Spike Suppression in a Bidirectional High-Frequency Transformer-Link Inverter Using a Regenerative Snubber.

§like §llllre§§ionn inn a Biiired:ionnan fiigt-Freqllenncy
'ranndormer-Linnk Inverter U§inng a Regennerative §nnllbber
Z. SaJam*, M. Z. Ramli, and L. S. Toh
*

Power Electronics and Drives Group. Department of Energy Conversion, Faculty of Electrical Engineering,
Universiti Teknologi Malaysia.
81310 UTM Skudai, Johor, Malaysia.
gogainet@time.net.my, leong_soon_toh@ieee.org, zainals@fke.utm.my

Keywords: Bidirectional, HF transformer, Inverter, Snubber,
Spike suppression.

Abstract
This

resistor,

Rs when the switch ns back on. This mandates

eiciency.

for

the use of high power R" which causes urther loss of inverter

In this paper, we introduce a regenerative snubber that

paper

presents

a

spike

suppression

method

for

Bidirectional High-Frequency Link (BHFL) inverter using a
regenerative

snubber.

Unlike

the

RCD

snubber,

this

Owing to the lossless nature of the snubber, the energy in the

efectively reduces the voltage spike to a very low value.

voltage spike is stored in the snubber, and subsequently

regenerative snubber dampens the vo ltage spike by chargi ng

transferred back to the power circuit. As such, the overall

its snubber capacitor during switch transition. The energy is

efficiency of the inverter can be improved.

then pumped back into the main power circuit. A IkVA
prototype inverter is constructed and the workability of the
regenerative snubber is tested on the inveter. The results

5%.

show that the voltage spike is significantly reduced. The
eficiency of the inverter is also increased by about

1

High-requency
nsfoner

Introduction

JII

High-requency link inveters have been applied in dc-ac

High-requency
square wave or PM

power conversion in which size and weight are of important

considerations. This

type

it is

of inverter utilises the high­

requency transformer. Threfore,

compact and light

high-frequency link inverters also have an inherent

weight compared to the line-requency transfomer inverters.
However,

due to the leakage inductance at the trnsfomer secondary.

probl em of voltage spike at the ransformer secondary. This is

During switch nsition, the current through the switch is

Figure

I: Sp i ke suppression using ReD snubber.

2 System Description
2.1 Power Circuit

resulting in high voltage spike to occur across the switch. If

The BHFL inverter is shown in Fi gure2 . The main conversion

not properly handled, the voltage spikes may lead to switch

(PWM) bridge, active rectifier and polarity-reversing bridge.

tuned off very quickly. Therefore, the di/dt is very high,

destruction.
In our

previous paper [3], a Bidirectional High-Frequency

(BHFL) inverter using centre-tapped transformer has been

proposed by [I] and [2].

described.

The circuit has reduced

compared

to the

topologies

number

of switches

transfomer secondary is double in amplitude due to the

However, it is known that the voltage across the switch at
is already high, additional voltage spike can be

centre-tapped configuration. As the voltage sress across the
switch

harmul to the power switch. The common method to dampen

the voltage spike is usi ng a RCD snubber, as depicted in

, can be quite large. As a result,

Figure 1. However, for adequate spike suppression, the
required snubber capacitor,

circuits

voltage,

are the high-frequency Pulse Width Modulation

VHF using the high requency PWM bridge. Then, this

The dc voltage, Vd, is converted into high-requency PWM
-

transformer. Next, the voltage is rectified using the active

voltage is isolated and stepped-up using the high-requency
switches and anti- parallel diodes, enables bidirectional power

rectifier.

