Efficient Neural Network Implementations on Parallel Embedded Platforms Applied to Real-Time Torque-Vectoring Optimization Using Predictions for Multi-Motor Electric Vehicles

The combination of machine learning and heterogeneous embedded platforms enables new potential for developing sophisticated control concepts which are applicable to the field of vehicle dynamics and ADAS. This interdisciplinary work provides enabler solutions -ultimately implementing fast predictions using neural networks (NNs) on field programmable gate arrays (FPGAs) and graphical processing units (GPUs)- while applying them to a challenging application: Torque Vectoring on a multi-electric-motor vehicle for enhanced vehicle dynamics. The foundation motivating this work is provided by discussing multiple domains of the technological context as well as the constraints related to the automotive field, which contrast with the attractiveness of exploiting the capabilities of new embedded platforms to apply advanced control algorithms for complex control problems. In this particular case we target enhanced vehicle dynamics on a multi-motor electric vehicle benefiting from the greater degrees of freedom and controllability offered by such powertrains. Considering the constraints of the application and the implications of the selected multivariable optimization challenge, we propose a NN to provide batch predictions for real-time optimization. This leads to the major contribution of this work: efficient NN implementations on two intrinsically parallel embedded platforms, a GPU and a FPGA, following an analysis of theoretical and practical implications of their different operating paradigms, in order to efficiently harness their computing potential while gaining insight into their peculiarities. The achieved results exceed the expectations and additionally provide a representative illustration of the strengths and weaknesses of each kind of platform. Consequently, having shown the applicability of the proposed solutions, this work contributes valuable enablers also for further developments following similar fundamental principles.Some of the results presented in this work are related to activities within the 3Ccar project, which has received funding from ECSEL Joint Undertaking under grant agreement No. 662192. This Joint Undertaking received support from the European Union’s Horizon 2020 research and innovation programme and Germany, Austria, Czech Republic, Romania, Belgium, United Kingdom, France, Netherlands, Latvia, Finland, Spain, Italy, Lithuania. This work was also partly supported by the project ENABLES3, which received funding from ECSEL Joint Undertaking under grant agreement No. 692455-2

Design and Analysis of High Frequency Power Converters for Envelope Tracking Applications

In the field of power electronics, designers are constantly researching new methods to improve efficiency while optimizing dynamic performance. As communication technologies progress we are more often dealing with systems of increasing speed and complexity. For instance, from 1991 to 2013 we have observed the mobile broadband communication sector evolve from ~230 Kbits/s (2G) speeds to ~100 Mbits/s (4G LTE), a 430% increase in communication speed. In contrast, we have not observed the same evolutionary development in industrial power converters. Most switch-mode power supplies are still manufactured for 100 KHz to 800 KHz operating frequencies. The main reason for this is that most electrical devices only require steady-state DC power, so high speed conversion performance is largely unnecessary. But as size expectations for portable electronic devices continue to decrease, the only way to meet future demand is to realize power electronics that operate at much higher switching frequencies. Furthermore there is increasing demand to improve the transient response requirements in processor-based systems and achieve practical envelope tracking in RF communication systems. The most straightforward method of increasing the dynamic response for these systems is to increase the switching frequency of the power electronics in a sustainable and coherent manner

