Traditional thermoelectric Peltier coolers exhibit a cooling limit which is primarily determined by the figure of merit, $\mathit{zT}$. Rather than a fundamental thermodynamic limit, this bound can be traced to the difficulty of maintaining thermoelectric compatibility. Self-compatibility locally maximizes the cooler's coefficient of performance for a given $zT$ and can be achieved by adjusting the relative ratio of the thermoelectric transport properties that make up $zT$. In this study, we investigate the theoretical performance of thermoelectric coolers that maintain self-compatibility across the device. We find that such a device behaves very differently from a Peltier cooler, and we term self-compatible coolers “Thomson coolers” when the Fourier heat divergence is dominated by the Thomson, as opposed to the Joule, term. A Thomson cooler requires an exponentially rising Seebeck coefficient with increasing temperature, while traditional Peltier coolers, such as those used commercially, have comparatively minimal change in Seebeck coefficient with temperature. When reasonable material property bounds are placed on the thermoelectric leg, the Thomson cooler is predicted to achieve approximately twice the maximum temperature drop of a traditional Peltier cooler with equivalent figure of merit ($zT$). We anticipate that the development of Thomson coolers will ultimately lead to solid-state cooling to cryogenic temperatures.

Variability of the power generated by photovoltaics due to passing clouds can cause instability in the utility grid. This variability can be mitigated by control strategies which include the integration of energy storage systems. This article proposes a combination of two novel methods, termed here as adaptive moving average control and adaptive state of charge control, to mitigate variability using energy storage. The adaptive moving average control uses an adjustable window size based on a variability metric quantified by a moving standard deviation of the input power, leading to improved mitigation. The adaptive state of charge control maintains flexibility of the storage system by keeping its state of charge close to a reference. This proposed combination reduces storage utilization during times of low variability, and improves the trade-off between the degree of smoothness achieved and the capacity requirement of the storage system. The advantage of the proposed strategy with respect to traditional algorithms is first presented in simulation. The result is further verified experimentally in a field test by using a battery energy storage system controlled by agents written for the Eclipse VOLTTRON platform.

Recently, a major challenge in the adoption of wide bandgap semiconductors for power electronic applications is the need to trade device performance for device safety. In this article, methods for predicting gate voltage overshoot in normally-OFF gallium nitride (GAN) high electron mobility transistors (HEMTs) are derived in order to deliver optimal device performance. Two models are proposed; a simple, yet less accurate second order model and a complex, yet more accurate fourth order model. These models allow for the calculation of gate resistances necessary for a desired amount of gate voltage overshoot. The nonlinear capacitances of the device are considered in the analysis. The models are validated with an experimental double-pulse tester. These newly developed models allow design engineers to extract the best possible performance of commercially available GaN devices while keeping the devices in their safe-operating region.

Vertical power devices require significant attention to their edge termination designs to obtain higher breakdown voltages without substantial increase in ON-state resistance. A simple edge termination structure for a GaN p-n diode is proposed, comprising a full layer lightly doped p-type GaN region underneath the higher doped ${p} +\!+$ contact layer. A TCAD model of the device is developed, and removal of the portions of ${p}$ ++ cap outside of the device active area in simulations is shown to increase the device blocking voltage capability. It causes the depletion width to increase in the lightly doped p-type layer and allows it to act similar to a junction termination extension (JTE). These predictions are validated empirically, resulting in a 52% measured increase in breakdown capability after selective removal of the ${p}$ ++ cap. This simple edge termination technique can be formed with only a single low-energy nitrogen implant or etching procedure, greatly increasing its manufacturability over more complex structures. Design optimization studies are pursued in TCAD to determine optimal parameter values for further improving breakdown performance. It is shown that the proposed edge termination technique can be employed to produce future high voltage vertical GaN devices without a significant gain in ON-state resistance and with wide tolerance to process variations.

The effect of various trapping centers on single event-transients (SETs) in GaN high-electron-mobility transistors (HEMTs) are examined via calibrated technology computer aided design (TCAD) simulations. A single-channel, Schottky-gate HEMT computational model is developed and validated with static characteristics and single-photon absorption laser data. Simulations of SETs show that a two-dimensional electron gas (2DEG) enhancement effect occurs, which leads to additional collected charge in excess of the generated charge. The origins of this effect are examined and shown to result from an increase in occupation rate of the surface donor traps as the influx of charge is developed in the charge track. Variations in trap characteristics are then introduced and their effect on internal charge collection processes examined. It is further shown the SET response is dominated by the properties of the surface donor traps (i.e., energy level and density) such that the SET drain current closely follows the transient decay of occupation rate back to the original DC level.

Under partial shading conditions (PSC), a photovoltaic (PV) system may produce multiple local maximum power points (LMPPs). Traditional maximum power point tracking (MPPT) techniques are not able to distinguish between LMPPs and the global maximum power point (GMPP), leading to sub-optimal PV array power outputs. This paper proposes a two-level algorithm for tracking the GMPP. The first level is a discretized global search, allowing the system to hone in on the neighborhood containing the GMPP. In the second level, the well-known ripple correlation control (RCC) technique is used to swiftly converge to the GMPP. Using the proposed two-level algorithm, it can be guaranteed that the GMPP is successfully found and tracked. A benchmark analysis involving other state of the art algorithm reveals that the proposed method is the most superior algorithm in terms of accurately and swiftly tracking the global maximum power point in dynamic partial shading conditions. The algorithm is implemented with a simple inexpensive microcontroller, and therefore can be readily adopted in a myriad of dynamic partial shading applications.Therefore, this work allows the penetration of future photovoltaic power conversion systems to be more efficient.