Active NPC Converter for Variable Speed Operation of Pumped Storage Hydropower Plant

This paper discusses the full size Active Neutral Point Clamped (ANPC) Converter for large scale (100 MW, 13-15 kV) synchronous machine in a pumped storage hydropower application to enable the variable speed operation. Such a converter provides the flexibility of fast transition of modes from pumping to generating or vice versa. This allows an easy integration of renewable energy sources to the grid. While starting the machine in pump mode, a very high starting torque is required if submerged in water. Two alternative converter configurations, namely, NPC and ANPC have been studied in this paper. These converter topologies are compared with regard to their capabilities in providing starting torque in pump mode. The loss distribution amongst the semiconductor devices has been presented using IGCT as the switching device. The results based on analytical calculations show that ANPC converter provides over 80% higher starting torque compared to NPC converter which is an essential requirement for this application.