Control of a Single-Phase Iductionn Generator - Essay Example

Control of a single-phase induction generator Student Name: Student Number: Course Name: Course code: Submission Date: Supervisor: Abstract- This paper presents an H-bridge inverter with more functionality, which aims to produce square wave, pure sine wave and modified sine wave base on selected mode by the user. Generated square waveform can be used to drive a DC motor with more driving abilities such as reverse, break and free run while sine waveform can be used to drive AC motors or any other AC devices. Pre calculated harmonics (switching times) are extracted from Fourier series expansion. This method, which is, known as Harmonic Elimination Technique is an offline approach and is suitable for open loop control while output voltage does not change significantly. PIC microcontroller and Voltage Source Inverter (VSI) are used to control switching and converting DC to AC respectively. Finally, a low cost hardware and software prototype for converting DC to optimized AC voltage and driving DC motors with more controlling capabilities is presented. Executive Summary This project consists of designing a module for single-phase induction generator to interface with existing H-bridge and enhance its functionality. This design will feature various inertial, position switches and utilize variable frequency drive (VFD) with the motor. Building the module this semester has involved investigation of electronics design with emphasis on high-speed control in motors, embedded system and miniaturizing circuits. Development of this system will allow for the investigation of single-phase induction generator and the circuit connections. The investigation will involve, motor speed control and voltage-frequency ratio studying and analyzing the circuit implementation and its practical use in the industries and home application. Lastly, the investigation gives a clear plan for future developments that are available from the project and its applications. 1. Introduction 1.1 Project global overview In many industrial, residential, utility utilization and commercial applications induction motors are used in control systems. Mainly, in the industrial controls and home appliances, the single-phase induction motors are used. Speed of linear or rotational current in an electric motor has its frequency controlled by the power that is supplied to the motor by a variable-frequency drive (VFD) is a system [2]. A variable frequency drive is a specific type of adjustable-speed drive. Variable frequency drives are also known as adjustable frequency drives (AFD); AC drives, variable-speed drives (VSD), inverter drives or micro drives. By controlling the speed of these motors, it provides multipurpose operation and multispeed operation [3]. In the early days, there were challenges that faced the variable speed drives, which included various limitations such as poor efficiencies, larger space, and lower speeds [3]. However, the invention of new power electronics appliances have changed the situation to have variable speed drives that are smaller in size, high reliability and higher efficiencies [4]. This paper discuses the basic concept that is used in v/f ratio and speed control, techniques of speed control and generic topologies. In addition, SPIM has H-bridge inverter and SPWM control circuit as the controlled method for the voltage and frequency of the entire system. Varying frequencies from drives have a wide use and applications in the control of fans, hoists, pumps and other machinery [5]. Speed control Induction motor has two types of speed that are widely known as the rated speed and the synchronous speed. Rated speed (N) of an induction motor is the actual motor speed, while the synchronous speed (Ns) on an induction motor is the speed at the magnetic field of the motor rotates. Where frequency, HZ; and Number of poles The based speed of the motor is proportional to the supply frequency and inversely proportional to the number of stator poles. By varying the supply frequency, this can change the motor speed. However, there are limitations associated with varying frequency only, which include core saturation and decrease in constant motor torque capabilities [4]. Therefore, voltage-frequency ratio is required to maintain a constant torque in the motor. V/f Control Induction motor develops a torque that is directly proportional to the ratio of frequency supply and applied voltage. However, varying the frequency and the voltage, and maintaining their ratio constant, torque developed can be kept constant throughout the range of the speed developed. This is what the v/f control tries to accomplish exactly [5]. 