Opening the Box: Survey of High Power Density Inverter Techniques From the Little Box Challenge

The Little Box Challenge (LBC) was a competition sponsored by Google and the IEEE Power Electronics Society in 2014-2015, where participants were challenged to design a high power-density single-phase 2 kVA inverter. This paper surveys the designs from eight different participating teams, including academic grant awardees, finalists, and the winners. Inverter topologies, power decoupling circuits, and thermal management strategies are overviewed for each team. Wide bandgap switches were heavily utilized in both the inverter and power decoupling circuits, particularly GaN switches. Most teams utilized a full-bridge inverter with some variations and the most common power decoupling strategy was the use of a synchronous buck converter and a power buffering capacitor. One team used a multi-level inverter approach and a number of teams proposed innovative power decoupling topologies. Heat sinks and active cooling systems, many of which were custom made, were crucial for teams to stay within the 50 ??C case temperature limit. The resulting power density of the surveyed teams ranged from 55.8 to 216 W/in3, all of which exceed the 50 W/in3 LBC requirement. This paper surveys the approaches for various teams, shares experimental results from the Taiwan Tech team, and highlights some innovations from the teams that participated in the LBC

Trade-off study of heat sink and output filter volume in a GaN HEMT based single phase inverter

This paper presents the trade-off study of heat sink and output filter volume of a GaN HEMT based single phase inverter. The selected topology is three-level Active Neutral point Clamped (ANPC) inverter, and the main aim is to explore the benefits of the GaN HEMTs at 600 V blocking class on the system level efficiency, and power density under wide range of operating conditions. The paper starts by introducing the inverter topology, selected PWM scheme and followed by the device features, static and dynamic characterisation and continues with presenting and discussing the results of extensive experimental and analytical characterisation. After this, the impact of GaN HEMTs on inverter volume is discussed in terms of heat sink and output filter volume analysis under different switching frequency and heat sink temperature conditions. The calculation of heat sink volume and single stage LC output filter volume are presented with respect to experimental results of single phase prototype. The findings from static, dynamic characterisation and single phase prototype results clearly show that GaN HEMT has excellent switching performance under wide load current and heat sink temperature conditions. The high performance of the inverter lead to reduction of the combined total volume, including output filter and heat sink volume

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

Toward high-efficiency high power density single-phase DC-AC and AC-DC power conversion - architecture, topology and control

Power conversion between the single-phase AC grid and DC sources or loads plays an indispensable role in modern electrical energy system for both generation and consumption. The renewable resources and electrical energy storage are integrated to the grid through inverters. Telecoms, data centers and the rest of the digital world is powered by the grid through rectifiers. Existing and emerging applications all demand the DC-AC and AC-DC systems to be not only more efficient to reduce energy consumption, but also more compact to reduce cost and improve portability. Therefore, new AC-DC and DC-AC converter designs that improve the efficiency and power density of the system is a critical area of research and is the focus of this dissertation. The recent development of wide band-gap devices stimulates a new round of improvement on efficiency and power density of AC-DC converters. However, despite the new transistors used, the fundamental system architecture and topology remain relatively unchanged, which is becoming the bottleneck for further improvement. This dissertation explores new architecture, topology and control to overcome this bottleneck, targeting an order-of-magnitude improvement on power density and comparable efficiency to the conventional design. The proposed solutions build on two key innovations: the series-stacked buffer architecture for twice-line-frequency power pulsation decoupling in single-phase AC-DC and DC-AC conversion, and the flying capacitor multilevel topology for power transfer and waveform conversion between AC and DC. This work provides complete solutions for these ideas, including the theoretical development, design procedure, control method, hardware implementation and experimental characterization

A comprehensive review on modular multilevel converters, submodule topologies, and modulation techniques

The concept of the modular multilevel converter (MLC) has been raising interest in research in order to improve their performance and applicability. The potential of an MLC is enormous, with a great focus on medium- and high-voltage applications, such as solar photovoltaic and wind farms, electrified railway systems, or power distribution systems. This concept makes it possible to overcome the limitation of the semiconductors blocking voltages, presenting advantageous characteristics. However, the complexity of implementation and control presents added challenges. Thus, this paper aims to contribute with a critical and comparative analysis of the state-of-the-art aspects of this concept in order to maximize its potential. In this paper, different power electronics converter topologies that can be integrated into the MLC concept are presented, highlighting the advantages and disadvantages of each topology. Nevertheless, different modulation techniques used in an MLC are also presented and analyzed. Computational simulations of all the modulation techniques under analysis were developed, based on four cascaded full-bridge topologies. Considering the simulation results, a comparative analysis was possible to make regarding the symmetry of the synthesized waveforms, the harmonic content, and the power distribution in each submodule constituting the MLC.This work has been supported by FCT—Fundação para a Ciência e Tecnologia, within the R&D Units Project Scope UIDB/00319/2020. Mr. Luis A. M. Barros is supported by the doctoral scholarship PD/BD/143006/2018, granted by the Portuguese FCT foundation

