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Abstract Modulation strategy plays an important role in the good performance of modular multilevel converter (MMC). Since MMC has a special structure as well as a large number of submodules (SMs), it is almost impossible to apply the conventional multilevel space vector modulation (SVM) algorithm in it. In this study, a simplified SVM implementation method is proposed by grouping SMs. With the presented method, the high‐level SVM process for MMC can be easily done by implementing multiple two‐level or three‐level SVM algorithm, while the complicated offline or online efforts/tasks about mapping switching states or sequences in the conventional multilevel SVM are not necessary any more. In order to improve the harmonic characteristics, the sampling time of different subunits (SUs), each of which is formed by grouping a few SMs, is staggered evenly, which helps to achieve a higher equivalent switching frequency and less low‐order harmonics. Further, the capacitor voltage balance of SMs is improved by rotation strategies between SUs or inside each SU even without any capacitor voltage detecting or sorting. Since the presented method is independent of the number of SMs, it can be very easily expanded into a high‐level MMC. These propositions are verified by experiment.

Modular multilevel converter (MMC) is distinguished by its modularity. In order to improve its reliability and avoid unscheduled maintenance, it requires the MMC to continue operating even though some of its submodules (SMs) have failed. In this paper, a grouping management method of SMs in MMC is first presented where every six SMs are conceptually grouped into a virtual subunit (SU), and on this basis, a simplified space vector modulation (SVM) implementation is developed. Then, the fault-tolerant solutions are proposed by investigating the post-fault operation of the MMC based on the virtual SU concept. It is analyzed that the SU failures can be categorized into three basic types, according to the phase where the failed SMs are located, and also multiple SM failures can be decomposed into one or multiple basic fault types. In this way, the fault-tolerant solutions are unified regardless of the number of faulty SMs. Further, the sorting capacitor voltage control is combined into the proposed methods to balance all of the SM capacitor voltages. With the proposed fault-tolerant method, the amplitude and THD of the line voltages are almost unchanged under fault conditions when compared with normal operations. The simulation and experiment verify the propositions.

In order to satisfy the various requirements of future network services, 5G wireless network is proposed and becoming a hot topic in academic and industrial field. Location-based services are widely used with the development of wireless communication and mobile Internet technology. A number of popular spatial-temporal cloaking technologies have been proposed, and the number of users in an anonymizing spatial region (ASR) is uncontrollable. This paper, based on the semi-trusted server architecture proposes a location cloaking algorithm (LCA) based on combinatorial optimization. First, the semi-trusted server architecture divides the information of mobile users into three parts, so adversaries are unable to obtain the location and identity at the same time, then utilize the spatial k -anonymity algorithm LCA to hide the real locations of user, which controls the number of real users to around k in the anonymous result sets (Aset), so that both the number of users in ASR and the area of ASR are minimized, thereby improving query precision and decreasing the resources consumption. Finally, complete further improvement that the location is distinguishable in ASR and the query contents are diverse in Aset. Simulations show that the LCA performs well on cloaking success rate, query precision, and resources saving.

Based on generalized Riccati transformation and some inequalities, some oscillation results are established for a class of nonlinear fractional difference equations with damping term. An example is given to illustrate the validity of the established results.