SPACE VECTOR PWM FOR CONTROLLING AC MOTORS USING VARIABLE ...

SPACE VECTOR PWM FORCONTROLLING AC MOTORS USINGVARIABLE FREQUENCY DRIVE

B.Pragathi1, Dr.M.Suman2

1Research Scholar, 2Associate Professor,Department of ECE,

Koneru Lakshmaiah Education Foundation,Vaddeswaram, Guntur, A.P, [email protected]

[email protected]

July 11, 2018

Abstract

The variable frequency drive is used for the speed ad-justment of AC motors. Adjusting the frequency and con-trolling the voltage there by controlling the speed of motoris an abrupt task. A novel method is been considered forproducing the associated DC power for the motor opera-tion using solar PV system. The battery is used for storingthe power during day and to supply the power to the mo-tor even when the solar power is unavailable. Space vectorPWM methods are used for reducing the THD levels of thevariable frequency drive.

Keywords: VFD, AC Motor, PV System, SVPWM,THD.

1 INTRODUCTION

Speed controlling of induction motors is the main task when con-trolling AC motors. Different topologies are used for three phase

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International Journal of Pure and Applied MathematicsVolume 120 No. 6 2018, 3037-3051ISSN: 1314-3395 (on-line version)url: http://www.acadpubl.eu/hub/Special Issue http://www.acadpubl.eu/hub/

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induction motor using different PWM methods [1]. Different effi-ciency measures are taken for testing the induction motor operationby varying the applied voltage [2]. Various control methods havebeen implemented for checking the variations between dynamic andswitching model of variable frequency drive [3]. Increasing the ef-ficiency by using renewable resources and measures are taken forimproving the power factor of the VFD, since the circuit is voltagedependent [4]. Variable frequency drive is used for energy conser-vation, where the induction motor is used for converting electricalenergy into mechanical energy [5]. A three phase transformer isused for checking the various emulator behavior of the three phaseinduction motor [6]. Variable frequency drive is used in transmis-sion system to lower the frequency of the household applications,thereby increasing the power production and reducing the losses[7]. Survey on motor control and automation is done in variouspapers for maximum power usage of the induction motor [8]. Vari-able frequency drive is simulated in Mat lab for improving the THDlevels in HVAC systems [9]. VFD can also be modelled in spice tocontrol the speed of ac motors by supplying constant power andmaintaining constant ratio between voltage and frequency [10].

2 METHODOLOGIES

Based on the type of conversion the VFD is classified as AC-ACconversion and DC-AC conversion. AC-AC CONVERSIONTYPE: The AC-AC conversion section consists of the AC source,rectifier, DC link, inverter and induction motor.

DC-AC CONVERSION TYPE: The DC-AC conversion is usedwhere the source of input is solar PV module.PV MODULE: The power from the sun is used to generate thedirect current. Photo voltaic cells are used for converting the lightenergy to electrical energy by the process known as photovoltaiceffect. The panel selection depends on the required load capacity

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of the induction motor. The PV cells are combined as series andparallel connection to obtain the required voltage. The PV modulecurrent depends on the photon current, reverse saturation currentand diode current given by equation as shown in figure 1.

Figure 1: PV cell model

The photovoltaic panel can be modelled using following equa-tions

The PV module in Simulink is shown in figure 2.Maximum Power Point: The power from the solar panels is fluc-tuating throughout the day depending on the temperature on thatparticular day. Constant power must be supplied to the inductionmotor for proper operation; otherwise the motor may get damaged.To overcome this problem maximum power tracking system is usedwhere it is used to track the maximum power delivered by the sun.Various algorithms have been used for maximum power tracking.The commonly used algorithm is the P O algorithm shown in figure3.

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Figure 2: PV module in Simulink

Figure 3: flowchart of P O algorithm

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DC-DC CONVERTER: According to the load power require-ment the DC power from the solar panel have to be step up or stepdown. A Buck-Boost converter is used for better matching of theload and with low duty cycle. The Buck-Boost converter is shownin figure 4.

