Direct Current Power Distribution System Research Articles

Bus-impedance-based stability improvement of DC power distribution system considering dynamic performance

A direct-current (DC) power distribution system (PDS) enjoys the benefits of flexibility and efficiency. However, increasing stability issues occur due to the interaction among feedback-controlled converters in PDS. For ensuring stability, various impedance-based method is discussed by scholars. Unlike the traditional analysis method based on minor-loop-gain (MLG), Passivity-Based Stability Criteria (PBSC) is a novel bus-impedance-based method. Although PBSC is a promising measure of stability analysis for the distribution system, the difficulty of stability margin calculation and dynamic characteristic analysis limits its application. Therefore, the relative stability margin (RSM) is proposed to assess the damping levels. Based on RSM, the dynamic performance optimization algorithm (DPOA) is presented to optimize the proposed MMC impedance reshaping (MIR) control. Compared with the past stability analysis, dynamic behaviour is considered in this paper when stability improvement is implemented. By means of the MIR and DPOA, the stability and dynamic performance of the distribution system are enhanced. Simulation results confirm the validity of the proposed viewpoints and method.

Intelligent decision optimization for energy control of direct current power distribution system with multi-port access for intelligent buildings

The structure of direct current (DC) appliances is simpler and more energy-efficient than that of alternating current (AC) appliances. With the proliferation of novel DC loads (e.g., e-bikes and electric vehicles), DC loads will dominate the loads in buildings. It is necessary to develop a DC power distribution method that better accommodates renewable energy, effectively improves the working efficiency of loads, and significantly enhances energy utilization efficiency. However, there is not yet a unified design for the multi-port converter of DC microgrids. The experience is severely lacking in the overall energy planning for buildings from the perspectives of economy and environmental friendliness. To solve the problems, this paper explores the intelligent decision optimization for energy control in DC power distribution system with multi-port access for intelligent buildings. Firstly, a feature analysis was carried out on the multi-port converter of the DC power distribution system for intelligent buildings. With economy and environmental friendliness as the goals, the authors designed constraints related to energy output power, power balance, and distribution node voltage, and established an intelligent decision optimization model for the energy control of the DC microgrid for intelligent buildings. The model was combined with the multi-attribute decision-making framework into a decision-making framework for the coordinated operation of distributed energy supply units, which is based on the interval evidential reasoning (IER). Finally, the authors proposed an evaluation method for the decision-making of the energy control of DC power distribution for intelligent buildings, based on the Maclaurin symmetric mean (MSM) operator, and the IER-based decision-making framework. The proposed method was proved effective through experiments.

Modified Minimum Spanning Tree for Optimised DC Microgrid Cabling Design

The construction of low-cost nanogrids could help speed up the electrification rate in remote communities in sub-Saharan Africa. One of the challenges in nanogrid design for these communities is the uncertainty in future load demand profiles impacting the cabling topology. We propose two new wiring design approaches for radial direct current power distribution systems. The first one is a modified minimum spanning tree (MST) algorithm and the second one is an adaptive shuffled frog leaping algorithm (SFLA). Their objective is to identify the optimal cable path and the lowest cost wiring characteristics to electrify rural areas with poor infrastructural development. A comparative study of computation burdens has shown the applicability limits relative to the SFLA based approach and encouraged the implementation of the MST as it is faster and does not imply any limitation regarding the number of dwellings to electrify, while providing low-cost wiring design option. The latter is applied to a village located in Kenya and demonstrated more than 25% savings on the entire system cabling cost compared to a classical wiring design based on shortest-path calculation.

