5th IN T E R N A T IO N A L C O N F E R E N C E
T R A N SP O R T S Y S T E M S T E L E M A T IC S T S T ’05
Z E SZ Y T Y N A U K O W E P O L IT E C H N IK I Ś LĄ SK IEJ 2005
T R A N S P O R T z.59, nr kol. 1691
multiresonant converter, :ero-voltage-switching (ZVS) E lżbieta SZY C H T A 1
M U L T IR E S O N A N T C O N V E R T E R TO BE A P PL IE D IN P O W E R SU PPL Y SY S T E M S O F T E L E M A T IC S E Q U IPM E N T
T h e article p resents properties o f Z V S bu ck m u ltiresonant co n v erter in p ow er supply system s o f teleco m m u n icatio n s equipm ent. C onfig u ratio n o f system elem ents enables application o f th e technique o f sw itc h in g sem ico n d u cto r elem ents at zero v oltage (ZV S). Z ero-voltage sw itch in g allow s for high frequencies o f the system operation w hile m aintaining a high energy efficiency and op eratin g reliability.
R esults o f sim ulation testin g o f the converter, based on S im plorer softw are, are presented.
M U L T IR E Z O N A N S O W Y P R Z E K S Z T A Ł T N IK D O Z A S T O S O W A N IA W S Y S T E M A C H Z A S IL A N IA U R Z Ą D Z E Ń T E L E M A T Y K I
A rty k u ł przed staw ia w łasności p rzek sz ta łtn ik a m u ltirezonansow ego Z V S o bniżającego napięcie D C do z a sto so w an ia w system ach zasilan ia u rządzeń telem atyki. K o n fig u rac ja elem entów układu um o żliw ia zasto so w an ie techniki przełączan ia elem en tó w półprzew o d n ik o w y ch przy zerow ym napięciu (ZV S), co pozw ala n a uzyskanie w ysokich częstotliw ości p racy układu p rzy zachow aniu w ysokiej sp raw n o ści energetycznej oraz n iezaw odności działania. P rz ed staw io n o w y n ik i b adań sym ulacyjnych p rzek sz ta łtn ik a w op arciu o program Sim plorer.
1. IN T R O D U C T IO N
D em and for high-frequency pow er processing has led to developm ent o f research into quasi-resonant converters, w here sem i-conductor pow er elem ents are sw itched at zero voltage (ZV S Q R C ) o r zero cu rrent (ZC S Q R C ) [1],
E nergy efficiency and operating reliability o f the converters depend to a large extent, on the conditions o f transistor and diode sw itching processes. P ow er losses occur during turn-on and turn-off, w hich are a result o f current in the sw itched circuit m ultiplied by voltage in the sw itched sem i-conductor elem ents. A t high frequencies, p arasitic inductances o f connections and tran sisto r and diode capacitances form resonant circuits w hich generate parasitic electrom agnetic oscillations. P arasitic im pact o f diode capacitance occurs in the state o f transistor conductance, w hile parasitic im pact o f transistor capacitance upon the circ u it’s operation obtains in th e condition o f diode conductance.
1 F acu lty o f T ransport, P o litech n ik a R adom ska, M a lczew sk ie g o 29, 26 -6 0 0 R adom , P oland e.szy ch ta@ p r.rad o m .p l
E lżbieta SZY C H , ZC S and ZV S quasi-resonant converters provide good sw itching conditions for either the transistor or the diode, but not for both the elem ents at the sam e tim e. U ndesirable oscillations, caused by parasitic capacitances o f sem i-conductor elem ents and parasitic inductance o f connections, as w ell as occurrence o f hard com m utation o f currents or voltages lim it the possibilities o f applying quasi-resonant converters to pow er processing at high- frequency sw itching [7],
R esearch into resonant system s w here sw itching o f all sem i-conductor elem ents occurs in advantageous conditions, i.e. at soft com m utation o f currents or voltages, has led to developm ent o f m ultiresonant converters [1,4]. The converters m ay be applicable in power supplies for transport telem atics equipm ent, w here supply o f constant voltage and precise value is required at high energy efficiency and operating reliability.
2. T O P O L O G Y OF ZV S BU C K M U L T IR E S O N A N T C O N V E R T E R
ZV S b uck m ultiresonant converter is show n in Fig. 1.
