Active Clamp Soft-Switched PWM High-Frequency Inverter for Induction Heated Hot Water Producer

Kassem, Rasha; Saleeb, Hedra; Sayed, Khairy F.

doi:10.21608/sej.2022.117926.1007

Active Clamp Soft-Switched PWM High-Frequency Inverter for Induction Heated Hot Water Producer

Document Type : Original Article

Authors

¹ Electrical Engineering Department, Faculty of Technology and Education, Sohag University, 82524, Sohag, Egypt

² Department of Electrical Engineering, Faculty of Technology and Education, Sohag University, 82524, Sohag, Egypt

³ Professor of Electrical Power and Machines, Faculty of Engineering, Sohag University

10.21608/sej.2022.117926.1007

Abstract

This paper presents a new concept of stainless-steel eddy current-based electromagnetic induction screw type for heat exchanger or double pack heaters in hot water product, steam boiler and high heating evaporator, which is more suitable and acceptable to consumers of a new generation for energy applications. In addition, the active clamped edge-resonant high-frequency PWM inverter using trench-gate IGBTs power module can operate according to the zero-voltage soft-switching principle with PWM and has been developed and proven for high-efficiency hot water heating boiler and product in consumer power applications. The power device for consumer induction heater using active-clamp soft-switched PWM high-frequency inverter is evaluated and discussed based on simulation through PSIM and experimental results. To extend the operating ranges of zero-voltage soft-switching under a low-power setting as well as improve efficiency, a high-frequency pulse density modulation strategy for a high-frequency soft-switched inverter is demonstrated. The practical effectiveness of induction heating power supply has been greatly proven from the point of view of induction heating application.

Keywords

Full Text

Active Clamp Soft-Switched PWM High-Frequency Inverter for Induction Heated Hot Water Producer

Rasha Kassem^a[*], Hedra Saleeb^a, Khairy Sayed^b

^a Electrical Engineering Department, Faculty of Technology and Education, Sohag University, 82524, Sohag, Egypt

^b Electrical Engineering Department, Faculty of Engineering, Sohag University, 82524, Sohag, Egypt

Abstract

Keywords: High-Frequency Inverter, Edge-Resonant Soft-Switching PWM, Duty Cycle Control, Induction Heated Steamer Dual Packs Heater, Consumer Power Electronics.

1. INTRODUCTION

The main source of heating, cooling, and electrical power generation applications is natural gas [1, 2], a fossil fuel, which in turn is exacerbating the looming global warming. Therefore, new-age residential induction heaters pave the way for the replacement of traditional electric and gas heating technologies. Induction Heating (IH) systems have inherent advantages, such as higher conversion efficiency, being cleaner, and having less time to acquire heat [3]. On the other hand, IH incurs more efficient clean energy disposal [4, 5]. Compared with traditional heating techniques such as resistive heating, flame heating, or arc furnaces, IH is more suitable for industrial applications because it is more effective and efficient [6-9]. More importantly, methodologies for an inherently safe pregnancy in IH are very favorable for many medical applications [10-14]. The portability and plug-and-play aspects of IH-supported devices mean that they are in high demand concerning home applications [15-17].

In recent years, electromagnetic induction eddy current-based heat energy processing and utilization systems using a variety of high-frequency high-power inverters have attracted special interest from the viewpoints of high efficiency, high reliability, safety, cleanliness, compactness in volumetric size, light in weight, rapid temperature response for particular high-power applications in industry automotive and consumer fields [18-20]. The electromagnetic IH is concerned with non-contact, high efficiency, and clean electric heating method due to the energy conversion heated device by induction eddy current based on Faraday's law of electromagnetic induction principle in addition to Joule's heating principle [21-23]. Induction heating technology has a wide range of usage areas such as melting, annealing, welding, tight passing, hardening, forming, cooking and plasma physics [24, 25].

There are various induction water heaters developed recently. But those heaters were designed for water heating. Also, academic studies have been focused on water heating. Thus, an induction water heater system seems to be a useful innovation [26]. The high-frequency inverters of induction heating applications can supply high-frequency power to IH load, which consists of working coil and eddy current-based heating materials. Some high-frequency inverters operating overpower frequency ranges from 20 kHz to several MHz need to be cost-effective, high efficiency and have high power density [19, 20, 27, 28]. There are various high-frequency inverter circuit topologies, such as full-bridge, half-bridge, single-ended push-pull, center tap push-pull and boost half-bridge. Of these, the voltage source type ZCS (zero current switching) [29], ZVS (zero voltage switching), SEPP (Single-Ended Push-Pull) resonant and the quasi-resonant hybrid high-frequency inverter has unique features, such as simple configuration, high efficiency, and wide soft commutation range [27-34]. The proposed inverter is configured by IGBTs and evaluated by simulation diagrams [19, 35].

