Power and spectrally efficient integrated high-speed LED drivers for visible light communication

Recent trends in mobile broadband indicates that the available radio frequency (RF) spectrum will not be enough to support the data requirements of the immediate future. Visible light communication, which uses visible spectrum to transmit wirelessly could be a potential solution to the RF ’Spectrum Crunch’. Thus there is growing interest all over the world in this domain with support from both academia and industry. Visible light communication( VLC) systems make use of light emitting diodes (LEDs), which are semiconductor light sources to transmit information. A number of demonstrators at different data capacity and link distances has been reported in this area. One of the key problems holding this technology from taking off is the unavailability of power efficient, miniature LED drive schemes. Reported demonstrators, mostly using either off the shelf components or arbitrary waveform generators (AWGs) to drive the LEDs have only started to address this problem by adopting integrated drivers designed for driving lighting installations for communications. The voltage regulator based drive schemes provide high power efficiency (> 90 %) but it is difficult to realise the fast switching required to achieve the Mbps or Gbps data rates needed for modern wireless communication devices. In this work, we are exploiting CMOS technology to realise an integrated LED driver for VLC. Instead of using conventional drive schemes (digital to analogue converter (DAC) + power amplifier or voltage regulators), we realised a current steering DAC based LED driver operating at high currents and sampling rates whilst maintaining power efficiency. Compared to a commercial AWG or discrete LED driver, circuit realised utilisng complementary metal oxide semiconductor (CMOS) technology has resulted in area reduction (29mm2). We realised for the first time a multi-channel CMOS LED driver capable of operating up to a 500 MHz sample rate at an output current of 255 mA per channel and >70% power efficiency. We were able to demonstrate the flexibility of the driver by employing it to realise VLC links using micro LEDs and commercial LEDs. Data rates up to 1 Gbps were achieved using this system employing a multiple input, multiple output (MIMO) scheme. We also demonstrated the wavelength division multiplexing ability of the driver using a red/green/blue commercial LED. The first integrated digital to light converter (DLC), where depending on the input code, a proportional number of LEDs are turned ON, realising a data converter in the optical domain, is also an output from this research. In addition, we propose a differential optical drive scheme where two output branches of a current DAC are used to drive two LEDs achieving higher link performance and power efficiency compared to single LED drive

A GALLIUM NITRIDE INTEGRATED ONBOARD CHARGER

Compared to Silicon metal–oxide–semiconductor field-effect transistors (MOSFETs), Gallium Nitride (GaN) devices have a significant reduction in gate charge, output capacitance, and zero reverse recovery charge, enabling higher switching frequency operation and efficient power conversion. GaN devices are gaining momentum in power electronic systems such as electric vehicle (EV) charging system, due to their promises to significantly enhance the power density and efficiency. In this dissertation, a GaN-based integrated onboard charger (OBC) and auxiliary power module (APM) is proposed for EVs to ensure high efficiency, high frequency, high power density, and capability of bidirectional operation. The high switching frequency operation enabled by the GaN devices and the integration of OBC and APM bring many unique challenges, which are addressed in this dissertation. An important challenge is the optimal design of high-frequency magnetics for a high-frequency GaN-based power electronic interface. Another challenge is to achieve power flow management among three active ports while minimizing the circulating power. Furthermore, the impact of circuit layout parasitics could significantly deteriorate the system interface, due to the sensitivity of GaN device switching characteristics. In this work, the aforementioned challenges have been addressed. First, a comprehensive analysis of the front-end AC-DC power factor correction stage is presented, covering a detailed magnetic modeling technique to address the high-frequency magnetics challenge. Second, the modeling and control of a three-port DC-DC converter, interfacing the AC-DC stage, high-voltage traction battery and low-voltage battery, are discussed to address the power flow challenge. Advanced control methodologies are developed to realize power flow management while maintaining minimum circulating power and soft switching. Furthermore, a new three-winding high-frequency transformer design with improved power density and efficiency is achieved using a genetic-algorithm-based optimization approach. Finally, a GaN-based integrated charger prototype is developed to validate the proposed theoretical hypothesis. The experimental results showed that the GaN-based charging system has the capability of achieving simultaneous charging (G2B) of both HV and LV batteries with a peak efficiency of 95%

Design and Advanced Model Predictive Control of Wide Bandgap Based Power Converters

The field of power electronics (PE) is experiencing a revolution by harnessing the superior technical characteristics of wide-band gap (WBG) materials, namely Silicone Carbide (SiC) and Gallium Nitride (GaN). Semiconductor devices devised using WBG materials enable high temperature operation at reduced footprint, offer higher blocking voltages, and operate at much higher switching frequencies compared to conventional Silicon (Si) based counterpart. These characteristics are highly desirable as they allow converter designs for challenging applications such as more-electric-aircraft (MEA), electric vehicle (EV) power train, and the like. This dissertation presents designs of a WBG based power converters for a 1 MW, 1 MHz ultra-fast offboard EV charger, and 250 kW integrated modular motor drive (IMMD) for a MEA application. The goal of these designs is to demonstrate the superior power density and efficiency that are achievable by leveraging the power of SiC and GaN semiconductors. Ultra-fast EV charging is expected to alleviate the challenge of range anxiety , which is currently hindering the mass adoption of EVs in automotive market. The power converter design presented in the dissertation utilizes SiC MOSFETs embedded in a topology that is a modification of the conventional three-level (3L) active neutral-point clamped (ANPC) converter. A novel phase-shifted modulation scheme presented alongside the design allows converter operation at switching frequency of 1 MHz, thereby miniaturizing the grid-side filter to enhance the power density. IMMDs combine the power electronic drive and the electric machine into a single unit, and thus is an efficient solution to realize the electrification of aircraft. The IMMD design presented in the dissertation uses GaN devices embedded in a stacked modular full-bridge converter topology to individually drive each of the motor coils. Various issues and solutions, pertaining to paralleling of GaN devices to meet the high current requirements are also addressed in the thesis. Experimental prototypes of the SiC ultra-fast EV charger and GaN IMMD were built, and the results confirm the efficacy of the proposed designs. Model predictive control (MPC) is a nonlinear control technique that has been widely investigated for various power electronic applications in the past decade. MPC exploits the discrete nature of power converters to make control decisions using a cost function. The controller offers various advantages over, e.g., linear PI controllers in terms of fast dynamic response, identical performance at a reduced switching frequency, and ease of applicability to MIMO applications. This dissertation also investigates MPC for key power electronic applications, such as, grid-tied VSC with an LCL filter and multilevel VSI with an LC filter. By implementing high performance MPC controllers on WBG based power converters, it is possible to formulate designs capable of fast dynamic tracking, high power operation at reduced THD, and increased power density

