ANDROID BASED KIT TO GENERATE PWM SIGNALS FOR DC-DC CONVERTERS CONTROL

Laio Oriel Seman1, Cleiton Gili2, Luiz Carlos Gili3, Adriano Péres4, Romeu Hausmann5 Department of electrical engineering and telecommunications, University of Blumenau, Blumenau, Brazil

laioseman@gmail.com1, cgili@furb.br2, luizcarlosgili@gmail.com3, aperes.furb@gmail.com4, romeuh@furb.br5

Abstract – Lessons in the classroom cannot often give sufficient time to teach students the necessary practice for learning. Towards this lack of time, a kit that can generate pulses for different dc-dc converter is made in order to facilitate learning and help the teacher. And it will be better if this kit is controlled by an Android device communicating with a computer. This can take the students' attention by the use of modern tools that are used in their day-to-day, all through USB (Universal Serial Bus) communication, present on most computers produced in the last 10 years. In the study all the required steps to build the kit are shown, divided into three stages, hardware, firmware and software.

Keywords - dc-dc converters, educational, pwm,

android

I. INTRODUCTION

Learning in static converters is critical for students of Electrical Engineering [1] [3]. An important tool to assist this learning is the realization of practical activities involving the various converter topologies [2] [4] [5].

The greatest difficulty found in static converters is generating the switch control signal, since each structure converter has specific features for controlling its semiconductors. The development of a platform that can bring convenience to assist teachers in the classroom to demonstrate the operation of static converters is an interesting contribution, if the cost is low.

This paper presents the study and implementation of a kit to generate control signals for some topologies of DC-DC converters in open-loop, since current and voltage feedback are needed for a complete closed-loop implementation of the converter. Proposed kit [6][7] was equipped with a cellphone with Android operating system and also a connectivity kit using a PIC18F4550 microcontroller model to connect through a USB interface server.

II. ANDROID

Nowadays Android systems are present in most tablets and smartphones. It is an interesting choice to bring the portability kit, so each user can have the software installed on his/her own device [8].

Android is an operating system based on Linux. It was designed primarily for touchscreen mobile devices, for example smartphones and tablet computers. Initially developed by Android, Inc., it was financed at the beginning by Google, and later bought in 2005. Android was created in 2007, with the founding of the Open Handset Alliance: a consortium of hardware, software, and telecommunication

companies dedicated to creating open standards for mobile devices.

Android is open source and it is under the Apache License. This open source code and permissive licensing permits the software to be freely modified and distributed by device manufacturers, wireless carriers and any developers. The source has a big community of developers writing applications that enhance the functionality of devices, written in a customized version of the Java language [9].

III. CONNECTIVITY

The interface kit connects a computer with dc-dc converter, as show in Fig. 1. A software written in Python serving as host on a computer to which the kit is connected. That’s possible to send commands to Android device via UDP (User Datagram Protocol).

The computer serves as an intermediary between a portable device, that can connect to it by local and remote network (internet) and the kit. Thus the control of converters is possible even at great distances.

Fig. 1. Interface kit

IV. HARDWARE

The entire kit concept is based on the generation of PWM command signals. To generate these pulses a PIC18F4550 microcontroller from Microchip was chosen [10].

The choice was mainly due to its low cost, and its special PWM modules with predefined internal registers to control Half-Bridge and Full-Bridge and topologies, which aroused great interest in the development kit.

The chosen microcontroller also features full integration with USB (Universal Serial Bus), a communication interface widespread in the market, and available in basically all computers released in the last 10 years.

Access point Smartphone

Host Computer DC-DC ConverterInterface Kit

978-1-4799-0272-9/13/$31.00 ©2013 IEEE 748

The PWM signal generation occurs through special registers, related to a timer, so every time there is an overflow at defined time, a new pulse is generated.

Figure 2 shows the interface kit developed, which has the PCB board shown in Fig. 3. Also a schematic diagram is shown in Fig. 4.

The kit simply consists in a microcontroller PIC18F4550 connected to a female USB socket used as a communication way with the host computer. Also four pins are available to ICSP (in-circuit serial programming) if the firmware has to be changed.

Fig. 2. Interface kit Developed

Fig. 3. Kit PCB board.

Fig.4. Kit schematic diagram.

V. FIRMWARE

All firmware code was based on the example provided by the Microchip known as Microchip USB stack, and also the examples of independent developer Simon Inns [11].

All mathematical operations are handled by the software, due to the higher processing capacity of the computer. The microcontroller fits only the task of generating the PWM signals with the needed characteristics for the working of the converter.

Basically the firmware works stuck in an infinite loop, in which each new interaction is verified to check if any additional information was received through the USB interface. If there is new information this is handled by a specific routine.

The data received / transmitted via the USB packet may consist of up to 64 bytes. Thus it was decided that the first byte of a packet sets the type of action to be taken by the microcontroller, and subsequent bytes are the parameters of this action, as well as the PWM frequency, working time, etc.

VI. SOFTWARE

Considering the vast processing power of personal computers, it was chosen to perform processing tasks. Thus, the microcontroller is used as an interface between the Android device, the server and the DC-DC converter to be controlled.

The first generation of PWM mode is set to "Generic PWM", as shown in Fig. 5, where the user can set two pulses as active / inactive (independent), their frequency and duty

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cycles (which are the relationship betwpulse remains high within a period of tim

In this model the user has the freedomwithout the need to harness them to a conoverall functioning.

Fig. 5. Generic mode.

The second generation mode is set amain functions relate to changes in frequdead time, as shown in Fig. 6.

