Multi modular converters with automatic interleaving for synchronous generator based wind energy system

Abstract

Growing trend of multi mega watt turbine installations is one of the reason behind the increasing popularity of modular converter technology. This paper focuses on direct driven synchronous generator (SG) based variable speed wind turbine (VSWT) that are connected to power grid via modular converter units. Compared to medium voltage, full rating power converter, multi modular design exhibit better harmonic performance and is also superior in terms of both system reliability and efficiency. Research previously conducted on modular converters focused on controller design that either had a centralized structure or had master slave configuration [1]. Designing autonomous/ distributed controllers for modular converter system is objective of this research. Besides equal power sharing among operational units, the other main challenge in design of distributed controller was to ensure, under all conditions, an interleaved operation of the parallel modules. In interleaving, parallel power stages share same switching frequency but have carrier phases displaced uniformly throughout the switching period. With interleaving, ripple in the output current is significantly reduced which enables use of smaller sized filter components [2]. An autonomous controller will greatly improve system's reliability and redundancy. In order to test the designed controller, simulation of a 4MW, direct driven synchronous generator (SG) based variable speed wind energy conversion system (WECS) was carried out in Simulink®. The system is connected to grid via two parallel operating converter (rectifier/inverter) units and was examined under various test conditions. Simulation results show good performance of the designed controller.