Darko P. Marcetic

Speed-Sensorless AC Drives With the Rotor Time Constant Parameter Update

This paper presents a new technique for online identification of an induction motor rotor time constant. The technique is designed for a shaft-sensorless indirect field-oriented control induction motor drive with a model reference adaptive system (MRAS)-based speed estimator. The MRAS estimator is sensitive to the changes in the rotor time constant, and online identification of that parameter is essential. If rotor parameter error exists, it does not only change the achieved rotor speed, but it also changes the dynamic behavior of the whole field control and speed estimation structure. The proposed rotor parameter update is exactly based on the newly introduced dynamic model of the potentially detuned MRAS-based speed estimator. The technique avoids the use of test signals and rather extracts the needed information from the ever-present signal jitter, which is inherent to the current and speed servo loops. This paper demonstrates that the phase angle difference between some spectral components of selected small signals within the speed estimator can be used for rotor parameter update. Computer simulations and experiments are performed under a variety of conditions to validate the effectiveness of the proposed rotor parameter update technique.

Discrete Rotor Flux and Speed Estimators for High-Speed Shaft-Sensorless IM Drives

In numerous motor drive applications, high rotor speed is the key factor for system cost, performance, and overall energy efficiency. As a result of energy crises and global market competition, the specified rotor speed and fundamental frequency of the induction motor (IM) in many drive applications noticeably go up. For the same cost and efficiency reasons, that increase of inverter fundamental output frequency cannot be followed with the increase of pulsewidth modulation (PWM) frequency. Therefore, a very low ratio between the PWM and motor fundamental frequencies is to be expected in the near future. In this paper, the shaft-sensorless drive performance is investigated at high speeds, with a very low sampling to fundamental frequency ratio. As a result, two main problems with rotor flux estimators were discovered: the integration problem in the current-based rotor flux model and the phase error in the voltage-based rotor flux model. Both problems were addressed, and a proper joint solution is suggested. The effectiveness of the proposed solution is tested in a model-reference-adaptive-system-based high-speed shaft-sensorless IM drive. The experimental results collected from the digitally controlled IM drive with a low frequency ratio validate the proposed solution.

Development of High-Reliability EV and HEV IM Propulsion Drive With Ultra-Low Latency HIL Environment

This paper proposes an improved and robust method of minimizing the error in propulsion-drive line-currents that are reconstructed from a single dc-link current measurement. The proposed algorithm extends and then shortens the relevant phase pulse-widths in order to provide optimal sampling of the dc-link currents in two consecutive pulsewidth modulation (PWM) periods. The proposed PWM pattern control enables an improved sampling method which cancels offset jitter-like waveform errors present in all three reconstructed line-currents, which is due to a specific combination of nonsimultaneously sampled dc-link current and line-current PWM ripple. The improvement in induction motor drive accuracy using a single current-sensor and no shaft sensor (as proposed in this paper), over that of conventional methods, is shown. Thanks to an ultra-low latency hardware-in-the loop (HIL) emulator, the proposed algorithm, its implementation on a DSP processor, code optimization and “laboratory” testing were all merged into one development step. In order to perform final tests of the proposed current-reconstruction algorithm and to verify the usefulness of the developed HIL platform by means of comparison, experimental results obtained on a real hardware setup are provided.

An Adaptive Resonator-Based Method for Power Measurements According to the IEEE Trial-Use Standard 1459–2000

This paper proposes an accurate and computationally efficient implementation of the IEEE Standard 1459-2000 for power measurements. The algorithm has two stages. In the first algorithm stage, the voltage and current signals are processed in parallel, and their spectrums are estimated independently of each other. Signal harmonics are estimated in a wide range of frequency using an efficient algorithm with reduced complexity. The algorithm is based on a recently introduced common structure for recursive discrete transforms and consists of digital resonators embedded in a common negative feedback loop. In the second algorithm stage, the unknown power components and other power quality indices are calculated according to definitions in the IEEE Standard 1459-2000. To demonstrate the efficiency of the proposed algorithm, the results of computer simulations and laboratory testing are presented. The laboratory results show accurate input power component estimates for a nonlinear load with rapid input current amplitude changes. In addition, a simple LabView implementation, based on the point-by-point processing feature, demonstrates the techniques modest computation requirements and confirms that the proposed algorithm is suitable for real-time applications.

