Implementation of Single Stage Three Level Power Factor Correction AC-DC Converter with Phase Shift Modulation

Transcription

1 Implementation of Single Stage Three Level Power Factor Correction AC-DC Converter with Phase Shift Modulation Ms.K.Swarnalatha #1, Mrs.R.Dheivanai #2, Mr.S.Sundar #3 #1 EEE Department, PG Scholar, Vivekanandha Institute of Engineering and Technology for Women, Tiruchengode,Tamilnadu, India. #2 EEE Department, Assistant Professor, Vivekanandha Institute of Engineering and Technology for Women, Tiruchengode,Tamilnadu, India. #3 EEE Department, Assistant Professor, Bannari Amman Institute of Technology, Sathyamangalam, Tamil nadu, India. Abstract A new single stage Three level ac-dc converter that can operate with standard phase shift modulation is proposed in this paper. The converter topology is very simple, and this method of control used to achieve both power factor correction and ac-dc conversion. Converter operation is explained and power factor is improved in this paper. Finally the efficiency of the new converter is compared with that of previously proposed converter. Keywords PSM (Phase Shift Modulation), TL (Three Level) converter, AC-DC converter, power factor correction (PFC), single stage converter. I. INTRODUCTION Power-electronic inverters are becoming popular for various industrial drives applications. In recent years also high-power and medium-voltage drive applications have been installed. To overcome the limited semiconductor voltage and current ratings, some kind of series and/or parallel connection will be necessary. Due to their ability to synthesize waveforms with a better harmonic spectrum and attain higher voltages, multi-level inverters are receiving increasing attention in the past few years. THE ac dc power supplies with transformer isolation are typically implemented with some sort of input power factor correction (PFC) to comply with harmonic standards such as IEC [1]. With the rapid rise in the use of electrical equipment in recent years, power converter manufactures are being pressed by regulatory to implement some form of PFC intheir products. High power factor and low input current harmonics are more and more becoming mandatory performance criteria for power converters. Although it is possible to satisfy by adding passive filter elements to the traditional passive diode rectifiers/lc filter input combination. The result of this converter is very bulky and heavy due to the size of the low frequency inductors and capacitors. Active power factor correction techniques have been used in AC-DC converter to improve power factor and reduce the harmonics. Active power factor correction can be classified into two stage scheme. Two stage PFC contains two independent power stages in cascade with PFC stage and DC-DC regulator. The total efficiency of the two stage is lower because the total power has to be processed twice with two cascade power stage. Cost of the circuit is increase several schemes have developed to combine stage into one stage [13]. The voltage feed single stage PWM (Phase Shift Modulation) full bridge converter have disadvantages that have limited their use. ISSN: Page 163

2 These are following, 1) They are controlled by single controller and the dc bus voltage is left unregulated [12-15]. 2) They are implemented with two level topologies that subject the converter components to voltage stresses[2],[15].the single stage AC-DC full bridge converter is based on some sort of voltage fed single stage PWM converter[12]-[15].this converter have a large energy storage capacitor connected across their primary side dc bus. They are operate with fixed switching frequency and the bus capacitor prevents voltage overshoots. The three level voltage fed single stage PWM converter was proposed in[15]. This converter does not have disadvantage of previously proposed single stage TL converter. This PWM method is not standard PWM and is therefore not found in commercially available integrated circuit. A new single stage TL AC-DC converter that can operate with standard PWM is proposed in this paper. Fig.1. Single Stage TL ac-dc converter [15]. Fig.2 Typical waveforms describing the modes of operation. II. PULSE WIDTH MODULATION (PWM) The energy that a switching power converter delivers to a motor is controlled by Pulse Width Modulated (PWM) signals, applied to the gates of the power transistors. PWM signals are pulse trains with fixed frequency and magnitude and variable pulse width. There is one pulse of fixed magnitude in every PWM period.however, the width of the pulseschanges from period to period according to a modulating signal. When a PWM signal is applied to the gate of a power transistor, it causes the turn on and turns off intervals of the transistor to change from one PWM period to another PWM period according to the same modulating signal. The frequency of a PWM signal must be much higher than that of the modulating signal, the fundamental frequency, such that the energy delivered to the motor and its load depends mostly on the modulating signal. ISSN: Page 164

