Design of Efficient ZVS Half-Bridge Series Resonant Inverter with Suitable Control Technique

Transcription

1 Harish Vegola et al. Int. Journal of Engineering Research and Application RESEARCH ARTICLE OPEN ACCESS Design of Efficient ZVS Half-Bridge Series Resonant Inverter with Suitable Control Technique Harish Vegola, P. Sucharitha, Durga Kuarasway 2Assistant Professor, Departent of EEE, Aurora s Research & Technological Institute, Warangal Institute, Warangal. 3Associate Professor, Departent of EEE, Aurora s Research & Technological Institute, Warangal Institute, Warangal. ABSTRACT:- During certain load conditions there will be considerable reduction or decrease in the efficiency of zero voltage switching half-bridge series resonant inverter and this is ainly because of high switching frequencies. In order to iprove efficiency, the technique naed variable frequency duty cycle (VFDC) control is used for both the ediu and low output power levels with the decreased switching frequencies. VFDC strategy efficiency iproveent is achieved by eans of a switching-frequency reduction, ainly at low-ediu power range, and with low quality factor loads. And this technique is used in Doestic induction heating application because of its special load characteristics. This paper includes a theoretical analysis of power balance as a function of control paraeters, an efficiency analysis to deterine the optiu operation point, Switching and conduction losses to exaine the overall efficiency iproveent are discussed. In addition, restrictions due to snubber capacitors and dead tie, and variability of the loads have been considered. Index Ters Hoe appliances, induction heating, inverters, resonant power conversion I. INTRODUCTION Hoe appliances represent a substantial part of the residential energy consuption. For this reason the efficiency of the power converter is a ey design aspect, as it defines not only the environental ipact but also the final appliance perforance and reliability. As a consequence, researches and developents on induction cooers, as one of the ore consuing appliances, pursue further efficiency iproveents. Doestic induction heating technology has becoe ore iportant in recent years due to advantages such as its iproved efficiency, safety and perforance. The ain blocs of an induction cooing appliance are outlined in Fig. 1. The ains voltage is rectified and filtered, generating a DC bus. Afterwards, the resonant inverter supplies variable frequency current (20 to 75 Hz) to the induction coil. This current produces an alternating agnetic field, which causes eddy currents and agnetic hysteresis heating up the pan. Traditional Square Wave (SW) odulation iplies operation at high switching frequencies to deliver low-ediu power. This entails inverter efficiency reductions, which is a basic fact to ensure reliability, Fig. 1. Bloc diagra of a doestic induction cooing appliance Maxiize output power capabilities and iniize heat sin and fan size. In the past, Pulse Density Modulation has been proposed to iprove the efficiency. However, it has soe liitations regarding flicer eissions and user perforance. The ai of this paper is to propose a control algorith optiization leading to an efficiency iproveent with no hardware changes required. To achieve this goal, a theoretical analysis of Variable Frequency Duty Cycle (VFDC) odulation schee has been carried out. Afterwards, efficiency obtained at different operation conditions has been estiated for different switching devices. Finally, experientation with a typical induction heating inverter has been used to validate the siulation results. PROJECT DESCRIPTION: The efficiency of ZVS half-bridge series resonant inverter can be decreased under certain load conditions due to the high switching frequencies required. The proposed Variable Frequency Duty Cycle (VFDC) control is intended to iprove the efficiency in the ediu and low output power levels because of the decreased switching frequencies. EXISTING SYSTEM: Traditional Square Wave (SW) odulation iplies operation at high switching frequencies to deliver low ediu power. This entails inverter 235 P a g e

