Multiple Input DC-DC Converters with Input Boost Stages

Transcription

1 Multiple Input DC-DC Converters with Input Boost Stages Frey Gerar #1, Babu Thomas *2, Thomas P Rajan #3 #1 PG Scholar, *, 2,3 Professor, Department of Electrical & Electronics Engineering M A College of Engineering, Kothamangalam Kerala, Inia Abstract A high voltage gain DC-DC converter is propose. This converter is capable of stepping up voltages as low as 20V to 400V. The propose converter can raw power from four inepenent sources which makes it suitable for applications like solar panels. The propose converter fins its application in integration of iniviual solar panels onto the 400V istribution bus in DC micro gris. The propose converter consists of Dioe-Capacitor voltage multiplier stages. The converters achieve a high voltage gain by charging an ischarging of the voltage multiplier capacitors. The esign an component selection proceures are presente. The simulation of converter is one using MATAB/SimulinkR2014 software. A 2W, 10kHz harware prototype of the base circuit with Vin=1V an Vout=20V is also implemente in the laboratory. PIC16F877A is use for generating the control pulse. mikroc software is use for programming the PIC. Keywors DC-DC Converter, Multi Port Converter, Boost Converter. I. INTRODUCTION A four input DC-DC converter is propose for renewable energy applications where several renewable sources are employe. The versatility multiple input converters topologies gives us the avantage of a large variety of connection. Furthermore, the multiport structures exten the opportunity of making the entire system more simple an compact. Multi-port converters have less component count an less conversion stage than the traitional power processing solution which aopts several inepenent two-port converters. Due to their avantages multi-port converters recently have attracte much attention in acaemia, resulting in many topologies for applications like integration of low voltage sources to 400V DC microgri system. The step-up stage normally is the critical point for the esign of high efficiency converters ue to the operation with high input current an high output voltage, thus a careful stuy must be one in orer to efine the topology for a high step-up application. Theoretically, the conventional boost DC-DC converter can provie a very high voltage gain by using an extremely high uty cycle. arge uty cycles result in high current stress in the boost switch. Due to large uty ratio parasitic elements has to be consiere an their effects reuce the theoretical voltage gain Some converters can easily achieve high step-up voltage gain. However, transformer volume is a concern. Transformer leakage inuctance can prouce high voltage stress, increases the switching losses an the electromagnetic interference problems, thus reucing the efficiency of converter. In orer to reuce the voltage stress certain measures, have to be consiere. Thus, the weight, volume an losses of the power transformer are limiting factors for the isolate DC-DC converters use in embee applications. Some other alternative step-up DC-DC converters without step-up transformers an couple inuctors were presente in [2] [6]. By cascaing ioe capacitor or ioe-inuctor moules, these kins of DC-DC converters can provie high voltage gain. But the passive elements an switch were uner high voltage stress in this cascae converter. Non-isolate DC-DC converter topologies using capacitor-ioe voltage multiplier cells can be use to, obtain high static gain, low voltage stress an low losses, improving the performance with relation the classical topologies. A high voltage gain ual input converter use voltage multiplier cells integrate with a classical boost converter is propose was propose [1]. Several multiplier cells are connecte together to boost up the output voltage without compromising the voltage stresses across the components. The main avantage is that voltage gain can be increase by aing of ioe capacitor stages. The propose converter can raw current from four inepenent sources. So in place of four ifferent converters we can use a single converter. Thus making the process of energy harvesting a very efficient. II. MUTIPE INPUT DC-DC CONVERTER WITH INPUT BOOST STAGES The working of the propose converter is inspire from the Dickson charge pump [7]. Dioe-capacitor voltage multiplier (VM) stages are integrate with ISSN: Page 52

2 boost stages at the input. The VM stages are use to help the boost stage achieve a higher overall voltage gain. The voltage conversion ratio epens on the number of VM stages an the switch uty ratios of the input boost stages. This converter is capable of stepping up voltages as low as 20V to 400V. The propose converter offers continuous input current an low voltage stress (1/4th of its output voltage) on its switches. Thus offering a gain of 20. III. OPERATING PRINCIPE The propose converter provies a high voltage gain using the moifie Dickson charge pump voltage multiplier circuit (See Fig. 3). On a closer look, it can be seen that the converter is mae up of two stages. The o numbere upper stages, which have same moe of operation an the even numbere lower stages, which have same moe of operation. Fig. 1: High-voltage-gain DC-DC converter propose in [1]. Fig. 3: The switching sequence Fig. 2: Propose multiple input DC-DC converter with input boost stages For normal operation of the propose converter, there shoul be some overlapping time when both the switches are ON an also one of the switches shoul be ON at any given Therefore, the converter has three moes of operation. The propose converter can operate when the switch uty ratios are small an there is no overlap time between the conuction of the switches. However, this moe of operation is not of interest as it leas to smaller voltage gains.. A. Moe I In this moe all the switches are ON. All the inuctors are charge from their input sources. The current in the inuctors rise linearly. The ioes in ifferent VM stages are reverse biase an o not conuct. The VM capacitor voltages remain unchange an the output ioe Dout is reverse biase Fig. V. Thus the loa is supplie by the output capacitor Cout. Fig. III: A Dickson Charge Pump B. Moe II In this moe switch S1 an S3 is ON. All the o numbere ioes are forwar biase an the inuctor current flows through the VM stage capacitors charging the o (C 1, C 3 ) an ischarging the even numbere capacitors (C 2, C 4 ) shown in Fig. 6. ISSN: Page 53