Photovoltaic potential in building façades

Tese de doutoramento, Sistemas Sustentáveis de Energia, Universidade de Lisboa, Faculdade de Ciências, 2018Consistent reductions in the costs of photovoltaic (PV) systems have prompted interest in applications with less-than-optimum inclinations and orientations. That is the case of building façades, with plenty of free area for the deployment of solar systems. Lower sun heights benefit vertical façades, whereas rooftops are favoured when the sun is near the zenith, therefore the PV potential in urban environments can increase twofold when the contribution from building façades is added to that of the rooftops. This complementarity between façades and rooftops is helpful for a better match between electricity demand and supply. This thesis focuses on: i) the modelling of façade PV potential; ii) the optimization of façade PV yields; and iii) underlining the overall role that building façades will play in future solar cities. Digital surface and solar radiation modelling methodologies were reviewed. Special focus is given to the 3D LiDAR-based model SOL and the CAD/plugin models DIVA and LadyBug. Model SOL was validated against measurements from the BIPV system in the façade of the Solar XXI building (Lisbon), and used to evaluate façade PV potential in different urban sites in Lisbon and Geneva. The plugins DIVA and LadyBug helped assessing the potential for PV glare from façade integrated photovoltaics in distinct urban blocks. Technologies for PV integration in façades were also reviewed. Alternative façade designs, including louvers, geometric forms and balconies, were explored and optimized for the maximization of annual solar irradiation using DIVA. Partial shading impacts on rooftops and façades were addressed through SOL simulations and the interconnections between PV modules were optimized using a custom Multi-Objective Genetic Algorithm. The contribution of PV façades to the solar potential of two dissimilar neighbourhoods in Lisbon was quantified using SOL, considering local electricity consumption. Cost-efficient rooftop/façade PV mixes are proposed based on combined payback times. Impacts of larger scale PV deployment on the spare capacity of power distribution transformers were studied through LadyBug and SolarAnalyst simulations. A new empirical solar factor was proposed to account for PV potential in future upgrade interventions. The combined effect of aggregating building demand, photovoltaic generation and storage on the self-consumption of PV and net load variance was analysed using irradiation results from DIVA, metered distribution transformer loads and custom optimization algorithms. SOL is shown to be an accurate LiDAR-based model (nMBE ranging from around 7% to 51%, nMAE from 20% to 58% and nRMSE from 29% to 81%), being the isotropic diffuse radiation algorithm its current main limitation. In addition, building surface material properties should be regarded when handling façades, for both irradiance simulation and PV glare evaluation. The latter appears to be negligible in comparison to glare from typical glaze/mirror skins used in high-rises. Irradiation levels in the more sunlit façades reach about 50-60% of the rooftop levels. Latitude biases the potential towards the vertical surfaces, which can be enhanced when the proportion of diffuse radiation is high. Façade PV potential can be increased in about 30% if horizontal folded louvers becomes a more common design and in another 6 to 24% if the interconnection of PV modules are optimized. In 2030, a mix of PV systems featuring around 40% façade and 60% rooftop occupation is shown to comprehend a combined financial payback time of 10 years, if conventional module efficiencies reach 20%. This will trigger large-scale PV deployment that might overwhelm current grid assets and lead to electricity grid instability. This challenge can be resolved if the placement of PV modules is optimized to increase self-sufficiency while keeping low net load variance. Aggregated storage within solar communities might help resolving the conflicting interests between prosumers and grid, although the former can achieve self-sufficiency levels above 50% with storage capacities as small as 0.25kWh/kWpv. Business models ought to adapt in order to create conditions for both parts to share the added value of peak power reduction due to optimized solar façades.Fundação para a Ciência e a Tecnologia (FCT), SFRH/BD/52363/201

Development of a vertical oscillator energy harvester: design and testing of a novel renewable resource power conversion system

