Ultra-High Power Density Magnetic-less DC/DC Converter Utilizing GaN Transistors

In this paper, a high step-up magnetic-less DC/DC nX converter is designed and experimentally evaluated. GaN transistors are applied in a nX converter topology, yielding ultrahigh power density and high conversion efficiency. The absence of magnetic materials results in a constant efficiency throughout the power range; the power capability of the system is only limited by the ratings of the semiconductor devices. To effectively extract the dissipated power, a novel micro-fluidic heat sink is designed, based on microchannels fabricated on Silicon substrate and a laser-cut acrylic manifold. The developed liquid cooling heat sink yields a much smaller volume and higher cooling capability compared to conventional heat sinks. A 10X converter prototype with the integrated micro-fluidic heat sink is experimentally evaluated at various operating conditions and different flow rates for the cooling system. At a transferred power of 1.2 kW the converter exhibits an overall efficiency of 96%, while occupying 260 mL of volume, resulting in 4.62 W/cm 3 , a notable power density for such a high step-up DC/DC converter

A manifold microchannel heat sink for ultra-high power density liquid-cooled converters

Increase in heat fluxes as a result of the miniaturization of power electronics demands new thermal management solutions such as liquid cooling, because of its high heat extraction capabilities. This work describes a new silicon-based heat sink that takes advantage of the high heat extraction capability of microchannel liquid-cooling at low power consumption by co-designing the heat sink and the electronics. A simple combination of cleanroom microfabricated silicon and laser-cutting of plastics was employed to make a microchannel heat sink that simultaneously cools down 20 active devices (hotspots) of a power electronic converter. By flowing liquid close to the active devices through narrow microchannels, we show that the power requirements of the pump can be minimized, resulting in a compact cooling system that allows integration with small and energy-efficient micropumps. The manifold microchannel heatsink is demonstrated on a ultra-high power density magnetic-less 10x-step-up DC/DC converter resulting in a smaller volume and higher cooling capability than conventional heat sinks. The converter was tested up to an output power of 1.2 kW, with an overall efficiency of 96%, and an average temperature rise of only 12.6 degrees C. The converter and heatsink occupy a volume of 260 mL, resulting in a maximum demonstrated power density of 4.62 W/cm(3), and a potential to reach a power density up to 26.9 W/cm(3)

Embedded Microchannel Cooling for Monolithically-integrated GaN Half-bridge ICs

Efficient and compact power conversion is a key requirement to achieve sustainable electrification of our society. GaN-based power devices offer major benefits compared to their silicon counterparts in terms of efficiency and integration but suffer from severe thermal challenges. Self-heating negatively impacts device performance and reliability, and the lateral integration of power devices and logic on a single integrated circuit cannot be fully exploited without novel cooling methods. In this work, we show a method to integrate microchannel cooling inside the silicon substrate of an off-the-shelf GaN-on-Si power IC and achieve a 25x-reduction on thermal resistance compared to forced air cooling. We investigate measurement techniques to measure the device temperature when no direct physical or optical connection can be made to the chip. A side-by-side comparison in electrical and thermal performance between conventional (forced) air-cooling shows that the integration of liquid cooling reduces the negative effects of self-heating on electrical performance while significantly improving its maximum current capability. The results show a first step toward making high-performance power converters with state-of-the-art thermal performance.POWERLA

Optimized kW-Range Boost Converter Based on Impulse Rectification with 52 kW/l and 98.6% Efficiency

Maximizing the efficiency and power density of dc-dc converters demands parallel optimizations in design and control, especially for variable-frequency converters operating over wide frequency ranges. This work presents the full-scale optimization of a kilowatt-range MHz-class boost converter based on impulse rectification. To maximize the heat extraction from the converter and increase its power density, the entire power stage is implemented on a single-layer insulated-metal substrate (IMS). For high efficiencies over wide frequency ranges, high-performance Gallium Nitride (GaN) transistors are employed and various high-frequency materials (MnZn, NiZn, air) with different geometries are compared to realize a wide-bandwidth inductor. Silicon Carbide (SiC) Schottky diodes with zero reverse recovery are utilized for efficient high-frequency rectification, and the impact of the device current rating on its generated reactive power and the overall system efficiency is investigated at different power levels up to 1 kW. A proposed optimum duty cycle control maximizes the conversion efficiency at different gains and powers and prevents fatal device hard switching at high frequencies. The optimized converter enables a peak efficiency of 98.6% along with an ultra-high power density of 52 kW/l (850 W/inch3). A loss breakdown summarizes major efficiency bottlenecks to be overcome by future advances in power electronics

Parallel pv configuration with magnetic-free switched capacitor module-level converters for partial shading conditions

