Xijun Yang

With the large-scale integration of renewable energy sources, grid-forming (GFM) converters with inherent voltage and frequency support capabilities have attracted significant attention. However, due to the limited overcurrent withstand capability of power electronic devices, the stable operation of GFM converters under grid faults such as grid voltage sags remains a critical challenge. To address this issue, this paper systematically investigates the mechanisms of power angle instability and overcurrent generation during grid faults by a unified equivalent impedance model. Based on this analysis, a comprehensive control strategy that simultaneously considers power angle stability and overcurrent suppression is proposed. By introducing an adaptive improved observer control (AIOC), the active power reference is adaptively adjusted to enhance the power angle stability of the system. Meanwhile, the voltage reference is dynamically regulated to effectively limit the fault current while enhancing the voltage support capability. Finally, comprehensive theoretical analysis and experimental validation are provided. The experimental results demonstrate that the proposed strategy is capable of ensuring power angle stability and limits the overcurrent to within 1.5 p.u. Meanwhile, the voltage magnitude is increased by approximately 6%. The results demonstrate the robustness and adaptability of the proposed method under various conditions.

Periodic energy control has been successfully applied to systems with single-time-scale operation. However, the control performance is hindered by the different time scales of the non-fully decoupled cascaded structure. In this article, a unified full-mode energy model with two-time-scale variables for the LCC-LCC compensated inductive power transfer (IPT) system with a rear-end four-switch buck-boost converter, which can accurately track the dynamic response, is proposed. To reduce the computational burden and improve the dynamic response speed, a full-mode energy control strategy conducting in the unified time scale is developed based on the two-time-scale model. Compared with the periodic energy control, the sampling of the load voltage and current can be avoided. A cascaded LCC-LCC compensated IPT-FSBB prototype is built, and the theoretical analysis shows excellent agreement with both the simulation and experimental results.

The operating frequencies of the dc–dc converter connected to the distributed energy resources and inductive power transfer (IPT) systems are often different, which makes it difficult to model the cascaded system accurately by using a single time scale. In this article, a two-time-scale model (TTSM) consisting of fast-time-scale and slow-time-scale state variables, which has high accuracy and efficient calculation, is proposed for the cascaded four-switch buck–boost IPT (FSBB-IPT) system. The full-mode operation and zero-voltage-switching (ZVS) conditions of the cascaded system are studied based on the TTSM. To overcome the failure of the traditional ZVS modulation strategies of the first-stage converter in the FSBB-IPT system, a hybrid ZVS modulation scheme in the new time scale is developed to reduce the root-mean-square value of the inductor current and improve the efficiency. An FSBB-IPT prototype with a wide input voltage range is built to verify the effectiveness of the proposed modulation scheme.

The traditional stroboscopic mapping (SM) only focuses on the behaviors in periodic time instants, which will lose the details of multiple state changes during an operating period and cannot be used to analyze the characteristics of the studied system accurately. In this article, an improved full-power SM (IFSM) model is proposed for high-order wireless power transfer (WPT) systems and dc–dc converters, which have generality and high accuracy. The dual-side LCC compensated WPT system for electric vehicles is taken as an example to present the derivation of the discrete-time model. Based on the proposed model, the possible zero current switching points of the system are calculated and compared for the optimal power transfer ability. The process of the boundary calculation of the output current operating in continuous conduction mode (CCM) and discontinuous conduction mode (DCM) is proposed, which aims to provide guidelines for adopting different control strategies when the battery packs are charged in different modes. It is found that the CCM/DCM boundaries are highly related to the operating frequency and equivalent resistance of the battery packs, while the coupling coefficient of coils has little influence on it. A dual-side LCC WPT prototype is built, and both the simulation and experimental results match well with the theoretical analysis.

The design of auxiliary power supply (APS) in solid-state transformers (SSTs) is quite challenging. To minimize the isolation requirement, this APS is usually powered by dc-link capacitors. However, it poses voltage unbalance issues when the main converter is not in operation. To address this problem, a compact and cost-effective APS design is proposed, which utilizes the isolation structure of main medium-frequency transformers (MFTs). The proposed APS system also provides half-duplex communication, which replaces the costly optical fiber system. The interference between main and auxiliary power transfer links has been significantly reduced by the decoupled transformer design and the dual-band scheme for inductor-inductor-capacitor (LLC) and inductor-capacitor-inductor-capacitor (LCLC) converters. In addition, a new startup strategy with a low standby power is applied to this APS system. A 3.2-kW SST prototype with a peak efficiency of 97.9% has been built, whose APS is 6 W. The experimental results verify the feasibility and performance of the proposed techniques.

Wireless power transfer charging of modern electric vehicles is complicated by widely varying charging battery pack voltages between different models. This article proposes a new resonant inductor integrated-transformer (RIIT)-based receiver. It is compact, low cost, and can adapt to different battery pack voltages without any significant change of resonant parameters. The design approach, power losses, and power transfer capacity of the proposed system are presented. In addition, methods of natural current sharing and voltage sharing among different RIITs are proposed. An LCC-LCC WPT prototype compatible with both 400 and 800-V battery pack voltages is built, and the system efficiency reaches 94% at 9.5 kW, which verifies the feasibility and performance of the proposed receiver.

With the continuous development of Regional Integrated Energy System (RIES), demand response (DR) is composed of diversified loads including electric load, heat load and gas load. Their cross‐dependencies reflecting the nonlinear coupling complementary relationship between each load type are one of the key factors to improve multi‐energy flow optimisation modelling and utilisation efficiency on the demand side. Accordingly, this paper proposes a DR dependency assessment method considering electricity‐heat‐gas loads based on the BOXCOX‐Pair Copula model. BOXCOX transformation is introduced to convert various probability distribution statistics of electricity‐heat‐gas loads into Gaussian distributed variables. C‐vine Pair Copula is used to characterise an ensemble‐of‐trees of high‐dimensional dependency structure among multi‐energy demand modalities. Then the combined model of BOXCOX transformation and C‐vine Pair Copula can be employed to determine the complex coupling dependency among electricity‐heat‐gas loads according to different DR statistics. Some metrics between the original empirical distribution and BOXCOX‐Pair Copula distribution are introduced to assess the dependency evaluation precision of the proposed model. Finally, the novel dependency assessment model is numerically tested utilising the electricity load, heat load and gas load data sequences in a real RIES. The results illustrate that the cross‐dependency of electricity‐heat‐gas integrated DR based on the BOXCOX‐C‐vine copula model is closer to that of actual sample data, which verify the effectiveness and superiority of the proposed approach.

The dual-side inductor–capacitor–capacitor (LCC) topology circuit has been widely adopted in wireless power transfer (WPT) systems due to its constant output current characteristic. However, most conventional control methods need specific synchronization techniques between the primary and secondary sides to avoid the oscillation in the system, which increases the cost and control complexity. To solve this issue, this article proposes a new duty cycle control (DCC) strategy for a dual-side LCC resonant converter with a semibridgeless active rectifier (SAR). With such a control strategy, gate signals of the primary- and secondary-side circuits do not need to be synchronized, which could reduce the complexity and the cost of the WPT system. Besides, the switching frequency of the secondary side can be decreased significantly. This article first presents the modal analysis of phase shift control (PSC) and DCC. Then, generalized state-space averaging (GSSA) modeling with PSC and the hybrid average modeling with DCC are performed. In addition, controllers’ design for both strategies is conducted to achieve the constant output voltage. Finally, the eigenvalues’ analysis is used to determine the stability region of the WPT system. The theoretical analysis has been validated by both simulation and experimental results.