i THREE PHASE INVERTER FOR INDUCTION MOTOR BY USING PIREPETITIVE CONTROLLER WITH ARDUINO MOHD NAJIB BIN HUSSIN A project report submitted in partial Fulfillment of the requirement for the award of the Degree of Master Electrical Engineering Faculty of Electrical and Electronic Engineering Universiti Tun Hussein Onn Malaysia JULY 2014 v ABSTRACT The proportional integral (PI) repetitive controller that is applied to the three phase inverter for the three phase induction motor is developed. This project is about to design a combination of PI-Repetitive controller simulation and fabricating the hardware to control the speed of a three phase induction motor. The controller eliminates the periodic errors on the output current due to inverter current nonlinearity and load disturbances. The controller is implemented on a gate driver, three phase inverter and filter prototypes which are constructed in laboratory. Open-loop and closed-loop condition are verified by means of simulation and experiments in order to investigate the stability of controller. The result of the controller’s performance between simulation and hardware are explained in this report in terms of the PWM output and three phase inverter output waveform. The PI-Repetitive controller will solve the starting problem of the three phase induction motor and minimizes the line current error to maintain the required steady state condition. vi ABSTRAK Kawalan motor aruhan tiga fasa jenis ‘Proportional Integral Repetitive’ yang diaplikasikan pada penyongsang tiga fasa dibangunkan. Projek ini adalah untuk merekabentuk gabungan pengawal PI-berulang secara simulasi dan seterusnya memfabrikasi perkakasan bagi tujuan ujikaji di makmal. Pengawal ini menghapuskan gangguan-gangguan berkala ke atas arus keluaran yang disebabkan oleh ketaklelurusan penyongsang dan gangguan semasa pada beban. Pengawal ini kemudiannya diaplikasikan pada prototaip yang dibina iaitu di litar ‘gate driver’, litar penyongsang tiga fasa dan litar penapis di dalam makmal. Kaedah gelung buka dan keadaan gelung tertutup secara simulasi dan eksperimen digunakan bagi mengkaji kestabilan pengawal PI-berulang. Hasil ujikaji direkodkan dalam laporan ini dari segi keluaran bentuk gelombang PWM dan keluaran penyongsang tiga fasa. Pengawal PIberulang akan menyelesaikan masalah motor induksi tiga fasa yang tidak stabil diawal permulaan pengoperasiannya dan meminimumkan gangguan pada arus semasa untuk mengekalkan keadaan motor agar lebih stabil. vii CONTENTS TITLE i DECLARATION ii DEDICATION iii ACKNOWLEDGMENTS iv ABSTRACT v CONTENTS vii LIST OF TABLE viii LIST OF FIGURES ix LIST OF SYMBOL AND ABBREVIATIONS xii CHAPTER 1 INTRODUCTION 1 1.1 Project background 1 1.2 Problem Statement: 3 1.3 Objectives: 5 1.4 Scope: 6 CHAPTER 2 LITERATURE REVIEW 7 2.1 Induction motor 7 2.2 Inverter DC to AC 3 2.2.1 Three phase inverter 3 Controller 6 2.3.1 Passive and adaptive controller 7 2.3 2.3.2 Propose controller 10 viii 2.4 Gate driver 12 2.5 Arduino 14 2.6 Other research 15 CHAPTER 3 METHODOLOGY 17 3.1 Hardware flow-chart 17 3.2 Hardware design 18 3.2.1 Gate Driver 18 3.2.2 Inverter 20 3.2.3 Filter 22 3.2.4 Transducer 22 3.2.5 Induction Motor 25 Software flow-chart 26 3.3.1 Kp and Ki analysis 30 3.3 CHAPTER 4 DATA ANALYSIS AND RESULT 34 4.1 Open-Loop Simulation Diagram and Result. 35 4.2 Closed-loop simulation process and analysis. 37 4.2.1 PI-Repetitive Controller 39 4.3 4.4 4.5 4.6 The comparison of PI, Repetitive and PIRepetitive controller. 44 4.3.1 PI-Controller 44 4.3.2 Repetitive-Controller 45 4.3.3 PI-Repetitive Controller 46 Experiment set up for hardware testing analysis. 46 Open loop hardware analysis 48 4.5.1 Pulsed Width Modulation (PWM) 48 4.5.2 Three phase inverter 50 Closed-loop hardware analysis. 51 ix 4.7 Output result for various input. CHAPTER 5 CONCLUSION AND RECOMMENDATION 54 57 5.1 Conclusion 57 5.2 Recommendation 58 REFERENCE 59 x LIST OF TABLES 3.1 List of the components for gate driver circuit 19 3.2 Parameters of Three Phase Induction Motor 26 3.3 Controller parameters for the Ziegler-Nichols frequency respons method 27 4.1 Experiment’s Parameters 47 4.2 Various parameters of input voltage versus input current reference 54 xi LIST OF FIGURES 1.1 Hardware block diagram 2.1 Torque-speed characteristic at constant voltage and 3 frequency 2 2.2 Hex bridge of inverter 4 2.3 Proportional Integral (PI) Controller block diagram 8 2.4 Repetitive control block diagram 11 2.5 PI-Repetitive control block diagram 12 2.6 Arduino board 15 3.1 Hardware process control 17 3.2 One phase Gate Driver schematic circuit 19 3.3 Three phase Gate Driver PCB layout 20 3.5 Current Sensor BB-ACS756 22 3.4 The circuit for the LC filter 22 3.6 Current Sensor BB-ACS756 pin configuration 23 3.7 Simulation block diagram for current converting 25 3.8 Three phase induction motor 25 3.9 Software process control 26 3.10 Step response of PI-Repetitive controller 30 3.11 Root Locus and Bode diagram of PI-Repetitive controller 31 3.12 PI-Repetitive Controller block diagram 32 3.13 Proportional integral repetitive controller simulation 32 3.14 PWM simulation generator block 33 xii 3.15 PWM simulation 4.1 Three phase inverter by using PI-Repetitive Controller 33 in MATLAB simulation. 