Explain the operation of single phase dual converter with. Numerical problems a for a current commutated chopper, peak commutating current is twice the maximum possible load current. What are the types of commutation with respect to commutation. When the chopper is on the current il flows through inductor. Stepdown choppers output voltage and current waveforms. Starting of dc motor the counteremf aids the armature resistance to limit the. Stepdown and stepup chopper control strategyforced commutated chopper voltage commutated, current commutated, load commutated, switched mode regulators buck, boost, buck boost converter, introduction to resonant converters. In this process, a charged capacitor momentarily reverse biases the conducting thyristor and turn it off. Explain the operation of single phase dual converter with circulating and non from ece 6503 at sri venkateswara college of engineering. T 1 main thyristor, t a auxiliary thyristor, l,c commutating components, r c charging resistor. It will help to improve controllability of the equipments also. May 02, 20 commutation techniques in power electronics 1.
Oct 12, 2018 single phase fully controllers convertersfully controlled converters, mid point power electronics chitode bridge connections with resistive, rl loads and rle load derivation of average load voltage and current line commutated inverters active and reactive power inputs to the converters without and with e,ectronics wheeling diode. Ee6503 power electronics syllabus regulation 20 anna university. Both of these current source type of choppers can be designed to operate at chopping frequencies in excess of 5 kilohertz which provides for a fast response. The capacitor always remains charged with the correct polarity. To get an overview of different types of power semiconductor devices and their switching characteristics. Chopper fed speed control of separatly excited dc motor using. The fundamental process that occurs in an hvdc system is the conversion of electrical current from ac to dc rectifier at the transmitting end, and from dc to ac inverter at the receiving end. Ee6503 power electronics previous year question papers. Chopper fed speed control of separatly excited dc motor using pi controller written by r. The basic circuit for the morgan chopper is shown in the figure a. Apr 23, 2015 in current commutated chopper, as the name suggests, chopper is commutated by current pulse. Voltage plwer of single phase inverters, single pulse width, multiple pulse width, and sinusoidal pulse width modulation. Duty cycle is defined as the ratio of the on time of the chopper to the total time period of the chopper. Ans chopper circuit output voltage current waveforms average load voltage from ee 1 at engineering college.
Ecomputer eee department,third year 5th semester ee6503 power electronics previous year question papers for the regulation 20. Ee6503 power electronics previous year question papers auhippo. Source, ujt triggering circuit of variable frequency, class d. Apparatus for increasing the available regenerative braking energy and for enabling low current control without frequency variation in a timeratio controlled main thyristor power circuit for a direct current traction motor. What are the advantages of current commuted chopper. Fast responseload commutated choppers iii from fig. The load current through the device at this instant, is the holding current of the device. Adtrons jones chopper is a selfcontained stand unit useful in the study and demonstration of the principle and working of a jones chopper. The efficiency of class d commutation is high because the commutation energy transfers in the load.
This form of thyristor natural commutation, which is illustrated in figure. The chopper can be viewed as an onoff switch that can rapidly connect or disconnect the source to load connection. The converter bridge connected in series in the dc transmission is of the current source line. High voltage direct current hvdctransmission systems. This paper describes two fast response load commutated choppers. Mar 23, 2017 the basic circuit for the morgan chopper is shown in the figure a. In the current waveform, it can be seen that during the interval t on the load current rises to the maximum value. More often than not commutating voltage is provided by an energy store usually a quenching capacitor belonging to the converter or is formed by increasing the resistance of the converter valve to be turned off e. Methods of commutations natural commutations forced commutationsa. To understand the operation, characteristics and performance parameters of controlled rectifiers. Morgan chopper click here to know in detail about the commutation types c based on the output voltage of the output, the choppers are classified as i stepdown chopper in this case the average output voltage is less than the input voltage.
Write down the expression for average output voltage for step up chopper. As chopper involves one stage conversion, these are more. In this process, a current pulse is made to flow in the reverse direction through the conducting thyristor and when the net thyristor current becomes zero, it is turned off. When energized from a dc source, current must havea natural tendency to decay to zero. Download fulltext pdf download fulltext pdf hvdc converter using self commutated devices article pdf available in ieee transactions on power electronics 6. For the class e thyristor commutation techniques, a transformer which can not saturate as it is having a sufficient iron and air gap and capable to carry the load current with small voltage drop compared with the supply voltage.
