Showing papers in "IEEE Transactions on Industrial Electronics in 2001"

Novel maximum-power-point-tracking controller for photovoltaic energy conversion system

Abstract: A novel maximum-power-point-tracking (MPPT) controller for a photovoltaic (PV) energy conversion system is presented. Using the slope of power versus voltage of a PV array, the proposed MPPT controller allows the conversion system to track the maximum power point very rapidly. As opposed to conventional two-stage designs, a single-stage configuration is implemented, resulting in size and weight reduction and increased efficiency. The proposed system acts as a solar generator on sunny days, in addition to working as an active power line conditioner on rainy days. Finally, computer simulations and experimental results demonstrate the superior performance of the proposed technique.

An optimal fuzzy PID controller

Abstract: This paper introduces an optimal fuzzy proportional-integral-derivative (PID) controller. The fuzzy PID controller is a discrete-time version of the conventional PID controller, which preserves the same linear structure of the proportional, integral, and derivative parts but has constant coefficient yet self-tuned control gains. Fuzzy logic is employed only for the design; the resulting controller does not need to execute any fuzzy rule base, and is actually a conventional PID controller with analytical formulae. The main improvement is in endowing the classical controller with a certain adaptive control capability. The constant PID control gains are optimized by using the multiobjective genetic algorithm (MOGA), thereby yielding an optimal fuzzy PID controller. Computer simulations are shown to demonstrate its improvement over the fuzzy PID controller without MOGA optimization.

Design of a contactless battery charger for cellular phone

Abstract: In this paper, the design of a contactless charger for the lithium-ion battery of a cellular phone is presented. In this charger, the primary core of the transformer is in the charger unit and the secondary core is in the telephone. The gap (3 mm) between them is the thickness of the two plastic cases. The transformer core design for the maximum coupling coefficient with the size constraint on the secondary side is presented. Analysis of the primary-side series resonant power converter with the loosely coupled transformer is performed, and the design optimization is presented. For the battery-charging control, a simple control circuit is presented and its performance is verified from the experimental results.

Hiding digital watermarks using multiresolution wavelet transform

Abstract: In this paper, an image accreditation technique by embedding digital watermarks in images is proposed. The proposed method for the digital watermarking is based on the wavelet transform. This is unlike most previous work, which used a random number of a sequence of bits as a watermark and where the watermark can only be detected by comparing an experimental threshold value to determine whether a sequence of random signals is the watermark. The proposed approach embeds a watermark with visual recognizable patterns, such as binary, gray, or color image in images by modifying the frequency part of the images. In the proposed approach, an original image is decomposed into wavelet coefficients. Then, multi-energy watermarking scheme based on the qualified significant wavelet tree (QSWT) is used to achieve the robustness of the watermarking. Unlike other watermarking techniques that use a single casting energy, QSWT adopts adaptive casting energy in different resolutions. The performance of the proposed watermarking is robust to a variety of signal distortions, such as JPEG, image cropping, sharpening, median filtering, and incorporating attacks.

The fusion of computationally intelligent methodologies and sliding-mode control-a survey

Abstract: This paper surveys how some "intelligence" can be incorporated in sliding-mode controllers (SMCs) by the use of computational intelligence methodologies in order to alleviate the well-known problems met in practical implementations of SMCs. The use of variable-structure system theory in design and stability analysis of fuzzy controllers is also discussed by drawing parallels between fuzzy control and SMCs. An overview of the research and applications reported in the literature in this respect is presented.

Performance analysis of image compression using wavelets

Abstract: The aim of this paper is to examine a set of wavelet functions (wavelets) for implementation in a still image compression system and to highlight the benefit of this transform relating to today's methods. The paper discusses important features of wavelet transform in compression of still images, including the extent to which the quality of image is degraded by the process of wavelet compression and decompression. Image quality is measured objectively, using peak signal-to-noise ratio or picture quality scale, and subjectively, using perceived image quality. The effects of different wavelet functions, image contents and compression ratios are assessed. A comparison with a discrete-cosine-transform-based compression system is given. Our results provide a good reference for application developers to choose a good wavelet compression system for their application.

Modeling and nonlinear control of magnetic levitation systems

Abstract: In this paper, the authors propose a nonlinear model for magnetic levitation systems which is validated with experimental measurements. Using this model, a nonlinear control law based on differential geometry is firstly synthesized. Then, its real-time implementation is developed. In order to highlight the performance of the proposed control law, experimental results are given.

