Modelling and Simulation of a DC Chopper UsingSingle Phase Matrix Converter Topology
Siti Zaliha Mohammad Noor Mustafar Kamal Hamzah Ahmad Farid AbidinFaculty of Electrical Engineering Faculty of Electrical Engineering Faculty of Electrical Engineering
Universiti Teknologi Mara Universiti Teknologi Mara Universiti Teknologi Mara40450 Shah Alam,Malaysia 40450 Shah Alam, Malaysia 40450 Shah Alam, Malaysiactzaliha.mn@ yahoo.com mustafar@ salam.uitm.edu.my
Abstract - Choppers are widely used for traction motor control in by Hossieni [8], Abdollah Khoei [9] and Saiful [10]. To date,electric automobiles and other electric transportation system. In the authors have only found those four published works onthose applications, control of dc motor's speed is required where SPMC but none has proposed the use of the SPMC topologythe supply is dc or an ac voltage that has been rectified. This SPMCchone appos.paper presents work on development of four quadrant DC inDC chopperapplications.chopper based on the SPMC topology, an advanced topology thathypothetically could perform many different converter functions.Prior to hardware implementation a computer simulation model Al Sa lSb S2a S2bwas developed using the Power System Block Set (PSB) within the LMATLAB/Simulink (MLS) environment, to study the behaviour Crof the proposed converter. Successful results presented are mainlydue to the use of resistive load to reduce complexities. Results I& I Ifrom PSB simulation are compared with those obtained from i S3b s4a S4bPSpice to ascertain its validity. The output is being synthesizedusing Pulse Width Modulation (PWM) technique. It is shown thatthe same SPMC topology could be used as a DC chopper Figure 1: AC-AC single-phase matrix converter topologyextending the versatility of the topology a desirable feature in thefuture as increases in costs for skilled manpower could be traded- In this work, DC chopper also known as dc-to-dcoff with versatile technology. converters were presented to operate as a variable dc voltage
from a fix dc voltage using SPMC topology that has been used
Power System Block Set (PSB), Pulse Width Modulation (PWM), in direct AC-AC converter application. Main focus will be theSingle-Phase Matrix Converter (SPMC), DC Chopper operational dc chopper functions in the first and third
quadrant, nevertheless the operation of the second and fourthI. INTRODUCTION quadrant are also described. To ascertain its feasibility
Choppers are widely used for traction motor control in simulation models were developed using MATLAB/Simulinkelectric automobiles and other electric transportation system. and PSpice to study the behaviour of the proposed technique.In those applications, control of dc motor's speed is required Successful results presented are mainly due to the use ofwhere the supply is dc or an ac voltage that has been rectified. resistive load without the introduction of inductances toOther applications of dc chopper also include high-current DC reduce complexities. The DC Chopper is based on four-applications in industries [1] which have many operational quadrant operation with the output being synthesized usingbenefits over conventional diode or thyristor rectifiers. Pulse Width Modulation (PWM) technique. The result of this
The Matrix Converter (MC) is an advanced circuit work has indicated that the same SPMC topology [7, 9, 10]topology that offers many advantages such as the ability to maybe used as a DC chopper. This versatility is a desirable
regenerate enrgbcktothuilt,insodfeature in the future as increases in costs for skilled manpowerregenerate energy back to the utility, sinusoidal Input andoutput current and controllable input current displacement maybe overcame by having a versatile technology.factor [2]. MC has the potential of affording an "all silicon" Results of loads with inductance are also included with asolution for AC-AC conversion, removing the need for brief description of problems encountered in the absence ofreactive energy storage components used in conventional suitable commutation strategies that results with voltagerectifier-inverter based system. Its topology was first proposed spikes that needs to be avoided. The commutation strategyby Gyugyi [3] in 1976. Obviously all published studies dealt used in this work has to a certain extent reduced the spikeswith mainly the three-phase circuit topologies [4-6]. that has been resulted but still requires further investigations in
*'arorveanalQ ZXIin an effort to solve the problems, a common phenomenon inThe Single-phase matrix converter denoted as SPMC was an efor tosletepolm,acmoXhnmnnifirst realised by Zuckerberger [7]. Other works includes those matrix converter topologies.
