Mehrdad Ehsani’s research while affiliated with Texas A&M University and other places

A new type of generator, a transgenerator, is introduced, which integrates the wind turbine and flywheel into one system, aiming to make flywheel-distributed energy storage (FDES) more modular and scalable than the conventional FDES. The transgenerator is a three-member dual-mechanical-port (DMP) machine with two rotating members (inner and outer rotors) and one stationary member (stator). The transgenerator–flywheel system is introduced with its configuration, transgenerator overview, flywheel operation principle and power management strategies, and control system. Simulations are performed in MATLAB 2023b/Simulink to verify the system viability, including control system verification and flywheel storage performance evaluation. The results show that the inner and outer rotors can be controlled independently with an accurate and fast control response, and the grid-side control works properly. The flywheel performs well, with considerable charging power and storage capacity.

Electric vehicles (EVs) are considered an alternative to conventional internal combustion engine vehicles (ICEVs) for reducing tailpipe CO ₂ emissions. However, their higher initial manufacturing pollution raises concerns about their lifetime CO ₂ emissions. Hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs) are traditionally viewed as intermediate solutions in terms of emissions. Previous research on emission comparisons among these vehicle types was often confined to specific regions. This study conducts a worldwide assessment of the lifetime CO ₂ emissions of the 2020 Chevrolet Bolt EV, a commercially available EV, and globally compares it with an ICEV, two types of HEVs, and three types of PHEVs, all with equivalent vehicle performance. The analysis utilizes the dynamic programming (DP) algorithm to theoretically optimize the lifetime emissions of HEVs and PHEVs. The findings indicate that, with DP optimization, HEVs and PHEVs can achieve lower worldwide lifetime emissions than both comparable EVs and IC engine vehicles without sacrificing vehicle performance.

Battery electric vehicles (BEVs) can recuperate the kinetic energy of the moving vehicle by the process of regenerative braking. However, this feature is limited by the battery recharge power rating that is often significantly less than the BEV propulsion power rating. This study proposes a powertrain for BEVs that is capable of improving regenerative braking significantly by utilizing a lightweight flywheel and small ultracapacitor pack as power buffers. In order to connect the flywheel and ultracapacitor to the drive shaft effectively and more efficiently, a two-shaft electric motor called the transmotor is utilized. Further, the proposed powertrain, transmotor–flywheel assisted by ultracapacitor, enables us to reduce the power rating of the battery pack to the extent that it only be used for low power demand loads such as cruising. A braking scenario simulation followed by an emulation test is presented to demonstrate the above enhancement.

Increased efforts toward climate change mitigation and achieving net zero (NZ) are occurring globally. This research addresses three challenges to meeting the target NZ goals: (1) quantifying energy use reduction approaches, including energy efficiency and renewable power; (2) obtaining measured data to verify NZ achievements; and (3) providing NZ definitions to a globally understandable concept. To do so, a reorganized NZ concept (NZX%(ORG)) is proposed that is practical, measurable, and adaptable to different regions and requirements. The “X%” presents the fraction of renewable energy to the total energy used, and the “ORG” defines the organization’s NZ definition that a project uses. The objective of this proposal is to create a universally NZ concept and method, using measured utility power data, by (1) determining a baseline NZX%(ORG); (2) projecting an optimized NZX%(ORG); (3) measuring and reporting the actual NZX%(ORG). This application is extendable from a building level to the community, city, and country levels (NZCX%(ORG)). The Serenbe community, a monitored case study in Georgia, was analyzed. The baseline NZ rating using metered data was NZC16%(ASHRAE). The analysis showed that improved energy efficiency measures (lighting, windows glazing, air sealing) along with increased on-site solar power generation (from 10% to 25% of all roof space), provided a projected NZC80%(ASHRAE). In addition, publicly available documentation of the measured utility power is required for reporting the actual NZCX%(ORG) in Serenbe. Using NZX%(ORG) provides recognition of partial success in moving toward 100% renewable power.

The cascaded (brushless) doubly fed induction machine (CDFIM) is a promising substitute for the commonly used doubly fed induction machine (DFIM) for wind power application. The CDFIM offers reliable performance and low maintenance due to the absence of slip rings and graphite brushes. In this study, a detailed analytical model for the CDFIM is proposed in order to clearly show the controllable input (i.e., current from the inverter side) and output (i.e., total output torque) relationship. The proposed model is expressed in the frequency (Laplace) domain. Field-oriented (i.e., vector) control approach is adopted in order to achieve a precise dynamic model for the grid-connected CDFIM. The steady-state and dynamic behaviors of derived torque terms are presented and explained individually. Dynamic response of the total output torque is calculated both analytically and numerically in a simulation, and the results are shown to be consistent. Next, the torque-sharing and power-sharing concepts of the CDFIM are presented to further study the system behavior under different rotor velocities. Finally, to verify the proposed model, an experimental setup using a cascaded DFIM was used, and the results are reported.