The

active

rectiier,

which

consists

of

power

low. For transfer of power rom the source to the load, the
diodes are utilised;
switches S3

and S3

for reverse power flow, the power
are tuned on. The rectified PWM

voltage, vpwmJect is then low-pass iltered, V"cl and unfolded to
obtain the sinusoidal output voltage, Va' The key waveforms

at the princip al conversion stages are shown in Fi ure

high discharge energy will be dissipated in the snubber

152

3.

ide

Centre-tapped
high-requency

Active

--'�"fi.I1t
e-T -___-'''-' ,
-Low-pass

Regenerative

ranSftnner -->re
j f-ct,ii_le;TI--_S_nu'b-b_eT

L

Vd,

+

c

V.ect

Load

Figre 2: Bidirectional High-Frequency Lik (BHFL) inverter with regenerative snubber.

>�

0 D 0 � ,� 0 D 0 �
DOD 0 � DOD 0 �

2.2 Regenerative Snubber

"

transformer seconday, substantial amplitude of voltage spike
Owing

Figre

Fiure

inductance

at

the

a

power resistor is
required. Consequently, the energy will be dissip ated n the
snubber circuit, resulting in reduc ed inverter eficiency. n
across

the switches.

For effective damping,

2. The aim of the snubber circuit is

this work, we propose a regenerative snubber, as denoted by
to reduce the voltage spike across the active rectifi er's
the dashed box in Figure

to a safe level. It comprises of snubber
D" snubber switch Ss and snubber capacitor Cs. The
operating principle of the regenerative snubber and its
corresp onding timing diagram are shown n Figure 5.

switches (S3 and S3)
diode

3: Key waveforms at the principal conversion stages_

4 shows the timing diagram of the gate conrol sinals

to conrol the power low at the active rectiier stage. Note

that the requency v, is half of vpwm• The conrol sigual for

voltage spike will occur on the adjacent (om switch. This is
When any of the active rectiier's switches is ned on,

because the energy stored in the leakage inductance is
released and appears as voltage spike with a sudden current
diode, Ds and snubber switch Ss are ideal. The voltage across

n-of. Referring to Figure 5, it is assumed that the snubber

�

'f

m � ooonn � U D ooono � I
bDDDDDDDDD�t
f
H

4: Gate conrol sin als for BHFL inverter.

leakage

relat i vely large snubber capacit or and a high

snubber

for the main conversion circuits. The control signal v, is used

Fire

of

rectifier switches during
trn sitions . The voltage spike is developed s a
result of hih di/dt. The comon practice to solve this
problem is to dampen the voltage spike by placing a RCD

�"
�

presence

switching

�

p olarity-reversing bridge is denoted as v•.

the

will be appear across the active

r
��.r

vpfn00000 � U D 00000 � �

to

•t

the snubber capacitor ,

C, without voltage spike is VI. hen
spike occurs, Vpwm_HF i ncreases, thus Ds is forward
bias ed and charges C,. he snubber capacitor, Cs mpens the

v oltage

I} to I] causes the snubber capacitor volage

Ve, to rise. When
voltage equals to

voltage spike by reducing its d/dt. he charging process rom
Ves equals Vb i.e. when the snubber capacitor

vpwm_HF, the c hrging process stops. At this point, the snubber

diode D, is reverse biased .

S ubsequently , Cs begins to

discharge its energy into the power circuit via Ss. The

has ended, Ss is ned of, and the
is maintained at its

discharging process continues until end of the PM pulse.
When the PM pulse

discharging process stops. Voltage Vs
equilibri um level

place.

153

(VI)

until the next charging process takes

+VLs

-

S3

VpwmJect

Ds

J

(�-Vl)
,

� � ••

r

+Vs

-

......

i;
!
:

1 •••1 ..

:

Discharging current
... eo ..... ••

I. eo eo

: rr····_·
.. .
t
.
.
,
ol
Yl·m. .:�:•....m.�
" -" '

:

:

:

.