Review on materials, microsensors, systems and devices for high-temperature and harsh-environment applications

Abstract: The considerable investment in silicon technology has rarely addressed device use in harsh environments such as high temperatures, aggressive media, and radiation exposure. A clear future requirement is to save weight, volume, and reduce costs in "unfriendly" environments like high temperatures. This can be achieved either by cooling systems or by electronic microsystem components suited to withstand high temperatures. The current status of cooling systems, harsh-environment sensors, and microsystems in view of markets, realized devices, material, properties, process maturity, and packaging technologies are reviewed. Possible semiconductor candidates for high-temperature applications are discussed. The main obstacles for the future of high-temperature and harsh-environment microsystems is highlighted.

Perfect tracking control based on multirate feedforward control with generalized sampling periods

Abstract: In this paper, a novel perfect tracking control method based on multirate feedforward control is proposed. The advantages of the proposed method are that: (1) the proposed multirate feedforward controller eliminates the notorious unstable zero problem in designing the discrete-time inverse system; (2) the states of the plant match the desired trajectories at every sampling point of reference input; and (3) the proposed controller is completely independent of the feedback characteristics. Thus, highly robust performance is assured by the robust feedback controller. Moreover, by generalizing the relationship between the sampling period of plant output and the control period of plant input, the proposed method can be applied to various systems with hardware restrictions of these periods, which leads to higher performance. Next, it is shown that the structure of the proposed perfect tracking controller is very simple and clear. Illustrative examples of position control using a DC servomotor are presented, and simulations and experiments demonstrate the advantages of this approach.

Torque-maximizing field-weakening control: design, analysis, and parameter selection

Abstract: The torque-maximizing field-weakening control scheme proposed by Kim and Sul is developed further. The performance under imperfect field orientation conditions is investigated, and it is shown that an overestimated-rather than an underestimated-model leakage inductance should be used. A slightly modified algorithm, which offers better robustness and reduced computational complexity, is presented. The importance, for good performance, of combining the scheme with current and speed controllers featuring antiwindup and improved disturbance rejection is emphasized. The dynamics of the resulting closed-loop system are analyzed. Obtained in the process, are rules for selection of all controller parameters, allowing tuning without trial-and error steps. Good performance of the resulting system is verified experimentally.

The use of matrix converters in direct torque control of induction machines

Abstract: In this paper, a new control method for matrix converters is proposed which allows, under the constraint of unity input power factor, the generation of the voltage vectors required to implement the direct torque control (DTC) of induction machines. Using this control method, it is possible to combine the advantages of matrix converters with the advantages of the DTC schemes. Some numerical simulations are carried out, showing the effectiveness of the proposed method in steady-state and transient conditions. Some experimental tests were also carried out demonstrating the practical feasibility of this control scheme.

A simple position-sensorless algorithm for rotor-side field-oriented control of wound-rotor induction machine

Abstract: A simple position-sensorless method for the rotor-side field-oriented control of a wound-rotor induction machine is described in this paper. The algorithm is based on axis transformations. Compared to the previously proposed methods, it is more direct and the dependence on machine parameters is also largely reduced. The algorithm can be started on the fly without the knowledge of the initial rotor position. Operation at synchronous speed, corresponding to zero rotor frequency, is stable, thus making it suitable for variable speed constant frequency operations. Simulation and experimental results show excellent performance of the scheme.

Fuzzy sliding-mode controllers with applications

Abstract: This paper concerns the design of robust control systems using sliding-mode control that incorporates a fuzzy tuning technique. The control law superposes equivalent control, switching control, and fuzzy control. An equivalent control law is first designed using pole placement. Switching control is then added to guarantee that the state reaches the sliding mode in the presence of parameter and disturbance uncertainties. Fuzzy tuning schemes are employed to improve control performance and to reduce chattering in the sliding mode. The practical application of fuzzy logic is proposed here as a computational-intelligence approach to engineering problems associated with sliding-mode controllers. The proposed method can have a number of industrial applications including the joint control of a hydraulically actuated mini-excavator as presented in this paper. The control hardware is described together with simulated and experimental results. High performance and attenuated chatter are achieved. The results obtained verify the validity of the proposed control approach to dynamic systems characterized by severe uncertainties.