2. Practically Implemented Circuit The power circuit is a full bridge inverter circuit. In our circuit, we use four MOSFET connecting in series at each leg of H-bridge. Four MOSFET is used to increase the current rating of circuit. Total 16 n channel MOSFET is used in our project. As microcontroller output is in maximum 5V which is direct to MOSFET gate but MOSFET is not active until 12V that why we need MOSFET driver for our circuit. For driving the high side MOSFET, we used TLP250 and a capacitor of 50V, 100μfarad in output of TLP250, this capacitor is called boost strip capacitor. The capacitor in the output of TLP is used for protection. For the low side of inverter we used totem pole configuration, where totem pole passes 12V to MOSFET gate [11]. There should be a resistance between MOSFET gate and source, as gate resistance to drive the MOSFET otherwise MOSFET cannot be on. There are used many protection diode in every stage of connection so that reverse current can’t hamper to other circuit component such as TLP250, BJT, microcontroller. As MOSFET is very heat sensitive, so for cooling purpose we used four heat sinks at four lags of H-bridge inverter. The drain of the MOSFET is mounted to heat sink. The output of the inverter is then passed to the transformer. The output is taken from the two lower MOSFETs drain as upper MOSFET source is connected to the drain of lower MOSFET. 3. Methodology 3.1 Selection of main components 3.1.1 Voltage source inverter The design comprises of a voltage source inverter with four-switch single-phase inverter source. The four switch three-phase inverter fed IM or induction motor circuit comprises of 4-switches S1, S2, S3, and S4 and split capacity C and Cdc. Rectifier switches rectify the single-phase AC input with fixed frequency. The power circuit single-phase four-switch inverter has two phases connected to the legs of the inverter and one connected directly to the centre point of the DC link capacitors. The VSI and the DL are used in the circuit to provide balance operation and parameters regulation for autonomous three-phase IG during single-phase supply [9]. The circuit has a capacitor bank an isolator and microcontroller. The isolator acts as a connector between the inverter and the microcontroller without direct conduction. 3.1.2 Microcontroller In our design, we are going to use Microcontroller because it is much cheaper, compact and light compared to computers. It has a simple application and easier to implement than microprocessor and less likely to fail, also its applications run much faster than it does on a computer. In microcontroller, we will use a high-level language (C) which is much simpler than the assembly language in microprocessor and widely used nowadays. PIC Microcontroller Architecture PIC16F73 has RISC Harvard architecture. Harvard architecture is a newer concept than von Neumann. It rose out of the need to speed up the work of a microcontroller. In Harvard architecture data bus and address bus are separate. Thus a greater flow of data is possible through the central processing unit and of course a greater speed of work. Separating a program from data memory makes it further possible for instructions not to have to be 8-bits for instructions which allows for all instructions to be one word instructions. It is also typical for Harvard architecture to have fewer instructions than von-Neumann's, and to have instructions usually executed in one cycle. Microcontrollers with Harvard architecture are also called "RISC microcontrollers. RISC stands for Reduced Instruction Set Computer. Microcontrollers with von-Neumann's architecture are called 'CISC microcontrollers', which stands for Complex Instruction Set Computer. PIC16F73 is a RISC microcontroller that means it has a reduced set of instructions; more precisely 35 instructions. 3.1.3 Optocoupler (isolator): The FOD3120 has 2.5A output current gate drive optocouplers, it is also easy to drive a 1200V/20A IGBTs and MOSFETs and achieve the industry’s highest CMR rating even in the noisiest industrial environment. In terms of the advantages, this device is offering support between power circuit and PIC microcontroller in order to get signals feedback. These devices also offer tight pulse width distortion (100ns), offering smaller filters which lead to improve power efficiency. 