_

_.-

t

S3

Figure 5: Regenerative snubber and its corresponding timing diagram.
3 Hardware Construction
IkVA prototype inverter has been constructed. The
regenerative snubber has been incorporated with the power
circuit. The high-requency PWM bridge is built using the
APT15GP60BDFI power IGBT. The device has good
switching capability with low conduction loss. The high­
requency ransformer is wound around the ETD59 ferite
core. Ferrite core is chosen as it is the most suitable material
for high frequency operations. The active rectiier is
constructed using the IRG4PH40K IGBT and STTAI212D
ultrafast high voltage diode. These devices have voltage
rating of 1200V, thus suitable to be applied at the centre­
tapped active rectifier. The polarity-reversing bridge is
constucted using the IRG4PC40FD IGBT. As the voltage
sp�ke has been suppressed before the polarity-reversing
bndge, the selected power switches are only rated at 600V.
By using low voltage power switches, the forward conduction
loss can be minimised. The regenerative snubber is built using
the IRF730 MOSFET as the snubber switch S" and the
snubber capacitor is chosen to be 2.2flF. All the power
switches are driven by the HCPL3120 gate driver chip rom
Hewlett-Packard. This chip has a built-in optocoupler with
power ouput stage, which is suitable for direct driving of
power switches. This "all-in-one-chip" solution has simp liied
the interfacing process. The DSII04 Digital Signal Processor
(DSP) rom dSPACE (64-bit loating-point processor with
TMS320F240 Slave DSP) is used to generate the control
signals for the power switches. The conrol signals will then
go through a series of extenal logic gates, shown in Figure 6,
and become the input signals of gate drives.
.,

SI

SI

A

52

S2

S3

S3

S4

S4
S5

5

Figure 6: Interface between DSP and power switches.
The photograph of the constructed prototype inverter is
shown in Figure 7. It is divided into two modules, namely the
gate drive module and the power circuit module. To obtain an
isolated power supply for the gate drivers, dc-dc converters
driven by SG3526 pulse generator have been constructed with
miniature high-requency transformers. The transformers are
designed such that there are two secondary centre-tapped
windings. This ensures two ni t s of gate drive power supply
to be constructed with minimum components. Dead-time
generators are also incorporated to provide suicient time for
complimentary switches to c om plete ly n off.

14

1I
I

I

�;
\

(b) Bottom view - power circuit module

(a) Top view - gate drive module

iv. DC link capacitors
Regenerative snubber circuit

Legend:

i.

Power switches and gate drivers

v.

ii. Gate drive power supplies

vi. High-requency ransformer

iii. Dead-time generators and logic gates

vii.LC low-pass filter

Figure

7: Photograph of the prototype inverter.

4 Experimental Results and Discussion

Vetical scaie:
Ouput voltage

To veriy the feasibility of the proposed spike suppression

lOOVIdiv

technique, he regenerative snubber has been tested on the

Output curent
51div

prototype inveter. The specifications of the system are as
follows:

o

o

o

p

= 150V
= 240Vms
ated output requency,!= 50Hz

Time scale:

Nominal in ut voltage, Vdc
Rated output voltage, Vo

inductive loads are shown in

4msldiv

The output voltage and current waveforms under resistive and

Fire 8(a) and

b) respectively.

Figure 8(b) indicates that the BHFL inverter is capable of

(a) Output waveforms under resistive load

carying bidirectional power low. Therefore, the BHFL
inverter is suitable for stand-alone Uninteuptible Power
Supply (UPS) applications.
Figure

Vertical scale:
Output voltage
IOOVldiv

9 depicts the key operation wavefos of the

regenerative snubber. As can be seen, the snubber capacitor

Output current

C, is charged and discharged in synchronised with the PWM

21div

pulses.

These

results

have

close

agreement

with

the

Time scale:
4msJdiv

theoretical prediction.
Figure 10 shows the collector-emitter voltage, VCE at the

active rectifier' switch (S3) before and ater insertion of the

e

regenerative s nubb r . It is obvious that before the insetion of
regenerative snubber, the voltage surge is about 40% of the
amplitude. Ater the regenerative snubber is inseted, the

b) Output waveforms under inductive load

voltage spike has been reduced to a negligible level.

