Seven self-lift DC-DC converters, voltage lift technique

Seven self-lift DGDC converters, voltage lift technique

F.L.Luo

Abstract: The voltage lift technique is a popular method widely applied in electronic circuit design. Because of the effect of parasitic elements, the output voltage and transfer efficiency of DC-DC converters are limited. The voltage lift technique provides a good way to improve the characteristics of DC-DC converters. Applying the voltage lift technique has created seven new DC-DC step-up converters, namely self-lift DC-DC converters. These converters perfom DC-DC voltage increasing conversion in simple structures. They are different from any other existing DC-DC step-up converters and possess many advantages, such as high output voltage with smooth ripples. Therefore, these converters can be used in computer peripheral equipment and industrial applications, especially for high-output voltage projects.

1 Introduction

The voltage lift technique is a popular method widely applied in electronic circuit design. It has been successfully applied in DC-DC converters [1-91. This paper introduces the skills to design new self-lift DC-DC converters using the voltage lift technique. The seven self-lift converters are a group of new DC-DC step-up converters, whch are developed from the basic prototypes. These converters perform DC-DC voltage increasing conversion in simple structures. In these circuits the switch S is a semiconductor device (MOSFET, BJT, IGBT, etc.), which is controlled by a pulse-width-modulated (PWM) switching signal with varia- ble frequency f and conduction duty k [lo-141. For all circuits, the load is usually resistive, i.e.

R , Z I*

R The normalised load is

Z N = - f Le, where Leq is the equivalent inductance [12-141.

Concentrating on the absolute values in the following description and calculations, the directions of all voltages and currents are defined and shown in the corresponding Figures. Assuming that the semiconductor switch and the passive components are all ideal, all capacitors are assumed to be large enough that the ripple voltage across the capacitors can be negligible in one switching cycle for the average value discussions.

For any component (e.g. C, L etc.), its instantaneous current and voltage are expressed as ix and vx Its average current and voltage values are expressed as I, and V,. The input voltage and current are VI and II and the output volt-

0 IEE, 2001 IEE Proceedings online no. 20010371 DO1 10.1049/ipepa:20010371 Paper fmt d v e d 2nd November 2000 and in revised form 21st February 2001 The author is with the Nanyang Technological University, Nanyang Avenue, Singapore 639798

age and current are Vo and Io. T and f are the switchmg period and frequency. The voltage transfer gain of the continuous conduction mode (CCM) is .

Detailed analysis of the seven self-lift DC-DC converters is given in the following Sections. Due to the length limit of the paper, only the simulation and experimental results of the type 1 self-lift converter are given. The results and conclusions of other self-lift converters are sirmlar to those of type 1.

2 Type 1 self-lift converter

The type 1 self-lift converter is derived from the Cuk converter and its equivalent circuits during switch-on and switch-off periods are shown in Fig. 1. S and D1 are on, and D is off during the switch-on period. D is on, and S and D, are off during the switch-off period.

2. I Continuous conduction mode In steady state, the average inductor voltages over a period are zero. Thus

v,, = vco = vo During the switch-on period, the voltage across capacitors C and C1 are equal. Since assuming C and C1 are sufficiently large

The inductor current iL increases during switch-on and decreases during switch-off. The corresponding voltages across L are V, and -(Vc - VI). Therefore

Hence

Vf = vc, = vo (1)

kTV1 = (1 - k)T(Vc - V I )

The voltage transfer gain in the CCM is

(3)

The characteristics of M against conduction duty cycle k are shown in Fig. 2.

