A multifunctional power flow controller for photovoltaic generation systems with compliance to power quality standards

This paper proposes a three-phase current controlled power inverter for both photovoltaic (PV) power grid injection and power quality improvement. The inverter operates as a shunt active power filter (APF) to compensate the unbalances, harmonics, reactive power and supply voltage fluctuations. It supplies simultaneously the power from the PV array to the load and the grid. The PV source is connected to the active power filter by an intermediate boost dc-dc converter which is controlled using the Maximum Power Point Tracking (MPPT) technique. The MPPT controller´s output determines the DC-bus voltage of the inverter according to PV maximum power. A nonlinear control scheme is proposed for the inverter in order to compensate the source voltage unbalance, the source voltage fluctuations, the current harmonics, the reactive power and the load unbalance. It avoids the use of passive filters that could affect severely the performance of the compensation system and slow down the dynamic response of the system. A bidirectional buck/boost converter is used to control the battery charging and discharging, which is essential in hybrid electrical vehicles or grid back-up sources during peak demand of energy. A combination of linear inductive load with single-phase and three-phase diode bridge rectifiers connected to DC R-L loads is considered. Simulation results that demonstrate the viability and effectiveness of the proposed configuration are presented and discussed.