Figure 8: Output waveforms for resistive and inductive loads.

155

To veriY the effectiveness of the regenerative snubber, the

CHI.

Vertical scale:
....

CHI.: IOVldiv
CH2.: 300Vfdiv
CH3a: IAidiv
CH4.: 50VIdiv
CHlb: 300V/div

inverter

CHlb

Vpwm_HF
CH3.: ic,
CH2.:

...I CH4.: vcs

CHlb: VpmJec'

CH3b
� ..

: : . . : .. . ;
'

.

..

.

.

�
,

. �" .

:

. , ..

: , , .. �
.

�
�
.

.

.

�. .

.
.

;

the

regenerative

2.2F and 22Q, respectively. These

and R, would be much higher. Figure II shows that the
regenerative snubber is able to increase the inveter eiciency
by about 5%. Note that higher RCD component values will
make the difference even larger.
95 ---�
0

�
� 0
E
=

85

"

CH3b: Vll at S3

Legend:
�

Snubber

Regenerative

- . - - - . - - . � ReD snubber

.

CH2b: Vc••t 83

75

70

10 20 300 40 SOO 60 70 BOO 900 100
Output Power )

�

'
-'
"

compared using

values are selected rather consevatively - typical values of C,

C2b: 600Vldiv

CHla: Vpwm

is

and Rs are chosen as

=��

Legend:

eiciency

snubber and the RCD snubber. For the latter, the values of C,

Figure II: Eficiency vs output power.

Figure 9: Key operation waveforms of regenerative snubber.

Vetical scale:
200V/div

Time scale:
5flsJdiv

5 Conclusion
A regenerative snubber for voltage spike suppression

n the

BHFL inverter has been described. To veriY the viability of
the proposed snubber, a IkVA prototype inveter has been
constructed.

The

experimental

results

show

that

the

regenerative snubber unctions s predicted. The voltage
spike across the active rectifier switch is reduced to a safe
leveL As compared to the RCD snubber, the regenerative
snubber

-." .. . ..
(a)

.

, .

.. .

.. _ -- - - - - - -- ·
.
.
·
.
.
- -----

o
·

·
. . . . . . . . . . . . . _. _
-

more

superior

performance.

The

overall

Acknowledgements

.

VeE at S3 before insertion of regenerative snubber

.

has

eficiency of the inverter is increased by about 5%.

-

---

•
.

.. .

.

- -.-.
•

.

-

.

Vertical scale:

.
,

.

....

•

.

200V/div

..

,

. . .-- .. . � ... . . . ., .. , .
.

.

. ,

.

.

.

..

Time scale:

The authors wish to acknowledge the Ministry of Science,
Technology and Innovation,

Malaysia (MOST!) for the

financial funding of this project.

References

[ I]

E. Koutroulis, J. Chatzakis, K. Kalaitzakis and N. C.
sinusoial, high-requency
inverter design," lEE Proceedings on Electric Power

Voulgaris, "A bidirectional,

5f1sldiv

Applications, vol. 148, no. 4, pp. 315-321, 2001.

[2]

-':" .: .

. .

.:

..

.

.

:.

M. Matsui, M. Nagai, M. Mochiuki and A: Nabae,
"High-frequency link defac converter with suppressed
voltage clamp circuits
angle

.

(b) VCE at 53 ater insertion of regenerative snubber'

Figure 10: VCE at S3 without and with regenerative snubber.

control

with

�

Naturally commuated phase

self

tum-off

Transactions on Industy Applications;

M.

devices,"

IEEE

Z. Ramli, Z. Salam, L. S. Toh and C. L. Nge, "A

pp. 293-300, 1996.
[3]

voL IA-32, no. 2,

bidirectional high-requency link inveter using center­
tapped transformer", IEEE PESC Conference Record,
voL 5, pp. 3883-3888, 2004.

156