329 IEE Proc-Electr. Power Appl., Vol. 148, No. 4, July 2001

C Fig. 1 a Self-lift Cuk converter b Equivalent circuit during switch-on c Equivalent circuit during switch-off

Self-[$ cuk converter and equivalent circuits

121

VO R

+

0 0.2 0.4 0.6 0.8 1 .o Fig. 2 Voltage trunfer gam M uguiut k

Since all the components are considered ideal, the power losses associated with all the circuit elements are neglected. Therefore the output power Po is considered to be equal to the input power PIN

Vo I o = VI VI

1 IO IL = I1 = -

1 - k

Thus

During switch-off

(4) 1

1 - k io = i~ ID = - IO

The capacitor CO acts as a lowpass filter so that

ILO = I o

The current iL increases during switch-on. The voltage across it during switch-on is V,, therefore its peak-to-peak current variation is

kTV1 L

A ~ L = -

The variation ratio of the current iL is

Aij-,/2 - ~ T V I - k ( l - k)2R - kR - c1=- - --

2 M 2 f L I L 2IL 2 f L ( 5 )

The variation of current io is kR

E = C 1 = m

The peak-to-peak variation of voltage V, is

The variation ratio of the voltage vc is

The peak-to-peak variation of the voltage vcl is

The variation ratio of the voltage vcl is

The peak-to-peak variation of the current iLo is approximately

The variation ratio of the current iLo is approximately

The peak-to-peak variation of voltages vo and vco is

1nzLoT 2 2 - Io(1 - k ) AV* = Avco = 2 -

CO 64 f 3 L ~ C 1 C ~ The variation ratio ofthe output voltage is

Avo/2 - - I O ( 1 - k ) E=--- Vo 128 f 3LoC1CoVo

(10) 1

128Mf3LoC1C0R - -

The voltage transfer gain of the type 1 self-lift converter is the same as the original boost converter. However, the output current of this converter is better and is continuous with small ripple.

The output voltage of this converter is higher than the corresponding Cuk converter by an input voltage. It retains one of the merits of the Cuk converter. They both have continuous input and output currents in continuous conduction mode. As for component stress, it can be seen that this converter has smaller voltage and current stresses than the original Cuk converter.

2.2 Discon tin uous conduction mode The type 1 self-lift converter operates in the discontinuous conduction mode (DCM) if the current io reduces to zero

330 IEE Proc.-Electr. Power Appl.. Vol. 148, No. 4 . July 2001

during switch-off. As a special case, when io decreases to zero at t = T, then the circuit operates at the boundary of CCM and DCM. The variation ratio of the current io is 1 when the circuit works in the boundary state.

M I O '

100

= 1 L R 2 M 2 f L

E = - -

k = 0.95

-

k = 0.80

k = 0.60

k = 0.33

k = 0.10

Therefore, the boundary between CCM and DCM is

a E

From the equations it can be seen that the discontinuous conduction mode is caused by the following factors: (a) Switching frequency f is too low (b) Duty cycle k is too small (c) Inductance L is too small (4 Load resistor R is too big. In the discontinuous conduction mode, current iL increases during switch-on and decreases in the period from kT to ( I - k)mT. The corresponding voltages across L are VI and -( V, - VI). kTV, = ( I - k)mT( Vc - VI). Hence

'

/

(1 - L)m

52.5

- Y 9

49.0

Since C, C, and CO are large enough

-

(7.9890m.51.187) (7.98101~1, 50.944)

rl (7.98000m, 49.7806)(7,98594m, 49.7808) (7.99136m,49.7807)

/ /

where zN is the normalised load R/(fL). The boundary between CCM and DCM is shown in

Fig. 3. The curve which describes the relationship between MB and zN has the minimum value MB = 1.5 and k = 113 when the normalised load z, is 13.5.

or

the voltage transfer gain in the DCM is

The relation between DC voltage transfer gain M and the normalised load at various k in the DCM is also shown in Fig. 3. It can be seen that in DCM, the output voltage increases as the load resistance R increases.