Thesis (M.S.) University of Alaska Fairbanks, 2020Remote Alaska communities have historically dealt with elevated electric power expenses due to high cost of transporting diesel fuel for power generation. To offset this cost, the installation of various renewable resources have been utilized, particularly wind and solar power. Hydrokinetic generation by harnessing river flows is an emerging and less commonly implemented renewable resource that offers great potential for power generation. Specifically, this study investigates the behavior of a novel concept for harnessing vertical oscillation that occurs when a bluff body is inserted into a flow path. Unlike traditional rotating turbines used in hydrokinetic energy, this particular device utilizes the fluid structure interactions of vortex-induced-vibration and gallop. Due to the unique characteristics of this vertical motion, a thorough examination of the proposed system was conducted via a three-pronged approach of simulation, emulation, and field testing. Using a permanent magnet synchronous generator as the electrical power generator, an electrical power conversion system was simulated, emulated, and tested to achieve appropriate power smoothing for use in microgrid systems present in many Alaskan rural locations.Alaska Center for Energy and Power (ACEP) at the University of Alaska Fairbanks (UAF)Chapter 1. Introductory material -- 1.1. Introduction -- 1.2. Research problem and objectives -- 1.3. Hydrokinetic power advantages -- 1.4. Hydrokinetic power difficulties -- 1.5. Vertical oscillator dynamics -- 1.6. Generator considerations -- 1.7. Generation stability -- 1.8. Power conversion -- 1.9. Harmonics -- 1.10. Thesis organization. Chapter 2. Literature review of relevant topics -- 2.1. Introduction -- 2.2. Generators -- 2.2.1. Synchronous generators -- 2.2.2. Induction generators -- 2.2.3. DC generators -- 2.3. Power conversion -- 2.3.1. rectifiers -- 2.3.2. DC converters -- 2.3.3. Inverters -- 2.3.4. Conversion efficiency -- 2.4. Microgrids -- 2.4.1. Distributed energy resources -- 2.4.2. Loads (demand) -- 2.4.3. Energy storage -- 2.4.4. Microgrid frequency response -- 2.5. Hydrokinetic power smoothing -- 2.5.1. Energy storage power smoothing -- 2.6. Maximum power point tracking (MPPT) -- 2.7. Conclusion. Chapter 3. Generator selection and modeling -- 3.1. Introduction -- 3.2. PMSG physical construction -- 3.3. Generator operating characteristics -- 3.4. Generator manufacturer's data -- 3.5. Model development -- 3.5.1. Permanent magnet synchronous generator block -- 3.5.2. Diode rectifier -- 3.5.3 DC link smoothing components -- 3.5.4. Inverter -- 3.6 Simulink® simulations -- 3.7. Model verification -- 3.8.Conclusion. Chapter 4. Test bench construction and experimental results -- 4.1. Introduction -- 4.2. Laboratory power supply -- 4.3. Prime mover -- 4.4. Variable frequency drive and circuit breaker -- 4.5. Transformer -- 4.6. load banks -- 4.7. Instrumentation -- 4.7.1. Precision power analyzer -- 4.7.2. LEM module -- 4.7.3. Current transformers (CTs) -- 4.7.4. Torque sensor -- 4.7.5. Power supply -- 4.7.6. Oscilloscope -- 4.7.7. multimeter -- 4.7.8. Tachometer -- 4.8. Miscellaneous supplies -- 4.9 Test bench design summary -- 4.10. Test bench experimental results -- 4.11. Conclusion. Chapter 5. Vertical oscillator design, construction, and field testing -- 5.1. Introduction -- 5.2. Vertical oscillator design and construction -- 5.2.1. Debris diverter -- 5.2.2. Bluff body -- 5.2.3. Power take-off system -- 5.2.4. Field testing electrical system -- 5.2.5. Mechanical system instruments -- 5.3. Field testing results -- 5.4. Field testing difficulties -- 5.5. Conclusion. Chapter 6. Power signal conditioning -- 6.1. Introduction -- 6.2. Power conditioning topologies -- 6.2.1. AC-DC-DC-AC topology -- 6.2.2. PMSG VFD with regenerative capability topology -- 6.2.3. Battery charge controller topology -- 6.3. Power converter design considerations -- 6.3.1. Power conversion -- 6.3.2. Inverter selection -- 6.3.3. Battery charging pulsations -- 6.4. Battery charging system simulation -- 6.4.1. Battery charging and DC load modeling -- 6.4.2. Battery charging topology with single-phase inverter -- 6.4.3. Battery charging topology with three-phase inverter -- 6.5. Conclusion. Chapter 7. Conclusion, future work, and lessons learned -- 7.1. Conclusion -- 7.1.1. Generator selection & modeling conclusions -- 7.1.2. Laboratory testing conclusions -- 7.1.3. Field testing conclusions -- 7.1.4. Power conditioning design conclusions -- 7.1.5. Final conclusions -- 7.2. Future work -- 7.3. Final thoughts -- References -- Appendices

