Available online at www.sciencedirect.com
ScienceDirect Procedia Engineering 170 (2017) 509 – 515
Engineering Physics International Conference, EPIC 2016
Design and Development of a Series-Configuration Mazzilli Zero Voltage Switching Flyback Converter as a High-Voltage Power Supply for Needleless Electrospinning Dian Ahmad Hapidina,b, Ismail Saleha,b, Muhammad Miftahul Munira,b, Khairurrijala,b,* a
Department of Physics, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Jalan Ganesa 10, Bandung 40132, Indonesia b ResearchCenter for Bioscience and Biotechnology, Institut Teknologi Bandung, Jalan Ganesa 10, Bandung 40132, Indonesia
Abstract Nanofiber is one-dimensional material that has broad application. It can be formed by applying a high-voltage source to a polymer solution so that the polymer solution becomes charged. Using the high electric field, the charged polymer solution is formed as a Taylor cone and then drawn to the collector to form long, nanoscale fibers. This method is known as electrospinning. There are two types of electrospinning method; they are needle and needleless electrospinning. The latter is intended for mass production nanofibers because it can make tens to hundreds of jets at a time. Therefore, the high-voltage source required for the needleless electrospinning process must have a higher voltage and current compared to those for the needle one. Accordingly, the high voltage power supply using a series-configuration Mazzilli ZVS flyback converter was designed and developed. The Mazzilli flyback converter was able to generate a high voltage with relatively high power. Two converters were connected in series to achieve more output voltage. The output voltage was adjusted by changing the input voltage. The single converter could generate a high voltage up to 34 kV whereas the series-configuration converter could increase the voltage by 98.41 % to be 67 kV. The output voltage of converter was relatively stable and good enough to perform nanofibers synthesis using the needleless electrospinning. Visual observation confirmed that the nanofibers were formed well on the collector. © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). © 2016 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the organizing committee of the Engineering Physics International Conference 2016 Keywords: Flyback converter; high voltage power supply; Mazzilli ZVS; nanofibers; needleless electrospinning
1. Introduction Nanofibers offer promising characteristics for diverse applications e.g. water purifiers [1], wound dressings [2], drug delivery systems [3], transparent conductive oxides [4], and air filters [5]. One efficient method to fabricate fine fibers is by applying a high voltage (HV) difference between the positively-biased needle tip of a syringe containing polymer solution and the grounded collector. The HV creates a strong electric field and simultaneously charges the polymer solution so that the Taylor cone is formed at the needle tip and the solution jet is drawn to the collector. This method is well known as electrospinning [6-9]. Although the needle electrospinning exhibits good performances, its production rate is low. This becomes a barrier for the industrial need that requires a high production rate. To overcome this limitation, researchers have attempted some improvements such as multi-nozzle [10] and needleless [11-13] electrospinning to boost up the production rate. The needleless electrospinning has the highest production rate because its geometry allows the generation of tens to hundreds of jets at a time. Consequently, the needle and needleless electrospinning have different processing condition, especially in the operating HV. The needle electrospinning needs a relatively low HV ranging from 5 to 20 kV [8, 9], whereas the needleless electrospinning does a higher HV reaching more than 50 kV [14, 15].
