Post on 29-Apr-2018
International Journal of Advances in Applied
Science and Engineering (IJAEAS)
ISSN (P): 2348-1811; ISSN (E): 2348-182X
Vol-1, Iss.-4, SEPTEMBER 2014, 36-41
© IIST
International Journal of Advances in Engineering and Applied Science Vol-1, Iss-4, 2014
36
PASSIVE SOFT SWITCHING SNUBBER FOR SPWM INVERTERS
SHASHANK HEGDE, SUDHARANI G, MAHESH RAYAR AND SANJEETH KUMAR
Department of Electrical & Electronics Engineering,
B. V. B College of Engineering & Technology,
HUBLI- 580031, Karnataka - INDIA
Email: shashankhegde03@gmail.com
ABSTRACT: This paper presents a regenerative passive snubber circuit for PWM inverters to achieve soft-switching purposes without significant
cost and reliability penalties. This passive soft-switching snubber (PSSS) employs a diode/capacitor snubber circuit for each switching device in an
inverter to provide low dv/dt and low switching losses to the device. The PSSS further uses a transformer-based energy regenerative circuit to recover
the energy captured in the snubber capacitors. All components in the PSSS circuit are passive, thus leading to reliable and low-cost advantages. over
those soft-switching schemes relying on additional active switches.
I. INTRODUCTION
To reduce switching stresses,
losses, and electromagnetic interference
(EMI), soft-switching techniques have been
developed for power converters. Soft-
switching inverters can be grouped into two
main categories: resonant dc link and
resonant snubber. The resonant dc link
provides zero dc link voltage or current
intervals to all phase legs during switching
instants, whereas the resonant snubber
diverts current from and provides zero-
voltage intervals to each main device at
switching instants.
All existing soft-switching inverters use
additional active devices to achieve soft-
switching, thus increasing costs and control
complexity and decreasing reliability.
This paper presents a regenerative
passive snubber circuit for PWM inverters
that is able to achieve all the soft-switching
objectives without significantly increasing
the cost. This passive soft switching
snubber (PSSS) employs a snubber circuit
consisting of diodes and capacitors for each
phase leg to provide low dv/dt and low
switching losses to the switching devices.
The PSSS further uses a transformer-
based energy regenerative circuit to
recover the energy captured in the snubber
capacitors. All components in the PSSS
circuit are passive, making it reliable and
low in cost.
II. PSSS CIRCUIT AND OPERATING
PRINCIPLE
Fig. 2(a) shows the proposed
PSSS circuit, which consists of a
diode/capacitor soft-switching snubber
(SSS) circuit for each phase leg, and an
energy recovery circuit shared among all
the phase legs.
Passive Soft Switching Snubber For SPWM Inverters
International Journal of Advances in Engineering and Applied Science Vol-1, Iss-4, 2014
37
The SSS circuit includes a snubber
diode, 𝐷𝑠𝑝 , and a snubber capacitor, 𝐶𝑠𝑝 , for
the upper main device, Sp, and,
symmetrically, 𝐷𝑠𝑛 and 𝐶𝑠𝑛 for the lower
main device, 𝑆𝑛 . The functions of the
snubber diodes, 𝐷𝑠𝑝 and 𝐷𝑠𝑛 , and snubber
capacitors, 𝐶𝑠𝑝 and 𝐶𝑠𝑛 , are very similar to
those of the traditional RCD snubber. They
are, however, arranged differently so that
both snubber capacitors are connected to
the midpoint of the phase leg. Since the
upper and lower main devices always
operate complementarily to each other
during normal PWM operation, the sum of
both snubber capacitors’ voltages should
remain constant and equal to the dc link
voltage, which is further guaranteed by a
larger snubber bus capacitor, 𝐶𝑠0,
connected across the two snubber
capacitors.
Fig.2 (b) shows the operating
waveforms during 𝑆𝑝 turn-off or 𝑆𝑛 turn-on.
Assuming the IGBT of Sp is conducting the
load current, turning off Sp will divert the
current into the snubber circuit, charging
the snubber capacitor 𝐶𝑠𝑝 , through the
snubber diode 𝐷𝑠𝑝 and discharging 𝐶𝑠𝑛 ,
through CS0.Therefore, 𝑉𝑐𝑠𝑝 , increases and
𝑉𝑐𝑠𝑛 , decreases as shown in Fig. 4.2,
whereas voltage, 𝑉𝑐𝑠0 remains almost
constant.
2.1 PSSS CIRCUIT DESIGN AND
CONSIDERATIONS
The 𝑑𝑣
𝑑𝑡 and
𝑑𝑖
𝑑𝑡 are determined by the
snubber capacitance 𝐶𝑠, and stray inductance 𝐿𝑠
and partially by the load current.
The highest 𝑑𝑣
𝑑𝑡 happens in Modes 4 and 7
when the dc link forms a resonant circuit
through the stray inductance and snubber
capacitor. For Modes 4 and 7, the upper
snubber capacitor voltage 𝑉𝑐𝑠𝑝 , can be
expressed as
𝑉𝑐𝑠𝑝(0) is the initial voltage of the upper
snubber capacitor, 𝐼𝑙𝑠(0) is the initial current
Passive Soft Switching Snubber For SPWM Inverters
International Journal of Advances in Engineering and Applied Science Vol-1, Iss-4, 2014
38
through the stray inductor, and = 1
2𝐿𝑠𝐶𝑠 is
the resonant frequency.
