Control Of A Switched Reluctance Motor Engineering Essay

Control Of A Switched hesitance Motor Engineering EssayThe principal(prenominal) objective of this chapter is to spot the light on the practical carrying into action of some form of tick off on an actual heterotaxyed faltering ride in discernment to merely theoretical method including simulation and caseling. Moreover, the design of the controller involves trim back the noise. The crucial motivation for this is to enhance new expertise, sensibly regarding racing circuit design and look the office of a Programmable interface controller (PIC).A bastinadoed reluctance repulse (SRM) has been appeargond since the nineteenth century, but the renewal of this motor has been to discover a soaring- provide throw offed maneuver 13. The earlier motor was facing a controversial issue in their control where the designer electronic switching was truly expensive and has many drawbacks.The Switched Reluctance Motor (SRM) is an electromagnetic, rotary machine in which tortuosity is produced by the tendency of its movable part to move to a position where the inductor of the excited air certain is maximized 12. Furthermore, (SRM) has been proposed for variable repair application programs 13. In oecumenical a salient-pole synchronous machine without dramatic art excitation or permanent magnet is c every last(predicate)ed a reluctance machine. From the general definition (SRM) is classified as a synchronous machine, but has different construction. These differences ar both stator coil coil and rotor coil coil have salient poles. However, the stator has wounding field coils but the rotor has no coils or permanent magnet. Moreover, the stator has broad(prenominal)er effect of poles or (tooth) than the rotor. While for each one(prenominal) pole in the rotor is excited by the opposer pole in the stator due to a sequence of underway pulses which produce magnetic field on each stator poles. The Switched Reluctance Motor (SRM) tolerate be more capable for variable drive on than AC and DC motor. Since it is simple, robust, has a high efficiency and high index density 3, 10, 12. depend 1.1 two- two poles SRM 12Over the past 30 years the agency electronics growth has made the exploit of the characteristics of reluctance machines sufficiently well. Consequently, several(prenominal) successful products be now manufactured. The rotation of the motor depends on the angle between the rotor poles and the stator poles where the current is switched on or off to each poles in the stator where the position of the rotor is very signifi micklet. For the motoring principle example, two- two poles (SRM) where stator has two poles with two wound field coils connected in serial publication and two poles in the rotor without magnets or winds and free to rotate as it shown in figure 1.1. If the rotor poles edge is started to be aligned, the current is switched on. Consequently, the inductance is increased and the torque in the rotor is occurred to wedge the rotor in clockwise direction. The direction of the rotation is addressed by the current. The current is switched off when the rotor poles be fully aligned with the stator poles that make the rotor free to move. However, if the current is not switched off the torque at the fully aligned is start out negative that produces an attraction between the poles where the negative torque and positive torque substructurecel each other 12. The ideal current waveform is therefore a series of pulses synchronized with the rising inductance intervals. The cycle of torque production associated with one current pulse is called a stroke.12 As a turn out, to increase the response more teeth erect be add to the stator and the rotor.From the instantaneous electromagnet torque equation which was derived by T.J.E.Miller(2001) 12 Te = i2/2 dL/d that shows the torque is proportional to the square of the current. Therefore, the current is always unipolar. However, at the end of each stoke the potential drop must be reversed to return the flux gene linkage to zero. The power switching IGBT, GTO and MOSFET or any other switching devices can be utilize in the power electronic topologies 3. These switches are used to pay and close the exiting power in the stator turn.1.5. Applications of SRMSince the SRM has a significant characteristic operation and design which shows many advantages and makes them suitable for various applications. R.Krishnan (2001) 10 shows the wide browse of applications. For example, machinator drive, air-handler motor drive, hand fork lift/ pallet truck motor drive, door actuator and washers and dryers machine, those applications are low power applications where the drives are little than 