• 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.
    • A novel genetic programming approach to the design of engine control systems for the voltage stabilization of hybrid electric vehicle generator outputs

      Gladwin, Daniel; Stewart, Paul; Stewart, Jill; University of Sheffield; University of Lincoln (Institution of Mechanical Engineers, 2011-07-13)
      This paper describes a Genetic Programming based automatic design methodology applied to the maintenance of a stable generated electrical output from a series-hybrid vehicle generator set. The generator set comprises a three-phase AC generator whose output is subsequently rectified to DC. The engine/generator combination receives its control input via an electronically actuated throttle, whose control integration is made more complex due to the significant system time delay. This time delay problem is usually addressed by model predictive design methods, which add computational complexity and rely as a necessity on accurate system and delay models. In order to eliminate this reliance, and achieve stable operation with disturbance rejection, a controller is designed via a Genetic Programming framework implemented directly in Matlab and, particularly, Simulink. The principal objective is to obtain a relatively simple controller for the time-delay system which does not rely on computationally expensive structures, yet retains inherent disturbance rejection properties. A methodology is presented to automatically design control systems directly upon the block libraries available in Simulink to automatically evolve robust control structures.
    • Torque maximisation of the Pmac motor for high performance, low inertia operation

      Stewart, Paul; University of Sheffield (Wiley, 2008-10-22)
      This paper describes the techniques applied to maximise the torque envelope of the permanent magnet AC (PMAC) motor operating under current and voltage constraints. Standard steady-state descriptions of the system are often suitable for control purposes when the rotor velocity is varying relatively slowly. In low inertia applications such as clutchless gearchange operations, where in the pursuit of driveability, the motor is required to accelerate and decelerate its own rotor inertia as quickly as possible. In this case, the voltage drop due to the current dynamics start to become significant. This paper presents a method to reserve voltage headroom dynamically in the field-weakening region in order to maximise the torque envelope when the effective inertia is low. Experimental results show the effectiveness of this approach.