Improving the functionality of synchronous machines using power electronics

Abstract: With the advent of modern power electronics there is reason to explore what can be achieved when it is applied to a mature technology like synchronous machines. In this text several concepts will be presented on how it is possible to control forces and how to get better performance out of synchronous machines by using power electronics. Methodologies to create radial forces by controlling the field current in a standard series connected rotor winding as well as when the winding is split in to several segments is presented. By segmenting the rotor a resulting force vector can be created to cancel forces due to unbalanced magnetic pull.It is also shown that inverting the field current with respect to the stator field enables line start of synchronous machines without using damper bars, frequency converters, or starting motors.Some first results from the installation and testing of an electromagnetic thrust bearing installed in unit U9 in the hydropower station in Porjus are presented. The benefits of the system is increased reliability and higher efficiency of the thrust bearing system.An evaluation of a 2-stage brushless excitation system was done, different rotating power electronics topologies were tested in the stationary frame connected to a six-phase permanent magnet brushless exciter. The rotating control and measurement system for the power electronics is presented. Potential benefits of the system is that there is no need for brushes to transfer the field current to the rotor winding, fast response time due to actively controlled electronics, independence of the station bus voltage, and reduced maintenance.

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