Three Phase Motor Drives

S.E.T. produce three phase variable voltage, variable frequency drives suited not only to our own permanent magnet motors, but capable also of soft-starting and running large industrial induction motors. S.E.T.’s motor drives are based on modern switch mode technologies, using IGBTs in most cases – with the smaller, lower voltage systems using MOSFET based technology for greater efficiency, particularly systems powered by banks of batteries. At the heart of all of S.E.T.’s motor drives is a powerful 16bit microcontroller providing full control and protection of the system.

Traction and RAILCAT Control Systems

S.E.T.s complete traction systems consist of a number of motor drives as above, along with various additional peripherals to create a complete system. At the heart of all traction systems is a master controller, which manages the power into and out of the system (in modes of both motoring and regenerating) and relays driver or user commands to the individual motor controllers. Additional functions such as jerk control and wheel slip detection can be implemented in larger systems as required. An interface is provided to the driver / user on a separate driver control unit (larger systems) or reported directly from the master controller (RAILCATs and smaller systems). Additional functions include the ability to manage the complete system and provide full diagnostic output with USB/Serial interfaces to a laptop for example. The overall system, distributed throughout the vehicle, is connected by means of CAN bus as standard.

Fault Tolerant Actuation System

A research and development project (funded by a TSB technology programme) has been undertaken by a consortium with a combination of academic, research and industrial partners to develop a simple and low cost fault-tolerant actuation system.

The developed system is based on electric or electro-mechanical actuator technologies, but a number of key innovations are explored to provide a high level of inherent redundancies with the minimum component count.

• Independent control of motor phases. The internal redundant capability of the PM brushless motors is explored by enabling the independent control of individual motor phases so that remaining phases will not be affected if any one (or more) phase fails to function properly.

• Reduced use of motors and power devices. The new power control configuration and integrated control method involves only the use of two permanent magnet motors and four power switch units to achieve a fault tolerance of two major faults in the system. Compared to the conventional system for the same three-level redundancy, the overall reliability is improved and cost reduced by around one-third due to the reduced component count.

• Reduced mechanical connections and interfaces. Conventional EM actuators use a gearbox to increase the torque output and, when a linear motion is required, rotary-to-linear translational mechanics. The mechanical interfaces are in general less reliable than the electrical components and require more frequent maintenance. The efficiency is compromised by losses from mechanical transmissions and from driving/braking the rotors/gears (the rotor inertia is magnified by the square of the gear ratio).

• Embedded intelligent fault-tolerant control. Detects and isolates faults in the system before taking corrective actions.