Input-series-output-parallel (ISOP) isolated bidirectional direct current (dc)/dc converter (IBdc) becomes a preferred scheme connecting high-voltage and low-voltage bus in dc distribution network. Input-voltage-sharing (IVS) among modules is essential to realize the stable operation of ISOP system. Nowadays, with large-scale access of distributed energy sources and loads in dc grids, the fluctuations in bus voltage and connected load become frequent and great, deteriorating the IVS performance and stable operation of ISOP structure IBdc. To solve this issue, a triple-close-loop IVS strategy is proposed in this article. Compared with the conventional IVS strategy with constant input impedance, the proposed IVS strategy reshapes input impedance to be a full-order model containing high-order components and sensitive to fluctuation of output voltage, and IVS control based on reshaped impedance improves dynamics feature, maintains ideal output power, and avoids false protection and potential instability for ISOP structure IBdc under frequent and large fluctuation. Experimental results verify the correctness and effectiveness of the analysis and proposed strategy, providing a feasible, efficient, and practical control scheme for ISOP system in dc distribution network.

The isolated bidirectional DC/DC converter (IBDC) plays an important role in DC buses connection, voltage conversion, electrical isolation and bidirectional power transmission for DC distribution networks. In this paper, a multiple modular IBDC scheme based on hybrid- dual-active-bridge (HDAB) for medium-voltage (MV) and high-voltage DC (HVDC) distribution network is proposed. In the proposed HDAB, the switches in diagonal position of full-bridge are replaced by half-bridge sub-modules (SMs), the proposed HDAB maintains advantages of conventional DAB and achieves bidirectional fault handling capability, avoiding the application of large DC-link capacitors and DC circuit breakers, reducing the volume and construction cost. Besides, high-frequency-link (HFL) voltage regulation strategy is also proposed in this paper, adjusting the HFL voltages in HDAB to match the HFL transformer voltage adaptively, thus improving the efficiency and applicability of IBDC under the fluctuation of power flow and DC bus voltage. The topology, operation principle, control structure and corresponding bidirectional fault handling and HFL voltage regulation strategy of proposed IBDC scheme are investigated. The experimental results verify correctness and effectiveness of proposed scheme and control strategy, promoting the adaptability and practicality for both IBDC and DC distribution network.

The intermittency of renewable energy sources, i.e., photovoltaic cells and wind power causes problems such as unreliability, harmonic pollution, unpredictability and inefficiency, which pose a great challenge for constructing a reliable modern microgrid. To address these problems, in this paper, we propose a novel structure of microgrid, where sensitive loads, non-sensitive loads and the concept of “load follows demand" are adopted and incorporated. Within the designed microgrid, energy storage systems (ESSs) are coupled with the non-sensitive loads to achieve the supply/demand balance. In addition, a particle swarm optimization (PSO)-based collective load control is employed in this study to create pure resistiveness and piecewise constant active power features in the microgrid, in order to resolve harmonics and unpredictability problems. The proposed microgrid experimental platform is established based on real-time (RT)-lab and dSPACE in a hardware-in-the-loop (HIL) environment, where the efficacy of the proposed microgrid structure is verified in both islanded mode and grid-connected mode, which is able to achieve nearly 100% utilization rate of the intermittent solar energy, piecewise constant power and unity power factor. The proposed microgrid structure and established testing environment also have the potential to be scaled up to multi-microgrid power systems for advanced and wider applicability.

This study develops a generalized additional voltage pumping solution for a series of high-step-up converters, whose topologies can be modeled by a generalized architecture. The newly designed converters can achieve additional voltage pumping by only applying an additional diode and capacitor to the conventional high step-up converter structure. Integrating the proposed solution into the existing high-step-up converters, five typical case studies with corresponding analyses and comparisons are conducted and presented, which verifies the proposed voltage pumping strategy. Additionally, five prototypes are built in this study, and the experimental results further validate the effectiveness of the proposed GAVPS solution. The proposed strategy in theory will work synergistically with all types of DC-DC converters, which demonstrates its unparalleled significance in expanding its applicability in contemporary power converter industries.

The traditional switched-inductor technique for high-step-up conversion is widely utilized in industrial applications, especially multicell technique is combined to realize ultra-high voltage. However, the component currents are accordingly increasing with the increasing number of cells, which results in high cost, low efficiency, and low stability. In order to solve these problems, an improved multicell structure of switched inductor is devised, which can be utilized to replace traditional switched-inductor cells for higher actual boost ratio and lower diode currents. An example of the proposed structure-based boost converter is demonstrated for a detailed analysis, and it is followed with a comparison to verify its features. Finally, simulations and experiments are conducted to validate the effectiveness.

The efficiency and safety issues caused by cell differences are the key factor to hinder the use of retired batteries. The reconfigurable battery technique is an effective method to break through the bottleneck. However, the potential short-circuit paths increase exponentially with the number of cells, which makes manual analysis unapplicable and brings serious risks in large scale reconfigurable battery systems. Existing researches are about topology and energy efficiency optimization, but the problem of short circuit is ignored. In this article, a systematic approach based on the sneak circuit theory is proposed to fundamentally avoid the short-circuit problem of reconfigurable battery systems. A novel sneak circuit theory based approach is creating a short circuit path table, which will be indexed to avoid connecting the anode and cathode of a battery cell/string. In addition, all the paths are further studied and analyzed, and the simplest path table can be obtained to improve the energy efficiency. To validate the theoretical foundation and feasibility of proposed approach, a reconfigurable battery system containing two kinds of batteries is developed. All experimental results well verify the effectiveness and feasibility of proposed approach. This work provides theoretical foundation for avoiding short-circuit paths in reconfigurable battery systems, which will break through the bottleneck in scale application.