As the demand for electric power increases and the proportion of distributed power sources connected to the power grid continues to increase,the micro-grid technology that can supply local power in the case of isolated islands and can be connected to the large power grid is widely used.The microgrid system is powered and connected to the grid by the inverter.However,the inverter is composed of a large number of power electronic components,although the power electronic components have a fast response speed but a hard output characteristic.Moreover,inertia and damping cannot be provided like a conventional synchronous generator,so the stability of the system is degraded,which easily causes the system to oscillate.In recent years,researchers have proposed virtual synchronous generator control to solve the shortcomings of the micro-inverter's smaller inertia and lower available kinetic energy.The controller allows the inverter to simulate the characteristics of the synchronous generator by simulating the equation of motion of the synchronous generator,making the microgrid system more stable.In the case of virtual synchronous generator control,the parameters of the equation of motion can be changed in real time to improve the transient response of the system,which is not possible in practical synchronous machines.In the control of microgrid inverter,a parametric adaptive virtual synchronous generator control strategy is proposed,which not only considers the role of virtual inertia but also considers the influence of virtual resistance coefficient on system stability.The control strategy of this paper is to develop the fitness function with the minimum angular frequency offset and system stability as the target.The improved particle swarm optimization technique can make the values of the virtual inertia and the virtual damping coefficient adaptively adjusted according to the load changes.Particle swarm optimization is used to solve the objective function minimization function.The Lyapunov direct method is used in this paper for transient stability analysis of microgrid inverter systems.In order to improve the reliability and scalability of multi-virtual synchronous generator systems,inverter paralleling is a common technique.However,the active power output from the virtual synchronous generator inverter system that is directly connected in parallel will be coupled,and the reactive power will also be coupled.Therefore,a power circulation is generated,so that the power of the system cannot be correctly allocated.Aiming at the above circulation problem,this paper proposes an adaptive virtual impedance control strategy,which enables each virtual synchronous generator in parallel to adaptively adjust the virtual impedance according to the output active power and reactive power.This strategy reduces the difference in the equivalent output impedance of the parallel virtual synchronous generator system to some extent.By maintaining the equivalent line impedance uniformity,the circulation between the virtual synchronous generators can be significantly reduced.By using the proposed control strategy,the circulating current between the parallel microgrid inverters can be greatly suppressed and the overall performance of the microgrid system can be greatly improved.In this paper,the proposed virtual inertia and virtual damping coefficient adaptive control algorithm is simulated.The experimental results show that the proposed adaptive control algorithm can not only suppress the frequency oscillation but also reduce the system frequency offset,realizing the virtual synchronous power generation.Adaptive control of the machine.The proposed multi-virtual synchronous generator parallel loop suppression control strategy is also simulated.The experimental results show that the proposed control strategy can realize the adaptive control of virtual impedance,thus suppressing the circulation between parallel virtual synchronous generators. |