Prof. Dr. Joachim Holtz
Editor-in-Chief
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Prof. Dr. Joachim Holtz |
Special Section on Predictive and Delayless Methods in Control Instrumentation
- Guest Editorial: Special Section on Predictive and Delayless Methods in Control Instrumentation
by Seppo Ovaska
- Polynomial Predictive Filtering in Control Instrumentation: A Review
by Sami Väliviita, Seppo J. Ovaska, and Olli Vainio
Abstract - Additional delay is an unavoidable drawback of conventional filters used frequently in industrial electronics. This delay is particularly harmful if the filtered primary signal is to be used for time-critical feedback or synchronization purposes. Therefore, predictive signal processing methods can offer significant advantages for these real-time applications. Polynomial predictive filters are specified without explicit pass- and stopbands, and they are behaving delaylessly or predictively for smoothly varying signal components. The degree of smoothness of the incoming signal sets the requirements for the applied filtering scheme and its parameters. Smoothness of a signal is a fuzzy and application- specific concept: the degree of smoothness depends on the ratio of the bandwidth of the primary signal and the applied sampling rate, as well as the noise component. In this paper, we review the most important polynomial predictive filtering methods and algorithms, their design and implementation techniques, and a collection of successful applications.
- Variable Sample Rate Delayless Frequency Adaptive Digital Filter for Synchronized Signal Aquisition and Sampling
by F. P. Dawson, L. Klaffke
Abstract - In this paper, a hardware-based, variable sample rate, delayless, frequency adaptive, cascaded digital filter is proposed. The open loop frequency adaptive and delayless property of a cascaded filter consisting of a median filter of length 3, a Blackman bandpass filter of length 30 and a predictive filter of length 25 is experimentally verified. Simulation results illustrating the filter's output response to input disturbances, in a synchronization signal aquisition application, are also presented.
- Predictive Interpolation and Decimation of Narrow-Band Signals
by Olli Vainio, Sami Väliviita
Abstract - A digital filter design and optimization method for sampling rate alteration of narrow-band signals is presented. The resulting predictive Finite Impulse Response (FIR) filters are used to remove the aliasing or imaging frequency components when the sampling rate is changed. The sampling rate can be changed either by an integer factor or a rational factor. A least-squares based generalization is developed for optimal wide-band noise attenuation.
- High Robustness of an SR Motor Angle Estimation Algorithm using Fuzzy Predictive Filters and Heuristic Knowledge based Rules
by Nesimi Ertugrul, Adrian Cheok
Abstract - In this paper, the operation of a fuzzy predictive filter used to provide high robustness against feedback signal noise in a fuzzy logic based angle estimation algorithm for the switched reluctance (SR) motor is described. The fuzzy predictive filtering method combines both fuzzy logic based time series prediction, as well as a heuristic knowledge based algorithm to detect and discard feedback signal error. As it is predictive in nature, the scheme does not introduce any delay or phase shift in the feedback signals. In addition, the fuzzy predictive filter does not require any mathematical modeling of the noise and therefore can be used effectively to control non-Gaussian impulsive type noise. An analysis of the noise and error commonly found in practical motor drives is given, and how this can effect position estimation. It is shown using experimental results that the fuzzy logic based scheme can cope well with erroneous and noisy feedback signals.
- Zero-Crossing Detection of Distorted Line Voltages using 1-bit Measurements
by Sami Väliviita
Abstract - In thyristor power converters, zero-crossings of the line voltage signal are used for the synchronization of thyristor gating pulses. In weak ac-systems, however, the line voltage can be distorted, and faulty zero-crossings occur. Besides, in isolated power transmission networks, the line frequency can alter. For the detection of true zero-crossings in such cases, we describe a neural network, which utilizes the measurements of the three line voltage components in a three-phase power delivery system. The line voltages are measured with comparators, thus enabling low-cost implementation. The neural network structure is extended by using a logic circuit, which produces the time elapsed from the previous detected zero-crossing instant as a feedback signal for the network. Thus, the knowledge that the true zero-crossings occur at regular intervals in practical power delivery systems is utilized. The simulation results show that the proposed neural network provides competitive performance.
- Nonlinear Predictive Control with Application to Manipulator with Flexible Forearm
by B. J. Song, Antti J. Koivo
Abstract - A neural network is constructed to represent the input-output relation of a dynamical model. The parameters are calculated by means of a second-order training algorithm. Then, a nonlinear predictive controller is designed on the basis of a neural network plant model using the receding horizon control approach. Based on the neural model, the control is calculated by minimizing a projected cost function that penalizes future tracking errors. As an illustration of the approach, the nonlinear dynamics of a planar two-joint arm with a flexible forearm are identified using a sigmoidal network and an off-line estimation procedure for a range of motions. The applicability of the approach is illustrated through computer simulations.