Digital repetitive learning controller for three-phase CVCF PWM inverter

Abstract: In this paper, a plug-in digital repetitive leaning control scheme is proposed for three-phase constant-voltage constant-frequency (CVCF) pulsewidth modulation inverters to achieve high-quality sinusoidal output voltages. In the proposed control scheme, the repetitive controller (RC) is plugged into the stable one-sampling-ahead-preview-controlled three-phase CVCF inverter system using only two voltage sensors. The RC is designed to eliminate periodic disturbance and/or track periodic reference signal with zero tracking error, The design theory of plug-in repetitive learning controller is described systematically and the stability analysis or overall system is discussed. The merits of the controlled systems include features of minimized total harmonic distortion, robustness to parameter uncertainties, fast response, and fewer sensors. Simulation and experimental results are provided to illustrate the effectiveness of the proposed scheme.

Modeling, control, and design of input-series-output-parallel-connected converter for high-speed-train power system

Abstract: In this paper, a charge control with an input voltage feedforward is proposed for an input-series-output-parallel-connected converter configuration for the high-speed-train power system application. This control scheme accomplishes the output current sharing. For the output-parallel-connected modules as well as the input voltage sharing for the input-series-connected modules for all operating conditions including the transients. It also offers the robustness for the input voltage sharing control according to the component value mismatches among the modules. This configuration enables the usage of a MOSFET for a high-voltage system allowing a higher switching frequency for a lighter system weight and smaller size. The performance of the proposed scheme is verified through the experimental results.

Variable-structure PID control to prevent integrator windup

Abstract: In this paper, the authors propose a new variable-structure (switching) method for the prevention of proportional-integral-derivative controller integrator windup in both continuous and discrete-time implementations. The method is easily implemented and tuned by practicing engineers. This new method is compared with several existing methods for the prevention of integrator windup.

Current control of unbalanced electrical systems

Abstract: The vector modeling approach is employed to describe the behavior of unbalanced three-phase (three-wire), unbalanced two-phase and single-phase systems. In the case of single-phase systems, a fictitious circuit is introduced in order to create the vector model. Continuous-time and discrete-time current controllers based on the vector approach are presented. The current control scheme is based on two controllers, one for the positive sequence and another for the negative sequence. The controllers are implemented in the synchronous reference frame and in the stationary reference frame. In the stationary reference frame, the use of the same integral gains for both controllers simplifies the equations of the control law especially for single-phase systems. Simulation and experimental results obtained with a pulsewidth modulation voltage-source inverter supplying unbalanced systems are presented.

A fast dynamic DC-link power-balancing scheme for a PWM converter-inverter system

Abstract: The authors propose a new power converter control scheme for a converter-inverter system. The strategy is to fully utilize the inverter dynamics in controlling the converter dynamics. The authors obtain the power dynamics for both converter and inverter systems, and control the converter power so that it matches the required inverter power exactly. Then, in the ideal case, no power flows through the DC-link capacitors and, thus, the DC-link voltage does not fluctuate even though a very small amount of the DC-link capacitance is used. In forcing the converter power to match the inverter power, the authors utilize the master-slave control concept. They control the DC-link voltage level indirectly through the stored capacitor energy in order to exploit the advantage of the linear dynamic behavior of the capacitor energy. This helps them to circumvent a complex control method in regulating the DC-link voltage. Through simulation and experimental results, the superiority of the proposed converter control scheme is demonstrated.

Speed-sensorless vector control of an induction motor using neural network speed estimation

Abstract: In this paper, a novel speed estimation method of an induction motor using neural networks (NNs) is presented. The NN speed estimator is trained online by using the error backpropagation algorithm, and the training starts simultaneously with the induction motor working. The estimated speed is then fed back in the speed control loop, and the speed-sensorless vector drive is realized. The proposed NN speed estimator has shown good performance in the transient and steady states, and also at either variable-speed operation or load variation. The validity and the usefulness of the proposed algorithm are thoroughly verified with experiments on fully digitalized 2.2 kW induction motor drive systems.

Fuzzy-controlled Li-ion battery charge system with active state-of-charge controller

Abstract: A fuzzy-controlled active state-of-charge controller (FC-ASCC) for improving the charging behavior of a lithium-ion (Li-ion) battery is proposed. The proposed FC-ASCC is designed to replace the general constant-voltage charging mode by two kinds of modes: sense and charge. A fuzzy-controlled algorithm is built with the predicted charger performance to program the charging trajectory faster and to keep the charge operation in a proposed safe-charge area (SCA). A modeling work is conducted for analyzing and describing the Li-ion battery in charging process. A three-dimensional Y-mesh diagram for describing the charging trajectories of the proposed FC charger is simulated. A prototype of a Li-ion battery charger with FC-ASCC is simulated and realized to assess the predicted charging performance. Experiment shows that the charging speed of the proposed FC charger compared with the general one increases about 23% and the charger can safely work in the SCA.