Thermal Protection of Vector-Controlled IM Drive Based on DC Current Injection

A technique for stator-resistance-based thermal protection suitable for a low-cost vector-controlled induction machine (IM) drive is suggested in this paper. In order to provide accurate stator resistance monitoring at medium and high speeds, the dc signal injection-based method is selected. The main property of the scheme is that small regulated dc current is periodically injected in the stator windings without interrupting the flux and torque control loops. In the proposed scheme, inverter nonlinearities are properly compensated and accurate resistance estimation is achieved with minimal level of injected dc current. This results in consistent and controllable torque ripple, which is minimal and constant for any actual stator resistance value. Estimated stator resistance can be also used for control algorithm tuning. The method is implemented in a fixed-point microprocessor and tested on a low-cost shaft-sensorless IM drive under various operation modes.

Grid-connected Voltage Source Converter operation under distorted grid voltage

This paper proposes new control strategy for grid connected three-phase Voltage Source Converter (VSC). The strategy is designed to overcome problems of conventional voltage oriented VSC control operating under distorted grid voltage. Proposed control strategy cancels the influence of characteristic distribution grid voltage harmonics, and injects close to sinusoidal current to the grid, with permitted current waveform distortion level.

Model of elevator drive with jerk control

A strong jerk which can cause passengers discomfort occurs when electric elevator starts and stops. If uncontrolled, the jerk have influence on the electrical and mechanical subsystem performance and reduce the system life expectance. Modern drives have ability to control speed, so we can indirectly control the jerk. This paper describes the control of real gear-less electric elevator drive with vector-controlled induction motor. Position trajectory is determined by the need that jerk is changed by the predefined function. A mathematical model of the drive is presented, and it is tested through computer simulations.

Advanced model of IM including rotor slot harmonics

Purpose – The purpose of this paper is to present a detailed advanced dynamical model of induction machine (IM) with unskewed rotor bars, including rotor slot harmonics. Design/methodology/approach – Procedure of IM modeling using results from finite element analysis (FEA). Series of magneto-static FEA simulations are used to obtain matrix of IM inductances as a function of rotor angular position and geometry. Each element in this matrix is represented by Fourier series (FS) and incorporated in proposed dynamical model. Using or neglecting various elements in FS of inductance matrix may be useful for determining which component of the series has dominant influence on harmonic content of stator currents, torque ripple or speed variation. The usefulness of application of presented model is verified comparing with time-stepping FEA simulations. Findings – Although the model is not suitable for usage in on-line regulation of IM drives, but the results of simulations may be used to thoroughly explain origins o...

Natural Field Orientation Sensorless Induction Motor Drive with On-line Stator Resistance Parameter Update

Abstract This article presents a new technique for on-line identification of an induction motor stator resistance parameter. The technique is designed as an upgrade of the natural field orientation system in a shaft-sensorless indirect field-oriented control induction motor drive. The proposed upgrade results in simultaneous rotor speed estimation and stator resistance parameter update, improving natural field orientation scheme robustness. The parameter update is based on information available in the d-axis back-emf component, investigated in detail using a steady-state model of potentially detuned natural field orientation scheme. The effectiveness of the parameter update technique is validated via practical experiments under a variety of conditions.

Broken Rotor Bar Fault Detection of IM Based on the Counter-Current Braking Method

This paper presents an improved method for the broken rotor bar detection in a squirrel-cage induction motor (IM). The method is based on the spectral analysis of the transient stator current signal during the counter-current braking (CCB). Contrary to the classical CCB, the proposed method results in the low braking current, which is a small fraction of the rated value and serves as a broken bar detection test signal only. This kind of the broken rotor bar fault diagnosis is independent of loading conditions and can be carried out even for a free shaft motor. The existence of spectral components in the low CCB current signal indicating the faulty conditions is first proven with the generalized theory of symmetrical components. The method is then verified via simulations, using an IM model based on the finite-element analysis and the magnetically coupled multiple circuits approach. Afterward, the experiments are performed, showing a good agreement with both the theoretical prediction and the simulation results, confirming the presence of the fault-induced components in the stator current spectra.