Three Phase Induction Motor Controlled by Analog Components Driving Wheelchair

CHAPTER 1

INTRODCUTION

1.1       BACKGROUND

Wheelchair is a chair with wheels that invented for transportation a long time ago. The main function of wheelchairs is to support people that difficult to walk due to injury and illness and now it becomes demand amongst disable people. The work principles of wheelchair are propelled by turning the rear wheels by hand and force stop also by hand force. Often there are handles behind the seat for someone else to do the pushing.  But nowadays, this device is updated by applied motor to turn the wheels. The application of wheelchairs are become widely used because of improvement of the technologies, designing with introduce some safety tools and economic market value. Thus with some technology and design improvement, the wheelchairs will be come as a short travel transport, load carrier, and mores. It can be used as a device to bring our stuff such as book, laptop or projector in class or outside class also. By the way, the traditional wheelchair pretends to use more hand energy to turn the wheel. Hence the rising of the motor industries will be created a good situation to improve the wheelchairs design according to the technology change. To less the used of the man energy to propel the wheelchair, the motor can be implemented to the wheelchairs itself. There are a lot of motors in the market such as direct current motor, stepper motor, induction motor and mores in the market. To control the wheelchair the motor must be have a high torque to overcome the load carrier. Thus, the induction motor is the best mechanism to be chosen to drive the wheelchair. However, there are some condition should be fulfilled to the specification of this project since the used of induction motor is there are a lot of techniques that can be used to control the induction motor and pulse-width modulation (PWM) is the one of that.

The induction motor applications are highly demand amongst industry especially in automotive because three phase induction motor is rugged, reliable and economical. In industrial applications, variable frequency and voltage are needed to control the induction motor. Induction motor is used to control important machines and robots with using the vary frequency and voltage that supplied by voltage source inverter (VSI) .The induction is operated by torque that is produced by electromagnetic from the magnetic field from stator windings. The stator windings will be caused the eddy current thus the magnetic region will be occurred. In induction motor mechanisms, the stator windings are connected with rotor especially has a small air gap, hence the change of the magnetic flux in the stator windings will cause the rotor speed will be changed. Therefore, the speed of rotor is corresponded to the stator windings. However, the three phase induction motor need the alternating current AC as an input source to obtain the inconstant waveform and difference phase. In work principles for three phase induction motor, the AC will be supplied by 240 AC V source and with some circuit of operational amplifiers, the sine wave will be multiplied to three waveform that have same magnitude but different phase. The unbalanced phase three waveforms will be compared to triangle wave and then inverted with octocouplers for produce toggle and upside down rectangular waveforms. The waveform then transferred to voltage source inverter (VSI) that generated by a constant direct current voltage form full bridge rectifier circuit. These outputs are transmitted to the gate driver circuit to operate the motor. Since the main circuit of this project is consumed by the analog circuit, hence the analog components properties will be analyzed first before making the whole circuit.   

Analog components such as resistor and capacitor are used to conduct the analog circuit. Analog components are things that can deal with continuously varying signal such as resistors, capacitors, transistors. However, these analog components also can be used in digital circuit. Transistor amplifiers, operational amplifiers and oscillators are some of the analog circuits that be found. For this project, the analog circuit is used to control the three phase induction motor for drive the wheelchair.

The “Three Phase Induction Motor Controlled by Analog Components Driving Wheelchair” project is dividing into three different tasks such as analysis the three phase induction motor, studies and designs the analog circuit and fabricate simply prototype the mechanical parts of wheelchair.

1.2      PROBLEM STATEMENT

Nowadays, three phase induction motor is frequent used compare to single phase induction motor. Mostly the induction motor is controlled by PWM technique. Gears, chain and bearings are needed to carry the electrical power from three phase induction motor by convert to mechanical power to operate wheelchair.

1.3      OBJECTIVE

Three phase induction motor controlled by analog components driving wheelchairs is developed with the listed objectives below:

·   To design and develop analog base PWM controller for running induction motor

·   To design the mechanical parts of motorized wheelchairs by using CATIA software

·   To fabricate simply prototype of the economic motorized wheelchairs

1.4      PROJECT SCOPE

The scope of this project is to design and fabricate the electrical and mechanical parts of the motorized wheelchairs by using analog components to control three phase induction motor.

