2015 17th UKSIM-AMSS International Conference on Modelling and Simulation
Design & Implementation of Single Phase Pure Sine Wave Inverter Using Multivibrator IC Meraj Hasan*, Junaid Maqsood*, Mirza Qutab Baig*, Syed Murtaza Ali Shah Bukhari*, Salman Ahmed** *Department of Electrical Engineering, Bahria University Islamabad, Pakistan **Sarhad University of Science and Information Technology, Peshawar, Pakistan
[email protected] to work properly and the energy be used efficiently, Pure Sine Wave Invertors are used the produce a pure sine wave at the output for the load [3], [4], [5], [6].
Abstract— Pure sine wave inverters are demand of modern era whenever it comes to utilization of DC power sources for both low and high power applications. These invertors not only increase the efficiency of the power system but also prevent the electrical components from damaging. Research has been carried out on producing cost-effective and efficient pure sine wave inverter in recent times and this paper proposes a design that is highly useful for low power based applications. Paper focuses on utilizing renewable solar energy by incorporating Multi vibrator IC (NE 555), in this case operating in A-stable mode, for the PWM generation technique used to drive pure sine wave inverter. It is shown that the design is easy to implement and proves to be cost effective for low power applications.
In [3] a low cost RISC Microcontroller (MC) PIC 16f877 is used that supports 20MHz clock input. At the output of the Pulse Width Modulation (PWM) generated by the MC a filter has been connected to make the square wave a sinusoid and to remove some of the harmonics. The PWM topology, as discussed in [3], is a 4 kHz signal that has a positive amplitude for the positive half cycle of the sine wave (50Hz) and a negative amplitude for the negative cycle. At the output of the MOSFET Bridge, we obtain a Sinusoidal PWM (SPWM). This paper includes mathematical analysis of PWM topology and the corresponding filter design. Further in the paper, there are discussed two methods for sustaining heavier loads: varying the PWM cycles and replacing the P-Channel MOSFETs with N-Channel MOSFETs.
Keywords—PWM; inverter; renewable energy; 555 Timer IC; H-Bridge; TLP 250; L-C Circuit; Harmonics
I. INTRODUCTION With an aim to cater energy needs of modern era, distributed systems address power concerns including backup power systems and power quality issues [1]. Pure Sine Wave Inverter is one of the most recognizable technologies that has been utilized by both industrial and private sectors in Distributed Power Generation (DG) Systems [2]. DG Systems are normally assisted by Photovoltaic (PV) systems and fuel cells on small scale [2]. Most of our present electrical systems are working on AC, therefore PV energies are first to be converted into AC to make them suitable for our regular loads or to connect it to grid [1]. In case of power back-up systems, which require batteries as a source, inverter topology is an integral block to be implemented with the system.
In [4] PIC 18F4431 MC is used for the PWM generation, PWM counting and isosceles triangular wave generation. Unlike [1], in [4] triangular wave is used that, for the sinusoidal reference wave, has positive and negative peaks both. Block diagram of this technique has been shown in Figure 1. The SPWM generated at the output of 20 kHz frequency has to experience an LC filter attached parallel to the load, that attenuates the PWM and in-turn produces a pure sine wave.
PWM pulse from PIC18F4431
Various realization techniques of Pure Sine Wave Inverters have been presented [9] and with the ever advancing technology these techniques are improving on daily basis. Most of the inverters which are available commercially and incorporated in UPS (Uninterruptible Power Supplies) are mostly square wave inverters or quasi square wave inverters which are not suitable for sophisticated electrical devices and equipment in daily use due to their output waveform which constitute of undesirable harmonics [3].
Optocoupler isolation circuit DC input (PV Array)
Switch Mode Power Supply
Full Bridge Inverter
Filter II. LITERATURE REVIEW The regulated square wave is not beneficial for the appliances as it may harm them, therefore for the appliances 978-1-4799-8713-9/15 $31.00 © 2015 IEEE DOI 10.1109/UKSim.2015.58
Fig 1: Proposed Model Realization
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Load
In [5] PIC 16F876 Microcontroller (MC) is used for controlling the switching pattern. With the objective to make cost effective yet reduced Total Harmonic Distortion (TDH) pure sine wave inverter, [5] has integrated a buck convertor to step up the voltages produced by the Photovoltaic (PV) Panels as shown in Figure 2. A low cost and low frequency transformer has been used for better performances and an extra Aluminum shield has been used above the surface of the transformer to further reduce the eddy currents. In [5], a ratio, MA (amplitude Modulation), between the reference sinusoidal signal and the full triangular wave has been kept around 0.8 to 0.9 for the best design of the filter used.
