Design and implementation of a High-Power Half-Bridge LLC converter: a comparative study of discretes and module based on MOSFET Technology.

Nowadays the state of the art of power electronics requires high power density and high efficiency. Furthermore, in many applications, the market pushes towards reducing the number of components and at the same time increasing the power density. To this end, increasing the switching frequency of power converters leads to the reduction of the passive component which, in turn, is an enabling factor to reduce costs, while achieving greater power density. However, the increase in switching frequency is also increasingly linked to higher switching losses which can significantly compromise energy efficiency. Improving energy efficiency is important in view of the goal of sustainable energy. High efficiency power converters are mandatory in battery powered applications. High-density high-frequency power conversion leads to overheating problems. The thermal operating conditions of the power devices are critical for the reliability of the system. A solution to this problem can be obtained by using power devices that ensure high efficiency at high frequency. The high frequency target requires very fast devices to high efficiency converters. In terms of technology, broadband devices such as silicon carbide (SiC) and even more so gallium nitride (GaN) hold great promise in higher switching frequency applications due to their lower switching energy losses. On the other hand, the SuperJunction (SJ) MOSFET has a higher maturity. It is an established device and the most used. The recent very fast SJ MOSFETs enable high-frequency, high-density power converters with the advantage of lower cost, making them compete with state-of-the-art broadband devices. The present thesis work aims to measure the power dissipated by switching in the MOSFETs of a high efficiency LLC resonant converter through a calorimetric method. The dissipated power for switching can weigh heavily on the total dissipated power of the device, and the consequent reduction in efficiency, and being able to quantify it correctly is the basis for optimizing the devices and increasing the efficiency of the converters themselves. In LLC converter, this type of dissipated power cannot be measured with standard methods, such as measurement with the oscilloscope, as there is a part of energy that is recovered and not dissipated. To use the calorimetric method, must have a fairly accurate measurement of thermal resistance and must to be able to measure the temperature of the die in an accurate way too. In order to have a more accurate measurement of the temperature, a device in a package module, called ACEPACK(TM) SMIT, was used, which incorporates a complete half-bridge and an NTC thermistor for reading the temperature inserted specifically for these tests. This device will also 6 be considered to carry out electrical tests with a device with the same die in TO-247 package, in order to demonstrate the difference in parasites in the circuit and the different operation of them. The devices under test are in SuperJunction technology, so first the production processes and the characteristics that distinguish them from traditional MOSFETs will be illustrated. There will also be a chapter that highlights the differences between the two packages mentioned above, in order to better understand the dimensions and characteristics before using them in the application. Subsequently, DC/DC power converters will be treated, with a greater focus on the LLC converter, showing the formulas, waveforms and problems inherent to this converter. Finally there will be the chapters related to transformer design, PCB design, electrical measurements, EMI measurements, thermal measurements, thermal simulations and power measurements.