1.5      THESIS OUTLINE

This thesis consists of seven chapters. Chapter 1 will discuss about the overview and background of the project, problem statements and objectives to overcome it and project scope.

Chapter 2 consists of literature review to describe the details about this project. In this chapter will explain the concept of the operating mechanisms system, the work principles and components that involved in this project.

Chapter 3 will explain about the project methodology. It consists of control plan of the project, flow chart of the process and all circuit diagrams and mechanical design that implemented to this project.

Chapter 4 will discuss about the result and discussion that obtained from this project including all recorded data from analyzer and stimulate.

Chapter 5 contain all the detail descriptions of this project. The conclusion will be taken and the recommendation steps or ideas will come out to improve the project specification quality.

Chapter 6 will discuss further about conclusion and all previous chapters before. All discussion will be recorded and stimulated due to requirement project specifications and needed.

Chapter 7 discuss the conclusion from previous chapter and make overall conclusion about the project. This chapter will explain more about the recommendation method that can be implemented for better future development of this project.

CHAPTER 2

LITERATURE REVIEW

2.1      CHAPTER OVERVIEW

This chapter will describe more on the theories on how to control the three phase induction motor by using analog components to drive the wheelchair. All sources are recalled from previous researches and will be some modify on them corresponding to the title itself. By referring to the chapter, much knowledge is needed to control the parameters of the induction motor especially three phase induction motor. To implement of this final year project, some of knowledge in electrical is applied to design the analog circuit for generate pulse width modulation (PWM) and all of its controller such as voltage source inverter (VSI), gate driver, opt-coupler, triangular wave , three phase sine wave and comparator. All techniques are combined to run the three phase induction motor and support the wheelchair load includes the user respectively.

Literature review was one of the gaining knowledge processes by searching, reading, discussing and researching on the various sources and designing the project based on requirement needed. These sources are gained from internet source such as previous research or project, thesis, reference books, and journals.

2.2      SINUSOIDAL PULSE WIDTH MODULATION (SPWM) TECHNIQUE

Sinusoidal Pulse Width Modulation techniques are characterized with the constant in the amplitude pulses by different duty cycles of each period. The widths of SPWM are modulated to gain inverter output voltage control.  In motor control and inverter application, the SPWM technique is widely used as controller which three sine waves and a high frequency triangular wave is used to generate the PWM signal. The single sine wave is generated by using LM324 low power quad operational amplifiers(op-amp)  from the power source then will be experienced to three inverter circuit that build up by three LM324 op-amps to generate three sine waves by each inverter  that carriers reference signal and have 120 degree phase difference with each others. These sinusoidal waves have frequency range 50-60 Hz. Generally, the frequency of sine waves required is lower compare to triangular wave frequency that generate from independent circuit by using two TL082 wide bandwidth dual JFET input operational amplifier(op-amps) . The carrier triangular wave usually has very high frequency (kHz). (Nazmul Islam Raju et al., Vol.3 No.3)

Figure 2.0: Functional Block Diagram of PWM Controller

The three sine waves and triangular wave will be compared to generate the switching signal by using the comparator circuit. The comparator circuit is designed using LM311 op-amps which low in input current voltage comparator. The comparator will produce a pulse after the sine voltage is higher than triangular voltage. This pulse will be used to trigger the respective inverter switches. Three comparator circuits are modified to generate three PWM waveforms.

Figure 2.1: Pulse Width Modulation switching signal generator

Source: Siti Nursyuhada Mahsahirun (2013)

The signal then will be inverted by VSI controller to generate the three phase PMW voltage source inverter. By using insulated gate bipolar transistor (IGBT) and gate driver or Intelligent Power Module (IPM) application, the three phase PWM signal will be applied to run three phase induction motor with the carrier load.

