Comparative Analysis of Improved Quality Three Phase AC/DC Boost s, using SIMULINK Shweta Srivastava 1, Sanjiv Kumar 2 1 Research Scholar, Department of Electrical Engineering, H.B.T.I. Kanpur, India. (e-mail: shweta_sri17@rediffmail.com) 2 Assistant Professor, Department of Electrical Engineering, H.B.T.I. Kanpur, India. (e-mail: sanjiv.iitr@gmail.com) Abstract This paper presents the comparative analysis of improved quality three phase AC/DC boost converters, using SIMULINK. Comparison of three phase controlled single switch and six switch AC/DC boost converters have been done to identify the boost converter with low cost/small size/high efficiency for three phase system. Three phase AC/DC boost converters with improved quality in terms of power factor correction reduced THD at input ac mains and regulated dc output are discussed [7],[8]. The performance of the three phase AC/DC boost converters are verified at 220 V rms phase voltage, 6.4 kw output power through simulation model and a good consistency is achieved. Keywords Improved Quality s, One-Cycle Controlled, PWM Generator, Three-Phase AC/DC Boost s, Total Harmonic Distortion (THD). I. INTRODUCTION AC/DC power converters are broadly used in various applications like power supplies, dc motor drives, front-end converters in adjustable-speed ac drives, HVDC transmission, SMPS, in process technology like welding, power supplies for telecommunications systems, aerospace, military environment and so on. The design, advance development and fruitful application of single-phase, improved quality converters in domestic, commercial and industrial environment has made possible the design and development of three-phase, improved quality converters and their extensive use in different applications. Harmonic pollution and low power factor in power system caused by power converters have been a great concern. To overcome these problems several converters and control schemes have been proposed in recent years. A new type of AC/DC converters is specifically known as Power Factor Correction s (PFCs), Switched Mode Rectifiers (SMRs), PWM s, Improved Power Quality s (IPQCs) [2], and High Power Factor s (HPFCs).They are included as an 427 inherent part of the AC-DC conversion system which produces excellent power quality at the line-side and loadside, higher efficiency, and reduced size. The power quality issues created by the use of conventional AC/DC converters are elegantly addressed by improved quality converters. The output voltage is regulated even under the fluctuations of source voltage and sudden load changes. The PWM switching pattern controls the switching of the power devices for input current wave shaping so that it becomes almost harmonic-pollution free and in phase with the source voltage, thus producing a nearly sinusoidal supply current at unity power factor. These converters provide improved quality not only at input ac mains but also at dc output for better design of overall equipment.. Improved quality converters are classified into categories on the basis of converter circuit topologies such as buck, boost, buck boost, multilevel, and multiples, unidirectional and bidirectional dc output voltage, current and power flow. Three-phase quality improvement converters can be classified on the basis of [1]: 1. topology as boost, buck, buck boost and multilevel converters with unidirectional and bi-directional power flow 2. Type of converter used as unidirectional and bidirectional converters Fig.1. Classification of improved quality converters
II. IMPROVED QUALITY THREE PHASE AC/DC BOOST CONVERTERS [3],[5] Conventionally, diode rectifiers or thyristor bridge converters were employed to synthesize dc voltage from the ac utility. These rectifiers pollute the utility with loworder harmonics, which are difficult to filter. Pulse width modulation (PWM) converters are employed to overcome this problem. These converters shift the frequency of the dominant harmonics to a higher value, so that they can be easily filtered by employing a small passive filter. The PWM converter draws a near-sinusoidal input current while providing a regulated output dc voltage. Advantages of Boost Topology 1. High efficiency 2. High power density 3. Inherent power quality improvement at input and output. Hence boost type converters not only provide regulated DC output voltage but also maintain near unity power factor and low THD on current at the input. The boost type ac-dc converters with various topologies [4] have found wide spread use in various applications. In this work, two power circuits and closed loop regulator are studied through simulation. Based on the number of switches controlled, improved quality converters can be divided into two groups: single switch PFC converters and multiple switches PFC converters. The ac-dc converter topologies considered are boost type and listed below. 