Short Paper
- Adaptive Derivative Estimation for Delay-Constrained Acceleration Measurement
by Olli Vainio
Abstract - The well-known noise problem in digital differentiation is addressed by means of using adaptive digital filtering for signal preprocessing. Rapidly responding differentiators with low-noise output can be constructed by using the adaptive filter in a predictor configuration. As the prefilter is adaptive, the approximation is more flexible than polynomial fitting. The RLS adaptive algorithm is used for prediction.
Power Electronics
- A DSP-based Single Phase AC Power Source
by K. S. Low
Abstract - This paper presents the development of a single phase AC power source, which is capable of generating high quality sinusoidal waveforms with adjustable amplitudes and frequencies over a wide range. Moreover, various types of arbitrary waveforms can also be generated. The system consists of essentially a well-controlled single-phase PWM inverter. To perform tight closed loop control of the inverter, a digital controller based on the Generalized Predictive Control (GPC) approach has been developed. The controller gains are determined by minimizing a cost function that reduces both the tracking error and the control signals. To evaluate the proposed approach, a DSP-based experimental prototype has been constructed. Experimental results under various loading conditions have demonstrated that the system performs well.
- A New Configuration of Single-Phase Symmetrical PWM AC Chopper Voltage Controller
by Nabil A. Ahmed, K. Amai, Masaaki Sakui
Abstract - With the increased availability of power MOSFET's and IGBT's, a new generationof simple choppers for ac inductive loads is foreseen. These new power semiconductors ease the use of forced commutations of thyristor switches to improve the supply power factor even with highly inductive loads. The ac controllers with thyristor technology can be replaced by PWM ac chopper controllers which have important advantages. In this paper, a symmetrical PWM ac chopper designed to operate with single-phase inductive loads with reduced number of controlled switches is described. The operation as a variable voltage source of this converter is evaluated. This includes the conversion characteristics, harmonic generation, harmonic distortion factor and input power factor. By digital simulation, these characteristics are investigated theoretically and to correlate the measurements with theory, an experimental set-up is presented to confirm the analytical analysis.
- Dual Current Control Scheme for PWM Converter under Unbalanced Input Voltage Condition
by Hong-Seok Song, Kwanghee Nam
Abstract - Voltage unbalance in a three-phase system causes performance deterioration of a pulse width modulation (PWM) converter by producing the 120Hz voltage ripples in the DC-link and by increasing the reactive power. To eliminate the DC-link voltage ripple and the DC component of the reactive power, both positive and negative sequence currents should be controlled simultaneously. We used two synchronous reference frames: a positive sequence current regulated by a PI controller in a positive synchronous reference frame (SRF); and a negative sequence current regulated by a PI controller in a negative SRF. In the positive SRF, which rotates counterclockwise, the positive sequence appears as DC, while the negative sequence appears as 120Hz. In contrast, in the negative SRF, which rotates clockwise, the negative sequence appears as DC, while the positive sequence appears as 120Hz. By deleting 120Hz components using a notch filter in each SRF, one can measure positive and negative sequence currents separately, and use them for constructing two feedback controllers. Since the negative sequence current is also controlled in its own SRF by a DC command, this approach yields better performance without increasing the control gain. Note that since the controller is implemented by a software routine in the DSP chip, using two SRFs does not require additional hardware. We demonstrated the effectiveness of the proposed control scheme by using computer simulation and experiments.
- A Review of Active Filters for Power Quality Improvement
by Bhim Singh, Kamal Al-Haddad, Ambrish Chandra
Abstract - Active filtering (AF) of electric power has now become a mature technology for harmonic and reactive power compensation in two wire (single-phase), three-wire (three-phase without neutral) and four-wire (three-phase with neutral) ac power networks, with non-linear loads. This paper presents a comprehensive review of AF configurations, control strategies, selection of components, other related economic and technical considerations and their selection for specific applications. It is aimed to provide a broad perspective on the status of AF technology to researchers and application engineers dealing with power quality issues. A list of more than two hundred research publications on the subject is also appended for a quick reference.
