Tianwen Zheng

General control strategy to limit peak currents of Virtual Synchronous Generator under voltage sags

Virtual Synchronous Generator (VSG) can facilitate friendly integration of distributed generations. However, during voltage sags, traditional VSG control cannot provide reactive power support, or limit the peak current. To solve these problems, a general control strategy of VSG under voltage sags is proposed. First, the topology of VSG and its control scheme are described to formulate the key problem. Then, three typical control modes are analyzed individually and the methods of generating power references are designed correspondingly. For practical application, the calculation of power reference is modified into a simple and unified form that is applicable to the three modes. Simulation results are reported to verify the validity and effectiveness of the proposed control strategy.

A novel control strategy for stand-alone Photovoltaic system based on Virtual Synchronous Generator

This paper proposes the concept of PV_VSG, which mainly means combining Photovoltaic (PV) and Virtual Synchronous Generator (VSG) together. To control PV_VSG operating well in stand-alone mode, a novel control strategy is proposed to match the PV output and the load, which can prevent the PV output voltage from collapsing. First, the topology and the operation scenarios are investigated. Then, the principles of DC voltage collapse and the operation stability regions are clearly analyzed. And the detailed control strategy is deeply presented. Simulation results are also demonstrated to verify the effectiveness of the proposed control strategy.

State feedback exact linearization control of virtual synchronous generator to improve transient performance

Virtual synchronous generator (VSG) is a grid-friendly way to integrate distributed energy. However, when the traditional VSG control method is used, the transient performance of the system may deteriorate when various short circuits occur. To solve this problem, a novel control strategy for VSG is proposed. Firstly, second order nonlinear state space model of signal VSG infinite bus system is analyzed to formulate the problem. Then, the model is transformed into a linear system by exact linearization and linear control law is gained with linear quadratic regulator. Finally, by carrying on inverse transformation, the nonlinear voltage control law is obtained. Simulation results are presented to verify the validity and effectiveness of the proposed control strategy.

A consensus-based frequency control for photovoltaic connected virtual synchronous generators in microgrid

This paper presents a novel consensus-based control strategy of multiple photovoltaic connected virtual synchronous generators (PV-VSG) in microgrid frequency control. The control object is to achieve a fair allocation of active power between different PV-VSGs and control the system frequency to converge to a reference value. Based on the consensus algorithm, a closed control loop is designed and the frequency deviation is considered into the input power reference. The proposed control strategy makes it possible to communicate only with the output variables of PV-VSGs so that communications between different devices are more applicable in practice. Furthermore, the control scheme is designed in an adjustable way without changing the structure of traditional VSG control. The effectiveness of the proposed control strategy is verified in a microgrid model with three PV-VSGs and one synchronous generator on the Matlab/Simulink platform.