IJBSTR RESEARCH PAPER VOL-1[ISSUE 5] MAY 2013
ISSN- 2320-6020
Performance Analysis of three phase SPWM Inverter Vinod Kr Singh Patel and A. K. Pandey ABSTRACT: This paper deals with study of a Sinusoidal Pulse Width Modulated Inverter and all the parameters used to reduce the harmonics and give the good efficiency of the inverter. The paper will be commenced by a basic understanding of the circuitry of the SPWM Inverter, the components used in its design and the reason for choosing such components in this circuitry. Generally, only single phase SPWM inverters are used industrially, and certain instabilities have been found in their operation. With improper selection of system parameters, the inverter suffers different type of instabilities and many types of harmonics. Our attempt will be to observe the same for three phase SPWM inverter and analyze its parameters used to get a pure sinusoidal output waveform and fewer harmonic in its output current and voltage waveform. It will be attempted to simulate a model circuit on any simulating software e.g. MATLAB and analyze the output waveforms for various values of the elements used in the circuit and hence observe the waveform distortion. KEYWORDS: SPWM, three phase inverter, total harmonic distortion.
1.
Introduction
What if we cannot use the stored power in a battery when we don’t have power supply. Since the energy stored in a battery is in dc form so to use this stored power in battery we need to convert this dc form of energy to ac form. So here comes the concept of power inverters. The devices which can convert electrical energy of DC form into AC form is known as power inverters. They come in all sizes and shapes, from a high power rating to a very low power rating, from low power functions like powering a car radio to that of backing up a building in case of power outage. Inverters can come in many different varieties, differing in power, efficiency, price and purpose. The purpose of a DC/AC power inverter is typically to take DC power supplied by a battery, such as a 12 volt car battery, and transform it into a 120 volt AC power source operating at 60 Hz, emulating the power available at an ordinary household electrical outlet. DC-AC inverters have been widely used in industrial applications such as uninterruptible power supplies, static frequency changes and AC motor drives. Recently, the inverters are also playing important roles in renewable energy applications as they are used to link a photovoltaic or wind system to a power grid. Like DC-DC converters, the DC-AC inverters usually operate in a pulse width modulated (PWM) way and switch between a few different circuit topologies, which means that the inverter is a nonlinear, specifically piecewise smooth system. In addition, the control strategies used in the inverters are also similar to those in DC-DC converters. For instance, current-mode control and voltagemode control are usually employed in practical applications. vinod Kr Singh Patel and A.K.Pandey DEPARTMENT OF ELECTRICAL ENGINEERING M.M.M. ENGINEERING COLLEGE, GORAKHPUR (U.P.) vinod.akg121@gmail.com, akp1234@gmail.com RESEARCH SCHOLAR (ELECTRICAL ENGINEERING, M.M.M. ENGINEERING COLLEGE)
In the last decade, studies of complex behavior in switching power converters have gained increasingly more attention from both the academic community and industry. Various kinds of nonlinear phenomena, such as bifurcation, chaos, border collision and coexisting attractors, have been revealed. Previous work has mainly focused on DC power supply systems including DC-DC converters and AC-DC power factor correction (PFC) converters. 2.
Pulse Width Modulation control
The Pulse Width Modulation (PWM) is a technique which is characterized by the generation of constant amplitude pulse by modulating the pulse duration by modulating the duty cycle. Analog PWM control requires the generation of both reference and carrier signals that are feed into the comparator and based on some logical output, the final output is generated. The reference signal is the desired signal output maybe sinusoidal or square wave, while the carrier signal is either a sawtooth or triangular wave at a frequency significantly greater than the reference [1, 2]. The advantages of PWM control are: 1. No additional components are required with this method. 2. Lower order harmonics are eliminated or minimised along with its output voltage control. Hence, the filtering requirements are minimised since higher order harmonics can be filtered easily. Different schemes of pulse-width modulation: 1. Single-pulse modulation 2. Multi-pulse modulation 3. Sinusoidal-pulse modulation 2.1 Single Pulse Width Modulation: In this modulation there is an only one output pulse per half cycle. The output is
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IJBSTR RESEARCH PAPER VOL-1[ISSUE 5] MAY 2013
ISSN- 2320-6020
changed by varying the width of the pulses. The gating signals are generated by comparing a rectangular reference with a triangular reference. The frequency of the two signals is nearly equal.
Fig1: Single Pulse Width Modulation The rms ac output voltage
Where ď ¤ď€ =duty cycle=
đ?‘Ąđ?‘Ą đ?‘œđ?‘œđ?‘œđ?‘œ đ?‘‡đ?‘‡đ?‘ đ?‘
Modulation Index (MI) =
đ?‘‰đ?‘‰đ?‘&#x;đ?‘&#x;
Fig2: Sinusoidal Pulse Width Modulation
đ?‘‰đ?‘‰đ?‘?đ?‘? Where Vr = Reverence signal voltage Vc = Carrier signal voltage By varying the control signal amplitude Vr from 0 to Vc the pulse width ton can be modified from 0 secs to T/2 secs and the rms output voltage Vo from 0 to Vs. 2.2 Sinusoidal Pulse Width Modulation: In this modulation technique are multiple numbers of Output pulse per half cycle and pulses are of different width. The width of each pulse is varying in proportion to the amplitude of a sine wave evaluated at the center of the same pulse. The gating signals are generated by comparing a sinusoidal reference with a high frequency triangular signal [1,5]. The rms ac output voltage
Where p=number of pulses and δ= pulse width
2.3 Features for comparing various PWM Techniques: • Switching Losses • Utilization of Dc power supply that is to deliver a higher output voltage with the same DC supply. • Linearity in voltage and current control. • Harmonics contents in the voltage and current. 3. Three Phase Inverters: Three phase inverters are generally used for high power applications. Three single phase half bridge inverters are to be connected in parallel to form a three phase inverter. The inverter is fed by a fixed dc voltage and has three phase-legs each comprising two transistors and two diodes. With SPWM control, the controllable switches of the inverter are controlled by comparison of a sinusoidal control signal and a triangular switching signal. The sinusoidal control waveform determines the desired fundamental frequency of the inverter output, while the triangular waveform decides the switching frequency of the inverter. The ratio of the frequencies of the triangle wave to the sinusoid is referred to as the modulation frequency ratio [2, 4].