Double Resonant High-Frequency Converters for Wireless Power Transfer

This thesis describes novel techniques and developments in the design and implementation of a low power radio frequency (40kHz to 1MHz) wireless power transfer (WPT) system, with an application in the wireless charging of autonomous drones without physical connection to its on-board Battery Management System (BMS). The WPT system is developed around a matrix converter exploiting the benefits such as a small footprint (DC-link free), high efficiency and high power density. The overall WPT system topology discussed in this thesis is based on the current state-of-the-art found in literature, but enhancements are made through novel methods to further improve the converter’s stability, reduce control complexity and improve the wireless power efficiency. In this work, each part of the system is analysed and novel techniques are proposed to achieve improvements. The WPT system design methodology presented in this thesis commences with the use of a conventional full-bridge converter. For cost-efficiency and to improve the converters stability, a novel gate drive circuit is presented which provides self-generated negative bias such that a bipolar MOSFET drive can be driven without an additional voltage source or magnetic component. The switching control sequences for both a full-bridge and single phase to single phase matrix converter are analysed which show that the switching of a matrix converter can be considered to be the same as a full-bridge converter under certain conditions. A middleware is then presented that reduces the complexity of the control required for a matrix converter and enables control by a conventional full-bridge controller (i.e. linear controller or microcontroller). A novel technique that can maximise and maintain in real-time the WPT efficiency is presented using a maximum efficiency point tracking approach. A detailed study of potential issues that may affect the implementation of this novel approach are presented and new solutions are proposed. A novel wireless pseudo-synchronous sampling method is presented and implemented on a prototype system to realise the maximum efficiency point tracking approach. Finally, a new hybrid wireless phase-locked loop is presented and implemented to minimise the bandwidth requirements of the maximum efficiency point tracking approach. The performance and methods for implementation of the novel concepts introduced in this thesis are demonstrated through a number of prototypes that were built. These include a matrix converter and two full WPT systems with operating frequencies ranging from sub-megahertz to megahertz level. Moreover, the final prototype is applied to the charging of a quadcopter battery pack to successfully charge the pack wirelessly whilst actively balancing the cells. Hence, fast battery charging and cell balancing, which conventionally requires battery removal, can be achieved without re-balance the weight of the UAV

Hybrid monolithic integration of high-power DC-DC converters in a high-voltage technology