34 4.2 PWM generator block prameter setting 35 4.3 PWM block diagram simulation 36 4.4 PWM output waveform of open-loop simulation 36 4.5 Inverter output waveform of open-loop simulation 37 4.6 Closed-loop simulation process. 38 4.7 Three Phase PI-Repetitive Controller for simulation 39 4.8 ADC output waveform From Current Sensor 40 4.9 DAC output waveform of PI-Repetitive Controller simulation 40 4.10 Simulation of error in controller 41 4.11 Output of PWM from simulation block 42 4.12 Block diagram of the inverter 43 4.13 Output waveform of the inverter (before filtering process) 4.14 43 Output waveform of the pi-rc system (after filtering process) 44 4.31 The output voltage waveform of the PI-Controller 45 4.32 The output voltage waveform of the RepetitiveController 4.33 The output voltage waveform of the PI-RepetitiveController 4.15 46 Three phase inverter by using pi-repetitive controller hardware. 4.16 45 47 PWM output waveform of open-loop hardware injected to gate driver. 48 4.17 Gate Driver. 49 4.18 Gate Driver output waveform of open-loop simulation 49 4.19 Inverter hardware 50 xiii 4.20 Inverter output waveform of open-loop process. 50 4.21 ACS756 Current Sensor. 51 4.22 The output waveform result of the hardware at current sensor at 0A. 4.23 52 The output waveform result of the hardware at current sensor at 0.75A. 52 4.24 The PWM output waveform for phase A and Phase B. 53 4.25 The LC filter 53 4.27 The output waveform of the PWM for input dc voltage = 20v, input reference (current) = 0.8amp 4.28 The output waveform of the PWM for input dc voltage = 30v, input reference (current) = 0.8amp 4.29 55 The output waveform of the PWM for input dc voltage = 20v, input reference (current) = 1amp 4.30 54 55 The output waveform of the PWM for input dc voltage =30v , input reference (current)= 1amp 56 xiv LIST OF SYMBOL AND ABBREVIATIONS ABS - Automatic Brake System AC - Alternating Current ADC – Analogue to Digital DAC - Digital to Analogue DC - Direct Current; DOL - Direct On Line DTC - Direct Torque Control DSP - Digital Signal Processing FFNN - Feed Forward Neural Network FOC - Field Oriented Control GA - Genetic Algorithms MV - Manipulated Variable PCB - Printed Circuit Board PD – Proportional Derivative PI - Proportional Integral PID - Proportional Integral Derivative; PWM - Pulse Width Modulation; VVVF - Variable Voltage Variable Frequency 1 CHAPTER 1 INTRODUCTION 1.1 Project background Induction motor or asynchronous motor is an AC electric motor in which the rotor torque produced is caused by electromagnetic induction from the stator winding of the magnetic field. Rotor induction motor can either type of wound or squirrel-cage. Its are the most widely used motors for appliances, industrial control, and automation, and often called the workhorse of the motion industry because of its robustness, reliable, low cost, high efficiency and durable [1, 2]. Three-phase induction motors are widely used in industrial drives and single-phase induction motors are widely used for smaller loads especially in domestic appliances, such as washing machines and fans. Conventionally, mechanical gear system is used to obtain variable speed. Recently, electronic power and control systems have matured to allow these components to be used for motor control in place of mechanical gears. These electronics not only control the motor’s speed, but can improve the motor’s dynamic and steady state characteristics. Before the development of semiconductor power electronics, induction motors were mainly used in fixed speed applications because it was difficult to vary the frequency. There are 4 ways to control the speed of three phase induction motor from stator side which are further classified as V / f control or frequency control , changing the number of stator poles, controlling supply voltage and by adding rheostat in the stator circuit. The speed controls of three phase induction motor also can be done from rotor side which are by adding external resistance on rotor side, 2 cascade control method and by injecting slip frequency emf into rotor side. There are a few methods for controlling the speed such as FOC and DTC. Another way is VVVF or V/f method which is most suitable for applications without position control requirements or the need for high accuracy of speed control . There are many types of digital controller like a microprocessor, microcontroller and DSP are widely used to control algorithm in motor controller. PID, Fuzzy logic, and neural network are the examples of algorithm techniques used in induction motor drive applications. Common controller for induction motor is a Proportional-Integral, but with the more demanding and sophisticated application, a conventional PI controller is designed accordingly for PWM current controller to produce a better controller such as PI-Fuzzy controller, PI-Time Delay controller, PINeural Network and PI-Repetitive controller. Repetitive control is an iterative approach that improves the transient response performance of processes whose tasks are repetitive or periodic. The concept of repetitive control was first introduced in . In this project, one method of controller with additional system will be implemented on a 3 phase 0.75kW, cage type induction motor. An Arduino Uno will be used to drive the