P.C. Kjaer

High-grade control of switched reluctance machines

This paper formulates the objectives associated with high-grade torque control of SR motors. Low torque ripple is a natural outcome of high bandwidth torque control. Existing torque ripple reduction techniques are reviewed. Smooth torque operation is only uniquely defined together with a secondary objective such as maximum efficiency, maximum torque-speed capability, maximum power factor etc. as the SR motor does not enjoy the inherent distribution between phases that characterises AC-drives. A systematic approach to waveform design is developed, and is evaluated using both simulation and experimental testing of an SR motor servo-drive system. This approach, which can be regarded as a functional equivalent of AC vector control, starts from machine parameters and gives smooth torque operation with maximised torque-speed range or efficiency. Excellent dynamic performance is obtained for speed and position control together with optimised low torque-ripple operation.

High-grade position estimation for SRM drives using flux linkage/current correction model

The paper proposes a principle of high resolution sensorless position estimation for a switched reluctance motor (SRM) drive, using either flux linkage or current to correct for errors in rotor position. The estimation algorithm makes full use of the nonlinear magnetic characteristics of the SRM through correlation of current, flux linkage and rotor position. The estimation model is simple, but with no loss in accuracy, leading to few real-time computations. Furthermore, a criterion is proposed to choose the phase most suited for position estimation when more than one phase conducts. The algorithm can also predict flux linkage, which in turn may be used to correct the position estimate further, and the features hereof are discussed. Simulations, real-time implementation and experimental results using the algorithm are presented, and confirm the concept.

A new energy optimizing control strategy for switched reluctance motors

This paper describes a new and machine-independent method to minimize the energy consumption of a speed controlled switched reluctance motor (SRM). The control strategy is to vary the duty cycle of the applied DC voltage in order to obtain the desired speed quickly and when operating in steady-state vary the turn-on angle (a/sub on/) of the phase voltage to minimize the energy consumption. The power flow is measured in the DC-link and used to control the turn-on angle. Simulations carried out on a three-phase 6/4 pole SRM justify the algorithm and the physical implementation in a Siemens SAB 80C517A microcontroller is described. Measurements on two different load systems show it is possible to minimize the energy consumption on-line in a speed controlled switched reluctance motor without losing the dynamic performance. A comparison with an ordinary mode-shift controlled SRM shows more than an 8% increase in overall efficiency for some operation points. The algorithm is fully applicable to other switched reluctance motors at other power levels or with other pole configurations. >

Dynamic testing of switched reluctance motors for high-bandwidth actuator applications

This paper examines the testing and assessment of high-bandwidth switched reluctance motor torque control for actuator and motion control applications. It is claimed that the torque control is sufficiently fast and accurate and that it does not, in itself, impose any significant limits on the performance of the overall system. To provide proof of concept, an experimental test rig that emulates a motion control application has been designed and built. The quality of torque control permitted the design of conventional velocity and position control loops in a transparent fashion. The paper reports high-performance motion control, in particular, four-quadrant operation, high-bandwidth speed and position control, low- and zero-speed operation in the presence of a load torque, and trapezoidal profiled motion have all been demonstrated through extensive experimental tests.

Fault-tolerant operation of single-phase switched reluctance generators

This paper studies fault-tolerant operation of switched reluctance generators (SRG), in particular an 8/8-pole single-phase switched reluctance machine. The combination of multiple coils per phase and innovative power electronic converter circuits suggests improved operation under faults compared with conventional topologies. Open and short-circuit coils are studied through linear analysis, finite-element analysis and measurements. A new power converter topology which connects coils two in parallel is proposed. Generated current is measured by simulating the proposed power converter under fault conditions. It is concluded that the 8/8-pole single-phase switched reluctance machine can generate half its normal power with the same coil current under loss of half coils with a proper winding configuration and the power converter proposed.

A study on operation under faults with the single-phase SR generator

This paper studies the operation of a multi-pole single-phase switched reluctance generator (SRG) under faults, in particular an 8/8-pole SR machine. A new power converter topology which connects two banks of coils in parallel is proposed. The combination of multiple coils per phase and the power converter circuit suggests improved operation under faults compared with conventional topologies. Output power per coil current under faults is studied by finite-element analysis and static torque measurement. Circuit equations under faults are derived and operation under faults is evaluated by simulation. An SRG controller is constructed and experiments are performed. The experimental results support the equations and simulation results. It is concluded that the SRG can continue generating operation even when open- or short-circuited coil faults occur with the proposed power converter and proper fault detection circuits.

6 – Instantaneous torque control

Publisher Summary This chapter explores the possibilities for instantaneous torque control to assess the potential of the switched reluctance motor as a servo motor in comparison with an induction motor with field-oriented control. The objectives are to produce smooth torque and rapid dynamic response, while overcoming the natural nonlinearities of the machine from a control point of view. The chapter describes the development of an advanced control scheme that permits high-grade control of the switched reluctance motor. The specific features of high-grade control include: (1) high-bandwidth torque control, (2) low torque ripple, (3) four-quadrant operation over a wide speed range including zero speed, and (4) seamless transition from maximum-efficiency operation to maximum field-weakening with efficient use of the controller voltage. This control strategy is regarded as the functional equivalent of a.c. vector control. It has been shown that the torque control is sufficiently fast and accurate that it does not impose any significant inherent limits on the performance of the overall system. It may be concluded that the switched reluctance motor and a torque controller of this type are amenable to motion control applications traditionally served by conventional servo motors.