This paper presents a new conceptual energy-saving type electromagnetic eddy current-based induction heater, which is more suitable and acceptable for induction heated hot water producer, boiler and steamer. On the other hand, active voltage-clamped type zero voltage soft switching PWM high-frequency inverter connected to utility AC 200V-RMS for consumer power applications is developed and demonstrated from a practical point of view [36-38]. In this paper, a new style compact induction heated hot water producer and steamer using soft-switching PWM high-frequency inverter is also discussed and evaluated from the experimental and simulation points of view.

This paper is organized as follows: In Section 2, induction eddy current-based heated hot water producer. In Section 3, new conceptual induction heater. In Section 4, active clamping quasi-resonant ZVS PWM high-frequency inverter. In Section 5, experimental results, and discussions and finally, the conclusion is in Section 6.

2. Induction Eddy Current-based Heated Hot Water Producer

2.1. Induction HeatedLoad Technology and Circuit Modeling

A prototype of the induction eddy current-based heated hot water producer and steamer is schematically illustrated in Fig. 1. This energy conversion device based on an electromagnetic induction-heated type heat exchanger composed of the dual pack's heater is made of a new conceptual induction heater which is built and tested by spiral stainless-steel assembly, working coil (Litz wire), nonmetal heating vessel made of the polycarbonate, high-frequency soft-switching inverter using IGBTs and diode rectifying converter.

Fig. 1. Induction heating water producer.

An electromagnetic induction heater for compact hot water producer and steamer using high-frequency inverter driven by the diode rectifier with a non-smoothing filter has to be designed for the following requirements: (a) uniform temperature distribution, (b) wide eddy current heating surface, (c) no erosion, (d) no thermal deformation for power injection or rejection, (e) small heat capacity. In this paper, a new conceptual induction heater made of non-magnetic stainless steel SUS316 plate is demonstrated that has a spiral assembly with a short circuit called copper bar end ring for quick temperature response in specified temperature setting. It is composed of the spiral assembly and its outside edge point is connected to the inside edge point by connecting the low resistance copper bar between two edge points. In this technique, it is possible to achieve a uniform temperature distribution of an electromagnetic induction eddy current-based joule’s induction heated type heat exchanger.

In general, it is difficult to form the spiral structure toward its center. In the case of rolling toward its center, effective increment of the heating surface could not expect actually. But if no obstacle is inserted in the center of the spiral plate structure, the heat exchange efficiency of this induction heater decreases because a large majority of the heated liquid flows through the center. To improve reduced heat exchange efficiency, the cylindrical polycarbonate material is inserted toward the center of this vessel. The geometric size and shape of this induction heater are designed as illustrated in Fig. 2.

Fig. 2. Top view appearance of electromagnetic induction eddy current-based heater.

3. Active Clamping Quasi-Resonant ZVS PWM High-Frequency Inverter

3.1. Circuit Description

Fig. 3 shows an active clamp high-frequency inverter circuit topology that can operate under a condition of zero voltage soft switching (ZVS) and constant frequency duty factor regulated mode asymmetrical pulse width modulation (PWM) control strategy for power regulation. This active voltage clamps high-frequency inverter using IGBTs, which has some advantageous points such as wide soft-switching operation range, low peak voltage stress for power switching devices and high efficiency, which is developed and implemented for electromagnetic induction eddy current-based heated hot water producer and steamer and boiler. Introducing the voltage-clamped capacitor (C_S) in series with an auxiliary active power switch, this high-frequency inverter can effectively clamp an excessive peak voltage applied to the main active power switch (SW₁). Besides introducing an auxiliary switch (SW_S), this high-frequency inverter can operate under a constant frequency asymmetrical pulse width modulation (PWM) control strategy. In Fig. 3 this induction heated hot water producer driven by this inverter is represented as the transformer type equivalent circuit model.

