Sliding mode control strategy of grid-forming converters via virtual flux orientation
The gradual penetration of new energy into the modern power system is causing more severe stability is-sues.Due to the unique merits in enhancing the system stability,grid forming control is becoming one of the main-stream control approaches in large scale integration of renewable power.Therefore,this paper aims to propose a no-vel sliding mod control method for grid-forming converters via the virtual flux orientation,which enables the con-verters with the characteristics of virtual synchronous generator to support grid integration and synchronized opera-tion of renewable energy.First of all,the concept of virtual flux for the grid-forming converter is proposed,which is denoted by the time integral of the voltage source converter(VSC)terminal voltage.Via a virtual flux controller,the virtual flux is reoriented to the reference axis of the swing equation of the virtual synchronous generator,thereby the grid synchronization is achieved.Moreover,the proposed virtual flux reorientation scheme is capable of control-ling the active/reactive power and voltage of the VSC.To prevent the overcurrent of the converters during grid fault condition,this paper also proposed a short circuit current limiting approach to enhance the low voltage ride through capability of the system.Finally,the effectiveness of the proposed method is validated in RTDS simulation plat-form.
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