Special Section Papers on Direct Torque
Control of AC Motors
1. G.S. Buja, M.P. Kazmierkowski, "Direct torque control of PWM inverter-fed AC motors - a survey," IEEE Trans. on Industrial Electronics, vol. 51, no. 4, pp. 744- 757, Aug. 2004. Full Text Link Abstract : This paper presents a review of recently used direct torque and flux control (DTC) techniques for voltage inverter-fed induction and permanent-magnet synchronous motors. A variety of techniques, different in concept, are described as follows: switching-table-based hysteresis DTC, direct self control, constant-switching-frequency DTC with space-vector modulation (DTC-SVM). Also, trends in the DTC-SVM techniques based on neuro-fuzzy logic controllers are presented. Some oscillograms that illustrate properties of the presented techniques are shown.
2. N.R.N. Idris, A.H.M. Yatim, "Direct torque control of induction machines with constant switching frequency and reduced torque ripple," IEEE Trans. on Industrial Electronics, vol. 51, no. 4, pp. 758- 767, Aug. 2004. Full Text Link Abstract : Direct torque control (DTC) of induction machines is known to have a simple control structure with comparable performance to that of the field-oriented control technique. Two major problems that are usually associated with DTC drives are: switching frequency that varies with operating conditions and high torque ripple. To solve these problems, and at the same time retain the simple control structure of DTC, a constant switching frequency torque controller is proposed to replace the conventional hysteresis-based controller. In this paper, the modeling, averaging, and linearization of the torque loop containing the proposed controller followed by simulation and experimental results are presented. The proposed controller is shown to be capable of reducing the torque ripple and maintaining a constant switching frequency.
3. Y.-S. Lai, Wen-Ke Wang, Yen-Chang Chen, "Novel switching techniques for reducing the speed ripple of AC drives with direct torque control," IEEE Trans. on Industrial Electronics, vol. 51, no. 4, pp. 768- 775, Aug. 2004. Full Text Link Abstract : The main theme of this paper is to present novel switching techniques, which insert zero-voltage vectors and/or more nonzero-voltage vectors to the conventional switching table, for AC drives with direct torque control. For the same sampling frequency of a drive controller, the proposed techniques are quite effective in reducing the torque pulsation and the speed ripples of the motors, as demonstrated in several experimental results. Moreover, the experimental confirmations have been made not only on an induction machine but also on a permanent-magnet synchronous machine.
4. V. Ambrozic, G.S. Buja, R. Menis, "Band-constrained technique for direct torque control of induction motor," IEEE Trans. on Industrial Electronics, vol. 51, no. 4, pp. 776- 784, Aug. 2004. Full Text Link Abstract : In this paper, a novel technique for the direct torque control (DTC) of an induction motor is proposed, which overcomes the trouble of high torque ripple afflicting the conventional DTC technique. With the novel technique, the inverter voltage vector selected from the switching table is applied for the time interval needed by the torque to reach the upper (or the lower) limit of the band, where the time interval is calculated from a suitable modeling of the torque dynamics. By this approach, the control system emulates the operation of a torque hysteresis controller of analog type since the application time of the inverter voltage vector is dictated by the allowed torque excursion and not by the sampling period. It is shown by experimental results that the technique yields a considerable reduction of the torque ripple. A further and ultimate reduction is obtained by compensating for the delay inherent in the discrete-time operation of the control system. The outcome is that the torque ripple of the motor is constrained within the hysteresis band of the torque controller, for a band of customary value. An ancillary merit of the technique is the almost full elimination of the average torque error inherent in the conventional technique. If the hysteresis band is shrunk, the torque ripple is bound to swing out the band limits. Under this circumstance, an extension of the technique is developed, which helps keep the torque ripple at minimum. To assess the characteristics of the proposed DTC technique, the following quantities: average torque error, rms value of the torque ripple, and inverter switching frequency are measured for different stator flux angular speeds and hysteresis bands of the torque and flux controllers. As a comparison, the same quantities are given for the conventional DTC technique.
