To reduce the voltage fluctuations inside the wind farm cluster (WFC), a combined active and reactive power control schemes based on model predictive control is proposed. The aims of the proposed control scheme are to maintain the collector bus and wind turbine (WT) terminal voltages within the feasible range. With the size of WFC increasing, conventional centralised optimal control may no longer be suitable for a large-scale WFC due to the high computation burden of the WFC central controller. To improve the calculation efficiency and protect information privacy, a two-tier control structure with alternating direction method of multipliers (ADMMs) algorithm is used to solve the large-scale optimisation problem in distributed/hierarchical manner. In the upper-tier distributed control, the active and reactive power outputs of the WFs are coordinated to enhance the voltage control performance. In the lower-tier control, an ADMM-based hierarchical control is developed to minimise the voltage deviation of the WT terminals. Case studies demonstrate the efficacy of the proposed two-tier combined active and reactive power controls.