nitride HEMTs in theory enable faster switching transitions than their silicon and silicon carbide MOSFET counterparts. To turn the transistor on and off fast its input capacitance therefore has to be charged and discharged fast too. In doing so, the critical factor is the minimization of the gate loop inductance, which slows down the current in and out of the gate capacitance. In this work, the concept of a coaxial gate loop is presented. Through the cancellation of the magnetic fields during the switching events, the resulting inductance can be reduced and the gate is charged and discharged faster. With this approach, the switching energies of a high voltage GaN Transistor have been decreased by up to 21% through reducing the length of the Miller plateau to 38 ns and therefore increasing the dv/dt during the turn-on transition. Furthermore, this design concept enables a physical separation of the gate driver module and the power module while maintaining the advantages of GaN-based power electronics.

Zusammenfassung

In this work, the characterization of the non-linear output capacitance of bidirectional GaN transistors is presented for the first time. An experimental characterization in an Unclamped Inductive Switching Circuit of the nonlinear output characterization of a discrete bidirectional GaN transistor consisting of two 650 V anti-serial unidirectional GaN transistors in common-drain and common-source configuration is shown. Besides the evaluation of the dissipated energy due to the non-linear output capacitance the influence of the negative gate source voltage is investigated. While the dissipated energy decreases with a more negative gate source voltage for a unidirectional switch the shows the inverse behavior. At 400 V the common drain configuration has with 17 μJ almost twice as much dissipated energy as the common source counterpart. Furthermore, an analysis into the origin of the losses will be given, which can be used to improve the modeling of bidirectional GaN transistors. Thus, a better understanding for the switched operation of a bidirectional switch is gained.

Zusammenfassung

GaN power transistors require packaging concepts that combine low parasitic inductance with excellent thermal management for demanding converter applications. Therefore in this work, a hybrid half-bridge package embedding two discrete 650 V GaN transistors on AIN DBC is proposed, combining module-level thermal performance with the electrical advantages and flexibility of discrete SMD packages and embedding technologies. Static measurements show no significant differences in transfer characteristics, leakage currents (all $I_DS, leak <1 A$ at 600 V), or capacitances compared to reference samples. The package achieves a thermal resistance $R_t h, j - c$ below $0.2 K / W$ and a parasitic power loop inductance below $6 0 0 ~ p H$, with power loop resistance close to twice the nominal $R_DS, on $. This approach enables compact, lowinductive, and thermally efficient half-bridge integration for high-performance power converter applications.

Zusammenfassung

In this work a highly-integrated, 24 V input, dual-output (5 to 1SV up to 1A and −1.3V up to 100mA), low-noise GaN-based DC/DC supply for the gate and drain bias of a GaN solid state power amplifier for E- and W-band applications in space ór phased-array applications is presented. By using two fast-switching GaN half-bridges as the main element of two highly-integrated DC/DC converters for gate and drain bias supply, $\approx$50% higher efficiency and an adjustable drain voltage (e.g. for orbital tracking) can be achieved compared to state-of-the-art solutions (LDOs only). The required drain supply of the GaN SSPA (5 to 18 V with currents up to 1 A) is generated by a 70 m$Ømega$, 100V monolithic GaN half-bridge based buck-converter switching at 3.1 MHz with high gate-resistors $(62Ømega/10Ømega)$, extended filtering (resulting in an ac voltage noise of below 5 mV RMS for most bias points) and efficiencies above 80% for the whole output current range. The gate supply $(-1.3V,\ 100mA)$ is provided by a multi-stage approach to achieve efficient conversion and low noise: In the first stage the battery voltage is down converted to 5 V in a 3.1 MHz buck-converter $(\eta90\ \%)$ with two 3.3 $Ømega, 65V GaN$ transistors, to optimize the efficiency of the second stage. The second stage (switched capacitor, 2 MHz circuit, $\eta\geq$ 80%) converts the voltage to −2 V. A final LDO stage converts the −5V to −1.3 V with $0.8 V$ RMS-noise, to avoid instabilities of the SSPA due to gate bias oscillations. The converter is not actively cooled and does not exceed a local hotspot temperature of 85 °C at any operation point.

Zusammenfassung

Emerging electromobility requires a comprehensive simulation environment of the inverter and motor stage to ensure their performance and efficiency. Digital prototypes are critical to shortening development time and reducing costs by providing realistic test scenarios for such systems. The WLTP (Worldwide Harmonized Light Vehicles Test Procedure) is often not simulated but plays an important role, as this cycle reflects real driving conditions and thus enables an accurate assessment of the performance of electric vehicles. This work examines the role of digital prototypes in the context of e-mobility and focuses on the importance of WLTP cycle simulations for application-oriented testing. Furthermore, the focus is on the development of low-voltage inverters based on GaN-HEMT’s and the performance of detailed simulations using Spice, which allows a reasonable tradeoff between physical details and simulation time. The electro-mechanical behavior of a BLDC motor operated at various switching frequencies up to 150 kHz is simulatively compared to real measurement data. Then, the standardized motor test cycle WLTC is simulated to estimate the power consumption in driving cycles. This simulation environment enables sweeping various parameters like switching frequencies and commutation schemes e.g. trapezoidal or sinusoidal. Higher switching frequencies promise a combined efficiency increase of approx. 8 % of the electro-mechanical sub-system in this application-oriented test cycle. This work serves as a basis for new rapid prototyping for small electric vehicles, which can easily be adapted for e.g. 800 V, high-power automotive inverters.