Publications

Global goals for a better and more sustainable world demanding electrification and power electronics

Full-Time-Scale Power Management Strategy for Hybrid AC/DC/DS Microgrid with Dynamic Concatenation and Autonomous Frequency / Voltage Restorations

Hybrid AC/DC microgrids with distributed energy storage (DS) improve power reliability in remote areas. Existing power management methods either focus on steady-state power sharing or transient inertia support, but rarely combine both. They also often ignore frequency and voltage deviations caused by droop control, which can harm sensitive loads. To overcome these issues, this paper proposes a full-time-scale (FTS) power management strategy that unifies transient inertia sharing and steady-state power allocation through a novel dynamic concatenator. It also introduces autonomous frequency/voltage restoration to eliminate steady-state deviations in each subgrid. Additionally, a global equivalent circuit model (GECM) is developed to simplify system analysis and design. Experiments confirm that the approach maintains nominal frequency and voltage in steady state while enabling seamless transition between transient inertia support and proportional power sharing across all time scales.

An Efficient Long Prediction Horizon Design for Generalized Predictive Control of DC/DC Boost Converter

Generalized predictive control (GPC) stands out as a prominent representative in the predictive control family due to its robustness. As a crucial parameter in the GPC controller, the prediction horizon significantly impacts the control performance. Short prediction horizons may result in instability, whereas long prediction horizons can lead to a high computational burden but better stability. Although the conventional design approaches can be realized by empirical prediction horizon selection or incorporating nonlinear observers, a theoretical approach has been overlooked so far. To bridge this gap, this article introduces a novel approach to design prediction horizons for GPC demonstrated on a dc/dc boost converter. This method involves constructing a closed-loop system model and assessing the impact of different prediction horizons on the system. Based on the system modeling, a rigorous boundary for the prediction horizon is obtained to ensure control stability. Finally, the accuracy of the design method has been confirmed in experimental conditions. Notably, beyond establishing a rigorous prediction horizon boundary, the proposed method demonstrates a reduction in computational time by at least 22% compared with the empirically selected prediction horizons within the studied system.

VVI-GFM: A Voltage Vector-Informed Grid-Forming Control for Postdisturbance Fast Synchronization Recovery

Maintaining synchronization stability after large grid disturbances is a vital requirement for grid-forming (GFM) converters. Existing enhanced GFM control strategies are often designed for a specific disturbance scenario, requiring extended recovery times or exhibiting frequency fluctuations. This paper reveals that synchronization instability triggered by two typical grid disturbance events, phase jumps and voltage sags, can be unified according to underlying similarities during the post-disturbance recovery. Based on these insights, this paper proposes a novel voltage vector-informed grid-forming (VVI-GFM) control strategy by fully leveraging the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$d$</tex-math></inline-formula>/<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$q$</tex-math></inline-formula> components of the point of common coupling (PCC) voltage vector, which can offer fast synchronization recovery and minimize frequency deviations under both phase jumps and voltage sags. The post-disturbance dynamics of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$d$</tex-math></inline-formula>/<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$q$</tex-math></inline-formula> components of the PCC voltage vector are quantitatively characterized, thus mechanistically demonstrating the effectiveness and applicability of the VVI-GFM control. Moreover, detailed guidelines about the feedforward path design and critical control parameter calculation are provided to ensure normal operation across varying grid strengths. Simulations and experimental results under diverse grid disturbance scenarios further validate the advantages and robustness of the proposed control strategy.

A novel physical extraction multi-step neural network algorithm for power lithium-ion battery state of charge and available capacity estimation

Adaptive Virtual Inertia Emulation and Control Scheme of Cascaded Multilevel Converters to Maximize Its Frequency Support Ability

To fully explore the frequency support ability of the cascaded multilevel converters (CMCs), this article has proposed an adaptive virtual inertia emulation and control scheme. First, the basic inertia emulation mechanism is introduced, which is achieved by absorbing and releasing the capacitor energy in the CMC. Second, considering the influence of reactive power generation of the CMC, the available variation range of the dc components of submodule (SM) capacitor voltages is redefined and recalculated. As a result, the maximum power exchange in SM capacitors in the CMC, which is used for frequency support, can be precisely characterized. Afterwards, the highest/lowest frequency value is estimated under different source/load power disturbance, and the adaptive virtual inertia emulation and control method is designed according to the dynamic frequency extremum estimation and the maximum variation range of SM capacitor voltages. Finally, simulation and experimental results verify that by the proposed method, the CMC can enhance its inertia support ability and reduce frequency deviation of the system. Under 0.02 p.u. load step condition, the frequency deviation is reduced by about 32.8%.

