Aydin Ersak

Simple Derivative-Free Nonlinear State Observer for Sensorless AC Drives

In this paper, a new Kalman filtering technique, unscented Kalman filter (UKF), is utilized both experimentally and theoretically as a state estimation tool in field-oriented control (FOC) of sensorless ac drives. Using the advantages of this recent derivative-free nonlinear estimation tool, rotor speed and dq-axis fluxes of an induction motor are estimated only with the sensed stator currents and voltages information. In order to compare the estimation performances of the extended Kalman filter (EKF) and UKF explicitly, both observers are designed for the same motor model and run with the same covariance matrices under the same conditions. In the simulation results, it is shown that UKF, whose several intrinsic properties suggest its use over EKF in highly nonlinear systems, has more satisfactory rotor speed and flux estimates, which are the most critical states for FOC. These simulation results are supported with experimental results

A comparative study on non-linear state estimators applied to sensorless AC drives: MRAS and Kalman filter

In this paper, two different nonlinear estimators applied to sensorless AC drives, Kalman filtering techniques (EKF and UKF) and model reference adaptive system (back emf and reactive power models), are discussed and compared to each other. Both of the observer types are studied and analyzed both experimentally and theoretically. In order to compare the observers precisely, the observers are tested under the identical conditions.

State estimation of induction motor using unscented Kalman filter

In this paper, a new estimation technique unscented Kalman filter (UKF) is applied to state observation in field oriented control (FOC) of induction motor. UKF, a recent derivative-free nonlinear estimation tool, is used for estimating rotor speed and fluxes using sensed stator current and voltages. In the simulations, UKF, whose several intrinsic properties suggest its use over EKF in highly nonlinear systems, turned out to be very similar to EKF in flux estimates. The simulation results also show that UKF has slightly better speed estimation performance than EKF while driven under the identical machine model and parameters (covariances).

A comparative study on Kalman filtering techniques designed for state estimation of industrial AC drive systems

In this paper, two different Kalman filtering techniques, unscented Kalman filter (UKF) and extended Kalman filter (EKF) are investigated and compared both experimentally and theoretically. These non-linear, stochastic observers are employed as a state estimation tool in field-oriented control (FOC) of sensorless AC drives in this work. Using the superiorities of Kalman filtering, rotor speed and dq-axis fluxes of an induction motor are estimated only with the sensed stator currents and voltages information. In order to compare the estimation performances of the observers explicitly, both of the observers are designed for the same motor model and run with the same covariance matrices under the same conditions. In the simulation results it is shown that, UKF, whose several intrinsic properties suggest its use over EKF in highly nonlinear systems, has more satisfactory rotor speed and flux estimates, which are the most critical states for FOC. These simulation results are supported with experimental results.

A fuzzy colour quantizer for renderers

Abstract This paper presents a new colour quantization method for ray tracing. Normally, quantization is carried out by generating statistics about the colours present in the original image. Then a colour look-up table is created which contains the colours available in the quantized image. Original quantized values are mapped into the nearest colour entries in the look-up table. Although the execution time is quick using this method (histogram analysis) the cost is that the image quality is poor. The fuzzy c -means clustering algorithm (FCM) is an alternative solution to ameliorate the degradation in image quality. However, FCM introduces a considerable amount of computational burden and the process is time-consuming. This paper shows that the dominant peaks of histograms yield the fuzzy centroids needed for the first estimate in FCM. This reduces the computational burden imposed by FCM and improves the overall execution time.

Compensation of dead-time effects in three-level neutral point clamped inverters based on space vector PWM

In this study the effects of dead-time in three-level neutral-point-clamped (NPC) inverter is analyzed and a compensation algorithm based on space vector pulse width modulation (PWM) is proposed. In three phase inverter applications, different modulation techniques are utilized depending on the application. Among these, space vector pulse width modulation (SVPWM) technique is the modulation technique with which best bus bar utilization is achieved. This modulation technique is also applicable to three-level NPC inverters. The most common space-vector modulation technique for three-level NPC inverters is the Nearest Triangle Vector (NTV) SVPWM technique. This paper focuses on the effects of dead-time in three-level neutral point clamped inverters based on NTV SVPWM. The proposed algorithm is implemented on software and does not require an additional hardware. The analysis and compensation algorithm are verified by computer simulation.

Dynamic cognitive force control for an automatic land excavation robot

The automation of the land excavation machines can find applications in the excavation of soil in both terrestrial and planetary mining and construction. The automation requires planning at different levels such as task and trajectory pre-planning, and the automatic execution of these pre-planned tasks. In the execution of the pre-planned digging trajectories, the unexpected soil properties along the trajectory raises problems such as excessive ram-forces that may harm the machine, or cannot be applied because of the power limitations. The cognitive force control for the automation of the land excavation is developed to include the dynamics of the excavator arm. The control of the ram forces of the arm is proposed by regulating the digging depth and the trajectory speed. The developed control system is able to track the preplanned digging trajectories, and if the ram-forces becomes excessive then the trajectory is modified in time and path to control the ram-forces.<<ETX>>

Analysis and compensation of nonlinear effects in an inverter with power MOSFETs

The output voltage of an inverter is distorted due to non-ideal characteristics of the power switches. In most of the applications, output voltage distortion causes serious problems such as instability or torque ripple in motor drive systems. Therefore, an accurate voltage synthesis at the output of the inverter is needed. This paper analyzes the output voltage distortion in an inverter with power MOSFETs and proposes a solution to this problem. The analysis and the proposed solution are verified through simulation and experimental work.

Harmonic minimization in a three-phase asymmetrical PWM rectifier

A new pulse-width modulation (PWM) method for a three-phase bridge rectifier developed here gives minimized low order harmonics. As a PWM rectifier, it offers better input and output characteristics than phase-controlled rectifiers. It has inherited the characteristics of the PWM rectifier such as having high power factor at the input with low harmonic content of the input current and zero phase-shift of input voltage and current. The availability of power transistors at high power ratings enabled the implementation of PWM rectifiers much easily. The modulation method is applied to a DC motor drive system at 1 kW rating. A high speed microcontroller produces the switching pulses.<<ETX>>

Compensation of nonlinear effects in three-level neutral-point-clamped inverters based on field oriented control

In this paper, the nonlinear effects in three-level neutral-point-clamped inverters will be studied and a compensation algorithm, based on field oriented control (FOC) technique, will be proposed. In voltage source inverters (VSIs), nonlinear effects such as voltage drops on power semiconductors, and their turn on/turn off times cause distortions at the output voltage. Also dead-time, inserted in order to avoid short-circuits, are another source of nonlinearity. The proposed compensation algorithm is developed by analyzing the effects of nonlinearities in each switching period and correcting modulation signals with compensation signals accordingly. The algorithm is implemented in software and does not require any additional hardware. The proposed algorithm is verified by simulation results and experiments.