Fig. 3. Active voltage-clamped edge-resonant high-frequency inverter.

3.2. Gate Pulse Control Implementation

Fig. 4 illustrates timing asymmetrical PWM pulse sequences for the high-frequency inverter shown in Fig. 3. These voltages pulses are supplied to the power semiconductor switching block; Q₁ (SW₁&D₁) and Q_S (SW_S&D_S). Duty Factor defined as D=ton/T serves as a control variable for the continuous power regulation for this edge-resonant soft-switching PWM inverter using IGBTs. Duty Factor is designed as a ratio of the conduction time including a dead time of the main active power switches during one period.

Fig. 4. Asymmetrical PWM gate voltage pulse signal sequences.

When the full power is delivered to the load, the conduction time of the main active power switch during one cycle is lengthened as indicated in Fig. 4 (a). On the other hand, when full power is not required for load, the conduction interval is shortened as indicated in Fig. 4 (b).

4. Simulation Results

4.1. PLL-Assisted PWM Control Technique

The most commonly used pulses with modulation [41] are applied to the IH system to control the output power. For variable loads, the power semiconductor switches enter into the hard-switching mode, which increases the switching stresses. To overcome this problem, dual-loop controls were developed using a phase-locked loop (PLL) and a PI controller [39, 40, 41, 42]. The PLL, the first loop control, is used to track the resonant frequency to maintain the soft switching in the inverter and the outer loop controls the output power. The general block diagram of the PLL-assisted PI control is shown in Fig. 5. The dual-loop controls make the system more complex and slower down the dynamic response. This problem required a solution to develop a suitable modulation technique that would be good for both the soft-switching action and the power control. The flowchart of the PLL-assisted PWM control technique is shown in Fig. 6.

Fig. 5. A general block diagram of PLL-assisted PI control.

Fig. 6. Flow chart of PLL-assisted PWM control technique.

4.2. Switching Voltage and Current Waveforms

Fig. 7 shows the steady state switching voltage and current simulation waveforms of Q₁ (SW₁&D₁) and Q_S (SW_S&D_S) under the zero-voltage soft switching condition with . In Fig. 7 both the main active power switch and the auxiliary active power switch can achieve soft switching completely. Besides, this active voltage clamp high-frequency load resonant inverter can suppress an excessive peak voltage applied to the main active power switch for Modes 3 and 4. This high-frequency inverter in steady-state includes periodically repeated operation with 6 modes.

Fig. 7. Steady state switching waveforms.

Fig. 8. (a) Input 50 Hz AC voltage and 20 kHz output voltage, (b) Output voltage and current of inverter, (c) Expanded view of output voltage, (d) Expanded view of Output current, (Simulation Results).

Fig. 9 represents duty factor versus input power regulation characteristics and duty factor vs. peak voltage characteristics for a new prototype of induction heating energy conversion device under a constant frequency asymmetrical PWM control strategy. Observing this Fig. 9 it is proved that the inverter output power can be continuously adjusted in the accordance with duty factor or duty cycle as a control variable.

Fig. 9. Duty factor vs. input power and peak voltage characteristics.

5. Experimental Results and Discussions

5.1. Design of Experimentally produced Hot Water Producer

An experimental prototype was developed to supply an induction heating load of 100W. Commercially available 50 Hz AC was rectified using four 1N4007 diodes and two IRF840 MOSFETs used to convert DC to HFAC. Hardware layout of IH power supply system is shown in Fig. 10. A PIC16F877A microcontroller is used to validate the used topology. Table 1 indicates the practical design specifications and circuit parameters of the feasible electromagnetic induction-based heated hot water producer and steamer using edge-resonant ZVS-PWM soft-switching high-frequency load resonant inverter using the IGBT modules.

Fig. 10. Test setup of IH power supply system.

Table 1. Design specification and circuit parameters

Item	Symbol	Value
DC Source Voltage	E	200 V
Switching Frequency		20 kHz
Edge-Resonant lossless Capacitor	C₁	0.18
Active Voltage Clamped Capacitor	C_s	3.96
Working Coil	L₁	50.9
Electromagnetic Coupling Coefficient	k	0.693
Load Time Constant		9.63

5.2. Temperature Characteristics

Fig. 11 illustrates the temperature response characteristics of the induction heated hot water producer and steamer composed of specially designed spiral type induction heater using active voltage clamp high-frequency inverter which is built and tested in the experiment. It is noted that this inverter type compact induction heated hot water producer and steamer using new conceptual electromagnetic induction eddy current-based heater in pipeline systems can heat rapidly than conventional gas combustion type or sheathed wired heating type.

