Adaptive Virtual Synchronous Generator Modulation Strategy Based on Moment of Inertia, Damping Coefficient and Virtual Impedance

The technology of virtual synchronous generator improves the limitations of inverter control strategy and enhances the acceptance of new energy generation in traditional power system, and yet it greatly affects the frequency dynamic regulation ability of the power grid. Meanwhile, in order to solve the problem of power coupling in medium and low voltage microgrid, many methods have been proposed to change the equivalent output impedance of the system by introducing virtual impedance to improve the stability of microgrid system. For this purpose of optimizing the frequency regulation ability of the system, this paper designs an adaptive control strategy of the moment of inertia and damping coefficient to improve the frequency response characteristics of virtual synchronous generator under the conditions of given active power change and grid frequency fluctuation. In addition, in order to solve the contradiction between the moment of inertia, damping coefficient and the frequency response speed, the voltage vector relationship of virtual synchronous generator under interference is analyzed from the perspective of virtual impedance, and an adaptive virtual impedance control strategy is proposed to accelerate the frequency modulation process of the system. Consequently, one cooperative adaptive control strategy of the moment of inertia, damping coefficient and virtual impedance is proposed. On the basis of ensuring the virtual synchronous generator to give full play to its own operation advantages, this method achieves the purpose of enhancing inertia and accelerating the frequency response speed from various perspectives. The simulation results prove the feasibility of the proposed control strategy

Advanced control techniques for modern inertia based inverters

”In this research three artificial intelligent (AI)-based techniques are proposed to regulate the voltage and frequency of a grid-connected inverter. The increase in the penetration of renewable energy sources (RESs) into the power grid has led to the increase in the penetration of fast-responding inertia-less power converters. The increase in the penetration of these power electronics converters changes the nature of the conventional grid, in which the existing kinetic inertia in the rotating parts of the enormous generators plays a vital role. The concept of virtual inertia control scheme is proposed to make the behavior of grid connected inverters more similar to the synchronous generators, by mimicking the mechanical behavior of a synchronous generator. Conventional control techniques lack to perform optimally in nonlinear, uncertain, inaccurate power grids. Besides, the decoupled control assumption in conventional VSGs makes them nonoptimal in resistive grids. The neural network predictive controller, the heuristic dynamic programming, and the dual heuristic dynamic programming techniques are presented in this research to overcome the draw backs of conventional VSGs. The nonlinear characteristics of neural networks, and the online training enable the proposed methods to perform as robust and optimal controllers. The simulation and the experimental laboratory prototype results are provided to demonstrate the effectiveness of the proposed techniques”--Abstract, page iv

An adaptive control strategy with a mutual damping term for paralleled virtual synchronous generators system

When multiple virtual synchronous generators (VSGs) operate in parallel, load disturbance or the change of setpoint can induce serious frequency and active power oscillations. To address this problem, an adaptive control strategy with a mutual damping term is proposed in this paper. Firstly, the impacts of the moment of inertia and damping coefficient on the characteristics of the VSGs are analyzed comprehensively. Then, an adaptive control method considering the frequency deviation and rate of change of frequency is proposed to improve the frequency dynamics. In order to further dampen the power oscillations of the system with multi-paralleled-VSGs, a mutual damping term is added. The stability proof of the proposed method is based on the Lyapunov Stability Theorem and design parameters guidelines are given. Finally, simulations in Matlab/Simulink and experiments are carried out to verify the effectiveness of the proposed method

Secondary frequency regulation scheme based on improved virtual synchronous generator in an islanded microgrid

To aim at the defects of the traditional VSG (virtual synchronous generator) control schemes to only complete the primary frequency regulation equivalent to droop control, and not to realize the secondary frequency regulation, this paper proposes a new control scheme to realize the secondary frequency regulation of the VSG, such that system frequency can return to the rated value. In this method, the torque change process of the rotor of synchronous generator is firstly analyzed when the system active power fluctuates. And then, a novel secondary frequency regulation control strategy of the VSG is proposed, where the small-signal model of power transmission of the VSG is established and transfer function is analyzed, and parameters design and stability analysis of the control system are conducted. Finally, simulation experiments show the correctness and effectiveness of the proposed method