Inverter for Grid Connection
A solar grid-tied inverter converts the DC output of PV modules into AC power suitable for transmission on the power grid, often deploying reactive power to meet new grid codes. It must always optimize the power output via MPPT (maximum power point tracking) and additionally monitor both the system and grid connection. In practice, each solar inverter installed in solar power plants needs to connect an array or string of PV modules to the power grid. The more efficient the inverter, the better the LCOE (levelised Cost of Electricity) generated by the system.
An on-grid solar inverter is composed of a DC-DC module, a DC-AC module and a control module. DC-DC module is built with a MOSFET, an inductor and a transformer, and functions to provide a stable DC output through rectifying and filtering the unstable DC power produced by PV modules; DC-AC module includes an IGBT array and an output filter circuit to convert the DC output of DC-DC module into an AC output suited for transmission on power grid. Control module is the core of whole system. It has a DSC, a voltage sensor, a current sensor, and a driver that drives MOSFET and IGBT module. DSC calculates the maximum power point of PV module array based on signals collected by sensors including PV modules’ voltage and current, power grid’s voltage and current, as well as phase. Accordingly it sends out instructions to driver which drives DC-DC and DC-AC modules. Furthermore, DSC is able to find out abnormal conditions such as transmission failure of power grid and take measures such as cutting off the connection between inverters and grid to prevent “island effect” occurrences on power grid. Additionally, the control module has an interface for external display showing PV modules’ status and input/output voltage and current, and integrates a RS232/RS485 communication interface to connect with control centers of solar power plants, so that real-time monitoring of solar panels and inverters can be implemented.