A novel zero-voltage and zero-current-switching PWM full-bridge converter using two diodes in series with the lagging leg

Abstract: This paper proposes a novel phase-shifted zero-voltage and zero-current-switching (ZVZCS) pulsewidth modulation full-bridge converter, which realizes ZVS for the leading leg and ZCS for the lagging leg. A blocking capacitor is added in series with the primary winding of the transformer to make the primary current decay to zero during zero state to ensure ZCS for the lagging leg. In order to prevent the primary current from reversing during zero state, two diodes in series with the lagging leg are added. The principle of operation, steady-state analysis, and design procedures are presented. The experimental results are also included to verify the theoretical analysis.

A simplified functional simulation model for three-phase voltage-source inverter using switching function concept

Abstract: In this paper, a functional simulation model for the voltage-source inverter (VSI) using the switching function concept is studied and the actual implementation of the model is proposed with the help of Matlab Simulink. Also, this concept is extended to the voltage-doubler-type pulse width-modulated (PWM) AC-DC rectifier and the PWM AC-DC-AC converter. With the developed functional model, the simplification of the static power circuits can be achieved so that the convergence and long run-time problems can be solved. Also, in the functional model, the design parameters, such as voltage and current ratings of the power semiconductor switches and load current, can be easily calculated. The general switching function concept is reviewed in brief and the proposed functional models for the VSI, voltage-doubler rectifier, and PWM AC-DC-AC converter and their implementations using Matlab Simulink are explained in detail. Also, several informative simulation results verify the validity of the proposed models.

A multimodule parallelable series-connected PWM voltage regulator

Abstract: This paper presents the analysis and design of a single-phase voltage regulator (VR) and its multinodule parallel control. The VR employs the pulsewidth modulation three-arm rectifier-inverter topology. The inverter side adjusts the load voltage with the series regulating structure aiming to minimize converter capacity and attain higher efficiency. The rectifier side regenerates the load power and executes the active power filter function to achieve unity power factor. Based on such high-performance VR, a resistive droop method combined with the P-V droop and Q-/spl delta/ shift scheme is then proposed to control the current sharing such that multiple VRs can be paralleled directly without any control interconnection. The proposed parallel control technique possesses the features of fast response, precise voltage regulation, equal fundamental and harmonic current sharing, tolerance for parameter mismatch, and so on. Two prototype 1 KVA VRs are implemented, and the effectiveness is demonstrated by some simulation and experimental results.

Neural-network-based self-tuning PI controller for precise motion control of PMAC motors

Abstract: In general, proportional plus integral (PI) controllers used in computer numerically controlled machines possess fixed gain. They may perform well under some operating conditions, but not all. To increase the robustness of fixed-gain PI controllers, we propose a new neural-network-based self-tuning PI control system. In this new approach, a well-trained neural network supplies the PI controller with suitable gain according to each operating condition pair (torque, angular velocity, and position error) detected. To demonstrate the advantages of our proposed neural-network-based self-tuning PI control technique, both computer simulations and experiments were executed in this research. During the computer simulation, the direct experiment method was adopted to better model the problem of hysteresis in the AC servo motor. In real experiments, a PC-based controller was used to carry out the control tasks. Results of both computer simulations and experiments show that the newly developed dynamic PI approach outperforms the fixed PI scheme in rise time, precise positioning, and robustness.

Six self-lift DC-DC converters, voltage lift technique

Abstract: The voltage lift technique is a popular method widely applied in electronic circuit design. Applying it has created six new DC-DC step-up power converters, namely, self-lift DC-DC power converters, which possess high output voltage with smooth ripple. Therefore, these converters can be used in computer peripheral equipment and industrial applications.

Design and implementation of the extended Kalman filter for the speed and rotor position estimation of brushless DC motor

