Minimum number of permanent-magnet synchronous generators for coordinated low-voltage ride-through of induction generators in hybrid wind farms

Coordinated low-voltage ride-through (LVRT) of induction generators (IGs) utilizing the excessive reactive power of permanent magnet synchronous generators (PMSGs) in hybrid wind farms is attractive due to saving investments on shunt compensators. The existing research is mainly based on dynamic simulations to given scenarios and does not quantify the necessary capacity and number of PMSGs. This paper newly proposes an analytical model to quantify the minimum number of the PMSGs for coordinated LVRT. The critical voltage at the point of common coupling (PCC) leading to slip instability of the IGs is quantified. To avoid instability, necessary var support from the PMSGs to improve the PCC voltage above the critical value is proposed. With the improved var control to the grid-side converter (GSC), the minimum number of PMSGs is determined. Numerical results are provided to validate any error of the proposed model, which shows that voltage drop at the PCC, power capability of the PMSGs, and control strategy of the GSC are the critical factors for coordinated LVRT.