Design Of DC/DC Converter Of DC Distribution Network And Research On Stability Control

With the emergence of energy shortage and environmental pollution problems,the rational development and utilization of renewable energy has become an urgent problem to be solved.In addition,the electricity load of each big city becomes intensive increasingly,the urban distribution network is confronted with the problem of line corridor tension,power supply capacity insufficiency and short power supply radius,which makes the traditional AC distribution system difficult to continue,DC distribution network which has many advantages is brought into schedule.The interconnection of DC distribution network with DC load,DC micro grid is the key to realize the DC distribution network.It will be an urgent demand for a DC/DC converter of high power and voltage,also known as DC solid state transformer.The DC/DC converter has the technical requirement such as galvanic isolation,high efficiency and small size,bidirectional power flow and low voltage harmonic.Besides,the voltage regulation method and stable operation technology of DC distribution network consisted of DC converters also have important significance.This kind of DC/DC converter usually adopts isolated topology.In this paper,the main circuit structure and control strategy of three-level DC/DC converter and input-series-output-parallel DC/DC converter are designed,the generalized state space average model is built and their characteristics are discussed and analyzed,and a physical model machine is set up to validate them.In the system level of DC distribution network,the preliminary assumption of DC distribution voltage rating and the suggested values of DC distribution voltage deviation are proposed.Based on these,a new hierarchical coordinated control and a novel droop control based on discrete consensus algorithm which realizes the current sharing of parallelled DC/DC converter when considering the line impedance are proposed,and it is validated on the existing experimental platform.In order to realize the stable operation of DC/DC converter in DC distribution network,the stability condition of DC distribution network is studied,and the influence of droop coefficient,line impedance and load type on system stability is studied by improved impedance analysis method.And an active damping control method based on series compensation is presented,and the correctness of the control strategy is verified in PSCAD/EMTDC.