M. Tatlow’s research while affiliated with University of Cambridge and other places

It is desirable to measure rotor quantities such as currents and temperatures in an electrical machine for design verification and condition monitoring purposes. A Bluetooth module which sends data from the rotor was previously reported in literature, but this module was battery powered, and therefore the duration of the tests was limited. This study presents a solution to this problem by developing a rotor-mounted power supply system which can harvest energy from the magnetic field inside the machine, by fixing an external loop to the rotor and making use of the induced voltage in the loop. A full-bridge rectifier, boost converter and battery charging module were developed to supply sufficient power to a bespoke Bluetooth transmission system and associated sensor circuitry.

A design procedure for the Brushless Doubly Fed machine is based on equations derived from a simplified equivalent circuit. The method allows the many variables in the design of this machine to be handled in straightforward way. Relationships are given for the division of slot area between the two stator windings and for the design of the magnetic circuit. The design method is applied to a frame size 180 machine. In particular, calculated values for flux densities in the machine have been verified by time stepping finite element analysis for actual operating conditions. The approach outlined can also be used as part of a design optimization routine.

In order to perform experiments on electrical machines, it is desirable to measure rotor parameters such as currents and temperatures. A Bluetooth module have been developed which sends data from the rotor, however this module is battery powered, and therefore the duration of the tests is limited. This paper presents a solution to this problem, by developing a rotor-mounted power supply system which can harvest energy from leakage magnetic flux inside the machine, by fixing an external loop to the rotor and making use of induced voltages in the loop. A full-bridge rectifier, boost converter and battery charging module was developed to supply sufficient power to the Bluetooth module.

A procedure has been established for obtaining equivalent circuit parameters for the brushless doubly fed machine, also known as the brushless doubly fed induction machine, by transforming a reduced coupled-circuit model into a sequence component form. This approach takes advantage of the model reduction procedure's ability to reduce a complex rotor structure to a single equivalent loop without significant loss of accuracy. An alternative method based on winding factors has also been developed and includes coupling via harmonic fields. Parameters determined in both ways are in close agreement with those determined from finite element analysis and experimentally. The advantages of each method are discussed in the conclusion section.

To further demonstrate the applicability of the brushless doubly-fed induction generator to wind turbine applications, a grid synchronization procedure is developed. Vector control of the converter-side stator winding is used to induce a voltage on the grid-side stator winding. A detector is developed to automatically connect the machine to the grid when the voltages are synchronized. Experimental results show that synchronization occurs within 0.4 seconds while the rotor is accelerating.

This paper presents the modelling and commissioning of a wind turbine emulator test-rig and a performance comparison of four different advanced control techniques.

This study presents the performance analysis and testing of a 250 kW medium-speed brushless doubly-fed induction generator (DFIG), and its associated power electronics and control systems. The experimental tests confirm the design, and show the system's steady-state and dynamic performance and grid low-voltage ride-through capability. The medium-speed brushless DFIG in combination with a simplified two-stage gearbox promises a low-cost low-maintenance and reliable drivetrain for wind turbine applications.

The paper presents the design and performance analysis of a 6 MW medium-speed Brushless Doubly-Fed Induction Generation (Brushless DFIG) for a wind turbine drivetrain. Two machines with different frame sizes have been designed to show the flexibility of the design procedure. The mediumspeed Brushless DFIG in combination with a two stage gearbox offers a low-cost, low-maintenance and reliable drivetrain for wind turbine applications.