- A New High-Performance Thyristor Gate Control Set for Line-Commutated Converters
by Mario Benedetti, Gustavo Uicich
Abstract - In this paper, a novel implementation to obtain the triggering pulses for thyristorized AC/DC power converters is presented. The system developed is a variant of the digital ramp-and-threshold strategy employing parallel hardware calculation. In order to reduce the number of components otherwise involved, innovative ideas that make feasible the use of only one low-cost FPGA as the digital core, have been introduced. Based on the proposed topology, a compact high-resolution optimum-speed thyristor gate control circuit (TGC) is achieved. The resulting system is very flexible and can be easily configured to drive series or parallel-connected multiple-pulse controlled rectifiers. Practical results are provided.
Drive Control
- Control Approaches for High Precision Machine Tools with Air-Bearings
by Christian Schmidt, Joachim Heinzl, Günther Brandenburg
Abstract - Numerous control strategies have been developed to compensate for the effects caused by friction in linear guideways of feed-drive systems. For ultraprecision machining applications these offer a wide variety of powerful, nonlinear algorithms, but generally use rather complex computing algorithms exhausting system resources.
By the use of sophisticated aerostatic bearing technology (FVM-air bearings) no friction and therefore no stick-slip exists within linear guideways. This entails a lack of damping in the feed-direction, which is a considerable setback for the classic cascaded control concept usually implemented in commercially available servo systems.
This paper presents an approach to obtain a superior behavior of the controlled system by combining the cascaded concept with a control design in the state space. Both simulation and implementation results are presented together with tuning methods and aspects.- Robust Control of Induction Motor with Neural-Network Load Torque Estimator and a Neural-Network Identification
by Tien-Chi Chen, Chich-Yi Huang, Ching-Lien Huang
Abstract - This paper presents a control scheme for an induction motor drive which consists of a compensator, neural network identification (NNI) and neural network load torque estimator (NNLTE) based on the conventional proportional-integral (PI) controller. The NNI is a two-layer neural network which uses a projection algorithm to estimate the parameters of the induction motor and to regulate the gain of the compensator such that the response of the induction motor follows that of the nominal plant. The NNLTE is a two-layer neural network which uses the steepest descent algorithm to estimate the load disturbance and forward feed resulting in equivalent control such that the speed response of the induction motor is robust against the load disturbance. Computer simulations and experimental results demonstrate that the proposed control scheme can obtain a robust speed control.
- Fuzzy Neural Networks for Identification and Control of Ultrasonic Motor Drive with LLCC Resonant Technique
by Faa-Jeng Lin, Rong-Jong Wai, Rou-Yong Duan
Abstract - This study demonstrates the applications of fuzzy neural networks (FNNs) in the identification and control of the ultrasonic motor (USM). First, the USM is derived by a newly designed high-frequency two-phase voltage source inverter using LLCC resonant technique. Then, two FNNs with varied learning rates are proposed to control the rotor position of the USM. The USM drive system is identified by a fuzzy neural network identifier (FNNI) to provide the sensitivity information of the drive system to a fuzzy neural network controller (FNNC). A backpropagation algorithm is used to train both the FNNI and FNNC on line. Moreover, to guarantee the convergence of identification and tracking errors, analytical methods based on a discrete-type Lyapunov function are proposed to determine the varied learning rates of the FNNs. In addition, the effectiveness of the FNN controlled USM drive system is demonstrated by some experimental results. Accurate tracking response can be obtained due to the powerful on-line learning capability of the FNNs. Furthermore, the influence of parameter variations and external disturbances on the USM drive system can be reduced effectively.
Robotics and Vision
- A Study on Robustness Property of Sliding Mode Controllers: A Novel Design and Experimental Investigations
by Kemalettin Erbatur, Okyay Kaynak, Asif Sabanovic
Abstract - The robustness property of sliding mode controllers makes them attractive for industrial control applications. However, this property is valid only under ideal sliding mode conditions. Additionally, practical sliding mode controllers are likely to exhibit high frequency oscillations in the plant output, called chattering, and to excite unmodeled dynamics. A novel, chattering free sliding mode control algorithm design, based on Lyapunov stability criteria is considered in this paper. The control algorithm developed is experimentally implemented on a direct drive manipulator for various payload configurations. It is seen that the controller carries a certain amount of robustness property, the trajectory following performance being only slightly affected by the changes in the payload. A comparison of the experimental results with those obtained by a well-tuned PD control is also given.
