Three Phase Rectifier Control Based On Virtual Synchronous Machine

At present,more and more renewable energy is connected to the power grid through power electronic converters.However,the converter using the traditional control concept does not have the same damping and inertia as those of the synchronous generator,as the result,the stability of the power grid become worse when the load fluctuates.The technology of Virtual Synchronous Generator(VSG)simulates the converter as a Synchronous Generator through the control algorithm,which makes the grid-connected converter have inertia and damping,to improve the stability of power grid.Recently,some scholars have proposed the concept of autonomous power system,which allows the converters connected to the power grid to be controlled as virtual synchronous machines,so as to unify the interface characteristics of the whole power grid and become the standard interface of the future energy power grid.The current research on virtual synchronous machine mainly focuses on the power generation side dominated by the inverter,while the research on the power consumption side dominated by the rectifier is less reported.This paper focuses on the control technology of virtual synchronous machine for the rectifier.The work of this paper includes:(1)This paper analyzes the basic principle of virtual synchronous machine technology,introduces how to control the rectifier as a synchronous motor--"the rectifier virtual synchronous machine control technology",and introduces two classic control models of virtual synchronous machine.(2)The virtual synchronous machine technology of the rectifier simulates the grid-side characteristics of the synchronous motor based on the current control algorithm,so its performance is greatly affected by the current controller.This paper presents a current switching control method based on Lyapunov method,which improves the current control performance.The work includes the design of the virtual synchronous machine,the establishment of the switch control model,the design of the switch control rule and the stability proof of the switch control rule.Finally,the algorithm is verified by simulation.The simulation results show that the proposed switching control is robust to the change of current loop parameters and achieve better dynamic performance than the traditional PI and PR control methods.(3)The virtual synchronous machine technique for the rectifier will produce the active power fluctuation under the three-phase imbalance of the power grid.Although the traditional algorithm to deal with the three-phase imbalance can suppress the fluctuation of active power,it is not applicable to the virtual synchronous machine technique or the two-level topology in this paper.In this paper,an dual virtual synchronous machine is proposed to control the negative sequence from virtual synchronous machine to suppress the active power fluctuation.Based on the least square recursive method with forgetting factor,a fast algorithm for separating positive and negative sequence current components is proposed.The simulation results show that the proposed dual virtual synchronous machine control algorithm can effectively solve the problem of active power fluctuation under the three-phase unbalance grid,while ensuring the characteristics of the virtual synchronous machine at the network side.(4)This paper proposes a cooperative control for virtual synchronous machine based the rectifier with energy storage.For the virtual synchronous machine,the local linearization modeling is carried out based on the small signal method,and the key parameters of the virtual synchronous machine are designed using the root locus method.For the energy storage part:according to the dynamic response of the system,the required capacity of the energy storage is discussed,the current control for the three-phase staggered parallel two-way dc-dc topology is designed,The energy storage management strategy is proposed for the cooperation with the rectifier control.Finally,the simulation results show that the proposed method makes the rectifier actively participate in the frequency regulation of the power grid without affecting the load performance.(5)A 5kW prototype rectifier was built.A soft starting method is proposed for the rectifier with VSG algorithm,the implementation of the proposed soft starting scheme is introduced in three steps.The overall architecture of VSG algorithm software is designed,and the effectiveness of the proposed VSG algorithm and soft start method is demonstrated through the experimental results.