Battery
Microcontroller PIC16F73
Totem Pole
FeedBack MOSFETS
Transformers
PV array
DC-DC Converter
DC-AC INVERTER
LC Filter
Transformer Filtering
MOSFET Driver
Output AC
Figure 4: Block Diagram of Proposed Solution
Literature [11] has explained the generation of Sinusoidal Pulse Width Modulation (SPWM) to create a Pure Sine inverter with integration of a Proportional Integral (PI) controller on simulation. The PI controller takes in the error voltage (difference voltage between load output and reference signal) as input and enforces the error to get minimized by regulating the inputs (switching frequency and pulse width).
Microcontroller generating SPWM Signal Fig 2: Block Diagram of Proposed Solution
Unlike [3], [4], [5], paper [6] has used Atmel AT 89C2051 – 24 PI Microcontroller for PWM and SPWM generation. After the SPWM generation, the output is made a pure sine wave, after passing it through an LC Filter. Isolation and driver circuits have been used in [6] to protect the switching circuitry and to drive the MOSFETs as shown in Figure 3.
Using Maximum Power Point Tracking (MPPT), Perturb and Observe (P&O) algorithm is another unique addition as implemented in [12]. The literature has simulated PV module followed by MPPT block to maximize the power obtained from PV module. Further a boost converter has been used which uses the net change in duty cycle obtained from MPPT calculations. Figure 5 shows the proposed solution as mentioned in [12]
UC Circuit Vin Isolation Circuit Gate Driver
Inverter Circuit
DC-DC CONVERTER
PV ARRAY
DC-AC INVERTER
LC FILTER
TRANSFORM ER
LC Filter MPPT
MOSFET DRIVE OUTPUT AC
Vout
Transformer MICROCONTROLLER GENERATING SPWM SIGNAL
Fig 3: Proposed System Overview Figure 5: Block Diagram of Proposed Solution
Similar to literature [5], a PIC Microcontroller (PIC 16F73) has been used in [10] proposing a low cost and harmonics inverter applicable for low powered applications. Distinctively, a Sine look up table has been constructed that stores the sampling figures of sine wave. Figure 4 shows the proposed solution as mentioned in [10]
III. STRUCTURE OF PROPOSED WORK Literature view has been done on available solutions and techniques to implement the Pure Sine Wave Inverter. But all above products are not versatile enough and are not in everyone’s scope while catering low power applications.
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Pure Sine Inverter may have series of modules to design and they must be able to operate along-with competitive efficiency, cost, ease of implementation & use. Figure 6 shows the block diagram of proposed technique. H-Bridge Inverter
PV Pannel
external capacitor. When the voltage is applied, the external capacitor charges via Resistor R1 and R2. The discharge Pin (7) is linked to a transistor internally and externally connected to the junction of those two resistors. The frequency of operation of the astable circuit is dependent upon the values of R1, R2, and C. The frequency can be calculated with the formula:
Filter
f = 1 / (0.693 x C x (R1 + 2 x R2)) 555 Timer Ic
TLP 250
The time intervals for the OFF and ON cycles of the output can be varied using Resistors values R1 & R2. The percentage of time duration when the signal is active for one cycle to the total period is known as the duty-cycle. The duty-cycle can be calculated with the formula:
Load
Fig 6: Structure of Proposed Solution
A. 555 Timer IC The main objective of this paper is to produce sinusoidal waveform using multi-vibrator ICs. Therefore, the application has been realized using NE555 timer IC which is suitable for both mono-stable and astable applications. Like others ICs, the on-off time of this IC is also dependent on external capacitor. The capacitor (C) takes finite period of time to charge and discharge through resistor (R) which can be determined using R & C values using expression: t=RxC
(2)
D = (R1 + R2) / (R1 + 2R2)
(3)
Since our proposed system is for low power AC applications which run on frequency of 50 Hz, so we set the frequency of our system to 50 Hz with 50% of duty cycle being generated from 555 timer IC. B. H-Bridge In order to convert the DC input waveform to AC, DCAC converters are used which take DC voltage at input and provide AC output voltage and frequency as per desired design specifications.