3.1.4 Circuit configuration The circuit comprises of a VARIAC, which is able of providing varying AC voltage followed by a Rectifier anterior to the designed drive circuit. VARIAC applications include changing the magnitude of AC voltage to monitor the system performance under low voltage. In this system, a single-phase full bridge rectifier alters the AC voltage to DC or unidirectional. This DC voltage is what goes to the inverter circuit from the power supply [6]. The MOSFET used in the circuit is driven by the pulse signal that is produced by ATMEGA microcontroller, which is then followed by negative and positive OP-AMP edge detector. The step down transformer, steps down the AC voltage to 8 V (peak volt). Later, the small half wave rectifier nullifies the negative wave. OP-AMP 741 attenuates the small-scale AC wave to 4 V (volts peak). This attenuated signal is then supplied from the Analog to Digital Converter PIN of the microcontroller. The peak value of the signal is then measured by the Analog to Digital Converter (ADC) registers and then circulates the input AC supply from the attenuated factor. Utilizing TIMER characteristic of microcontroller, gate pulse of wanted frequency is generated in order to keep a fixed voltage frequency ratio [10]. As MOSFET necessitates, at least 15 volt or more must be maintained to reach saturation, microcontroller digital pulse is further amplified using OP-AMP. The circuit configuration of driver circuit is provided in Figure 1 and followed by the Pulse generating circuit in Figure 1. Figure 1: Hardware Circuit diagram the inverter dc/ac Figure 2: Hardware and PC schematic 3.1.4 PIC kit 3: The figure above is a H-bridge square modulation circuit, which usually uses 50 Hz or 60 Hz applications. In the connection, the initial voltage is always is zero and it help in regulating the root mean square of the load voltage. 3.2 Test framework Fig 3 is a H-bridge configuration inverter. The inverter has four switches, which are MOFSET. The inverter operation: SW1-SW2 ON: when both switches are on, they create short circuits across the available DC and they are rendered invalid. SW3-SW4 ON: when switched on, both switches create short circuits across the available DC source and are rendered invalid. SW1-SW4 ON: when switched on a positive voltage is applied to the load and positive current flows through the switches SW1-SW4. SW2-SW3 ON: when switched on negative voltage flows across the load and a negative current passes through SW2- SW3 drawing available energy from the supply. SW1-SW3ON: when switched on no voltage that flows through the load. SW2- SW4ON: when switched on no voltage that flows through the load. To activate the switches, that is, MOSFETs pulses are needed, and to get pulses SPWM technique is used [11]. Figure 3: -Bridge inverter configuration Corresponding values of 1) A+ closed and B– ,closed, 2) A+ closed and B+ ,closed, 3) B+ closed and A– ,closed, 4) B- closed and A– ,closed, = 0 3.3 Hardware and software design Figure 4: Practical set up 1 Figure 5: practical setup 2 Figures 4 and 5 show the practical circuit and testing with complete circuit and observation set up. 4. Project Timeline Progress against Methodology steps and timeline Title of Activity Timelines First Semester Final Semester 1. Research/proposal/ideas 2. Project/Research/ideas final draft 3. Writing research introduction and literature review and designing the circuit 4. Identification of system configuration, designing circuit, and control system VSI 5. Coding using C programming language 6. Configuring the microcontroller and Programming the it using the c source code 7. Configuring the microcontroller and Programming the it using the c source code 8. Delivery to client 5. Problems/issues identified, and mitigation or changes made During the project implementation, some of the issues that were indentified included the need to use high voltage to test the system. The system used only 240 volts, which is only a household based power supply. Therefore, the system requires high voltage testing to enable industrial application if required in the future use. In addition, no power factor testing that was done during the project test phase, this was necessary to prevent such issues like reactive power development in the system and short circuit development. 6. Results and Discussion A MATLAB simulation is obtained by maintaining the V/f ratio as a constant for different values of voltage and frequency. Then the torque-speed characteristics of the motor used is observed and compared to determine the varying differences. Figure 6 below shows the inverter output voltage when the system in connected to synchronizer and the data box. Figure 6: V-out 50 v ac and V-control 2, V-triangular Figure 7: T1 and T4 are off while T3 and T2 are on Figure 8: T1 and T4 are on while T3 and T2 are off Figures, shows speed-torque characteristics. We can observe that speed changes in all the three cases but torque remain constant. We can conclude that, as the speed changes Torque remain constant. 