Rotor Angular Position Research Articles

Sensorless Control of a Stepper Motor Based on Higher Order Sliding Modes

A robust control for a stepper motor with no position nor velocity sensors and only needing current and voltage measurements is designed. Second order sliding mode based observers are realized to estimate both rotor angular position and velocity. Moreover, a robust control law, which is also based on second order sliding modes and which uses the estimates of the observer, is designed. The stability of the observer based control loop is discussed. The results obtained in simulations indicate the usefulness and the robustness of the method.

Back EMF Sensorless-Control Algorithm for High-Dynamic Performance PMSM

In this paper, a low-time-consuming and low-cost sensorless-control algorithm for high-dynamic performance permanent-magnet synchronous motors, both surface and internal permanent-magnet mounted for position and speed estimation, is introduced, discussed, and experimentally validated. This control algorithm is based on the estimation of rotor speed and angular position starting from the back electromotive force space-vector determination without voltage sensors by using the reference voltages given by the current controllers instead of the actual ones. This choice obviously introduces some errors that must be vanished by means of a compensating function. The novelties of the proposed estimation algorithm are the position-estimation equation and the process of compensation of the inverter phase lag that also suggests the final mathematical form of the estimation. The mathematical structure of the estimation guarantees a high degree of robustness against parameter variation as shown by the sensitivity analysis reported in this paper. Experimental verifications of the proposed sensorless-control system have been made with the aid of a flexible test bench for brushless motor electrical drives. The test results presented in this paper show the validity of the proposed low-cost sensorless-control algorithm and, above all, underline the high dynamic performances of the sensorless-control system also with a reduced equipment.

Unified winding function approach for dynamic simulation of different kinds of eccentricity faults in cage induction machines

The multiple coupled circuit model of a three-phase cage induction machine and the uses of a modified winding function theory to calculate the time-dependent inductances of the motor with a general eccentricity fault, including static, dynamic and mixed eccentricities, in a unified manner are considered. By defining the inverse air gap function of the eccentric machine, determining its indefinite integral and assuming step variations for the turn functions at the centres of the slots, precise analytic equations are obtained for the inductances. Differentiating these analytic equations against the rotor angular position also gives precise analytic equations to calculate the derivatives of the inductances, which may be used to determine the electromagnetic torque. Consequently, dynamic simulations of an induction machine with any eccentricity type and degree as well as a healthy one is made possible in the frame of a single Simulink program. At the beginning of the simulation process, the eccentricity components' degree and position are introduced and the program is then executed accordingly. A simple technique was used to make an industrial induction motor temporarily eccentric, with varying degrees, and experiments were conducted on it. By defining and applying effective air gap length and effective eccentricity components' degrees, good agreements are achieved between the simulated and the experimental results, which implies that the whole unified simulation program is effective.

Development and validation of a general-purpose ASIC chip for the control of switched reluctance machines

A general-purpose application specific integrated circuit (ASIC) chip for the control of switched reluctance machines (SRMs) was designed and validated to fill the gap between the microcontroller capability and the controller requirements of high performance switched reluctance drive (SRD) systems. It can be used for the control of SRM running either in low speed or in high-speed, i.e., either in chopped current control (CCC) mode or in angular position control (APC) mode. Main functions of the chip include filtering and cycle calculation of rotor angular position signals, commutation logic according to rotor cycle and turn-on/turn-off angles ( θ on/ θ off), controllable pulse width modulation (PWM) waveforms generation, chopping control with adjustable delay time, and commutation control with adjustable delay time. All the control parameters of the chip are set online by the microcontroller through a serial peripheral interface (SPI). The chip has been designed with the standard cell based design methodology, and implemented in the central semiconductor manufacturing corporation (CSMC) 0.5 μm complementary metal-oxide-semiconductor (CMOS) process technology. After a successful automatic test equipment (ATE) test using the Nextest’s Maverick test system, the chip was further validated through an experimental three-phase 6/2-pole SRD system. Both the ATE test and experimental validation results show that the chip can meet the control requirements of high performance SRD systems, and simplify the controller construction. For a resolution of 0.36° (electrical degree), the chip’s maximum processable frequency of the rotor angular position signals is 10 kHz, which is 300,000 rev/min when a three-phase 6/2-pole SRM is concerned.

English

Switched reluctance motors (SRM) are emerging as promising competitors to the vector-controlled induction motor (VCIM) drives and permanent magnet (PM) motor drives in the variable-speed drive market owing to their robust nature coupled with low cost, simplicity, and capabilityto operate in harsh environments. They are also suitable for nuclear and aerospace applicationsdue to their low inertia and capability to be fed from a dc supply through a simple power converter.The principle of torque production in SRM makes rotor position information mandatory foreffective control of the drive. The torque produced by any particular phase of the SRM isdependent upon the exciting current and the period during which the current is carried by thatphase winding. The conduction period of any particular phase is termed as dwell angle whenit is specified in terms of rotor angular position. In the present work, the SRM operation has beenanalysed in sensor mode and in sensor-less mode, paying special attention to the relationshipbetween dwell angle and output torque ripple. The performance has been studied for differentvalues of dwell angle and the resultant torque profile has been analysed. From the analysis, amethodology has been devised to deduce an appropriate value of dwell angle for minimising thetorque pulsations, given the values of speed and load torque, thus improving the performanceof the SRM drive.