100 . IO' 1 02 1 03

R/fL a

b Fig. 3 a Boundaxy between CCM and DCM h Voltage transfer gain M against the normalised load at various k

Charucterirtics of the type I self-/@ converter

When M MB, the circuit operates in the DCM. In this case the diode current io decreases to zero at t = tl = [k + ( 1 - k) m] T where

LT < tl < T and 0 < m < 1 Define m as the current filling factor. After mathematical manipulation

1 M 2

2f L

m = - = - E k R

IEE Proc.-Electr. Power Appl. , Vol. 148, No. 4, July 2001

2.3 Simulation results Microsim Design Center (including PSpice) is a standard electronic circuit simulation software package. The use of the Design Center 8 (evaluation version) to simulate the proposed new DC-DC converters is a helpful method for circuit design. In the simulation, the switch is NMOS IRF540 and the diode is MR824. The other parameters are; R = 30Q, k = 0.4, C = C, = CO = 100p.F and L = Lo = 100p.H. Input voltage is VI = 30V. The simulation waveforms are shown in Fig. 4. From the simulation waveforms, it can be seen that the output voltage is essentially a DC voltage.

4'0/ (7.9800m. 1.2259) - (7.98401~1. 2.4718)

.r - (7.9840m, -0.9980) (7.990001~1, -994.9742m)

-4.01

2.4 Experimental results A particular breadboard prototype of this proposed converter was constructed. The semiconductor switch S is

33 I

NMOS IRFP460. The diode is MR824. The other parameters are; R = 30-340Q k = 0.1-0.9, C = CO = 1OOp.F and L = 470p.H. Input voltage is VI = 0-30V. The experimental waveforms shown in Fig. 5 are that channel 1 of the oscil- loscope is the PWM switching signal; channel 2 is the output voltage. It can be seen that the output voltage is essentially a DC voltage. There are spikes in the switchng point because the PWM signal is not ideal and the components are not ideal.

a

b Fig. 5 Experinem1 w.uvejomw of the type I self-lijl converter


The type 2 self-lift converter is derived from the positive output Luo converter and the equivalent circuits during the switch-on and switch-off periods are shown in Fig. 6. It is the self-lift circuit of the positive output Luo converters [l]. S and D1 are on, and D is off during the switch-on period. D is on, and S and D1 are off during the switch-off period.

3.1 Continuous conduction mode In the steady state, the average inductor voltages over a period are zero. Thus

vc = vc, = v, 332

C

Fig. 6 a Type 2 self-lift converter b Equivalent circuit during switch-on c Equivalent circuit during switch-off

Type 2 self-l$ converter und its equivalent circuits

During the switch-on period, the voltage across capacitor Cl is equal to the source voltage. Since C and C, are sufficiently large

VCl = VI The inductor current iL increases in the switch-on period and decreases in the switch-off period. The corresponding voltages across L are Vf and -( V, - V,,).

Hence kTV1 = (1 - k)T(Vc - Vc1)

1 1 - k v, = - VI


Since all the components are considered ideal, the power loss associated with all the circuit elements are neglected. Therefore the output power Po is considered to be equal to the input power PI,,,

Thus Vofo = VI = I I

1 1 - L I I = - 10

The capacitor CO acts as a low pass filter so that

The charge on capacitor C increases during switch-on and decreases during switch-off.

Q+ = I c - o ~ k T = IokT Q- = I C - O F F ( 1 - k ) T = f ~ ( 1 - k ) T

In a switching period, Q+ = (2- lc

1 - k I , = - IO

I E E Proc.-Electr Power Appl. . Vol. 148, No. 4 , July 2001

During the switch-off period

Therefore i D = a~ + Z L O

In DCM, the output voltage increases as the load resistance R increases.

For the current and voltage variations and boundary condition, the following equations can be obtained using a similar method to that used in the analysis of the type I self-lift converter: Current variations:

where Leq refers to LLO Le, = ____

L + L o Voltage variations:

k 1 E=--

M 1 gz=--

k 1 p=-- 2 f C R 2 f C l R 8M f2LoCo

3.2 Discontinuous conduction mode The type 2 self-lift converter operates in the DCM if the current io reduces to zero during switch-off. As a special case, when io decreases to zero at t = T, then the circuit operates at the boundary of CCM and DCM. The variation ratio of the current iD is 1 when the circuit works in the boundary state.