5. C. Lascu, I. Boldea, F. Blaabjerg, "Variable-structure direct torque control - a class of fast and robust controllers for induction machine drives," IEEE Trans. on Industrial Electronics, vol. 51, no. 4, pp. 785- 792, Aug. 2004. Full Text Link Abstract : A family of variable-structure controllers for induction machine drives is presented, in which the principles of direct torque control (DTC), variable-structure control (VSC), and space-vector pulsewidth modulation are combined to ensure high-performance operation, both in the steady state and under transient conditions. Three new VSC schemes are designed following the DTC voltage-control-based philosophy. These provide robust, fast, and accurate torque and flux control, without the penalty of high chattering. Comparative results demonstrate that proposed techniques preserve the DTC transient merits, while the steady-state behavior is significantly improved. Experimental results prove the strong robustness, accuracy, quickness, and low-ripple sensor-less operation of a drive that uses the new schemes.
6. J. Luukko, O. Pyrhonen, M. Niemela, J. Pyrhonen, "Limitation of the load angle in a direct-torque-controlled synchronous machine drive," IEEE Trans. on Industrial Electronics, vol. 51, no. 4, pp. 793- 798, Aug. 2004. Full Text Link Abstract : The basic direct torque control (DTC) principle is to rotate the flux linkage forward, if the torque must be increased, and reverse, if the torque must be decreased. The torque is, however, increased only up to a maximum torque of the machine, which corresponds to a load angle of about 90/spl deg/ in a synchronous machine. This paper presents a method to overcome the possible loss of synchronism when using DTC. This requires either that the rotor angle is measured or estimated. Both of these cases are considered. Simulation and laboratory results are presented to show the effectiveness of the presented method.
7. M.F. Rahman, Md.E. Haque, Lixin Tang, Limin Zhong, "Problems associated with the direct torque control of an interior permanent-magnet synchronous motor drive and their remedies," IEEE Trans. on Industrial Electronics, vol. 51, no. 4, pp. 799- 809, Aug. 2004. Full Text Link Abstract : This paper investigates problems associated with the implementation of a direct torque control (DTC) strategy for an interior permanent-magnet synchronous motor drive. The DTC technique is increasingly drawing attention because of elimination of current controllers and, hence, their inherent delays, and elimination of the rotor position sensor. The latter advantage perhaps is the main impetus for considering this new approach of torque control. Problems associated with this controller, namely, the offset in the current measurements, the stator resistance variation, and the requirement of initial rotor position are addressed in this paper. Ways of mitigating of these problems are also investigated in this paper. These are evaluated with modeling and experimental studies, results of which are also presented.
8. A. Steimel, "Direct self-control and synchronous pulse techniques for high-power traction inverters in comparison," IEEE Trans. on Industrial Electronics, vol. 51, no. 4, pp. 810- 820, Aug. 2004. Full Text Link Abstract : High-power inverters for traction drives employ in the upper range of stator frequency special pulse control methods, optimized synchronous pulsewidth modulation (PWM), mainly in combination with rotor-flux-oriented control schemes, and direct self-control (DSC) which encompasses motor control and pulse pattern generation. The well-known symmetrized sinusoidal PWM is only to be used in the lower speed range. This paper presents and compares exemplarily the stationary behavior of these two control methods; criteria are inverter peak current, motor harmonic losses, torque ripple, and DC-link harmonics. For these low switching frequencies DSC shows, in spite of its simplicity, a very good overall performance, mainly by avoiding the imperfect use of switching frequency by the synchronous pulse patterns.
9. K. Yoshida, H. Takami, A. Fujii, "Smooth section crossing of controlled-repulsive PM LSM vehicle by DTC method based on new concept of fictitious section," IEEE Trans. on Industrial Electronics, vol. 51, no. 4, pp. 821- 826, Aug. 2004. Full Text Link Abstract : This paper presents propulsion control for the permanent-magnet linear synchronous motor vehicle Marine-Express 03 (ME03) to pass through the two sections in the mass-reduced mode by a new direct torque control (DTC) method. A fictitious section is introduced for pass-through-section control. It has been done by introducing a fictitious section defined by "one section including section boundary." The lift and thrust forces for the pass-through section are obtained by the DTC method based on voltage equations per one fictitious section. The vehicle ME03 has been controlled successfully to pass through the two sections in the mass-reduced mode by experiment.
