Voltage, current and fault control of a multi-port power converter for a grid-connected photovoltaic system
New smart power grids apply automatically controlled power systems that require a modernization of existing technologies. Renewable energy systems such as Photovoltaic power plants convert solar energy into electricity. Conventional 60Hz transformers in such systems can be replaced by novel power converter systems, which reduce production costs, size, and improve efficiencies. This thesis presents a power interface for a large scale solar power plant, utilizing an innovative power balance and fault tolerance control to feed electricity reliably and efficiently to the medium voltage 13.8kV utility grid. This interface consists of a multi-port converter configuration which achieves a high power DC-AC conversion. Each port consists of an array of PV solar panels, a multi-level dual active bridge, a neutral point clamped inverter, and a connection circuit to the grid. This combination of ports is arranged for a three phase output. A connection to the grid entails a system level controller, which can be achieved by a voltage and current balancing control, using a nonlinear concept with integrated feedback loops. Autonomous operation requires the establishment of a fault-tolerant control algorithm, attained by a continuously monitored fault detection circuit. A novel multi-port control is proposed to realize a voltage, current and fault control strategy among cascaded ports. This control is verified in Matlab/Simulink; detailed analysis and simulation results are provided.