Boost Converter and THD is Minimized using Trapped Filter

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International Journal of Advance Electrical and Electronics Engineering (IJAEEE)

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ISSN (Print): 2278-8948, Volume-3 Issue-4, 2014 13

Three phase Inverter is Driven by Buck- Boost Converter and THD is Minimized using Trapped Filter

1Rajesh B, ²Manjesh

Dept. of Electronic Science, Bangalore University, Bangalore, India Email: ¹[email protected], ²[email protected]

Abstract: The Buck Boost converter is a DC-DC power converter which has characteristics of both buck and boost converter and can be applied in both step up and step down applications. The system demands step up and step down voltages with a higher degree of dynamic response to either disturbance or control reference signal, the converter topology can be used. The industry attracts power electronic system to work under any faulty conditions, the researchers done good reforms in drastic change the scenario of these problems in power electronic systems. Immense research work has been carried out with three phase PWM inverter is referred as traditional inverter drive. In major issue all inverters produce harmonics. Harmonics are the additional current and voltages doesn’t contribute any mechanical force to the motors, instead it is simply dissipated as heat in the motor.

In industry most of the applications are motors as the load.

The generation of harmonics can be minimized using tapped LCL filter at the output of inverter. The total harmonic distortion (THD) with and without the buck- boost converter and filter is studied by simulation method presented in this paper.

Keywords: Non inverting Buck-Boost converter, LCL filter, THD, PWM inverter, Harmonics.

I. INTRODUCTION

The buck-boost is a popular non-isolated, non-inverting power stage topology, sometimes called a step-up/down power stage. Power supply designers choose the buck- boost power stage because the required output is non- inverted from the input voltage, and the output voltage can be either higher or lower than the input voltage. The three phase inverter drives are mainly developed to control the speed of the three phase induction motor, the three phase induction motor has been a work horse of the industries [1,2]. In most of the induction motor applications the speed of the motor is required to be controlled, this can be done by v/f control method. The controlling of harmonic distortion is limiting the current pulses. This is generally accomplished through the use of inductor coils, which may also be called reactors or chokes, on the input of the drive [3,4]. The major objective of this paper is to investigate and minimize the harmonic content produced by PWM inverter in electrical system. The harmonics are the unwanted currents or voltages that are multiples of the

fundamental frequencies overlap on the fundamental frequency, these Harmonics may cause cables to overheat, damaging their insulation [5]. In industrial applications Induction motors are widely used as the load, the harmonic content at the output of the inverter may heat the stator windings of the motor drastically reduce the life span of the induction motor, and also become noisy and torque oscillations in the rotor can lead to mechanical resonance and vibration [6].

Harmonic is defined as a sinusoidal component of a periodic wave having a frequency that is an integral multiple of the fundamental frequencies. The percentage of harmonics in a AC circuit output waveform is called THD (total harmonic distortion). THD is expressed as a percentage with respect to the value of fundamental current or voltage. A harmonic filter is a circuit used to block the content of different harmonic orders from coupling source to the load. The harmonics will affect to the low impedance devices [7]. Many of the harmonic filters designs are available today and it consists of parallel connected capacitor and inductor circuits to create a low impedance device. These filters will be considered as passive devices. The PWM inverters are the best choice to control the speed of the induction motor. The major disadvantage of using inverters and converters system produces harmonics. This reduces the life span of the induction motor, hence these harmonics are reduced or suppressed at the output of the PWM Inverter. Many techniques are employed to minimize the harmonics at the PWM inverter are Modulation techniques, different conduction modes, filters are widely used methods to suppress the harmonic content in the output of the inverter. The harmonic components are assumed to be in phase with the fundamental. The resulting wave shape will depend on the magnitude and the phase relation of each of the harmonic components.

The tapped LCL filter is used minimize the harmonic content of the output of the inverter drive [8].

II. SYSTEM DESIGN AND WORKING

A. Traditional Inverter Drive:

The Traditional inverter drive or PWM drive has 6 switches. The Fig.1 shows the circuit diagram of the traditional inverter drive. The IGBT’s are used as

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switches, gating signal to each switch is provided through a pulse generator. Each phase is120⁰ out of phase with each other. The S-3 is turned on with a phase delay of 120⁰ with respect S-1, similarly S-5 is tuned on with a phase delay of 120° with respect S-3. The switches S-1,3,5 are the upper switches and switches S- 2,4,6 are the lower switches. A dead time is provided between upper and lower IGBT’s to avoid short circuit, at any instant of time no two switches in the same leg can be ON. The switching pattern of the switches are ON, one from the lower group and two from the upper group or one from the upper group and two from the lower group are ON. This produces a three phase output power used to drive the load. The Load RLC-1,2,3 are of the values R=11Ω and L=47mH.The input resistor R=0.1Ω, C1=1000 µF. V_in=200V.

