Author Archives: Koushik

Resistive Superconducting Fault current limiter integrated with Hybrid DC Circuit Breakers for HVDC System Protection

High voltage direct current (HVDC) transmission system in the subsea industry is being considered as an efficient power transmission solution as the number of power conductors and the reactive power consumption are minimal. However, one of the key challenges in HVDC transmission systems lies in the lack of reliability against short circuit faults. Serious faults can generate surge currents more than one hundred times the normal operating currents. These faults can result in damage to expensive equipment if circuit breakers (CBs) are not fast enough and rated for such a high level of faults. For offshore HV transmission systems, the cost of an unplanned outage as a result of a fault on a HVDC export cable is typically 10-fold to 100-fold the cost of the same failures in onshore HV networks. In view of this, it is desirable to introduce a reliable means of limiting the fault currents so that the CBs open at lower fault currents without any damage.


Resistive-type superconducting fault current limiters (R-SFCLs) made with high-temperature superconducting (HTS) tapes are expected to be the most effective, small-sized and offer reliable protection against such faults due to high critical current density and quick superconducting to normal-state transition. In this project, the fault current limiting performance of DCCB topology, without and with R-SFCL integration, is obtained. Further, the response time of various CB topologies like MCB, Resonant CB (RCB), IGBT based HCB (similar to ABB topology) and thyristor based CIHCB (also called DCCB topology) are also investigated. The integration of R-SFCL decreases the peak current flowing through the breaker, and this enables reduction in the size of breaker. Further, the power loss of CBs for different response time of R-SFCL is analyzed to select the superconductors for R-SFCL and suitable CB topology for future subsea HVDC power transmission systems.

Multi-Port Energy Router Using Intelligent Transformers (MERIT) To Interconnect Renewable Resources

Nearly 1,500 oil and gas (O&G) rigs are located offshore across the globe, the largest share of which are in the North Sea and Gulf of Mexico. The recent trend in O&G industry is to install the subsea processing loads on the seabed for reducing the required space on the platform or even removing the platform altogether. The subsea processes (or subsea factory) include gas compression, boosting, water injection, and separation. Typical power consumption of the Subsea loads is in the range of 5-300 MW, traditionally supplied by local gas turbines or diesel generators. Such power generation strategies have led to significant increase in greenhouse gas emissions. Also, the electric distribution system of O&G platforms is characterized as a weak electric grid, resulting in poor power quality, lower power factor, voltage and current harmonics, voltage notches, and common mode voltages. All these result in increased losses and also affect the long-term reliability.

Block diagram of the system for integration of renewable energy sources

This project proposes a system of Multi-port Energy Routers using Intelligent Transformers (MERIT) to interface renewable resources and subsea O&G factories with the HVDC (or MVDC) Grid. In this project, we will investigate combining the energy from wind, wave, floating PV panels and fuel cell – based generators, all located near the subsea factories, to power the loads. Intelligent power converters, including solid state transformers (SSTs), are critical to enhance the power density, reliability and efficiency of the proposed MERIT system. SSTs enable seamless interconnectivity and interoperability between the various energy sources. SSTs support features such as instantaneous voltage compensation, power outage compensation, fault isolation, bi-directional power flow, etc. This research will also investigate how to optimally design and integrate SSTs into the MERIT system to have the best performance both during transient and steady state conditions. It is expected that widespread implementation of the proposed synergies can lead to over 50 % reduction in emissions.

As one of the foremost requirements of a subsea power delivery system is reliability, HVDC protection units must conform to extremely stringent specifications in terms of fault interruption time and fault level. However, a major challenge in the growth of DC power market is the lack of reliable protection against short-circuit faults. A fault in a DC system results in fast ramp up of the fault current. Moreover, DC fault current does not experience any natural zero-crossing. Therefore, DC circuit breakers (DCCBs) should be capable of fast fault quenching in order to prevent damage to the DC system and maintain grid resiliency. Additionally, a DCCB should operate with minimal power loss as a closed switch. Fault interruption using a DCCB causes enormous energy dissipation and voltage stress. If a DC fault current is 4-5 times higher than the rated DCCB, then it cannot work efficiently without expanding its components. Therefore, the use of a fault current limiter is essential, and the superconducting fault current limiter (SFCL) is the most promising choice together with a fast-switching DCCB in series. Resistive type superconducting fault current limiter (R-SFCL) is one of the most ideal, compact, small size current limiting devices to protect the power system and electrical equipment. It can limit the fault current effectively in power systems where CBs can work safely and prevent damage to the circuit components within several milliseconds.

