Coordinated control of grid-connected three-level NPC converter under distorted grid voltage

This paper presents complete control algorithm for grid-connected Pulse Width Modulated (PWM) AC/DC converter intended for industrial drives and renewable energy applications. The objective of control is to limit current harmonics distortion and provide ride through capability during voltage dips. Following improvements to Voltage Oriented Control are presented: synchronization loop with positive sequence extraction, resonant current controllers for higher harmonics compensation, grid voltage feedforward loop for dips compensation and DC voltage filter. Algorithm is tested in simulations and on experimental 15kVA platform using three-level NPC converter with LCL filter.