3hp. Moreover, the medium power applications range is less than 300kw such as industrial general purpose drive, train air conditioning drive and mining drive. However, the SRM did not find much(prenominal) attention by the manufacturers in this range of p ower. The high power drives are still under study for drives up to 1000hp for fan and pump applications where the converter is very competitive. The high reanimate applications such as screw rotary compressor drives, centrifuge for medical applications, and aerospace applications the SRM is a perfect option for them due to the small size of the rotor and high power density. Some efforts of study are in Mild Hybrid Vehicles that is account by (Watterson, P.A. et al) 17 in 2008.1.6 Research areaSince the SRM has appeared and has disadvantages such as reduction of acoustic noise and torque ripple. According to the noise and vibration sources can be classified into four main categories magnetic, mechanical, aerodynamic, and electronic. The classification was done by R.Krishnan (2001) 10 as it shows in figure 1.2. Most researches are beggarlyd on the design of the motor or in the controller to improve the motor performers and crop the noise. Iqbal Husain (1994) 8 discusses the effec t of the high ripple toque which causes vibration and acoustic noise. The case was in driving SRM for low speed and high performance applications by a new PWM strategy current control. The method was ground on optimum profiling of the phase current during an extended overlap sword lilyg conduction head of two phases. The result shows a smooth operation with minimum torque pulsations by controlling the current profiling. Moreover, other studies were in magnetic radial eviscerate as M. N. Anwar (2000) 1 shows the lower noise is occurred when the dominant mode frequencies is high. As a result the research has experimented a proposed design considerations to a 4-phase, 8/6 (1-repetition) and a 3-phase, 12/8 (2-repetition) 1.0 kW SRM with low acoustic noise requirement. The results of the proposal design shows that the noise level has been reduced however, a 3-phase SRM is noisier than a 4-phase SRM. There are other research was on reducing the noise by Adding extra idle words to the phase winding to reduce magnetic stress during commutations with Two spirit level power converter. Adding extra winding to the phase winding in 6/4 SRM with Two stage power converter shows a significant profit in the efficiency and reduce in the vibration and noise 16. The electronic sources of noise occur by reason of the harmonics of potential and current. The significant research is reported by (Lecointe J.P et al) in (2004) 11. The research was in adding an auxiliary winding to the model of a BDFRM (brushless doubly-fed reluctance machine) to shows that the additional winding has a benefit in reducing the noise in SRMs where a specially derived current is injected to create a suppression force. The BDFRM is used to analyse the equivalent circuit where the equivalent circuit of the model is similar to SRM. However, the process still needs to be complete victimisation two current sources.Figure 1.2 sources of noise in galvanic machines 10Advantages and disadvantages of 3 s taple fibre power electronic circuitsThere are many power electronic topologies that is used for SRM depends on the machine phase configurations. R. Krishnan (2001) 10, figure 1.3, has classified the power converters for switched reluctance machines. The simple three topologies areFigure 1.3 Classification of power converters for SRM 101.7.1. Single-Switch-per-Phase Circuits (Split dc supply converter)The canonical operation of this topology, figure 1.4, is to split the reverse dc power supply into two capacitors. The phase voltage is half the dc voltage when the switch is on and negative half voltage when the switch is off. Consequently, this configuration is a disadvantage. Moreover, the maximum speed and the output power are half the rated while the current and the voltage are half. This topology is only used for low- personify application due to the high power losses. However, the advantages of this topology are simple and less cost. 3, 10Figure 1.4 Single-Switch-per-Phase Circ uits (Split dc supply converter) 101.7.2. Single-Switch-per-Phase Circuits (Bifilar type)The basic operation of this topology uses a bifilar winding, figure 1.5, with the motor winding to regenerate the stored get-up-and-go to the supply that the phase winding is connected in series with the switch, and the diode is connected in series with the bifilar winding. The reflected energy is an advantage for this topology in some applications, where the electronic transistor voltage is much higher than the supply voltage. However, the cost increases as the extra winding is added to the motor and the complex design of the power electronic. Moreover, the power density of the motor reduces because of the bifilar winding. 