* Corresponding author. Tel.: +62-22-2500834; fax: +62-22-2506452. E-mail address:
[email protected]
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of the Engineering Physics International Conference 2016
doi:10.1016/j.proeng.2017.03.081
510
Dian Ahmad Hapidin et al. / Procedia Engineering 170 (2017) 509 – 515
The HV source can be obtained by various methods e.g. voltage multiplier [16], Mazzilli zero voltage switching (ZVS) converter [17, 18], and flyback converter [19, 20]. The flyback converter is low cost and it is easy to generate an HV source. We have developed a low-cost programmable high-voltage power supply (HVPS) from a CRT flyback transformer for the needle electrospinning [20]. However, its output voltage is only able to reach 18 kV, which is not enough for the needleless electrospinning. The Mazzilli ZVS flyback converter offers a promising way to generate an HV source with a high output voltage [18]. It is a self-oscillating ZVS converter that has good efficiency and can drive a flyback transformer at relatively high power. The input to output conversion of the converter can be increased by choosing appropriate components or combining some topologies in series- or parallel-configurations [17, 19, 21]. Davari, et al. have significantly increased the input to output voltage conversion of the flyback converter circuit by connecting several circuits in series [19]. In this regard, the development of series-configuration Mazzilli ZVS flyback converter as an HVPS for the needleless electrospinning was proposed. The HVPS used a CRT flyback transformer and to increase the output voltage of HVPS, two flybacks transformer with a series-connected output were arranged. The arrangement was well isolated by the epoxy resin to prevent arcing and corona generation. Each flyback in the configuration was driven by a Mazzilli ZVS flyback converter. The output voltage of the single Mazzilli ZVS flyback converter could reach 34 kV. When they were in a series configuration, the output voltage was become 67 kV. The developed HVPS was tested on the needleless electrospinning with a wire spinneret to observe the jets and nanofibers generation. It was confirmed that the nanofibers were formed well at the collector. The converter circuit and needleless electrospinning apparatus will be discussed in detail. 2. System Design and Development 2.1. Mazzilli ZVS Converter Circuit Figure 1 shows the Mazzilli ZVS flyback converter circuit. This circuit, which was invented by Vladimiro Mazzilli, is an improvement of Royer Oscillator topology [18]. This topology is a self-oscillating converter that can drive a flyback transformer with a high power and a good efficiency [18]. In the proposed HVPS design, we used a commercial CRT flyback transformer BSC25-0109A for the HV generation. The commercial CRT flyback transformer has some internal parts i.e. a secondary winding, a primary winding, and the auxiliary windings. The secondary winding (Ls) has many turns and is equipped with an HV diode (Ds) and an HV capacitor (Cs) to rectify the HV output. This winding, as well as the whole flyback body, is supported by the HV isolation so that it can withstand an HV up to tens of kilovolts. The primary winding (Lp) is connected to the converter circuit. The auxiliary windings (are not shown in the figure), which are to generate specific voltage levels for other components in a CRT, is not used in the proposed HVPS design. In order to accommodate the Mazzilli flyback converter circuit, we did not use the original flyback primary winding, but rather used an addition center tapped winding that was wound on the same ferrite core. The primary winding along with the capacitor C1 forms an LC oscillator circuit with the frequency satisfying Equation (1).
.
(1) Mazzilli Driver Circuit 1
Vin
R2
R1
470
470
Z1 Z
R3
10k
Z2
L1 46.2uH
R4
CRT Flyback
10k
L Q1 IRFP260 IRFP260
D1
Ls
HVout Ds
D2 C1
Q2 2
Fig. 1. Mazzilli ZVS flyback converter circuit.
3 Cs
Dian Ahmad Hapidin et al. / Procedia Engineering 170 (2017) 509 – 515
Since the circuit operates at high power, significant heat can be dissipated through the capacitor C1. In order to prevent a capacitor failure, five Mylar capacitors of 68 nF/630 V were connected in parallel as C1. The Lp value was chosen to be 54.1 μH, and the oscillator frequency is therefore about 37.1 kHz. The gate voltage of each MOSFET IRFP260 was powered by the power supply Vin. The gate has a capacitance that will become a serious problem if the circuit is operated at a high frequency. An overvoltage may occur and causes a gate breakdown. This issue could be solved by placing 12 V Zener diodes (Z1 and Z2) to limit the gate voltage. In addition, the MOSFETs should be equipped with a good heat sink as well as a cooling system to prevent overheating during operation. 2.2. Operating Principle The working principle of the circuit is divided into four stages as illustrated in Figure 2. In stage 1, the capacitor C1 is completely discharged as the drain voltages of Q1 and Q2 (see Figure 1) approach zero. During this stage, all resonant energy is stored in the inductor Lp which is the primary winding of the flyback transformer. Because there is no voltage across the Lp, thus there is no power transfer from the primary winding Lp to the secondary winding Ls as well as the output voltage. The cross-coupling circuit, which is provided by the diodes D1 and D2 (see Figure 1), ensures only one MOSFET will turn ON as another turn OFF. When the Q1 turns OFF, and Q2 turns ON, the resonance between the Lp and the C1 occurs which is the beginning of stage 2. In stage 2, the energy which was stored in the Lp is transferred as a current to the C1 and charges it. During the charging process, the drain voltage of Q1 rises simultaneously. When the entirety energy in the Lp has completely transferred to the C1, the charging process stops. As the charging process stops, the C1 undergoes the discharging process so that the current flows back to the Lp, followed by the falling of the Q1 drain voltage. During this stage, the energy is transferred from the Lp to the Ls and the current flows through the diode Ds to the load RL while charging the capacitor Cs. Stage 3 begins after the completion of the C1 discharging process. As the discharging process completed, the Lp stores all energy just like the stage 1 but in opposite voltage polarity. The MOSFET Q1 begins to turn ON while Q2 turns OFF. No power transfer from the Lp to the Ls occurs at this stage [18]. Stage 1
Q1 turning OFF
Stage 2
Lp
Q1 OFF
Lp
C1 Ires
Ires Idc
Ds Cs
ICs
RL
Stage 4
Q1 ON
Lp
C1 Ires
Q2 turning OFF
ILoad
-
Stage 3
Q1 turning ON
Iout
+
C1
Q2 ON
Q2 turning ON
Ls
Idc Ires
Q2 OFF
Lp
ILoad
Ls
-
Ds Cs
C1
ICs
RL
+
Fig. 2. The stages of Mazzilli ZVS converter working principle.