Wide Bandgap Based Devices: Design, Fabrication and Applications, Volume II

Wide bandgap (WBG) semiconductors are becoming a key enabling technology for several strategic fields, including power electronics, illumination, and sensors. This reprint collects the 23 papers covering the full spectrum of the above applications and providing contributions from the on-going research at different levels, from materials to devices and from circuits to systems

High Power Density, High Efficiency Single Phase Transformer-less Photovoltaic String Inverters

abstract: Two major challenges in the transformer-less, single-phase PV string inverters are common mode leakage currents and double-line-frequency power decoupling. In the proposed doubly-grounded inverter topology with innovative active-power-decoupling approach, both of these issues are simultaneously addressed. The topology allows the PV negative terminal to be directly connected to the neutral, thereby eliminating the common-mode ground-currents. The decoupling capacitance requirement is minimized by a dynamically-variable dc-link with large voltage swing, allowing an all-film-capacitor implementation. Furthermore, the use of wide-bandgap devices enables the converter operation at higher switching frequency, resulting in smaller magnetic components. The operating principles, design and optimization, and control methods are explained in detail, and compared with other transformer-less, active-decoupling topologies. A 3 kVA, 100 kHz single-phase hardware prototype at 400 V dc nominal input and 240 V ac output has been developed using SiC MOSFETs with only 45 μF/1100 V dc-link capacitance. The proposed doubly-grounded topology is then extended for split-phase PV inverter application which results in significant reduction in both the peak and RMS values of the boost stage inductor current and allows for easy design of zero voltage transition. A topological enhancement involving T-type dc-ac stage is also developed which takes advantage of the three-level switching states with reduced voltage stress on the main switches, lower switching loss and almost halved inductor current ripple. In addition, this thesis also proposed two new schemes to improve the efficiency of conventional H-bridge inverter topology. The first scheme is to add an auxiliary zero-voltage-transition (ZVT) circuit to realize zero-voltage-switching (ZVS) for all the main switches and inherent zero-current-switching (ZCS) for the auxiliary switches. The advantages include the provision to implement zero state modulation schemes to decrease the inductor current THD, naturally adaptive auxiliary inductor current and elimination of need for large balancing capacitors. The second proposed scheme improves the system efficiency while still meeting a given THD requirement by implementing variable instantaneous switching frequency within a line frequency cycle. This scheme aims at minimizing the combined switching loss and inductor core loss by including different characteristics of the losses relative to the instantaneous switching frequency in the optimization process.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

Design of miniaturized radio-frequency DC-DC power converters

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 321-325).Power electronics appear in nearly every piece of modern electronic hardware, forming an essential conduit from electrical source to load. Portable electronics, an area where a premium is placed on size, weight, and cost, are driving the development of power systems with greater density and better manufacturability. This motivates a push to higher switching frequencies enabling smaller passive components and better integration. To realize these goals this thesis explores devices, circuits, and passives capable of operating efficiently into the VHF regime (30-300 MHz) and their integration into power electronic systems of high power density. A good integrated power MOSFET presages high-density converters. Previous VHF systems were demonstrated with bulky and expensive RF Lateral, Double-Diffused MOSFETs (LDMOSFET). We show that through a combination of layout optimization and safe operating area (SOA) extension integrated devices can achieve near-parity performance to their purpose-built RF discrete cousins over the desired operating regime. A layout optimization method demonstrating a 2x reduction in device loss is presented alongside experimental demonstration of SOA extension. Together the methods yield a 3x reduction in loss that bolsters the utility of the typical (and relatively inexpensive) LDMOS IC power process for VHF converters. Passive component synthesis is addressed in the context of an isolated VHF converter topology. We present a VHF topology where most of the magnetic energy storage is accomplished in a transformer that forms an essential part of the resonant network. The reduced component count aids in manufacturability and size, but places difficult requirements on the transformer design. An algorithm for synthesizing small and efficient air-core transformers with a fully-constrained inductance matrix is presented. Planar PCB transformers are fabricated and match the the design specifications to within 15%. They are 94% efficient and have a power density greater than 2kW per cubic inch. To take full advantage of good devices and printed passives, we develop an IC for the isolated converter having optimized power devices, and integrated gate driver, controller, and hotel functions. The chip is assembled into a complete converter system using the transformers and circuits described above. Flip-chip mounting is used to overcome bondwire parasitics, and reduce packaging volume. The final system achieves 75% efficiency at 75 MHz at 6W.by Anthony D. Sagneri.Ph.D