gates at a logic output voltage of 5V. Then the gate driver will drive the voltage 15V to the inverter. The motor used in this project is rated for 1.5A so the current will most likely operate in the ranges most likely conducive to IGBTs implementation. For controller, a PI plus Repetitive controller will be implemented to control the current since the speed of the motor is proportional to it. The combination design method PI and Repetitive system controllers possess high performances in different areas. PI is used in the steady state area because it gives a zero error while closed-loop hybridization of Repetitive is a robust control strategy that able to track or reject unknown periodic signals of a known period. Repetitive control resembles what is called iterative learning control, where the error in tracking a finite-duration reference signal is reduced by means of correcting the input in each iteration, based on the error observed in the preceding iterations. For experimental analysis, matlab simulink version 2013a will be used. 3 DC Three Induction Phase Motor Inverter Current Gate Arduino Sensor Driver Figure 0.1: Hardware block diagram Figure 1.1 shows the whole system of the project. They are three phase inverter, arduino and gate driver. which are working together with current sensor to make the induction motor function as needed. The PI-Repetitive controller will be connected to the Arduino where Arduino UNO is used as interface instrument to communicate between hardware and software. The computer simulation program, which will be used to predict the performance of the designed PI-Repetitive controlled system. The variables of the simulated program such as currents, voltages etc., are observed from the scope graphic window. The waveforms obtained from the simulation results are evaluated and compared with the output of experiment in laboratory. 1.2 Problem Statement Induction motor which is also called asynchronous motor derive their name from the way the rotor magnetic field is created from the rotating stator magnetic field that induced currents in the short circuited rotor. The three-phase induction motor is the most widely used electric motor worldwide in industrial facilities and large buildings. 4 It is the most favourable drive solution in terms of price and quality. The three phase induction motor are classified into two types which are Squirrel cage induction motor and Slip ring induction motor or wound induction motor or phase wound induction motor . Speaking of 3-phase induction motor, the main thing is concerned with how to control the speed and keep the motor speed maintain to the desired value. The speed control of induction motor is more important to achieve maximum torque and efficiency. Generally, to control the speed of three-phase Induction Motor is by using DOL, variable resister and frequency inverter. When focusing attention on the speed control segment of the three phase induction motor, conventional controller have some problems such as less efficiency due to slow respond, steady state error or sluggish response to the perturbation in reference setting. The conventional control method such as PI, PD and PID controller is widely used in motor control system due to the simple control structure and easiness of design. However tuning the parameters of controller is a difficult task for varieties of plant parameters and the nonlinear operating condition, fixed gain PI controllers cannot provide the desired control performance . The control and estimation of ac drives in general are considerably more complex than those of dc drives, and this complexity increases if high performances are demanded. The main reasons for this complexity are the need of variable-frequency, harmonically optimum converter power supplies, the complex dynamics of ac machines, machine parameter variations, and difficulties of processing feedback signals in the presence of harmonic PI controller can never achieve perfect control, that is, keep the speed of induction motor continuously at the desired set point value in the presence of disturbance or set point changes . To enhance the capabilities of traditional controller, several approaches such as GA, fuzzy logic, Time Delay or Repetitive have been suggested to be add to the system in order to make speed more stable. 5 1.3 Objectives: Objectives of this project are listed as follows: i. To design a closed-loop control for a three phase induction motor. ii. To design a combination of PI-Repetitive controller to control the speed of a three phase induction motor. iii. To develop the hardware of gate driver and three-phase inverter to control the three phase induction motor. iv. To successfully make a communication between computer and three phase induction motor using Matlab software and Arduino. 