II. SINGLE PHASE MATRIX CONVERTER reference [15, 16]. The polarity of the output voltage and thedirection of the energy flow cannot be change. By referring to
The SPMC requires 4 bi-directional switches as showni in the combination shown in fig Sb, if the load is a separatelyFigl; each capable of conducting current in both directions, excited motor of constant field, then the positive voltage andblocking forward and reverse voltages [10] Using carefully positive current in the first quadrant, give rise to a "forwarddesigned switching sequences the following step-up and step- drive". Changing the polarity of both the armature voltage anddown frequency AC-AC conversion could be realised [11, 12] the armature current result in a "reverse" drive (quadrant III)as shown in fig. 2. It requires the use of bidirectional switches while in quadrants II and IV, the direction of energy flow iscapable of blocking voltage and conducting current in both reversed and the motor operates as a generator braking ratherdirections. Unfortunately there is no discrete semiconductor than driving.device currently that could fulfil the needs [13, 14] and hencethe use of common emitter anti-parallel IGBT, diode pair as ddVdshown in Fig. 3. The IGBT were used due to its popularityamongst researchers that could lead to high-powerapplications with reasonably fast switching frequency for fine Forward Forward V -+ve VV+vecontrol. Reverse Reversode VL -ve -yeId
Drive Braking 1L-ve L, +ve
II-"SIZ IV III IV
Figure 5a: Four quadrant operation Figure 5b: The polarities--- - - ~~~~~~~~(b) IV. DC CHOPPER BASED ON SPMC
Proposed DC chopper is as shown in fig.4. It has similarstructure with those of the SPMC as shown in fig. 1, thedifference being the input dc voltage. Practical realization ofmatrix converters requires the use of four-quadrant switch
A mia Dlbr2b Sla Slb S2b capable of bi-directional operation [10]. In comparison withSlal tDb 2 0 .' Slal Sib S2B S2b conventional dc chopper of fig.3 it has 4 bi-directional
t1 > X t Ed'kR L switches as opposed to the use of 4 switch and 4 diodes inEd,~ ~ L
T 17 m m conventional dc chopper. This arrangement was chosenD3b D4b S3aD3b S4a S4b because it allows within each switch independent control of{ 4 P4 . the current in both direction. This back-to-back bi-directional
arrangement of the matrix convertef also has lower conductionFigure 3 :Conventional dc chopper Figure 4: DC chopper using SPMC losses than a diode bridge switch arrangement during
commutation of the load current [14]. In this circuitconfiguration, the IGBTs were used because of its high
III. CONVENTIONAL DC CHOPPER switching frequency and high current handling capabilities.A dc chopper converts directly from dc to dc anud also Diodes arranged in series to provide the reverse voltage
known as a dc to dc converter. It is conlsidered a dc equivalent blocking capability [17].of an AC transformer with a continuously variable turn's ratio.It can be used to step down or step up a dc voltage source [15]. A. Pulse-Width Modulation (PWM)Apart from those applications it can also be used in The output of the dc chopper maybe controlled using theregenerative braking of dc motors, dc voltage regulators and (PWM), generated by comparing a triangle wave signal withalso used in conjunction with an inductor, to generate a dc an adjustable dc reference and hence the duty cycle of thecurrent source, especially for current source inverter switching pulse could be varied. This algorithm is required toapplications [16]. A conventional dc chopper is as illustrated provide a stream of PWM train to turn on and off the switchesin fig. that will synthesize the required dc to dc conversion. This is asThe input voltage of matrix converter operated at Figure 3 is: illustrated in fig.4.
EdC=R.i+L-+E (1)dt
for passive R, L and E load. [8]DC choppers may be classified according to the number of
quadrants of the Vd-Id diagram as shown in fig.5a and thepolarities as in fig. Sb in which they are capable of operating.Detailed treatment of the theory could be obtained from
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Vg Trangularwavesignal Rebrece sgnal in the diagram represents the safe commutation switch during/c8r~ers~na~ (a/ustab1e) each particular state that is continuously turned-on as in Table
1. The dark arrow on the switch indicates that the switch is4 7B T DODE ei turned-on and behaves as the power switches performing the
CuFbnw Cuntw required converter operation.
