FACULTY OF ELECTRICAL ENGINEERING. Eng. Paku Robert THESIS SUMMARY

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1 FACULTY OF ELECTRICAL ENGINEERING Eng. Paku Robert THESIS SUMMARY CONTRIBUTIONS TO THE RESEARCH AND IMPLEMENTATION OF THE A.C. MAINS ACTIVE LINE CONDITIONING WITH THE HELP OF PWM D.C. CONVERTERS Thesis evaluation committee: Scientific supervisor, Prof.dr.eng. Richard Marschalko PRESIDENT: MEMBERS: - Prof.dr.eng. Radu Ciupa - dean, Faculty of Electrical Engineering, Technical University of Cluj-Napoca; - Prof.dr.eng. Richard Marschalko Scientific supervisor, Faculty of Electrical Engineering, Technical University of Cluj-Napoca; - Prof.dr.eng. Petre Ogruţan - Reviewer, Transilvania University of Braşov; - Prof.dr. eng. Octavian Popescu - Reviewer, Politehnica University of Bucharest; - Prof.dr.ing. Dan Micu Reviewer, Faculty of Electrical Engineering, Technical University of Cluj-Napoca.

2 1. Introduction In the last few decades, as a result of continuous development of electrical and electronic equipments and devices a new problem arose. The overwhelming majority of these devices and equipment contains reactive elements like electrical motors and transformers as well as nonlinear components like semiconductor devices or elements based on electric arc discharge which can cause the degradation of the power quality supplied via mains power distribution networks. These degradations are reflected in low power factors and harmonic distortions introduced in the mains power supply at a point of common coupling (PCC). As a result, standards and norms were established worldwide as well as in the EU, in order to limit the content of electrical pollutions introduced by different consumers in the power distribution networks. However, these standards do not state clearly the necessity of improving the quality of the mains power, they only specify limits for the harmonic distortions and power factor. At high and very high powers, the public network s operators are using special equipments placed at a high power point of common coupling in order to improve the quality of the power supplied by the a.c. mains. In the meanwhile, at low and medium power (below 16A), the task of ensuring a proper quality of the power at a PCC is in the hands of the designers and manufacturers of electrical and electronic equipments and devices. Exploiting the back-door provided by the standards, these manufacturers only produce equipments to comply with the limitations imposed by the regulations. This means that their products will have low negative effects on the mains operating in a so-called linefriendly operation mode. However they will not improve the situation at the point of common coupling. The present thesis aims to provide the manufacturers of medium and low power electric and electronic equipment a new control concept which will allow not only the compliance with the standards but furthermore, will enable these devices to actively improve the quality of the mains power. Since the grate majority of electronic equipments are working with d.c. power, the PWM d.c. converters represents the central point of investigations in the present thesis. As more and more complex control strategies are developed for these types of converters in order to improve their main functionality of power conversions, very few researches are done to exploit the secondary function of active improvement of the mains quality of the public distribution network of these converters. Partially this could be explained by the concerns regarding power distribution line stability when several converters interfere in several points of the mains in order to improve the quality of the supplied power. Therefore, the opportunity and originality of this thesis is ensured by the absence of concrete and oriented researches in the field of line conditioning with the help of PWM d.c. converters. A new philosophy in the investigation of the operation modes of these types of converters is introduced. It will be shown that, besides their main functionality of power conversion, these PWM d.c. converters can successfully overtake line conditioning capabilities. The thesis is structured in six chapters which will be summarized in the followings. The first chapter represents the introduction and a short description of each chapter. The second chapter is dedicated to the investigation of the actual status of the mains conditioning and the necessity of a new approach in the field of public distribution line conditioning. The new control concept of active line conditioning is presented in detail in chapter 3 as well as the modifications needed in the structure of PWM d.c. converters in order to provide these converters with active line conditioning capabilities. With the help of modeling and simulation in MATLAB/SIMULINK/SIM-POWER-SYSTEMS it is investigated the dynamic behavior of these converters operating with the new proposed control strategy. Chapter 4 proposes a MATLAB/SIMULINK simulation model of a possible line monitoring and conditioning signal generating system. It is presented in detail its operation through modeling and simulation. In the end of the chapter, the active line conditioning with the help of PWM d.c. converters is investigated with the help of a simplified distribution network model and converter MATLAB/SIMULINK/SIM-POWER-SYSTEMS toolboxes. Chapter 5 presents in detail the hardware design and implementation of a possible line monitoring and conditioning signal generating system. It is presented in detail the design of each block and in the end an experimental workbench is set up and some experimental results are presented. The last chapter, chapter 6 presents the final conclusions and contributions. A few appendices presents some basics concerning power definitions under sinusoidal conditions, a possible way to calculate the power factor compensating capacitor as well as the Matlab script for calculating the 2D and 2