6 1.4 Scope: In this project the scope of work will be undertaken in the following four developmental stages: i. Design the closed-loop control with current feedback for the 0.75kWatt, 1.5A three phase induction motor type squirrel cage. ii. Design the PI-Repetitive controller to control the current of a three phase induction motor. Design the PWM signals which enables the inverter to control the motor within a speed of 10% - 100% (V/F open loop control). This implied that the range of frequency used to control the motor varies between 5 Hz – 50 Hz. iii. Build the hardware, which is the rating of three-phase induction motor squirrel cage types is 0.75kW, 50Hz, 1.5A, 1500 rpm with 4 poles, gate-driver that generate 15 volt for the inverter and the inverter is using Hex bridge of IRF530 MOSFET. iv. Successfully make a connection between Matlab's Simulink and Arduino Uno. 7 2 CHAPTER 2 LITERATURE REVIEW 2.1 Induction motor Three-phase induction motor is a very popular motor and most widely used in the electrical industry. They run at a constant speed from no load to full load. However, speed is frequency dependent and so the motor cannot be easily adapted to control the speed. That’s why it is essentially be known as a constant speed motor and its speed cannot be changed easily. For this factor, the DC motor is said to be even better when dealing with the factor of speed variations. However, 3-phase induction motors is simple, durable, low price, easy to maintain and can be made with features to suit most requirements of the industry . The most popular type is the 3-phase, squirrelcage AC induction motor. It is a maintenance-free, less noisy and efficient motor. The stator is supplied by a balanced 3-phase AC power source . The synchronous speed ns of the motor is calculated by Equation 2.1: (2.1) Where; ns = synchronous speed fe = the synchronous stator frequency p = the number of stator poles. 2 The principle of operation of three phase induction motors is based on creating a rotating magnetic field in the air gap between the stator and rotor. The rotating field can be obtained by feeding the stator windings from a three phase alternating current source. Thus, the currents in the windings generate are revolving magnetic field having the same angular speed of the source frequency in the air gap. Meanwhile, the continuous change in the stator field induces currents in the rotor's squirrel-cage bars causing another field in the rotor. Both the rotor and stator fields interact with each other in the air gap causing the rotor to rotate. The rotor flux lags that of the stator causing the rotor speed to slip. The ratio of slip and synchronous speeds is called the motor slip as Equation 2.2 below. (2.2) Where; The motor speed is controlled by variation of a stator frequency with the influence of the load torque. Motor Torque Work Point Torque Load Torque Speed Motor Generator Figure 2.1: Torque-speed characteristic at constant voltage and frequency 3 2.2 Inverter DC to AC Power converter which is known as inverter is an electrical device that can change direct current DC to alternating current AC. The converted AC can be at any required of voltage and frequency usually used in transformer , switching and control circuit. It also be used from small switching power supplies to large high-voltage electric equipment applications that transport bulk power and solid-state inverters have no moving parts. Commonly inverter is used to supply solar panels or batteries and it perform the opposite function of a rectifier. The electrical inverter is high-power electronic oscillator because generally AC to DC converter was made to work in reverse and thus was inverted which is to convert DC to AC. 2.2.1 Three phase inverter The standard three-phase inverter has as its genesis, the hex-bridge . There are two kinds of switches that were considered for this range of power applications, Insulated Gate Bipolar Transistors (IGBTs) or MOSFETs. The hex-bridge takes a DC voltage and uses six switches (MOSFETS) arranged in three phase legs as shown in Figure 2.2. The power circuit consists of six self-commuted semiconductor switches S1 to S6. The switch pairs (S1, S4), (S3, S6), and (S5, S2) form three legs of the inverter. The switches in the same leg conduct alternately. Sometime must elapse before the turn-off of one switch and turn on of another to ensure that both do not conduct simultaneously. Their simultaneous operation will cause a short circuit of the dc source resulting in a very fast rise in current. This fault, known as short-through fault can only be cleared by fast-acting fuse links . 4 S11 S31 S51 S41 S61 S21 Vdc A B C Figure 2.2: Hex bridge of inverter The single phase voltage source inverters PWM technique can be used in three-phase inverters, in which three sine waves phase shifted by 0°, 120°, 240° with the frequency of the desired output voltage is compared with a very high frequency carrier triangle, the two signals are mixed in a comparator whose output is high or wide in time range when the sine wave is in positive side of the triangle and the comparator output is low or thin in time range when the sine wave signal is in negative side of the triangle. This phenomenon is shown in Figure 2.3. As is explained the output voltage from the inverter is not smooth but is a discrete waveform and so it is more likely than the output wave consists of harmonics, which are not usually desirable since they deteriorate the performance of the load, to which these voltages are applied . 