The three phase signals will be contained some errors which can lead to electrical noises when interfering with other section circuit. To reduce or minimize the errors, the isolator is designed to the circuit. MCT2 opt-coupler application is the one of the isolator that use to isolate one section circuit from another which each section have different in signal voltage levels. Opt-coupler ensures to compatibility between the signal voltage levels itself. Six MCT2 opt-coupler circuits are designed to generated three pairs of PWM signal which is three for high voltage levels and three low voltage levels.

Figure 2.2: PWM waveform with different duty cycle

Source: Michael Barr (2007)

Figure 2.2 shows the PWM signals with different duty cycles for switching technique. Duty is resulted from the fall and rise time when the three sine waves are compared with triangular wave.

2.3      INTELLIGENT POWER MODULE (IPM) AS PWM CONTROLLER

IPMs are standing for intelligent high performance components in construction of semiconductors. IPMs have high efficiently in controlling the electricity and voltage. IPM is invented with application of an insulated-gate bipolar transistor (IGBT) on it that can minimize switching losses and lead to improve the energy consumption from engines, inverters and other technology. By optimised gate-driver and protection circuitry, IPMs use a very fast and low loss IGBT that enable to achieve high flexibility in regards to their performance range which is from 10 A/600 V up to 800 A/1200 V. Epoxy based isolation system and ceramic isolation material is used to modulate low and higher power IPMs respectively. By comparing to conventional bipolar transistors, IPMs can provide high protection and performance against outages.

IPMs are becoming very smaller, get faster and more powerful. They enabled to generate the production of acoustically noiseless inverters with an up to 20 kilohertz carrier frequency. IPMs are one of the power electronic components that widely used in industries due to its high efficiency and good performance. The solar and wind power technology also use the application of IPMs to transform the direct current from solar cells or wind turbine input into alternating current.

 Figure 2.3: Functional Block Diagram of PWM Controller with Intelligent Power Module

Figure 2.4: Intelligent Power Module (SKiiP 613 GD123-3DUL V3)

Source: Datasheet (SKiiP 613 GD123-3DUL V3)

2.4      THREE PHASE INDUCTION MOTOR

Induction motor is the electrical motor that converts electrical (input) energy to mechanical (output) energy to carry or overcome the load applied especially in industry application. In industry application, three phase induction motor becomes very demand due to cheaper cost, more rugged and easy to control compare to another electrical machines.

Figure 2.5: Three Phase Induction Motor Mechanism

Source: Robotic_31 (2013)

The figure shows the some common parts in induction motor that each part has its own function. All of these parts also effect to the temperature of the motor, the efficiency and mores. Three phase induction motor have two main parts in working principle that is stator and rotor.

The Stator is the stationary part that in it consists of the rotor that acts as a rotating mechanism of the induction motor. The air-gap between the stator and rotor is varying about 0.5 to 2 mm. Therefore in operating there will be some losses by the air-gap.  Three phase alternating current source is connected to the three phase winding circuit in the stator that build by numbers of slots that arrange in such a manner. Thus when the AC is supplied, the rotating magnetic field will be produced and rotate at synchronous speed. The rotor is build consists of cylindrical laminated core which design in the parallel slots to carry conductors that is heavy copper or aluminium bars. The conductor fits in each slot. At the end rings, the conductor is short circuited.

Figure 2.6: Stator and Rotor of Three Phase Induction Motor

Source: AC Induction Motor (2003)

Figure 2.6 shows the stator and rotor winding in three phase induction motor. The windings are consisted of three pair of poles in stator winding. The three phase sine waves are needed to generate the magnetic flux in stator winding that show in Figure 2.7.

Figure 2.7: Three pair of poles in stator winding

Source: Jason Chong Nao Chen, UMP (2010)

The rotating of the rotor is effected by the current that induce by electromagnetic force (e.m.f) from the revolving magnetic field that produced in the stator and cuts across the conductive bars of the rotor. The current flow is opposite to the back e.m.f that can twist motion or torque in the rotor. Therefore the speed of the three phase induction motor can be controlled by controlling the ac source input parameters.  (Source: Electrical Engineering Portal 2012)

Figure 2.8: Stator and Rotor Working Principle

Source: Basic Theory Motor (2003)

The rotating rotor in three phase induction motor is carried the synchronous, n_sync and rotor speed, n_m.

               n_{sync =120f/p}                     (2.0)

                                             n_m =  (1-s) n_sync               (2.1) 

                                                                         

where f is the frequency Hz of the system and P is the number of poles in stator winding. The slip speed of the machine, s is the difference between the n_sync and n_m (rad/s). The rotating magnetic field B then will be passed over the rotor bar and induced a voltage, e_ind that that show in figure 2.9 below.

