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An Augmented DC-DC Buck Converter Using Auxiliary-Stage with Multple-Single-Cycle Non-Linear Control (MSCNLC) For Fast Load Transient Response

Description
High density dc/dc power management system for computing, automotive, and industry applications requires Power-Management-Integrated-Circuits (PMICs) to present high power-density/efficiency and fast transient response. Recently, state-of-the-art digital loads such as micro-processors, DSPs and FPGAs with high current slewing characteristics and tight supply voltage margin put increasing demand on the supply regulators.…

High density dc/dc power management system for computing, automotive, and industry applications requires Power-Management-Integrated-Circuits (PMICs) to present high power-density/efficiency and fast transient response. Recently, state-of-the-art digital loads such as micro-processors, DSPs and FPGAs with high current slewing characteristics and tight supply voltage margin put increasing demand on the supply regulators. The load transient response of DC-DC buck converters with conventional two-level topology is primarily restricted by the efficiency vs. dynamic-response trade-off. In this paper, an augmented DC-DC buck converter consisting of a lower-frequency main converter and a normally-off fast-switching secondary stage operating in parallel is proposed. The main-stage of the converter uses emulated-current-mode hysteretic control. For the auxiliary transient-suppression stage a nonlinear control scheme termed multiple-single-cycle nonlinear control (MSCNLC) is developed. The proposed augmented regulator improves the load transient response without compromising the overall efficiency of the converter, breaking the well-known efficiency vs. dynamic-response trade-off. The high power-efficiency main-stage operating at switching frequency of 500kHz provides the steady-state DC regulation voltage. The auxiliary-stage adopts a small inductor of 100nH and is only activated when load transient events are detected, providing fast load response and minimizing output voltage deviation. The load transient events are detected through an output capacitor charge tracking circuit, which effectively makes the auxiliary-stage a fast Current-Controlled-Current-Source (CCCS) during load transient response. The buck converter is designed for, VIN=3V-5.5V, VOUT=0.5V-1.1V and ILOAD=0.5A-8A. It is fabricated in 0.18μm BCD process. The measurement results show that with MSCNLC enabled, the undershoot and overshoot is reduced to 27mV and 58mV during the step-up (di/dt=8A/us) and step-down (di/dt=16A/us) response with 2.5A load step by a factor of close to 2, respectively. The recovery time is improved by ~1.7x. The converter achieves a peak efficiency of 90.5% at 2.2W output power with VIN=3.3V and load regulation of 0.63mV/A at VIN=3.3V/5V and VOUT=0.5V/1.1V. The line transient response at VOUT=1V, ILOAD=1.5A for VIN=3V ↔ 3.6V and 4.5V ↔ 5.5V is smaller than the output voltage ripple peak-to-peak magnitude (8mV).
ContributorsGuo, Fan (Author) / Bakkaloglu, Bertan (Thesis advisor) / Kitchen, Jennifer (Committee member) / Ranjram, Mike (Committee member) / Garrity, Douglas (Committee member) / Arizona State University (Publisher)
Created2024

Application of WBG Devices in Power Converters: Topologies, Control, and Hardware Design Considerations

Description
Wide-BandGap (WBG) material-based switching devices such as gallium nitride (GaN) High Electron Mobility Transistors (HEMTs) and Silicon Carbide (SiC) Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) are considered very promising and valuable candidates for replacing conventional Silicon (Si) MOSFETs in various industrial high-frequency high-power applications, mainly because of their capabilities of higher switching…

Wide-BandGap (WBG) material-based switching devices such as gallium nitride (GaN) High Electron Mobility Transistors (HEMTs) and Silicon Carbide (SiC) Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) are considered very promising and valuable candidates for replacing conventional Silicon (Si) MOSFETs in various industrial high-frequency high-power applications, mainly because of their capabilities of higher switching frequencies with less switching and conduction losses. However, to make the most of their advantages, it is crucial to understand the intrinsic differences between WBG-based and Si-based switching devices and investigate effective means to safely, efficiently, and reliably utilize the WBG devices. Firstly, a comprehensive understanding of traditional Modular Multilevel Converter (MMC) topology is presented. Different novel SubModule (SM) topologies are described in detail. The low frequency SM voltage fluctuation problem is also discussed. Based on the analysis, some novel topologies which manage to damp or eliminate the voltage ripple are illustrated in detail. As demonstrated, simulation results of these proposed topologies verify the theory. Moreover, the hardware design considerations of traditional MMC platform are discussed. Based on these, a 6 kW smart Modular Isolated Multilevel Converter (MIMC) with symmetrical resonant converter based Ripple current elimination channels is delivered and related experimental results further verify the effectiveness of proposed topology. Secondly, the evolution of GaN transistor structure, from classical normally-on device to normally-off GaN, is well-described. As the benefits, channel current capability and drain-source voltage are significantly boosted. However, accompanying the evolution of GaN devices, the dynamic on-resistance issue is one of the urgent problems to be solved since it strongly affects the GaN device current and voltage limit. Unlike traditional methods from the perspective of transistor structure, this report proposes a novel Multi-Level-Voltage-Output gate drive circuit (MVO-GD) aimed at alleviating the dynamic on-resistance issue from engineering point of view. The comparative tests of proposed MVO-GD and the standard 2-level gate driver (STD-GD) are conducted under variable test conditions which may affect dynamic on-resistance, such as drain-source voltage, gate current width, device package temperature and so on. The experimental waveforms and data have been demonstrated and analyzed.
ContributorsLIU, YIFU (Author) / Lei, Qin (Thesis advisor) / Ayyanar, Raja (Committee member) / Ranjram, Mike (Committee member) / Mallik, Ayan (Committee member) / Arizona State University (Publisher)
Created2022