5 1 0 -1 Time (sec) 1 0 Time (sec) Figure 2.3: PWM illustration by the sine-triangle comparison method (a) sine triangle comparison (b) switching pulses 1 (a) S1 0 1 (b) S3 0 1 (c) S5 0 Figure 2.4: Generation of the switching signals for top devices (a) S1 (b) S3 (c) S5 6 1 (a) S4 0 1 (b) S6 0 1 (c) S2 0 Figure 2.5: Generation of the switching signals for bottom devices (a) S4 (b) S6 (c) S2 The advantage of inverter is to reduce the consumption of power by converting DC to AC. This alternated power can be maintained in any frequency or voltage with the use of an appropriate transformers, circuits and switches to support the electrical equipment at home and office. Disadvantages of inverter are not ideal for inductive AC and motor loads. It is also sensitive electronics devices can be damaged by poor waveforms. 2.3 Controller In order to compete with DC motor in term of controlling the speed, additional system which is consist of power electronic devices is needed for better output of induction motor. Induction motor is difficult to maintain a constant speed whenever the load is changed. Recently, many controllers have been developed and they can be divided into two classifications which is passive and adaptive power controller. The example for passive power controller is hysteresis, relay and sliding mode control and for adaptive power controller is PID, fuzzy, Repetitive and P-resonant controller. Each of 7 them has their own advantages and disadvantages, such as simple structure and low maintenance cost. 2.3.1 Passive and adaptive controller Passive controller is something that is built into the system and is always there and cannot give a good response to any changes of disturbances. A cars brakes for instance, it is like a car without ABS – when we push the pedal, brakes go on and there is no computer in the system to make them do ABS things. Adaptive controller is a controller that can modify its behaviour in response to changes in the dynamics of the process and the disturbances. A great number of industrial control loops are under adaptive control. These include a wide range of applications in aerospace, process control, ship steering, robotics and other industrial control systems. 22.214.171.124 Proportional- Integral (PI) controller The most commonly used controller for the speed control of Induction motor is PI controller. The combination of proportional and integral terms is important to increase the speed of the response and also to eliminate the steady state error. The PID controller block is reduced to P and I blocks only as shown in Figure 2.3 below. 8 + e P + Plant Y I Figure 2.3: Proportional Integral (PI) controller block diagram The proportional and integral terms is given by Equation 2.3: (2.3) Kp and Ki are the tuning knobs, are adjusted to obtain the desired output, e is error and R is reference currents. However, the PI controller has some disadvantages such as the high starting overshoot, sensitivity to controller gains and sluggish response due to sudden disturbance. So, the relatively a new intelligent controller by using Matlab/Simulink package give better responses than the traditional PI controller for the speed control. Torque is the fundamental variable of an induction machine, to get the accurate control of speed and position is by controlling the torque of induction machines. The performance of intelligent controller for the speed control has been verified compared with the conventional PI controller performance. It is very good dynamic performance and robustness during the transient period and during the sudden load disturbance . 9 126.96.36.199 Fuzzy controller A fuzzy control system is a system based on fuzzy logic. Fuzzy means uncertainty, fuzzy computes uncertainty by assigning values between 0 and 1 compared to conventional computation 0 or 1. This fuzzy logic involves computing using knowledge base and rule base. In fuzzy systems, input variables are assigned with a membership function. Each membership function is assigned with specified values. Fuzzy logic comprises of three stages which is fuzzification, fuzzy inference and defuzzification. The advantages and disadvantages of the fuzzy logic are stated below: Advantage of fuzzy logic control include the following : i. A large number of system variables can be evaluated. ii. It similar to the way humans think because linguistic variable and not numerical values are used iii. It use permits a greater degree of uncertainty because the output is related to the input, so better control is possible for some types of system, requires little maintenance. iv. It can be used for the solution of previously unsolved problems v. It is more robust. Some of the disadvantages of fuzzy logic include: i. Extracting a model from a fuzzy system is difficult. ii. Fuzzy systems require finer tuning before they are operational. 