Assoc. Prof.Jinsong Tao School of Electrical Engineering and Automation, Wuhan University, China | With the progress of social economy, Direct Current (DC) loads, DC power supplies and other kinds of equipment are increasing. The need for decentralized access and application of all kinds of new energy puts forward new requirements for modern distribution network. Thus, the distribution network urgently needs a DC distribution system to play the load transfer control function. A flexible DC transmission technology combined with a DC micro grid was adopted to form such a flexible DC power distribution system. It can realize the coordinated distribution of power among converter stations, with more diverse operation modes, and improve system reliability. As power control becomes relatively complicated, it is not only necessary to consider the voltage and power control of each station itself, but also to consider the coordinated control strategy between the stations and the problem of power flow reversal. We first introduce the main structure of a multi-terminal flexible DC distribution network demonstration project in a certain area of China Southern Power Grid.Combining the existing coordinated control method and the multiple operating conditions of a main loop topology in a certain area of China Southern Power Grid, an analysis revealed the coordinated operation conversion mode of the main working status of the three-terminal power supply and the corresponding control strategy scheme when the power supply fails at each terminal. A voltage droop control with voltage dead zone is adopted on the basis of droop control. Finally, the power failure control strategy scheme was used to realize a three-terminal-to-two-terminal operation mode, and verified by simulations. The proposed control strategy can realize the balanced distribution of power and ensure the coordinated operation of the three terminals. A DC micro grid model was built on the three-terminal parallel loop network simulation model. A comparison of the field test and the simulation experiment, verified the feasibility of the simulation model of the multi-terminal flexible DC distribution system with the DC micro grid as proposed in this paper. |
Assoc. Prof. Sohrab MIRSAEIDI Beijing Jiaotong University,China | Title: Improvement of Capacitor-Commutated-Converter-Based and Fault-Current-Limiting-Based Commutation Failure Prevention Approaches in HVDC Transmission Networks Abstract: Line-Commutated Converter based High Voltage Direct Current (LCC-HVDC) technology has been extensively utilized around the world for long-distance bulk-power transmission due to its merits such as the thyristors superior power handling capability and lower operating power losses. Nevertheless, the development of LCC-HVDC systems suffers from some well-known challenges such as poor voltage regulation ability and vulnerability to commutation failures during inverter AC fault incidents, which can lead to a temporary cessation of transmitted power, overheating of the valves, and misoperation of the protective relays. Commutation failures are frequent dynamic incidents which have been recorded in several existing LCC-HVDC projects around the world. They would become more problematic when several HVDC links terminate in one AC system such as concurrent commutation failures and forced blocking of five converter stations resulting from an inverter AC fault in South China Power Grid in 2010. This accident led to a drastic frequency reduction in the inverter AC system and an overload of the adjacent HVAC lines. Also, the generators at the rectifier side were tripped and spinning reserves were activated at the inverter side to compensate for the loss of active power transfer. Accordingly, commutation failure elimination has been extensively studied over the decades and a large number of approaches have been proposed. These approaches can be classified into three main categories, i.e., modification of the HVDC control system, deployment of capacitor-commutated-converter-based methods, and fault-current-limiting-based techniques. In this talk, the structure of an improved Controllable Commutation Failure Inhibitor (CCFI) is presented which obviates the main drawbacks of the existing capacitor-commutated-converter-based and fault-current-limiting-based strategies. Under normal circumstances, the developed CCFI improves the steady-state stability and the power transfer capability of the inverter AC lines, while it does not cause excessive voltage stress on the converter valves. In addition, it would reduce the risk of commutation failure occurrence, since it does not lead to any voltage drop in the commutation circuit. When a fault occurs at one of the inverter AC systems, its corresponding CCFI limits the fault current depending on the reduced extinction angle. This would not only inhibit the successive commutation failures on the HVDC converter, but also extend the lifetime of components in the inverter AC systems. |
Assoc. Prof. ANWAR ALI Zhejiang Sci-Tech University, China | Title: Design and Development of a Small Satellite Subsystems-AraMiS-C1 Abstract: The nanosatellite market is rapidly growing for scientific and commercial applications. The main reason is the availability of low-cost commercial-off-the-shelf (COTS) components and already-developed subsystems in the market. This evolution also enabled many universities and small & medium-sized enterprises (SMEs) to develop their own satellites. The problem with small satellites is the available space and weight constraints for housing a large number of required subsystems, such as power, attitude determination and control, telecommunication, and payload. The ultimate solution is to make all subsystems smaller, lighter, and cost effective. In this conference we are going to discuss the subsystems of a small satellite with CubeSat dimension called AraMiS-C1 and specifically power management, attitude determination & attitude control, and telecommunication subsystems. The power management, attitude determination & attitude control subsystems were developed on a single PCB with CubeSat dimensions called CubePMT tile while the telecommunication subsystems (transceivers, RF frontend and antenna) were developed on another CubeSat dimensions PCB called CubeTCT tile. The complete AraMiS-C1 satellite has four CubePMT and two CubeTCT tiles on the external six faces. The developed AraMiS-C1 satellite is light in weight, has lower cost, most of the subsystems is reconfigurable and has a large space inside the cube for payload. |