The load current affects the initial voltage of
the upper capacitor, 𝑉𝑐𝑠𝑝(0), and initial
current, 𝐼𝑙𝑠(0). The 𝑑𝑣
𝑑𝑡 from is obtained as
The highest 𝑑𝑖
𝑑𝑡 also occurs in Modes 4 and
7, which can be expressed as
Therefore, it is obvious that the stray
inductance and snubber capacitor are
employed to limit both 𝑑𝑣
𝑑𝑡 and
𝑑𝑖
𝑑𝑡. Given
target numbers for 𝑑𝑣
𝑑𝑡 and
𝑑𝑖
𝑑𝑡, snubber
capacitance and stray inductance can be
determined. The rule of thumb for
estimating the stray inductance is 1µH per
1-meter-long conductor.
III.HARMONIC COMPARISIONS
A square wave inverter is subjected to higher degree
of harmonics due to the effect of square wave
switching. Harmonics produced at every odd order
of fundamental frequency .hence an spwm technique
is been employed in order to decrease the effect of
harmonic abstractions in the inverters thus providing
more effective way of approaching the efficiency
standards.
A mathematical model of both spwm inverters and
square wave inverters is been illustrated along with
harmonic spectrum comparison done in qtgrace
software
3.1 MATHEMATICAL MODELING OF
SPWM & SQUARE WAVE INVERTERS
3.2 HARMONIC SPECTRUM COMPARISON
Passive Soft Switching Snubber For SPWM Inverters
International Journal of Advances in Engineering and Applied Science Vol-1, Iss-4, 2014
39
i)the red colored graph indicates the harmonic
spectrum of a square wave inverter.
It occurs for every odd order of frequency ie for
n*f where n is series of odd numbers
ii)the blue colored graph is the harmonic
spectrum of SPWM inverters based on the
frequency modulation of the inverter
If 𝑚𝑓 is even, then harmonics at 𝑚𝑓 +2
If 𝑚𝑓 is odd, then harmonics at 2𝑚𝑓+1
IV. SIMULATION RESULTS
1) WITHOUT SNUBBER
Fig.4.1(a) Output voltage waveform of the saber
simulation without snubber.
2) WITH SNUBBER
Fig.4.1(b) Output voltage waveform of the saber
simulation with snubber circuit.
4.1 HARDWARE IMPLEMENTATION OF FULL-
BRIDGE SQUARE WAVE INVERTER
Fig 4.1 Hardware setup of the experiment
V) OUTPUT WAVEFORMS
(i) FULL BRIDGE INVERTER OUTPUT WITHOUT
INDUCTIVE LOAD
Passive Soft Switching Snubber For SPWM Inverters
International Journal of Advances in Engineering and Applied Science Vol-1, Iss-4, 2014
40
Fig.5.1(a) full bridge inverter waveform without
inductive load
(II) FULL BRIDGE INVERTER OUTPUT WITH
INDUCTIVE LOAD
Fig.5.1(b) full bridge inverter waveform with
inductive load
HARDWARE OUTPUT FOR PASSIVE SOFT
SWITCHING SNUBBER
(I) WITHOUT SNUBBER
Fig 5.1(c) Output voltage waveform without
snubber.
(II) WITH SNUBBER
Fig 5.1(d) Output voltage waveform of the
hardware with snubber circuit.
VI) CONCLUSION AND FUTURE SCOPE
The presented PSSS circuit has the following
features:
employing only passive components;
requiring no additional control;
allowing any PWM schemes;
eliminating dc bus plane layout;
utilizing stray inductance;
reducing 𝑑𝑣
𝑑𝑡and
𝑑𝐼
𝑑𝑡;
Lowering cost and improving reliability.
Passive Soft Switching Snubber For SPWM Inverters
International Journal of Advances in Engineering and Applied Science Vol-1, Iss-4, 2014
41
The PSSS provides a viable alternative to the
existing soft-switching inverters. The PSSS is
especially suited for silicon carbide (SiC) device
inverters because SiC diodes have no or
minimal reverse recovery current, which
reduces 𝑑𝑣
𝑑𝑡 uniformly at both turn-on and turn-
off to further soften the switching.
The PSSS circuits can be widely implemented
in power electronics wherein no additional
active source is requiring for the development of
Snubbers .The PSSS circuit provides a wider
scope in 𝑑𝑣
𝑑𝑡 protection and loss free switching of
semiconductor switching in inverters which is a
major fact when high frequency and high power
applications are considered
VI) REFERRENCE
1] Visit to the “MARS INDUSTRY” an inverter manufacturing
industry near gokul road,HUBLI-580031
2] Passive Snubbers by FZ Peng, IEEE TRANSACTIONS ON POWER
ELECTRONICS, VOL. 19, NO. 2 MARCH 2004.
3] Analysis on Passive soft switching snubbers by Huaguang
Zhang, Qiang Wang, Enhui Chu, Xiuchong Liu,Limin Hou, IEEE
TRANSACTIONS ON POWER ELECTRONICS,Volume: 26 , issue2009
4] A passive lossless snubber cell with minimum stress and wide soft-
switching range by Li, R.T.H.; Chung, H.S.H. Energy Conversion
Congress and Exposition, 2009. ECCE 2009. IEEE
5]Rashid M. H, Power Electronics: Circuits, Devices and Applications,
2nd edition.
6]Ned Mohan, Tore M. Undeland, William P. Robbins, “Converters,
Application and design”-3rd Edition,Wiley India Pvt. Ltd.