3 C. Moe III In this moe switch S2 an S4 ON. Now the even numbere ioes are forwar biase an the inuctor current flows through the VM stage capacitors charging the even numbere capacitors an ischarging the o numbere capacitors as shown in Fig.7. IV. VOTAGE GAIN The charge is transferre progressively from input to the output by charging the VM stage capacitors. Here V(in1) = V(in2) =V(in3) = V(in4) = V = 20V. An uty ratio of all switches are same an equal to From the working of Dickson charge pump. Vout 5 (1) V 1 in V. DESIGN OF COMPONENTS The simulation of a converter rate at 400 W with V in1 = V in2 =V in3 = V in4 =20 V an V o =400 V is simulate. So the Output current Io=1A. Switching frequency f sw =100kHz. Number of voltage multiplier (VM) stages, N=4. Duty ratio is given by V0 Vin *(N 1) (2) V 0 Fig. 5: Moe I Operation Fig. 6: Moe II Operation A. Inuctor Design The inuctor currents in the boost stages epen on the number of VM stages connecte to each leg. The inuctor esign is similar to that of the normal boost converter. The inuctor value is selecte such that the boost stages operate in continuous conuction moe(ccm). The minimum inuctor value for the CCM operation of the boost stages is given by, I 1) * Vin1 *f *(N 1) 1 1min (3) out sw ) * V 3 3 in3 3min (4) Iout *fsw *(N 1) I *f ) * V * N 2 2 in2 2min (5) out sw I *f ) * V * N 4 4 in4 4min (6) out sw B. Capacitor Design Fig. 7: Moe III Operation The output capacitor is selecte base on the amount of charge that is transferre to the output for a esire output voltage ripple. Assuming a voltage ripple of 0.02% of output voltage, the require capacitance is given by, C I ) 0 out (7) fsw *ΔV0 The VM stage capacitors are selecte such that the equivalent series resistance ue to charging/ischarging of the capacitors is low keeping the total capacitance to reasonable levels, thus improving the efficiency an output voltage regulation. It is important to select VM stage ISSN: Page 54

4 capacitors with low ESR to minimize the losses, for that purpose thin film capacitors are selecte as they have low ESR values. VI. SIMUATION PARAMETERS The simulation parameters use for multiple input DC-DC converter are shown in Table I. The uty ratio an input voltage for all the branches are taken same. TABE I Simulation parameters Components Rating Input Voltage Output Voltage oa Resistance 20V 400V 400Ω Duty Ratio 75% Inuctors 100µH VM stage capacitors 20µF Output Capacitor 22µF VII. SIMUATION MODE AND RESUT A 400W moel of converter is simulate in MATAB/ SIMUINK environment. Fig. 9: Voltage Stress across switch (a) S 1 (b) S 3 (c) S 2 () S 4 Fig. 9 shows the voltage stress across the switches. A voltage stress of 80V is experiences by the switches. Compare to the output voltage of 400V the value is small (25%). So the switching stress is low. Fig. 10: Current through inuctor (a) 1 (b) 3 (c) 2 () 4 Fig. 8: Simulation moel of the propose converter The switching sequence for S 1, S 3 are same an switching sequence of S 2, S 4 are same. The inuctor current an the input current are the same. The current through inuctor 3 is slightly higher than other inuctors, this anomaly is contribute by the voltage imbalance between the VM stage capacitors. ISSN: Page 55