3 IV. CURRENT RATING OF MOSFETs AND DIODES Let the rms value of the line current of the load be I L Therefore I L I L =squre root of (2/3)*I I rms MOSFET= I rms diode = Fig: two types of PWM signals Above Figure, shows two types of PWM signals, symmetric and asymmetric edge-aligned. The pulses of a symmetric PWM signal are always symmetric with respect to the center of each PWM period. The pulses of an asymmetric edge-aligned PWM signal always have the same side aligned with one end of each PWM period. Both types of PWM signals are used in this application. III. PULSE WIDTH MODULATION TECHNIQUES The control of output voltage is done using pulse width modulation. The commonly used techniques are 1. Single pulse width modulation. 2. Multiple pulse width modulation. 3. Sinusoidal pulse width modulation. 4. Modified sinusoidal pulse width modulation. 5. Phase displacement control. It is easily seen that the peak forward blocking as well as the peak reverse voltage on the MOSFET is equal to the maximum capacitor voltage. Hence the voltage rating of the thyristor is equal to V co. V. VOLTAGE RATING OF DIODES The peak reverse voltage across a diode occurs just before the switch in the same leg is fired and is given by (V co -IR/3). This could be taken as V co itself for a safe design. VI. PSM TECHNIQUE FOR TL SINGLE-STAGE CONVERTERS The proposed converter, shown in Fig. 3, integrates an ac dc boost PFC into a TL dc/dc converter. It is almost the same as the converter proposed in [15] and with a flying capacitor between two clamping diodes. The PFC is performed by using an auxiliary winding taken from the main transformer that acts like a switch that turns on and off in an appropriate manner. Typical converter waveforms are shown in Fig. 4, and equivalent circuit diagrams that show the converter s modes of operation with phase-shift modulation (PSM) are shown in Fig. 5. The diode rectifier bridge output is replaced by a rectified sinusoidal source, and the thick lines represent the paths of current conduction. ISSN: Page 165

4 discharges through Cf until Cs4, the output capacitance of S4, clamps to zero. The energy stored in the input inductor during the previous mode starts to be transferred into the dc-link capacitors. This mode ends when S4 turns on with zero-voltage switching (ZVS). Fig3: Proposed single stage TL converter. 3) Mode 3 (t2 < t < t3) [Fig. 5(c)]: In Mode 3, S1 is OFF and S2 remains ON. The energy stored in the input inductor during Mode 1 is completely transferred into the dc-link capacitors. The amount of stored energy in the input inductor depends upon the rectified supply voltage. This mode ends when the input inductor current reaches zero. Also, during this mode, the load inductor current freewheels in the secondary of the transformer. Fig4: typical waveform of proposed converter. The converter has the following modes of operation. 1) Mode 1 (t0 < t < t1) [Fig. 5(a)]:During this mode, switches S1 and S2 are ON, and energy from dc bus capacitor C1 is transferred to the output load. Since the auxiliary winding generates a voltage (Naux/N1 =2) that is equal to the total dclink capacitor voltage (sum of C1 and C2), the voltage across the input inductor is the rectified supply voltage, and thus, the input inductor current starts rising. 2) Mode 2 (t1 < t < t2) [Fig. 5(b)]: In this mode, S1 is OFF and S2 remains ON. Capacitor Cs1 charges and capacitor Cs4 ISSN: Page 166

5 5) Mode 5 (t4 < t < t5) [Fig. 5(e)]: In this mode, S1 and S2 are OFF, and the current in the transformer primary charges capacitor C2 through the body diode of S3 and switch S4. This mode ends when switches S3 and S4 are switched on and a symmetrical period begins. 4) Mode 4 (t3 < t < t4) [Fig. 5(d)]: In this mode, S1 is OFF, the primary current of the main transformer circulates through diode D1 and S2, and the load inductor current freewheels in the secondary of the transformer. VII. SIMULATION DIAGRAM FOR THREE LEVEL AC-DC CONVERTER ISSN: Page 167

