Abstract-- This paper presents a specially designed power switching generator device that produces 4 types of waveforms; square-wave, sinusoidal PWM, quasi-sinewave or multilevel and high-frequency DC pulses with a total of 14 different distinctive characteristics. The generator is exceptionally a useful tool to the students and researchers that dedicate themselves primarily in power electronics areas which could simplifies their studies. The device is capable of generating the selected waveforms which can deliver a 30W maximum power into a particular load. It is highly useful in harmonics analysis of inverters, true RMS measurements, switching devices driving signals, high-frequency switching transformer designs and filtering components for selective harmonics elimination.

Index Terms—Power switching generator; harmonics analysis; driver signals; high-frequency switching transformer designs.

I. INTRODUCTION

ITH such interests in power electronics presently either in the research institutions and power industries, having

the right tool or equipment that suitable to perform the required function is vital in order to save the cost and time in the studies. There are widely available common function generators that normally used in electronic labs to produce sinewave, square-wave, triangular and saw-tooth waveforms. Using this kind of laboratory function generator to further extend the studies and analysis in power switching areas would be limited or even useless. Besides it cannot produce switching waveforms, the normal function generator also cannot deliver significant current and maintain its voltage to run a small load. By considering of the shortcomings to students and researchers that involved in the power electronics areas, it is highly necessary and useful to have another kind of special function generator that can produce basic switching waveforms with enough current and stable voltage suitable to power-up a relatively small load.

Rosnazri Ali is currently a PhD student in the School of Electrical Systems

Engineering, Universiti Malaysia Perlis, Malaysia (e-mail: rosnazri@unimap.edu.my).

I.Daut, T.M. Nizar, N.H. Baharudin and I. Misrun are all with the School of Electrical Systems Engineering, Universiti Malaysia Perlis, Malaysia.

Soib Taib is with the School of Electrical & Electronic Engineering, Universiti Sains Malaysia (USM), Malaysia (e-mail: soibtaib@eng.usm.my).

The Universal Power Switching Generator that was developed is quite simple equipment; implementing few circuits consist of an H-bridge inverter, voltage regulator and microcontroller with its dedicated programming firmware.

This designed generator could produce 4 types of output. First, is a square-wave with selectable duty ratios (DT) of 25%, 50%, 75% and 100%. Secondly, sinusoidal pulse-width modulation (SPWM) with selectable outputs of 3 pulses, 5 pulses, 7 pulses and 9 pulses. Thirdly, a quasi-sinewave or multilevel which can be chosen as 50Hz or 60Hz waveforms. Fourthly, the high-frequency (HF) DC pulses with selectable 10 kHz, 25 kHz, 50 kHz and 100 kHz waveforms. The generator is capable of delivering a maximum voltage of 40Vp-p and current of 1.5A through all the respective waveforms into a particular load which is equivalent to 30W of power. It is also has an amplitude adjust function which can be controlled to get desirable voltage output levels where 1 to 5-level multilevel inverter waveforms can be generated as intended.

As switch-mode power supplies and inverters are now becoming popular electronic products that dominated the consumers, the analysis of various shapes of switching waveforms is equally important to students and researchers. Voltage harmonics and current harmonics analysis can be done using the designed generator to determine the harmonic profiles of certain waveforms. Other applications include determination of average-responding RMS and true RMS multimeters, switching devices driving signals, high-frequency switching transformer designs and filtering components for selective harmonics elimination.

In this paper, the designed circuit of the generator to produce various switching waveforms is presented. The main circuit consists of a voltage regulator IC (LM350) with series biasing resistors connected to the adjustment terminal of the IC regulator to get different output voltages as the selection of the resistors is controlled by a microcontroller (PIC16F877). A set of program was written into the microcontroller to control the function of the respective resistors in correct sequence and control the MOSFETs of the bridge inverter in order to get the desirable switching waveforms [1]-[7].

