Improved Power Factor Related Welding Power Supply Utilizing Zeta Converter B. HARI PRASAD 1, M. J. NAVEEN 2, G. N. S. VAIBHAV 3

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1 ISSN Vol.05,Issue.11, November-2017, Pages: Improved Power Factor Related Welding Power Supply Utilizing Zeta Converter B. HARI PRASAD 1, M. J. NAVEEN 2, G. N. S. VAIBHAV 3 1 Assistant Professor, Dept of EEE, EEE, P.V.K.K Institute of Technology, Affiliated to JNTUA, Andhra Pradesh, India, vanoorhari@gmail.com. 2 PG Scholar, Dept of EEE, EEE, P.V.K.K Institute of Technology, Affiliated to JNTUA, Andhra Pradesh, India, eps@outlook.in. 3 Assistant Professor & HOD, Dept of EEE, EEE, P.V.K.K Institute of Technology, Affiliated to JNTUA, Andhra Pradesh, India, vaibhavnaidu.naidu@gmail.com. Abstract: A power factor corrected single stage, two-switch isolated zeta converter is proposed for arc welding. This modified zeta converter is having two switches and two clamping diodes on primary side of high frequency transformer (HFT). This, in turn, results in reduced switch stress. The proposed converter is designed to operate in discontinuous inductor current mode(dicm) to achieve inherent power factor correction at the utility. The DICM operation substantially reduces the complexity of the control and effectively regulates the output DC voltage. The proposed converter offers several features like inherent overload current limit and fast parametrical response to the load and source voltage conditions. This, in turn, results in an improved performance in terms of power quality indices and enhanced weld bead quality. The proposed modified zeta converter is designed and its performance is simulated in MATLAB/Simulink environment. The performance of the system is investigated in terms of its input power factor (PF),displacement power factor (DPF), total harmonic distortion(thd) of AC mains current, voltage regulation and robustness to prove its efficacy in overall performance. Keywords: High Frequency Transformer (HFT), Power Factor (PF), Displacement Power Factor (DPF). I. INTRODUCTION Welding is a standout amongst the most imperative assembling forms. Among different welding systems, curve welding is the most regularly utilized fabrication process in each industry - substantial or little. At display, bend welding has turned into a basic piece of a few enterprises like auto thought process, aviation, development, medicinal, vitality, substance and so forth. A lot of aggregate created electrical vitality is devoured by circular segment welding power supplies (AWPSs) and it is relied upon to increment immensely in the wake of an ever increasing number of businesses coming up. Different topologies have been accounted for to meet the fundamental necessities of global power quality (PQ) measures like IEC These have prompted the advancement of a few exchanged mode control supplies (SMPSs) with high DC present and low DC voltage yield for welding. Although these SMPSs are highly efficient, however, due to their nonlinear behavior they draw highly distorted current resulting in low power factor (PF) and high total harmonic distortion (THD). This deterioration in PQ leads to increased system losses, degrading the reliability of electrical equipment, high electromagnetic interference, etc. Subsequently, it is basic to utilize a power factor adjustment (PFC) based AWPS with enhanced PQ. The welding execution of an AWPS is identified with its over-current reaction, circular segment strength, scatter era and so forth and thus its control turns into a troublesome undertaking. To keep up a steady circular segment length, a welding power supply with consistent yield voltage trademark is normally favored. Additionally, the real duty of the AWPS is to direct yield voltage and in addition yield current amid a welding procedure to get top notch weld. Casanueva et al. have also proposed a boost converter to incorporate PFC in AWPS. However, boost converters suffer from major drawbacks such as high start-up inrush current and lack of current limiting during overload conditions. These two factors violate primary requirements of an AWPS. Full bridge buck converter and half bridge buck converter have also been reported in the literature for AWPS. However, half-bridge inverter entails large electrolytic capacitors and a soft-start circuit for restraining inrush current. bulky electrolytic capacitors increase the overall size of the power supply. Besides, they are not well-suited for high frequency current of commutation. This restricts the half bridge inverter based AWPS from high-frequency applications. Moreover, buck-boost converters offer better PFC at the input as compared to buck converters. Several single stage isolated PFC topologies are reported in the literature that possess simple power circuit with easy control schemes as compared to two stage PFC converters. It results in reduction in cost and complexity of upcoming PFC converters. Amongst them, isolated zeta converter offers reduced inrush current and excellent overload current 2017 IJIT. All rights reserved.