3 3D operating space of a PWM d.c. converter operating in active line conditioning mode and the detailed schematics of the monitoring and conditioning signal generating system described in chapter Actual status concerning the conditioning of the power distribution network In the beginning of this chapter it is presented the multiple disturbances introduced by different consumers into the public mains like for example: voltage sags, voltage swells, voltage fluctuations, flickers, transients, harmonic distortions, etc. [1], [2]. From the variety of possible polluting effects on the mains, the current thesis concentrates mainly on the power factor. Some worldwide [3], [4], [5] and European standards concerning the limitation of the negative effects of the electric and electronic devices on the power distribution networks are shortly presented. It is drawn the conclusion that these standards do not state clearly the necessity of improving the quality of the mains power, they only specify limits for the harmonic distortions and power factor. Taking into account the highly distorted mains, there are presented some power definition concepts used in non-sinusoidal conditions. Starting from the distorted power concept introduced by professor Budeanu [6], [7], it is presented the FBD method [8], [9], [10], [11] as well as the instantaneous power theory introduced by professor Akagi [12]. After then, the solutions applied by the power distribution network operators are presented. These operators interfere at high power level in the public main in order to improve the power quality at a point of common coupling. The so-called line conditioning equipments used by the operators consists mainly of capacitor banks, thyristor controlled reactors, thyristor switched capacitors, thyristor controlled transformers, thyristor controlled series capacitors, dynamic voltage restorers, static phase shifters, passive and active filters, static VAR compensators, unified power flow controllers, etc. [13], [14], [15], [16], [17]. In the other hand, designers and manufacturers of medium and low power consumers are looking only to ensure the compliance with the standards and regulations producing equipments operating in the so-called line-friendly mode. This means that these devices have low negative effects on the mains but are not able to improve the general situation at a PCC. From this category two types of converters were presented: the so-called unity power factor rectifiers (UPFR) [18], [19], [20], [21] and the switch mode power supplies with active power factor correction (SMPS with APFC) [20], [22]. 3. The concept of line conditioning with the help of PWM d.c. converters In the presentation of the active line conditioning control strategy, it is started with an example of an actual power distribution network containing the mains, a local distribution network, resistive, inductive and nonlinear consumers and PWM d.c. converters operating in line-friendly operation mode [23], [24], also called in this thesis simple line conditioning. It was shown with the help of phasor diagrams that, although these PWM d.c. converters operating in line-friendly operation mode are working with unity power factor, tey are not able to compensate the negative effect of the other consumers connected to the mains at a PCC. In order to provide these types of converters with the ability to compensate the negative effects of the other consumers on the power factor in the PCC, a new control strategy is proposed [25], [26], [27]. Supposing a distribution network with sinusoidal voltages and currents and that there are at a moment of time connected at a PCC several consumers which operate at an apparent power lower than their nominal one, it is possible for the converter to shift its own current with respect to its input voltage as presented in the figure below: 3

4 Figure 1: Phasor diagram in the case of capacitive active line conditioning mode This shifting of the current s phase will cause the converter to draw its rated current I N greater than the one consumed in the simple conditioning mode. It will result an active component I d equal to the one consumed in line-friendly operation and a non-active (or reactive) component I q which will be used to support the mains. The active power drawn by the consumer will not modify with respect to the operation in simple line conditioning mode since only the active component of the current, I q contribute to this power. And the active component of the current does not change from one operation mode to the other. Because this new control method allows the PWM d.c. converters not only to operate in linefriendly operation mode but also to actively take part in the improvement of power quality at the PCC, this mode of operation was called active line conditioning mode [25], [26], [27]. Since the mains can have resistive, inductive or capacitive behavior, three types of active line conditioning are possible. If the mains has resistive behavior, there is no need for support and simple line conditioning mode is entered by the converters. If the power distribution network has inductive behavior, the converter must act as a capacitor in order to compensate the power factor. This mode is called capacitive active line conditioning. If the mains has capacitive behavior, the converters will shift their current s phase in the opposite direction as before. Thus, the so-called inductive active line conditioning mode is entered in order to compensate the power factor. According to the new active line conditioning control strategy, the structure of the power distribution network is changed as presented in figure 2. Figure 2: Example of a possible structure of the power distribution network according to the new active line conditioning control strategy In the figure above, it can be seen that in order to enable the active line conditioning of the public distribution network a line monitoring and conditioning signal generation system must be used in order to inform the PWM d.c. converters connected to the PCC about the necessity to work in simple or one of the two active line conditioning modes. Also the structure of the converters control block must be changed as seen in figure 3. 4