10 2.3.2 Propose controller This paper is proposed PI-Repetitive controller used as the controller design for the system control. The PI control scheme is named after its two correcting terms whose sum constitutes the manipulated variable (MV) by Equation 2.4, (2.4) Proportional term of output ( ) and Integral term of output are the contributions to the output from the PI controller from each of the two terms. The proportional term (sometimes called gain) makes a change to the output that is proportional to the current error value. The proportional response can be adjusted by multiplying the error by a constant , called the proportional gain. The proportional term is given by Equation 2.5: (2.5) If the proportional gain is too high, the system can become unstable In contrast, a small gain results in a small output response to a large input error, and a less responsive (or sensitive) controller. If the proportional gain is too low, the control action may be too small when responding to system disturbances. In the absence of disturbances, pure proportional control will not settle at its target value, but will retain a steady state error that is a function of the proportional gain and the process gain. The contribution from the integral term (sometimes called reset) is proportional to both the magnitude of the error and the duration of the error. Summing the instantaneous error over time (integrating the error) gives the accumulated offset that should have been corrected previously. The accumulated error is then multiplied by the integral gain and added to the controller output as Equation 2.6. The magnitude of the contribution of the integral term to the overall control action is determined by the integral gain, . (2.6) 11 The integral term (when added to the proportional term) accelerates the movement of the process towards set point and eliminates the residual steady –state error that occurs with a proportional only controller. However, since the term is responding to accumulated errors from the past, it can cause the present value to overshoot the set point value (cross over the set point and then create deviation in the other direction). PI controllers are good for tracking or rejecting step signals. But for inverters, the signals are sinusoidal. In order to have good tracking performance, Repetitive control system should be added. The basic Repetitive control transform functions is shown in Equation 2.7. (2.7) where is the resonant frequency equal to the synchronous frequency of the stator voltage outputs [15, 16]. The general Repetitive control block diagram is in Figure 2. 4. Ref P + W S2 + W 2 Figure 2.4: Repetitive Control block diagram 12 Set Point Output ∑ ∑ error W S2 + W 2 Figure 2.5: PI-Repetitive control block diagram In past research, a new control scheme named Repetitive control has been introduced. The stability conditions and the synthesis algorithms have been investigated for linear and nonlinear repetitive control systems . In the proposed scheme, the high accuracy tracking property for periodic reference commands can be achieved by locating the generator for periodic signals in the closed-loop. The scheme has been applied to the trajectory control of a three-link manipulator and the simulation has showed the tracking error could be reduced to low level by repetitive operation . Repetitive control is said to be among the best way to make the system stable in speed condition because of the application of ‘close-loop’ task that being applied. The use of memory-loops is beneficial in systems with repetitive disturbances or tasks. In order to improve the capabilities of repetitive controllers for the cases where the periodicity is hard to measure and is subject to variation, an extension of repetitive control is developed . Figure 2.5 is one of modified controller that will be done where the PI controller is combine with Repetitive controller. 2.4 Gate driver The gate driver circuit which is consist of IGBT’s HCPL3120 is used to improve the performance of motor drives because it directly related to the availability of power control of semiconductor devices. The purpose of using a gate driver is the 13 application of a charge pump circuit to the gate of the MOSFET in inverter . By doing so, it allows the gate voltage to be lifted and maintain the ON position in the switch. The circuit for the gate driver was designed to meet the specifications needs where the gate to source voltage needed for desired operation of the inverter is on a 15V level. In addition, the high side MOSFETs in the hex-bridge do not have the source connected to ground, so the actual voltage needed to drive the gate depends on the varying voltage at the source. 14 2.5 Arduino Arduino is an open-source electronics prototyping platform based on flexible, easy-touse hardware and software. Arduino board can sense the environment by receiving input from a variety of sensors and can affect its surroundings by controlling lights, motors, and other actuators. Arduino projects can be stand-alone or they can communicate with software on running on a computer (e.g. Flash, Processing, MaxMSP). It includes 6 to 10-bit analogue inputs and can be used for ultra-inexpensive data acquisition. The Arduino Uno is based on the ATmega 328 that consist of 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analogue inputs, a 16 MHz ceramic resonator, a USB connection, a power jack and a reset button. It contains everything needed to support the microcontroller where just simply connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery to get started. Additionally, daughter boards can be added to the Uno to allow for many more functions, such as amplified motor output, battery powered operation, Ethernet communication and electronics prototyping. In this project, the analogue to digital converter, ADC is really important because of this feature is use to get the current feedback from the current sensor . The ADC feature of Arduino Uno depends from the ATmega 328 microcontroller itself. It contains 10-bit successive approximation ADC. The operation of translating an analogue voltage value into different levels is what we call Analogue to Digital Conversion. This project needs the signal from Pulse Width Modulation, PWM, which is a powerful way of controlling analogue circuits and systems, using the digital outputs of microprocessors. Defining the term, we can say that PWM is the way we control a digital signal simulating an analogue one, by means of altering its state and the frequency. Figure 2.6 is the Arduino board that will be used in this project. 