A Four-Mode Three-State (FMTS) Swinging Bus Controller for PV Micro-Inverters to Achieve Reactive Power Compensation and Remove Electrolytic Capacitor

To manage the instantaneous input and output power mismatch, existing Photovoltaic (PV) inverters usually utilize large electrolytic capacitors or an extra ripple port, leading to short lifespan, low power density or high cost of the system. To address this issue, recently the swinging bus (SB) technique was proposed which only requires thin film capacitors to handle power mismatch. However, existing SB controllers have not yet experimentally demonstrated reactive power capability, which is a requirement in newly released grid codes. In addition, SB controllers are normally unique to specific inverter topologies. To address these challenges, this paper proposes a Four-Mode Three- State (FMTS) swinging bus controller that is applicable to many types of single-phase PV inverter topologies. The approach manages power mismatch using only a small film capacitor, even while achieving reactive power compensation. Simulation and experimental results, based on a series-capacitive-link PV inverter topology, have verified the effectiveness of FMTS SB controller.