5 Figure 3: Block diagram of the PWM AC-to-DC converter provided with active line conditioning capability Besides the main blocks which can be found in the structure of a regular PWM a.c.-to-d.c. converter with current mode control, in figure 3 it can be seen an Active line-conditioning control unit [25], [26], [27]. Based on the information concerning the actual status of the mains provided by a socalled conditioning signal c(t), this block will decide which conditioning mode will be applied by the converter. This block is presented in detail in the thesis. After the presentation of the structure of such a converter capable of operating in active line conditioning modes, it is calculated the steady-state characteristics of these converters. The steady-state operation is investigated via the 2D and 3D operating space of these types of converters [28]. The dynamical performances are studied with the help of MATLAB/SIMULINK/SIM-POWER- SYSTEMS modeling [29], [30], [31]. Simulation results showed that indeed the PWM a.c.-to-d.c. converters can operate also in active line conditioning mode without affecting their main functionality of power conversion [29], [30], [31]. Simulations made under non-sinusoidal mains voltage conditions have proved that these converters are able to enter active line conditioning mode even if the input voltage is highly distorted. However, this control strategy does not allow the improvement of the distorted voltage s waveform. In order to compensate also the distortions of the waveform, a more complex control strategy must be applied, strategy called complex line conditioning. The complex line-conditioning does not represent the subject of the present thesis. 4. Investigation of the line conditioning strategy with the help of PWM a.c.-to-d.c. converters via modeling and simulation in MATLAB/SIMULINK/SIM-POWER-SYSTEMS From figure 2 it can be seen that the only part missing in order to complete the whole power distribution network is the line monitoring and conditioning signal generation system. According to the proposed control strategy, the line monitoring and conditioning signal generation system connected in the PCC will replace the conventional line conditioning units. This system will monitor continuously the 5

6 status of the mains and will generate a signal to inform the converters, provided with ALC capabilities, connected to the public mains about the necessity for power factor compensation. A possible structure for such a system is presented in the figure below [32]: Figure 4: Block diagram of the line monitoring and conditioning signal generation system All the blocks from the structure presented in figure 4 are described in detail in the thesis. Simulations made to investigate the proper functionality of this system showed that the best solution for the generation of the conditioning signal is a tri-level hysteresis controller based on the phase between line voltage and line current. Having ready the simulation models of the PWM a.c.-to-d.c. converters capable of operating in active line conditioning mode as well as the model of the line monitoring and conditioning signal generation system, it is simulated the entire distribution system from figure 2. Figure 5: MATLAB/SIMULINK/SIM-POWER-SYSTEMS model of the entire power distribution system Simulation results presented in figure below, showed once again the capability of the PWM a.c.- to-d.c. converters to operate also in active line conditioning mode without affecting their main functionality of power conversion. Also the fact that the converters operating in the active line conditioning mode can improve the power factor in the PCC has been proven [32]. 6

7 Figure 6: Simulation results 5. Practical implementation of a line monitoring and conditioning signal generation system The practical implementation of PWM a.c.-to-d.c. converters capable of operating in active line conditioning mode doesn t represent something new. In present days there are produced lots of such converter types having more and more sophisticated control strategies to ensure their main functionality of power conversion. Also the reconfiguration needed in the structure of the converter s control system in order to enable the active line conditioning mode can be easily made by software written in a microcontroller. Therefore, the line monitoring and conditioning signal generation system was chosen to be practically implemented. The thesis describes in detail the hardware design of such a system. As a result, the experimental workbench from figure 7 was built. This workbench consists of three PCBs: one representing the current and voltage transducer s block, one representing the microcontroller and its adjacent processing circuitry and one representing the power supply of the other two blocks. 7