Non-Isolated High Gain DC-DC Converters for Electric Vehicle and Renewable Energy Applications

Description
DC-DC converters are widely employed to interface one voltage level with another through step-up or step-down operation. In recent years, step-up DC-DC converters have been a key component in harnessing energy through renewable sources by providing an interface to integrate low voltage systems to DC-AC converters or microgrids. They find…

DC-DC converters are widely employed to interface one voltage level with another through step-up or step-down operation. In recent years, step-up DC-DC converters have been a key component in harnessing energy through renewable sources by providing an interface to integrate low voltage systems to DC-AC converters or microgrids. They find increasing applications in battery and fuel cell electric vehicles which can benefit from high and variable DC link voltage. It is important to optimize these converters for higher efficiency while achieving high gain and high power density. Non-isolated DC-DC converters are an attractive option due to the reduced complexity of magnetic design, smaller size, and lower cost. However, in these topologies, achieving a very high gain along with high efficiency has been a challenge. This work encompasses different non-isolated high gain DC-DC converters for electric vehicle and renewable energy applications. The converter topologies proposed in this work can easily achieve a conversion ratio above 20 with lower voltage and current stress across devices. For applications requiring wide input or output voltage range, different control schemes, as well as modified converter configurations, are proposed. Moreover, the converter performance is optimized by employing wide band-gap devices-based hardware prototypes. It enables higher switching frequency operation with lower switching losses. In recent times, multiple soft-switching techniques have been introduced which enable higher switching frequency operation by minimizing the switching loss. This work also discusses different soft-switching mechanisms for the high conversion ratio converter and the proposed mechanism improves the converter efficiency significantly while reducing the inductor size. Further, a novel electric vehicle traction architecture with low voltage battery and multi-input high gain DC-DC converter is introduced in this work. The proposed architecture with multiple 48 V battery packs and integrated, multi-input, high conversion ratio DC-DC converters, can reduce the maximum voltage in the vehicle during emergencies to 48 V, mitigate cell balancing issues in battery, and provide a wide variable DC link voltage. The implementation of high conversion ratio converter in multiple configurations for the proposed architecture has been discussed in detail and the proposed converter operation is validated experimentally through a scaled hardware prototype.
ContributorsGupta, Ankul (Author) / Ayyanar, Raja (Thesis advisor) / Lei, Qin (Committee member) / Bakkaloglu, Bertan (Committee member) / Ranjram, Mike (Committee member) / Arizona State University (Publisher)
Created2022

Addressing Dielectric Challenges in Power Dense Systems Utilizing Field Grading Materials

Description

As high-power equipment becomes more compact, there is an increasing need for effective insulating materials to ensure reliability. High-voltage systems often face issues with uneven electric fields, especially at ”triple points” where metal, dielectric, and gas meet, leading to material degradation and failure risks. Additionally, advanced semiconductor technology introduces higher…

As high-power equipment becomes more compact, there is an increasing need for effective insulating materials to ensure reliability. High-voltage systems often face issues with uneven electric fields, especially at ”triple points” where metal, dielectric, and gas meet, leading to material degradation and failure risks. Additionally, advanced semiconductor technology introduces higher voltage demands, which challenge dielectric integrity in power electronics, causing frequent partial discharges (PD) and surface flashovers. Square wave voltages, in particular, produce higher magnitude PD events that accelerate insulation aging more than sinusoidal voltages.This Ph.D. project investigates ways to mitigate these electric stresses in high-voltage insulation. First, nonlinear field grading (NLRFG) materials are studied for their ability to reduce electric field stress in equipment like cable joints, and results are modeled in finite element analysis (FEA). Next, capacitive field grading composites (FCFGCs) are tested for PD reduction in motor windings under rapid power electronic pulses. Finally, the effectiveness of NLRFG and FCFGC in mitigating stress on direct bonded copper (DBC) substrates is evaluated, alongside the impact of electret films on reducing PD in liquid metal polymer composites (LMPCs).
ContributorsFaruqe, Omar (Author) / Park, Chanyeop (Thesis advisor) / Bailey, Christopher (Committee member) / Ranjram, Mike (Committee member) / Mantooth, Alan (Committee member) / Arizona State University (Publisher)
Created2025

Control Strategies for Feeder Voltage Management Under High Distributed Energy Resource Penetration and Converter Topology for Grid Edge Devices