Outut PWMpulsetrin DIODE IGBT 1) First Quadrant (QJ)[1 - r r r f E r r | rThe load current are positive as shown in fig. 8. The load
. _ i | ! _ T current flows from the supply to the load. To achieve this
Figure 6: PWM waveform Figure 7: Bi-directional switch condition, SI a and S4a are tured-on and act as a powerswitch performing the required converter operation
B. Commutation Problem synthesizing the output dependent on the control algorithmbeing developed. During turn-off of Sla, switches S3b and
The use of Pulse Width Modulation as in fig.6 as the Saaemitie scniuul Ndrn hscce 4switching algorithm in this converter, results with possible to c pe thel f cunti returNand ts co ction- ' ~~~~~~~~~~tocomptlete the loopz for current return and acts in con unctionreversal current if inductive loads are used, during switch turn- w Soff. Detailed treatment on safe-commutation problem can be turned OFF.obtained in reference [18] restated here briefly forcompleteness. 2) Second Quadrant (Q2)
Theoretically the switching sequence in the SPMC must be The load voltage is positive with negative load current asinstantaneous and simultaneous; unfortunately impossible for shown in fig 9. The loads current flows out of the load. Topractical realization due to the turn-off IGBT characteristic, achieve this condition, Switch S3a and S4b will operate whilewhere the tailing-off of the collector current will create a short Slb will be continuously turned-on, the voltage E will drivescircuit with the next switch turn-on. This problem occurs current through the load and when both switch S3a and S4bwhen inductive loads are used. A change in current due to are turn off, load dissipates energy through S lb to the supply.PWM switching will result in current and voltage spikes being TABLE 1: Switching pattern for four-quadrant dc-to-dc matrix convertergenerated resulting in the occurrence of a dual situation. Firstcurrent spikes will be generated in the short-circuit path and Switches Quadrant_ Quadrant |Quadrant Quadrantsecondly voltage spikes will be induced as a result of change Sla Modulate Off Off Offin current direction across the inductance. Both will destroy Continuouslythe switches in use due to stress. A systematic switching Sib Off On Off Offsequence is required that allows for the energy flowing in the S2a Off Off Modulate OffIGBT's to decay in a free-wheel manner. Continuously
S2b Off Off Off OnIn conventional dc chopper, the free-wheeling diode is used Continuously
to this purpose. In SPMC this does not exist, hence a S3a Off Switching On Offswitching sequence needs to be developed to allow forced on S3b Continuously ContinuouslyS3b ~ On Off Off Oncontrolled free-wheeling. This is to protect the converter from Continuouslybeing damaged as a result of voltage and current spikes as S4a On Off Off Switchingdescribed. In conventional converter this is normally Continuously Continuouslyimplemented in the form of free-wheeling diodes in inverter 54b Off On On Off
systems arranged in anti-parallel with power switchingdevices. In this study, we will focus our attention to switchingspikes and assume that there is no-change in the direction of Sia Sib S2a S2b t 5 K islb S2acurrent so as to minimise the complexities. E E
C. Switching Strategies 1 R RAiS3a\ zSb S4ai \ S4b S3af\FS3b Sa \ 2S4b
The implementation of the SPMC as a dc chopper requiresL
SL SL Sdifferent bi-directional switching arrangements depending onthe desired operational requirements of the four quadrants Figure 8: First Quadrant Figure 9: Second quadrantdefined. The magnitude of the output voltage of the converteris controlled by PWM variations in duty cycle. The switching 3) Third Quadrant (Q3)sequences are designed to follow Table 1. The load voltage and load current are negative as shown in
Figs.8 to 11 illustrates the four quadrant operation of dc fig. 10. It is the reverse of first quadrant, where the load currentchopper using SPMC topology. The dotted line flow of current flows from the supply to the load through a different route. To
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achieve this condition, S2a and S3a are turned-on and act as a practical results are presented to verify some of the results.power switch performing the required converter operation Parameters used are as shown in table 2.synthesizing the output dependent on the control algorithmbeing developed. During turn-off of S2a, switches S3a and | RrVER
S4b are maintained as continuously ON during this cycle; S3a lll l _ Il
to complete the loop for current return and acts in conjunction Cnn - _ Cnnwith S4b to provide free-wheel operation whenever S2a is Con! RE Conn2
turned OFF. + _Ar--nA -
Source
T7 T ~~~~~~~~~~~~~~~DRrVERISia Sib Sa Sia Sib S2874S2b 1n2 1 *n2
E I L...,..J EL.rJ~~~~~~~~~~~~~~ Connl ConnlW?~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ CDC DC~~~n4' I. A a..Conn2 Conn2DC I~~~~~~~~~~~~~~.VVV~~~~~~~~~~~~~~rW1~~~~~~~~~~SubsystemtSubsystemtiR~~~~~~~~~~~~
C 23.S S4. Sdb SS3a b S4a S4b Figure 12: Top level main model of SPMC in MLSL LCConn
DIode2iGBT I L Terminator
Figure 10: Third Quadrant Figure 11: Fourth Quadrant E eTerm
4) Fourth quadrant (Q4) oioeI IGBT2
In the fourth quadrant, the load voltage is negative but the 1 Tload current is positive as shown in fig. 10. The loads current conal sit l
flows out of the load. To achieve this condition, Switch S3a Fand S4b will operate while Slb will be continuously turned- C Oan
on, the voltage E will drives current through the load andwhen both switch S3a and S4b are turn off, load dissipates C O posite ov1energy through Slb to the supply.