8 Most of the hardware blocks were tested but the numerical processing and the software support represents a subject for future researches Figure 7: Experimental workbench 6. Conclusions The present thesis aims to investigate and present modern conditioning systems for power distribution networks using PWM d.c. converters. As the standards tend to establish lower and lower limits of the quantity of disturbances introduced by different consumers into the mains, this thesis introduces a new concept of active line conditioning whit the help of PWM d.c. converters. Simulations and calculations made in the thesis proved that indeed these types of converters provided with the proposed control strategy are able to overtake also line conditioning capabilities as a secondary function. Furthermore this auxiliary function will not affect their main functionality of power conversion. The thesis was elaborated by taking into account the actual status in the field of line conditioning and power quality enhancement, which was reflected in the reference used: 17 books, 63 scientific articles and 22 internet sites. The contributions of the thesis are as follows: 1) synthesis concerning power quality criteria in public distribution networks 2) synthesis concerning available standards and regulations on the limitation of disturbances introduced by certain consumers in the network 3) analysis of the actual status in the field of power line conditioning possibilities at low, medium and high power 4) mathematical and Matlab/Simulink model of the active line conditioning block from the structure of the PWM ac-to-dc converters 5) calculation of steady state characteristics of a PWM ac-to-dc converter operating in active line conditioning mode 6) operating space in 2D and 3D of the PWM ac-to-dc converter operating in active line conditioning mode using Matlab/Simulink method 8

9 7) operating space in 2D and 3D of the PWM ac-to-dc converter operating in active line conditioning mode using only Matlab method 8) Matlab/Simulink toolbox of an ideal PWM ac-to-dc converter operating in active line conditioning mode 9) Matlab/Simulink/Sim-Power-Systems toolbox of a real PWM ac-to-dc converter operating in active line conditioning mode 10) Matlab/Simulink model of the line monitoring and conditioning signal generation system 11) Investigation through modeling and simulation in Matlab/Simulink/Sim-Power-Systems of an example of power distribution network provided with PWM ac-to-dc converter operating in active line conditioning mode 12) practical implementation of a line monitoring and conditioning signal generation system References [1] Pierluigi Caramia, Guido Carpinelli, Paola Verde Power Quality Indices in Liberalized Markets, John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex, [2] C. Sankaran Power Quality, CRC Press, Boca Raton, London, New York, Washington, D.C., 2002 [3] IEEE Standard Guide for Application of Shunt Power Capacitors. [4] IEEE Standard Standard for Shunt Power Capacitors. [5] IEEE Standard Guide for Application and Specification of Harmonic Filters. [6] C.I. Budeanu Puissances reactives et fictives, Instytut Romain de l Energie, pub. no. 2, Bucharest, [7] C.I. Budeanu The different Opinions and Conceptions Regarding Active Power in Nonsinusoidal Systems, Instytut Romain de l Energie, pub. no. 4, Bucharest, [8] Fryze. S -: Wirk-, Blind- U. Scheinleistung in elektrischen Stromkreisen mit nichtsinusforrmigem Verlauf von Strom und Spannung Elektrotechn (1932). pp.s96-s9y, [9] Buchholz, F -: Das Begriffsystem Rechtleistung, Wirkleistung, totale Blindleistung, Selbstverlag Miinchen 1950 [10] M. Depenbrock, - The FBD-Method. a Generally Applicable Tool for Analysing Power Relations, IEEE Trins. Power Syst. PS-8 ( I 993) 2, pp [11] M. Depenbrock, V. Staudt The FBD-Method as Tool for Compensating Total Non-Active Currents [12] Akagi, H., Watanabe E. H., Aredes, M.: Instantaneous Power Theory and Applications to Power Conditioning, John Wiley &Sons, Hoboken, New Jersey, 2007 [13] R. Mohan Mathur, Rajiv K. Varma THYRISTOR-BASED FACTS CONTROLLERS FOR ELECTRICAL TRANSMISSION SYSTEMS, John Wiley & Sons, Inc, 2002 [14] E. Acha, V. Agelidis, O. Anaya, TJE Miller Power Electronic Control in Electrical Systems, [15] Leonard L. Grigsby Electric Power Engineering Handbook Power Systems, Second Edition, CRC Press, 2006 [16] K. R. Padiyar FACTS CONTROLLERS IN POWER TRANSMISSION AND DISTRIBUTION, New Age International (P) Ltd. Publishers, New Delhi,Bangalore, Chennai, Cochin, Guwahati, Hyderabad Jalandhar, Kolkata, Lucknow, Mumbai, Ranchi, 2007 [17] X-P. Zhang, C. Rehtanz, Bikash P. Flexible AC Transmission Systems: Modelling and Control, Springer- Verlag, Berlin, Heidelberg, 2006 [18] Kolar, J.W.; Drofenik, U.; Zach, F.C. VIENA Rectifier II - A Novel Single-Stage High Frequency Isolated Three-Phase PWM Rectifier System, 13'th IEEE Power Electronics Conference, Anaheim, February 15-19, USA, [19] Kolar, J.W.; Drofenik, U.; Zach, F.C. VIENA Rectifier III - A Novel Single-Stage Buck-Derived Unity Power Factor AC-to-DC Converter System, Nordic Workshop on Power Electronics, Espo, August, 26-27, Finland, [20] Kolar, J.W.; Ertl, H. Status of the Techniques of Three - Phase PWM Rectifier Systems with Low Effects on the Mains, PCIM 99, Power Conversion and Intelligent Motion Conference, Seminar 27, Volume I and II, Nürnberg,, Germany, [21] Kolar, J.W.; Ertl, H.; Edelmoser, K.; Zach, F.C. Analysis of the Control Behaviour of a Bidirectional Three - Phase PWM Rectifier System, Record of the 4'th European Conference on Power Electronics and Applications, Firenze, September 3/6, Vol.2, pp , Italy, [22] Marschalko, R. Investigations Concerning High Efficiency DC - to - DC Converter Circuits, PCIM 99, Power Conversion and Intelligent Motion Conference, Power Conversion Proceedings, pp , Nürnberg,, Germany,