2 Harish Vegola et al. Int. Journal of Engineering Research and Application efficiency reductions, which is a basic fact to ensure reliability, axiize output power capabilities and iniize heat sin and fan size. In the past, Pulse Density Modulation has been proposed to iprove the efficiency. However, it has soe liitations regarding flicer eissions and user perforance. But the disadvantage of the existing syste is that the efficiency of ZVS half-bridge series resonant inverter can be decreased under certain load conditions due to the high switching frequencies required. PROPOSED SYSTEM: The proposed Variable Frequency Duty Cycle (VFDC) control is intended to iprove the efficiency in the ediu and low output power levels because of the decreased switching frequencies. The study perfored in this paper includes, in a first step, a theoretical analysis of power balance as a function of control paraeters. In addition, restrictions due to snubber capacitors and dead tie, and variability of the loads have been considered. Afterwards, an efficiency analysis has been carried out to deterine the optiu operation point. Switching and conduction losses have been calculated to exaine the overall efficiency iproveent. VFDC strategy efficiency iproveent is achieved by eans of a switching frequency reduction, ainly at low-ediu power range, and with low quality-factor loads. BLOCK DIAGRAM: AC SUPPLY EMC FILTER RECTIFIER AND FILTER INDUCTOR PAN MODEL INVERTER odulation paraeters (Fig. 2 (b)) are switching frequency (fs) and duty cycle (D). Reduction in D allows reducing fs and, as a consequence, switching losses can be iniized. Miniu D and fs are liited by Zero Voltage Switching (ZVS) coutation conditions Fig. 2 The half-bridge series resonant inverter: (a) scheatic and (b) ain wavefors and paraeters A:- SIMULATION PROCEDURE: A versatile siulation tool has been developed using MATLAB to allow varying odulation paraeters and perforing the required calculus. The power stage has been siulated using the haronic decoposition. Since voltage vo(t) and its haronics coposition Voh are nown, the output power can be calculated as follows. CONTROL SIGNAL II. VARIABLEFREQUENCYDUTYCY CLE The half-bridge series resonant inverter (Fig. 2) is the ost used topology due to its siplicity, efficiency, and its cost- effectiveness. The resonant load consists of the pan, the induction coil and the resonant capacitor. Induction coil and pan coupling is odeled as the series connection of an inductor and a resistor, based on its analogy with respect to a transforer, and it is defined by the values of Leq and Req. VFDC control is a generalization of SW and classical Asyetrical Duty Cycle controls. Its Besides, a teporal analysis can be achieved obtaining io(t) through Fourier series. where ih represents phase delay between h-order haronic and ain haronic, and it is given in (3). 236 P a g e

3 Harish Vegola et al. Int. Journal of Engineering Research and Application ensure ZVS operation has been included. It is shown that axiu fs reductions are achieved with loads with low Q (Fig. 3 (a), (c)) operating with low snubber capacitor values (Fig 3. (a), (b)). B:- INFLUENCE OF LOAD, SNUBBER NETWORK AND DEAD TIME Equivalent load paraeters Leq, Req and Cr copose the inverter resonant tan and, hence, the load has a direct influence on the operation conditions. Different loads can be classified by their quality factor (Q), defined as usual (4), and the resonant frequency fo. For doestic induction heating Q = 1.66 is considered as a coon value for ferroagnetic pots, although this analysis has been extended for Q = 1, 2, 4 and 8. In addition, coercial power stages use snubber networs and iniu-fixed dead tie to iniize the power losses and to ensure the reliability of the appliance. This entails teporal restrictions, given in the following expression, which ust be satisfied to eep ZVS operation. As a consequence, potential fs reduction and efficiency iproveents are liited. Where tdiode is the diode conduction tie, td is the dead tie, ts nubber the tie until snubber capacitor reaches bus voltage, Cs the snubber capacitor and if all the turn-off current. The influence of both the load and the snubber networ has been analyzed through the power distribution shown in Fig. 3, where output power as a function of fs for duty cycle fro 0.5 to 0.15 is represented. All the agnitudes have been noralized to their values at resonance frequency and D = 0.5. In addition, the iniu D value to III. EFFICIENCY ANALYSIS An efficiency analysis has been carried out considering the contribution of conduction (Pon) and switching losses (Psw) to total losses (Ploss). Conduction losses analysis has been coputed odeling the switch as the series connection of a resistance (Ron) and a voltage source (Von). Thus, power losses are calculated as follows where I and Irs are the device average and rs currents respectively. Switching losses have been calculated assuing linear current and voltage turn-off characteristics of the switching devices, so Psw for a transistor with current fall tie tf all are given by VFDC control schee achieves power loss reduction by decreasing switching frequency. Fig. 4 shows switch-off power loss iproveent for different transistor tf all ties (a) and total power loss iproveent (b). The power losses have been noralized with the value operating with D = 0.5 to provide a clear evaluation of VFDC control schee. Siulation results show a reduction of the switching losses up to 14% for high coutation speed devices (Fig. 4 (a)). Besides, the overall iportance of switching losses reduction and, hence, efficiency iproveent, depends on the relative weight of switching and conduction losses. 237 P a g e