V. SIMULATION IMPLEMENTATION ReptinSe*q uencel
In this simulation implementation, Power System Block Set Figure 14: PWM model circuit in PSB(PSB) in MLS and PSpice are used to model and simulate the 4-
circuit. The DC Chopper was supplied by 30V DC voltage 851(0554u 3 0 81(856 4Cj3 52 4' N386T ~ F2Lsource; the load takes the form of a pure resistive 50 Q2 with *.*t7!-8-4000battery E representing a back emf of a dc motor. Fig. 12 and 0(1(3 b5 LJF0013 show the MLS model circuit used to implement the 5o-- I BUKOO 5,.\,. cItsimulation, whilst fig. 15 is the Pspice implemented circuit 50model for comparison. 80085 o4 7 SIN 3 'U8.71 D31X,00 4b
The PWM model is as shown in fig. 14. A constant , f- 44-t E-representing a straight line or reference signal is compared T; 0G738001 44bZ5; .3
duo _______ 8(5-0( dwith the triangular wave as a carrier signal to produce the -ua i-required respective PWM output. In PSB, the comparison ofthese two different signals is done by using the "RelationalOperator" Block. The "constant2" block represents the i! xTABLE 1':maximum magnitude of the pulse generated the "Repeating j1ev3 0!03Sequence" Block act as triangular wave and "constant2"represents the modulation index of the PWM. i
VI. RESULTS Figure 15: Model circuit in PSpice
Simulation results are presented in this section arranged in TABLE 2: Parameter for simulation model in MATLAB and Pspiceaccordance to the followings; neglecting inductance, with no Input Source (DC) 30 V,,,commutation during switch turned-off and with safe Sample Modulation Index (mi) 0.75commutation switching arrangements. Simulations are carried Resistance R =50 Q)out with MATLAB and Pspice to study the behaviour. Some Inductance L = 0.004H
830
A. Neglecting Inductance B. RL Load (with no-commutation)To simplify inductance is neglected with results in fig. 16 to Inductance is introduced to represent windings in machines.
23. All the results are as expected in theory. Without commutation results are as in fig.24 to 25, with spikesW "Eurrent
generated tabulated in Table 3. Severe voltage spikes areVoltV,or>; *v! Curr nt noticeable. For an input of 30V, the voltage spike is in theregion of +176 to -196, a cause for concern.
Figure 16: Output voltage and current for Ql operation with PSB.Voltage -Current
Figure 23: Output voltage and current for Q4 with PSpice.Voltage- Current
Figure 17: Output voltage and current waveform for Ql with PSpice.Voltage Current. . goK f[
Figure 24: Output voltage and current for Q I PSB without commutation
Figure 18: Output voltage and current waveform for Q2 with PSB.
Voltage CurrentCurrent
Figure 25: Output voltage and current for Q3 PSB without commutation
C. RL Load (with safe-commutation)Figure 19: Output voltage and current waveforrn for Q2 with PSpice. Safe-commutation results with the following figs. 26 & 27,
where spikes are reduced.
Voltage .qrei,'
Figure 20: Output voltage and current waveform for Q3 with PSB. *, . Ij 11 * = .
Figure 26: Output voltage and current for Ql PSB with commutation.
Voltage Current -I - -.
Figure 21: Output voltage and current for Q3 with PSpice. Figure 27: Output voltage and current for Q3 PSB with commutation,
TABLE 3: Simulation result for RL load with no commutationOperation Voltage Current Voltage Current
Figure 22: Output voltage and current waveform for Q4 with PSB. 3 -26.2 -0.51 179 -140 0.23 1 -0.1544 -3.4 0.03 5.9 -15.5 0.007 ] -0.012
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VII. EXPERIMENTAL RESULT ACKNOWLEDGMENT
A simple laboratory test-rig was developed to ascertain the Financial support from University Technology Mara forvalidity of some of the results. Fig. 28 to 29 shows carrying out this work is gratefully acknowledged.measurement from oscilloscope for first and third quadrant REFERENCESrespectively. The MC was supplied with 30V DC and loadedwith R = 50 Q and back emf, E = 5V and operated at [1] Vince Scaini & Tom MA, "High-current DC choppers in the Metalmodulation index = 0.75. Inductance was not used to reduce Industry", IEEE Industry applications Magazine, April2002, pp 26-complexities in the absence of suitable switchingp . [2] Venturini M., "A New Sine Wave in Sine Wave Out, Conversionarrangements that could eliminate those spikes as a result of Technique Which Eliminates Reactive Elements," ProceedingsPWM switching sequences. Results presented are in good Powercon 7, pp.E3_1-E3_15, 1980.agreement those simulated. [3] Gyugyi,L and Pelly,B.R, "Static Power Chargers, Theory,
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