15 Figure 2.6: Arduino board Some of the hardware provided on the Arduino board is: 2.6 USB (Power) Power indicator Voltage regulator Digital input Barrel jack (Power) PWM output 3.3V supply Analogue Ref input 5V supply Reset button Ground Rx,Tx indicator analogue input Main IC Other research In another past research , hybrid controller produces better performances in terms of rise time, overshoot, undershoot and settling time. There is no steady-state error in the speed response during the operation. In terms of rise time and Settling Time, good torque response is obtained with hybrid controller at all-time instants and speed response is better than only using PI controllers. The speed response with this controller has no overshoot and settles faster in comparison with conventional 16 controller. It is also noted that there is no steady-state error in the speed response during the operation when hybrid controller is activated. Good torque response is obtained with hybrid controller at all-time instants and speed response is much more better. From an International Journal of Innovative Computing, Information and Control ICIC International , the PI controller in DTC of induction motor was tuned by an adaptive mechanism based on FFNN where the system will approximate mapping the input output of linear and nonlinear system. The paper is concentrated on the development of the FFNN tuning of PI controller parameters based on changing speed of induction motor and load torque of electric ship and the effectiveness of the complete proposed control scheme is clarified through a matlab/simulink simulation FFNN was utilized to tune the gain of PI speed controller. Meanwhile, training data used in this model were taken from the optimum value of gain PI controller for each rotor speed and load torque conditions. Load torque of the induction motor applied in the electric propulsion system were depending on the rotor speed of the induction motor directly connected the propeller. From the results showed that the rotor speed of induction motor for PI-FFNN controller method provides small steady state error compared with fixed PI controller. The electromagnetic torque which is used to accelerate and decelerate the speed of the induction motor by using PI-FFNN controller was smaller than with using fixed PI controller. Since the magnitude of the stator current is proportional to the electromagnetic torque of the induction motor speed, the magnitude of the stator current of the induction motor using PI-FFNN controller was smaller than with using fixed PI controller. 17 CHAPTER 3 METHODOLOGY The whole system developed is based on PI-Repetitive controller with Arduino, threephase Inverter, which is used for Induction motor. Also, the three phase 1 input 2 output Gate Driver is used to produce 15v for the Inverter. The work includes stages such as designing, simulation, implementation and verification. The designing part involves using Proteus software for inverter and gate design. The simulations is conducted by using Matlab / Simulink software version R2013a for controller design, download and implemented on the Arduino UNO board in the implementation stages. Lastly, the testing of the controller design using a hardware development is done to verify its correctness. 3.1 Hardware flow-chart Start DC Supply Voltage 3 Phase Current Source Inverter Current Sensors Gate Driver Arduino 3 Phase Induction Motor Figure 0.1: Hardware process control 18 From the flow chart in Figure 3.1, the system implemented converts a DC input voltage at a power rating of 750 W to AC by using a three phase inverter, and a LC filter which assists in stabilizing the output of AC voltage. The three phase inverter is droved by the gate driver that is amplified the PWM signals generated by the DSP board and produce the appropriate gate signals. The hex-bridge uses a dc bus voltage and the gate drive signals to produce balanced three-phase sinusoidal output which drives the induction machine. Current sensor will detect the three phase current (Ia, Ib and Ic) and feed to the Arduino. The PI-Repetitive controller that is developed will analyse and reduce the error if detected after compared to the reference current and then will generate the PWM before feeding to gate driver. All of the steps of minimizing the error and generating the PWM will be done in Arduino. The gate driver will feed the voltage up to 15V for three phase inverter. The three-phase induction motor is rated at 0.75kW, 1.5A, 1500 rpm. 3.2 Hardware design Figure 3.1 shows the hardware process control of the system. They are consists of gate driver, inverter, filter, current sensor and induction motor. Gate driver, inverter and filter is fabricated in laboratory while current sensor and ac drives is already available in laboratory. 