(1)
One of the most common operational modes of this IC is its use as Astable multi-vibrator for varying duty cycle generation. Astable multi-vibrator is arrangement of bistable multi-vibrator to switch states periodically. Bistable multivibrator is connected with RC network in feedback loop to control the RC time constant [8]. In this mode, it simply acts as an oscillator generating a continuous waveform of rectangular ON-OFF pulses alternating between two voltage levels. The frequency and duty cycle can be set using Resistor (R) & capacitor (C) values. Figure 7 shows the operating configuration of NE555 Timer IC.
A typical DC-AC converter is known as H-Bridge which is most commonly used inverter for said purpose. This paper has presented Voltage Source Inverter (VSI) topology to implement pure sine wave inverter. The block diagram of HBridge circuit has been shown in Figure 8. Switching has been done in two groups. For generating one cycle, Q1 and Q4 are turned ON together. For generating negative cycle, Q3 and Q2 are turned ON together using PWM coming through NOT Gate.
Fig 7: NE555 Timer IC Configuration Fig 8: H-Bridge Inverter Circuit
The 555 is connected as an astable multi-vibrator. Trigger (pin 2) and Threshold (pin 6) to the two comparators are shorted together. Both pins are connected to
H-Bridge has different operation modes, which are based on quadrant operation; this paper utilized the bipolar technique. In this paper 4 quadrant drive is implemented.
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conversion part by Opto-coupler which is inbuilt in TLP 250. It provides protection to our control part from any high reverse current surges from H-Bridge converter. Figure 11 shows the simulation of the proposed system.
The advantage of bipolar PWM technique is that 555 Timer needs to generate only one PWM signal to drive our bridge. C. Gate Driver The MOSFETs incorporated in H-Bridge design do not run simply by applying control signals at their gate [3]. For MOSFETs, gate voltage requirement is higher than control signal magnitude that is coming from a controller or 555 Timer IC in our case. Therefore, to provide suitable signal to drive MOSFET, it is needed to connect gate driver IC between our control signals. In our paper, TLP 250 drive IC [10] has been used to drive MOSFET. The great feature of this IC is that it provides two features in one IC; Optoisolator plus Gate Driver feature. Figure 9 shows the IC working configuration.
Fig 11: Proposed System Realization
DC input from PV Panel is fed to the power rail of HBridge Inverter which needs to be turned down to AC. The MOSFETs in H-bridges are driven using pulses coming from 555 Timer IC through TLP 250 and the switching combination produces alternating waveform of DC rail at HBridge output terminals.
Fig 9: TLP 250 Driver IC Configuration
This waveform is not pure sinusoid, therefore, filter needs to be applied to obtain pure sinusoid waveform at its output.
D. Filter In design of Sine Waver Inverter, there are harmonics produced in output waveform caused by semiconductor switching. For harmonics reduction, a Chebyshev Low Pass filter is implemented [12]. A 7th order LCL filter as shown in figure 10 is implemented for harmonics reduction which will produce pure sinusoid waveform. Cut off frequency is one of the important parameter of filter design which should be half of the switching frequency of our H-Bridge inverter for filter having adequate attenuation in switching frequency range. [7]
IV. RESULTS Figure 12 shows the pulses that are supplied at MOSFETs’ gates and the output filtered waveform. The simulation results show that output of H-Bridge inverter (Channel C) is being filtered to an extent where pure sinusoid waveform is obtained (Channel D). Same has been observed in practical realization of inverter, that is, the waveform at the output of H-Bridge is not pure sinusoidal infact a triangular wave is obtained from bridge output. This triangular waveform is then turned into pure sinusoidal waveform using the filter.
