Low Voltage DC to Medium Voltage AC Step-up PV Grid-Connected Inverter Module With Robust DC-link Voltage Balancing, MPPT and Grid-Side Control

This paper proposes a combined voltage balancing, fault voltage mitigation and grid-side control technique for a two-stage low voltage DC (LVDC) to medium voltage AC (MVAC) step-up five-level based inverter for PV energy conversion system. In the presented system, a DC-DC front-end converter for providing maximum power point tracking while several inputparallel output-series (IPOS) modular step-up resonant dc/dc converters are employed to boost the PV output voltage to the MVDC level. A five-level grid-side inverter is then used to interface with the MVAC grid, hence, the conventionally used low frequency step-up transformer is eliminated. A voltage balancer is used to both balance the DC-link capacitor voltages and minimize the fault-voltage. In addition, the balancer controller is able to operate without impacting the maximum power extraction and grid-feeding capabilities of the front-end DC/DC converter and the grid-side five-level inverter. Results are provided in PSCAD on a 2MW, 34.5kV grid voltage PV farm operating with different faults to validate the effectiveness of the proposed MV PV inverter system.