Feng-Chieh Lin

Instantaneous Shaft Radial Force Control with Sinusoidal Excitations for Switched Reluctance Motors

In general, unbalanced radial force acting on rotor shaft is undesirable since it causes vibrations. Due to its special structure, the shaft radial force and torque of a three-phase 12/8 switched reluctance motor can be separately controlled by proper selection of pole currents of the energized phase. In this paper, a sinusoidal current excitation scheme is proposed for the torque and radial force control of a 12/8 pole SRM. When controlled with the selected sinusoidal currents the SRM can produce the desired shaft radial force in any direction of the rotational plane without disrupting the rotational torque. Also, since the pole currents are individually controlled a more sophisticated phase commutation strategy is proposed for smoother torque and radial force ripples. The proposed schemes were verified experimentally.

An Approach to Producing Controlled Radial Force in a Switched Reluctance Motor

Unbalanced radial force acting on a rotor shaft is undesirable because it causes motor vibrations. However, motor vibrations can be reduced with intentionally produced shaft radial force which cancels the existing unbalanced radial forces due to a nonuniform air gap or external load. Due to its special structure, the shaft radial force and torque of a switched reluctance motor (SRM) can be separately controlled when all pole currents are controlled independently. However, control of SRM radial force is rarely discussed in the existing literature. This paper presents a scheme that produces a controlled radial force for a 12/8-pole SRM. In this scheme, mutual inductances between stator poles are included in the control model. The motor torque is controlled with the conventional method, i.e., all poles in the conduction phase are energized with the same current to produce the desired torque. Two extra poles from the descending-inductance phase are energized to produce the desired radial force. The cross-coupling torque produced by the force producing poles is compensated. The experimental results have verified that when controlled with the proposed scheme, the SRM was able to produce a controlled radial force when at standstill or running, and subjected to a load torque.

Adaptive fuzzy logic-based velocity observer for servo motor drives

As the position transducers commonly used in industry do not inherently measure an instantaneous velocity, signal processing is generally required to improve the accuracy of velocity estimation at each sampling instant. This estimated signal is then used as the velocity feedback for the velocity loop control in servo motor drives. In this paper, an adaptive fuzzy logic-based observer is proposed to estimate velocity from the measured motor position. The proposed observer has a structure similar to that of the conventional state observer except that the state feedback is replaced with a fuzzy logic feedback. The observer has two adaptation mechanisms: the first one is used to vary the fuzzy output, and the second one is used to identify the motor parameters. The experimental results show that the noise in the estimated velocity caused by the quantization of the measured position can be reduced dramatically with the proposed observer. In addition, the observer has good transient responses in both normal and in low speeds.

Self-Bearing Control of a Switched Reluctance Motor Using Sinusoidal Currents

Due to its special structure, the shaft radial force and torque of a switched reluctance motor can be separately controlled when all of the pole currents are independently controlled. In this paper, a control scheme for self-bearing operation of a 12/8 pole SRM drive is proposed. The rotor needs only one bearing for rotation and constraining the axial movement. The other end can move freely in the radial direction but is balanced with the radial force produced by the motor. A model for torque and radial force is derived and used to design the controller. Mutual inductance between the stator poles is included in the analysis to improve the model accuracy. The conduction phase pole currents are energized with phase-shifted sinusoidal currents. Depending on the requested radial force and torque, a descending-inductance phase may also be energized to increase radial force production. The requested force and torque are synthesized from the force and torque produced by these phases. The experimental results demonstrate successful SRM self-bearing operations. The rotor can be effectively balanced to the center of the air gap. The maximum radial position error was about 0.07 mm when the motor was rotating at 1500 r/min under full load torque.

Instantaneous shaft radial force control with sinusoidal excitations for switched reluctance motors

Unbalanced radial forces acting on a rotor shaft exist in motor applications where the external load is not balanced or when the rotor is not centered causing a nonuniform air gap. These forces are undesirable as they cause motor vibrations. In view of its special structure, the shaft radial force and the torque of a three-phase 12/8 pole switched reluctance motor (SRM) can be separately controlled by proper pole current selection in the energized phase. Therefore, radial forces can be produced intentionally to cancel the existing radial force produced by rotor eccentricity and the unbalanced load inertia. The motor vibrations are thereby reduced. In this paper, a sinusoidal current excitation scheme is proposed for the torque and radial force control of a 12/8 pole SRM. When controlled with the selected sinusoidal currents, the SRM can simultaneously produce the desired shaft radial force in any rotational plane direction and the required rotational torque. As all pole currents are individually controlled, a more sophisticated phase commutation strategy is also proposed that provides smoother torques and radial force ripples.