Fig 10: Filter Realization
E. Proposed System Realization The proposed system has two main parts. One is power processing side and other one is control side. Power processing side contains the H-Bridge Inverter while the control side contains the 555 Timer IC and Gate Driver TLP 250. The control part is electrically isolated from power
Fig 12: Simulation Results of Proposed System
Waveforms of practical realization of sine wave inverter have been shown in Figure 13. The figure shows the
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Conference on Applied Power Electronics and Expostion, 2009, pp. 889-893 [3] A.Ali Qazalbash, Awais Amin, Abdul Manan and Mahveen Khalid “Design and Implementation of Microcontroller based PWM technique for Sine wave Inverter,” International Conference on Power Engineering, Energy & Electrical Drives, 2009. [4] Rafid Haider, Rajin Alam, Nafisa Binte Yousuf, Khosru M. Salim, “Design and Construction of Single Phase Pure Sine Wave Inverter for Photovoltaic Application,” International Conference on Informatics, Electronics & Vision (ICIEV), 2012. [5] Ahmed Sony Kamal Chowdhury, M. Shamir Shehab, M. Abdul Awal, M. Abdur Razzak, “Design and Implementation of a Highly Efficient Pure Sine-Wave Inverter for Photovoltaic Applications,” International Conference on Informatics, Electronics & Vision (ICIEV), 2013, pp. 1-6. [6] B. Ismail, S.Taib MIEEE, A. R Mohd Saad, M. Isa, C. M. Hadzer, “Development of a Single Phase SPWM Microcontroller-Based Inverter”, IEEE International Power and Energy Conference, 2006, pp. 437-440. [7] Jirri Lettl, Jan Bauer, Libor Linhart, “Comparison of Different Filter Types for Grid Connected Inverter”, Progress in Electromagnetics Research Symposium (PIERS), 2011, pp, 1426-1429 [8] Adel S. Sedra, Kenneth C. Smith, “Microelectronic Circuits”, 2004 [9] E.Koutroulis, J.Chatzakis, K.Kalaitzakis and N.C.Voulgaris, “A bidirectional, sinusoidal, high-frequency inverter design”, IEEE Proc.Electr. Power Appl., Vol. 148, No. 4, July 2001, pp. 315-318 [10] A. A. Mamun, M. F. Elahi, M. Quamruzzaman, M. U. Tomal, "Design and Implementation of Simgle Phase Inverter", International Journal of Science and Research (IJSR), Vol. 2, Issue 2, Febuary 2013. [11] Sandeep Phogat, "Analysis of Single Phase SPWM Inverter", International Journal of Science and Research (IJSR), Vol. 3, Issue 8, August 2014. [12] Sridhar Dandin, Dr. Ashwini Kumari, "Highly Efficicent Pure SineWave Inverter for Photovoltaic Applications with MPPT Technique", International Journal of Engineering Research and Technology (IJRET), Vol. 3, Issue 5, May 2014.
waveform that is being obtained at the output of bridge inverter which is close to sinusoid waveform.
Fig 13: Practical waveform at output of bridge inverter
V. FUTURE WORK & RECOMMENDATIONS The results shown are being carried out for an open loop system. So for a closed loop system, better results can be obtained by implementing appropriate feedback and control systems. Moreover, voltage can be regulated and inverter can be controlled more independently if we realize this design using Microcontroller and feedback control (closed loop inverter) especially for high power applications. VI. CONCLUSION A lot of work has been done in the field of Pure Sine Wave Inverter but to obtain a waveform with reduced number of harmonics along-with high efficiency is still an open challenge. There are techniques available to do so, but need is to adapt a solution which is easy to implement as well specifically for low power applications. This paper has discussed available techniques and tried to come up with a solution for low power applications which is easy to implement, cost efficient and reliable from consumers’ perspective. We have tried to come up with a design for low power applications which is cheap to realize. We plan to extend this work as mentioned in future work and present a better solution for low as well as high power applications. ACKNOWLEDGMENT On completion of this research, we would like to acknowledge efforts of our respected faculty member Sir Saad Ul Hasan with appreciation whose technical support in field of inverters was very valuable in conducting research and practical implementation of inverter.
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[2]
Krismadinata Chaniago, J. Selvaraj, N. A. Rahim, “Implementation of Single-Phase Grid Connected Inverter Using TMS320F2812,” 3rd IEEE Conference on Industrial Electronics and Application, 2008, pp. 1498-1502. Eunsoo Jung, Seung-ki Sul, “Implementation of Grid-connected Single Phase Inverter Based on FPGA”, 24th Annaul IEEE
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