3,10Figure 1.5 Single-Switch-per-Phase Circuits (Bifilar type) 101.7.3. Two-switch/phase unsymmetrical Bridge ConverterFrom the half brace topology that is illustrated in figure 1.6. if both Q1 and Q2 are turned on the make voltage at the winding is equal to the supply vo ltage. However, if both Q1 and Q2 are turned off the apply voltage at the winding is equal to a negative supply voltage where D1 and D2 to avoid the freewheel currents. The advantages of this topology that it can give a negative voltage to reduce the torque ripple refer to noise for a high performance SRM drive system and it can be used for generator or motor operations. The disadvantages more control is needed, more fault in the switching 3, 10, 12.Figure 1.6 Two Switched / Phase Asymmetric Bridge Converter 121.8 Speed and Position ControllerThe switched-reluctance motor is basic control system form of a torque-controlled drive as compared in performance to a D.C motor (separately-excited). vernacularly, controlled speed or even position is the most requirements. The SR motors speed increases if torque is still produced. As the D.C. drive the torque of SR motor controller is included within a speed regulating loop. The rotor position sensor, which is the encoder, is used as a fee dback to derive the speed of the motor readily as it shown in figure 1.7. From the figure it can be seen that an additional feedback is introduced to achieve the position control of the SRM 3.Figure 1. 7 basic speed and position controller for SRM 3Aims and ObjectivesThe aims of the project are to design, build and test a power electronic circuit for Switched Reluctance motor (SRM) using Bifilar type.The objectives are as followingUnderstand the operation of two- two poles SRM to realise the behavior of the motor and their characteristic. We can know from their characteristic how to make the motor spin and the control techniques that is used for them.Select and Design Power Electronic Circuit can help to active a high efficiency, low noise and low cost. campaign Power Electronic Circuit with Resistive Load to find the advantages and disadvantages of the circuit when the resistive load is applied to the motor.Design, Build and Test current limiting circuit where the current limitatio n can achieve low torque rebel. From the low torque rebel the noise can be decrease.Rotate motor using direct feedback where the position of the rotor is important to detect the moment of switching on and off.Study and understand PIC 18F 46K20.Program PIC to control SR Motor by designing a simulation using the MATLAB or other programmes.Chapter 2Choosing power electronic component2. OverviewOver the time motor control has a significant growth in the industrial control where digital manifestation processors together with external hardware and distract software are used widely. In order to control the motor the switching device should switch on and off according to the position of the motor rotor and the apply current to the stator winding. The aim of this chapter is to highlight the details of the components that were used in the controller design.2.1 Technical operation of Simple SRMThe simple SRM has 2 poles in the stator and 2 poles in the rotor, figure 1 which the stator iron c ore has square shape with two winding in the upper side opposite the poles. Both stator and rotor are salient poles where the free spinning rotor is placed between the stator poles. In order to spin the rotor, stator poles are energised by the winding when the rotor poles are unaligned with stator poles. The inductance increased and the torque is produced as the rotor approaches the aligned. At this point the stator winding is demagnetised allows the rotor free to spin. The time of the energised and de-energised of the motor windings depend on the rotor speed.Figure 2.1 (a) Simple SRM 2/2 poles with bifilar winding122.3 Winding connectionsThe motor has a bifilar winding to build up the current in the stator quickly, figure 1, which facilitates the higher torque and magnetic flux densities occurring. As a result the stored energy regenerated to the supply that the phase winding is connected in series with the switch device. This leaded to three achievable connections, figure 2, for b ifilar winding.Figure 2.2 workable winding connectionsThe first connection shows the parallel connection that has a granting immunity connected in parallel to the motor windings to reduce the power losses when the switch is off. This connection