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 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/ 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. Softswitching 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 softswitching, 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/ and low switching losses to the switching devices. The PSSS further uses a transformerbased 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. 36
through CS0.Therefore, V csp, increases and V csn, decreases as shown in Fig. 4.2, whereas voltage, V cs0 remains almost constant. The SSS circuit includes a snubber diode, D sp, and a snubber capacitor, C sp, for the upper main device, Sp, and, symmetrically, D sn and C sn for the lower main device, S n. The functions of the snubber diodes, D sp and D sn, and snubber capacitors, C sp and C sn, 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, C s0, connected across the two snubber capacitors. Fig.2 (b) shows the operating waveforms during S p turn-off or S n 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 C sp, through the snubber diode D sp and discharging C sn, 37 2.1 PSSS CIRCUIT DESIGN AND CONSIDERATIONS The dv and di are determined by the snubber capacitance C s, and stray inductance L s and partially by the load current. The highest dv 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 V csp, can be expressed as V csp (0) is the initial voltage of the upper snubber capacitor, I ls(0) is the initial current
1 through the stray inductor, and = is 2L s C s the resonant frequency. The load current affects the initial voltage of the upper capacitor, V csp (0), and initial current, I ls(0). The dv from is obtained as harmonic spectrum comparison done in qtgrace software 3.1 MATHEMATICAL MODELING OF SPWM & SQUARE WAVE INVERTERS The highest di 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 di and. Given target numbers for dv and di, snubber capacitance and stray inductance can be determined. The rule of thumb for estimating the stray inductance is 1µH per 1-meter-long conductor. 3.2 HARMONIC SPECTRUM COMPARISON 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 38
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 m f is even, then harmonics at m f +2 If m f is odd, then harmonics at 2m f +1 Fig.4.1(b) Output voltage waveform of the saber simulation with snubber circuit. 4.1 HARDWARE IMPLEMENTATION OF FULL- BRIDGE SQUARE WAVE INVERTER IV. SIMULATION RESULTS 1) WITHOUT SNUBBER Fig.4.1(a) Output voltage waveform of the saber simulation without snubber. Fig 4.1 Hardware setup of the experiment 2) WITH SNUBBER V) OUTPUT WAVEFORMS (i) FULL BRIDGE INVERTER OUTPUT WITHOUT INDUCTIVE LOAD 39
Fig.5.1(a) full bridge inverter waveform without inductive load (II) FULL BRIDGE INVERTER OUTPUT WITH INDUCTIVE LOAD Fig 5.1(c) Output voltage waveform without snubber. (II) WITH SNUBBER Fig.5.1(b) full bridge inverter waveform with inductive load Fig 5.1(d) Output voltage waveform of the hardware with snubber circuit. HARDWARE OUTPUT FOR PASSIVE SOFT SWITCHING SNUBBER (I) WITHOUT SNUBBER 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 di and ; Lowering cost and improving reliability. 40
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 uniformly at both turn-on and turnoff 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 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 softswitching 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, 2 nd edition. 6]Ned Mohan, Tore M. Undeland, William P. Robbins, Converters, Application and design -3 rd Edition,Wiley India Pvt. Ltd. 41