Description

The large-scale integration of distributed energy resources (DERs) into the electric grid comes with unforeseen challenges for the utilities. Voltage rise due to the high penetration of DERs is an important problem to be solved to increase renewable energy generation in modern grids. Utilizing grid-connected power converters for improving the…

The large-scale integration of distributed energy resources (DERs) into the electric grid comes with unforeseen challenges for the utilities. Voltage rise due to the high penetration of DERs is an important problem to be solved to increase renewable energy generation in modern grids. Utilizing grid-connected power converters for improving the distribution grid power quality, reliability, and resilience is becoming increasingly popular with the widespread adoption of DERs. This report proposes two distribution grid voltage regulation schemes using DERs to regulate the grid voltage effectively. A distributed voltage control scheme using only local measurements, similar to volt-VAr control, is suggested to overcome some drawbacks related to voltage-reactive power control. An active distribution grid control is proposed to regulate the node voltage for all the nodes in the feeder effectively, with an emphasis on minimizing the total reactive power. These controls are tested on a large, 8000+ node distribution feeder with peak instantaneous penetration of over 230% from DERs. The controls are implemented in a real-time power hardware testbed to validate the implementation and the performance.

In addition to DER inverters, the penetration levels of several other multi-kW scale, grid-edge devices controlled by power electronic converters have also been rapidly increasing. These include on-board electric vehicle chargers, residential energy storage, and high-power computers used for data mining with power levels of 2 kW or above. They all need to meet stringent requirements on harmonic and high-frequency distortion limits, high efficiency, and high power factor with a front-end power factor correction circuit (PFC). Power density is also a very important metric, especially for electric vehicle chargers. This work proposes and experimentally validates a new circuit topology based on an active clamped SEPIC converter for the isolated, power-factor correction circuits well-suited for the above applications.

The increasing integration of Inverter-Based Resources (IBRs) within transmission grids introduces novel challenges related to stability, reliability, and control, which stem from their distinct dynamics, rapid-response characteristics, and limited short-circuit current capability. While traditional simulation tools are proficient, they encounter challenges in accurately depicting the real-time interactions and behaviors of IBRs under various operating conditions. This thesis briefly explores the necessity of digital twins for analyzing IBR-dominant transmission grids, emphasizing their significance in stability analysis. It also proposes a co-simulation framework based on HELICS to develop a digital twin by incorporating multi-domain simulation tools such as ePHASORSIM and PSCAD, facilitating a comprehensive real-time simulation for large-scale IBR-dominant power systems.
ContributorsSondharangalla, Madhura B (Author) / Ayyanar, Raja (Thesis advisor) / Vittal, Vijay (Committee member) / Ranjram, Mike (Committee member) / Srinivasan, Devarajan (Committee member) / Arizona State University (Publisher)
Created2025

Advanced Edge Computing and Monitoring for High Impedance Fault Detection in Distribution Systems

Description
Total situational awareness is imperative for a healthy and safe grid. As more distributive energy resources (DERs) are connected to grid, the grid becomes more decentralized, meaning generation can be more widespread than relying solely on large plants burning fossil fuels or using water to spin generators far away from…

Total situational awareness is imperative for a healthy and safe grid. As more distributive energy resources (DERs) are connected to grid, the grid becomes more decentralized, meaning generation can be more widespread than relying solely on large plants burning fossil fuels or using water to spin generators far away from loads. Photovoltaic inverters are one such DER. They convert direct current (dc) which is produced by solar panels into alternating current (ac) to transmit on the grid. However, their advent introduces a variety of issues that must be tackled as utility companies and homeowners begin implementing more in everyday use. Voltage regulation can be difficult during times of high solar generation. In addition, if faults occur, they must be detected and cleared as soon as possible. Inverters are becoming smarter and their features can help solve some of these issues. Edge data (i.e. from inverters) must swiftly and securely reach a centralized controller for system operators to effectively take care of the grid. This is done with Supervisory Control and Data Acquisition (SCADA) protocols as well as internet connectivity through MQTT. In addition, operators must be able to send commands to individual generators to control power generation during peaks and dips to ensure grid stability. Thus, a secure two-way communications system is critical to achieving issues related to introducing greener energy sources. Once information from the edge-side inverter reaches the cloud, machine learning algorithms can use them to infer potential faults and locate them. This report will dive into the details of why green DERs are being added to the grid, various SCADA protocols, the OSI model for internet connectivity, and present the lab work prepared, including modeling a real feeder in real time for communication testing and OpenDSS for fault studies. Two gateway devices are developed and implementation is extensively detailed. With voltage data from the inverters in the cloud, a number of machine learning algorithms are built and tested for high impedance fault detection on the feeder model. A summary of scientific contributions to the community is also given, including publications and presentations.
ContributorsMoldovan, Dan (Author) / Ayyanar, Raja (Thesis advisor) / Srinivasan, Devarajan (Committee member) / Ranjram, Mike (Committee member) / Goryll, Michael (Committee member) / Arizona State University (Publisher)
Created2024