6 VIII. RESULT AND DISSCUSION New TL Output Waveform DC Output Waveform IX. CONCLUSION A new TL single-stage converter has been proposed in this letter. In this paper, the operation of the converter was explained, and its feasibility was confirmed with experimental results obtained from a prototype converter. The efficiency of the new converter was compared to that of a previously proposed converter of the same type. It was shown that the new converter had a better efficiency, and power factor is improved for particularly under light-load conditions, and it was explained that this was because energy from the input inductor can always be used to ensure that at least two switches can turn on with ZVS. REFERENCES 1. D. D. C. Lu, D. K. W. Cheng, and Y. S. Lee, Singlestage AC DC power-factor-corrected voltage regulator with reduced intermediate bus voltage stress, Proc. Inst. Elect. Eng. Elect. Power Appl., vol. 150, no. 5, pp , Sep G. Moschopoulos, A simple ac dc PWM full-bridge converter with integrated power-factor correction, IEEE Trans. Ind. Electron., vol. 50, no. 6,pp , Dec S. Luo,W. Qiu,W.Wu, and I. Batarseh, Flyboost power factor correction cell and a new family of single-stage ac/dc converters, IEEE Trans.Power Electron., vol. 20, no. 1, pp , Jan Y. Jang, M. M. Jovanovic, and D. L. Dillman, Softswitched PFC boost rectifier with integrated ZVS twoswitch forward converter, IEEE Trans.Power Electron., vol. 21, no. 6, pp , Nov A. Lazaro, A. Barrado, M. Sanz, V. Salas, and E. Olias, New power factor correction AC DC converter with reduced storage capacitor voltage, IEEE Trans. Ind. Electron., vol. 54, no. 1, pp , Feb D. D.-C. Lu, H. H.-C. Iu, and V. Pjevalica, A singlestage ac/dc converter with high power factor, regulated bus voltage, and output voltage, IEEETrans. Power Electron., vol. 23, no. 1, pp , Jan S. K. Ki and D. D.-C. Lu, Implementation of an efficient transformer-less single-stage single-switch ac/dc converter, IEEE Trans. Ind. Electron.,vol. 57, no. 12, pp , Dec H. Ma, Y. Ji, and Y. Xu, Design and analysis of single-stage power factor correction converter with a feedback winding, IEEE Trans. PowerElectron., vol. 25, no. 6, pp , Jun H. J. Chiu, Y. K. Lo, H. C. Lee, S. J. Cheng, Y. C. Yan, C. Y. Lin,T. H. Wang, and S. C. Mou, A single-stage soft-switching fly back converter for power-factorcorrection applications, IEEE Trans. Ind. Electron.,vol. 57, no. 6, pp , Jun J. Zhang, D. D.-C. Lu, and T. Sun, Fly back-based single-stage power factor-correction scheme with timemultiplexing control, IEEE Trans.Ind. Electron., vol. 57, no. 3, pp , Mar J. M. Kwon, W. Y. Choi, and B. H. Kwon, Singlestage quasi-resonant fly back converter for a costeffective PDP sustain power module, IEEETrans. Ind. Electron., vol. 58, no. 6, pp , Jun H. S. Ribeiro and B. V. Borges, Analysis and design of a high-efficiency full-bridge single-stage converter with reduced auxiliary components, IEEE Trans. Power Electron., vol. 25, no. 7, pp , Jul H. L. Cheng, Y. C. Hsieh, and C. S. Lin, A novel single-stage high-power factor ac/dc converter featuring high circuit efficiency, IEEE Trans. Ind.Electron., vol. 58, no. 2, pp , Feb H. Ribeiro and B. Borges, New optimized full-bridge, single stage ac/dc converters, IEEE Trans. Ind. Electron., vol. 58, no. 6, pp , Jun M. Narimani and G. Moschopoulos, A new singlephase single-stage three-level power factor correction ac dc converter, IEEE Trans. PowerElectron., vol. 27, no. 6, pp , Jun ISSN: Page 168