4 Harish Vegola et al. Int. Journal of Engineering Research and Application Fig. 3 Noralized output power as a function of noralized switching frequency with different duty cycles for loads with Q = 1.66 (a) and Q = 8 (b) operating without snubber, and Q = 1.66 operating with 15 nf snubber capacitor (c) This is characteristic of the switching device and, as a consequence, it ust be previously defined. For this analysis it has been considered the coercial device Fairchild 20N60 IGBT which includes antiparallel diode. Fig. 4 (b) shows the noralized power losses and the D selected to iniize it. The axiu efficiency benefits are obtained in the low-ediu power range and, as previously shown, with low Q loads, because of the higher fs reduction feasible. Fig. 4 Siulation results for different duty cycles and load with Q = 1.66: (a) noralized switching power losses to supply 2200 W and (b) total power loss reduction and its optiu duty cycle associated for the whole output power range. IV. EXPERIMENTAL VERIFICATION A half-bridge series resonant inverter has been used to test the proposed control schee. In order to avoid second order effects with teperature and frequency when using coercial pots, a discrete RL load has been ipleented (Q = 1.4). It has been designed with forced-cooling in order to operate with output powers up to 3500 W. Measureents have been carried out with a digital oscilloscope and power analyzer YOKOGAWA PZ4000. The power converter is controlled in open loop through a PC interface (Fig. 5 (a)). Digital control has been ipleented in a PIC18F2520, which controls a versatile PWM odulator ipleented in an ASIC. The ain inverter specifications are suarized in Table I 238 P a g e

5 a a E g C E a a g C Harish Vegola et al. Int. Journal of Engineering Research and Application are achieved with a load with Q = 1.4. For a final application, it should be also considered the effects of the dc-lin voltage ripple, due to the non-linear behavior of both the induction load and the switching losses. Since the higher pea current increases significantly the switching losses, VFDC control is recoended to reduce the switching frequency. Besides, the axiu efficiency point for a certain output power is achieved with the lower D possible. Therefore, the axiu efficiency point tracing becoes siple and with a straightforward digital ipleentation. V. SIMULATION MODEL AND RESULTS B5 Pulses PWM Generator Continuous powergui D D2 B3 IGBT/Diode i + - Scope1 AC Voltage Source B4 IGBT/Diode1 Current Measureent + - v Voltage Measureent Scope D1 D3 Branch B1 B2 Fig. 5 Experiental verification: (a) experiental set up, (b) easured power loss reduction, and (c) efficiency for different output power and duty cycle. Experiental easureents show the power loss reduction and efficiency iproveent achievable with the use of VFDC odulation technique (Fig. 5 (b) and (c)). It is shown that the efficiency iproveent is higher at the low/ediu power range, and power loss reductions higher than 25% 239 P a g e