II. METHODOLOGY

The block diagram of the designed generator is as shown in Fig. 1. The voltage regulator IC with biasing resistors is

Special Designed Universal Power Switching Generator Simplifies Power Electronics Studies

Rosnazri Ali, Ismail Daut, Soib Taib, T.M.Nizar T.Mansur, Nor Hanisah Baharudin, Irwanto Misrun

W

The 5th International Power Engineering and Optimization Conference (PEOCO2011), Shah Alam, Selangor, Malaysia : 6-7 June2011

978-1-4577-0353-9/11/$26.00 ©2011 IEEE 98978-1-4577-0354-6/11/$26.00 ©2011 IEEE

represented as the Programmable Adjustable Voltage Regulator block.

Fig. 1. Concept of the Universal Power Switching Generator

A. Design components of the voltage regulator

Fig. 2. Typical application of LM350.

Referring to the Fig. 2, the output voltage (Vo) is determined by,

21

2 )1(25.1 RIRR

VV ADJo ++= (1)

where R1 and R2 are the biasing resistors and IADJ is the adjustment terminal current which is normally less than 100uA.

For simplicity, an empirical formula is used to get the output voltage as required. R1 is chosen to be 120 Ω .

96

1202 +=

RVo (2)

Let’s consider that R2 consists of 4 identical resistors Ra, Rb,Rc, Rd with small signal transistors (T1, T2, T3 & T4) connected across them as indicated in Fig. 3. The purpose of the transistors is to switch the biasing resistors in sequence in order to generate 4 different voltage levels to the output. By applying (2) and consider that Ra = Rb = Rc =Rd = 560 Ω , then the output voltages (Vo) are shown in Table I.

Fig. 3. LM350 circuit with switching transistors.

TABLE ISELECTION OF OUTPUT VOLTAGES (VO)

T o ta l V oa b c d R 2 (O hm s) (V o lts )1 1 1 1 0 1 .310 1 1 1 560 7 .150 0 1 1 1120 12 .900 0 0 1 1680 18 .750 0 0 0 2240 24 .58

Log ic 0 - Low (0V )Log ic 1 - H igh (+5V )

Log ic

By applying logic signals to the base of transistors T1 ~ T4, the total resistance R2 that acts as the biasing resistant to the voltage regulator IC will change its value accordingly. Hence producing different output voltages (Vo) whereby providing direct supply to an H-bridge inverter and is necessary to generate quasi-sinewave or multilevel output function.

B. Microcontroller and H-Bridge Inverter Circuit

To generate the necessary logic signals and sequential controls for the voltage regulator IC and H-bridge inverter, a microcontroller PIC16F877A is used as the main controller. Fig. 4 shows the diagram of the circuit.

(30Volts)

R2 = Ra + Rb + Rc +Rd

99

Fig. 4. Microcontroller and bridge inverter circuit.

C. Simplified output functions of the generator Basically the functional control software that was

programmed into the microcontroller is as shown in Fig. 5. It was written to generate 4 types of waveform; square-wave, high-frequency DC pulses, sinusoidal pulse-width modulation and quasi-sinewave/multilevel.

Fig. 5. Functional control program in the microcontroller.

III. RESULTS

The complete circuit of designed switching generator was assembled into proto-boards as shown in Fig. 6. Excessive heat is expected to develop across the voltage regulator IC due to the potential difference of Vo and Vi, especially when the load current is around 1A. Therefore, an appropriate sizing of heat sink was installed to ensure adequate heat dissipation out of the IC so that the IC temperature is within its operating region.

Fig. 6. View of the prototype assembled into a box.

Fig. 7 shows the front view of the switching generator where the output is being displayed by an oscilloscope.

Fig. 7. Front view of the switching generator tested with an oscilloscope.

Fig. 8 displays the output waveform of the generator for the square-wave output with 25% duty cycle observed through an oscilloscope.

100

Fig. 8. Square-wave output with 25% DT.

Fig.9 shows the output waveform sample of high-frequency DC pulses similar to a 10kHz output.

Fig. 9. 10kHz high-frequency DC pulses output

The output waveform of the switching generator for an SPWM output is as shown in Fig. 10.

Fig. 10. 5-pulse SPWM output.