has the main disadvantage due to the high loss.The second connection shows series connection that two switching devises are used which increase the cost of the design. However, this topology is the most special K one for SRM according to reduce the switching heat losses, protections and their control flexibility that is handling the phase current and the machines acoustic noise.The triad connection is the most cost effective and easier to control for the simple SRM figure 2. Moreover, it is offering the zero voltage supply as a reference for all power switching that make it suitable for low- voltage systems. Simply this configuration operates as it shows in figure 2.3, When the current of phase-A is turned off by removing the base drive s ignal to T1, the induced EMF in the winding is of such polarity that D1 is forward biased. This leads to the circulation of current by means of with(predicate) D1, the bifilar secondary winding, and the source, thus transferring energy from the machine winding to the source. The various timing waveforms of the circuit are shown in Figure 2.3. During current turn-off, the applied voltage across the bifilar secondary winding is equal to the dc link voltage. The voltage reflected into the main winding is dependent upon the turns ratio of the windings. Considering the turns ratio between the main winding in series with the power switch and the auxiliary winding in series with the diode as a, the voltage across the power switch is VT 1 = Vdc + aVdc =(1 + a)Vdc This shows that the voltage across T1 can be very much greater than the source voltage. One switch per phase comes with a voltage penalty on the switch. The volt ampere (VA) power of the switch will not be very different for one switch compared to two switches per phase circuit. 10Figure 2.3 (a) Converter for an SRM with bifilar windings (b) operational waveforms of bifilar converter. 10Thus, Figure 4 shows the primary plan for designing the current limiting circuit for the third connection of SRM and each block are explained next.Figure 2.4 basic configurations for current limiting2.4. Power switching componentNowadays semiconductor and electronic switching devices offer a significant performance to control the electrical motors. Moreover, their size and cost make them more convenient to use in the motor control. The electronic devices has a significant role to control SRM where the switching on and off for the voltage is the major role to control the SRM with high performance. As a result, the main electronic devices that can be used are field effect transistors. There are two types of the field-effect transistor J-FET and MOSFET (see the appendix figure 3) 4. The MOSFET has taken a widely role as a best pickaxe to the simple SRM for many reasons that is discussed later in this chapter.2.4.1 N-channel power MOSFET (STP36NF06)Simply the MOSFET is a metal-oxide-semiconductor field effect transistor where the MSFET has a significant characteristic 2. The characteristic of N-channel MOSFET shows a significant use in switching. The structures of the MOSFET are shown in figure 5 where the MOSFET consist of Si P material substrate, two N material substrate that one is the source and the other is drain, and between them there is an insulator Sio2 and at the top metal conductor which is know as a penetration. The length (L) beneath the gate and between the source and the drain is known as a channel. Fundamentally, the MOSFET output current is proportional to the charge in the semiconductor material by the control electrode15.Figure 5 MSFET structures 6The MOSFET is used as a switching device to provide a high speed switching. The significant advantages of the field-effect transistor are Higher operation temperature.Lower switching leakage.High input impedance.Low noise.Lower power dissipation during switching.In addition, The N-channel MOSFET has advantages such as ease to use for high frequency switching and simpler to control where the MOSFET gate drive do not require a continuous current to switch ON. When the MOSFET is needed to switch ON positive room access voltage is needed to apply to the gate drive and Zero current to completely switch off. Moreover, the N-channel MOSFET has higher density consolidation and possible in rapid reduction in capacitances. 