Synchronous Power Control of Grid-Connected Power Converters under Asymmetrical Grid Fault

Abstract

[...]the statics and dynamics of the renewable power generation units are both different compared with the synchronous generators. According to grid code requirements, grid-connected power converters should be capable of getting through grid fault scenarios to let generation units remain connected under such adverse conditions, and further provide ancillary services to support the grid voltage and frequency. The mechanical part of the SPC generates the reference frequency, ωr*, which corresponds to the inner frequency of a synchronous generator, and it swings around the rated frequency ωs following the relation expressed as: ωr*=ωs+(P*−P)ωn2/Pmaxs+2ξωn where P* is the active power reference, P the generated active power, Pmax is a transmission gain between the load angle and the generated power used in the active power control loop modeling, ξ, and, ωn, the damping factor and the natural frequency of the second-order power loop transfer function. Since the form of Equation (1) is deducted based on the dynamics of the generator rotor, ωn can be translated to the inertia constant, H, following Equation (2). The transfer function for each branch has the same form and can be generalized as: ΔirefΔv(s)=1Rn+sLn,n=1,2,3 Then, we can estimate the settling time of the virtual admittance that responds to a variable input. Since in this application the input signals for the admittances, Δv, can be assumed sinusoidal, the time response can be estimated by the response of the magnitude of the two output signals that are generated by giving two sinusoidal input signals in quadrature.