Grid-Tie Control of Cascade Dual-Buck Inverter With Wide-Range Power Flow Capability for Renewable Energy Applications

This paper presents a grid-tie control system for cascade dual-buck inverter with both active and reactive power flow capability in a wide range under two types of renewable energy sources. A fuel-cell power-conditioning system (PCS) is a Type I system with active power command generated by balance of plant of each unit; and photovoltaic or wind PCS is a Type II system with active power harvested by each front-end unit through maximum power point tracking. Reactive power command is generated by distributed generation control site for both systems. Selective harmonic proportional resonant controller and admittance compensation controller are first introduced to cascade inverter grid-tie control to achieve better steady-state and dynamic performance. Detailed analysis and derivation of both control systems were conducted. A 1-kV·A cascade dual-buck inverter system was designed and interfaced to 120-V, 60-Hz grid to verify the control strategy. Pure active power, pure reactive power, and mixed power flow with leading and lagging angles were fully tested under steady-state and command-dynamic conditions for both systems. The experimental results proved the effectiveness of the designed grid-tie control for both systems.