Active Projects

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Grid-Interactive Smart Inverters

A grid-interactive inverter featuring ancillary services and power sharing is called a smart inverter. However, broader functionalities will be necessary for the next generation of inverters. These features can be categorized as self-governing, self-adapting, self-security, and self-healing. Therefore, high-penetration of inverter-based grid-interactive power generators, particularly renewable energy sources, can be implemented.

Goal: To operate in grid-forming and grid-supporting control modes, achieve stable dynamics under varying grid conditions, detect malicious setpoints due to cyber-physical attacks, reduce the stress, and tolerate the fault under anomalies.

Techniques Proposed: A reference model approach is proposed to examine and determine cyberattacks versus healthy supervisory control commands from the utility.

Hardware Set-up: 12 kW GaN-based grid interactive smart inverter test bed is under development.

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Control and Stability Enhancement of Grid-Interactive Voltage Source Inverters under Grid Abnormalities.

Voltage source inverters (VSIs) serve as a necessary interface for grid integration of renewable energy resources and energy storage systems. However, the operation of grid-interactive VSIs is sensitive to grid abnormalities. Therefore, different control and stability enhancement techniques have been developed to mitigate these grid abnormalities.

Goal: To improve the control and stability of the grid-interactive VSIs under grid anomalies.

Techniques Proposed: A feed-forward virtual inductance control strategy is developed to enhance the stability of VSIs. Moreover, a signal reformation based direct phase-angle detection (DPD-SR) technique for three-phase inverters supporting asymmetrical grids has been developed.

Hardware Set-up: The proposed techniques' performance is verified through a three-phase grid-interactive hardware setup, where a three-phase 20kW Allen-Bradley Powerflex 755 VSI and a 12 kW Primate Power grid emulator is utilized.

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Smart Three-Phase Power Converters for More Electric Powertrains

Electric powertrains are directly coupled to the engines. Hence, constant voltage magnitude and variable-frequency is generated. This changing frequency can cause parameter mismatch and affect the dynamic performance of variable-frequency converters. To address this issue, "Smart Three-Phase Power Converters for More Electric Powertrains" is developed.

Goal: To seamlessly regulate the output DC voltage while maintaining unity power factor with very low total harmonic distortion in three-phase input currents.

Techniques Proposed: Different control techniques are proposed for this application such as a Lyapunov-based adaptive parameter estimation algorithm, a multi-variable direct model reference adaptive control, and step-ahead predictive control.

Hardware Set-up: 1.5 kW SiC-MOSFET two-level voltage-source converter topology is used.

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Synchronous Machine Design with Finite Element Analysis

There are three significant parts such as design, optimization, and material selection for the electric machines and wireless power transfer devices. The finite element-based computational tools like ANSYS is convenient and powerful to assist in electrical machine design, wireless charger design, and performance estimation.

Goal: To design synchronous, permanent magnet, induction machines, reconstruct 3-D coils for wireless charger circuits for electric vehicles, analyze their magnetic behaviors, decrease the capital cost while improving system reliability using 3-D Finite Element (FE) analysis including 3-D time-stepping finite element circuit analysis.

Techniques Proposed: A novel asymmetrical multi-coil wireless electric vehicle charger device with improved misalignment tolerance and enhanced charging profile is developed.

Software Set-up: ANSYS software is used to design a 1.5 MW generator for direct-drive wind turbines.

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Completed Projects

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A Boost Current Source Inverter-Based Generator-Converter Topology for Direct Drive Wind Turbines

In wind energy conversion systems, nearly 30% of the failures can be attributed to the DC bus electrolytic capacitors. To address this issue in direct-drive wind turbine systems, the grid-side converter is replaced with a boost current source inverter (CSI). Moreover, novelty of the proposed technique lies in utilizing the synchronous inductance of the permanent magnet generators as the DC-link inductor. Thus, weight and volume can be reduced, and overall system efficiency can be enhanced.

Goal: To eliminate the use of electrolytic capacitors, convert low DC voltage to higher three-phase AC voltage with relatively high boost ratio, reduce the system cost, and increase the efficiency.

Techniques Proposed: Phasor pulse-width modulation (PPWM) technique is proposed to to control the boost current source inverter.

Hardware Set-up: 1.5 kW, 240 V laboratory scale set-up includes an eight-pole permanent magnet synchronous generator, SiC-based three-phase voltage source converter connected to the turbine side, and the VSC is connected to boost CSI which is formed using reverse-blocking-insulated gate bipolar transistors (RG-IGBTs).

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Design and Control of Smart Loads in Nanogrids

Nanogrid is defined as a medium-to-low voltage power grid with the capability of operation in islanded mode using low or no inertia sources. One of the challenges in low-inertia power generation is voltage and power fluctuations due to pulse loads and abnormal grid conditions. To mitigate voltage and power oscillations in islanded nanogrids, critical loads are connected in series with voltage source inverters, that form smart load configuration, to establish grid-connection.

Goal: To compensate voltage and power deviations caused by load variations, power generation, and abnormal grid conditions as well as reducing the stress on the energy storage units. Number of battery banks can also be reduced.

Techniques Proposed: Small-signal state-space model is proposed to analyze the stability of smart loads, and eigenvalue analysis is performed due to the changes in different parameters of smart loads.

Software Set-up: PSCAD is used for simulation purposes. Grid of nanogrids (GNG) are formed by combination of nanogrids connected to the main GNG AC bus. Each nanogrid includes inverters powered by battery banks and renewable energy sources, smart critical loads, conventional non-critical loads, and solid-state transformers (SSTs). Additionally, Nanogrid 1 (NG1) includes a diesel generator.

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Corrective Schemes for Internal and External Abnormalities in Cascaded Multilevel Inverters

Multilevel Cascaded H-bridge (CHB) converters are considered a promising alternative to integrate renewable energy resources with the grid because of their modularity, scalability, and increased efficiency.

Goal: To develop analytical techniques to facilitate analysis of grid-interactive CHB under abnormal conditions such as grid imbalance as well as during continued operation after CHB cell faults.

Techniques Proposed: The PQ plane operational region for grid-interactive symmetric and asymmetric CHB converters has been developed. Also, an open-circuit insulated-gate bipolar transistor fault detection technique for cascaded H-bridge (CHB) multilevel converters is proposed. Moreover, a technique for maximizing the linear modulation region by injecting a common mode component into PWM references is developed for microgrid-interactive cascaded H-bridge (CHB) converters.

Hardware Set-up: An Altera EP3C16F484C6 FPGA used to implement different proposed techniques on a symmetric CHB with M=3 cells.

Related Publications:

  1. Enabling Cybersecurity, Situational Awareness and Resilience in Distribution Grids with High Penetration of Photovoltaics (CARE-PV).