10. J. Rodriguez, J. Pontt, S. Kouro, P. Correa, "Direct torque control with imposed switching frequency in an 11-level cascaded inverter," IEEE Trans. on Industrial Electronics, vol. 51, no. 4, pp. 827- 833, Aug. 2004. Full Text Link Abstract : This paper presents the application of direct torque control in an induction motor, using a multilevel cascaded inverter with separated DC sources. The control strategy operates with imposed switching frequency, improving torque behavior. The paper studies the theoretical concepts related to this method, like vector selection, state variables estimation, and commutation time calculation. In addition, this paper presents results for a three- and eleven-level inverter-fed drives, from which it can be appreciated that the increase of levels of the load voltage reduces the torque ripple.
Power Electronics
11. J. Rodriguez, J. Pontt, P. Correa, P. Cortes, C. Silva, "A new modulation method to reduce common-mode voltages in multilevel inverters," IEEE Trans. on Industrial Electronics, vol. 51, no. 4, pp. 834- 839, Aug. 2004. Full Text Link Abstract : This paper proposes a new modulation strategy for multilevel inverters, which selects voltage vectors that generate zero common-mode voltage in the load, working at low switching frequency. Experimental results confirm that the method is highly effective and simple to implement in a modern microprocessor. The voltage distortion (total harmonic distortion), the number of commutations, and the linearity are also studied. Finally, it is concluded that the proposed strategy is highly suited for inverters with a high number of levels.
12. M.D.L. del Casale, N. Femia, P. Lamberti, V. Mainardi, "Selection of optimal closed-loop controllers for DC-DC voltage regulators based on nominal and tolerance design," IEEE Trans. on Industrial Electronics, vol. 51, no. 4, pp. 840- 849, Aug. 2004. Full Text Link Abstract : This paper discusses a tolerance design approach for the feedback compensation networks of DC/DC switching regulators, identifying the most reliable solutions among different feasible alternatives that fulfil closed-loop design constraints. A voltage-mode-regulated DC/DC buck converter is considered as a case study. Given the performance and stability constraints, as tolerance ranges for crossover frequency and phase margin, feasible design solutions are sought by means of Monte Carlo and interval arithmetic computations. The search space is a set of available commercial values of RC parameters and related tolerances. Best design is identified by a weighted fitness function, exploring the set of solutions provided by different design approaches. The results presented in the paper highlight that the tolerance design approach allows one to find compensation networks that fit the given performance/robustness priorities better than those ones found by means of the classical nominal design approach.
13. J. Diaz, F. Nuno, J.M. Lopera, J.A. Martin-Ramos, "A new control strategy for an AC/DC converter based on a piezoelectric transformer," IEEE Trans. on Industrial Electronics, vol. 51, no. 4, pp. 850- 856, Aug. 2004. Full Text Link Abstract : Piezoelectric transformers (PTs) are an attractive solution to reduce size and weight in ac/dc converters. In this paper, a PT-based topology is presented together with a control method. As an application, an 8-W ac/dc adapter (110 V/sub AC/ input, 12 V/sub DC/ output) is presented operating at frequencies around 500 kHz.
14. J. Diaz, J.A. Martin-Ramos, A.M. Pernia, F. Nuno, F.F. Linera, "Intelligent and universal fast charger for Ni-Cd and Ni-MH batteries in portable applications," IEEE Trans. on Industrial Electronics, vol. 51, no. 4, pp. 857- 863, Aug. 2004. Full Text Link Abstract : In this paper, a new fast charger is presented for Ni-Cd and Ni-MH batteries, which are the most frequently used in portable applications. In this charger, the control and supervision of the process has been entrusted to a microcontroller, which provides a powerful and intelligent tool to undertake complex tasks, and reduces the requested circuitry to the microcontroller itself and a few additional components. The resulting charger is able to work out the initial battery state (detecting deteriorated devices), decide the suitable way to charge it (ensuring a long cyclic life), and determine when the charge process must be finished. This way, the state of the battery is always controlled, preventing any damage to it and providing a fully protected operation mode. This paper summarizes the design and construction of the presented charger, as well as shows the experimental results obtained in the prototype tests.
15. Y.P.B. Yeung, K.W.E. Cheng, S.L. Ho, K.K. Law, D. Sutanto, "Unified analysis of switched-capacitor resonant converters," IEEE Trans. on Industrial Electronics, vol. 51, no. 4, pp. 864- 873, Aug. 2004. Full Text Link Abstract : A family of switched-capacitor resonant circuits using only two transistors is presented. The circuit operates under zero-current switching and, therefore, the switching loss is zero. It also offers a wide choice of voltage conversions including fractional as well as multiple and inverted voltage conversion ratios.