- A Decentralized Indirect Adaptive Control for a Class of Two-Time Scale Nonlinear Systems with Application of Flexible-Joint Manipulators
by R. A. Al-Ashoor, K. Khorasani
Abstract - In this paper the problem of an indirect adaptive decentralized control for a class of two-time scale interconnected systems is considered. The concept of an integral manifold is first utilized to construct the dynamics of corrected slow subsystems. Fast subsystems are also constructed to represent the dynamics of the fast modes. A composite control scheme based on full state feedback is then developed to guarantee stability and robustness of the closed-loop system. The controller is designed by taking into account the effects of unmodeled dynamics, identification errors and parameter variations. Stability analysis of the resulting closed-loop full-order system subject to the composite controller is presented. To demonstrate the application of the proposed algorithm, an example of a two-link flexible-joint manipulator is considered. Simulation results are provided to validate the applicability of the proposed control scheme.
Signal Processing
- Temperature Control for Food in Pots on Cooking Hobs
by Uwe Has, Dimitar Wassilew
Abstract - A control system for the temperature of food is described. The food is heated in a pot. The pot is heated on a modern ceramic cooking hob. The temperature of the pot side represents the temperature of the food in the pot. This temperature is measured without direct contact by using an infrared detector. The infrared detector is a thermopile. An optical system focuses the infrared radiation of the pot side into the thermopile.
The optic is formed by a concave mirror. A spectral range from 6 µm to 15 µm is used for measurement. The food, the pot and the hob form a thermal system. This system is modelled by using an electrical circuit. The maximum heat transfer through the pot bottom varies in the range from about 6 W/cm² to 9 W/cm². If the food temperature has reached the set point than the energy transfer is reduced to about 1%.
The sensor signal is evaluated by a simple rule based controller. The controller compensates every nonlinearity that occurs in the system. The user may choose 5 different set points. These set points vary from 65 °C (keep liquids hot) to 180 °C (deep frying). If the system has reached its working point then the temperature error of the food is less than 1,5 Kelvin.
The system is simple, extremely robust and very user friendly. An exact temperature settlement in a consumer hob is available for the first time. The system is used for automatic cooking.
Short Papers
- A Power Factor Controller for Single-Phase PWM Rectifiers
by Jee-Woo Lim, Bong-Hwan Kwon
Abstract - A novel power factor controller for single-phase pulse-width-modulated (PWM) rectifiers is proposed. The unity power factor controller for a sinusoidal input current is derived using the feedback linearization concept. Two active switches and two diodes are utilized for ac-to-dc power conversion. Experimental results obtained on a 4 kW prototype are dicussed.
- Accurate and Fast Speed Measurement using Ramp-Waveform Sampling Technique
by Saeed Fararooy
Abstract - A novel 'ramp-waveform sampling technique' for accurate and fast speed measurement is presented. Square pulses from an encoder are turned into ramps using analog electronics. They are then sampled and linear regression is used on ramp-waveform sample points to extrapolate backwards and determine the starting point of each pulse very accurately.
- Leakage Inductances Identification for Autocommissioned Induction Motor Vector Control
by José Luiz Silvino, Balduino Cezar Rabelo Jr.
Abstract - This work proposes an alternative knowledge based method to determinate the standard induction machine leakage inductances. As their values are low when related to the magnetising inductance, they are usually neglected on controllers design. When using either air-gap field oriented vector control or under supersynchronous operation on high performance drives, better accuracy of these parameters is required. Hence, on this study a set of induction machines parameters were established from both laboratory tests and known machines from the literature. Then a surface was built as a function of the parameters and a search routine was utilised, having the stator transient inductance and the machine class as inputs, in order to output an estimate of the leakage inductances. This surface represents the loci of the leakage and magnetising inductances and can be generated for each standard machine class. The search algorithm determines the point on the surface that best suits a pre-defined error criterion between the previous estimated and the hereby-calculated value of the stator transient inductance. Results of the proposed technique are shown and compared to a known method. The accuracy depends on the number of available parameters and this number can be largely increased through interpolation. Hence, the boundary will be the accuracy itself and the time required. No a priory knowledge of the rotor speed is required making it suitable for sensorless commissioning schemes.
- Adaptive Pseudo Reduced-Order-Flux Observer for Speed Sensorless Field-Oriented Control of IM
by Yih-Neng Lin, Chern-Lin Chen
Abstract - An adaptive pseudo reduced-order-flux observer(APRO) for speed sensorless field-oriented control(FOC) is presented. In comparison with the adaptive full-order-flux observer(AFO), the proposed method consumes less computational time and illustrates better speed performance. Simulations and experiments on a 3-hp induction motor (IM) verify the validity of the proposed method.