Transient Inrush Current Analysis and Suppression for Grid-Forming Converters Under Grid Faults

Grid-forming (GFM) converters have emerged as essential technologies for ensuring the stability of power systems dominated by renewable energy sources. Nevertheless, their restricted overcurrent capacity may trigger protection during grid faults. While existing studies emphasize the design and optimization of overcurrent mitigation strategies, precise characterization of fault current and dynamic analysis of transient inrush current are still lacking, leading to occurrences of protection malfunction. To bridge this research gap, this article considers the impact of filter parameters and current loop parameters on the equivalent impedance of the converter, and on this basis, establishes a precise fault current characterization model for GFM converters. Based on the model, the key factors influencing inrush current can be analyzed, including voltage amplitude, impedance magnitude, and power angle. Finally, a precise virtual impedance-based inrush current suppression method is proposed, which effectively limits the inrush current to the desired level while ensuring system stability. Both theoretical analysis and experimental results are carried out to validate the robustness and adaptability of the proposed strategy under various grid strengths and grid voltage sags.

Integration of Wind Turbines into Power Systems

LCL Resonance Analysis and Damping in Single-Loop Grid-Forming Wind Turbines

A dynamic phenomenon known as LCL resonance is often neglected when stability analysis is carried out for grid-forming (GFM) control schemes by wind turbine systems, due to its high frequency. This paper shows that this simplification is not always valid for single-loop (SL) control schemes. A detailed small-signal analysis reveals that reactive power (RAP) control significantly influences the resonant modes, which may be dominant in determining overall system stability, even if the resonant frequency is high. The underlying mechanism via which the LCL resonance may dominate the overall system stability is systematically analyzed. Furthermore, various RAP control strategies are compared to assess their different effects on resonant modes. An active damping (AD) strategy favorable for SL-GFM control is then designed. We also provide a comparison between SL-GFM and well-studied grid-following control schemes, highlighting quite different resonance features between them. Finally, case studies associated with a 14-bus, 5-machine IEEE test system are presented. These show that instability originates from the LCL resonance rather than low-frequency interactions among multiple machines, validating the theoretical analysis and the proposed AD strategy.

Physics-Informed Neural Network for Parameter Identification: a Buck Converter Case Study

System-level condition monitoring methods estimate the electrical parameters of multiple components in a converter to assess their health status. The estimation accuracy and variation can differ significantly across parameters. For instance, inductance estimations are generally more accurate and stable than inductor resistance in a buck converter. However, these performance differences remain to be analyzed with a more systematic approach otherwise the condition monitoring results can be unreliable. Therefore, this paper analyzes the training loss landscape against multiple parameters of a buck converter to provide a systematic explanation of different performances. If the training loss is high and smooth, the estimated circuit parameter typically is accurate and has low variation. Furthermore, a novel physics-informed neural network (PINN) is proposed, offering faster convergence and lower computation requirements compared to an existing PINN method. The proposed method is validated through simulations, where the loss landscape identifies the unreliable parameter estimations, and the PINN can estimate the remaining parameters.

A novel wave energy converter with an extended operational range for a wide range of wave conditions

A Novel Single-Phase Interleaved-Based Three-Level PFC Rectifier

Power quality is a concern and more and more relevant due to the numerous technologies requiring an interface with the power grid through power electronics converters. Thus, efficient power factor correction (PFC) circuits, ensuring unitary power factor, sinusoidal AC currents, and controlled DC voltages, are of utmost importance. Aligned with such importance, a novel Single-phase Interleaved-based Three-level (SIT) PFC rectifier is proposed in this paper, which can be used in various applications for AC-DC conversion. A thorough explanation of the SIT PFC rectifier is given, supported by a comparison with the traditional solutions. Additionally, a predictive-based current control is discussed. The obtained simulations permit to examine the complete operation principle of the SIT PFC rectifier (i.e., sinusoidal AC current, interleaved-based mode, three levels of voltage, controlled DC voltage), revealing its accuracy even when operating in critical conditions of operation.