Stage 4 has a similar process with the stage 2. When the MOSFET Q1 turns ON, and Q2 turns OFF, the oscillation occurs between the C1 and the Lp. The current flows from the Lp to the C1 and flows back to the Lp, followed by the rising and the falling of the Q2 drain voltage. During this process, the power is transferred from the Lp to the Ls. The voltage induced in the Ls has reversed polarity with that in stage 2. Therefore, the current cannot flow through diode the Ds. As a result, the load RL gets current by discharging the capacitor Cs. The stages 1 to 4 occur alternately following the oscillation of Lp and C1 as an LC circuit [18].
511
512
Dian Ahmad Hapidin et al. / Procedia Engineering 170 (2017) 509 – 515
2.3. Series-Configuration Design Figure 3 shows the configuration of the proposed HVPS design where the points 1, 2, and 3 refer to Figure 1. The design combined two Mazzilli ZVS circuits where each CRT flyback was driven by single Mazzilli driver. The secondary windings of both flybacks were connected in series in which the point 2 of the first CRT flyback was connected to the point 3 of the second CRT flyback. The overall HV output was determined by the voltage difference between the output terminal of the first flyback (HVout) and the ground terminal of the second flyback. The HVout of the configuration was controlled by changing the input voltage provided by the variable voltage supply ranging from 12 to 35 V.
!
!
Fig. 3. The configuration of two flybacks with a series-connected output which is driven by double Mazzilli driver.
For HV displaying and calibrating purposes; the HVout was conditioned by an HV monitor circuit which is similar to the circuit used in Reference [20]. It works by reducing the HV output to only a few volts by placing a voltage divider circuit consisting of 10 G and 10 M resistors. For the calibration procedure, the output voltage of the monitor circuit was connected to the multimeter (Fluke, 8808A). For displaying the HVout value, the output voltage of HV monitor circuit was converted to digital data by the 10-bit internal ADC of Atmega8 microcontroller. The HVout value was then displayed on the LCD screen. The HVout value was high enough to trigger corona discharge which can lead to significant voltage losses. Therefore, the HV shield was applied to the flybacks and HV terminal using a material with high dielectric breakdown such as epoxy resin. 2.4. Needleless Electrospinning and Polymer Solution Preparation The designed HVPS was tested on the wire-spinneret needleless electrospinning apparatus as illustrated in Figure 4. The HVout was connected to the wire while the HV ground was connected to a rotating drum collector. The distance (d) between the wire and the collector was 12 cm. The polymer solution for needleless electrospinning process was prepared by adding polyvinyl acetate (PVAc) with a molecule weight of 500.000 g/mol to ethanol with the concentration of 9 wt%. The mixture was then stirred with a magnetic stirrer at room temperature until clear, viscous solution was obtained. The polymer solution was delivered to the wire by a solution feeder which could move in the horizontal track to keep the wire wet as the jets were formed. The solution jets were observed and recorded by a camera with 40 times magnification.
Fig. 4. The configuration of needleless electrospinning.
Dian Ahmad Hapidin et al. / Procedia Engineering 170 (2017) 509 – 515
3. Results and Discussion 3.1. HVPS Performance Test Figure 5 exhibits the gate and drain voltage waveforms of the Mazzilli ZVS converter for the input voltage of 11.69 V. The gate of the MOSFETs was switched alternately with the frequency of 34 kHz, which was lower than that calculated using Equation (1). The switching waveforms of this converter have neither a voltage spike nor a ringing as found in a conventional flyback converter in Reference [20]. This was an advantage of the Mazzilli converter because the voltage spike could cause gate breakdown and damage other components while the ringing could lead to EMI and induce false triggering. Gate 1
Voltage
Gate 2
Drain 1
Drain 2
Time (μs) Fig. 5. The voltage waveforms of the Mazzilli converter.