Fig. 6. Half-bridge mod

ween the time that a me). m to generate pulses nverter, to view their

as "half-bridge". The ency, duty cycle and

e.

Finally, the "full-bridge" muser, presented in Fig. 7. Heconverter must be consideredmotor, considering the four bring to the possibility of aperform acceleration acounterclockwise regime obraking in both directions.

Fig. 7. Ful

The ability to disable oneuser. It can be seen in Fig. 8.

Fig.8. Activate

mode brings more options to the ere not only the operation of the d, but also its use to drive a DC r quadrants. The four quadrants a motor full control, being able and both clockwise and operation, and also providing

ll-bridge mode.

e of the pins is also given to the

e/deactivate options.

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It is also given the ability to set certaiActive-High-Low, which raises the pomore converters can be triggered. Fig. 9 s

This definition refers to what happenoverflow, in which case the pin can go toequivalent to a NOT logical port.

Fig. 9. Active high/low opt

VII. EXPERIMENTAL RE

After the assembly of the kit as shotheir generation modes were tested. In Fshow the experimental results obtainedmode PWM frequency of 30 kHz with and 30%, while Figure 11 shown the samActive-Low option selected for P1A pin.

Fig. 10. Generic PWM tes

n pins as Active and ossibility that even shows this ability. ns in when the timer o level 1 or 0. This is

tions.

SULTS

own in Figure 2, all Figure 10, the pulses d by using Generic duty cycles of 80%

me configuration with

sted.

Fig. 11. Generic m

Full-bridge (Figure 12)converters to drive DC motodirection of rotation and Fig15 and 16 show acceleraoscilloscope in mean mode, of samples and plot the mepossible to verify the duty cy

Fig.12. Full bridge co

Fig. 13. Full-bridge

mode with Active-Low.

mode as used in chopper ors in shown in Figure 13 in one gure 14 in another. Also Figures ation and desaceleration using which capture a defined number

ean signal of them, this way is ycle increasing or decreasing.

onnection schematic [10].

e signal in one direction.

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Fig. 14. Full-bridge signal in another direction.

Fig. 15. Full-bridge acceleration mode.

Fig. 16. Full-bridge deceleration mode.

The half-bridge method configuration, present in Fig. 17, permits to generate command signals with or without the presence of dead time. In Fig. 18 and Fig. 19 are shown experimental results of the signals generated for controlling the half-bridge converter with and without dead time, respectively.

Fig. 173. Half-bridge connection schematic [10].

Fig. 184. Half-bridge signal without dead time.

Fig. 59. Half-bridge command with dead time.

Figure 20 shows half-bridge signal running with inverted signals for converters with current entrance.

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Fig.20. Inverted half-bridge signal.

VIII. CONCLUSION

During the study a survey was done on the Android operating system and its communication through the UDP protocol.

During the tests of the prototype was verified that the signals generated were consistent with the expected and necessary for the control of DC-DC converters.

As a suggestion for future works is the possibility of discarding the computer (server) as intermediary device, bluetooth or another near field communication protocol could resolve this issue.

Finally, the importance of sharing code was evident since the completion of this work would not have been possible without the collaboration of independent developers who provided their code for free over the Internet.

REFERENCES

[1] I. Barbi, D. C. Martins. Eletrônica de potência - Conversores CC -CC básicos não isolados. Edição dos autores, Florianópolis, 2000.

[2] C. A. Canesin, F. A. S. Gonçalves, L. P. Sampaio, “Simulation Tools for Power Electronics Courses Based on Java Technologies”, IEEE Transactions on Education, vol. 53, no. 4, pp. 580-586, Nov. 2010.

[3] J.A. Pomilio; C.A. Canesin; F. L. M. Antunes; F. S. dos Reis; L. P. Sampaio, "Power electronics courses for the new paradigms of the electrical system", Power Electronics Conference (COBEP), 2011 Brazilian , vol., no., pp.1027,1031, 11-15 Sept. 2011

[4] L. P. Sampaio; M. A. G. de Brito; G. A. de Melo; C.A. Canesin, "Power Electronics course: Analysis and evaluation of the educational software and the environment learning", Power Electronics Conference (COBEP), 2011 Brazilian , vol., no., pp.1044,1049, 11-15 Sept. 2011

[5] F. A. S. Gonçalves; C. A. Canesin; L. P. Sampaio, "Interactive DC-DC converters tools for instant design and education", Power Electronics Conference, 2009. COBEP '09. Brazilian, vol., no., pp.1074, 1081, Sept. 27 2009-Oct.

[6] L. O. Seman, R. Hausmann, C. Gili, L. C. Gili. “Kit experimental de conversores CC-CC controlados através de interface USB utilizando software livre sob GPLv3”, In: VIII International Conference on Engineering and Computer Education - ICECE '2013.

[7] C. Gili, A. Péres, S. V. G. Oliveira. Plataforma experimental para o ensino de eletrônica de potência. In: 39º Congresso Brasileiro de Educação na Engenharia - COBENGE, 2011, Blumenau.

[8] GOOGLE Inc.. Android development website. Available on: <http://developer.android.com/>.

[9] WIKIPEDIA the Free Encyclopedia. Available on: <http://en.wikipedia.org/wiki/Android_(operating_system) >.

[10] MICROCHIP TECHNOLOGY Inc.. PIC18F4450 datasheet. Available on: <http://ww1.microchip.com/downloads/en/devicedoc/39632c.pdf>.

[11] INNS, S. Personal web site. Available on: < http://www.waitingforfriday.com>.

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