Fig. 11. Fluid temperature response characteristics of IH hot water producer and steamer.

5.3. Observed Waveforms

Fig. 12 illustrates the steady state observed switching voltage and current waveforms of , , and under the specified condition of duty cycle . Besides, it is proved that this active clamp edge-resonant ZVS-PWM high-frequency inverter using IGBTs can completely work under the operating principle of zero voltage soft switching commutation for a wide duty factor control scheme. This active clamped edge-resonant high-frequency inverter can limit an excessive peak voltage applied to the main active power switch. Accordingly, the conduction power losses as well as voltage and current peak or dynamic derivative stresses of switching power semiconductor devices; IGBTs can be considerably reduced in this high-frequency inverter circuit topology.

Fig. 12. Experimental voltage and current waveforms (Duty Factor ).

6. Conclusion

In this paper, the novel prototype of electromagnetic induction eddy current-based hot water producer and steamer using active clamp high-frequency quasi-resonant inverter has been successfully proposed and demonstrated from a practical point of view. In addition, an active voltage-clamped edge-resonant ZVS-PWM high-frequency load resonant inverter using the latest trench IGBT module, which can efficiently operate under a zero-voltage soft commutation based on asymmetrical PWM (Duty Ratio Control) strategy. These induction heated appliances for pipeline fluid heating using active voltage clamp edge-resonant high-frequency inverter could be more cost-effective than the conventional gas combustion heating type or sheathed wired heating type. In the future, the power loss analysis of this soft-switching high-frequency inverter using the CSTBTs in new generation should be done for consumer induction-heated hot water producer and boiler, and steamer as well as super-heated steamer in pipeline systems.

References

[1] F. Y. Liang, M. Ryvak, S. Sayeed and N. Zhao, “The role of natural gas as a primary fuel in the near future, including comparisons of acquisition, transmission and waste handling costs of as with competitive alternatives,” Chemistry Central Journal, vol. 6, (Suppl. 1), S4, April 2012.

[2] H. Bai, X. Wang and F. Blaabjerg, “Passivity enhancement in renewable energy source based power plant with paralleled grid-connected VSIs,” IEEE Transactions on Industry Applications,vol. 53, no. 4, pp. 3793-3802, July-Aug. 2017.

[3] J. Acero et al., “Domestic induction appliances,” IEEE Industry Applications Magazine, vol. 16, no. 2, pp. 39-47, March-April 2010.

[4] O. Lucia, P. Maussion, E. J. Dede and J. M. Burdio, “Induction heating technology and its applications: past developments, current technology, and future challenges,” IEEE Transactions on Industrial Electronics, vol. 61, no. 5, pp. 2509-2520, May 2014.

[5] H. Sarnago, O. Lucia and J. M. Burdio, “A versatile resonant tank identification methodology for induction heating systems,” IEEE Transactions on Power Electronics, vol. 33, no. 3, pp. 1897-1901, March 2018.

[6] J. Choi et al., “Design and performance evaluation of a multi-purpose hts dc induction heating machine for industrial applications,” IEEE Transactions on Applied Superconductivity, vol. 25, no. 3, pp. 1-5, June 2015.

[7] P. Amestoy et al., “Shared-memory parallelism and low-rank approximation techniques applied to direct solvers in FEM simulation,” IEEE Transactions on Magnetics, vol. 50, no. 2, pp. 517-520, Feb. 2014.

[8] J. Egalon, S. Caux, P. Maussion, M. Souley and O. Pateau, “Multiphase system for metal disc induction heating: modeling and RMS current control,” IEEE Transactions on Industry Applications, vol. 48, no. 5, pp. 1692-1699, Sept.-Oct. 2012.

[9] M.G. Lozinskii, “Industrial applications of induction heating,” Pergamon Press Publications, Oxford, New York, 1969.

[10] L. Tonthat, Y. Yamamoto, F. Aki, H. Saito and K. Mitobe, “Thermosensitive ferromagnetic implant for hyperthermia using a mixture of magnetic micro-/nanoparticles,” IEEE Transactions on Magnetics, vol. 54, no. 7, pp. 1-6, July 2018.