1. Single-Switch Boost converter 2. Six-Switch Boost A. Single Switch Boost [6], [7] Three phase improved quality converter have gained considerable attention due to the increasing demand to power quality. Fig.2. Three Phase Single Switch Boost 428 These types of converters are widely used nowadays as a replacement of a conventional diode rectifier to provide: Unity power factor Reduced THD at ac mains Constant-regulated dc output voltage even under fluctuations of ac voltage and dc load. Operation of The operation of the three-phase single-switch PFC converter with a constant switching frequency is analyzed. Single-switch three-phase ac/dc boost converter Fig.2 consists of two main power conversion stages. The first stage is a three phase ac to dc rectifier consisting of an input filter, a boost inductor, a three-phase diode rectifier, an active power factor correction stage, and a dc link filter capacitor. The second stage can be modeled as any type of load requiring a regulated or unregulated dc bus such as general purpose single-phase or three-phase inverters or dc-dc converters with high frequency isolation. The active waveshaping of the input current waveform is obtained through the use of the three boost chopper components L a2, Q b, D b. as shown in Fig.2. The boost switch is turned on at constant frequency. The duty cycle of Q b, is varied for load variation only and it is such that the input current is always discontinuous. To simplify the analysis of the converter system, the following assumptions are made. 1. The system components are ideal, such as: resistors, inductors, capacitors. 2. Switching frequency is much higher than the line frequency, the input voltages are considered to constant within a switching period. 3. The 3 inductors operate in DCM. With constant frequency PWM, the single-switch threephase improved quality converters have a larger current distortion, so it s not suitable to high power level. According to IEC555-2(A) standard, the power level of converter can t be increased in order to meet the maximum permissible harmonic current. However, if in order to meet the IEC555-2(A) specifications, the output voltage of three phase rectifier must be boosted to 900V. Such designs increase the voltage stress of switch. Advantages 1. Simplicity 2. Low cost 3. High efficiency
Disadvantages 1. The DCM operation is associated with a higher voltage or current stress. 2. High switching losses. B. Six Switch Boost [6],[7] Fig.3. Three-Phase Six Switch Boost Generally, the control structure of a three-phase sixswitch PWM boost converter consists of an inner current control loop and an outer voltage control loop. The current controller senses the input current and compares it with a sinusoidal current reference. To obtain this current reference, the phase information of the utility voltages or current is required. Generally, this information is obtained by employing either a phase-locked loop (PLL) or a current phase observer digital technique. To simplify the control structure of these grid-connected systems, one-cyclecontrol (OCC) based ac-to-dc converters have been proposed [12], [13]. This control technique does not require the service of the PLL. Moreover, in these schemes, the switching frequency of the power semiconductor devices is held constant, which is an added advantage for mediumand high-power applications. component of the source current of the converter. Using the signal V M, a bipolar sawtooth waveform of amplitude V M and having a time period of Ts is synthesized [12]. This is achieved by integrating the signal V M with a time constant Ti, Ti = Ts/2 (1) where Ts is the time period of clock pulses, which resets the integrator. The switching frequency of the converter devices is the same as that of the frequency of the clock pulses. Instants depicting intersections among the sawtooth waveform with three-phase currents drawn at a particular switching cycle, wherein i A > i B > i C. At the point where three phase currents intersect sawtooth waveform, pulses generated. These generated pulses are the gate signals for six switches respectively. Since the utility considered is a three-phase three-wire system i A + i B + i C =0 (2) Hence, these topologies are discussed in detail. According to the application need best topology is used. Switch mode improved quality ac/dc converters with high efficiency and power density are being used as front end rectifiers for variety of applications. III. SIMULATION RESULTS AND ANALYSIS Simulation study of three-phase AC/DC boost converters has been done through MATLAB/SIMULINK software. A. Single Switch Boost Operation of One-Cycle Controlled [8], [9] To understand the principle of operation of the OCC-based ac-to-dc converter, first, the basic one-cycle controlled acto-dc converter presented in is explained. The schematic power circuit diagrams of three-phase six-switch boost converters are shown in Fig.3.The dc link capacitor voltage V 0 is sensed and compared with the desired value V 0 *. This error is processed by a proportional integral (PI) controller to generate a signal V M. Therefore, at steady state, when V 0 is equal to V 0 *, the signal V M is proportional to the real 429 Fig.4. Simulation Circuit Diagram of Single Switch Boost
Simulation Parameters (1) Input voltage (V s ) = 311V (peak value), supply frequency = 50 Hz, switching frequency = 10 khz (2) Boost inductor (l) = 0.21mH, EMI Filter : L f = 6mH, C f = 4µF, C 0 = 220µF, K p = 2, K i = 5 (3) Load (P out ) = 6.4 kw Fig.6. Output Voltage of Single Switch AC/DC Boost B. Six Switch Boost Fig.7. Harmonic Analysis of Single Switch AC/DC Boost Fig.8. Power Factor of Input Side for Single Switch Boost Analysis of Result: Fig.5. Simulation Circuit Diagram of Six- Switch Boost Simulation Parameters (1) Input voltage (V s ) = 311 V (Peak Value), supply frequency = 50 Hz, switching frequency = 10 KHz (2) Boost inductors (L a, L b, L c ) = 2mH, C 0 = 1000µF, K p = 1, K i = 0.1 (3) Load (P out ) = 6.4 kw Simulation results for three phase AC/DC boost converters in terms of output voltage & output current, THD analysis of input current and input voltage & input current for their power factor analysis are given here. They are as follows: 1. Output voltage (V 0 ) = 800 volt, 2. Total Harmonic Distortion (THD) =6.35 %, 3. Input Power Factor = 0.997 4. The Power Density and Cost is low for this converter. Fig.9. Output Voltage of Six- Switch AC/DC Boost 430
