Publications

In recent years, Finite Control Set Model Predictive Control (FCS-MPC) has been widely used in power converters due to its advantages of fast dynamic response, no regulator and multi-constraint control. However, due to traversing all possible voltage vectors, the computational burden of traditional FCS-MPC is relatively heavy. In order to reduce the computational complexity of FCS-MPC strategy in rolling optimization, a simplified control method based on support vector machine ( SVM ) is proposed in this paper. The SVM model is trained by collecting the input and output data of the controller during the steady-state operation of the system, and the mapping relationship between the system state and the optimal vector is established. In the control process, SVM is used to quickly predict the optimal vector and construct a candidate vector set, thereby reducing the search space and performing optimization. The simulation model of three-phase two-level LCL grid-connected inverter is built in MATLAB / SIMULINK. The simulation results show that the consistency rate of this method with full vector search is 98 % in steady state, which significantly reduces the computational burden and improves the control efficiency.

Synchronization stability assessment of grid-forming (GFM) converters is essential during and after large disturbances in the external grid, where the active power control (APC) loop is perceived as the key concern since it is employed to generate the voltage phase angle. However, the impacts of the internal voltage amplitude dynamics and current saturation, determined by the reactive power control (RPC) loop and current limiter, are often neglected. This paper considers dynamic interactions between internal voltage magnitude and phase angle to derives an improved power-angle curve of the circular current-limited GFM converter, which facilitates more accurate identification of the critical angle margin for evaluating the synchronization stability after phase jumps. Furthermore, the impact of the RPC coefficient is quantified to provide parameter design recommendations for enhancing the post-phase jump synchronization stability. The analytical results are validated by simulations and experimental tests.

One of the advantages of finite control set model predictive control (FCS-MPC) is that it allows for the consideration of multiple constraints simultaneously, thereby facilitating the achievement of multi-objective control. The configuration of weighting factors (WFs) in its cost function is the key to ensuring a balance between various control objectives and achieving optimal performance. However, there is a paucity of mature theoretical guidance to determine these WFs, which usually depends on experience or trial and error. This has the consequence of leading to a cumbersome debugging process and difficulty in obtaining optimal control effects. The paper proposes a strategy for the design of WFs, based on the particle swarm optimisation algorithm (PSO) and the radial basis function neural network algorithm (RBFNN). This strategy is intended to develop a set of scientific and systematic design processes for the selection of WFs. To verify the effectiveness of the proposed method, a three-phase LCL grid-connected inverter is selected as the control object, and a large number of simulations and experiments are carried out.

The transition to renewable energy is crucial in addressing climate change, yet the intermittent availability of wind and solar power presents challenges to energy reliability. To overcome this, effective energy storage solutions are essential for stabilizing and scaling energy supply. Power-to-X (P2X) technologies have emerged as a key strategy for converting surplus renewable electricity into storable energy carriers, with hydrogen production through electrolysis being a prominent approach. By splitting water into hydrogen and oxygen, excess renewable energy can be efficiently stored and later utilized as a clean and versatile fuel. Solid Oxide Electrolysis Cells (SOECs) offer a highly efficient pathway for large-scale hydrogen production in P2X systems. However, widespread deployment is hindered by challenges such as material degradation, thermal instability, and high operational costs. Operating SOECs under elevated pressure has been identified as an effective method to enhance performance, reduce capital expenditures (CAPEX), and improve hydrogen output. This study introduces a novel high-pressure SOEC setup, integrating nickel/yttria-stabilized zirconia (YSZ) cathodes, YSZ electrolytes, and lanthanum strontium cobaltite (LSC) air electrodes. The system operates in a controlled gas environment, with precise pressure regulation maintained via Equilibar back-pressure regulators. To ensure system stability, pressure is gradually increased at a rate of 0.5–1 bar per hour. Electrochemical performance is assessed through open-circuit voltage (OCV) measurements, current-voltage (I/V) curves, and electrochemical impedance spectroscopy (EIS). A novel AC:DC cycling strategy has been developed to enhance thermal and electrochemical stability under pressurized conditions. This method alternates between electrolysis and fuel cell modes, incorporating periodic reverse pulses to regulate thermal distribution and mitigate nickel migration—a primary cause of SOEC degradation. The optimization of the AC:DC cycling profile is currently under investigation, with switching frequencies ranging from 30 Hz to 0.91 Hz. Experimental results reveal a slight voltage drop and a notable increase in cell impedance as frequency increases during electrolysis and fuel cell operations, respectively. At low frequencies, a significant voltage drop in fuel cell mode is observed, likely due to mass transfer limitations affecting hydrogen availability at the reaction site (electrode/electrolyte interface), leading to localized "starvation" of the cell. The findings suggest that operating at frequencies above 10 Hz improves system performance. At different cycling frequencies, local SOEC temperature variations along the gas flow direction play a crucial role. Higher frequencies lead to more uniform temperature distribution, increasing the overall average operating temperature and reducing thermal gradients. When the cycling frequency exceeds 10 Hz, both the average operating temperature and the maximum temperature gradient stabilize, as shorter cycle durations prevent significant gas composition fluctuations. At the lowest tested frequency (0.91 Hz), gas composition and temperature undergo considerable variations within each cycle, influencing overall system stability. By maintaining a thermoneutral balance, this cycling strategy promotes system stability and mitigates stress-induced degradation. Long-term testing exceeding 600 hours is currently underway, comparing DC-only and AC:DC cycling modes. Post-mortem analysis is being conducted to evaluate degradation mechanisms and material stability. Preliminary results indicate enhanced charge and mass transfer, increased hydrogen production efficiency, and reduced degradation under pressurized conditions. These findings demonstrate the feasibility of integrating high-pressure SOEC operation with dynamic cycling for large-scale hydrogen production. The advancements presented in this study contribute to the development of more durable and cost-effective electrolysis technologies, supporting the transition to sustainable hydrogen production and green energy solutions on a global scale.