2. MOSFET (STP36NF06) gate requires drive properly the later components are used to limit the current and the gate signal for the MOSFET. The gate drive is a power amplifier that accepts a low power input from a controller devices and generate the appropriate high current gate drive for a power MOSFET4.2.5. Bipolar junction TransistorTransistors are considered one of the main elements of semiconductors that have been discovered in modern times. Transistors are used in the amplifiers of electrical signals and electronic switching, which have helped a number of factors such as small size, ease in manufacturing, cost effective and consume less power to extend significantly.Figure 2.6 (a) transistor structures (b) npn and pnp structures2.5.1. ZTX 653 NPN transistorThe NPN transistor is a type of bipolar transistors known as a medium power transistor. The NPN ZTX 653 transistor has interesting features that make it suitable for the pressure pull topology and amplifier topology (pre totem pole connections). The features of NPN ZTX 653 transistor are 6* 100 Volt VCEO* 2 Amp continuous current* Low saturation voltage* Ptot=1 Watt5.5.2. ZTX 753 PNP transistorThe PNP transistor is another type of bipolar transistors that is used in the push pull topology. The PNP ZTX 753 transistor is suitable to employ in the push pull topology (Totem Pole) according to their features. Their features are 6* 1 00 Volt VCEO* 2 Amp continuous current* Low saturation voltage* Ptot=1 WattFigure 2.7 npn and pnp characters2.5.3 Gate drivers (Totem Pole)This type of connection is known as a discrete drivers or push pull drives which is in common use today. Figure 2.8 shows the complimentary arrangement pair bipolar NPN and PNP emitter configuration. Moreover, the N-channel and P-channel MOSFT can be employing for totem pole connection. However, the N-channel and P-channel MOSFT driver suffers from shoot through current, caused by the threshold voltage overlap during ON and OFF transitions, resulting in increased drive power requirements 9.Figure 2.8 push pull configurationThe bipolar Totem Pole, figure 2.8, is non- vacateing and offers no voltage gain to improve the pre-driver rise or fall times. It does provide current gain to reduce the driver impedance to speed the charge and discharge of the device capacitances. Once the input capacitances are charged and the power device has been switched, the driver does not require holding current. It has medium speed and does not perform well at higher conversion frequencies 9.This circuit uses a complementary pair of transistors similar betas and power rating one is an npn power Darlington, and the other is a pnp power Darlington. When a high voltage (e.g., +15 V) is applied to the input, the upper transistor (npn) conducts, allowing current to pass from the positive supply through the motor and into ground. If a low voltage (0 V) is applied to the input, the lower transistor (pnp) conducts, allowing current to pass through the MOSFET gate from ground into the negative supply terminal.142.5.4. Common emitter amplifier (inverter)This configuration is a simple electronic circuit that is used to boost and invert the low signal. Figure 2.9 shows the circuit that contain a high resistance value with NPN transistor. The low signal is switch on and off the transistor where the resistance is limiting the current that apply to the transist or. This topology is used to boost and invert the output of signal processing unit to appropriate the signal that can switch the MOSFET as it will be discussed in the following point.Figure 2.9 common emitter configuration2.6. Current control and limitingThe winding current is controlled inorder to be not more than 8A. When the MOSFET is switched ON without any current limiting circuit, the current shoots up without any control. As a result, the technique for current limiting is arranged as followsWhen the winding current is less than 8A the MOSFET switches ON.When the winding current is exceeds 8A the MOSFET switches OFF.Therefore for appropriate current control, square wave signal is applied to the gate of the MOSFET. The frequency of input signal at the gate of the MOSFET is take into account to make the MOSFET switch properly with regard to the above current control arrangement. In order to do that feedback from the source of the MOSFET is carried to non-inverting terminal of th e comparator. Figure 10 shows the operational waveform of the MOSFET. It can be seen that, the MOSFET needs to switch off when the voltage at inverting input of the comparator reaches 0.8V and switch on when the voltage is zero. Moreover, the reference voltage is 0.8 volt from the voltage rail-splitter law when a 0.1 resistance is connected to the source of the MOSFET. The 555 horologe can offer the control of MOSFETs switching frequency.Figure 2.10 the expected waveforms from the design.2.6.1 Timer NE555PThe 555 horologe IC is an incredibly useful precision timer that can act as either a timer or an oscillator. In timer mode is known as mono fixed mode the 555 simply acts as a one-shot timer when a trigger voltage is applied