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IJBSTR RESEARCH PAPER VOL-1[ISSUE 5] MAY 2013
ISSN- 2320-6020
Fig4: Square Wave Inverter Output 3.1.2. Modified Square Wave Inverter: A modified sine wave inverter actually has a waveform More like a square wave, but with an extra step or so. Because the modified sine wave is noisier and rougher than a pure sine wave, clocks and timers may run faster or not work at all. A modified sine wave inverter will work fine with most equipment, although the efficiency or power will be reduced with some. But with most of the household appliances it works well.
Fig5: Modified Square Wave Inverter Output 3.1.3 True Sine Wave Inverter: This type of inverter provides output voltage waveform which is very similar to the voltage waveform that is received from the Grid. The sine wave has very little harmonic distortion resulting in a very „clean‟ supply and makes it ideal for running electronic systems such as computers, digital fx racks and other sensitive equipment without causing problems or noise. Things like mains battery chargers also run better on pure sine wave converters.
Fig 3: Basic Circuitry of a three phase inverter
3.1 Inverter Types: There are generally three types of inverter for general purpose. • Square Wave Inverter • Modified Square Wave Inverter • True Sine Wave Inverter 3.1.1. Square Wave Inverter: This is the basic type of inverter. Its output is a alternating square wave. The harmonic content in this wave is very large. This inverter is not efficient and can give Serious damage to some of the electronic equipment. But due to low cost, it has some limited number of applications in household appliances.
Fig6: True Sine Wave Inverter Benefits of using True Sine Wave Inverter: • Most of the electrical and electronic equipments are designed for the sine wave.
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IJBSTR RESEARCH PAPER VOL-1[ISSUE 5] MAY 2013 • • •
ISSN- 2320-6020
Some appliances such as variable motor, refrigerator, microwave will not be able to provide Rated output without sine wave. Electronic clocks are designed for the sine wave. Harmonic content is less.
4. SIMULATION RESULTS With the help of the designed circuit parameters,the MATLAB simulation is done and results arepresented here. The waveforms of theline voltage are shown in Fig.6. It can beseen that the phasor voltages are displaced by 120°.The stator current waveforms are shown in Fig 7.They are quasi sinusoidal in shape and displaced by120°. The waveforms of THD analysis of voltage and current are shown in fig-7.
Fig8: Subsystem of SPWM generator
Fig7: SPWM BASED INVERTER
Fig9: switching signal of SPWM generator
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IJBSTR RESEARCH PAPER VOL-1[ISSUE 5] MAY 2013
ISSN- 2320-6020
Fig12: Line voltage Vca
Fig10: Line voltage Vab
Fig13: phase current Ia
Fig11: Line voltage Vbc
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IJBSTR RESEARCH PAPER VOL-1[ISSUE 5] MAY 2013
ISSN- 2320-6020
Fig16:THD Analysis of Line voltage Vab
Fig14: phase current Ib
Fig17: THD Analysis of phase current Ia
Fig15: phase current Ic
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IJBSTR RESEARCH PAPER VOL-1[ISSUE 5] MAY 2013
ISSN- 2320-6020
5. Conclusion This paper deals with the analysis of Three Phase Sinusoidal Pulse Width Modulation (SPWM)-VSI. It includes simple SPWM-VSI. The Simulink model for simple inverter has been simulated in MATLAB.It was found that for Simulation, the output current and voltage waveforms of the inverter were of the desired sinusoidal nature with expected amplitude and frequency. For the same simulation, the unfiltered voltage and IGBT/Diode current waveforms were of similar nature. In this paper we deal with the THD analysis of voltage and current and obtained THD 68.64% in voltage and 94.03% in current. 6. REFERENCES [1].M. Depenbrock, “Pulse width control of a three-phase inverter with non-sinusoidal phase voltage of a three-phase PWM inverter”, Proc. IEEE Int. semiconductor Power Conversion Conf., Orlando, Florida, USA, pp. 399-403, 1977. [2].A.M. Hava, “Carrier based PWM-VSI drives in the over modulation region”, PhD Thesis, University of WisconsinMedison, 1998. [3]. J.A. Houdsworth and D.A. Grant, “The use of harmonic distortion to increase output voltage of a three-phase PWM inverter”, IEEE Trans. Industry Appl., vol. IA-20, pp. 11241228, Sept./Oct. 1984.
[4]. Maswood. Ali.I & Al-Ammar. Essam "Analysis of a PWM Voltage Source Inverter with PIController under Nonideal conditions" International Power Engineering Conference-IPEC, 2010. [5]. Lin.W.Song & Huang.I.Bau “Harmonic Reduction in Inverters by Use of Sinusoidal Pulse WidthModulation” IEEE Transactions on Industrial Electronics - IEEE TRANS IND ELECTRON , vol.IECI-27, no. 3, pp. 201-207, 1980.
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