[11] S. C. Huang, Y. Y. Chang, Y. J. Chao, Y. S. Shan, X. Z. Lin and G. B. Lee, “Dual-row needle arrays under an electromagnetic thermotherapy system for bloodless liver resection surgery,” IEEE Transactions on Biomedical Engineering, vol. 59, no. 3, pp. 824-831, March 2012.

[12] C. -C. Tai et al., “Deep-magnetic-field generator using flexible laminated copper for thermotherapy applications,” IEEE Transactions on Magnetics, vol. 50, no. 11, pp. 1-4, Nov. 2014.

[13] H. Ishizawa, T. Tanabe, D. Yoshida, S. H. R. Hosseini, S. Katsuki and H. Akiyama, “Focusing system of burst electromagnetic waves for medical applications,” IEEE Transactions on Dielectrics and Electrical Insulation, vol. 20, no. 4, pp. 1321-1326, August 2013.

[14] J. R. Oleson, “A review of magnetic induction methods for hyperthermia treatment of cancer,” IEEE Transactions on Biomedical Engineering, vol. BME-31, no. 1, pp. 91-97, Jan. 1984.

[15] O. Lucía, H. Sarnago and J. M. Burdio, “Soft-stop optimal trajectory control for improved performance of the series-resonant multiinverter for domestic induction heating applications,” IEEE Transactions on Industrial Electronics, vol. 62, no. 10, pp. 6251-6259, Oct. 2015.

[16] J. Acero, I. Lope, J. M. Burdio, C. Carretero and R. Alonso, “Performance evaluation of graphite thin slabs for induction heating domestic applications,” IEEE Transactions on Industry Applications, vol. 51, no. 3, pp. 2398-2404, May-June 2015.

[17] I. Lope, J. Acero, J. M. Burdío, C. Carretero and R. Alonso, “Design and implementation of PCB inductors with litz-wire structure for conventional-size large-signal domestic induction heating applications,” IEEE Transactions on Industry Applications, vol. 51, no. 3, pp. 2434-2442, May-June 2015.

[18] T. Ahmed, et al., “Asymmetrical duty cycle controlled edge resonant soft switching high frequency inverter for consumer electromagnetic induction fluid heater,” Automatica, vol. 44, no. 1-2, pp. 21-26, Dec. 2003.

[19] K. Sayed and M. Nakaoka, “Performance of induction heating power supply using dual control mode pulse-width modulation-pulse-density modulation high-frequency inverter,” Electric Power Components and Systems, vol. 43, no. 2, pp. 157-166, 2015.

[20] O. Lucia, P. Maussion, E. J. Dede and J. M. Burdio, “Induction heating technology and its applications: past developments, current technology, and future challenges,” IEEE Transactions on Industrial Electronics, vol. 61, no. 5, pp. 2509-2520, May 2014.

[21] O.F. Rafael and M.C. Roberto, “Water heater by magnetic induction,” 23rd International Conference on Electronics, Communications and Computing, pp. 192-197, CONIELECOMP 2013.

[22] A. A. Amrhein, “Induction heating of aluminum cookware,” Virginia Tech, 2015.

[23] H. Sugimura, et al., “Utility AC frequency to high frequency AC power conversion circuit with soft switching PWM strategy,” KIEE International Transactions on Electrical Machinery and Energy Conversion Systems, vol. 5, no. 2, pp. 181-188, 2005.

[24] S. M. W. Ahmed, M. M. Eissa, M. Edress and T. S. Abdel-Hameed, “A multi-output high frequency cycloinverter operation for induction-heating cooking appliances - harmonic study,” 4th IEEE Conference on Industrial Electronics and Applications, pp. 2267-2272, 2009.

[25] S. Arumugam and S. R. Reddy, “Simulation results of single stage AC-AC converter for induction heating,” The Annals of “Dunarea de Jos “University of Galati. Fascicle III, Electrotechnics, Electronics, Automatic Control, Informatics, vol 33, no. 2, pp. 61-67, 2010.

[26] H. M. Unver, “A new induction water heating system design for domestic heating,” Energy Education Science and Technology Part A: Energy Science and Research, vol. 29,no. 2, pp. 1133-1138, 2012.