2 B. HARI PRASAD, M. J. NAVEEN, G. N. S. VAIBHAV protection. However, the conventional isolated zeta AC-DC converter suffers from a major drawback of high voltage stress across the switch i.e. (Vd+nVo) where Vd is the input voltage, Vo is the output voltage and n is the turns ratio of high frequency transformer (HFT). This, in turn, increases the switching losses. However, in case of a two switch zeta converter, the voltage stress of the switches is limited to only the input DC voltage Vd. Murthy-Belluret. al.have presented the continuous conduction mode (CCM)operation of two switch zeta converter which adds the requirement of input current sensing to incorporate PFC feature. In order to minimize the switch stress and complexity of the control circuitry by way of eliminating the input current sensor, this paper deals with the analysis, design and development of two switch modified zeta converter operating in DICM, with highfrequency isolation, regulated output voltage and improved power quality. For achieving wider operating range, DICM operation is convenient which also offers additional advantages like reduction in the number of sensors and component size. Fig.1.Proposed modified zeta converter based AWPS. This, in turn, reduces the complexity of the control circuit and makes the power supply compact. Moreover, an effort has been made to incorporate over-current withstand capability in the proposed converter to make it suitable for arc welding. This, in turn, enhances the quality of weld bead. Therefore, this PFC converter based AWPS is used to control various variables, such as welding current, welding voltage, pulse duty cycle, over-load current, etc. It exhibits excellent welding characteristics by maintaining constant DC voltage at the output. The performance of the proposed AWPS is verified by means of modeling the proposed power supply in MATLAB/ Simulink platform. Finally, the obtained test results of proposed isolated zeta converter are presented to validate its feasibility. Its performance has been evaluated over a wide range of load and Supply voltage. The obtained results confirm an excellent performance of the AWPS with improved PQ at the AC mains. II. PROPOSED MODIFIED ZETA CONVERTER BASED AWPS Fig.1. shows the configuration of modified isolated zeta converter for a single-phase AWPS. It comprises of a single phase supply followed by a diode bridge rectifier (DBR), anl- C filter, and a modified zeta converter connected to a welding load. The HFT provides a galvanic isolation between the input AC mains and the output. Two diodes D1 and D2 are connected across switches S1 and S2. Both the switches are turned on and off simultaneously. The proposed zeta converter can convert a single-phase 220V AC power supply into 19VDC output voltage in a single-stage power conversion process with an inherent PFC feature. The DICM operation in this zeta converter is defined by the current discontinuity through the magnetizing inductance, Lm. The detailed description for unity PF for discontinuous conduction mode is given in Appendix. The operating stages of the proposed converter during a complete switching cycle are described as follows. A. Operating Modes Three operating modes of the proposed zeta converter within one complete switching period, Ts are shown in Fig2.

3 Improved Power Factor Related Welding Power Supply Utilizing Zeta Converter stored energy. This enforces the intermediate capacitor s voltage and output voltage o decrease. This stage continues until both the switches start conducting. The associated waveforms for this converter over one switching period are presented in Fig. 3(d). B. Control Strategy The proposed converter for AWPS is made to operate in DICM to obtain various benefits like inherent PFC, simple control etc. This, in turn, reduces spatter generation and provides stability to the arc length. Both switches S1 and S2 are operating synchronously during each PWM period. Thus, the same gating signal is used to drive both the power switches. This simplifies the control circuit significantly. The DC voltage is observed and compared with the reference voltage to generate the voltage error Ve. The voltage error Ve at kth sampling instant is defined as, (1) The generated voltage error signal is then processed by the proportional and integral (PI) controller. The output of the PI voltage controller at the kth sampling instant is given by, Fig.2. Operating modes of proposed based AWPS, (a) Mode I; (b) Mode II;(c) Mode III; (d) Waveforms during one switching period. In order to analyze the operating principle, all semiconductor devices are considered to be ideal. The supply voltage, vs is considered to be constant within each switching cycle as the switching frequency, fs (=20 khz) is much higher than the line frequency, f (=50 Hz). Mode-I: During this interval, both switches, S1 and S2, are turned on; the power source supplies energy to transformer magnetizing inductance, Lm. Thus, the currents through the transformer magnetizing and output inductors ilm and ilo increase linearly. On the other hand, diodes D1 and D2 remain off. The equivalent circuit for this operating mode is shown in Fig.3 (a). Diode Do, is reversed biased during this stage. Intermediate capacitor, C1 discharges through output inductor Lo, output capacitor Co and welding load Ro. Mode-II: Fig. 3(b) illustrates the second operating interval during which both switches S1 and S2, are turned off and diodes D1 and D2 start conducting. Thus the energy stored in the magnetizing inductance Lm of HFT is transferred to DC link capacitor Co. Diode Do also becomes forward biased. Lm and Lo transfer the energy stored to the intermediate capacitorc1 and output capacitor Co respectively. During this time interval, the current through diode Do decreases, until it becomes zero. (2) Where Kp and Ki are proportional and integral gains of the PI controller. Concurrently, a current loop is implemented for restraining the output current within the desired limit. The DC output current is compared with the reference output current limit ISC to generate the current error Ie. This Ie is given to a PI current controller to integrate the overload current handling capability in the proposed AWPS. Thus, the output of the PI current controller at the k th sampling instant is given by, (3) The outputs of both PI controllers (CV and Ci) are compared and whichever is lower is given to the PWM generator to generate the gating pulses. The PWM duty cycle is adjusted in accordance with changes required in the output DC voltage and output welding current. III. SIMULATION OF PROPOSED AWPS The proposed PFC converter based AWPS is modelled in MATLAB/SIMULINK environment. The performance of the proposed AWPS is analysed on the basis of several performance indices. Mode-III: Referring to Fig. 3(c), the third stage starts when the absolute values of currents in Lm and Lo (ILm and ILo )become equal to each other thereby reverse biasing the diode Do again. Thus, the magnetizing inductor, Lm enters DICM. The intermediate capacitor, C1 and the output capacitor, Co discharge during this period to release their Fig. 4.Simulink Diagram of AWPS.