= 1 k R <=--

2M2 f Le, Therefore the boundary between CCM and DCM is

where z, is the normalised load RI(&,) and Le, refers to

LLO Le, = ___ L + L o

When A 4 > MB the circuit operates at the DCM. In this case the circuit operates as the diode current io decreases to zero at t = tl = [k + (1 - k)m]T, where kT < tl < T and 0 < m < 1. m is the current filling factor and is defined

In DCM, current iL increases in the switch-on period kT and decreases in the period from kT to (1 - k)mT. The corresponding voltages across L are V, and -( Vc - Vel).

and

Hence

kTVI = (1 - k)mT(Vc - VCl)

v, = vco = vo vc, = VI

(1 - k ) m ] V I

So the real DC voltage transfer gain in DCM is


The type 3 self-hft converter is a reverse output circuit that is derived from the positive output Luo converter and the equivalent circuits during the switch-on and switch-off periods are shown in Fig. 7. It is derived from the self-lift positive output Luo converter. S and D1 are on, and D is off during the switch-on period. D is on, and S and DI are off during the switch-off period.

I

a

"I tj7fc To I/ R vo - iL +

c Fig. 7 a Type 3 self-Mt converter b Equivdlent circuit dunng switch-on L Equvalent circuit dunng switch-off

Type 3 self-llft converter and zts equivalent circuits


During the switch-on period, the voltage across capacitor C is equal to the source voltage plus the voltage across C1. Since C and C, are suffciently large

VCl = VI + vc Therefore

vc, = vi0 = vo

1 VI VI = - VCI = VI + - 1 - k 1 - k

k

(23)

(24)

1 1 - k

The voltage transfer gain in the CCM is vo 1 V I 1 - 5

vo = vco = VCl = - VI

M = - = -

Since all the components are considered ideal, the power losses on all the circuit elements are neglected. Therefore the output power Po is considered to be equal to the input power Pm

VoIo = VIII

IEE ProcElectr. Power Appl., Vol. 148, No. 4, July 2001 333

Thus 1

I1 = - IO 1 - k

JLO = I o The capacitor CO acts as a lowpass fdter so that

The charge on capacitor C, increases during switch-on and decreases during switch-off.

&I+ = I C I - O N ~ T and

Since el+ = so &I- I ~ o ( 1 - k ) T = I o ( l - k ) T

1 - k 5 ICI -ON = - IO

1 - k 1 IC

Io = -Io IC-ON = ILO + I c l - 0 ~ = I o + - (25)

IC

The charge on capacitor C increases during switch-off and decreases during switch-on.

1 k Q+ = Ic-oFF(1-IC)T Q- = I c - o ~ k T = -IoICT

In a switching period Q+ = Q-

1 - k 1 IC-OFF = - IC-ON=- I o (26) 1 - k

1 1 - k

Therefore

I L = ILO + IC-OFF = I o + - IO

During switch-off io = iL - iLO. Therefore I D = I L - ILO = I o

For the current and voltage variations and boundary condition, the following equations can be obtained using a similar method to that used in the analysis of the type 1 self-lift converter: Current variations:

1 R [=-- IC R L R (2 - k )M2 fL '' Z f L o 2M2 f Le,

where Leq refers to LLO Le, = ~


1 1 p=-- 2k f C R 2M f C l R 16M f 2CoLo

IC 1 &=--

1 1 g1=--

4.2 Discontinuous conduction mode The type 3 self-lift converter operates in the DCM if the current io reduces to zero at t = T during switch-off, then the circuit operates at the boundary of CCM and DCM. The variation ratio of the current io is correspondingly unity when the circuit works in the boundary state.

k R [=-- 2M2 f Le,

= 1

Therefore the boundary between CCM and DCM is

where zN is the normalised load RIVZ,,) and L,, refers to

334

L L O Le, = ~

L + L o When M > MB ,the circuit operates in the DCM. In this case the diode current io decreases to zero at t = t l =, [k + (1 - k)m] T, where kT < tl < T and 0 < m < 1. m is the current filling factor.