7. Conclusions and Future work 7.1 Conclusion In this work, a single phase PWM inverter has been implemented with PIC16F73 microcontroller and gate driver’s IC TLP250, totem-pole. Several outstanding features of the developed Sinusoidal PWM inverter are fewer harmonic, low cost, simple and compact. The implemented inverter is for low power and low voltage application. The use of a Variable Speed Drive for a speed control application usually offers an energy efficient and economic solution. Simple and straightforward VSD’s, such as the PWM inverter drives, are available for applications where the speed control accuracy is required. This compact inverter had its hardware reduced to a minimum using H-bridge inverter. The variable speed drive with variable frequency and voltage control method will offer new, low-cost solutions for light commercial and consumer applications. From Matlab Simulation conclusion can be made that we can vary frequency from 16 Hz to 50 Hz at for changing the speed of induction motor. It is observed that speed can be change from 500 RPM to rated speed in case of 2-pole single-phase capacitor start-run induction motor. 7.2 Future work In this project, no work was done involving power factor improvement. However, in regular uses power factor is deemed as vital factor in the design. In case there are cases of low power factor, problems such as the reactive power increase may arise, and loss will increase, short circuit lines may arise, harmonics may generate, and the entire system may crumble. Therefore, there is a need to have a future evaluation for power factor correction. Likewise, no work has been done on regulation of the voltage. Thus, there is also an open chance for future work on the project. Besides these, this project work has not been tested on high voltage power supply. Only 240 volts, which is within the household range has been used. This further provides an opportunity for future scope on the project. Since there is, an increase in power demand as days goes on, there is a chance for high DC voltage transmission requirement for industrial use and this will be another good opportunity for future scope. The system requires more enhancements. A larger transformer is required for the system. However, these changes come at a cost, thus, a huge amount will be required making project finance a critical issue when considering future enhancement. 8. References [1] Yamamoto T. et al., 2012, Voltage Control of Self-Excited Induction Generators Using a Three-Phase Magnetic Flux Controlled Type Variable Reactor,” Juornal of International Council on Electrical Engineering, 2(3), pp. 309-316. [2] Saravanasundaram, S. et al., 2008, Embedded Controlled four Switch Three Phase Inverter Fed Induction Motor. International Journal of Applied Engineering Research, 3(5), pp. 717-724. [3] Georgeet, A. et al., 2010, Low Cost SVPWM Controller for Five-Phase VSI Using PIC18F4550. India, Colleeg of Engineering, Kalavakkam, pp. 1-2. [4] Sutar, A. et al., 2013, Advanced Three Phase PWM Inverter Control Using Microcontroller. Journal of Electrical and Electronics Engineering , 5(1), pp. 21-28. [5] Yedamale, P. et al., 2002, Speed Control of 3-Phase Induction Motor Using PIC18 Microcontrollers, India: Microchip Technology Inc. [6] Ion, C. et al., 2013, Micro Hydro power plant with three-phase induction generator feeding single-phase consumers, Istanbul, Turkey, 4th International conference on Power Engineering Energy and Electrical Drives, pp. 13-17. [7] Antal, R. et al., 2010, Novel, Four-Switch, Z-Source Three-Phase Inverter. IEEE, pp. 619-624. [8] Ion, C. P . et al., 2008, Single-Phase Operation of an Autonomous Three-phase induction generator Using VSI-DL control system”. Brasov, IEEE. [9] Machado, R. Q. et al., 2004, Three-phase to single-phase direct connection rural cogeneration systems. 19th Annual IEEE applied Power electronics Conference and Exposition , Volume 3, pp. 1547-1553. [10] Muhammad, A. et al., 2002, the 8051 Microcontroller and Embedded Systems, pp. 169-253. [11] Larabee, J. et al., 2005, Induction motor starting methods and issues. Petroleum and Chemical Industry Conference 2005. Industry Applications Society 52nd Annual, vol., no., pp. 217- 222, 12-14. [12] Mohaiminul, S. M. & Islam, G., 2009, Microcontroller Based Sinusoidal PWM Inverter for Photovoltaic Application”, First International Conference Developments in Renewable Energy Technology (ICDRET), IEEE, pp. 1-4. [13] Ismail, B., November 28-29, 2006, Development of a Single Phase SPWM Microcontroller-Based Inverter, First International Power and Energy Conference PEC, Putrajaya, Malaysia: IEEE.pp. 437. Read More