Ick Choy

Commutation torque ripple reduction in brushless DC motor drives using a single DC current sensor

This paper presents a comprehensive study on reducing commutation torque ripples generated in brushless DC motor drives with only a single DC-link current sensor provided. In such drives, commutation torque ripple suppression techniques that are practically effective in low speed as well as high speed regions are scarcely found. The commutation compensation technique proposed here is based on a strategy that the current slopes of the incoming and the outgoing phases during the commutation interval can be equalized by a proper duty-ratio control. Being directly linked with deadbeat current control scheme, the proposed control method accomplishes suppression of the spikes and dips superimposed on the current and torque responses during the commutation intervals of the inverter. Effectiveness of the proposed control method is verified through simulations and experiments.

New zero-current-transition PWM DC/DC converters without current stress

This paper presents novel zero-current-transition (ZCT) PWM DC/DC converters without additional current stress and conduction loss on the main switch during the resonance period of the auxiliary cell. The auxiliary cell consists of a resonant inductor, a resonant capacitor, an auxiliary switch and an auxiliary diode in parallel with the main switch and the zero-current-switching (ZCS) ranges of the main and the auxiliary switch of the proposed converters are entirely achieved by operating the auxiliary cell. In addition, the resonant inductor of the proposed ZCT cell helps soft turn-on of the main switch. The theoretical analysis and the operation principle of the new ZCT technique are described in detail using a boost converter as an example. To verify the validity of the proposed ZCT technique, the simulation and the experiment were performed on the nonisolated and the isolated converter, respectively. Here, the nonisolated converter is a boost converter having 100 kHz switching frequency, 1 kW rating power, and the isolated converter is a full-bridge (FB) converter having 50 kHz switching frequency, 1 kW rating power.

Improvement of low-speed operation performance of DTC for three-level inverter-fed induction motors

A direct torque control algorithm for three-level inverter-fed induction motors is presented. Basic voltage selection methods similar to a two-level inverter provoke some problems such as stator-flux drooping phenomenon and undesirable torque control deterioration appeared, especially at low-speed operation. To overcome these problems, an algorithm with the basic switching sectors subdivided and intermediate voltage vectors applied is proposed in this paper. This algorithm basically considers applications in which direct torque-controlled induction motors are fed by three-level inverters with maximum switching frequency lowered around 1 kHz. An adaptive observer is also employed to bring better responses at the low-speed operation, by estimating some state variables and motor parameters which take a deep effect on the performance of the low-speed operation. Simulation and experiment results verify effectiveness of the proposed algorithm.

Torque ripple reduction in DTC of induction motor driven by 3-level inverter with low switching frequency

A torque ripple reduction technique of direct torque control (DTC) for high power induction motors driven by 3-level inverters with the inverter switching frequency limited around 0.5-l kHz level is presented. It is noted that conventional DTC algorithms to reduce torque ripple are devised for applications with relatively high switching frequency above 2-3 MHz. Such conventional algorithms cannot accomplish satisfactory torque ripple reduction for 3-level inverter systems with lower switching frequency. A new DTC algorithm, especially for low switching frequency inverter system, illustrates relatively reduced torque ripple characteristics all over the operating speed region. Simulation and experimental results show effectiveness of the proposed control algorithm.

Sensorless vector control of induction motor using a novel reduced-order extended Luenberger observer

A synthesis method of the reduced-order extended Luenberger observer (ROELO) and its design procedure for a nonlinear dynamic system are presented. This paper proposes a method to reduce the order of the observer and to select the observer gain matrix. The main features of the proposed observer are discussed and compared with the characteristics of the other observers. The proposed algorithm is applied for high-performance induction motor drives without a speed sensor. The simulation results show that the proposed ROELO provides both the rotor flux and rotor speed estimation with good transient and steady state performance.

Improving crest factor of electronic ballast-fed fluorescent lamp current using pulse frequency modulation

In case where electronic ballast employing a valley-fill passive power-factor correction (PFC) circuit is used for feeding fluorescent tamps, a new method to reduce crest factor of the lamp current is studied in this paper. It is known that a 50% valley-fill passive PFC provided for high input power factor results in undesirable value of crest factor of the fluorescent lamp current, In order to reduce crest factor to a lower value, a pulse frequency modulation technique based on the waveform of the DC-link voltage which is predetermined by the passive PFC circuit is taken into the switching control action of the electronic ballast. An equation-based analysis between the crest factor of lamp current and the effect of varying the inverter switching frequency is comprehensively performed. Several simulation and experiment results illustrate the Effectiveness of the proposed control scheme.

Sliding Mode Controller for Torque and Pitch Control of PMSG Wind Power Systems

We propose a torque and pitch control scheme for variable speed wind turbines with permanent magnet synchronous generator (PMSG). A torque controller is designed to maximize the power below the rated wind speed and a pitch controller is designed to regulate the output power above the rated wind speed. The controllers exploit the sliding mode control scheme considering the variation of wind speed. Since the aerodynamic torque and rotor acceleration are difficult to measure in practice, a finite time convergent observer is designed which estimates them. In order to verify the proposed control strategy, we present stability analysis as well as simulation results.

On-line efficiency optimization control of a slip angular frequency controlled induction motor drive using neural networks

Online efficiency control optimization of induction motor drives is important from the viewpoints of energy saving and controlling a system whose characteristics are not fully unknown. The paper presents a neural network-based online efficiency control optimization for an induction motor drive which adopts slip angular frequency control. In the proposed scheme, a neurocontroller adjusts the slip angular frequency adaptively for minimum loss operation based on the measured input power. Simulation results show that considerable energy savings are achieved in comparison with the conventional method of operating under the condition of constant voltage to frequency ratio.

Design of a Robust Stable Flux Observer for Induction Motors

This paper presents a robustly adaptive flux observer for speed-sensorless induction motor control. The proposed approach employs additional robustifying signals to cope with the parametric uncertainties instead of designing an estimator, which has been normally used in power electronic drives. For that, the sliding-mode like adaptive controls are designed and their gain parameters are determined so that the observer dynamics are stable in the sense of Lyapunov, and furthermore they can guarantee the robustness against parametric uncertainties in induction motor systems. Estimated rotor speed is to be used to generate feedback control signal for the speed sensorless vector control system. To show the validity and efficiency of the proposed system, simulation results are presented.

An inertia identification using ROELO for low speed control of electric machine

A new scheme to estimate the moment of inertia in the motor drive system in very low speed is proposed in this paper. The simple speed estimation scheme, which is usually used in most servo system for low speed operation, is sensitive to the variation of the machine parameter, especially the moment of inertia. To estimate the motor inertia value, reduced-order extended Luenberger observer (ROELO) is applied. The effectiveness of the proposed ROELO is applied by simulations.