The output voltage of HVPS was adjusted by varying the input voltage of the converter, and the results are given in Figure 6(a). It was found that the single flyback can generate HV output voltage up to 34 kV. In the series-configuration flybacks, the output voltage of HVPS could be increased significantly by 98.41 % to be 67 kV. One must note that there is a forbidden input voltage (Vin) region which is lower than the gate voltage of the MOSFET. In this region, the MOSFETs were not switched because of insufficient gate voltage. Since the MOSFET used IRFP260, Vin must not be lower than 10 V. The forbidden region could be narrowed by choosing MOSFETs with lower gate voltages. However, there was a drawback of this action. As can be seen in Figure 5, the gate voltage did not completely fall to zero at “off” condition, but it was above zero originating from the opposing drain voltage plus a diode drop. In normal operation, this is not a serious issue. However, at a high-current and highvoltage operation, as MOSFET Rds-on increases fast, the high current induces a significant voltage on the drain during “on” condition. If this occurs, the “off” voltage on the gate may be very near or even above Vgate so that both MOSFETs will latch on. This case will cause the component overheat and failure since the current in the input inductor ramp up indefinitely [18].
(a)
(b)
HVout
HVout (kV)
Single Mazzilli: 2 Vout = 0.992*Vin – 0.661 | R = 0.999 Series Configuration Mazzilli: 2 Vout = 1.874*Vin + 0.819 | R = 0.998
FORBIDDEN Vin Region (Vin Vgate)
Single Series Configuration Mazzilli
Vin (V)
Time (s)
Fig. 6. (a) The relationship between the input and the output voltages of single and double flyback and (b) the output voltage stability test for double flyback.
513
514
Dian Ahmad Hapidin et al. / Procedia Engineering 170 (2017) 509 – 515
Figure 6(b) shows the HVPS output voltage stability test for the input voltages of 15 V, 20 V, and 25 V. The test was done by logging the HVPS output voltage every second for 5 minutes using the 10-bit internal ADC of Atmega8 microcontroller. This test was carried out to identify whether the output voltage has a tendency to increase or decrease over time. This was important because nanofibers membrane fabrication using electrospinning usually needs a long time. The figure therefore says that the HVPS has good output voltage consistency. 3.2. Needleless Electrospinning Test The designed HVPS was tested on the needleless electrospinning apparatus with PVAc solution. The jets formation on the wire was recorded by a camera with 40 times magnification and the collected electrospun fibers were captured by a microscope. The jets formation was initiated at 30 kV. The higher voltage applied to the apparatus would increase the number of jets which was formed along the wire. Figure 7(a) shows a jet formation on the wire segment at 50 kV. Furthermore, the fibers were formed well on the collector as confirmed by Figure 7(b). Therefore, the series-connected of Mazzilli ZVS flyback converter can be used as a HV source for the needleless electrospinning application. (a)
(b)
Jet
Fig. 7. (a) The formation of the jets during the needleless electrospinning test at 50 kV and (b) the microscope image of electrospun PPAc fiber on the collector.