Change in direction of current make the thyristorturn off. The input dc voltage can be increased stepup or decreased stepdown in output side so a dc chopper circuit can be considered as dc equivalent to an transformer. But load current flows through the diode fd, making the load shortcircuited. The application of the class d commutation is in the jones chopper. The exciting current of the saturable reactor is neglected. Commutation is reliable as load current is less than the peak commutation current. In this paper, a commonly reported singlephase fourswitch ac chopper topology is compared with a sixswitch topology in terms of the total harmonic distortion thd of the input current, power.
Jun 08, 2019 dc to dc converter is very much needed nowadays as many industrial applications are dependent upon dc voltage source. Plot all of them on a graph paper in time phase relation with the. Chopper controlled dc drives electronics electronic. A chopper may be considered as dc equivalent of an ac transformer since they behave in an identical manner. Us4096423a direct current motor chopper propulsion system. Observe voltage waveform across th1, th2, c, l and the load. Voltage equation for the circuit shown in figure 2. Above are the output voltage and current waveforms of a chopper circuit. Current commutated chopper through simulink free download as word doc. Slowly vary v1 in steps of 2v and note down vak and iak at each step till scr.
Download link is provided and students can download the anna university ee6503 power electronics pe syllabus question bank lecture notes syllabus part a 2 marks with answers part b 16 marks question bank with answer, all the materials are listed below for the students to make use of it and score good maximum marks with our study materials. A commutation circuit for the turnoff of thyristor switches has been. Power electronics notes pdf pe pdf notes smartzworld. So current flows through diode d and treated as negative. In t off condition the chopper is off so, the load voltage becomes zero. This is the only website,where you can download the previous year anna university question papers in pdf. Ee6503 power electronics syllabus regulation 20 anna. Inverter and chopper power inverter direct current. Unit iii dc choppers introduction a chopper is a static device which is used to obtain a variable dc voltage from a constant dc voltage source.
So, power flows from load to source and operation of typeb chopper is restricted in second quadrant of v o i o plane. Apr 06, 2009 a chopper is a static device which is used to obtain a variable dc voltage from a constant dc voltage source. Jul 08, 2016 voltage commutated chopper waveform the values of commutating components c and l can be obtained. The auxiliary scr is naturally commutated as its current passes through zero value. For a maximum load current of 200a, calculate i the values of. This is the only website,where you can download the previous year anna university question papers in pdf format with good quality and with out any water marks. Essentially, a chopper is an electronic switch that is used to interrupt one signal under the control of another. Dc to dc converter is very much needed nowadays as many industrial applications are dependent upon dc voltage source. Download as ppt, pdf, txt or read online from scribd. This is a major advantage, because high current rectifiers are usually the biggest consumers of electrical energy in the. It converts input power at one frequency to output power at another frequency with one stage conversion. A chopper is considered as a dc equivalent of an ac transformer as they behave in an identical manner. The thyristorconverter offers greater efficiency, faster response, lower maintenance, smaller size and smooth control. Observe also the current waveforms through th1,c and load using the 0.
With this technique, the input current of the chopper rectifier can be highly sinusoidal with a total harmonic distortion thd of 2% to 5% see fig. This form of thyristor natural commutation, which is. Holding current it is the minimum value of anode current below which if it falls, the scr will turn off. Current commutated chopper through simulink power inverter. The capacitor always re mains charged with the correct polarity. Since the proposal of a chopper type, dcdc thyristor converter by morgan, many circuits have been studied and used extensively for electric railway and various types of dc power control 21.
In electronics, a chopper circuit is used to refer to numerous types of electronic switching devices and circuits used in power control and signal applications. After t 3 i c supplies load current io and the excess current. Hence current i o is always negative here but v o is positive sometimes zero. What are the advantages of current commutated chopper. Impulse commutated chopper both constant frequency and variable frequency operations. The concept of modernization permanently produces the lower indus basin, with the letters a, b, i, about.
The latching current may be defined as the minimum value of anode current which at must attain during turn on process to maintain conduction even if gate signal is removed. Keerthana published on 20180424 download full article with reference data and citations. Ee6503 power electronics syllabus regulation 20 anna university free download. Close the switch, initially capacitor short circuited, after 4 5 time constants, v c v s.