(28) 1 M 2 m y - = - < k&

In the discontinuous conduction mode, current iL increases during switch-on and decreases in the period from kT to (1 - k)mT. The corresponding voltages across L are VI and -Vc Therefore, kTV, = (1 - k)mTVc and

Hence VCI = vco = vo VCl = VI + vc

k vo = [1+ IV1 (1 - k ) m

1 + k2(1 - k)- 2 f Le,

So the real DC voltage transfer gain in the DCM is

(30) R MDCM = 1 + k 2 ( l - I C ) -

?f L It can be seen that in DCM, the output voltage increases as the load resistance R increases.


The type 4 self-lift converter is derived from the negative output Luo converter and the equivalent circuits during the switch-on and switch-off periods are shown in Fig. 8. It is the self-lift circuit of the negative output Luo converter [2]. The function of capacitor C, is to lift the voltage V, by a source voltage V,. S and Dl are on, and D is off during the switch-on period. D is on, and S and Dl are off during the switch-off period.

iL0 io - - vci 4 -

il - ------c

+ V

VI i L l l , "0

R +

C

Fig. 8 a Type 4 self-lift converter h Equivalent circuit during switch-on c Equivalent circuit during switch-off

Type 4 selJl$ converter and its equivalent circuits

IEE Proc.-Electr. Power Appl. , Vol. 148, No. 4, July 2001


vc = VCO = vo During the switch-on period, the voltage across capacitor C1 is equal to the source voltage. Since we assume that C and Cl are sufkiently large

VCl = VI Inductor current iL increases in the switch-on period and decreases in the switch-off period. The corresponding voltages across L are VI and - (V, - V,,). Therefore, kTVI = (1 - k)T( VC ~ Vel) Hence

(31) 1

1 - k The voltage transfer gain in the CCM is

vo = v, = vco = - Vl

Since all the components are considered ideal, the power loss associated with all the circuit elements are neglected. Therefore the output power Po is considered to be equal to the input power PIN

Thus VOIO = VlI,

1 I1 = - IO 1 - k

The capacitor CO acts as a lowpass filter so that JLo = Io. For the current and voltage variations and boundary

condition, the following equations can be obtained using a similar method to that used in the analysis of the type 1 self-lift converter: Current variations:

k R <=-- 2M2 f L

k R k 1 C 1 = s f L 2 - - - -16 f2LoC

Voltage variations:

k 1 M 1 k 1

5.2 Discontinuous conduction mode The Sype 4 self-lift converter operates in the DCM if the current io reduces to zero at t = T, then the circuit operates at the boundary of CCM and DCM. The variation ratio of the current iD is 1 when the circuit works at the boundary state.

k R <=-- 2M2 f L = I

Therefore the boundary between CCM and DCM is

where Leq refers to Lcq = L and Z, is the normalised load

When M > MB, the circuit operates in the DCM. In this case the diode current io decreases to zero at t = t , = [k + (1 - k)m]T, where kT t , < T and 0 < m < 1. m is the current filling factor and is defined as

"e,)

In the discontinuous conduction mode, current iL increases during switch-on and decreases during the period from kT to (1 - k)mT. The voltages across L are VI and -(Vc -

kTV1 = (1 - k)mT(Vc - Vci)

VCI = v, v, = vco = vo

VCl).

and

Hence

(1 - k)m

VI


We can see that in DCM, the output voltage increases as the load resistance R is increasing.


The type 5 self-lift converter is a reverse circuit that is derived from the negative output Luo converter and the equivalent circuits during the switch-on and switch-off periods are shown in Fig. 9. During the switch-on period, S and D1 are on, and D is off. During the switch-off period, D is on, S and D1 are off.