[27] B. Saha, et al., “Selective dual duty cycle controlled high frequency inverter using a resonant capacitor in parallel with an auxiliary reverse blocking switch,” Journal of Power Electronics, vol. 7,no. 2, pp. 118-123, 2007.

[28] S. Arumugam, S. Ramareddy and M. Sridhar, “Implementation of low frequency AC to high frequency AC with single stage ZVS-PWM inverter,” IJECCE, vol. 2,no. 2, pp. 123-128, 2011.

[29] H. Saleeb, K. Sayed and E. El-Zohri, “Analysis and design for interleaved ZCS buck DC-DC converter with low switching losses,” Int. Journal of Power Electronics, vol. 8, no. 3, pp.210–231, May 2017.

[30] N. A. Ahmed and M. Nakaoka, “Boost-half-bridge edge resonant soft switching PWM high-frequency inverter for consumer induction heating appliances,” IEE Proceedings-Electric Power Applications, vol. 153, no. 6, p. 932-938, 2006.

[31] K. Fathy, et al., “Dual duty cycle controlled voltage source soft-switching high frequency inverter with Ac load side reverse blocking switched resonant capacitor,” CES/IEEE 5th International Power Electronics and Motion Control Conference, pp. 1-5, 2006. doi: 10.1109/IPEMC.2006.4778211.

[32] K. Fathy, et al., “A switched-capacitor lossless inductor ZCS snubber-assisted series load resonant high frequency inverter with dual mode pulse modulation scheme,” CES/IEEE 5th International Power Electronics and Motion Control Conference, pp. 1-5, 2006. doi: 10.1109/IPEMC.2006.4778212.

[33] K. Fathy, et al., “A novel switched capacitor lossless inductors quasi-resonant snubber assisted ZCS PWM high frequency series load resonant inverter,” The 3rd IET International Conference on Power Electronics, Machines and Drives, pp. 141-145, 2006.

[34] Y. S. Kwon, et al., “Half-bridge series resonant inverter for induction cooking applications with load-adaptive PFM control strategy,” Proceedings of the KIPE Conference, The Korean Institute of Power Electronics, pp. 1018-1023, 1998.

[35] K. Bhaumik, A. Datta and P. K. Sadhu, “Analysis of leakage inductance for multi-zone induction heater,” Rev. Roum. Sci. Techn.– Electrotechn. et Energ., vol. 62, no. 4, pp. 388-393, 2017.

[36] H. Saleeb, R. Kassem and K. Sayed, “Artificial neural networks applied on induction motor drive for an electric vehicle propulsion system,” Electrical Engineering, 2021. https://doi.org/10.1007/s00202-021-01418-y.

[37] H. Saleeb, K. Sayed, A. Kassem and R. Mostafa, “Control and analysis of bidirectional interleaved hybrid converter with coupled inductors for electric vehicle applications,” Electrical Engineering, vol. 102, no. 1, pp. 195-222, Nov. 2019.

[38] N. Ashraf, et al., “New single-phase direct frequency controller having reduced switching count without zero-crossing detector for induction heating system,” Electronics, vol. 9, no. 3, 430, 2020.

[39] H. P. Ngoc, H. Fujita, K. Ozaki and N. Uchida, “Phase angle control of high-frequency resonant currents in a multiple inverter system for zone-control induction heating,” IEEE Transactions on Power Electronics, vol. 26, no. 11, pp. 3357-3366, Nov. 2011.

[40] B. Nagarajan, R. Sathi, and P.Vishnuram, “Fuzzy logic based voltage control scheme for improvement in dynamic response of the class D inverter based high frequency induction heating system,” Turkish Journal of Electrical Engineering and Computer Sciences,vol. 24, pp. 2556–2574, April 2016.

[41] O. Lucia, J. M. Burdio, I. Millan, J. Acero and D. Puyal, “Load-Adaptive Control Algorithm of Half-Bridge Series Resonant Inverter for Domestic Induction Heating,” IEEE Transactions on Industrial Electronics, vol. 56, no. 8, pp. 3106-3116, Aug. 2009.

Y. L. Cui, K. He, Z. W. Fan and H. L. Fan, “Study on DSP-based PLL-controlled superaudio induction heating power supply simulation,” In Proceedings of the 2005 International Conference on Machine Learning and Cybernetics, Guangzhou, China, vol. 2, pp. 1082-1087, 18-21 August 2005.