3.2.1 Gate Driver The schematic diagram of the gate driver as Figure 3.2 was designed to meet the specifications needs where the gate to source voltage needed for desired operation of the inverter is on a 15 volt level. The input of the gate driver is 5 volt and it will boost up to around 15 volt practically. Table 3.1 shows the list of components for the development of gate driver. While the Figure 3.3 below shows the three phase gate driver PCB layout for it’s fabrication. 19 S1 S2 S3 U2:A U1:B D1 3 S1 1N4748A 1 R1 4.3k 1 U1:C 4 5 7414 3 6 2 4081 +15V1 U2:B 7414 C1 5 4 1nF 6 U1:A U3 1 N/C1 2 ANODE 3 CATHODE 4 N/C2 4081 2 7414 U2:C 8 VDD R2 4.3k 10 9 C2 1nF D2 13 U1:E 12 11 R4 U2:D 10 12 11 1N4748A 7414 7414 13 4081 560 J3 1 2 10 +15V2 G15V1 CONN-H2 HCPL3120 560 4081 U1:D R3 R5 8 VCC 7 VO1 6 VO2 5 VEE R6 U4 1 N/C1 2 ANODE 3 CATHODE 4 N/C2 10 8 VCC 7 VO1 6 VO2 5 VEE J4 1 2 CONN-H2 G15V2 HCPL3120 Figure 0.2: One phase gate driver schematic circuit Table 0.1: List of the components for gate driver circuit No Component Unit 1. IL0515S 6 2. IN4748A 6 3. Capacitor 1nF 6 4. Resistor 4.3kΩ 2 5. Resistor 560Ω 2 6. Resistor 10Ω 2 7. Resistor 10kΩ 12 8. IC 7414 3 9. IC 4081 3 10. HCPL3120 6 20 Figure 0.3: Three phase gate driver PCB layout 3.2.2 Inverter Figure 3.4 shows the schematic diagram while Figure 3.5 shows the PCB layout for three phase inverter. This circuit consists of power transistor MOSFET (SPP11N60C3) and a 470µH 100v power capacitor. The general function of inverter is used to transform DC power into three phase AC power. For inverter operation, power flow from the DC side to the AC side and able to carry the voltage supply up to 400 volts. The three phase inverter circuit consists of several components as listed in the Table 3.2. 21 Figure 3.4: Schematic diagram of three phase inverter Table 0.2 : List of components for three phase inverter No Component Unit 1. MOSFET SPP11N60C3 6 2. Capacitor 470µF (450V) 1 Figure 0.5: PCB layout for three phase inverter 22 3.2.3 Filter The LC filter structure is employed to filter the switching frequency components of the rectangular voltage pulses generated by the inverter. However it increases the output impedance of the system and causes distortion due to the harmonics of the load current . The filter will enable the required frequencies to be passed through the circuit, while rejecting those that are not needed. In this project, the value of L and C is choose for L=68mH and C=22F. Input Output Inductor Capacitor Figure 0.4: The circuit for the LC filter 3.2.4 Transducer Figure 0.5: Current Sensor BB-ACS756 Current Sensors as shown in Figure 3.5 and 3.6 are used of controlling, monitoring or measuring AC currents. The sensors serve as feedback elements between the output line current of inverter and control circuitry providing accurate regulation of switch mode power supplies. The BB-ACS756 is used to measure current and provide the 23 feedback signal to the PI-Repetitive controller. It is also can be used for over current fault protection. The BB-ACS756 is come with the one set of T-connector and a 3 ways angle pin header. The ACS756 is power up with 5V and gives output voltage to indicate the direction and current value. The initial condition (no current) the output voltage is 2.5 volt. When the voltage increase mean the current is flowing the one of the direct and the voltage is proportional to the current. This also applies in the other direct of the current if the voltage drop. The output sensitivity of this transducer is 40 milivolt per ampere and it can measure maximum up to 5A, meaning the maximum output voltage is 2.7 volt. Figure 0.6: Current Sensor BB-ACS756 pin configuration According to datasheet of ACS756, the sensor has sensitivity of 40mV/A. This explain every rise of 1 A will increase 40mV to VIOUT pin of BB-ACS756. This sensor can be used in both AC and DC circuit. Initially, the sensor produces output of 2.5V from VIOUT pin for 0 A current reading. Since the sensor can measure up to ±50A, thus the maximum voltage for positive current measurement is 4.5 V (+50A) and negative current measurement is 0.5 V for (-50A). 24 188.8.131.52 ADC for Current conversion The output of the sensor is voltage which it needs further calculation to convert it to current. By taking the ratio and sensitivity of the sensor, it can be written as Equation 3.1:- = (0.1) Change of voltage can be written as follows:- Change of voltage = (Sensor Reading – Initial Reading) bits Change of voltage is different between output voltage at the time (sensor reading) and initial output voltage which is around 2.5V. Since 2.5V give 512 in 10 bits ADC in Arduino, thus change of voltage can be written as Equation (3.2):- Change of voltage = (Sensor -512) bits Combining Equation (3.2) and Equation (3.1) gives:- I (mA) = (1000mA) Hence, I(mA) = ( Or )(122) (0.2) 59 REFERENCE  P. Farmanzadeh, M. R. Azizian, and A. 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