Fig. 1. Z V S b u ck m u ltiresonant converter
T he circuit is supplied w ith voltage E. T ransistor M O SF E T T o f output capacitance Cos is sw itched at the frequency f . A ntiparallel diode D s represents the body diode o f a MOSFET.
The rectifying diode D is characterised by a parasitic output capacitance Co d■ The converter’s resonant circuit com prises passive elem ents: resonant inductance L, resonant capacitance Cs in parallel w ith th e tran sisto r T, and the capacitance Cd in parallel w ith the diode D. Elements o f the resonant circuit operate w ith the circ u it’s parasitic reactances, that is, inductance L
’’absorbs” the leakage inductance o f the transform er and the capacitances Cs and Cd in parallel connections ’’absorb” parasitic capacitances Cos, Cod■ C onfiguration o f the elements allow s for application o f the zero voltage sw itching technique o f both the transistor and the rectifying diode. C apacitance C f and inductance L f are filter com ponents.
3. O P E R A T IO N O F T H E B U C K M U L T IR E S O N A N T C O N V E R T E R
D uring the sw itching cycle, the buck ZV S ( F ig .l) operates in four topological stages as show n in Fig. 2. The high filter inductance L f lets th e load be presented as a current source Io- T he control m ethod should ensure sw itching o f the transistor T at zero voltage.
M ultiresonant converter to be applied in pow er supply system s o f telem atics equipm ent 463 In the first operating stage (Fig.2a), the transistor T conducts, and the resonant current 4 is low er than the load current I0. The current source I0 forces the rectifying diode D to conduct the current difference Io - 4- V oltage o f the drain - source transistor ucs is zero and the d io d e’s voltage is u c d■ W hen the resonant current 4 reaches the value I0, the diode D is turned off, the process o f com m utation begins, and the circuit enters the second operating interval.
In the second operating stage (Fig.2b) rectifying diode D is off, and the resonant current 4 is conducted by: the transistor T, inductance L, capacitances Cd and Cod■ V oltage o f the drain - source transistor uCs is zero. The process o f charging capacitance CD and the parasitic capacitance Cod o f the diode D w ith resonant current 4 begins. The second operating range ends w hen the tran sisto r is turned o f f (at zero voltage uCs)-
In the third operating stage (Fig.2c) transistor T and diode D do not conduct.
C apacitance Cs and the parasitic capacitance Cos o f the transistor, capacitance Cd and the parasitic capacitance Codo f the diode overload with the resonant current 4 . I f the voltage uCd
o f capacitance Cd and capacitance Codreaches zero, and the voltage ucs o f capacitance Cs and capacitance Cos is still positive, the third operating stage finishes, and the diode D turns on. In the fourth operating stage (Fig.2d) capacitance Cs and the parasitic capacitance Cos o f the tran sisto r T discharge w ith the resonant current 4 w hen the rectifying diode D conducts.
The fourth stage ends w hen the transistor voltage ucs reaches zero. T ransistor T is ready to turn on in the next cycle o f converter operation.
If, in the end o f the third operating stage, the voltage uCs o f capacitance Cs and capacitance Cos reaches zero, and the voltage ucd o f capacitance C d and capacitance Cod is still positive, then, in the fourth operating stage (Fig.2e), capacitance Cd and parasitic capacitance Cod o f th e diode D discharge w ith the resonant current 4 w hile the antiparallel diode D s is conducting. The fourth stage ends w hen th e voltage uCd o f the diode D reaches zero. T ransistor T is ready to turn on in the next operating cycle o f the converter.
Fig.2. R esonant circuit a) in the first stage, b) in the second stage, c) in the third stage, d) in the fourth stage i f cap ac itan c e C o and capacitance Coddisch arg ed earlier; e) in th e fourth stage i f capacitance C s and capacitance C os discharged earlier
E lżbieta SZY C H T ^ T he m ethod o f control allow s the transistor to turn on at the m om ent w hen the resonant current fr reaches zero. W ithin th e range o f the tran sisto r’s conduction, the cu rrent it is:
C + C
—J1——21L . £ - s in
4 L (C D + C0D)
(
1)
M axim um tim e tmax by w hich the transistor m ust be turned o ff is defined for the value o f current iL equal to the load current /<*, that is:
;r - arcsin(Z)
^max j (2)
4 L(Cd + C od)
where:
\C D + C (3)
w here: k - norm alized load current.