4 Fig.5. Performance of proposed AWPS. The waveforms of AC mains voltage (vs), source current (is), output DC arc voltage (Vo), output welding load current (Io), switch stress (vsw, isw), output inductor current (ilo) and intermediate capacitor voltage (vc1) are observed. Various power quality indices such as PF, DPF, distortion factor (DF) and THD are investigated to illustrate the improved power quality operation of the proposed AWPS. In Fig. 5, the steady state performance of the proposed AWPS at rated load condition is shown. The intermediate capacitor and output inductor are operating in CCM whereas the magnetizing current through inductor Lm is becoming discontinuous in a switching period. The input AC mains current is sinusoidal in nature and in phase with the supply voltage. It can be clearly seen from Fig.4 that the peak value of switch stress is quite low (almost equal to Vd) as compared to the normal zeta converter. The THD of AC mains current remains below 5% thereby complying with the standard IEC B. HARI PRASAD, M. J. NAVEEN, G. N. S. VAIBHAV IV. CONCLUSION A single-stage PFC based AWPS has been proposed operating in a wide range of loads and supply voltage conditions. The proposed converter for welding has been realized using high frequency isolation, ease of control and single stage power conversion. Using simple closed loop PI controller, the zeta converter based AWPS has been designed, modelled and implemented in hardware to improve the PQ at the utility interface. Test results of prototype have depicted that the proposed AWPS has fast dynamic response and over current protection. It is able to maintain constant output voltage irrespective of load and supply voltage variations. Because of the reduced voltage stress across the devices it would possess high reliability. The improved performance during overload conditions results in an improved weld quality. The main advantage of the proposed AWPS is its simplicity in control since only one gating signal is used to drive both the switches. The DICM operation of proposed zeta converter facilitates the inherent PFC feature. Besides these features, it is important to emphasize that the proposed PFC converter achieves significant PQ improvement irrespective of the load and supply voltage variations. The PQ indices obtained for this power supply have shown its adherence to the international PQ standards. The converter also possesses reduced voltage stress across devices. In all, the proposed PFC converter has shown acceptable performance and meets most of the requirements of a commercially viable arc welding power supply. V. REFERENCES [1] Limits for Harmonic Current Emissions, International Electro technical Commission Standard, , [2] M.K. Kazimierczuk, Pulse-width Modulated DC-DC Power Converter, John Willey & Sons, USA, [3] B. Singh, S. Singh, A.Chandra, K. Al-Haddad, Comprehensive study of single-phase ac-dc power factor corrected converters with high frequency isolation, IEEE Trans. Ind. Informatics, vol. 7, no. 4, pp , Nov [4] Jian-Min Wang, Sen-Tung Wu, A novel inverter for arc welding machines, IEEE Trans. Ind. Electronics, vol. 62, no. 3, pp , Mar [5] Qing Fang Teng, Wei Zhong Zhang, JianGuo Zhu, You GuangGuo, Modeling of arc welding power supply,proc. Applied Superconductivity and Electromagnetic Devices, pp ,2011. [6] N.R. Mandal, Welding Techniques, Distortion Control and Line Heating,Narosa Publication House Pvt. Ltd., India, [ ] R. Casanueva,.J.Azcondo,.J.D az, C.Branas, TIG Welding Machines, IEEE Ind. Applications Magazine, vol. 17, no. 5, pp , [8] Jian-Min Wang, Sen-Tung Wu, Shang-Chin Yen, Huang- Jen Chiu, A simple inverter for arc-welding machines with current doubler rectifier, IEEE Trans. Ind. Electron., vol. 58, no. 11, pp , [9] Y.M. Chae, Y. Jang, M.M. Jovanovic, J.S. Gho, G.H. Choe, A novel mixed current and voltage control scheme for Fig.6.Waveforms of AWPS.

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