With the rapid development of rene wable energy (e.g., wind and photovoltaic energy) and energy storage, the dc collector has become an effective conversion link of distributed energy access to medium-voltage power distribution grids. However, considering the inconsistency of dc voltage and the duty cycle of each submodule, the traditional carrier phase-shifting modulation is difficult to achieve the excellent harmonic characteristic in the dc collector, thereby introducing difficulties in the design of passive filters. To solve this problem, this article proposes a selective virtual synthetic vector embedding algorithm to realize full-range current harmonic suppression in the dc collector system. In this scheme, the switching voltage vectors outputted by each submodule are sorted, and the voltage vectors are selectively extracted and synthesized to calculate the embedded virtual voltage vector. Afterward, the voltage vector of each submodule is rotated and calculated online from the perspective of space geometry, and the optimal carrier phase combination in variable-angle carrier phase-shift modulation is obtained. Finally, the experimental results show that the proposed control algorithm can not only be used in the dc collector with any number of modules but also achieve fast and effective harmonic suppression in the whole operating range.

With the continuous development of distributed energy, the energy storage system (ESS) is indispensable in improving power quality. Aiming at the application of large-capacity storage battery access to medium voltage dc power grid, a dc cascaded ESS based on the dc collector is proposed, and the characteristic, topology, and control are presented in detail. In this scheme, the low-voltage storage batteries are accessed to medium voltage dc bus directly with dc collectors, which not only has higher efficiency, but also improves power density. Especially, the diversity of state of charge is only reflected in the duty cycle of submodules (SMs), rather than the voltage deviation. Further, a variable angle carrier phase-shifted modulation with gradient descent method is discussed to eliminate the dominant current harmonics. By calculating the harmonic amplitude and solving the Jacobian matrix, the gradient that reduces harmonic current is obtained, and the optimal combination of the carrier phases is deduced by iterative calculation. Meanwhile, the method can be extended in the dc collector with any number of SMs to eliminate the dominant harmonics. Finally, the experimental prototype is built and the benefit of the proposed solution is verified.

This research proposes a solid-state dc circuit breaker for low voltage dc system based on reverse-blocking integrated gate-commutated thyristor (IGCT). The circuit breaker topology gets easier as a result of reverse-blocking IGCTs’ ability to withstand reverse voltage. To further enhance the breaking process, we develop a snubber branch with metal oxide varistors (MOVs) and capacitance. The advantages and disadvantages of three distinct snubber branches—the no-snubber, the resistance–capacitance ( RC ), and the MOV-C snubber branch—are then contrasted. In addition to suppressing high-frequency oscillation caught by the parasitic MOV parameters, the structure with MOV-C snubber branch also blocks low-frequency harmonics brought on by RC snubber branch. Moreover, this structure can slow down the rate at which the voltage rises during the breaking process. Comparatively speaking to the RC snubber branch and no-snubber branch structures, it is more appropriate for solid-state dc circuit breakers. Finally, a solid-state dc circuit breaker prototype based on RB-IGCT and MOV-C branch has been created. The maximum overvoltage is 1.5 kV and the rated voltage is 750 V. The maximum breaking current is 10 kA and the rated current can be 2 kA.

The Energy Internet is a new energy ecosystem based on electricity with high penetration of renewable energy, high synergy of multiple energy types, high synergy of energy value chains from supply to demand and from planning to operation, and high participation of stakeholders. In this paper, we discuss the background and significance, basic connotation, dynamic development, current domestic and foreign status, scientific issues, and future development of the Energy Internet. The Energy Internet is based on the fusion of Internet Thinking, advanced information technology, energy industry, synergistic energy network, cyber-physical energy system, and innovative energy business models. It supports the energy revolution in achieving green, coordinated, and efficient development and drives the economic growth.

In a voltage-source converter DC grid, a DC fault current limiter is a key apparatus. When faults occur, it is supposed to effectively and immediately suppress transient short-circuit current to protect other equipment, e.g. converters. Additionally, it is required to bring as little negative effect as possible under normal operation. Although the respective advantages are highlighted in different FCLs, one or two key disadvantages can significantly decrease the overall performance. In this paper, a novel magnetic coupling FCL (MCFCL) is proposed and achieves a good balance among its advantages and disadvantages. An MCFCL consists of a mutual inductor and some power electronic switch modules. The mutual inductor metallic primary winding is connected in series to the transmission line and magnetically coupled with the secondary winding. The secondary side impedance is controlled by the power electronic switch modules. The novel 4-segment model is proposed to demonstrate the current-limiting physics, formulate the current-limiting effect and support the design. One medium voltage (10kV) case study is carried out based on numerical simulation. The MCFCL shows a better current-suppressing effect and a lower impedance under normal operation than the benchmark Reactor FCL. Finally, this study is validated on a scaled-down experimental facility.