Figure 4: Buck-Boost Converter

VSI SECTION: Voltage source inverter is used to convert the DCpower to AC through inverter section. Six IGBT switches are usedfor the operation. The drive signal for the IGBT is provided usingthe PWM signal. The inverter section is shown in figure 5.SPACE VECTOR PWM: To improve the THD level space vec-tor PWM is used. It consists of six switches each switch activatedfor 60 degrees with 120 phase shift each. It consists of upper threeleg switches and lower three leg switches, with one or two switchesof each leg ON at a time. A total of three switches are activated ata time leading to eight vector possibilities. The space vector sectordetermination is shown in figure 6.

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Figure 5: Inverter Section

Figure 6: Space Vector Sector Determination

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INDUCTION MOTOR: The motor can be a single phase orthree phases AC operated. The magnetic field in the motor statorsection induces an opposing current in the rotor secondary windingand makes the motor rotate. The model of a induction motor isshown in figure 7.

Figure 7: Induction Motor

OPERATOR INTERFACE: The operator interface provideswith the user defined options for controlling the motor operation.Speed of the motor is adjusted manually or automatically accordingthe operation. Display unit is provided in the front with indicationsof various operations and provided with lights for indication. Ex-ternal peripheral interface port is also provided in the VFD circuit.The operator interface front panel is shown in figure 8.

Figure 8: Operator Interface Front Panel

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DRIVE OPERATION: The drive operation of induction motoroperates in four quadrants as shown in figure 9. Forward accelera-tion and deceleration is in I and II quadrants. Reverse accelerationand deceleration is shown in III and IV quadrants.

Figure 9: Drive Operation of Induction Motor

3 PROPOSED SYSTEM

The proposed system of variable frequency drive with space vectorPWM control method for controlling the frequency and voltagethere by controlling the speed of the induction motor is shown infigure 10.

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Figure 10: Proposed System

4 RESULTS

The PV system is used for the DC power generation. The Boostconverter is used to step up the PV output. The output of theBoost converter is shown in figure 11. The V-I characteristics ofinduction motor stator is shown in figure 12. The stator RMS,Vrms and frequency waveforms are shown in figure 13. And valuesare shown in figure 14.

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8cm

Figure 11: Boost Converter Output

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8cm

Figure 12: V-I Stator Characteristics

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Figure 13: Stator RPM, Vrms, Frequency values

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Figure 14: Stator RPM, Vrms, Frequency waveform

5 CONCLUSION

The design of space vector PWM for controlling the operation ofvariable frequency drive is achieved. The improvement in THDlevels by using the novel method of adjusting the frequency andvoltage is been implemented. The generation of PWM signals usingVerilog coding can be a desirable up come of the proposal.

References

[1] Ali S, Ba-Thunya, Rahul Khopkar, Kexin Wei Hamid Toliyat,Single phase induction motor drives - A literature survey Elec-tric Machines and Drives Conference, 2001.

[2] Emmanuel B. Agamloh, Scott Peele and Joseph Grappe, Oper-ation of Variable-Frequency Drive Motor Systems with SourceVoltage UnbalanceIEEE Transactions on Industry Applica-tions 2017.

[3] Xiaodong Liang and Wilsun Xu, Modeling variable frequencydrive and motor systems in power systems dynamic studiesIEEE Industry Applications Society Annual Meeting 2013.

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[4] Mahesh Swamy, Energy efficient drive systems InternationalConference on Optimization of Electrical and ElectronicEquipment Intl Aegean Conference on Electrical Machinesand Power Electronics 2017.

[5] Prasad Bhase and Mahesh Lathkar, Energy conservation usingVFD International Conference on Energy Systems and Appli-cations 2015.

[6] Artur Ulatowski and Ali Bazzi, Induction motor emulation forvariable frequency drives testing IEEE International ElectricMachines Drives Conference 2015.

[7] Vishv Mohan, variable frequency drives in power distributionInternational Journal of Scientific Engineering Research 2013.

[8] Anuradha Tomardevesh singh, Literature Survey on VariableFrequency drive Engineering Science and Technology: An In-ternational Journal 2012.

[9] Tamal Aditya, Research to study Variable Frequency Driveand its Energy Savings International Journal of Science andResearch 2015.

[10] Sumedh Tonapi, Piyush Chopade, Tanmay Kadam, Junaid Ju-laha and Priti Tyagi, Speed Control of AC Motor Using VFDInternational Journal of Innovative and Emerging Research inEngineering 2015.

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