to its trigger lead, the chips output goes from low to high for a duration set by an external RC circuit. In oscillator mode is known as astable mode the 555 acts as a rectangular-wave generator whose output waveform (low duration, high duration, frequency , etc.) can be adjusted by means of two external RC charge/discharge circuits.14 In this project the monstable circuit is highlighted due to it has one stable state.Figure 2.11 (a) monostable configuration of timer 555 (b) monostable operations14In the monostable configuration, figure 2.11(before a trigger pulse is applied) the 555s output is low, while the discharge transistor in on, shorting pin 7 to ground and keeping C discharged. Also, pin 2 is normally held high by the 10-k pull-up resistor. Now, when a negative-going trigger pulse (less than 13VCC) is applied to pin 2, comparator 2 is forced high, which sets the flip-flops Q_ to low, making the output high (due to the inverting buffer), while turning off the discharge transistor. This allows C to charge up via R1 from 0 V toward VCC. However, when the voltage across the capacitor reaches 23VCC, comparator 1s output goes high, resetting the flip-flop and making the output low, while turning on the discharge transistor, allowin g the capacitor to quickly discharge toward 0 V. The output will be held in this stable state (low) until another trigger is applied 14.According to the operation of the monstable the pulse width can be modified by changing the value of R1 and C.T= 1.11 R1CThus, to obtain capable functioning of the circuit the variable resistance R1 with a maximum value 100K and the threshold capacitance C value is 100nf are chosen.The timer input is the output of the comparator where the two values of the voltage are compared to make the output of the timer based on these two values. The two voltages are one is 5V and the other is the feedback from the MOSFETs source.2.6.2. (LM393) ComparatorThe comparator is used to compare the voltage between the source voltage and the feedback from the MOSFET. This is important to control the current by triggering the timer to limit the current as it is mentioned before. LM393 has several advantages for timer input which areHigher accuracy in comparators.High vo ltage range (2.0V to 36V)Biasing with lower input current.Lower input offset current 5 nAFigure 2.12 LM393 connections to the circuitIn order to establish the reference voltage variable resistance is required in the voltage dividers law. The operation of the comparator is simply as followsIf IN+ IN- the comparator output = V8.If IN+ From the previous operation it can be seen that the comparator send the signal to trigger the input of the timer and the timer acts upon the applied signal therefore the MOSFET switches on and off with regard to the timer output. However, the output of the timer switches on the MOSFET when the current is high which will be disastrous to the motor. To avoid this not to happen, a design of system of logic gates are incorporated in the current limiting topology of the SRM.2.6. 3. Logic gate design (SN74LS00N)Logic gate is designed according to the output of the timer which gives the positive pulses when the current exceeds to 8A and no pulse when the cur rent is less than 8A. With the purpose of switch (totem pole) the gate of the MOSFET turns on and off at required instants of time using an external Drive Signal. Figure 2.13 shows the technique of the combination between the Drive Signal and the timer output to control the MOSFET. SN74LS00N has four NAND gates that can be used to reduce the number of ICs in PCB connection. The logic gate is connected to the timer output which will be inverted with a common emitter configuration to switch on the MOSFET when the timer output is low (ItimerFigure 2.13 (a) SN74LS00N chip (b) logic circuit connection (c) NAND gate logic signal.The MOSFET behaviour that is need according to the timer output is shown in table 1. To do that the NOT gate, OR gate and AND gate are needed before the pre totem pole connections (common ammeter topology).Current conditionTimer(A)Drive Signal(B)Output of the logic gate (C)MOSFET gate signal (Output after totem pole)I 8AMOSFET must be off10101110I MOSFET can be o n00100101Table 2.1 digital signal behaviourBoolean algebraFrom the logic gate output we can get the function(1)This function can be simplified(2)Figure 2.14 (a) logic gate from equation 2 (b) table shows the equavelant NAND gates 7(c) the final simblified gates using the table (b)2.7 Curant limiting circuit simulationCurent limiting circuit ,figure 2.15 , is the simulation circuit and the combination of each part that discussed previously.Figure 2.15 current limiting circuit