Figure 2.9: Armature loop working principles when magnetic flux takes place

Source: Learn-About-Electronics.com (2011)

The induced voltage can be expressed as in Eq. (2.2)

e_ind = (v x B).l         (2.2)       

                                                                                     

where v is the velocity of the rotor bar and l is the length of conductor in magnetic field. The e_ind  in the rotor will be carried the motor speed, ω_m then produed the motor torque, τ.

Figure 2.10: Field and armature winding in induction motor

Source: Howard W Penrose, Ph.D.

Since the loss in air gap is approximately equal to zero, hence the e_ind is equal to field voltage, Ea at the stator winding.

Ea= e_ind        

             (2.3)

e_ind =KΦω               (2.4)                

P=τω                          (2.5)

where K is a constant represent the construction in the machine and Φ is the flux. The motor speed, ω is directly proportional to field voltage, Ea. The power of the motor, P is expressed in form of torque and speed of rotor that will be connected to wheelchair by shaft and gear applications. (Electric Machine and Power System Fundamental, Stephen J.Chapman)

2.5       POWER DRIVER FOR WHEELCHAIR

The motor that use to support the wheelchair must be has high speed, high torque and easy to control. The wheelchair and the user load are considered and calculated respectively in designing and fabricating the whole electrical and mechanical parts. A shaft is needed to convert the electrical to mechanical power to run the wheelchair. The shaft is fixed by two gears which one is fixed on itself and another one is fixed on motor shaft.

Figure 2.11: Gear-chain-gear as a connecter between shaft of wheelchair and induction motor

The torque from motor is carried through the gear to rotate the wheels with rotational velocity, v is effected by the motor speed and obtained by equation below.

                                           V=rω                                  (2.6)

where r is the radius of the gear. The tension of the chain is ignored due to just two gears are used. The wheelchair will be increased when the motor speed is increased.

CHAPTER 3

METHODOLOGY

This chapter will be described on the developing process for this project. According to the project requirements, this chapter will explain more on the methods how to design and fabricate the electrical parts in software and hardware designation. Both of these main parts will be discussed in details along the figure related.

3.1       PROJECT PROCESS FLOWCHART

Figure 3.1: Electrical process flowcharts

The figure 3.1 shows the process flowchart of designing electrical mechanisms. All of the stages are started from designation in NI Multisim software with some troubleshoots for the real circuit in hardware parts until the circuit is performed well when the load is applied. There are some important stages in designing the analog circuit for three pairs of PWM output. These stages are performed by block diagram below.

3.2      CIRCUIT DESIGN

Figure 3.2: PWM circuit block diagram

3.2.1   SINE WAVE GENERATOR

First at all, the PWM circuit is designed in NI Multisim by using discrete components. The reference single sine wave is applied from the power source and inverted back by resistor and application of op-amp to produce three balanced sinusoidal sine waves that each is carried with 120 degree different phase. These sinusoidal waves are generated by LM324 IC op-amps. Hence, four LM324 IC are needed to conduct reference and three sine waves. The LM324 IC has saturated voltage +Vcc and –Vcc about +15V and -15V respectively. These sinusoidal sine waves are defined according to equations below.

V_sw1 (t) = sin 2πt              (3.0)

V_sw2 (t) = sin (2π/3)t        (3.1)

V_sw3 (t) = sin (4π/3)t        (3.2)

Figure 3.2: Three signal phase sine waves circuit using LM324 IC op-amps

Figure 3.3: Stimulation of three phase sine waves

Figure 3.3 shows the output from the three different circuits that carried the same different phase to each other.