110 io

a

t

VO

R -

C

Fig. 9 n Type 5 self-lift converter b Equivalent circuit during switch-on c Equivalent circuit during switch-off

Type 5 self@ converter and its equivalent circuits

6. I Continuous conduction mode In the steady state, the average inductor voltages over a period are zero. Thus

vc, = vco = VO The inductor current iL increases in the switch-on period

335

1 M2 m = - = - k&

IEE Proc.-Elecrr. Power Appl. , Vol. 148, No. 4, July 2001

(34)

and decreases in the switch-off period. The corresponding voltages across L are VI and -Vc

Hence kTVI (1 - k)TVc

k 1 - k vc = - VI

During the switch-on period, the voltage across capacitor CI is equal to the source voltage plus the voltage across C. Since C and C, are sufficiently large

Therefore vc1 = VI + vc

1 VI = - VI vc1 = V I + - k

1 - 5 1 - k 1

1 - k vo = vco = vc1 = - VI


(37)


V o I o = V I I I Thus

1 I1 = - IO 1 - k

The capacitor CO acts as a low pass filter so that

ILO = Io The charge of capacitor Cl increases during switch-on and decreases during switch-off.

&+ = I c i -o~kT Q- = I c 1 - o ~ ~ (1 - k ) T = 10 ( 1 - k)T

In a switching period, Q+ =

1 - k 1 - k I C - O F F = - IO k ICl-ON = -

The charge on capacitor C increases during switch-on and decreases during switch-off.

Q+ = Ic-oNkT Q- = I c ~ - o F F ( ~ - k ) T

1 - k 1 k

In a switching period, Q+ =

I o -t Io = - I o 1 ~ 1 - 0 ~ = I c 1 - 0 ~ + L o = - k k 1 1

IO IC-0p.J = - --Io = - k 1 - k k 1 - k IC-OFF = - 1 - k

Therefore

During the switch-off period 1

1 - k i D = i L I D = I L = - IO

For 'the current and voltage variations and the boundary condition, the following equations can be obtained using a similar method to that used in the analysis of the type 1 self-lift converter: Current variations:

Voltage variations: 1 1 1 1

gl=-- E=- p=-- 1 1 2k f C R 2M f C l R 128M f3LoC1CoR

6.2 Discontinuous conduction mode The type 5 self-lift converter operates in the DCM if the current ill reduces to zero during switch-off. As a special case, when iD decreases to zero at t = T, the circuit operates at the boundary of CCM and DCNM. The variation ratio of the current io is 1 when the circuit works in the boundary state.

The boundary between CCM and DCM is

where zN is the normalised load RI(fZ,,) and Le, = L. When M > M,, the circuit operates at the DCM. In this

case, diode current iD decreases to zero at t = t , = [k + (1 - k)m]T where kT < t l < T and 0 < m < 1 with m as the current filling factor.

(39)

In the discontinuous conduction mode, current iL increases in the switch-on period kT and decreases in the period from kT to (1 - k)mT. The corresponding voltages across L are V[ and -V,. Therefore,

kTVI = ( 1 - k)mTVc and Vel = Vco = Vo Vel = VI = Vc

Hence

vo= 1 + (1 - k)m ] V I [ The voltage transfer gain in the DCM is

It can be seen that in DCM, the output voltage increases as the load resistance R increases.


The type 6 self-lift converter is derived from SEPIC. The equivalent circuits during the switch-on and switch-off periods are shown in Fig. 10. It is derived from the SEPIC (with output filter). S and DI are on, and D is off during the switch-on period. D is on, and S and D1 are off during the switch-off period.

7. I Continuous conduction mode In the steady state, the average voltage across inductor L over a period is zero. Thus

vc = VI During the switch-on period, the voltage across capacitor Cl is equal to the voltage across C. Since C and C1 are sufficiently large

v,, = vc = v, IEE Proc -Electr Power Appl , Vol 148, No 4, July 2001 336

a

!LO io - - LO +

b

L I

C

Fig. 10 U Type 6 self-lift converter 6 Equivalent circuit during switch-on c Equivalent circuit during switch-off

Type 6 self-lift converter r x d its equivalent circuits

In the steady state, the average voltage across inductor Lo over a period is also zero. Thus

vc, = vco = vo The inductor current iL increases in the switch-on period and decreases in the switch-off period. The corresponding voltages across L are VI and -(Vc - Vc, + Vc2 - VI). Therefore,

kTV1 = (1 - k)T(Vc - Vi1 + Vc, - VI)

or kTV1 = (1 - k)T(Vo - VI)

Hence 1

1 - k vo = - VI = vco = VCZ



The capacitor CO acts as a lowpass filter so that

ILO = Io The charge of capacitor C increases during switch-off and decreases during switch-on.