Fig 1: Traditional inverter drive with RL Load B. Traditional inverter drive with Buck-Boost converter and Tapped LCL filter:

The Buck-Boost non inverting converter Circuit is as shown in Fig.2. In Fig.2 the two MOSFET’s M1 and M2 are used to control the buck and boost operations respectively. By recording the voltage at the input using at VM1, the voltage is fed to a subsystem where it determines the pulse width for buck and boost operation depending on the operation required for both the MOSFET’s receive the signals and the buck or boost operation is achieved.

Fig 2: Non inverting Buck-Boost converter

The inverter Positive is connected at the positive of the capacitor and Ground is connected at the negative. The inverter circuit consists of a filter in between the load.

The Fig.3 shows the circuit diagram of the inverter with filter.

Fig 3: Traditional inverter with tapped LCL filter The values of L1=L2=L3=L4=L5=L6=18mH, C1=C2=C3=1000µF, R1=R2=R3=50Ω, CC=1mF, RLC1=RLC2=RLC3=11 Ω, 1000 µF. The filter is connected in between the phases hence called as tapped LCL filter. A resistance of 50Ω is connected after the capacitor to provide the voltage stability required for the load.

III. RESULTS

The simulation of the above circuit has been carried out in this paper. The results are obtained after repetitive trials and various values to all the elements. The Fig.4 shows the line to line voltage wave form of a traditional inverter drive.

Fig 4: Line to line voltage wave form of Traditional Inverter Drive

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Fig 5: Harmonics plot of Line to Line voltage of Traditional inverter drive

The Fig.5 shows the plot of harmonics of line to line voltage of traditional inverter drive. The Fig.6 show that the wave is more sinusoidal than the square wave output of the line to line voltage with filter and buck boost converter.

Fig 6: Line to line voltage waveform of Traditional inverter drive with buck boost converter and tapped

LCL filter.

The harmonics plot of line to line voltage of traditional inverter drive with buck boost converter with tapped LCL filter is as shown in Fig.7.

Fig 7: Harmonics plot of line to line voltage of Traditional inverter drive with buck boost converter and

tapped LCL filter.

The THD of traditional inverter drive without filter and with Buck Boost converter and tapped filter is tabulated as shown in Table.1.

Table 1: THD in percentage with and without filter

Filter THD in %

Without filter 31.04

With buck boost converter and tapped

filter

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IV. CONCLUSION

The study of Harmonics and its THD of Traditional Three phase PWM Inverter has been simulated. The percentage of Harmonics present at the output of the inverter drive is obtained. A tapped filter is designed to eliminate the dominant lower order harmonics at the output of the inverter and studied its THD at the output of the Three Phase PWM inverter and the result obtained with and without tapped filter. The results have been compared and it is found that the THD using tapped filter used at the output of the three phase PWM inverter along with buck boost converter is found to be less as shown in the results.

REFERENCES

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Bidirectional Positive Buck-Boost Converter". In Proceedings EPE-PEMC -13th International Conference on Power Electronics and Motion Control,Poznan,Poland.

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[3] Ying-Tung Hsiao,” Design of Filters for Reducing Harmonic Distortion and Correcting Power Factor in Industrial Distribution Systems.”

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[5] M. A. Latif1, M. J. Alam2, M. A. Rashid*3, A.

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Microcontroller based PWM Inverter for Speed Control of a Three Phase Induction Motor.” M.

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[6] Jaw-Kuen Shiau and Chien-Wei Ma, "Li-Ion Battery Charging with a Buck-Boost Power Converter for a Solar Powered Battery Management System"Energies 2013, 6,1669- 1699;doi:10.3390/en6031669

[7] Khandker Tawfique Ahmed, Mithun Datta, Nur Mohammad,"A Novel Two Switch Non-inverting Buck-Boost Converter based Maximum Power

Point Tracking System"International Journal of Electrical and Computer Engineering (IJECE) Vol. 3, No. 4, August 2013, pp. 467~477.

[8] Swetha.S.G, Nagabhushan Patil,"Design of DC Link Filter and Inverter Output Filter for Induction Motor Drive System", International Journal of Engineering Science Invention, Volume 2 Issue 1, January. 2013,PP.06-12.

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