Yue Cao

This work proposes a novel post-fault maximum power point tracking (MPPT) control scheme for fixed-pitch hydrokinetic turbines (HKTs). The proposed scheme leverages an existing 4th-leg fault-tolerant converter topology to enable long-term, power-derated operation after a single-phase fault, a condition where standard control approaches are unsuitable for HKTs. Unlike strategies focused on short-term survival, the proposed approach intelligently adjusts the turbine's operating point to manage component stress while maximizing energy capture. The controller's practicality is verified with Hardware-in-the-Loop (HIL) simulations, demonstrating stable fault transition and post-fault operation under realistic hydrodynamic conditions. Furthermore, a comprehensive multi-physics evaluation framework, utilizing a one-year water mission profile, is developed to quantify the system's impact on reliability and cost-effectiveness. The results provide a quantitative basis for optimizing HKT maintenance schedules and show that the fault-tolerant system achieves a 22.83% increase in annual energy generation compared to a non-fault-tolerant system with seasonal maintenance.

Hybrid energy storage systems (HESS) involve multi-physics real energy storage and possible virtual energy storage, interfacing through power electronics. Such complex energy systems often employ a hierarchical control approach. Higher-level controls consider the energy management within the system and the dispatching of resources, while lower-level controls manage the power flow, voltage regulation, and SOC balancing of connected storage devices, realized through the connected power electronics. This work proposes a generalized bandwidth-based control scheme for HESS in a dc system that addresses the literature gap of filtration-based controls that have previously prevented them from being used in practice and also within hierarchical control strategies. The generalization unifies control objectives that are commonly considered separately for different storage devices. It also provides a flexible control design framework based on a universal energy storage model (UESM) that is applicable to many hybrid systems and storage devices. Using the UESM, control coefficients are algebraically defined by the model parameters, making this control approach suitable for many storage types. The proposed control scheme is validated on a HESS supported dc microgrid, demonstrating its effectiveness in managing the power flow and SOC regulation within the HESS, while also achieving high-level energy management objectives such as preemptive charging and peak load shaving.

Wave Energy Converters (WECs) rely on effective Power Take-Off (PTO) control strategies to maximize energy absorption under dynamic sea conditions. Traditional hydrodynamic modeling techniques may require computationally intensive convolution calculations, making real-time control implementation challenging. This paper presents an alternative approach by leveraging instantaneous frequency estimation to dynamically adjust PTO damping in response to varying wave frequencies. Two real-time frequency estimation methods are explored: the Hilbert Transform (HT) and Phase-Locked Loop (PLL). The Hilbert Transform method provides accurate frequency tracking but introduces a delayed response due to its dependence on causal data. Conversely, the PLL approach demonstrates strong potential in frequency tracking but requires careful gain tuning, particularly in complex sea states. Comparative evaluations across multiple test cases—including sinusoidal variations, amplitude steps, frequency step changes, and real-world JONSWAP spectrum waves—highlight the strengths and limitations of each method. The two different PTO control techniques across the various frequency estimation methods were tested under real-sea states using a state-space model of a point-absorbing Wave Energy Converter. The Capture Width Ratio (CWR) is used as a performance metric, with results showing that the HT achieves a 10.6% improvement, while the PLL estimation yields a 0.9% improvement relative to the fixed parameter control baseline. These results highlight the effectiveness of real-time frequency estimation in improving energy absorption compared to static control parameters.

Hydrokinetic turbines (HKTs) are a promising renewable energy source due to the consistency and high energy density in river and tidal resources. One of the primary barriers to the widespread adoption of HKT technologies is a high levelized cost of energy (LCOE). Considering the marine operating environment, the operation and maintenance costs are substantial. The power electronic converter, a key element in the electrical energy conversion system, is a common point of failure in direct-drive turbine applications—leading to increased maintenance efforts. This work presents a reinforcement learning (RL) method built within a quadratic feedback torque control framework to balance energy generation with power electronic device lifetime. The effectiveness of the RL-based control scheme is compared against a static baseline controller through two year-long tidal case studies. The results showed that the proposed method reduced cumulative damage on the device by upwards of 75% but reduced energy generation by up to 25.2%. Using a custom real-time cost estimation function that considers the sale of energy and an estimate of the costs associated with operating a device at a given temperature, it was found that the RL method can increase net income by up to 45.4% depending on the energy market conditions.

A universal modeling framework for hybrid energy storage systems is proposed. The framework can model various energy storage types, both real and virtual. Hybrid systems employ power electronics connected in various topologies to coordinate the operation of multiple storages, which this framework generalizes into a single, switching-averaged model. Multiple common dc/dc converter types are shown to be compatible with this framework. The universal model aims to simplify system design and analysis by recognizing the commonalities of hybrid topologies, converter operation, and storage dynamics to focus on the overall system behavior and energy bandwidth requirements. The generalized parameters can be transformed into real values to continue the system design process. This paper focuses on defining the theory of the universal model. A demonstration of the model shows the framework's validity by comparing simulation results to the proven physics switching models.