Q- = I c - o ~ k T &+ = I c I - O F F ( 1 - k)T = I I (1 - k)T

I E E Prot -Electr Power A p p l , Vol 148. No 4, July 2001

In a switching period, Q+ = Q

1 - k 1 - k I C - O F F = - 1, I c - 0 ~ = -

k The charge of capacitor C, increases during switch-off and decreases during switch-on.

Q2- = I C Z - O N ~ T = I O ~ T In a switching period, Q2+ = Q2-

Q2+ = I c ~ - o F F ( I - k )T

k IC-N = - 10

k I C 2 - O F F = - 1 - k 1 - k

The charge of capacitor C1 increases during switch-on and decreases during switch-off.

&I+ = I C l - O N k T &I- = I C I - O F F ( ~ - k)T In a switching period, e,+ = Q,-

Therefore

ILl = I C I - O N - IC-ON = 0 During switch-off, io = iL - iL1. Therefore,

1 1 - k I o = I I = - 10

For the current and voltage variations and the boundary condition, the following equations can be obtained using a similar method to that used in the analysis of the type 1 self-lift converter: Current variations:

k R [=----- c1=sz c 2 = 1 6 = 2M2 f L e q

k R k R

where LLO Leq = ___


7.2 Discontinuous conduction mode The type 6 self-lift converter operates in the DCM if the current io reduces to zero during switch-off. As a special case, when io decreases to zero at t = T, the circuit operates at the boundary of CCM and DCM. The variation ratio of the current io is 1 when the circuit works in the boundary state.

k R = 1 [=-----

2M2 f Le, Therefore the boundary between CCM and DCM is

where zN is the normalised load RIVZ,,) and

LLO Le, = ~

L + L o 337

When M > MB, the circuit operates in the DCM. In ths case the diode current io decreases to zero at t = tl = [k + (1 - k)m]T where kT < tl < T and 0 < m < 1. m is defined as

(44)

In the DCM, current iL increases during switch-on and decreases in the period from kT to (1 - k)mT. The corresponding voltages across L are Vl and -( ?, - Vcl + V a - VI) Thus,

kTVI = (1 - k)T(Vc - V,l + vc2 - VI)

and

Hence vc = VI VCl = vc = VI vc2 = vco = vo

k (1 - k ) m

1 + k 2 ( 1 - k ) - 2.f Le,


(45) R

M D C M = 1 + k2(1 - k ) - 2.f Le,

In DCM, the output voltage increases as the load resistance R increases.


The type 7 self-lift converter is a super self-lift converter circuit and the equivalent circuits during the switch-on and switch-off periods are shown in Fig. 11. It is derived from the self-Mt positive output Luo converter [I] with swapping the positions of switch S and inductor L.

iL0 io i l

! - ~ ~ + ~ - ~ ~ +

VO

R -

Fig. 1 1 Type 7 converter

During the switch-on period, S and D, are on, and D is Off.

and vc = vc,

V I

L A ~ L = -kT

During switch-off D is on, and S and Dl are off.