Computer Vision-based Framework for Power Converter Identification and Analysis

This research work is mainly focused on identifying the individual components in a hand-drawn schematic diagram, and thus performing simulative analysis of a power converter. YOLOR (You Only Learn One Representation) – the state-of-the-art deep learning-based object detection model is used to detect the electronic components i.e. resistor, capacitor, diode, etc. in a circuit diagram. A Hough transform algorithm is used to trace the horizontal and vertical wire connection, whereas KMeans clustering is used to segregate the points-of-intersection between those horizontal and vertical lines to identify the nodes in the circuit. By using all of this circuit information, a netlist of the circuit is generated – that can be fed into any spice-based circuit simulators. In this work, PySpice – an open-source python module, is used to auto-simulate the identified hand-drawn schematic diagram. In future, this work will be extended to automate the PCB design of the detected hand-drawn circuit diagram. The overall workflow algorithm of this research work is as depicted in the flowchart.

Proposed method for the automated simulation of a hand-drawn schematic of the power converters

Power Conversion for 4G/5G Envelope Tracking

Wireless communication uses radio frequency power amplifiers (RFPAs) to amplify the signal before transmitting. Traditional RFPAs in communication base stations use fixed voltage DC power supplies. For the communication signal with high peak to average power ratio (PAPR), linear RFPAs will be inefficient and excess power will dissipate as heat. Therefore, a larger cooling system will be required and make communication base station system bulky. To improve the efficiency and miniaturize the system, envelope tracking power supplies are being used. Envelope tracking (ET) power supply utilize envelope extractor to obtain the envelope of the transmitted signal waveform. The output voltage is modulated to track the envelope of communication signal and supply the RFPAs. Communication signal will be distorted if the converter switching frequency is less than signal bandwidth. Thus, ET power supplies are required to switch at several tens of MHz for 4G/5G signals.


4-phase Buck Converter for 4G Envelope Tracking

Gallium Nitride-Based Miniaturized Pulsed Power System Architecture for Mission-Critical Applications (ARPA-E)

This project involves technology that will improve the converter system’s power density, efficiency, and operational life across pulsed power applications such as healthcare tech (e.g., MRI) and water purification; where the miniaturized size of the system will also disruptively reduce the cost of downhole well logging tools used in fossil and geothermal energy production. The project is funded by the U.S. Department of Energy’s Advanced Research Projects Agency with a $1 million grant for three years starting in April 2022. Part of the project will include designing a DC-DC converter with a few Kilowatts and the capability to work with high-temperature operations up to 175 degrees Celsius for downhole tools to perform sub-surface characterization and the other part involved power converter development for MRI application.

High Density Power Conversion Using GaN devices and Machine Learning Based Prediction of Remaining Useful Life

Characterization of GaN devices at
different load profiles

This project focuses on the development of compact and robust power electronics systems for military installations, especially on ships and aircraft with limited space onboard. It is funded by the U.S. Department of Defense with a $2.5 million grant for three years starting in April 2020. Using Gallium Nitride (GaN) power technology, the first part of the project includes developing power converters using gallium nitride (GaN) devices, capable of quickly storing and discharging energy to operate the radar systems. With higher operating switching frequency, it is contributed to allows passive components in the circuit – including capacitors and inductors – to be designed at much smaller dimensions.

The other part focused on using machine learning to predict the lifespan of GaN devices, as well as of circuits employing these devices – based on real datasets. The use of GaN technology in power applications is relatively new, and online assessing how long they will continue to operate in a circuit remains a challenge. Hence, this part focuses on designing a compact-onboard health monitoring to predict the lifetime of individual components, primarily GaN and capacitors that may be extended to other components as well. This project involved the support of Tagore Technology, a semiconductors company based in Arlington Heights, Illinois, USA.

Characterization of electrolytic capacitors
at different load profiles

Bharat Bohara

Bharat Bohara received his Bachelors of Engineering (B.E) in Electrical and Electronics Engineering from the Kathmandu University (KU), Nepal in 2015, and Masters of Technology (M.Tech) in Energy and Control System Engineering from the Indian Institute of Technology (IIT) Bombay, India in 2019. He worked as a Computer Vision Engineer from Aug. 2019 to Aug. 2021 at the Emotix, a robotic startup company in India that builds AI-based companion robots for children. He is currently pursuing a Ph.D in Electrical and Computer Engineering at the University of Houston, TX, USA. His research interests include applications of machine learning in power electronics, computer vision, reinforcement learning, and efficient neural network implementation in FPGAs.

TITLE

Ph.D Student

EMAIL

bbohara@cougarnet.uh.edu

OFFICE

N308 Engineering Building 1