The supply of electrical energy to home, commercial, and industrial users has become ubiquitous, and it is hard to imagine a world without the facilities provided by electrical energy. Despite the ever increasing efficiency of nearly every electrical application, the worldwide demand for electrical power continues to increase, since the number of users and applications more than compensates for these technological improvements. In order to maintain the affordability and feasibility of the total production, it is essential for the distribution of the produced electrical energy to be as efficient as possible. In other words the loss in the power distribution is to be minimized. By transporting electrical energy at the maximum safe voltage, the current in the conductors, and the associated conduction loss can remain as low as possible. In order to optimize the total efficiency, the high transportation voltage needs to be converted to the appropriate lower voltage as close as possible to the end user. Obviously, this conversion also needs to be as efficient, affordable, and compact as possible. Because of the ever increasing integration of electronic systems, where more and more functionality is combined in monolithically integrated circuits, the cost, the power consumption, and the size of these electronic systems can be greatly reduced. This thorough integration is not limited to the electronic systems that are the end users of the electrical energy, but can also be applied to the power conversion itself. In most modern applications, the voltage conversion is implemented as a switching DC-DC converter, in which electrical energy is temporarily stored in reactive elements, i.e. inductors or capacitors. High switching speeds are used to allow for a compact and efficient implementation. For low power levels, typically below 1 Watt, it is possible to monolithically implement the voltage conversion on an integrated circuit. In some cases, this is even done on the same integrated circuit that is the end user of the electrical energy to minimize the system dimensions. For higher power levels, it is no longer feasible to achieve the desired efficiency with monolithically integrated components, and some external components prove indispensable. Usually, the reactive components are the main limiting factor, and are the first components to be moved away from the integrated circuit for increasing power levels. The semiconductor components, including the power transistors, remain part of the integrated circuit. Using this hybrid approach, it is possible in modern converterapplications to process around 60 Watt, albeit limited to voltages of a few Volt. For hybrid integrated converters with an output voltage of tens of Volt, the power is limited to approximately 10 Watt. For even higher power levels, the integrated power transistors also become a limiting factor, and are replaced with discrete power devices. In these discrete converters, greatly increased power levels become possible, although the system size rapidly increases. In this work, the limits of the hybrid approach are explored when using so-called smart-power technologies. Smart-power technologies are standard lowcost submicron CMOS technologies that are complemented with a number of integrated high-voltage devices. By using an appropriate combination of smart-power technologies and circuit topologies, it is possible to improve on the current state-of-the-art converters, by optimizing the size, the cost, and the efficiency. To determine the limits of smart-power DC-DC converters, we first discuss the major contributing factors for an efficient energy distribution, and take a look at the role of voltage conversion in the energy distribution. Considering the limitations of the technologies and the potential application areas, we define two test-cases in the telecommunications sector for which we want to optimize the hybrid monolithic integration in a smart-power technology. Subsequently, we explore the specifications of an ideal converter, and the relevant properties of the affordable smart-power technologies for the implementation of DC-DC converters. Taking into account the limitations of these technologies, we define a cost function that allows to systematically evaluate the different potential converter topologies, without having to perform a full design cycle for each topology. From this cost function, we notice that the de facto default topology selection in discrete converters, which is typically based on output power, is not optimal for converters with integrated power transistors. Based on the cost function and the boundary conditions of our test-cases, we determine the optimal topology for a smart-power implementation of these applications. Then, we take another step towards the real world and evaluate the influence of parasitic elements in a smart-power implementation of switching converters. It is noticed that the voltage overshoot caused by the transformer secondary side leakage inductance is a major roadblock for an efficient implementation. Since the usual approach to this voltage overshoot in discrete converters is not applicable in smart-power converters due to technological limitations, an alternative approach is shown and implemented. The energy from the voltage overshoot is absorbed and transferred to the output of the converter. This allows for a significant reduction in the voltage overshoot, while maintaining a high efficiency, leading to an efficient, compact, and low-cost implementation. The effectiveness of this approach was tested and demonstrated in both a version using a commercially available integrated circuit, and our own implementation in a smart-power integrated circuit. Finally, we also take a look at the optimization of switching converters over the load range by exploiting the capabilities of highly integrated converters. Although the maximum output power remains one of the defining characteristics of converters, it has been shown that most converters spend a majority of their lifetime delivering significantly lower output power. Therefore, it is also desirable to optimize the efficiency of the converter at reduced output current and output power. By splitting the power transistors in multiple independent segments, which are turned on or off in function of the current, the efficiency at low currents can be significantly improved, without introducing undesirable frequency components in the output voltage, and without harming the efficiency at higher currents. These properties allow a near universal application of the optimization technique in hybrid monolithic DC-DC converter applications, without significant impact on the complexity and the cost of the system. This approach for the optimization of switching converters over the load range was demonstrated using a boost converter with discrete power transistors. The demonstration of our smart-power implementation was limited to simulations due to an issue with a digital control block. On a finishing note, we formulate the general conclusions and provide an outlook on potential future work based on this research

Power Semiconductors for An Energy-Wise Society

This IEC White Paper establishes the critical role that power semiconductors play in transitioning to an energy wise society. It takes an in-depth look at expected trends and opportunities, as well as the challenges surrounding the power semiconductors industry. Among the significant challenges mentioned is the need for change in industry practices when transitioning from linear to circular economies and the shortage of skilled personnel required for power semiconductor development. The white paper also stresses the need for strategic actions at the policy-making level to address these concerns and calls for stronger government commitment, policies and funding to advance power semiconductor technologies and integration. It further highlights the pivotal role of standards in removing technical risks, increasing product quality and enabling faster market acceptance. Besides noting benefits of existing standards in accelerating market growth, the paper also identifies the current standardization gaps. The white paper emphasizes the importance of ensuring a robust supply chain for power semiconductors to prevent supply-chain disruptions like those seen during the COVID-19 pandemic, which can have widespread economic impacts.The white paper highlights the importance of inspiring young professionals to take an interest in power semiconductors and power electronics, highlighting the potential to make a positive impact on the world through these technologies.The white paper concludes with recommendations for policymakers, regulators, industry and other IEC stakeholders for collaborative structures and accelerating the development and adoption of standards