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.

This paper proposes a single-stage bridgeless buck-boost power factor correction (SSBLBB-PFC) converter with two-terminal outputs. By adopting a minimized loop inductance design and using only one high-frequency switching device in both the boost and buck modes, the circuit loss has been significantly reduced. Additionally, the twoterminal output structure is more versatile than the conventional three-terminal output structure, and it can also reduce voltage stress. Additionally, the single inductor is reused to achieve power conversion in the positive and negative input voltage, achieving 100% utilization of the DC inductor. The dead beat control (DBC) is used to control the inductor current to achieve PFC. A detailed analysis was conducted on the working modes and control strategies of the converter. The simulation results under the 220 V power grid prove that the proposed inverter has a better dynamic performance.

This paper describes modeling of wind farm controllers. The paper contributes to the IEA Annex XXI “Dynamic models of wind farms for power system studies” and was presented at the Annex XXI workshop in EWEC 2006. The wind farm controllers are developed with features, which make the wind farms able to participate in the control of the power system. The modeled wind farms provide active and reactive power control in the point of common coupling of the wind farm, which can be combined with automatic frequency and voltage control with droop and dead band.

This paper presents a low-model-dependency adaptive droop control strategy for islanded direct current microgrids (DCMGs), integrating real-time state estimation and fuzzy logic-based damping. The decentralized approach combines an Extended Kalman Filter (EKF) for local estimation of output current and DC bus voltage, with a Fuzzy Logic Controller (FLC) that dynamically adjusts a virtual damping term to suppress low-frequency oscillations. Designed for buck-converter-based distributed generation (DG) units, the proposed method improves voltage stability and power sharing without requiring inter-unit communication. A detailed nonlinear model of the DCMG, incorporating converter dynamics and line impedances, is validated through MATLAB/Simulink simulations under two realistic scenarios: step load variation and plug-and-play DG reconnection. Results show an oscillation-free response, enhanced voltage regulation, and reduced power-sharing error compared to conventional droop control, confirming the method's robustness and suitability for decentralized microgrid applications.

After a total or partial system outage, black-start serves as a critical measure to restore the system to the normal operation. In the later stage of restoration, various types of loads will be energized, the pick-up sequences of which may affect the success probability of the black-start. In this context, a block loading strategy for the inverter-based low-inertia systems is explored, with special consideration given to the inertial support by induction motors. Through detailed analysis, it is shown that initiating induction motors at an early stage leads to improved frequency stability during subsequent loads pick-up. The advantages of prioritizing motor energization are validated from multiple perspectives, including motor starting success rate, the timing of block load pick-up, and the overall system stability. Both simulation results and hardware-in-the-loop validations confirm these observations.

This IEC White Paper establishes the critical role that power semiconductors play in transitioning to an energy wise society. It takes an in-depth look at expected trends and opportunities, as well as the challenges surrounding the power semiconductors industry. Among the significant challenges mentioned is the need for change in industry practices when transitioning from linear to circular economies and the shortage of skilled personnel required for power semiconductor development. The white paper also stresses the need for strategic actions at the policy-making level to address these concerns and calls for stronger government commitment, policies and funding to advance power semiconductor technologies and integration. It further highlights the pivotal role of standards in removing technical risks, increasing product quality and enabling faster market acceptance. Besides noting benefits of existing standards in accelerating market growth, the paper also identifies the current standardization gaps. <br/>The white paper emphasizes the importance of ensuring a robust supply chain for power semiconductors to prevent supply-chain disruptions like those seen during the COVID-19 pandemic, which can have widespread economic impacts.<br/>The white paper highlights the importance of inspiring young professionals to take an interest in power semiconductors and power electronics, highlighting the potential to make a positive impact on the world through these technologies.<br/>The white paper concludes with recommendations for policymakers, regulators, industry and other IEC stakeholders for collaborative structures and accelerating the development and adoption of standards.