3.2.2   TRIANGULAR WAVE GENERATOR

The signal sine waves then will be compared with triangle wave carrier signal. The triangular wave is generated by triangular wave generator that consists of integrator and square wave generator circuit. These circuits are conducted by using TL082 wide bandwidth dual JFET input operational amplifier with saturated voltage +Vcc and –Vcc about +15V and -15V respectively. The figure below shows the connection in triangular wave generator circuit.

Figure 3.4: Triangular wave generator circuits by using TL082

The bandwidth of triangular wave is produced from bandwidth of square wave (right side in the circuit) in the other words these two bandwidth are same to each other. The resistors R11 and Rf5 in the square wave circuit are acted as voltage divider and output feedback. The output that in square wave form will be feedback to the integrator circuit as input voltage. When the power is swift off there are no voltage flow along the resistor R9, hence the voltage across capacitor C1 is zero.  When the power supply start to swift on, input square wave voltage will be flowed through the resistor R9 due to capacitor C1 is charging. In the integrator circuit, the capacitor is charged at the initial moment until fully charged and then discharged to generate the triangular wave. This process will be continued again and again. Assume that TL082 is the ideal op-amp. 

Figure 3.5: Stimulation of triangular wave

Figure 3.5 show the stimulation output from triangular wave generator which carried a high range frequency.

3.2.3    COMPARATOR

The sine wave signals and triangular wave then will be compared together to form three pulse width modulation signals (HIGH). The comparator circuit is conducted from LM311 amplifier with low input current voltage comparator. This amplifier has saturated voltage +Vcc and –Vcc about +15V and -15V respectively. Three comparators are needed to generate three PWM (HIGH) which is one LM311 is used for each circuit. The output in PWM form will be generated to octocouplers.

Figure 3.6: Comparator circuit using LM311 amplifier

Figure 3.7: Stimulation of comparator output

Figure 3.7 shows the stimulation output from the comparators which have three PWM signal with different in duty cycles.

3.2.4   OPTOCOUPLER

After sine and triangular wave are compared, the output is then transferred to octocoupler circuit to generate HIGH LOW pairs of PWM signals. Octocopuler is allowed all signals to be transferred between circuits and at the same keep those circuits electrically isolated from each other .Six octocoupler circuits that designed in pairs are used to modulate three pair of PWM signals. The three pair of PWM signal will be passed to Intelligent Power Module (IPM) that acted as a controller between the main circuit and three phase induction motor. The function of these optocouplers are to avoid the rapidly change in voltages or high voltages on one side of a circuit from distort transmissions or damage components on the other side of the circuit. The optocoupler contains a light source that placed near to an LED which converted electrical input signal into light, a closed optical channel and a photo sensor, which detected incoming light and modulated electric current flowing from an external power supply. The octocouplers are designed must be have high output current and can be operated at the high surrounding temperature. HCPL-J314 family is fulfilled the needed in controlled three phase induction due to high voltage and current are used with saturated voltage about +9V. This octocoupler type is ideally suited in driving power insulated gate bipolar transistor (IGBT) and metal oxide semiconductor field effect transistor (MOSFET) in induction motor controlling that used potentiometer as a controller the current flow.

Figure 3.8: Octocoupler circuit using HCPL-J314

Figure 3.9: Stimulation of HIGH PWM at octocoupler

Figure 3.10: Stimulation of LOW PWM at octocoupler

Figure 3.11: Stimulation of HIGH LOW PWM pairs

Figure 3.9 – 3.11 show the stimulation output at octocouplers which carried out with three pair of PWM that been isolated then will be transferred to intelligent power module.