Abstract: A method for speed and rotor position estimation of a brushless DC motor (BLDCM) is presented in this paper. An extended Kalman filter (EKF) is employed to estimate the motor state variables by only using measurements of the stator fine voltages and currents. When applying the EKF, it was necessary to solve some specific problems related to the voltage and current waveforms of the BLDCM. During the estimation procedure, the voltage- and current-measuring signals are not filtered, which is otherwise usually done when applying similar methods. The voltage average value during the sampling interval is obtained by combining measurements and calculations, owing to the application of the predictive current controller which is based on the mathematical model of motor. Two variants of the estimation algorithm are considered: (1) speed and rotor position are estimated with constant motor parameters and (2) the stator resistance is estimated simultaneously with motor state variables. In order to verify the estimation results, the laboratory setup has been constructed using a motor with ratings of 1.5 kW, 2000 r/min, fed by an insulated gate bipolar transistor inverter. The speed and current controls, as well as the estimation algorithm, have been implemented by a digital signal processor (TMS320C50). The experimental results show that is possible to estimate the speed and rotor position of the BLDCM with sufficient accuracy in both steady-state and dynamic operation. Introducing the estimation of the stator resistance, the speed estimation accuracy is increased, particularly at low speeds. At the end of the paper, the characteristics of the sensorless drive are analyzed. A sensorless speed control system has been achieved with maximum steady-state error between reference and actual motor speed of /spl plusmn/1% at speeds above 5% of the rated value.

Control strategies for enhanced power smoothing in wind energy systems using a flywheel driven by a vector-controlled induction machine

Abstract: This paper presents a novel control strategy for power smoothing in wind energy applications, especially those feeding a stand-alone load. The system is based on a vector-controlled induction machine driving a flywheel and addresses the problem of regulating the DC-link system voltage against both input power surges/sags from a wind turbine or sudden changes in load demand. The control is based on a feedforward compensation scheme augmented by a nonlinear controller. Two feedforward compensation schemes are discussed and the limitations and performance of each scheme are analyzed. Experimental results are presented which verify the excellent performance of the feedforward compensation technique.

Total sliding-mode controller for PM synchronous servo motor drive using recurrent fuzzy neural network

Abstract: In this paper, the dynamic responses of a recurrent-fuzzy-neural-network (RFNN) sliding-mode-controlled permanent-magnet (PM) synchronous servo motor are described. First, a newly designed total sliding-mode control system, which is insensitive to uncertainties, including parameter variations and external disturbance in the whole control process, is introduced. The total sliding-mode control comprises the baseline model design and the curbing controller design. In the baseline model design, a computed torque controller is designed to cancel the nonlinearity of the nominal plant. In the curbing controller design, an additional controller is designed using a new sliding surface to ensure the sliding motion through the entire state trajectory. Therefore, in the total sliding-mode control system, the controlled system has a total sliding motion without a reaching phase. Then, to overcome the two main problems with sliding-mode control, i.e., the assumption of known uncertainty bounds and the chattering phenomena in the control effort, an RFNN sliding-mode control system is investigated to control the PM synchronous servo motor. In the RFNN sliding-mode control system, an RFNN bound observer is utilized to adjust the uncertainty bounds in real time. To guarantee the convergence of tracking error, analytical methods based on a discrete-type Lyapunov function are proposed to determine the varied learning rates of the RFNN. Simulated and experimental results due to periodic step and sinusoidal commands show that the dynamic behaviors of the proposed control systems are robust with regard to uncertainties.

Piezomechanics using intelligent variable-structure control

Abstract: The so-called piezomechanics contain three parts: piezoelectric translator, carriage mechanism, and control system. It is well known that piezomechanics have three drawbacks: (1) it should only be loaded axially; (2) it contains a hysteresis feature; and (3) its expansion is dependent on temperature. The first drawback is tackled by the design of the carriage mechanism. This paper focuses on dealing with the second and third drawbacks by using an intelligent variable-structure control. First, a neural network is employed to learn the dynamics of the piezomechanism. Second, a novel forward control based on the learned model is employed to achieve an acceptable tracking result. Because the tracking performance by a forward control cannot be guaranteed as the system is subject to uncertainties, a discrete-time variable-structure control is synthesized to improve the performance. No state estimator is required for the proposed control. The stability of the overall system is verified via the Lyapunov analysis. Experiments are also presented to confirm the effectiveness of the proposed control.

Analysis and prediction of inverter switching frequency in direct torque control of induction machine based on hysteresis bands and machine parameters

Abstract: In this paper, the influences of the hysteresis bands on the direct torque control (DTC) of an induction motor are analytically investigated, and the switching frequency of the inverter is predicted based on the analysis. The flux and torque hysteresis bands are the only gains to be adjusted in DTC, and the inverter switching frequency and the current waveform are greatly influenced by them. Therefore, the magnitude of the hysteresis band should be determined based on reasonable guidelines which can avoid excessive inverter switching frequency and current harmonics in the whole operating region. This paper predicts the inverter switching frequency according to torque and flux hysteresis bands based on induction machine parameters and control sampling period, and investigates the effect of hysteresis bands to line current harmonics. The simulated and experimental results prove the usefulness and feasibility of the proposed method.