Neutral-Point Voltage Balancing for Mission Profile Emulator of Three-Level T-type PV Inverter Using Extra Bridge

Abstract

Mission profile emulation (MPE) is a promising method that uses converters to emulate grid characteristics in laboratory tests of Three-Level T-type PV inverters (3LT2I). The shared DC-link between emulator and 3LT2I realizes energy recycling, but introduces an extra zero-sequence loop. This loop deactivates conventional 3LT2I neutral-point balancing methods that generate common-mode voltage, bringing excessive current burden to common-mode choke. Therefore, a neutral-point voltage balancing method using an extra converter leg is proposed in this paper, which is implemented by controlling the DC-link as an LC-filtered converter. In this scheme, the pressure of common-mode choke can be relieved, and the behaviors of the extra bridge is fully decoupled from 3LT2I under test, ensuring isolation and accuracy of testing during emulation. Simulation and results further confirm the feasibility and effectiveness of proposed method.