Research On Small Signal Stability Analysis And Parameter Optimization Design Of Medium Voltage DC Distribution System

With the introduction of more and more distributed energy sources and the emergence of DC loads,the traditional AC power distribution system is unsustainable.The advantages of DC power distribution system,such as easy access to distributed energy,few AC/DC conversion links of source and load,excellent power quality,low line loss,low cost,and high transmission capacity,are expected to become an important form of future power grid development.Compared with low-voltage DC distribution systems,medium-voltage DC distribution systems are more suitable for industrial parks and areas with dense power supply loads,and will be the main component of future DC distribution systems.Considering that the topology and control of many different types of converters in the medium voltage DC distribution system are quite different,and the coupling characteristics of electrical parameters are obvious,which may easily cause system instability problems and cause busbar voltage collapse and other conditions that affect the safe and stable operation of the system.Therefore,it is necessary to analyze the small signal stability of the medium voltage DC distribution system.This paper takes the medium voltage DC distribution system as the research object,analyzes the factors affecting the stability of the system with small disturbances,gives different parameter constraint boundaries,provides theoretical guidance for system material selection,planning and design,etc.,and proposes corresponding control parameters to optimize stability.The control strategy provides a reference for the actual operation of the medium voltage DC distribution system.The research work of this article mainly includes the following contents:First of all,this article takes the medium voltage DC power distribution system as the research object,introduces the topological structure,operation mode and control strategy of the medium voltage DC power distribution system,establishes small signal models of key converters,and builds multiple series and parallel connections Combine the equivalent model of the integrated module unit.The accuracy of the small-signal model of the medium-voltage DC distribution system is verified by the frequency sweep method and the dynamic process of comparing the numerical value and the electromagnetic transient simulation.Secondly,in order to determine the factors affecting the small-signal stability of the medium-voltage DC distribution system,based on the sensitivity,the key parameters in the system that have a greater impact on the characteristic values of the low-frequency range with low stability margins are selected.Analyze the change trend of system stability through the change of characteristic root locus.It is concluded that too small line resistance,MMC converter arm capacitance,and LLC resonant converter magnetizing inductance may lead to system instability,while excessive MMC converter arm inductance and control parameters may also cause system unstable operation,Resulting in adverse effects such as the DC bus voltage and the large oscillation of the converter output current.Third,in view of the control parameters that have a greater impact on the system stability analyzed in the previous chapter,a control parameter design based on the whale optimization algorithm is proposed: considering the system’s small signal stability and dynamic response speed and other factors to determine the control parameter value range,To improve the stability margin of the system,that is,to increase the distance between the eigenvalue and the virtual axis,the whale algorithm is used to achieve this optimization problem,which improves the dynamic performance of the system bus voltage and transmission power under small disturbances.Finally,this paper builds a simple medium voltage DC power distribution system model based on the RT-LAB semi-physical experiment platform,and conducts control parameter optimization design experiments.Experimental results show that the control parameter optimization and stability control strategy proposed in this paper effectively improves the dynamic process and adjustment time of the bus voltage and transmission power under small disturbances such as load or light fluctuations.