AC “back to back” switching device in industrial application

In industrial applications, among several varieties of semiconductor devices available, a silicon-controlled rectifier (SCR) is often used in managing and protecting various systems with different applications. Hence, it is of the utmost importance to design a control system which can operate over a range of electrical loads without any modifications in its hardware and/or software. This paper analyzes and investigates in detail the power circuit effects on conduction delay and SCR functioning. Moreover, two different commonly used driving systems for SCR application have been introduced, discussed, and evaluated. Concerning driving systems, here, three aspects have paramount importance and are consequently taken into consideration, namely the driver system losses, the conduction delay, and in particular, some power quality indices. The conduction delay is a parameter of great importance, as being able to control and reduce it to the minimum allowed by the application can bring significant practical advantages (both in terms of application and economic terms, as better summarized in the article). Theoretical analysis has been performed, followed and verified by simulation studies and, for some cases, laboratory experimental test results are presented which provide credibility to the study.©2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license http://creativecommons.org/licenses/by/4.0/fi=vertaisarvioitu|en=peerReviewed

Gallium-Nitride Efficacy for High-Reliability Forward Converters in Spacecraft

Gallium Nitride (GaN) devices show particular promise for space-rated power conversion applications that rely on MOSFET technology whose performance is severely limited by the radiation hardening processes. Though GaN failure mode classification and radiation hardened device variety is limited, the current space-rated selection pool can still yield significant efficiency and power density improvements. However, the context of GaN research is often future oriented such that the application of GaN to common, proven, space-rated converter designs is rare. The presented work quantifies the performance benefits of market available, space-rated GaN HEMTs over radiation hardened MOSFETs for a synchronous forward converter, which remains an extremely popular topology for isolated, medium power, DC-DC conversion on NASA satellite systems. Two 75-Watt, space-rated forward converters were designed, implemented, and benchmarked, with the power switch technology being the single variable of change. By forming pareto-optimal fronts of the key device metrics, optimal Rad-hard MOSFETs were chosen so that the baseline converter performance was considered best-case. The frequency limitations of common, available, Rad-hard PWM controllers limited power density in the GaN and Si converter alike, however, efficiency gains proved sizeable. The GaN based converter saw a peak efficiency of 86%, which was a 4.54% improvement over the Si baseline. Detailed efficiency and loss differential plots are presented which show the GaN converter’s reduced sensitivity to input voltage. Extreme similarity between the waveforms and functional characteristics of the two converters verified the design of the experiment. Furthermore, the performance of the baseline Si converter proved very similar to that of a large sampling of space-rated forward converters, making the experimental results have a high degree of utility for manufacturers

An Integrated IGBT Active Gate Driver with Fast Feed-Forward Variable Current

The Insulated-Gate Bipolar Transistor (IGBT) is a hybrid of bipolar and MOSFET transistors. As a consequence, IGBTs can handle higher current typical of bipolar transistors with the ease of control typical of MOSFETs. These characteristics make IGBTs desirable for high power Switch Mode Power Supplies (SMPS). In high power systems such as these, devices must be very reliable, as device failures may result in safety hazards such as fires in addition to the failure of the system. Conventional Gate Driver (CGD) circuits typically design for reliability in these systems by including a resistor between the gate driver and gate of the IGBT. This slows the switching waveforms, reducing stress on the IGBT while sacrificing efficiency. This solution is suboptimal, however, and as such Active Gate Drivers (AGD) have been designed to control voltage and current slopes through the IGBT by modulating the gate signal. AGD circuits found on the market today consist of a combination of an CGD with external components to implement the variable current necessary for protection. This requires a large amount of area on a Printed Circuit Board (PCB), and thus can be costly. Therefore, it can be desirable to integrate the AGD functionality into an on-chip system. In this thesis, an AGD is designed, fabricated and analyzed to show that IGBT gate voltage can be controlled in a manner capable of reducing overvoltage, as well as slowed when desired using an on-chip system. The current provided by this gate driver is controlled by feedback signals indicating the switching state of the device, as well as input bits that determine total output current