The Norwegian Network Code FIKS from the Norwegian Transmission System Operator (TSO) Statnett, states that synchronous generators ≥ 25 MVA must have a static excitation system. It also includes requirements on the step time response and the available field winding ceiling voltage of the excitation system. An improved brushless excitation system is in operation in some pilot power plants. A rotating thyristor bridge is controlled via Bluetooth. The step time response is as fast as conventional static excitation systems. However, a ceiling voltage factor of 2 requires the thyristor bridge to operate at firing angles about 60 degrees. High torque pulsations, low power factor and low utilization of the exciter is the end result. New power electronic interfaces on the shaft results in a betterutilization of the designed exciter and improves the mechanical performance as well as the controllability of the generator field winding. Permanent magnet rotating exciters increase the field forcing strength of the synchronous generator, yielding improved transient stability (Fault Ride-Through req.). Brushless exciters also reduces regular maintenance of the generator. The thesis includes experiments on a state of the art synchronous generator test setup including constructed PM exciter and different power electronic solutions. Some investigations has been done on industrial power plants as well.

The grid code, FIKS, from the Norwegian transmission system operator (TSO), Statnett, states that synchronous generators > 25MVA, must have a static excitation system. However, an improved brushless excitation system is in operation on some commercial power plants (36MVA, 93.75rpm & 52MVA, 166.67rpm) with grid-assisting performance beyond the conventional static system. The convenional diode bridge is replaced with a remote-controlled thyristor bridge on the shaft. If wireless communication is not allowed, a control signal through brushes should be employed instead. The thesis explores the expected new era for large brushless hydrogenerators. The proposed brushless system have benefits of reduced regular maintenance due to elimination of brushes and reduced unscheduled maintenance due to redundancy; causing a redused cost-of-energy. A six-phase exciter design with a hybrid-mode thyristor bridge interface leads to improved fault-tolerance, better controllability, minimized torque pulsations and reduced armature currents of the exciter. Excitation boosting (EB) capability is included in the brushless system without additional components or circuitry, contrary to the static excitation system. The brushless excitation system is made insensitive to voltage dips in the interconnected grid, causing improved fault ride-through (FRT) capability and power system stabilizer (PSS) actions. 

In a synchronous machine, radial, tangential, and axial forces are generated. In this thesis, three different technologies to control them are proposed. The first one, involves the utilization of the radial forces that arise between the rotor and the stator. This is achieved by segmenting the rotor field winding into groups of poles and controlling their corresponding magnetization individually. This technology is particularly useful to achieve magnetic balance and to create controllable radial forces. The second technology, involves the control of the rotor field in order to influence the tangential forces that produce torque. This is achieved by inverting the rotor field winding polarity with respect to the stator field. With this technique, breaking and accelerating torques can be created. It is particularly useful to start a synchronous machine. Finally, the application of axial forces with a magnetic thrust bearing is discussed. The main benefits of this technology are higher efficiency and increased reliability.

The work presented in this thesis was carried out within the Division of Electricity in the Department of Engineering Sciences at Uppsala University. It is based on original research supported by analytical calculations, computational simulations and extensive experimental work.

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.