A Modular Multilevel Converter with Power Mismatch Control for Grid-Connected Photovoltaic Systems

Date
2017-05-17
Authors
Duman, Turgay
Marti, Shilpa
Moonem, M. A.
Abdul Kader, Azas Ahmed Rifath
Krishnaswami, Hariharan
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract

A modular multilevel power converter configuration for grid connected photovoltaic (PV) systems is proposed. The converter configuration replaces the conventional bulky line frequency transformer with several high frequency transformers, potentially reducing the balance of systems cost of PV systems. The front-end converter for each port is a neutral-point diode clamped (NPC) multi-level dc-dc dual-active bridge (ML-DAB) which allows maximum power point tracking (MPPT). The integrated high frequency transformer provides the galvanic isolation between the PV and grid side and also steps up the low dc voltage from PV source. Following the ML-DAB stage, in each port, is a NPC inverter. N number of NPC inverters’ outputs are cascaded to attain the per-phase line-to-neutral voltage to connect directly to the distribution grid (i.e., 13.8 kV). The cascaded NPC (CNPC) inverters have the inherent advantage of using lower rated devices, smaller filters and low total harmonic distortion required for PV grid interconnection. The proposed converter system is modular, scalable, and serviceable with zero downtime with lower foot print and lower overall cost. A novel voltage balance control at each module based on power mismatch among N-ports, have been presented and verified in simulation. Analysis and simulation results are presented for the N-port converter. The converter performance has also been verified on a hardware prototype.

Description
Keywords
dual active bridge, maximum power point tracking (MPPT), multilevel, neutral-point clamped, utility scale photovoltaic (PV) system
Citation
Energies 10 (5): 698 (2017)
Department
Electrical and Computer Engineering