Control of a two-phase linear stepping motor with three-phase voltage source inverter

This paper presents a current control scheme for the micro-stepping of two-phase linear stepping motor drive using three-phase voltage source inverter. The purpose of this scheme is for cost reduction since all the control loops are executed digitally and standard three-phase voltage source inverter is used. Because the operating frequency is quite high, the cross-coupling between motor phase currents are removed to preserve the dynamical characteristics of the current controller as frequency varies. A space vector PWM for a two-phase motor is also presented. The scheme is based on the principle of harmonic injection for three-phase motors. Because the inverter leg voltages are imbalanced when driving a two-phase motor, the dead-time effect of the inverter power switches must be compensated for or significant current error may occur. Good static and dynamic performances were obtained in the experimental verifications.

Loss-minimization control of vector-controlled induction motor drives

It is well known that the efficiency of induction motor drives under partial load can be improved via manipulation of its field. Among the numerous loss-minimization schemes proposed previously, the scheme that uses motor power factor as the main control variable has the advantages of high sensitivity and ease of implementation. But the problem of how the optimal power factor commands can be generated is not well documented. In this paper, a scheme that uses power factor control with automatic measurement of the minimum-loss power factor commands is proposed. A fuzzy logic compensator is included in the controller to improve the accuracy of the generated commands. The scheme is simple for implementation and does not require an a priori knowledge of motor parameters. Experimental results have validated the effectiveness of this scheme to minimize the motor operating losses.

Micro-stepping control of a two-phase linear stepping motor with three-phase VSI inverter for high-speed applications

This paper presents a synchronous frame current control scheme for micro-stepping of two-phase linear stepping motor drive using three-phase voltage source inverter. Due to the wide operating frequency the frequency dependent voltages are decoupled from the controller in order to reduce the current following errors and to preserve the dynamical characteristics as frequency varies. A motor cogging force compensation scheme performed in the synchronous frame is proposed to reduce the positioning error and the velocity ripple caused by detent force. A space vector PWM scheme is used for the modulation of motor voltage. The scheme is based on the principle of harmonic injection originally derived for three-phase motor drives. Good static and dynamic performances were obtained in the experimental verifications.

Modeling and Control of Radial Force in Switched Reluctance Motor

Unbalanced radial force acting on a rotor shaft is undesirable because it causes motor vibrations. Yet, motor vibrations can be reduced with intentionally produced shaft radial force which cancels the existing unbalanced radial forces due to a non-uniform air gap or external load. Due to its special structure, the shaft radial force and torque of a switched reluctance motor can be separately controlled when all pole currents are controlled independently. However, control of SRM radial force is rarely discussed in existing literature. This paper presents a scheme that produces a controlled radial force for a 12/8 pole SRM. In this scheme, mutual inductances between stator poles are included in the control model. The motor torque is controlled with the conventional method, i.e. all poles in the conduction phase are energized with the same current to produce the desired torque. Two extra poles from the descending-inductance phase are energized to produce the desired radial force. The cross-coupling torque produced by the force producing poles is compensated. The experimental results have verified that when controlled with the proposed scheme, the SRM was able to produce a controlled radial force when at standstill or running, and subjected to a load torque.

Radial Force Control of a Switched Reluctance Motor with Two-Phase Sinusoidal Excitations

Due to its special structure, the shaft radial force and torque of switched reluctance motor can be separately controlled by proper selection of pole currents. When all the pole currents are controlled independently, it is possible to produce the required radial force to cancel the existing radial force caused by non-uniform air gap or external load, and consequently motor vibrations can be reduced. In this paper, a radial force control scheme which use single or two phase sinusoidal excitations for 12/8 pole SRM is proposed. The pole currents of the conduction phase are energized with phase-shifted sinusoidal currents. Depending on the requested radial force and motor torque, the phase with descending-inductance may also be energized to increase radial force production. The requested force and torque are synthesized from the force and torque produced by these phases. The proposed scheme was verified with finite-element analysis and experiments