3.2.5   INTELLIGENT POWER MODULE (IPM)

Pulse width modulation with HIGH LOW signals then will be connected or transferred to gate driver. The gate driver acted as power amplifiers that can accept a low input power from controller circuit and produce a high driver current input for the gate high power transistor IGBT. The IGBT is used as efficient switching devices for the inverter power circuits, so simple and efficient transistor drive circuits can be used. Also, the overlap protection is taken into consideration. The PWM inverter is to feed an induction motor with adjustable voltage to frequency in a proper relation to maintain approximately constant rated flux in the machine over the operating frequency range (1-50 Hz). Hence, the drive system is used to control the speed of a three phase induction motor from very low speed to the motor rated speed at a constant torque. This PWM switching strategy is proposed to minimize the harmonic distortion that cause by analog circuits. The gate driver and IGBT circuit are performed as a connecter between the main analog carriers signal circuits and three phase induction motor. Implementation of intelligent power module (IPM) as a controller to three phase induction motor can be maximized the efficiency of the motor. The IPM that consisted of the gate driver and IGBT circuit can be performed high level of switching technique, prevent losses and at the same time the harmonic distortion will be reduced.

Figure 3.12: Intelligent power module (IPM) internal circuits

3.2.6    Y-CONNECTION THREE PHASE INDUCTION MOTOR

The three pairs of HIGH LOW PWM output from IGBT (IPM) then will be connected to the Y-connected induction motor. These three-phase voltage sets will be applied to the stator of the three phase induction and a three-phase current set in stator are started to flow and produce the magnetic field in the stator which is rotated counter clockwise direction. The magnetic field will be passed over the rotor bar by air gap between the stator and rotor that will be leaded to induce voltage will be generated. The current that is flowed along the rotor will be produced a rotor magnetic field. These magnetic fields that are generated by stator and rotor will be caused rotor start to be rotated and induced torque.

Figure 3.13: Stator and rotor winding in three phase induction motor

3.3      PROJECT PROCESS FLOWCHART

Figure 3.14: Mechanical process flowcharts for wheelchair modification

The figure 3.8 shows the process flowchart of designing mechanical mechanisms of wheelchair. All of the stages are started from Catia software sketching to fabricate some modification parts with some reworks will be done if the target is not achieved. All these process will be done until the desired design is achieved.

3.3.1   WHEELCHAIR PARTS

Figure 3.15: Basic manual of wheelchair in CATIA software

The figure 3.9 shows the basic parts of the wheelchair. All of these parts have their own functions. For modification wheelchair especially when the motor is applied, some of these parts will be undergo modified or dismissed. The motorized wheelchair is needed a shaft and a spoke will be designed as a connecter between the load that is wheelchair to the three phase induction motor. The electrical power from three phase induction motor will be converted to mechanical power by rotates the gears that connected with shaft to the wheelchair.  The shaft is connected to the both of the wheels by a bearing each to run the wheelchair. The torque of the motor will be defined how much the load can be carried by the motor. The rotational speed of the motor through the output power will be decided the shaft and wheelchair rotational speed.

Figure 3.16: Gear at shaft of induction motor and the wheelchair connection

Assume that the tension of chain in the chain is ignored and gear diameter of motor (gear A) is same to gear connection at shaft (gear B), thus radius of gear at motor is equal to gear connection at shaft. Since the gears are connected to each other, hence the angular speed is equal.

                     V_A =r_Aω                   (3.6)

V_B=r_Bω                    (3.7)

ω_A=ω_B                     (3.8)

T_A=T_B=F_AXR_A      (3.10)

                                                                                                                         

Tangential speed of gear at the motor,V_A (m.rad/s)

Tangential velocity of gear at the wheelchair shaft,V_B (m.rad/s)

Radius of gear,r  (m)

Torque carrier of the gear, T (N.m)

Force carrier of the gear,F (N)

The angular velocity and torque carrier of the shaft will be transferred to the wheels through bearings and will be converted to mechanical power to operate the wheelchair.

P_mech=T_loadω            (3.11)

Mechanical Power of motor, P_mech (W)

Torque of load, T_load (N.m)

Rotational speed of the wheelchair shaft in (rad/s)

Speed of the induction motor with load applied can be controlled by controlling the analog input such as input voltage control, switching frequency and mores. However a lot of things should be considered especially in the wheelchair mechanism and losses through the analog circuit and the three phase induction motor itself.

for more info,please visit this video..thank you

https://www.youtube.com/watch?v=HpQQk3kvpEs&feature=youtu.be