Publications

This paper proposes a single-stage single-inductor Buck-Boost inverter (SIBBI) with leakage current suppression capability. By controlling the DC-side electrolytic capacitor voltage to remain balanced, common-mode leakage current can be eliminated. Compared to traditional half-bridge Buck-Boost inverters, the SIBBI uses only one inductor for energy regulation, thereby improving the utilisation rate of the inductor during both positive and negative half-cycles, reducing losses and costs, and further enhancing power density. The SIBBI employs a multi-modal control algorithm based on dead-beat control (DBC), ensuring that only one switch is in the high-frequency state at any given time, thereby reducing switching losses. Additionally, when the capacitance of the electrolytic capacitor decreases, the SIBBI can operate in pure Buck-Boost mode, thereby extending the lifespan of the electrolytic capacitor. This makes it suitable for photovoltaic inverter applications.

For the renewable energy sources whose outputs vary continuously, a Z-source current-type inverter has been proposed as a possible buck-boost alternative for grid-interfacing. With a unique X-shaped LC network connected between its dc power source and inverter topology, Z-source current-type inverter is however expected to suffer from compounded resonant complications in addition to those associated with its second-order output filter. To improve its damping performance, this paper proposes the careful integration of Posicast or three-step compensators before the inverter pulse-width modulator for damping triggered resonant oscillations. In total, two compensators are needed for wave-shaping the inverter boost factor and modulation ratio, and they can conveniently be implemented using first-in first-out stacks and embedded timers of modern digital signal processors widely used in motion control applications. Both techniques are found to damp resonance of ac filter well, but for cases of transiting from current-buck to boost state, three-step technique is less effective due to the sudden intermediate discharging interval introduced by its non-monotonic stepping (unlike the monotonic stepping of Posicast damping). These findings have been confirmed both in simulations and experiments using an implemented laboratory prototype.

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.

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%.

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.

The durability and dependability of lithium-ion batteries (LIBs) play a crucial role in advancing energy storage technologies that power modern applications, including electric vehicles (EVs), consumer electronics, and large-scale energy storage systems. Effective battery health monitoring is essential not only for ensuring safe and efficient operation but also for optimizing battery performance and facilitating second-life applications. Conventional diagnostic techniques, such as voltage and current profiling or impedance spectroscopy, have been widely utilized for LIB assessment. However, these methods often face challenges, such as susceptibility to environmental influences, the need for offline analysis, and dependence on direct electrical connections, limiting their suitability for real-time monitoring. Acoustic Emission (AE) technology has gained attention as a promising, non-destructive approach for real-time monitoring of LIB degradation. By detecting mechanical waves generated during battery operation, AE provides insight into internal structural changes and helps identify key degradation phenomena, including electrode cracking, gas formation, and electrolyte leakage. These acoustic signals offer a unique perspective on stress accumulation and material transformations within LIBs, contributing to a deeper understanding of aging mechanisms. In this study, AE was employed to investigate LIB degradation mechanisms, beginning with graphite/Li and NMC/Li coin cells assembled in a glovebox using LiPF6 in a 1:1 EC:DEC electrolyte. During charging at a 0.5 C-rate, a differential wideband sensor was affixed to the coin cell surface to capture AE signals. The recorded acoustic fluctuations were analyzed, and identical coin cells were aged under similar conditions for validation. Observations revealed significant graphite exfoliation at the fully charged state, with an amplitude of 65 dB. Incremental analysis indicated that the highest amplitude occurred at the peak value, corresponding to the phase transition point, suggesting a strong correlation between AE signals and structural changes during cycling. Post-mortem analysis was conducted to establish correlations between AE signals and electrode structural changes, providing a preliminary link between acoustic signatures and degradation processes. Subsequent experiments focused on commercial LIBs, where testing was carried out within a specially designed foam enclosure to minimize background noise. Advanced digital processing techniques were applied to the AE data to filter out interference and categorize acoustic events based on coin cell spectra. Initial results suggest that AE signals, such as those associated with microcracking, provide distinct markers of electrode degradation. These findings demonstrate AE’s potential as a diagnostic tool for tracking LIB health and detecting critical aging phenomena. Future research will aim to establish more precise correlations between AE events and specific electrochemical reactions occurring within LIBs. By integrating AE with complementary characterization techniques, a more comprehensive understanding of battery aging mechanisms can be achieved. Overall, this study underscores the potential of AE technology to transform LIB health monitoring by providing a real-time, non-invasive, and scalable diagnostic solution. This advancement contributes to improving battery reliability, extending operational lifetimes, and supporting the development of more sustainable and efficient energy storage solutions for future applications.

Power-to-X in Regional Energy Systems discusses the role of these technologies in achieving a carbon-neutral economy and the impact on the energy markets, with implications for electricity, gas, hydrogen, and ancillary services. It focuses on the challenges and benefits of implementing PtX technologies in regional-scale applications. Emphasizing the role of PtX technologies as enablers of sector coupling, the book provides a comprehensive understanding of how these technologies integrate and interact with the industry, transportation, and residential sectors. It describes the significance of PtX, optimal planning, and cost-effective operation of PtX technologies across different sectors and the impact of PtX devices on energy markets. The book considers investing in PtX technologies and contributing to the transition to a sustainable economy. The book will interest professionals and policymakers working in various energy sectors. Researchers and academics in electrical engineering, power systems, renewable energy, and energy economics will also find the content useful.

The operation of water electrolyzers with renewable energies means that long-term operation also involves several start-up/shut-down cycles of the system. In particular, for alkaline water electrolyzers (AWE) it is known that shut-down leads to reverse currents, which causes electrochemical degradation and thereby reducing the efficiency. In this work, a modeling framework is proposed and implemented for the electrochemical degradation of nickel electrodes in AWE stacks under start-up/shut-down (SU/SD) operation, and it is achieving good agreement with experiments. Such a model can be used for digital twins of electrolysis plants as well as optimizing its operation.

Voltage sags are a major problem in present distribution systems. Therefore, different solutions have been examined to compensate these sags to avoid production losses at sensitive loads. In particular, Dynamic Voltage Restorers (DVRs) can realize this goal. Presently, a system wide integration of DVRs is hampered because of their high cost, in particular, due to the expensive DC-link energy storage devices. The cost of these DC-link capacitors remains high because the DVR requires a minimum DC-link voltage to be able to compensate a sag. As a result, only a small fraction of the energy stored in the DC-link capacitor can be used, which makes it almost impossible for the DVR to compensate relatively long voltage sags. Present control strategies are only able to minimize the distortions at the load or to allow a better utilization of the storage system by minimizing the needed voltage amplitude. To avoid this drawback an optimized control strategy is presented in this paper, which is able to reduce the needed injection voltage of the DVR and concurrently to mitigate the transient distortions at the load side. In the following paper a brief introduction of the basic DVR principle will be given. After this, an optimized control strategy will be briefly described. Finally, experimental results using a medium-voltage 10 kV DVR setup will be shown to verify and prove the functionality of the presented control strategy in both symmetrical and asymmetrical voltage sag conditions.