16. Wennan Guo, P.K. Jain, "A power-factor-corrected AC-AC inverter topology using a unified controller for high-frequency power distribution architecture," IEEE Trans. on Industrial Electronics, vol. 51, no. 4, pp. 874- 883, Aug. 2004. Full Text Link Abstract : High-frequency power distribution architecture (HFPDA) has gained more and more attention from both academics and industry in recent years. It is not only applicable in space systems, but also found attractive in power system design for emerging telecommunication and computer systems. As the technology has matured, HFPDA even seems to be attractive for powering the desktop computers employing the latest generation fast microprocessors. This paper presents an ac-ac inverter for HFPDA. The inverter includes a high-frequency resonant inverter and a buck-boost converter for power-factor correction (PFC). A unified controller controls both the resonant inverter and the PFC stage. Unlike other single-stage power-factor-corrected inverter topologies, the proposed inverter system has reduced dc-bus voltage stress for the universal input line voltage. The proposed inverter is found attractive in low-power applications.
17. D. Alexa, A. Sirbu, D.-M. Dobrea, "An analysis of three-phase rectifiers with near-sinusoidal input currents," IEEE Trans. on Industrial Electronics, vol. 51, no. 4, pp. 884- 891, Aug. 2004. Full Text Link Abstract : An analysis of a three-phase low-harmonic diode rectifier equipped with inductors, capacitors, and diodes is presented. Inductors and capacitors are used in conjunction with the three-phase diode rectifier bridge to improve the waveform of the currents drawn from the utility grid. The operation of the proposed converter is analyzed and, on this basis, design considerations are commented upon. The converter characteristics are determined as a function of the load current. Comparisons between the studied converter and other rectifiers (classical rectifiers, with passive or active filters, and three-phase low-harmonic rectifiers applying the third-harmonic current injection) are also presented. Several possible applications of the three-phase rectifiers with near-sinusoidal input currents are mentioned. Analytically obtained results are experimentally verified.
18. Tzann-Shin Lee, "Lagrangian modeling and passivity-based control of three-phase AC/DC voltage-source converters," IEEE Trans. on Industrial Electronics, vol. 51, no. 4, pp. 892- 902, Aug. 2004. Full Text Link Abstract : In this paper, we investigate the dc-bus voltage regulation problem for a three-phase boost-type pulsewidth-modulated (PWM) ac/dc converter using passivity-based control theory of Euler-Lagrange (EL) systems. The three-phase PWM ac/dc converters modeled in the a-b-c reference frame are first shown to be EL systems whose EL parameters are explicitly identified. The energy-dissipative properties of this model are fully retained under the d-q-axis transformation. Based on the transformed d-q EL model, passivity-based controllers are then synthesized using the techniques of energy shaping and damping injection. Two possible passivity-based feedback designs are discussed, leading to a feasible dynamic current-loop controller. Motivated from the usual power electronics control schemes and the study of Lee, the internal dc-bus voltage dynamics are regulated via an outer loop proportional plus integral (PI) controller cascaded to the d-axis current loop. Nonlinear PI control results of Desoer and Lin are applied to theoretically validate the proposed outer loop control scheme. The PWM ac/dc converter controlled by the proposed passivity-based current control scheme with outer loop PI compensation has the features of enhanced robustness under model uncertainties, decoupled current-loop dynamics, guaranteed zero steady-state error, and asymptotic rejection of constant load disturbance. Experimental results on a 1.5-kVA PC-based controlled prototype provide verification of these salient features. The experimental responses of a classical linear PI scheme are also included for comparative study.
Signal Processing And Control
19. S. Kansal, G. Cook, "Use of a sinusoidal series for modeling discrete windowed data as an alternative to interpolation," IEEE Trans. on Industrial Electronics, vol. 51, no. 4, pp. 903- 909, Aug. 2004. Full Text Link Abstract : The use of a sinusoidal series representation as an alternative to interpolation is introduced. The method is applied to both one-dimensional and two-dimensional data. It is noted that the Fourier series can be used here only if the variable of interest has no discontinuities and has the same values at the end boundaries. For situations where this is not the case we introduce the idea of adding to the Fourier series sinusoids at half the fundamental frequency. The procedure is extended to two-dimensional data and applied to terrain modeling where coarse range scanning has been performed and a model of finer resolution is then obtained. Results are shown to be excellent.