A i L = ~ vc - “ (1 - k)T L

so 1

1 - k vc = - VI

The output voltage and current and the voltage transfer gain are:

2 - k vo = VI + v,, = ( 1 + - l : k ) v I = 5 VI

1 - k 2 - k Io = - II

1 2 - k M = 1 + - - - - 1 - k 1 - k

Average voltages: 1 1

1 - k 1 - k VI and VC, = - VI v, = -

2 - k 1 - k

Average currents:

ILO = Io and I L = - Io = I I

then 2 - k

VI 1-lc 1 - k M = 3 = +1=-

9 Conclusions

This paper introduces the skills of the voltage lift techmque, applying it in the design of DC-DC converters. A group of new DC-DC step-up (boost) converters (seven self-lift converters) has been developed by applying the voltage lift technique. These converters are different from conventional converters, and have higher output voltage and better characteristics. The voltage lift technique is used to add certain additional capacitors and diodes in series and/or in parallel in present converters. It is easy to create new converters with higher voltage transfer gain. In the meantime, it can be seen that the ripples (variation ratio) of the output voltage and current are outstandingly reduced. It states that simple circuit modification will improve the characteristics of DC-DC converters significantly. These converters are good examples of increasing output voltage straightfor- wardly. They will be used in consumer engineering projects and industrial applications, especially for higher-output voltage projects.

10 References

(46)

(47)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

LUO, F.L.: ‘Positive output Luo converters: Voltage lift technique’, IEE Proc. B, Electr. Power Appl. Proceedings, 1999, 146, (4), pp. 415- 432 LUO, F.L.: ‘Negative output Luo converters: Voltage lift technique‘, IEE Proc. B, Electr. Power Appl. Proceedings, 1999, 146, (2), pp. 208- 224 LUO, F.L.: ‘Double output Luo converters: An advanced voltage lift technique’, IEE Proc. B, Electr. Power Appl. Proceediizgs, 2000, 147, (6), pp. 469485 LUO, F.L.: ‘Re-lift converter: Design, test, simulation and stability analysis’, IEE Proc. B Electr. Power Appl. Proceedings, 1998, 145, (4), pp. 315-325 LUO, F.L.: ‘Re-lift circuit: A new DC-DC step-up (boost) converter’, Electron. Lett., 1997, 33, (I), pp. 5-7 LUO, F.L., and CHEN, X.F.: ‘Self-lift DC-DC converters’. Proceed- ings of the 2nd IEEE Intemational Conference PEDES’98, Perth, Westem Australia, 30 November-3 December 1998, pp. 441446 LUO, F.L.: ‘Luo converters - Voltage lift technique’. Proceedings of the IEEE Power Electronics Specialist Conference IEEE-PESC‘98, Fukuoka, Japan, 17-22 May 1997, pp. 1783-1789 LUO, F.L.: ‘Negative output Luo converters - Voltage lift technique’. Proceedings of the second World Energy System Intemational Confer- ence WES98, Toronto, Canada, 19-22 May 1998, pp. 25S260 LUO, F.L.: ‘Luo converters, A series of new DC-DC step-up (boost) conversion circuits’. Proceedings of IEEE-PEDS97, Singapore, Republic of Singapore, 26-29 May 1997, pp. 582-588 MAKSIMOVIC, D., and CUK, S.: ‘Switching converters with wide DC conversion range’, IEEE Truns. Power Electron., 1991, 6, (l), pp. 151-157 LIU, Y., and SEN, P.C.: ‘New class-E DC-DC converter topologies with constant switching frequency’, IEEE Truns., 1996, U-32, (4), pp. 961-969 MASSEY, R.P., and SNYDER, E.C.: ‘High voltage single-ended DC-DC converter’, IEEE Power Electron. Spec., 1977, Cod. Rec., pp.

JOZWIK, J.J., and KAZIMERCZUK, M.K.: ‘Dual sepic PWM switching-mode DC-DC power converter’, IEEE Truns. Ind Electron., 1989, 36, (I), pp. 6470 MARTINS, D.C.: ‘Application of the zeta converter in switch-mode power supplies’. Proceedings of IEEE APEC‘93, USA, February 1993,

35c-159

pp. 21&220

IEE Proc.-Electr. Power Appl., Vol. 148. No. 4, July 2001 338

Documents

Seven self-lift DC-DC converters, voltage lift technique