Fig. 11 shows the output voltage waveform of the multilevel / quasi-sinewave. It can be seen clearly the 5-step voltages that forming the waveform and the output is approximately similar to a sinewave.

Fig. 11. Waveform of the 50Hz multilevel / quasi-sinewave output.

All of the output waveforms produced by the Universal Power Switching Generator unit can be analyzed to determine their respective voltage and harmonic levels. As an example below, an analysis study of the multilevel / quasi-sinewave output waveform was taken using a power analyzer PM100 and the results are tabulated in Table II. All even harmonic values were too small and insignificant to be taken into account.

Vo = 13.84 Vrms Voltage THD = 10.81% 1st Harmonic (fundamental) Voltage = 13.762 Vrms

TABLE IIHARMONIC NUMBERS AND PERCENTAGE HARMONICS

Harmonic No. 3 5 7 9 11 13% 0.568 3.871 3.561 1.614 3.864 1.284

The harmonics spectrum of the output waveform is then plotted as depicted in Fig. 12 below.

Percentage Harmonics of the Voltage Output

0

1

2

3

4

5

3 5 7 9 11 13

Harmonic Numbers

% H

arm

onic

of

Fund

amen

tal

Fig. 12. Harmonics spectrum of the output waveform.

101

IV. CONCLUSION

A special power switching generator as a useful tool to students and researchers in the power electronics areas was designed and tested. It is proven that some of the unique features that are not available to an ordinary laboratory function generator in providing switching waveforms can be complemented by the use of the designed generator. The unit is performed to generate four types of switching waveforms, i.e. square-wave, SPWM, quasi-sinewave / multilevel and HF DC pulses. Nevertheless, these kinds of waveform are very important in power electronics studies and the device will certainly reduce the time taken and overall cost in constructing individual circuits to produce such desirable waveforms that need to be learned and analyzed.

V. REFERENCES

[1] MH Rashid, “Power Electronics Circuits, Devices and Applications”, 3rd

Ed.,Prentice-Hall, 2003, pp 406~430, pp 761~789. [2] SK Mazalan, “Design, Construct and Evaluate a Step-up Inverter using

High Frequency Switching Technique”, UG Thesis, Electrical Eng. Department 2008, Universiti Malaysia Perlis. pp 21~23.

[3] Ali, R.; Daut, I.; Taib, S.; Jamoshid, N.S.; , "A 5-level multilevel inverter using LM350 voltage regulator IC," Power Engineering and Optimization Conference (PEOCO), 2010 4th International , vol., no., pp.137-141, 23-24 June 2010.

[4] Khomfoi, S.; Aimsaard, C.; , "A 5-level cascaded hybrid multilevel inverter for interfacing with renewable energy resources," Electrical Engineering/Electronics, Computer, Telecommunications and Information Technology, 2009. ECTI-CON 2009. 6th International Conference on , vol.01, no., pp.284-287, 6-9 May 2009

[5] Ahmad, M.I.; Husin, Z.; Ahmad, R.B.; Rahim, H.A.; Abu Hassan, M.S.; Md Isa, M.N.; , "FPGA based control IC for multilevel inverter," Computer and Communication Engineering, 2008. ICCCE 2008. International Conference on , vol., no., pp.319-322, 13-15 May 2008

[6] Ali, R.; Daut, I.; Taib, S.; Jamoshid, N.S.; Razak, A.R.A.; , "Design of high-side MOSFET driver using discrete components for 24V operation," Power Engineering and Optimization Conference (PEOCO), 2010 4th International , vol., no., pp.132-136, 23-24 June 2010.

[7] LM350 datasheet.

VI. BIOGRAPHIES

Rosnazri Ali received his B.Eng.(Electrical) from Royal Melbourne Institute of Technology in 1988 and M.Sc.(Electrical) from Universiti Sains Malaysia in 2007. His major interest of researches includes renewable energy, energy efficient systems and power electronics.

Ismail Daut is presently a Professor and Deputy Vice Chancellor (Research and Innovation) Universiti Malaysia Perlis (UniMAP). His main research interests are energy conservation, renewable energy and electrical machines design.

102