A full-size converter-fed synchronous machine (CFSM) for variable speed operation of a pumped storage power plant exhibits multiple advantages over the state-of-the-art doubly fed induction machine (DFIM) technology. The CFSM technology is emerging as the most flexible system for pumped storage plants for efficient operation in a wide range of water flows, which is not the case in existing power plants.  This article presents steady-state control strategies to execute the variable speed operation of the pumped storage power plants in both turbine and pump mode using a full-size back-to-back converter. Furthermore, the starting method of the power plant in pump and turbine mode from a standstill is proposed. In addition, the seamless transition of operating modes from the turbine to pump mode and vice versa is presented, which is an essential feature required to adapt to the varying power generation from renewable energy sources like solar and wind. The behavior of the power plant during a voltage dip on ac grid, and the low-voltage ride-through (LVRT) capability in both turbine and pump modes are also presented. The proposed control strategies are experimentally verified with a 100 kVA machine and converter setup with an emulated reversible pump turbine (RPT) and waterways.