Hydrokinetic turbine (HKT) shows promise as a renewable energy source, but high maintenance costs and low energy output hinder their widespread adoption. Limited literature investigates HKT electric drivetrain designs, resulting in a knowledge gap towards increasing generation efficiency and lowering cost. Multi-physics and multi-timescale modeling of HKT energy conversion system focusing on power converters is an essential tool to be developed. This paper first presents an integrated HKT energy conversion system using a MATLAB average model that incorporates electrical, mechanical, and thermal domains as well as aging behaviors across different time frames, such as fixed-point and mission profiles. A power electronics switching enabled PLECS model is then introduced, including maximum power point tracking control for the HKT, d-q reference framed modeling for the AC-DC-AC power converters, and a dynamic thermal framework, all together to predict fast transients and accurately maintain system stability. The developed models facilitate component-level optimization and improve the integrated performance of the system. Average and dynamic multi-physics models are validated through hardware experiments, hardware-in-the-loop testing, and various simulations.

A novel solid-state circuit breaker (SSCB) topology with two combined tripping schemes is proposed in this paper: 1) fault current bypass (FCB) tripping and 2) soft turn-off tripping by transient commutation current injection (TCCI). There are four main contributions in this work. 1) Flexible combined dual tripping schemes are realized by one single topology. 2) The traditional monotonous hard switching FCB tripping with fast isolation speed cannot handle heavy load faults due to gate oscillations caused by higher d i /d t and d v /d t . Compared to pure FCB tripping, the combined soft turn-off tripping by TCCI in this work realizes zero current switching (ZCS) for the semiconductor switch to suppress its gate oscillations at heavy load fault interruption. 3) The capacitors in the TCCI circuits are automatically self-charged by the dc bus during the off state of SSCB, which greatly simplifies the design by getting rid of external capacitor charging circuits. 4) Reclosing and immediate reopening operations are realized, which enhances the practicality of this work A 375 V/20 A SSCB is designed and developed to experimentally validate the proposed dual tripping schemes at light load fault (57 A) and heavy load fault (325 A). The SSCB demonstrates an ultrafast response speed of 5.2 μs with FCB tripping and 19.6 μs with TCCI soft turn-off tripping. The reclosing and reopening operation is also validated based on IEEE Standard C37.14. This paper is accompanied by a slide as multimedia material demonstrating the contributions of the presented work.

Turboelectric propulsion is emerging as an enabling technology for the future aviation industry, aiming to reduce its carbon footprint. To provide electrified thrust for aircraft, the converter-fed motor drive system is a promising solution for the energy conversion between an onboard dc distribution bus and a high-speed electric machine. However, the neutral-point potential fluctuation and even drifting can be an outstanding issue when employing three-level neutral-point-clamped (3L-NPC) topologies, which puts the converter output performance and the lifespan of capacitors at risk. To address these problems, in this paper, a new hybrid active pulse-width-modulation (PWM) strategy is proposed for the studied airborne electric propulsion systems. With the versatile dual-mode modulation signals, not only can the proposed PWM algorithm keep capacitor voltages balanced at the entire range of operating points but also switching losses can be lowered with the help of discontinuous pulse trains during the cruise. Moreover, the computational burden rendered by a short switching cycle is reduced by the sextant coordinate-based analytical derivation. The effectiveness of the presented modulation technique are validated through simulation results from a Simulink/PLECS model and experimental results obtained from a 200 kVA silicon-carbide (SiC) based T-type 3L-NPC prototype with a variable output fundamental frequency.

Wind and hydrokinetic turbines play an essential role in the transition to carbon-free electricity generation, and improving the economics of turbine systems can accelerate this change. Recognizing that operational costs represent a significant share of the total generation costs, researchers have proposed methods for optimizing the turbine system maintenance while considering the impact of power-electronic converter lifetime on the maintenance costs. This work considers how peak-shaving can be applied to turbine units across an array to exchange energy generation for prolonged power-electronic converter lifetimes and reduced maintenance visits. This work proposes an online peak shaving controller (PSC) that finds the optimal peak-shaving actions by minimizing a function of the predicted levelized cost of energy (LCOE). This real-time minimization of LCOE via a model predictive control style framework ensures the PSC is economically beneficial to the system. The PSC simulates the turbine system with different peak-shaving actions over a prediction horizon, then calculates LCOE considering the power-electronic converter lifetimes and turbine array energy generation. A hardware test demonstrates the real-time peak-shaving action leveraged by the PSC, while a simulation case study for a wind turbine array demonstrates the economic benefit offered over the array's full lifecycle.

Wireless power transfer (WPT) has proven to be an effective solution for electric vehicle charging. As two mainstream near-field WPT technologies, inductive and capacitive power transfer (IPT and CPT) have many similarities. This paper aims to explore the remaining opportunities in CPT systems, not yet reported in existing literature, based on duality with the mature IPT technology. First, a generic modeling method based on two-port network theory is proposed, which contributes to unified modeling and analysis for both inductive and capacitive couplings. Then, power transfer mechanism of IPT and CPT couplers is compared, and unified transfer efficiency is derived, promoting CPT theory developments. Last, the duality between existing IPT and CPT circuits is demonstrated in two aspects: compensation circuit configuration and resonant relationship. 14 CPT topologies are derived based on duality with the existing 7 mainstream IPT circuits, of which 11 circuits do not exist in literature, offering future opportunities in CPT. Detailed comparison and evaluation of the derived 14 CPT circuits are conducted, and high-performance circuits are recommended. As a demonstration, a case study of a 2.1kW 3MHz CPT system is implemented in hardware based on the newly proposed M ₁ - SS topology. This example system achieves a peak efficiency of 93.19% with the predicted circuit properties of load-independent constant-voltage (CV) output and zero-phase-angle (ZPA) property.