Stability Analysis And Control Of DC Power Distribution System Based On Virtual Synchronous Generator

With the increasing penetration of distributed energy sources,DC distribution networks have become an effective way to absorb renewable energy.The DC distribution network is highly efficient,stable,and highly reliable.There are no problems such as reactive power,frequency,three-phase unbalance,and power angle stability.However,the DC distribution network is a low-inertia,weakly damped network.Frequent switching and power fluctuations of the load and power supply in the network will affect the system stability.In this paper,the control strategy of the virtual synchronous generator in the DC distribution network is studied,aiming to improve the DC bus voltage in the DC distribution network to suppress the voltage transient oscillation,provide inertial support for the DC distributio n system,and then improve the stability of the DC distribution system.The main work completed is as follows:(1)Analyze the traditional virtual synchronous generator control strategy in the AC system,and analyze its working principle in detail to obtain the active-frequency regulation equation and reactive-voltage regulation equation,and then obtain the overall virtual synchronous generator control strategy.Contrasting the expression and physical meaning of inertia in AC and DC systems,combined with the analogy in the control method of AC and DC systems,a virtual synchronous generator control strategy for DC systems is proposed.It will lay a foundation for the follow-up research of improved control technology and stability analysis of virtual synch ronous generators in DC distribution system.(2)A virtual synchronous generator control method for DC distribution system with adaptive virtual inertia coefficient is proposed.The small-signal model and transfer function of grid-connected inverter under the control of DC virtual synchronous generator are established.Using the step response of the transfer function and the pole-zero distribution map,the influence of the values of the inertia coefficient and the droop coefficient on the response speed,t he system steady-state value and the system stability is obtained.And on this basis,according to the DC bus voltage oscillation characteristics,an adaptive inertia coefficient control strategy is proposed.(3)Propose the control method of DC virtual synchronous generator based on leading lag link.The characteristics of the first-order virtual inertia virtual synchronous generator control strategy were analyzed,and a small-signal closed-loop transfer function of DC bus voltage was established.By analyzing the characteristics of its zero-pole distribution,damping ratio,adjustment time,and steady-state power error,it is concluded that the values of inertia coefficient and droop coefficient cannot take into account the contradictory relationship between small steady-state power error,large dynamic damping,and fast adjustment speed.In response to this contradictory relationship,the lead lag link is added to the DC virtual synchronous generator control to compensate,while increasing the system dampi ng,the system response speed is accelerated,and the DC bus voltage overshoot is also suppressed.(4)In the DIg SILENT simulation platform,the traditional DC virtual synchronous generator control,adaptive coefficient DC virtual synchronous generator con trol and lead lag link compensation DC virtual synchronous generator control simulation model are built,and the proposed control strategy is verified In different scenarios,it can play a role in improving the stability of the system's DC distribution,pr oviding inertial support and improving the quality of the DC bus voltage.