A Position Sensorless Control System of SRM over Wide Speed Range

This paper presents a position sensorless control system of SRM over wide speed range. Due to the doubly salient structure of the SRM, the phase inductance varies along with the rotor position. Most of the sensorless control techniques are based on the fact that the magnetic status of the SRM is a function of the angular rotor position. The rotor position estimation of the SRM is somewhat difficult because of its highly nonlinear magnetizing characteristics. In order to estimate more accurate rotor position over wide speed range, Neural Network is used for this highly nonlinear function approximation. Magnetizing data patterns of the prototype 1-hp SRM are obtained from locked rotor test, and used for the Neural Network training data set. Through measurement of the flux-linkage and phase currents, rotor position is able to estimate from current-flux-rotor position lookup table which is constructed from trained Neural Network. Experimental results for a l-hp SRM over 16:1 speed range are presented for the verification of the proposed sensorless control algorithm.

Inverse modelling and pulsating torque minimization of salient pole non-sinusoidal synchronous machines

Sinusoidal motor's mathematical models are usually obtained using classical d– q transformation in the case of salient pole synchronous motors having sinusoidal field distribution. In this paper, a new inverse modelling for synchronous motors is presented. This modelling is derived from the properties of constant torque curves in the Concordia's reference frame. It takes into account the non-sinusoidal field distribution; EMF, self and mutual inductances having non-sinusoidal variations with respect to the angular rotor position. Both copper losses and torque ripples are minimized by adapted currents waveforms calculated from this model. Experimental evaluation was carried out on a DSP-controlled PMSM drive platform. Test results obtained demonstrate the effectiveness of the proposed method in reducing torque ripple.

FREE DERIVATIVE STATE OBSERVERS TO TRACK BRUSHLESS MOTOR ROTOR

In this paper, we propose a method to estimate angular position and speed of a brushless motor rotor by using a free derivative state observer. The proposed approach seems to be very promising from the viewpoint of the computational load, estimation accuracy and response time. Moreover, it comes out a novel procedure for the tuning of the endogenous parameters of the filter based on the using of stochastic search algorithms.

The Flow Rate Influence on the Interaction of a Radial Pump Impeller and the Diffuser

This article presents the results of a detailed flow investigation within a centrifugal pump equipped with a vaned diffuser. The measurements were made with a laser Doppler velocimeter and were carried out at different operating points. The flow was investigated for different rotor–stator relative positions.Unsteady velocity measurements, obtained in phase with the rotor angular position, gave access to the flow inside the impeller channels where three sections were explored. In the diffuser, five sections were studied. Thus, time resolved details of the flow were examined for a better understanding of the complex unsteady flow existing between the two interacting blade rows.Results obtained at different operating conditions show that the rotor‐stator interaction is affected by the diffuser position and the flow rate.

Robust control of switched reluctance motors for direct-drive robotic applications

This paper discusses the robust control of switched reluctance motors (SRM's) for driving manipulators directly. A mathematical model of the SRM with unmodeled dynamics is proposed which describes the relationship among electromagnetic torque, rotor angular position, and phase currents. The parameters and boundaries of the unmodeled dynamics in this model are estimated by the least square approximation method. Based on this model, a robust controller is designed. Compared with the ordinary controller, the robust controller can produce an auxiliary control input to overcome the influence of model uncertainties on system performance. Overall stability of the system is proven using Lyapunov techniques. Following a theoretical analysis, some related experiments are introduced. The experimental results show that the controller provides a steady-state performance although the system contains unmodeled certainties.

A new robotic drive joint friction compensation mechanism using neural networks

The knowledge of realistic dynamic models to robotic actuators would be of great aid in the synthesis of control laws to robot manipulators, mainly in cases of great precision robotic or even for manipulators with flexible links. In this paper we present a training scheme and propose a structure of neural network (NN) to learn the friction torque of a geared motor drive joint robotic actuator. To train the NN was used experimental data obtained by an harmonic-drive actuator, equipped with an encoder to measure the rotor angular position. It was considered the motor torque and the rotor angular velocity as NN input, while the friction torque was the only output, which was used in the proposition of a non-linear friction compensation mechanism. The experimental results attested the efficiency of the NN friction estimation and compensation with the proposed mechanism.

Brushless exciter modeling for small salient pole alternators using finite elements

In this paper, the self and mutual inductances of an exciter for a genset alternator are estimated for different rotor angular positions by the use of finite-element (FE) techniques. These inductances, which are described by complex functions, are measured using a stationary test and compared with calculated values. A real-time computer model for the exciter, the load and the diode bridge mounted on the rotor is then proposed, and a sample of performance prediction and measurement for a specific transient condition of the exciter is presented here as confirmation of the method. The model thus validated is ultimately to be included in the evolving total system model used for simulation of genset transient and steady-state performance.

