Practical Applications of Permanent Magnet Generators and Power Converters in Hydro

摘要

Permanent magnet generators (PMG) recently have made breakthrough in the wind turbine industry. The higher torque density and compact size of PMGs permits the design of generators suitable for direct connection to slow speed hydro turbines for low head applications, providing an attractive alternative to the use of speed increasing gear boxes. For that reason Andritz Hydro introduced the EcoBulb? in 2002, an axial Bulb Turbine with a direct connected PMG with the objective to tap low head potential with economic results. The paper will compare some of the equipment solutions available to the market for low head applications and explore some of the considerations that lead to the development of the EcoBulb? design. While there are several advantages to the EcoBulb? Turbine a PMG does come with one principle downside; the uncontrollable air-gap flux density due to permanent magnet excitation leads to high overvoltage in case of load rejection and the inability to achieve power factor control and bump-less synchronization. This can sometimes prevent the technology from meeting the interconnection requirements of the local grid operator. Medium voltage power converters are now commercially available for powers from 1 MW up to tens of MW. The use of power converters when teamed with PMG’s enables the project to meet all of the requirements for interconnection including, power factor control, voltage support, smooth synchronization and Low Voltage Ride through (LVRT). An additional benefit from power converters in a hydro context is that it permits the turbine to operate at variable speed. This can improve the efficiency of turbines operating in applications where the head varies.