passive soft switching snubber for spwm … · connected across the two snubber ... more effective...

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: [email protected]

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


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



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



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



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.



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.

http://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=63

passive soft switching snubber for spwm … · connected across the two snubber ... more effective...

Documents