M ultiresonant ZV S converter is characterised by the follow ing param eters:
1 1 f C + C U
f — . f — 1 r _ r OD . . x _ ^_o__
2p \ ]l{Cs + Cos) D 2P Jl(c d+cJ ’ N f s ’ N Cs + Cos ' E
w here: / - sw itching frequency, fs, f o - resonant frequencies, f n - norm alized sw itching frequency,
C,v - ratio o f capacitance,
M - conversion ratio (relative input voltage).
Param eters A /a n d k are necessary to design the co n v erter’s circuit [1], O n the basis o f a fam ily o f control characteristic curves M = f(fn) for CV = var, in consideration o f the changes o f m axim um transistor voltage in function o f norm alized sw itching frequency f N for C,v= var, the circuit’s operation area at zero-voltage sw itching is defined that ensures stable course o f characteristic curves in the full rage o f voltage and load and at m inim um possible value of ratio Cfj.
4. S IM U LA TIO N TESTS
M ultiresonant converter ZV S was subject to sim ulation testing w ith the aid o f Sim plorer. The sim ulation testing w as carried out for the m odel show n in Fig.3. The sim ulation m odel uses a transistor M O SFE T IR FP460 (output capacitance C os=870pF) and an ultrafast diode H F A 25T B 60 (output capacitance Co/r= lOOpF) o f International Rectifier.
M ultiresonant converter to be applied in pow er supply system s o f telem atics equipm ent 465 The resonant circuit includes elem ents o f the follow ing values: L = 7 pH , C.y = lOnF, Cd = var.
R esonant frequency f s = 577kH z. S upply voltage E = 200V , load current / = 10A. B ased on observation o f voltage and current w aveform s resulting from th e sim ulation, a range o f sw itching frequency w as selected w here ZV S sw itching for the target value o f load current is ensured. F or the presented circuit param eters, w here Cn = 2,3, the range is 625kH z < / <
909kH z.
Fig.4. C urrent an d v oltage w aveform s o f buck Z V S M R C , obtained as a result o f sim ulation, C \ = 2 , 3 , / = 625kH z
-200.0
•400.0
oaoou 82-OOu 64.00u B8.00U 68 00u
'
-2 5 .0 0
(¡O.OOu « 2 .0 0 U S4 0 0 U «e.O Ou 6 8 OOu
v r ' v "
5 0 .0 0 10 [A ]
2 5 .0 0
\ ....
l\
K ~ t ~ ~K
0
\ \ \ lx
v
-2 6 .0 0
-5 0 .0 0
6 0 . 0 0 U 62 . OOu 6 4 .0 0 U 6 8 -OOu 6 8 .0 0 U
•»#.0 ■ - ...
H
-4 0 0 0
«O.OOu 8 3 .004) 64 00u M O O u 6>.00u
Fig.5. C urrent and v oltage w av efo rm s o f b u c k ZV S o b tain ed as a resu lt o f s im u la tio n ,C \= 2 , 3 , / = 909kH z
Fig.4 and 5 show cu rrent and voltage w aveform s o f th e converter during steady operation for th e values o f frequency / = 625kH z a n d / = 909kH z, w hen Cn = 2,3. C urrent and voltage w aveform s in the steady state are stable in nature. W hen / = 625kH z, th e transistor voltage ucs does n o t exceed the value o f voltage E, and the diode voltage ucd does not exceed double the value o f voltage E. T he increase o f sw itching fre q u e n c y /in flu e n c e s grow th o f the transistor voltage u Cs and drop o f the diode voltage uCd, and reduces losses in th e transistor, as the im pact o f p arasitic capacitance on the circ u it’s operation increases in the circum stances.
Param eters o f the tran sisto r and the diode lim it th e range o f the co n v erter’s switching frequency.