Research on the Optimal Operation Method of DC Microgrid Base on the New DC Power Distribution Management System

The grid-connected operation of the distributed generation (DG) via the direct current (DC) microgrid is the operation mode of the DC power distribution system in the future. Considering the grid-connected operation of multiple DC microgrids, we have proposed a new type of DC power distribution management system aiming at the lowest operating cost of the entire DC power distribution system. Our proposed DC power distribution management system can be used to carry out the optimized dispatching for the connected DC microgrids, thereby achieving the economic, safe, and stable operation of DC power distribution management systems. At the same time, through the different nodes where the modular multilevel converter (MMC) is connected to the alternating current (AC) distribution network, a DC power distribution management system can control the active and reactive power generated by the MMC, achieving the control of the load flow of the upper-stage AC grids in real time. The example simulation shows that the method proposed in this paper has a great role in reducing the transmission losses of the power distribution network, achieving electric power peak-load shifting, and utilizing renewable energy. Thus, it can not only maximize the use of distributed renewable resources, but also enable mutual support and optimal scheduling between a DC power distribution system and multiple microgrids.

Research on Access Mode of the Flexible DC Power Distribution System into AC System

The connection mode of the direct current (DC) power distribution system and the alternating current (AC) system is the foundation of system design, and it is also one of key technologies of the DC power distribution network. Based on the topology structure, grounding method, main equipment parameters, load parameters and system control protection strategy of the DC power distribution system, this paper establishes the system simulation model in the case of configuring the connection transformer and not configuring the connection transformer. Simulation results show that, when no connecting transformer is installed, the interaction between AC and DC systems will be great when faults occur, and the cost of converter valves and DC reactors will be increased. When connecting transformers are installed, the interaction between AC and DC systems can be effectively isolated, and the operation reliability of the system will be greatly improved while the cost is saved. Therefore, it is recommended to configure an independent connection transformer in the DC distribution system.

A Hybrid Building Power Distribution System in Consideration of Supply and Demand-Side: A Short Overview and a Case Study

As the quantity of direct current (DC) load and wireless power transmission (WPT) devices are continuously increasing in building, in order to efficiently utilize renewable energy (which outputs DC power) such as photovoltaic (PV), especially for building integrated photovoltaic (BIPV), and regeneration energy from elevators (which also outputs DC power), a novel building power distribution system architecture is explored in consideration of the characteristics of supply and demand-side in this paper. The proposed architecture is a hybrid framework integrated with conventional alternating current (AC) power distribution system, DC power distribution and WPT system. The applied AC and DC hybrid power distribution system has higher conversion efficiency than a single AC power system, which indicates that the former is becoming an important trend of building power distribution. In addition, the results of experimental test in a case study suggest that the proposed architecture can provide fine service for efficient application of renewable energy and regeneration energy in building. The obtained results also can serve as a foundation to promote the development of building power distribution system and related practical application in building.

Power Quality in DC Power Distribution Systems and Microgrids

This review paper discusses power quality considerations for direct current (DC) electric power distribution systems, particularly DC microgrids. First, four selected sample DC architectures are discussed to provide motivation for the consideration of power quality in DC systems. Second, a brief overview of power quality challenges in conventional alternating current (AC) distribution systems is given to establish the field of power quality. Finally, a survey of literature addressing power quality issues in DC systems is presented, and necessary power quality considerations in DC distribution system design and operation are discussed.

Design Methodology of Bidirectional CLLC Resonant Converter for High-Frequency Isolation of DC Distribution Systems

A bidirectional full-bridge CLLC resonant converter using a new symmetric LLC-type resonant network is proposed for a low-voltage direct current power distribution system. This converter can operate under high power conversion efficiency because the symmetric LLC resonant network has zero-voltage switching capability for primary power switches and soft commutation capability for output rectifiers. In addition, the proposed topology does not require any snubber circuits to reduce the voltage stress of the switching devices because the switch voltage of the primary and secondary power stage is confined by the input and output voltage, respectively. In addition, the power conversion efficiency of any directions is exactly same as each other. Using digital control schemes, a 5-kW prototype converter designed for a high-frequency galvanic isolation of 380-V dc buses was developed with a commercial digital signal processor. Intelligent digital control algorithms are also proposed to regulate output voltage and to control bidirectional power conversions. Using the prototype converter, experimental results were obtained to verify the performance of the proposed topology and control algorithms. The converter could softly change the power flow directions and its maximum power conversion efficiency was 97.8% during the bidirectional operation.