SPACE VECTOR PWM FOR CONTROLLING AC MOTORS USING VARIABLE FREQUENCY DRIVE

Transcription

1 Volume 120 No , ISSN: (on-line version) url: SPACE VECTOR PWM FOR CONTROLLING AC MOTORS USING VARIABLE FREQUENCY DRIVE B.Pragathi 1, Dr.M.Suman 2 1 Research Scholar, 2 Associate Professor, Department of ECE, Koneru Lakshmaiah Education Foundation, Vaddeswaram, Guntur, A.P, India pragathibellamkonda@gmail.com suman.maloji@kluniversity.in July 11, 2018 Abstract The variable frequency drive is used for the speed adjustment of AC motors. Adjusting the frequency and controlling the voltage there by controlling the speed of motor is an abrupt task. A novel method is been considered for producing the associated DC power for the motor operation using solar PV system. The battery is used for storing the power during day and to supply the power to the motor even when the solar power is unavailable. Space vector PWM methods are used for reducing the THD levels of the variable frequency drive. Keywords: VFD, AC Motor, PV System, SVPWM, THD. 1 INTRODUCTION Speed controlling of induction motors is the main task when controlling AC motors. Different topologies are used for three phase

2 induction motor using different PWM methods [1]. Different efficiency measures are taken for testing the induction motor operation by varying the applied voltage [2]. Various control methods have been implemented for checking the variations between dynamic and switching model of variable frequency drive [3]. Increasing the efficiency by using renewable resources and measures are taken for improving the power factor of the VFD, since the circuit is voltage dependent [4]. Variable frequency drive is used for energy conservation, where the induction motor is used for converting electrical energy into mechanical energy [5]. A three phase transformer is used for checking the various emulator behavior of the three phase induction motor [6]. Variable frequency drive is used in transmission 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 various papers for maximum power usage of the induction motor [8]. Variable frequency drive is simulated in Mat lab for improving the THD levels in HVAC systems [9]. VFD can also be modelled in spice to control the speed of ac motors by supplying constant power and maintaining constant ratio between voltage and frequency [10]. 2 METHODOLOGIES Based on the type of conversion the VFD is classified as AC-AC conversion and DC-AC conversion. AC-AC CONVERSION TYPE: 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 used where the source of input is solar PV module. PV MODULE: The power from the sun is used to generate the direct current. Photo voltaic cells are used for converting the light energy to electrical energy by the process known as photovoltaic effect. The panel selection depends on the required load capacity

3 of the induction motor. The PV cells are combined as series and parallel connection to obtain the required voltage. The PV module current depends on the photon current, reverse saturation current and diode current given by equation as shown in figure 1. Figure 1: PV cell model The photovoltaic panel can be modelled using following equations The PV module in Simulink is shown in figure 2. Maximum Power Point: The power from the solar panels is fluctuating throughout the day depending on the temperature on that particular day. Constant power must be supplied to the induction motor for proper operation; otherwise the motor may get damaged. To overcome this problem maximum power tracking system is used where 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 figure

4 Figure 2: PV module in Simulink Figure 3: flowchart of P O algorithm

5 DC-DC CONVERTER: According to the load power requirement the DC power from the solar panel have to be step up or step down. A Buck-Boost converter is used for better matching of the load and with low duty cycle. The Buck-Boost converter is shown in figure 4. Figure 4: Buck-Boost Converter VSI SECTION: Voltage source inverter is used to convert the DC power to AC through inverter section. Six IGBT switches are used for the operation. The drive signal for the IGBT is provided using the PWM signal. The inverter section is shown in figure 5. SPACE VECTOR PWM: To improve the THD level space vector PWM is used. It consists of six switches each switch activated for 60 degrees with 120 phase shift each. It consists of upper three leg switches and lower three leg switches, with one or two switches of each leg ON at a time. A total of three switches are activated at a time leading to eight vector possibilities. The space vector sector determination is shown in figure

6 Figure 5: Inverter Section Figure 6: Space Vector Sector Determination

7 INDUCTION MOTOR: The motor can be a single phase or three phases AC operated. The magnetic field in the motor stator section induces an opposing current in the rotor secondary winding and makes the motor rotate. The model of a induction motor is shown in figure 7. Figure 7: Induction Motor OPERATOR INTERFACE: The operator interface provides with the user defined options for controlling the motor operation. Speed of the motor is adjusted manually or automatically according the operation. Display unit is provided in the front with indications of various operations and provided with lights for indication. External 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

8 DRIVE OPERATION: The drive operation of induction motor operates in four quadrants as shown in figure 9. Forward acceleration and deceleration is in I and II quadrants. Reverse acceleration and 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 vector PWM control method for controlling the frequency and voltage there by controlling the speed of the induction motor is shown in figure

9 4 RESULTS Figure 10: Proposed System The PV system is used for the DC power generation. The Boost converter is used to step up the PV output. The output of the Boost converter is shown in figure 11. The V-I characteristics of induction motor stator is shown in figure 12. The stator RMS, Vrms and frequency waveforms are shown in figure 13. And values are shown in figure

10 8cm Figure 11: Boost Converter Output

11 8cm Figure 12: V-I Stator Characteristics

12 Figure 13: Stator RPM, Vrms, Frequency values

13 Figure 14: Stator RPM, Vrms, Frequency waveform 5 CONCLUSION The design of space vector PWM for controlling the operation of variable frequency drive is achieved. The improvement in THD levels by using the novel method of adjusting the frequency and voltage is been implemented. The generation of PWM signals using Verilog 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 Electric Machines and Drives Conference, [2] Emmanuel B. Agamloh, Scott Peele and Joseph Grappe, Operation of Variable-Frequency Drive Motor Systems with Source Voltage UnbalanceIEEE Transactions on Industry Applications [3] Xiaodong Liang and Wilsun Xu, Modeling variable frequency drive and motor systems in power systems dynamic studies IEEE Industry Applications Society Annual Meeting

14 [4] Mahesh Swamy, Energy efficient drive systems International Conference on Optimization of Electrical and Electronic Equipment Intl Aegean Conference on Electrical Machines and Power Electronics [5] Prasad Bhase and Mahesh Lathkar, Energy conservation using VFD International Conference on Energy Systems and Applications [6] Artur Ulatowski and Ali Bazzi, Induction motor emulation for variable frequency drives testing IEEE International Electric Machines Drives Conference [7] Vishv Mohan, variable frequency drives in power distribution International Journal of Scientific Engineering Research [8] Anuradha Tomardevesh singh, Literature Survey on Variable Frequency drive Engineering Science and Technology: An International Journal [9] Tamal Aditya, Research to study Variable Frequency Drive and its Energy Savings International Journal of Science and Research [10] Sumedh Tonapi, Piyush Chopade, Tanmay Kadam, Junaid Julaha and Priti Tyagi, Speed Control of AC Motor Using VFD International Journal of Innovative and Emerging Research in Engineering

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