• Commutation of permanent-magnet synchronous AC motors for military and traction applications

      Stewart, Paul; Kadirkamanathan, Visakan; University of Sheffield (Institute of Electrical and Electronic Engineers, 2003-06-05)
      The permanent-magnet ac (PMAC) motor requires accurate position information to be supplied to the controller so that the applied currents can be modulated in synchronism with the rotor. In the flux-weakening region of operation, accurate rotor position information is critical to control the relative phase of the applied stator voltages. The design of controllers, which can operate without direct position feedback, have been the subject of intense development. The most commonly cited justifications for the elimination of the absolute position encoder are those of cost, and the reduction of the overall dimensions of the motor. However, certain military specifications apply stringent constraints to the use of both sensors and estimation techniques. Absolute encoders are frequently prohibited for applications such as tank turret drives due to their relatively fragile nature. Fully sensorless operation has been the focus of development for all classes of electric motors, but again is precluded not only in certain military applications, but also in traction applications for a number of manufacturers.
    • Dynamic model reference PI control of permanent magnet AC motor drives

      Stewart, Paul; Kadirkamanathan, Visakan; University of Sheffield (Elsevier, 2001-11)
      The permanent magnet AC motor drive (PMAC) is a multivariable, non-linear, closely coupled system subject to saturation due to finite DC supply voltage and hard current limits for protection of the drive hardware. Model following controls can be applied to this class of motor with PI current controllers enabling tracking of quadrature current command values. The presence of a finite supply voltage constraint results in reduced system performance when the current regulators saturate. A dynamic model reference controller is presented which includes the currents and voltage limits, constraining the magnitude of the command signals, operating the system to just within the bound of saturation, allowing the PI controllers to accurately track the commanded values and retain control of the current vectors. This regime ensures maximum possible dynamic performance of the system. The system and controller is simulated and experimentally verified, controller gain being found by Monte Carlo simulation.
    • Dynamic model tracking design for low inertia, high speed permanent magnet ac motors

      Stewart, Paul; Kadirkamanathan, Visakan; University of Sheffield (Elsevier, 2007-01-17)
      Permanent magnet ac (PMAC) motors have existed in various configurations for many years. The advent of rare-earth magnets and their associated highly elevated levels of magnetic flux makes the permanent magnet motor attractive for many high performance applications from computer disk drives to all electric racing cars. The use of batteries as a prime storage element carries a cost penalty in terms of the unladen weight of the vehicle. Minimizing this cost function requires the minimum electric motor size and weight to be specified, while still retaining acceptable levels of output torque. This tradeoff can be achieved by applying a technique known as flux weakening which will be investigated in this paper. The technique allows the speed range of a PMAC motor to be greatly increased, giving a constant power range of more than 4:1. A dynamic model reference controller is presented which has advantages in ease of implementation, and is particularly suited to dynamic low inertia applications such as clutchless gear changing in high performance electric vehicles. The benefits of this approach are to maximize the torque speed envelope of the motor, particularly advantageous when considering low inertia operation. The controller is examined experimentally, confirming the predicted performance.