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An advantage for some wide bandgap materials, that is often overlooked, is that the thermal coefficient of expansion (CTE) is better matched to the ceramics in use for packaging technology. It is shown that the optimal choice for uni-polar devices is clearly GaN. It is further shown that the future optimal choice for bipolar devices is C (diamond) owing to the large bandgap, high thermal conductivity, and large electron and hole mobilities. A new expression relating the critical electric field for breakdown in abrupt junctions to the material bandgap energy is derived and is further used to derive new expressions for specific on-resistance in power semiconductor devices. These new expressions are compared to the previous literature and the efficacy of specific power devices, such as heterojunction MOSFETs, using GaN are discussed.

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This paper first presents a step-by-step tutorial on modal analysis of a doubly-fed induction generator (DFIG)-based series compensated wind farm. The model of the system includes a wind turbine aerodynamics, a sixth-order order induction generator, a second-order two-mass shaft system, a fourth-order order series compensated transmission line, an eighth-order rotor-side converter (RSC) and grid-side converter (GSC) controllers, and a first-order DC-link model. Then, using modal analysis and time-domain simulations, it is shown that a fixed-series compensated DFIG is highly unstable due to the subsynchronous resonance (SSR) mode. In order to damp the SSR mode, the wind farm is interfaced with the gate-controlled series capacitor (GCSC) -which is a new series flexible AC transmission system (FACTS) device. A SSR damping controller (SSRDC) is designed for the GCSC using residue-based analysis and root locus diagrams, and an effective input control signal (ICS) to the SSRDC is identified in order to simultaneously increase damping of both the SSR and super-synchronous (SupSR) modes. The IEEE first benchmark model on SSR is adapted with an integrated DFIG-based wind farm to perform studies. Matlab/Simulink is used as a tool for designing process, and PSCAD/EMTDC is used for time-domain simulations.Nomenclature R line transmission line resistance (pu) X line transmission line reactance (pu) X T transformer reactance (pu) X S system reactance (pu) X C fixed series capacitor (pu) X tg transformer reactance in grid-side converter (GSC) (pu) i lq , i ld transmission line qd-axis currents (pu) i qg , i dg GSC qd-axis currents (pu) i qs , i ds stator qd-axis currents (pu) i qr , i dr rotor qd-axis currents (pu) v qs , v ds generator's terminal qd-axis voltages (pu) v qc , v dc qd-axis voltages across the fixed series capacitor (pu) v qr , v dr generator's rotor qd-axis voltages (pu) v qg , v dg GSC terminal qd-axis voltages (pu) E Bq , E Bd infinite bus qd-axis voltages (pu) Q s 0.5(v qs i ds −v ds i qs ), stator reactive power (pu) P s 0.5(v qs i qs + v ds i ds ), stator active power (pu) Q r 0.5(v qr i dr −v dr i qr ), rotor reactive power (pu) P r 0.5(v qr i qr + v dr i dr ), rotor active power (pu) Q g 0.5(v qg i dg −v dg i qg ), GSC reactive power (pu) P g 0.5(v qg i qg + v dg i dg ), GSC active power (pu) Q line 0.5(v ql i dl −v dl i ql ), transmission line reactive power (pu) P line 0.5(v ql i ql + v dl i dl ), transmission line active power (pu)T e 0.5X M (i qs i dr −i ds i qr ), electric torque (pu) i 0s , v 0s stator zero sequence components (pu) i 0r , v 0r rotor zero sequence components (pu) T tg mechanical torque between two masses (pu) P w , T w wind power and wind torque (pu) D g , D t damping coefficient of generator and turbine (pu) D tg damping coefficient between two masses (pu) K tg inertia constant of turbine and generator (pu) H t , H g inertia constants of turbine and generator (s) C DC-link capacitor (F) I DC DC-link current (A) v DC DC-link voltage (V) V w wind speed (m/s) R rotor radius of the wind...