V. PERFORMANCE EVALUATION OF BOOST CONVERTERS. Table: 2 Comparison of Topologies with Various parameters (V 0= 800V, I 0= 8A) S.No. Parameters Topology Single Switch Boost Six- Switch Boost Fig.10. Harmonic Analysis of Six- Switch AC/DC Boost 1. Power Density Lowest High 2. Cost Lowest High 3. Switching Losses High Very high 4. Voltage Stress High Very high 5. Power Flow Unidirectional Unidirectional Fig.11. Power Factor of Input Side for Six- Switch AC/DC Boost Analysis of Result: 1. Output voltage (Vo) = 800 volt, 2. Total Harmonic Distortion (THD) =4.68%, 3. Input Power Factor = 0.996 4. The Power Density and Cost is high for this converter. IV. COMPARISON OF TOTAL HARMONIC DISTORTION AND POWER FACTOR S.No Table: 1 Improved Quality Parameters of Various Topologies (At 800V DC 6.4kW Load) Topology 1. Single- Switch Boost 2. Six-Switch Boost THD (% of Is) PF Design values of components and control parameters 6.35 0.997 Boost inductor= 0.21mH, EMI filter: L f =6mH, C f = 4µF, C 0 =220 µf, K p = 2, K i = 5 4.68 0.996 Boost inductor(l a, L b, L c) = 2mH, C 0 = 1000 µf, K p = 1, K i = 0.1 Hence, two topologies are discussed here. According to the application need best topology is used. VI. LATEST TRENDS AND FUTURE DEVELOPMENTS The new developments are improved control algorithms and soft-switching techniques to reduce switching losses in improved quality boost converters even at high switching frequency, to enhance the dynamic response, and to reduce the size of energy storage elements (filters at input and output, high-frequency transformers). The new developments toward single-stage conversion have resulted in increased efficiency, reduced size, high reliability, and compactness of improved quality boost converters. The further improvement in solid-state device technology in terms of low conduction losses, higher permissible switching frequency, ease in gating process, and new devices, especially low voltage drop and reduced switching losses, will give a real boost for improved quality boost converters. 431
VII. CONCLUSION This paper has attempted to give a comparative analysis of three-phase, improved quality AC/DC boost converters. The converters are divided into two groups: singleswitch boost converter and six- switch boost converter. Though the six- switch boost converters are high-power high performance application, the increased number of switches and the complexity of their control make them too expensive in medium power levels. So the single-switch three-phase boost converter is an attractive topology because of its simplicity, low cost and high efficiency. The improved quality three- phase ac/dc boost converters are gaining popularity in a variety of applications ranging from low to high power levels due to their improved power quality both at the input as well as the output terminals. The use of these converters results in equipment behaving as a linear load at three-phase ac mains and solves the quality improvement problems due to ac/dc converters. REFERENCES [1] B. Singh, B.N. Singh, A. Chandra, K. Al-Haddad, A. Pandey, D.P. Kothari, A Review of Three-phase Improved Power Quality AC/DC s, IEEE Trans. Ind. Electron 51, (2004) [2] Abdul Hamid Bhat, Pramod Agarwal, Three-phase, Power Quality Improvement AC/DC, Electric Power Systems Research 78 (2008) [3] A. Muthuramalingam, R. Madhivanan, R. Kalpana, Comparative Study Of High Performance Rectifiers, India International Conference on Power Electronics (2006) [4] Pandey P, Comparative Study of Single Phase Unity Power Factor AC-DC Boost, in Proc. EPE (2004) [5] Abdul Hamid Bhat and Pramod Agarwal, Improved Power Quality AC/DC s, EPSR 79 (2009) [6] A. R. Prasad, Phoivos D. Ziogas, and Stefanos Manias, An Active Power Factor Correction Technique for Three-phase Diode Rectifiers, IEEE transactions on Power Electronics, vol. 6 (1991) [7] Zhanlong Li and Yupeng Tang, Simulated Study of Three-Phase Single-Switch PFC with Harmonic Injected PWM by MATLAB, IEEE transactions on Power Electronics, (2006) [8] Dharmraj V. Ghodke, Kishore Chatterjee, and B. G. Fernandes Modified One-Cycle Controlled Bidirectional High-Power-Factor AC-to-DC IEEE Transactions on Industrial Electronics, vol. 55 (2008) [9] Chongming Qiao and Keyue M. Smedley, Unified Constantfrequency Integration Control of Three-phase Standard Bridge Boost Rectifier, IEEE transactions on Power Electronics, (2000) [10] Keyue M. Smedley, Luowei Zhou, and Chongming Qiao, Unified Constant-Frequency Integration Control of Active Power Filters Steady-State and Dynamics, IEEE Transactions on Power Electronics, vol. 16, (2001) 432 [11] Chongming Qiao, and Keyue M. Smedley, Unified Constant- Frequency Integration Control of Three-Phase Standard Bridge Boost Rectifiers With Power-Factor Correction, IEEE Transactions on Industrial Electronics, vol. 50, (2003) [12] Housheng Zhang, Research and Design of Three-Phase Six-Switch High Power Factor Rectifier with One Cycle Control, IPEMC,IEEE (2009) [13] Keyue M. Smedley and Slobodan Cuk, One-Cycle Control of Switching s, IEEE Press. (1995)