Stephen J. Dodds

Comparison of sliding mode and forced dynamics control of electric drive with a flexible coupling employing PMSM

The paper presents comparison of two control techniques (a) sliding mode and (b) forced dynamics for control of electric drives employing permanent magnet synchronous motors with flexible coupling. The designed controllers are of the cascade structure, comprising an inner speed control loop and an outer position control loop. The inner speed control loop for both controllers is based on forced dynamics and respects the principles of vector control. The outer position control loops are designed to control load mass angle in the presence of a vibration mode with an external load torque. Derived control laws requires estimates of the load torque and the second one also its derivatives, which are estimated in the especially designed load torque observer. The simulations presented indicate that the control systems operate according to theory and therefore further investigations including experimental implementation are recommended.

Forced Dynamic Control of Electric Drives with Vibration Modes in the Mechanical Load

The general theory of forced dynamic control is first given. Its application to electric drives with significant vibration modes in the mechanical load is then considered. Simulation and experimental results are compared for a two-mass system comprising a DC motor driving a balanced mass via a thin shaft.

Sliding mode vector control of PMSM drives with minimum energy position following

The original contribution of this paper is the direct use of a six switch inverter as the switching element of a multivariable sliding mode controller to achieve vector control for permanent magnet synchronous motor drives precisely realising a prescribed dynamic response to the rotor speed reference inputs. The extreme robustness against changes in the mechanical load parameters and external disturbance torques enables the user to set up the drive without any controller tuning, the only information required being the prescribed position step response settling time. The only information needed to design the controller is the relative degree (i.e., rank) of the plant with respect to the controlled outputs, i.e., the rotor speed and the direct axis current vector component. An outer position control loop is closed and a zero dynamic lag pre-compensator applied to achieve precise following of a pre-planned rest-to-rest manoeuvre that minimises the frictional energy loss for a given position change and manoeuvre time. Simulations predict that despite no knowledge of the load moment of inertia or the viscous friction coefficient, a) the precisely defined closed loop dynamics of the position step response is attained, b) precise following of pre-planned rest to rest manoeuvres is attained and c) step load torques cause negligible transient position errors.

Analytical thermal modelling for permanent magnet synchronous motors

This paper concentrates on the development and analysis of a new generic steady state thermal model for mapping the heat transfer throughout a permanent magnet synchronous motor by considering its individual components as elements of an overall thermal equivalent circuit. This model includes (a) conduction resistances for the stator laminations and housing, conduction resistances between the copper winding and the stator teeth and yoke, between the housing and the stator, and between the housing and the flange, (b) heat flow in the air-gap for vortex and turbulent flow, (c) natural convection and forced cooling for the housing surface and the mounting flange surface, and (d) radiation resistance for the housing surface and mounting flange. The results obtained from the model are compared with corresponding experimental tests for the stall and rated performance with natural and forced cooling for two different motors, one with a rated speed of 1500 r/min and 130 Nm stall torque having 30 slots and 10 poles, and the other with a rated speed of 3000 r/min, and 15 Nm stall torque having 18 slots and 6 poles. The results achieved demonstrate a good correlation between the experimental results and the theoretical results obtained from the thermal model.

Nonexciting Control by Orientation of Flexible Space Vehicles

Abstract The interaction of the orientation control moment of a flexible vehicle (FV) with the elastic oscillations in the mechanical structure is considered. With fmite control actuator saturation limits, this interaction can be the cause of instability of the closed-loop system in which the elastic oscillations increase in amplitude to a point ultimately limited by non-linearities in the structure. An approach to circumvent the problem is presented here which is based upon consideration of the resonance interaction of the non-linear controller with the elastic oscillations. This enables the controller parameters to be optimised to minimise the modal excitation. Some digital simulation results are discussed.

Forced dynamics control of electric drives employing pmsm with a flexible coupling

A control system based on the principle of forced dynamics control for an electric drive with a permanent magnet synchronous motor and a flexible coupling is presented and verified by simulations. The controller is of the cascade structure, comprising an inner speed control loop and an outer position control loop. The inner forced dynamics speed control loop respects the principles of vector control and requires an estimate of the load torque, which is estimated in an observer. The outer position control loop based on the same principle is designed to control the rotor angle or load mass angle in the presence of a vibration mode due to the flexible coupling and with an external load torque. The derived control law requires estimates of the load torque and its derivatives, which are estimated in the load torque observer. The simulations presented indicate that the control system operates according to theory and therefore further investigations including experimental implementation are recommended.

Sliding Mode Block Control of Uncertain Nonlinear Plants

Abstract This paper combines the block control, sliding mode and high gain robust control techniques to form a stabilising control law for nonlinear systems with matched and unmatched uncertainties. A generalised observer is presented to cater for plants subjected to an unknown matched disturbance. The approach is applied to form a non-chatiering sliding-mode observer-based control law for robotic manipulators driven by DC motors.

Sliding mode control of PMSM drives subject to torsion oscillations in the mechanical load

A control system for permanent magnet synchronous motor electric drives with a significant torsion vibration mode is presented based entirely on sliding mode principles to achieve robustness against external load torques and parametric modelling uncertainties in the motor and/or the driven mechanical load. The sliding mode control law respects the vector control condition by keeping the direct axis current component approximately zero as well as controlling either the rotor or load position to follow the demanded position with prescribed closed loop dynamics. When controlling the load position, the torsional oscillations are completely eliminated. To avoid control chatter, a boundary layer is introduced by replacing the relay control switching transfer characteristic (signum function) by a high gain with the same control saturation limits. The user is only required to provide the demanded position and specify the settling time of the step response, no controller tuning being necessary. The simulations predict that the desired robustness will be achieved.

Cogging analysis for fractional slot/pole permanent magnet synchronous motors

Analytical and FEA predictions of cogging torque are compared with experimental results for a range of non-skewed PMSMs of similar size but with slot/pole ratios of 18/8, 12/10 and 30/8 (fractional) together with 30/10 and 18/6 (integer). The two analytical methods and the experimental data show close agreement and predict that stator or rotor skewing would be required to reduce the cogging torque to acceptable levels for the motors with the integer ratios, but the cogging torques for the fractional ratios are sufficiently small to obviate the need for skewing, thereby reducing the manufacturing operations. Finally the 12/10 ratio is recommended since this yields a higher stall torque than the 18/6 or 30/8 ratios. The explanation of this is that the 12/10 ratio enables a higher slot fill to be obtained than the 30/8 ratio. Also the winding overhang can be significantly reduced for the 12-10 design with a segmented stator in contrast with all the other slot pole combinations.

Nonlinear sliding surface design in the presence of uncertainty

Abstract This paper combines the block control, sliding mode and high gain robust control techniques to derive a stabilizing control law for nonlinear systems with matched and unmatched uncertainties.