10 [23] Marschalko, R. Extended Control Strategy for a PWM Line- Friendly AC-to-DC Converter, EPE'93, European Conference on Power Electronics and Applications, Brighton, Great Britain, [24] Csatlós, E.; Marschalko, R., - Investigation of a PWM Line-Friendly AC-to-DC Converter System with the consideration of the Commutation, Acta Electrotechnica Napocensis, 2002, Vol. 43, Number 1, pp , Ed. Mediamira, Cluj, România. [25] Bojan, M., Paku, R., Marschalko, R.: AC Line Active Conditioning with the Help of PWM AC - to - DC Converters, OPTIM'2004, Proceedings of the 9'th International Conference on Optimisation of Electric and Electronic Equipments, Brasov, 2004, p [26] Paku, R., Popa, C., Bojan, M., Marschalko, R.: Appropriate Control Methods for PWM AC-to-DC Converters Applied in Active Line- Conditioning, EPE-PEMC 2006, Proceedings of the 12 th International Power Electronics and Motion Control Conference, Portoroz, [27] C. Popa, R. Paku, M. Bojan, R. Marschalko CONTROL METHODS FOR PWM AC - to - DC CONVERTERS APPLIED IN ACTIVE LINE CONDITIONING, a 13-a Conferinţă naţională de acţionări electrice CNAE 06, Ploieşti, octombrie, [28] Paku, R., Marschalko, R.: Operating space of a bidirectional PWM ac-to-dc converter applied in active line conditioning, AQTR 2008, 2008 IEEE International Conference on Automation, Quality and Testing, Robotics, Cluj Napoca, Romania, [29] Paku R., Popa C. ISZM egyenirányító MATLAB toolbox alkalmazása a váltakozó áramú aktív kondicionálásának kútatásában, MATLAB Toolbox for PWM d.c. Converters Applied in Active Line Conditioning of the A.C. Mains, ENELKO2006, Nemzetközi Energetika Elektrotechnika Konferencia, Cluj- Napoca 2006, Romania. [30] Paku, R., Marschalko, R. Matlab/Simulink/Sim-Power-Systems model for a PWM AC-to-DC converter with line conditioning capabilities, Acta Electrotehnica [31] Paku, R., Balogh, P. Marschalko, R Investigation of a new Matlab/Simulink/Sim-Power-Systems toolbox for a PWM ac-to-dc converter applied in active line conditioning, IEEE International Conference on Automation, Quality and Testing, Robotics, AQTR 2010, Cluj Napoca, Romania, 2010, pp [32] Paku, R., Balogh, P.- Researches on the active ac line conditioning possibilities with the help of PWM ac-todc converters Hubloldt-Kolleg Förderung der nachhaltigen Entwicklung im Donauraum durch kulturelle und wissenschaftliche Zusammenarbeit, Klausenburg/Cuj-Napoca, Romania, Mai