4. Conclusion The high-voltage power supply (HVPS) using a series-connected Mazzilli ZVS flyback converter for needleless electrospinning application has been developed. The single Mazzilli converter could generate HV up to 34 kV and the seriesconnected configuration could increase HV by 98.41 % to be 67 kV. The performance test showed that the converter has good stability over time. The designed HVPS was tested to run needleless electrospinning process with a straight wire as the spinneret. The evaluation on the needleless electrospinning demonstrated that the HVPS is able to form polymer jets on the wire which was initiated at 30 kV. The microscope image of the electrospun fibers have showed that the nanofibers were formed well on the collector. Acknowledgement This research was financially supported by Directorate of Research and Community Engagement of Ministry of Research, Technology and Higher Education, the Republic of Indonesia under the University’s Excellence Research (PUPT) Grant in the fiscal year 2016. References [1] [2] [3] [4] [5] [6] [7] [8]
A. Rajak, M. M. Munir, M. Abdullah, Khairurrijal, Photocatalytic activities of electrospun TiO2/styrofoam composite nanofiber membrane in degradation of waste water, Mater. Sci. Forum 827 (2015) 7-12. A. Y. Nuryantini, D. Edikresnha, M. M. Munir, Khairurrijal, Electrospun polyvinylpyrrolidone as a carrier for leaves extracts of Anredera cordifolia (Ten.) steenis, Mater. Sci. Forum 827 (2015) 91-94. A. Rahma, M. M. Munir, Khairurrijal, A. Prasetyo, V. Suendo, H. Rachmawati, Intermolecular Interactions and the Release Pattern of Electrospun Curcumin-Polyvinyl(pyrrolidone) Fiber, Biol. Pharm. Bull. 39 (2016) 163-173. M. M. Munir, F. Iskandar, K. M. Yun, K. Okuyama, M. Abdullah, Optical and electrical properties of indium tin oxide nanofibers prepared by electrospinning, Nanotechnology 19 (2008) 145603. C. S. Kim, L. Bao, K. Okuyama, M. Shimada, H. Niinuma, Filtration efficiency of a fibrous filter for nanoparticles, J. Nanopart. Res. 8 (2006) 215-221. S. Ramakrishna, K. Fujihara, W. E. Teo, T. C. Lim, Z. Ma, An Introduction to Electrospinning and Nanofibers, World Scientific, Singapore, 2005. M. M. Munir, A. B. Suryamas, F. Iskandar, K. Okuyama, Scaling law on particle-to-fiber formation during electrospinning, Polymer 50 (2009) 49354943. M. M. Munir, F. Iskandar, Khairurrijal, K. Okuyama, High performance electrospinning system for fabricating highly uniform polymer nanofibers, Rev. Sci. Instrum. 80 (2009) 026106.
Dian Ahmad Hapidin et al. / Procedia Engineering 170 (2017) 509 – 515 [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21]
M. M. Munir, F. Iskandar, Khairurrijal, K. Okuyama, A constant-current electrospinning system for production of high quality nanofibers, Rev. Sci. Instrum. 79 (2008) 093904. A. Y. Nuryantini, M. M. Munir, M. P. Ekaputra, T. Suciati, Khairurrijal, Electrospinning of poly(vinyl alcohol)/chitosan via multi-nozzle spinneret and drum collector, Adv. Mater. Res. 896 (2014) 41-44. H. Niu, T. Lin, Fiber generators in needleless electrospinning, J. Nanomater. 2012 (2012) 725950. H. Niu, X. Wang, T. Lin, Needleless electrospinning: Influences of fibre generator geometry, J. Textile Inst. 103 (2012) 787-794. A. L. Yarin, E. Zussman, Upward needleless electrospinning of multiple nanofibers, Polymer 45 (2004) 2977-2980. W. J. Liu, H. F. Zhang, D. W. Li, C. Huang, X. Y. Jin, Study on needle and needleless electrospinning for nanofibers, Adv. Mater. Res. 750-752 (2013) 276-279. I. Bhattacharyya, M. C. Molaro, R. D. Braatz, G. C. Rutledge, Free surface electrospinning of aqueous polymer solutions from a wire electrode, Chem. Eng. J. 289 (2016) 203-211. Z. Zhiguo, Z. Lin, Analysis and design of isolated flyback voltage-multiplier converter for low-voltage input and high-voltage output applications, IET Power Electron. 6 (2013) 1100-1110. B. R. Lin, H. Y. Shih, ZVS converter with parallel connection in primary side and series connection in secondary side, IEEE T. Ind. Electron. 58 (2011) 1251-1258. S. L. McClusky, High Voltage Resonant Self-Tracking Current-Fed Converter, Master of Science, Faculty of California Polytechnic State University, California Polytechnic State University, San Luis Obispo, 2010. P. Davari, F. Zare, A. Ghosh, H. Akiyama, High-voltage modular power supply using parallel and series configurations of flyback converter for pulsed power applications, IEEE T. Plasma Sc. 40 (2012) 2578-2587. M. M. Munir, D. A. Hapidin, Khairurrijal, Designing of a high voltage power supply for electrospinning apparatus using a high voltage flyback transformer (HVFBT), Appl. Mech. Mater. 771 (2015) 145-148. B. R. Lin, B. R. Hou, Implementation of a series resonant converter with series-parallel connection, in Proc. 2011 6th IEEE Conf. Industrial Electronics and Applications, ICIEA 2011, 2011, pp. 1179-1184.
515
