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This paper proposes a multi-bus flexible interconnection scheme to balance the power of multiple transformers in low-voltage distribution systems. Unlike feeder interconnection schemes that may lead to extra infrastructure cost and potential stability problems, the proposed scheme adopts transformer bus interconnection instead by using a multi-terminal voltage-source converter. With the integration...
With the development of offshore wind power generation, large-capacity medium-voltage wind turbine becomes the development trend. In this paper, the cascaded multi-cell topology with four-quadrant operation capacity is applied to medium-voltage wind power converters, which consist of a large number of switching devices, so it is essential to improve the converter's fault-tolerant ability. Once the...
This paper proposes the dc bus current optimization control strategy in DFIG wind power systems with current source converter (CSC). In CSC-based systems, the converter losses are dependent on the dc bus current so that it is important to reduce it to minimum. The dc current is chosen as the larger value of rotor side converter (RSC) current and grid side converter (GSC) current. The RSC current is...
In this paper, we study wireless power transfer in a multiuser multiple-input single-output (MISO) system, where a base station equipped with N antennas wirelessly transfers power to distributed single-antenna users. To reduce the implementation cost, we propose a constant-envelope analog beamforming scheme to simultaneously transfer power to multiple users which requires only a single radio frequency...
We consider training-based channel estimation for cloud radio access networks (CRANs), in which a large amount of remote radio heads (RRHs) and users are randomly scattered over a certain service area. In this model, assigning orthogonal training sequences to all users, if possible, will cause a substantial overhead to the overall network. Instead, we introduce the notion of local orthogonality, in...
This paper presents a systematic step-by-step design procedure for the dc inductance of a current source converter (CSC). The design is based on the analysis of acceptable ripple level in the dc current of the CSC. A model of current source inverter (CSI) under the operation of space vector modulation is established to estimate the dc current ripples in the system. The influence of different switching...
Among the mathematical optimization algorithms, simplex algorithm is a popular and practical algorithm which was listed as one of the top 10 algorithms of the twentieth century by the journal Computing in Science and Engineering. Although simplex algorithm is efficient in the linear programming, the quality of convergence is unacceptable in practice as a numerical breakdown of the algorithm, even...
Proven to be a viable and cost effective solution for ubiquitous internet access, wireless access network have proliferated at homes, offices, and cafes all over the globe. Being placed at the very edge of the computer network, with increasingly powerful computational ability, wireless access points are more and more suitable for deploying configurable and personalized services for mobile clients...
Due to the inherent DC fault handling ability and small transformer size, isolated modular multilevel DC-DC converter (IMMDCC) is attractive for medium- and high-voltage DC-DC conversion applications. However, with increasing of the operation frequency at the AC stage, the voltage balancing of the floating cell capacitors is a new challenge because the existing modulation and voltage balancing strategies...
DC wind farm (DCWF) with series-connected DC wind turbines (DCWT) is proved to be a potential solution of offshore wind power collection. The coupling behavior of series-connected DCWTs is described in detail. Possible wind energy curtailment during the period of wind turbine voltage limitation and its key impact factors are firstly quantitatively derived. A decoupling control strategy is proposed...
A low-voltage (LV) pulse-width modulated current-source converter (CSC) using reverse-blocking insulated gate bipolar transistor (RB-IGBT) devices is proposed in this paper for megawatt wind energy conversion systems (WECSs) with a permanent magnet synchronous generator. Benefiting from using the latest generation of reverse-blocking power semiconductors, the presented configuration is able to push...
The bipolar configuration is regarded as a promising way for the integration of distributed/centralized energy resources (CER and DER) in future meshed DC grid. In order to achieve a DC-DC voltage conversion capability with bipolar integration, a monopolar-to-bipolar DC-DC converter interface is usually requested for the inner power collection network of a given CER/DER with the monopolar configuration...
The isolated modular multilevel dc-dc converter (IMMDCC) constructed by two MMCs and a medium frequency transformer is attractive for medium-and high-voltage dc-grid applications by offering the following features: the modular multilevel structure provides the capability to handle high voltages with the series connection of lower voltage submodules; the utilization of the square-wave operating mode...
DC substation with three and more terminals is an important element for interconnected DC grid. This paper aims to explore the configurations and operation strategy of DC substation. A series of DC substation topologies have been derived in duality of classical AC substations. Among the derived counterparts, ring type DC substation is selected and developed for integrating two DC windfarms with two...
This paper presents a novel isolated DC-DC converter with high efficiency by utilizing the proposed double full bridge double tapped inductor (DFBDTI) topology. PWM plus phase-shift modulation algorithm and dual-target control strategy are used in the converter to reduce switching loss and reactive power in the transformer when the output voltage fluctuates widely around its rated value. Thus, high...
A systematic control strategy for Non-inverting Buck-Boost converter based on equivalent duty ratio is presented in this paper. Extend-Buck mode and Extend-Boost mode are first derived as transition mode for least inductor current in constant frequency operation and are modified with consideration of parasitic elements. Equivalent duty cycle is introduced to switch among different working modes and...
Derived from the classical phase-shift control DC-DC converter, isolated modular multilevel (MML) DC-DC converter has two MMCs connected via a medium frequency AC transformer. Due to the high voltage handling ability, small transformer size, and natural ZVS soft switching this topology is attractive for medium-and high-voltage DC-DC conversion applications. However, in conventional modulation methods...
The modular multilevel converter (MMC) is one of the most promising converter topologies for medium/high-power applications. One of the technical challenges associated with the control of an MMC is the capacitor voltage balancing among arm capacitors. This paper presents a novel capacitor voltage balancing method combined with the carrier-phase-shifted pulse-width modulation (CPS-PWM) for MMC without...
In this paper the modular multilevel converter (MMC) is proposed as the wind power converter for offshore dc grids. MMC has been widely used for high-power high-voltage applications, and it is able to connect a low ac voltage source to a high dc voltage source, which makes it a promising solution for wind power converter in offshore wind farm dc grids. This paper presents the analysis and design of...
We consider a parallel multiple-input multiple-output (MIMO) relay network, in which a source node communicates with a destination node assisted by multiple parallel relays. In such a network, it is costly to acquire global channel state information (CSI) at every relay node. In this regard, we assume local CSI, i.e., each node in the network knows perfect CSI of the links from and to this node, but...
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