A Novel Microgrid Demand-Side Management System for Manufacturing Facilities

Thirty-one percent of annual energy consumption in the United States occurs within the industrial sector, where manufacturing processes account for the largest amount of energy consumption and carbon emissions. For this reason, energy efficiency in manufacturing facilities is increasingly important for reducing operating costs and improving profits. Using microgrids to generate local sustainable power should reduce energy consumption from the main utility grid along with energy costs and carbon emissions. Also, microgrids have the potential to serve as reliable energy generators in international locations where the utility grid is often unstable. For this research, a manufacturing process that had approximately 20 kW of peak demand was matched with a solar photovoltaic array that had a peak output of approximately 3 KW. An innovative Demand-Side Management (DSM) strategy was developed to manage the process loads as part of this smart microgrid system. The DSM algorithm managed the intermittent nature of the microgrid and the instantaneous demand of the manufacturing process. The control algorithm required three input signals; one from the microgrid indicating the availability of renewable energy, another from the manufacturing process indicating energy use as a percent of peak production, and historical data for renewable sources and facility demand. Based on these inputs the algorithm had three modes of operation: normal (business as usual), curtailment (shutting off non-critical loads), and energy storage. The results show that a real-time management of a manufacturing process with a microgrid will reduce electrical consumption and peak demand. The renewable energy system for this research was rated to provide up to 13% of the total manufacturing capacity. With actively managing the process loads with the DSM program alone, electrical consumption from the utility grid was reduced by 17% on average. An additional 24% reduction was accomplished when the microgrid and DSM program was enabled together, resulting in a total reduction of 37%. On average, peak demand was reduced by 6%, but due to the intermittency of the renewable source and the billing structure for peak demand, only a 1% reduction was obtained. During a billing period, it only takes one day when solar irradiance is poor to affect the demand reduction capabilities. To achieve further demand reduction, energy storage should be introduced and integrated

A Novel Microgrid Demand-Side Management System for Manufacturing Facilities

Thirty-one percent of annual energy consumption in the United States occurs within the industrial sector, where manufacturing processes account for the largest amount of energy consumption and carbon emissions. For this reason, energy efficiency in manufacturing facilities is increasingly important for reducing operating costs and improving profits. Using microgrids to generate local sustainable power should reduce energy consumption from the main utility grid along with energy costs and carbon emissions. Also, microgrids have the potential to serve as reliable energy generators in international locations where the utility grid is often unstable. For this research, a manufacturing process that had approximately 20 kW of peak demand was matched with a solar photovoltaic array that had a peak output of approximately 3 KW. An innovative Demand-Side Management (DSM) strategy was developed to manage the process loads as part of this smart microgrid system. The DSM algorithm managed the intermittent nature of the microgrid and the instantaneous demand of the manufacturing process. The control algorithm required three input signals; one from the microgrid indicating the availability of renewable energy, another from the manufacturing process indicating energy use as a percent of peak production, and historical data for renewable sources and facility demand. Based on these inputs the algorithm had three modes of operation: normal (business as usual), curtailment (shutting off non-critical loads), and energy storage. The results show that a real-time management of a manufacturing process with a microgrid will reduce electrical consumption and peak demand. The renewable energy system for this research was rated to provide up to 13% of the total manufacturing capacity. With actively managing the process loads with the DSM program alone, electrical consumption from the utility grid was reduced by 17% on average. An additional 24% reduction was accomplished when the microgrid and DSM program was enabled together, resulting in a total reduction of 37%. On average, peak demand was reduced by 6%, but due to the intermittency of the renewable source and the billing structure for peak demand, only a 1% reduction was obtained. During a billing period, it only takes one day when solar irradiance is poor to affect the demand reduction capabilities. To achieve further demand reduction, energy storage should be introduced and integrated