Research

Advanced Power Electronics Control

Cycle-by-Cycle Digital Control

We investigate a new method to model and control variable-frequency power converters in a switching-synchronized sampled-state space for cycle-by-cycle digital control. There are a number of significant benefits in comparison to other methods including fast dynamic performance together with ease of design and implementation. Dynamic voltage scaling for microprocessors and LiDAR are among the applications that can benefit.

High-frequency Control Conditioning

Current-mode control is one of the most popular controller strategies for power converters. With the advent of wide bandgap devices including GaN and SiC, higher switching frequencies have become more viable at higher power because of lower switching losses. However, the advantage of higher switching frequency for faster, higher bandwidth control is squandered because of current sensor interference. We present a framework for characterizing and analyzing this interference as uncertainties to the controller model.

These uncertainties introduce additional dynamics and nonlinearity that can result in instability and poor transient performance of the current control loop. We provided a model framework based on a new control conditioning approach that guarantees global stability and a strategy for optimizing transient performance. We presented the analysis, design, and hardware validation of three effective solutions.

Energy Storage Systems

Lite-Sparse Hierachical Partial Power Processing (LS-HiPPP) for Second-Life Battery Energy Storage Systems

The growth of electric vehicles (EVs) will be followed by a surge in retired EV batteries, which could be repurposed since they might still have nearly 80% available capacity. Repurposing automotive batteries for second-use battery energy storage systems (2-BESS) has both economical and environmental benefits. The challenge with assembling and aggregating second-use batteries to work together in a system is the heterogeneity in their capacity and power limits that can be evolving based on their degrading state of health. We proposed a new strategy to optimize 2-BESS performance despite the heterogeneity of individual batteries while reducing the cost of power conversion. By leveraging a new lite-sparse hierarchical partial power processing (LS-HiPPP) approach, the study demonstrates that LS-HiPPP architectures offer the best tradeoff between battery utilization and converter cost.

Microgrid Operation, Control, and Stability

Large-Signal Stability Criteria and Enhancement of Converter-Dominated DC Microgrid

With the increasing adoption of power electronic devices, the stability of future power systems faces challenges due to potential large disturbances. However, traditional small-signal stability analysis is inadequate for power electronics-enabled power systems during significant disturbances like faults, pulse power loads, or load switching. To tackle this issue, we introduce the first rigorous derivation of sufficient criteria for large-signal stability in DC microgrids with distributed-controlled DC-DC power converters and design a novel type of closed-loop converter controller.

Power Processing Systems for Electric-Vehicle Charging Nanogrid

As the number and power levels of electric vehicle chargers increase, the stress on the electric grid also grows. Energy buffering, which involves point-of-use energy storage, can mitigate peak power stress on the grid while meeting EV charging demands and reducing the need for costly grid upgrades and peak demand charges. In a case study of an EV charging nanogrid, the feasibility of deploying second-use battery energy storage systems (2-BESS) is explored. Our study demonstrates that the LS-HiPPP approach significantly improves battery energy utilization, decreases the derating, and achieves higher captured value compared to conventional partial power processing (C-PPP) and full power processing (FPP).