20. S.J. Ovaska, O. Vainio, "Evolutionary-programming-based optimization of reduced-rank adaptive filters for reference generation in active power filters," IEEE Trans. on Industrial Electronics, vol. 51, no. 4, pp. 910- 916, Aug. 2004. Full Text Link Abstract : We introduce an evolutionary-programming-based method for designing robust and computationally efficient adaptive bandpass filters. These predictive filters are optimized for generating current references in active power filters (APFs). The accuracy (phase/amplitude) of the reference current is crucial in current-injection-type systems, because it directly affects the harmonics reduction ability of the APF. Our digital filtering approach has the following advantages: selective bandpass response, efficient attenuation of specific harmonic components, capability to handle typical frequency alteration, small number of multiplications, and structural simplicity. In addition, practically no prior knowledge of the electricity distribution network and its loading characteristics is needed for designing the current reference generator. In an illustrative example, the total harmonic distortion of an artificial current waveform was reduced from 36.7% to less than 3.7% within the line frequency range 49-51 Hz. The proposed scheme is a combination of the hard-computing (HC)-type multiplicative general parameter method and evolutionary programming that, on the other hand, is a constituent of soft computing (SC). Such open-minded fusion thinking is emerging among researchers and engineers, and it can potentially lead to efficient combinations of HC and SC methodologies*both on the algorithm level and on the system level.
21. W. Panusittikorn, Min Cheol Lee, P.I. Ro, "Modeling and sliding-mode control of friction-based object transport using two-mode ultrasonic excitation," IEEE Trans. on Industrial Electronics, vol. 51, no. 4, pp. 917- 926, Aug. 2004. Full Text Link Abstract : This paper introduces a magnetic-free object transport system driven by a friction force on an ultrasonic flexural vibrating beam. This driving mechanism offers unique advantages of silent operation and lubricant-free structure. The characteristics are ideal for a transport system in a clean-room environment. However, the friction drive described by Hertzian contact and Coulomb friction theories is highly nonlinear. The transport system needs a sophisticated control design to deliver a load to a precise location. A traditional feedback controller and sliding-mode control were implemented in the presence of sensor noise and hardware limitation. It is experimentally shown that the tracking performance of the proposed control scheme is superior to the traditional control design.
Letters To The Editor
22. Sewan Choi, M. Jang, "A reduced-rating hybrid filter to suppress neutral current harmonics in three-phase four-wire systems," IEEE Trans. on Industrial Electronics, vol. 51, no. 4, pp. 927- 930, Aug. 2004. Full Text Link Abstract : This letter proposes a reduced-rating hybrid filter to suppress neutral current harmonics in three-phase four-wire systems. Under unbalanced loading, the proposed filter eliminates only harmonics in the neutral current while it does not affect the fundamental. The VA rating of the inverter is significantly reduced compared to the conventional one since only fundamental current due to unbalanced loading could flow through the inverter switch.
23. Jee-Hoon Jung, Gang-Youl Jeong, Bong-Hwan Kwon, "Stability improvement of V/f-controlled induction motor drive systems by a dynamic current compensator," IEEE Trans. on Industrial Electronics, vol. 51, no. 4, pp. 930- 933, Aug. 2004. Full Text Link Abstract : Stability improvement of V/f-controlled induction motor drive systems by a dynamic current compensator is proposed. The proposed method uses a dynamic current compensator to improve the stability of the V/f-controlled induction motor drive systems. This method is easy to implement and helps eliminate the oscillations causing the instability of V/f-controlled induction motor drive systems.
24. Ming Tsung Tsai, "Design of a compact series-connected AC Voltage regulator with an improved control algorithm," IEEE Trans. on Industrial Electronics, vol. 51, no. 4, pp. 933- 936, Aug. 2004. Full Text Link Abstract : This letter presents an improved control algorithm for the compensation of ac source voltage fluctuation. The proposed idea can be used to regulate both the overvoltage and undervoltage situations with only unidirectional energy transmission. Theoretical analysis has been achieved based on the power flow theory. A case study is demonstrated by means of a prototype experiment to prove its performance and effectiveness.
IEEE Transactions on Industrial Electronics