Self commutated converters need no separate ac voltage source for commutation. During the interval t off, the load current decays. If speed is less then eb is less hence motor current flows which develop motor torque. Lecture notes on power electronics veer surendra sai. Afetr t 4, a constant current equal to io flows through v s, c, l, d 2 and load. A chopper is a static power electronic device that converts fixed dc input voltage to a variable dc output voltage. Current commutated two quadrant thyristor chopper ieee xplore. What are the types of commutation with respect to commutation process. C connects in parallel with r useful for dc circuits. Here you can download the free lecture notes of power electronics notes pdf pe pdf notes materials with multiple file links to download. What are the different types of chopper with respect to commutation process. A chopper is a static device which is used to obtain a variable dc voltage from a constant dc voltage source. Jul 07, 2016 since oscillating current through t1 turns it off it is called current commutated chopper.
Impulse commutated choppers are widely used in high power circuits where load fluctuation is. Pdf ee6503 power electronics pe books, lecture notes. Comparison of pwm ac chopper topologies request pdf. Power electronics pdf notes pe notes pdf notes book starts with the topics thyristors silicon controlled rectifiers scrs,three phase converters three pulse and six pulse converters. In chapters 11 and 12 thyristor devices were used in conjunction with an ac supply which causes thyristor turnoff at supply current reversal. The scr t1 is main scr whereas diode d1, capacitor c and saturable reactor sr makes commutation circuit for the scr t1. Close the switch, initially capacitor short circuited, after 4 5 time constants, v c v s at t 0, t 1 is on, load is connected across the supply v o v s tank circuit starts conduction diode forward bias. Ans chopper circuit output voltage current waveforms average. This type of chopper is suitable for forward braking operation. Average output voltage for step down chopper v 0 vs. The values depend upon turn off time of main thyristor t1. The process of the current flowing through the thyristor is forced to become zero by external circuitry is called as forced commutation. Here thyristor conducts current from anode to cathode with a very small voltage drop.
Pdf power electronics 2 marks suresh muthusamy academia. The chopper goes into operation with a humming noise. Set the gate current ig ig1 such that forward break over voltage is between 15 to 20 v, by varying r2 and v2. Ee6503 syllabus power electronics pdf free download. For a maximum load current of 200a, calculate i the values of the commutating inductor and capacitor.
Conclusion in this paper we successfully study the simulation of current commutated chopper and voltage commutated chopper on matlab. Self commutated semiconductor converters including direct d. A chopper is a device that converts fixed dc input to a variable dc output voltage directly. Then the delay time can be explained as time during which the gate current attains 0. A read is counted each time someone views a publication summary such as the title, abstract, and list of authors, clicks on a figure, or views or downloads the fulltext. If the thyristor t is triggered, then the current will flow through the load and pulse transformer. Commutation is reliable as load current is less than the peak commutation current icp. Chopper fed speed control of separatly excited dc motor. The chopper frequency is selected as 50 hz, and the commutating circuit is optimally designed to reduce the commutating interval. Since oscillating current through t1 turns it off it is called current commutated chopper.
Explain the working of current commutated chopper with aid of circuit diagram and necessary waveforms. Speed control of dc motor using chopper allied journals. Nov 16, 1971 in a chopper or inverter having power thyristors that are switched on a control energization of a load from a dc source, and having commutating capacitors to which current is diverted from the power thyristors when they are to be switched off, recycling means are provided for recharging each commutating capacitor to bring it back to its. Forced commutation topologies in thyristor chopper circuits.
Class d commutation impulse commutation or auxiliary. An optimum control strategy for controlling the average output voltage of the chopper is given. If these semiconductor devices are arranged appropriately, a chopper can work in any of the four quadrants. Power electronics lab manual vii sem ec set r1 and r2 to mid position and v1 and v2 to minimum. When the chopper is on, v 0 is zero but the load voltage e drives the current through the inductor l and the chopper, l stores the energy during the time t on of the chopper. The thyristor converter offers greater efficiency, faster response, lower maintenance, smaller size and smooth control.
Thyristor forced commutated dc choppers springerlink. Chopper basics, types, applications power electronics a to z. Hamaguchi members faculty of engineering, osaka university 1 introduction. Natural commutated converters are most used in the hvdc systems as of. The performance of these applications will be improved if we use a variable dc supply. The auxiliary thyristor ta is naturally commutated as its current passes through zero value. Types of chopper circuits type a, type b, type c, type d. So to turn it off we require external commutation circuit. In type b or second quadrant chopper the load must always contain a dc source e.
Rc is so large such that it can be treated as open circuit during the commutation interval. The output voltage of the chopper consists of rectangular pulses of 2 ms. Commutation circuit has to supply 5a current in opposite direction to the. Also, the choppers are commutated independently of supply voltage and load variations. The auxiliary thyristor ta is naturally commutated as its current. In power electronics chopper circuits, unidirectional power semiconductors are used.