Spice-based dynamic analysis of a switched reluctance motor with multiple teeth per stator pole

The paper describes a nonlinear modeling of a switched reluctance motor (SRM) having two teeth per stator pole using Pspice. For the modeling procedure, static test data of flux linkage and torque for different rotor positions from the aligned to the unaligned position for various stator winding excitation currents of the SRM were available. In the procedure, the curves of flux linkage versus rotor angular position and stator current are fitted with an analytical equation and its coefficients are determined. The electrical part of the motor is modeled by the induced back-electromotive force (back-EMF) and mechanical part by torque versus rotor position and stator winding current. Performance of the model is studied by using a conventional inverter and the simulation results are compared with test and other simulation results. The paper shows that a Pspice model based on the static test data is more accurate than models obtained numerically by the same data and Pspice models with three flux-linkage curves.

Brushless Exciter Modeling for Small Salient Pole Alternators Using Finite Elements

The self and mutual inductances of an exciter for a genset altemator are estimated for different rotor angular positions by the use of finite element (FE) techniques. These inductances, which are described by complex functions, are measured using a stationary test and compared with calculated values. A real-time computer model for the exciter, the load, and the diode bridge mounted on the rotor is proposed, and a sample of performance prediction and measurement for a specific transient condition of the exciter is presented as confirmation of the method. The model thus validated is ultimately to be included in the evolving total system model used for simulation of genset transient and steady-state performance.

Modeling of the front end of a new capacitive finger-type angular-position sensor

A robust capacitive finger-type angular-position and angular-speed sensor for automotive and metrology applications is presented. The advantages of the capacitive sensor principle are simplicity, high response speed and resolution (/spl plusmn/0.04/spl deg/), compact sensor outlines, and insensitivity to dirt and condensation. Additionally the presented finger-type geometry allows easy mounting and replacement. The paper describes the working principle, the design and the layout of a prototype sensor. It models the front-end topology and derives the transfer function of the input circuit. The required relationships for computing the angular rotor position are presented, and measurement results obtained from a prototype sensor are discussed.

Unbalanced force calculation in switched-reluctance machines

This paper presents a detailed analytical model for computing the radial magnetic forces that arise in switched reluctance machines (SRM's). The model is general and includes iron saturation, displacements of the rotor from its center location, and arbitrary angular rotor positions. The force between an individual stator pole and its corresponding rotor pole is calculated. The model is used to calculate the unbalanced magnetic forces on the SRM rotor, due to the rotor being displaced from its center location, by calculating the difference in the radial magnetic forces on opposite stator poles. The calculation of the unbalanced magnetic rotor forces requires an especially accurate model for the radial magnetic forces since the unbalanced forces are the difference between the two large radial forces on opposite sides of the rotor. The side pull created by the unbalanced forces will stress the bearings of the motor. The detailed analytical model presented here will simplify the bearing system design and will be especially useful if less stiff magnetic bearings are being employed. Finite-element analysis is used to validate the detailed analytical model. This same model for calculating the radial magnetic forces can be used as the input to a calculation of stator yoke ovulation due to radial magnetic forces and of the resulting acoustical noise production.

A permanent-magnet rotor containing an electrical winding to improve detection of rotor angular position

Sensorless detection of rotor angular position is desirable for decreasing the cost and increasing the reliability of permanent magnet AC motor drive systems. This paper describes tests performed on a rotor that has surface-mounted magnets and a conducting winding that links only the d axis of the rotor. The rotor winding increases the variation of the stator winding inductance that occurs as the rotor rotates and improves the accuracy of rotor angular position estimates.

Adaptive control of variable reluctance motors: a spline function approach

This paper considers nonlinear adaptive control of a variable reluctance motor (VRM) in a low-velocity high-torque mode of operation. A simple dynamic model for the relationship among electric torque, rotor angular position, and phase currents is proposed. The model incorporates spline functions and a set of "Fourier" sinusoids and captures several experimentally verified VRM characteristics, including flux saturation effects. Based on this model, an adaptive controller is derived using the certainty equivalence principle. The controller provides asymptotic tracking of a desired rotor position trajectory. So-called "torque-sharing functions" are employed to smooth the commutation among phases and to increase the peak torque available from the motor, when compared to "hard" commutation that energizes only one phase at a time. Experimental results from a laboratory VRM provide motivation for the model and illustrate the controller's design and trajectory tracking performance.

A capacitive 4-turn angular-position sensor

A robust, capacitive 4-turn angular-position sensor for automotive and metrology applications is presented. The main advantages of this low-cost system are its simplicity, speed, high accuracy (/spl plusmn/0.35/spl deg/), and resolution (/spl plusmn/0.02/spl deg/) over the absolute measurement range of more than /spl plusmn/720/spl deg/, compact sensor outlines, and insensitivity to dirt or condensation. The paper describes the working principle, derives the required relationships for computing the angular rotor position, and discusses measurement results obtained from a prototype sensor with small outlines (50 mm diameter and 8 mm thickness) used as a steering sensor in vehicles.

Some aspects of torque calculations in electrical machines

Torque calculations are performed using both the Maxwell stress and virtual work methods for an induction motor in a variety of studies. The dependence upon the mesh, Maxwell stress path taken, rotor angular position and time instant are each evaluated individually.