S im ulation te sts have confirm ed the influence o f transistor and diode param eter values, and values o f elem ents o f the resonant circuit, on the converter’s stability and efficiency. The value o f capacitance C s should be m arkedly higher than th at o f parasitic capacitance Cos, in o rder to take over a dom inant share o f resonant current. C hoice o f a transistor o f the lowest possible output capacitance Cos, results in increased efficiency o f the converter. I f the ratio Cn is sm all, the co n v e rter’s operation proves unstable. In the case o f presented circuit param eters, the co n v erter’s operation is stable if C V > 2,2. The value o f capacitance ratio Cn is increased by choice o f th e capacitance C d values (w hile keeping in m ind the presence o f parasitic capacitance C o d ) -
M ultiresonant converter to be applied in pow er supply system s o f telem atics equipm ent 467
Fig.6 show s current and voltage w aveform s o f the converter during stable operation w hen Cn = 4,6. The higher the ratio Cn is, the higher the m axim um value o f resonant current in th e inductance L and the conducting losses, thus the low er the circ u it’s efficiency. G row th o f the ratio Cn low ers the sw itching frequency, raises the transistor voltage uCs, and reduces the diode voltage u c d -
5. C O N C LU SIO N
S im ulation testin g o f th e converter under analysis leads to the follow ing conclusions:
1. S w itching o f the transistor and the rectifying diode at zero voltage in resonant converters (ZV S ) enables to obtain high operating frequencies o f the converter w hile m aintaining high energy efficiency and operating reliability, since parasitic capacitances o f the tran sisto r and the diode, parasitic inductances o f connections and the leakage inductance o f the transform er are involved in the resonant circuit.
2. Z ero-voltage-sw itching m ultiresonant converters provide advantageous conditions for zero-voltage sw itching o f b oth the transistor and the diode. The transistor and the diode voltage levels, and m agnitudes o f parasitic capacitance currents can be reduced by choice o f parallel resonant capacitances.
3. M ultiresonant buck ZV S converter generates D C voltage w ithin a range o f frequency in the area o f stable operation and can be used in pow er supplies for transport telem atics equipm ent, w here h igh energy efficiency and operating reliability are required.
4. R esearch should continue on real m odels to verify and confirm results o f sim ulation testing u nder conditions o f the converter’s pow er supply and load. A ctual tests should determ ine perm issible ranges o f operating frequency, w here electrom agnetic com patibility o f telecom m unications, control and m onitoring equipm ent used in transport telem atics is obtained.
B IB LIO G R A PH Y
[1] C IT K O T., T U N IA H ., W IN IA R S K I B. „U kłady rezonansow e w en ergoelektronice” (R eso n an t Converters in P o w er E lectro n ics), W y d aw n ictw a P olitechniki B iałostockiej, B iały sto k 2001.
[2] JA N U S Z E W S K I S., Ś W IĄ T E K H ., Z Y M M E R K. „P ó łp rzew o d n ik o w e p rzyrządy m o cy ” (Sem i-C onductor P o w er D evices), W arszaw a. 1999, W K Ł.
[3] S Z Y C H T A E. “H ig h F requency V oltage Inverter w ith an A dditional R esonant C ircu it” , Jakość i U żytkow anie E nergii E lektrycznej, vol. 10, bo o k 1 /2 ,2 0 0 4 .
[4] S Z Y C H T A E. “ W łasności m u ltirezonansow ych przek ształtn ik ó w D C ” (Properties o f D C M ultiresonant C onverters), P rz eg ląd E lek tro tech n iczn y , in th e Press.
[5] S Z Y C H T A E. “ W pływ p o jem n o śc i w yjściow ych tranzystorów ty p u M O SF E T na pracę jednofazow ego szeregow ego falo w n ik a n ap ięcia” (Im p act o f Input C apacitances o f M O SF E T T ran sisto rs upon the O peration o f O n e-P h ase S eries V oltage Inverter), P rzegląd E lektrotechniczny, nr4 2005.
[6] T A B IS Z W .A ., L E E F.C . “D C analysis and design o f zero-voltage-sw itched m u lti-reso n an t converters”, P ow er E lectronics S p ecialists C onference, 1989. P E S C '89 R ecord., 20th A nnual IEEE V olum e, Issue, D ate: 2 6 -2 9 Ju n 1989, p. 243 - 251 v o l.l.
[7] T A B IS Z W .A ., Lee F.C .Y . “Z ero -v o ltag e-sw itch in g m u ltiresonant technique-a novel ap p ro ach to improve perform ance o f h ig h -freq u en cy q uasi-resonant co nverters” , P o w er E lectronics, IEE E T ransactions on V olum e 4 , Issue 4, D ate: O ct 1989, p. 4 5 0 - 4 5 8 .
R eview er: Ph. D. Jerzy Mikulski
