An Alternative Control Structure for Grid-Following Converters of Inverter-Based Resources

In this paper, an alternative control structure of grid-following control is proposed and applied in inverter-based resources (IBRs). An IBR’s grid-following control normally employs Power/Voltage (P/V) control strategy to control the output real power and the voltage at the point of common coupling bus. Compared with the conventional cascade structure, the proposed alternative control structure follows the principle of robust cascade structure. It has the same inner current control for current order tracking while the outer loop is redesigned. This new design leads to power order and voltage order tracking without use of integral control. This point alone is advantageous since an integral control has the known issue of saturation and anti-freezing has to be implemented. The purpose of such structure is to be robust against the uncertainty in the inner feedback system. We implement the robust cascade control and examine its capability of accommodating choke filter parameter variation. Besides this capability, the control’s weak grid stability performance and low voltage ride through performance are also examined. Using nonlinear analytical model-based eigenvalue analysis and nonlinear dynamic simulation, we find that the robust cascade control structure can be designed to accommodate choke filter parameter variation, improve weak grid stability, and avoid overvoltage after fault clearance.