The Research On The Control Strategy And Simulation Of DC Grid

With the increasing depletion of fossil energy, China has been rising up the development of renewable energy to an important position, and gradually realizes the strategic adjustment of energy structure. Traditional power equipment, power grid construction and operation technology in facing these challenges, in particular to accept very large scale, low quality of new energy, has appeared increasingly to be inadequate, And new technology, equipment and network structure should be adopt to meet profound changes in future energy landscape. This paper analyzes the intermittency and instability characteristics of renewable energy, as well as stability problems associated with connection of centralized renewable energy generation and AC network, pointing out that the use of HVDC flexible technology can Suppress reactive power fluctuations and solve active volatility by building wide-area coverage of the DC power to effectively implement smooth access solutions of renewable energy sources. Building a national backbone DC transmission grid can not only make use of renewable energy more efficiently, but will also actively promote the construction of smart grid. DC grid has a greater advantage in future Urban DC power distribution, micro grid and other fields compared with AC systems. HVDC is experiencing end to end HVDC-multi-terminal HVDC/DC Grid development process.Since DC Grid contains many DC terminals, how to control the DC terminals to ensure stable operation of the system is an important research topic of DC power grid construction. DC grid control system can be divided into three levels:system-level control, station-level control, valve-level control. The DC grid station-level control and valve-level control for is basically the same with end-to-end DC system. The system-level control refers to the coordination and control of the terminals, mainly consist of master-slave control and droop control. For master-slave control, the master station control DC voltage, and slave station achieve constant power or constant current control of power supply; for droop control, multi-station control system DC voltage. In master-slave control mode the voltage regulation performance and load distribution has good rigidity, but requires dispatch system for power distribution and higher volume of the master station, droop control can basically achieve proportional power supply and stabilize power supply with no communication and dispatch system to some extent, but the DC voltage deviation exists. Additionally the master-slave control and droop control can be used in combination. In this paper, for the DC grid dendrimers, ring and mesh typical topologies, simulation is done to study the three control strategy, comparing the advantages and disadvantages of different control strategies.Based on973Project " large-scale new energy electricity security and efficient use in smart grid basic research", the DC grid physical simulation platform is designed in this paper, which can accomplish network connection of a variety of new energy under different topologies simulation with scalability of DC lines and terminals, verify the DC power control strategy, and implement the principle verification and performance comparison of DC power critical equipment include different types of DC circuit breakers, DC/DC converters, etc.