PI Torque Controller Research Articles

High performance DTC of induction motor drives over a wide speed range

This paper presents an effective scheme to minimize the torque ripples for direct torque control (DTC) of induction motor drives. The switching strategy compares the torque error from a PI torque controller with two triangular waveforms, and then produces a constant switching frequency, which is determined by the frequency of the triangular waveforms and is almost independent of the speed. The gains of PI torque controller are designed based on root-locus plot to guarantee a good convergence of the torque error. In order to examine the performance of the proposed DTC scheme for an induction motor drive, a complete simulation model is developed using MATLAB/Simulink and validated under a wide speed range. The proposed DTC drive is also implemented and tested in real-time using a DSP-DS1102 control board for a prototype 1 KW induction motor. Simulation and experimental results show that the proposed DTC drive exhibits a good dynamic and steady state performances with low torque ripples over a wide speed control range.

Impedance Control of a Rotary Series Elastic Actuator for Knee Rehabilitation

This paper deals with impedance control of a rotary Series Elastic Actuator designed to assist in flexion/extension of the knee joint during physical therapy. The device includes a DC motor, a worm gear and a customized torsion spring. Since the elastic element is the most important component in the actuator design, a finite element analysis is used to meet the specific requirements of knee assistance. The proposed impedance control scheme comprises three cascade controllers: an inner-loop PI velocity controller, a PI torque controller, and an outer-loop PD position controller. The impedance controller's performance is evaluated through the Frequency Response Function analysis, and experimental results demonstrate the ability of the system to reproduce impedance behavior within an amplitude and frequency range compatible for gait assistance.

High Performance of Space Vector Modulation Direct Torque Control SVM-DTC Based on Amplitude Voltage and Stator Flux Angle

Various aspects related to controlling induction motor are investigated. Direct torque control is an original high performance control strategy in the field of AC drive. In this proposed method, the control system is based on Space Vector Modulation (SVM), amplitude of voltage in direct- quadrature reference frame (d-q reference) and angle of stator flux. Amplitude of stator voltage is controlled by PI torque and PI flux controller. The stator flux angle is adjusted by rotor angular frequency and slip angular frequency. Then, the reference torque and the estimated torque is applied to the input of PI torque controller and the control quadrature axis voltage is determined. The control d-axis voltage is determined from the flux calculator. These q and d axis voltage are converted into amplitude voltage. By applying polar to Cartesian on amplitude voltage and stator flux angle, direct voltage and quadratures voltage are generated. The reference stator voltages in d-q are calculated based on forcing the stator voltage error to zero at next sampling period. By applying inverse park transformation on d-q voltages, the stator voltages in α and β frame are generated and apply to SVM. From the output of SVM, the motor control signal is generated and the speed of the induction motor regulated toward the rated speed. The simulation Results have demonstrated exceptional performance in steady and transient states and shows that decrease of torque and flux ripples is achieved in a complete speed range.

POSITION/TORQUE CONTROL OF A SPACE ROBOTICS ARM

Torque sensors are used in space robot joints to increase robot capabilities and operational flexibility. Cascaded to a load position loop, a torque loop increases the performance of a position servo facing large variations of load inertia, typical of space robot arms. The issue specifically addressed in this paper is to what extent non linear elements, like sensor resolutions and friction, affect performance of the cascaded position/torque control strategy for a joint of a space arm. The detrimental effects of the comparatively low resolution of the load position sensor are discussed. A solution to this problem is proposed based on the adaptation of a Kinematic Kalman Filter. Finally it is pointed out that the adoption of a PI torque controller, in addition to a PID position controller, easily induces limit cycles of the hunting type, thus supporting the adoption of a proportional torque controller.

Parameter Estimation and Digital Control with Continuous-Time Models and Application to a Combustion Engine Dynamometer

A combustion engine dynamometer described by ordinary differential equations is identified by least squares estimation and state variable filters. The estimated parameters of the dynamometer are compared with the parameters achieved from theoretical modelling. Based on the estimated parameters a disturbance compensation, a PI-torque controller and a state space controller are designed. The three control algorithms are compared.