Traffic flow velocity disturbance characteristics and control strategy at the bottleneck of expressway

In the three-phase traffic flow studies, the traffic flow characteristic at the bottleneck section is a hot spot in the academic field. The controversy about the characteristics of the synchronized flow at bottleneck is also the main contradiction between the three-phase traffic flow theory and the traditional traffic flow theory. Under the framework of three-phase traffic flow theory, this paper takes the on-ramp as an example to discuss the traffic flow characteristics at the bottleneck section.In particular, this paper mainly conducts the micro-analysis to the effect of lane change under the two lane conditions, as well as the effect of the on-ramp on the main line traffic flow. It is found that when the main road flow is low, the greater the on-ramp inflow rate, the higher the average speed of the whole road section. As the probability of vehicles entering from the on-ramp increases, the flow and the average speed of the main road are gradually stabilized, and then the on-ramp inflow vehicles no longer have a significant impact on the traffic flow. In addition, this paper focuses on the velocity disturbance generated at the on-ramp, and proposes the corresponding on-ramp control strategy based on it, and the simulation verified that the control strategy can reasonably control the traffic flow by the on-ramp, which can meet the control strategy requirements to some extent.

Sequential auto-reclosing strategy for hybrid HVDC breakers in VSC-based DC grids

The use of overhead lines for power transmission in the future high-voltage and large-capacity voltagesource converter(VSC)-based direct current(DC) grid will significantly increase the probability of temporary faults.To eliminate potential adverse impacts such as erroneous protection, line-insulation failure, and even damage to power electronic devices resulting from a DC breaker reclosing operation with the traditional sequential autoreclosing strategy, a new sequential auto-reclosing strat-egy for hybrid HVDC breakers(HHBs) in VSC-based DC grids is proposed. This strategy is based on the step-by-step operation of the transfer branch in the HHB. As a result,du/dt resulting from the HHB reclosing operation is greatly reduced, and therefore those potential negative impacts can be eliminated. Several other advantages are also presented.The feasibility and validity of the proposed strategy are verified in a four-terminal annular VSC-based DC grid electromagnetic transient model.

Overview on Fault-Tolerant Four-Switch Three-Phase Voltage Source Converters

With the rapid development and widespread applications of power electronic converters,strong fault-tolerant capability of power electronic converters is required since they play important roles in power systems.In this paper,a review of one of the most promising fault-tolerant topologies for semiconductor open-circuit fault,called four-switch three-phase(FSTP)topology,is presented in terms of modeling analysis,modulation techniques,and control strategies.The configuration of FSTP voltage source converter(VSC)is illustrated.To minimize the negative effects caused by the innate drawbacks of this fault-tolerant converter topology,considerable research has been carried out regarding modulation techniques and control strategies.The modulation principle for FSTP topology is explained in detail,since the performance of FSTP VSCs relies on it.This paper aims to illustrate current research progress on this fault-tolerant FSTP VSC topology.