5 TABE II Components use for prototype Components Rating Inuctors 30µH Capacitor 22µF Dioe Controller MOSFET Driver IC IN5819 PIC16F877A IRF540 TP250 Fig. 11: Voltage across capacitor (a) C 1 (b) C 3 (c) C 2 () C 4 Fig. 11 shows the voltage across each voltage multiplier stage capacitors. The voltage across each capacitor will be a multiple of 80V. The output of each boost stages will be 80V. Similar to the working of Dickson charge pump [7] the voltage across each capacitor will increase by 80V. Fig 12 shows the output waveforms of obtaine in the simulation. Output voltage is 400V an the output current is 400A. The simulation moel is rate for 400W. Fig. 13: Experimental setup Fig. 12: Output (a) Voltage an (b) Current VIII. EXPERIMENTA SETUP AND RESUTS A 2 W, 10kHz prototype of the DC-DC converter with high voltage gain an two input boost stages with input 1V is implemente. Table 2 shows the specification. Fig. 14: Output voltage waveform The power supply consist of a step own transformer, full brige ioe rectifier, filter capacitor an a regulator IC (7812). IRF540 MOSFET is use as the switches. TP250 river is use to rive the MOSFET. To generate the switching signal PIC16F8771A was programme in the laboratory an necessary waveforms were obtaine. The Switches are working in 10kHz ISSN: Page 56

6 frequency an have a uty ratio of IX. CONCUSION A high voltage gain DC-DC converter is introuce that can offer a voltage gain of 20, i.e., to step up a 20V input to 400V output. The output voltage, switching stress, inuctor current an capacitor voltage are observe. Output voltage of 400V was obtaine uring the simulation. The observe values from the simulation are similar to the calculate values. Compare to the classical DC-DC converters the voltage stress across switches is low. The voltage across the switch was 80V which is a small value com- pare to the output voltage. The current through S 2 shows a spike because of the voltage imbalance between ifferent voltage multiplier stages. The size of the converter woul be less because high frequency operation an absence of wining transformer. On comparing with resonant converter the absence couple inuctor makes this converter superior, since leakage flux an stray magnetic fiel loss is not present. Since it is a multi-port converter with a high voltage gain, inepenent sources can be connecte an power sharing, MPPT algorithms can be implemente inepenently at each input port. The main problem associate with the propose converter is that, as the stages increases the size of capacitor becomes large. Thus making the circuit bulky. The converter fins its application in integration of iniviual solar panels onto the 400V istribution bus in ata centers, telecom centers, DC builings an microgris. Harware prototype of 2W, 10 khz of the base circuit [1] was implemente. [8] Marcos Pruente, uciano. Pfitscher, Gustavo Emmenoerfer, Euaro F. Romaneli, an Roger Gules, Voltage Multiplier Cells Applie to Non-Isolate DC DC Converters, IEEE Transactions on Power Electronics, vol. 23, no. 2, pp , Mar [9] Kuo-Ching Tseng, an Chi-Chih Huang, High step-up high-efficiency interleave converter with voltage multiplier moule for renewable energy system, IEEE Transactions on Inustrial Electronics, vol. 61, no. 3, pp , Mar [10] Chung-Ming Young, Ming-Hui Chen, Tsun-An Chang, Chun-Cho Ko, an Kuo-Kuang Jen, Cascae Cockcroft Walton Voltage Multiplier Applie to Transformerless High Step-Up DC DC Converter, IEEE Transactions on Inustrial Electronics, vol. 60, no. 2, pp , Feb REFERENCES [1] V. A. K. Prabhala, P. Fajri, V. S. P. Gouribhatla, B. P. Baipaiga, an M. Ferowsi, A DC-DC Converter With High Voltage Gain an Two Input Boost Stages, IEEE Trans. on Power Electronics, volume 31, pp , [2] Zhao an F. C. ee, High-efficiency, high step-up c c converters, IEEE Trans. Power Electronics, vol. 18, no. 1, pp , Jan [3] R.-J. Wai an R.-Y. Duan, High step-up converter with couple-inuctor,ieee Transactions Power Electronics, vol. 20, no. 5, pp ,Sep [4] R.-J. Wai an R.-Y. Duan, High-efficiency power conversion for low power fuel cell generation system, IEEE Transactions on Power Electronics, vol.20, no. 4, pp , Jul [5] Y. Jang an M. M. Jovanovic, Interleave boost converter with intrinsic voltage-oubler characteristic for universalline PFC front en, IEEE Transactions Power Electron., vol. 22, no. 4, pp , Jul [6] A. Z. Rehman, I. Al-Bahaly, an S. Mukhopahyay, Multi input DC-DC converters in renewable energy applications: An overview, Renewable an Sustainable Energy Reviews, Vol. 41, pp , [7] John F. Dickson, On-chip high-voltage generation in MNOS integrate circuits using an improve voltage multiplier technique, IEEE Journal of Soli-State Circuits, vol. 11, Issue: 3, pp , Jun ISSN: Page 57