In this paper, a module-level photovoltaic (PV) architecture in parallel configuration is introduced for maximum power extraction, under partial shading (PS) conditions. For the first time, a non-regulated switched capacitor (SC) nX converter is a used at the PV-side conversion stage, whose purpose is just to multiply the PV voltage by a fixed ratio and accordingly reduce the input current. All the control functions, including the maximum power point tracking, are transferred to the grid-side inverter. The voltage-multiplied PV modules (VMPVs) are connected in parallel to a common DC-bus, which offers expandability to the system and eliminates the PS issues of a typical string architecture. The advantage of the proposed approach is that the PV-side converter is relieved of bulky capacitors, filters, controllers and voltage/current sensors, allowing for a more compact and efficient conversion stage, compared to conventional per-module systems, such as microinverters. The proposed configuration was initially simulated in a 5 kW residential PV system and compared against conventional PV arrangements. For the experimental validation, a 10X Gallium Nitride (GaN) converter prototype was developed with a flat conversion efficiency of 96.3% throughout the power range. This is particularly advantageous, given the power production variability of PV generators. Subsequently, the VMPV architecture was tested on a two-module 500 WP prototype, exhibiting an excellent power extraction efficiency of over 99.7% under PS conditions and minimal DC-bus voltage variation of 3%, leading to a higher total system efficiency compared to most state-of-the-art configurations.</p

Active-Device Losses in Resonant Power Converters: A Case Study with Class-E Inverters

Recent research has reported an undesirable OFF-state loss in high-frequency soft-switching power converters, such as resonant converters. This loss is attributed to a hysteresis loss related to the charging-discharging process of the output capacitance of the power transistor. However, precise estimation of transistor power loss and its breakdown into ON-state and OFF-state losses is challenging in the MHz-range operation due to the small circuit size, parasitic effects, and limited accuracy in existing methods to measure low-loss systems. We present a measurement concept to perform a complete loss breakdown of MHz-range resonant converters, as well, directly determine the OFF-state losses in transistors, which is demonstrated for a GaN-based class-E inverter operating at 10 MHz. A novel and compact calorimeter was designed to measure the converter active-device losses down to 20 mW within a 5% error. This measured loss is then separated into four components using a combination of average and instantaneous electrical measurements: transistor ON-state loss, transistor OFF-state loss, gate-driver internal loss and gate loss. A simple no-load technique was devised to evaluate the gate-driver internal loss. The proposed approach directly determines output-capacitance hysteresis losses during the actual converter operation, which is not possible with existing measurement methods. The presented knowledge of individual loss components permits better optimization of MHz-range power converters.POWERLA

H-terminated polycrystalline diamond p-channel transistors on GaN-on-Silicon

In many semiconductor technologies, including GaN, the lack of p-channel devices is a major obstacle for complementary operations. Here, we demonstrate high-performance polycrystalline diamond p-channel transistors on GaN-on-Si. Following the optimization of the microwave-plasma chemical-vapor-deposition of diamond on GaN, the polycrystalline layer was hydrogenated to form a 2D hole-gas at the surface, acting as p-channel. Relying on a rather simple fabrication process, these devices exhibited excellent electrical and thermal performances with on-off ratio of 109, breakdown voltage of 400 V, specific on-resistance of 84 mΩ·cm2, and thermal conductivities higher than 900 W/m·K. The presented hetero-integration technology provides a promising platform for future complementary logic operations, gate drivers, complementary power switch applications such as integrated power inverters and converters, simultaneously serving as a very efficient thermal management solution in high power density applications

Seed Dibbling Method for the Grow of High-Quality Diamond on GaN

The integration of diamond and GaN has been highly pursued for thermal management purposes as well as combining their exceptional complementary properties for power electronics applications and novel semiconductor heterostructures. However, the growth of diamond-on-GaN is challenging due to the high lattice and thermal expansion mismatches. The weak adhesion of diamond to GaN and high residual stresses after the deposition often result in the diamond film delamination or development of cracks, which hinder the subsequent device fabrication. Here, we present a new seed dibbling method for seeding and growing high-quality diamond films on foreign substrates, in particular on cost-effective GaN-on-Si, with significantly improved adhesion. Diamond films grown conformally on patterned GaN-on-Si presented high quality with significantly larger grains and a 95% sp(3)/sp(2) ratio, excellent interface between diamond and GaN, and lower residual stresses (as low as 0.2 GPa) compared to conventional methods. In addition, the method provided excellent adhesion, enabling a reliable polishing of the as-grown diamond films on GaN on Si without any delamination, resulting in smooth diamond-on-GaN substrates with subnanometer root-mean-square roughness. Diamond layers deposited via seed dibbling resulted in a 2-fold improvement in the effective thermal conductivity for GaN-on-Si with only a 20 mu m thick diamond layer. This method opens many new possibilities for the development of high-performance power electronic devices and integrated devices with excellent thermal management based on a diamond-on-GaN platform. In addition, this technique could be extended to other substrates to combine the outstanding properties of diamond with other kinds of devices.POWERLA