6 Harish Vegola et al. Int. Journal of Engineering Research and Application Fig. Extended Result for ZVS Series Resonant Inverter VI. CONCLUSION The efficiency of the power converter deterines the axiu output power and reliability of a doestic induction heating appliance. In this paper, a ethod to iprove efficiency in the half-bridge series resonant inverter has been presented through a generalization of SW and ADC controls. VFDC control strategy is intended to replace classical SW and PDM strategies in order to get iproved perforance and user experience. It has shown efficiency iproveents due to the switching frequency reduction which leads to reduced switching power losses. The ost favorable operation range coprises loads with low Q operating in the low/ediu power range. The analytical results presented in this paper have been verified through an induction heating testbench. Experiental results confir the benefits of VFDC control, iproving efficiency in the whole power range, and achieving power loss reduction higher than 25% for a typical doestic induction heating load. As a consequence, VFDC control schee is proposed as a solution to iprove efficiency with easy digital control integration. REFERENCES [1] J. Acero, et al., "The doestic induction heating appliance: An overview of recent research," in Applied Power Electronics Conference and Exposition, 2008, pp [2] S. Llorente, F. Monterde, J. M. Burdio, and J. Acero, "A coparative study of resonant inverter topologies used in induction cooing," in Applied Power Electronics Conference and Exposition, 2002, pp [3] B. Saha, K. Soon Kurl, N. A. Ahed, H. Oori, and M. Naaoa, "Coercial frequency AC to high frequency AC converter with boost-active clap bridge single stage ZVS-PWM inverter," IEEE Transactions on Power Electronics, vol. 23, no. 1, pp , January [4] M. K. Kaziierczu and S. Wang, "Frequencydoain analysis of series resonant converter for continuous conduction ode," IEEE Transactions on Power Electronics, vol. 7, no. 2, pp , April [5] F. P. Dawson and P. Jain, "A coparison of load coutated inverter systes for induction heating and elting applications," IEEE Transactions on Power Electronics, vol. 6, no. 3, pp , July [6] O. Lucía, J. M. Burdío, I. Millán, J. Acero, and D. Puyal, "Load-adaptive control algorith of half-bridge series resonant inverter for doestic induction heating," IEEE Transactions on Industrial Electronics, vol. 56, no. 8, pp , August [7] N. Par, D. Lee, and D. Hyun, "A power-control schee with constant switching frequency in class-d inverter for induction-heating jar application," IEEE Transactions on Industrial Electronics, vol. 54, no. 3, pp , June [8] P. Ibertson and N. Mohan, "Asyetrical duty cycle perits zero switching loss in PWM circuits with no conduction loss penalty," IEEE Transactions on Industry Applications, vol. 29, no. 1, pp , Jan./Feb [9] O. Lucía, J. M. Burdío, I. Millán, J. Acero, and S. Llorente, "Efficiency optiization of halfbridge series resonant inverter with asyetrical duty cycle control for doestic induction heating," in European Conference on Power Electronics and Applications EPE09, [10] J. M. Burdio, L. A. Barragan, F. Monterde, D. Navarro, and J. Acero, "Asyetrical voltagecancelation control for full-bridge series resonant inverters," IEEE Transactions on Power Electronics, vol. 19, no. 2, pp , March [11] L. A. Barragan, J. M. Burdio, J. I. Artigas, D. Navarro, J. Acero, and D. Puyal, "Efficiency optiization in ZVS series resonant inverters with asyetrical voltage-cancellation control," IEEE Transactions on Power Electronics, vol. 20, no. 5, pp , Septeber [12] F. Forest, S. Faucher, J.-Y. Gaspard, D. Montloup, J.-J. Huselstein, and C. Joubert, "Frequency-synchronized resonant converters for the Supply of ultiwindings coils in induction cooing appliances," IEEE Transactions on Industrial Electronics, vol. 54, no. 1, pp , February [13] W. Zhang, W. Chen, W. Yao, and Z. Lu, "A novel optiized snubber with tie-varying capacitor for synchronous rectification, analysis and ipleentation," in Applied Power Electronics Conference and Exposition, 2009, pp [14] B. W. Willias, Power Electronics, Devices, Drivers and Applications, 2nd ed. New Yor: MacMillan, P a g e