Module-10b Rectifier & Inverter Circuits Professor: Textbook: Dr. P. Enjeti with Michael T. Daniel Rm. 024, WEB Email: enjeti@tamu.edu michael.t.daniel@tamu.edu Power Electronics Converters, Applications & Design (Third edition), by: Ned Mohan et al., John Wiley COURSE WEBPAGE: http://ecampus.tamu.edu 1
DC-AC Inverters Single Phase - Half-bridge Inverter - Full-bridge Inverter - Dual output voltage configuration - Output filter design Three Phase Inverter - Dead-time effect PWM Techniques - Sinusoidal PWM - Selective harmonic elimination (SHE) -Space vector PWM 2
Voltage Source Inverter Advantages & Disadvantages Voltage source inverter (VSI) is a buck type converter ac output voltage is limited and cannot exceed the dc-link VSI cannot tolerate short circuits dead time between the gating of upper and lower switches need to be provided Three switches are on at any given instant VSI can supply multiple loads Output voltage in PWM and exhibits high dv/dt.in the case of long motor leads, voltage reflections cause over voltages at the motor terminals. Furthermore, high dv/dt and common mode voltages contributes to ground currents and bearing fluting 3
Voltage Source Inverter Common mode voltage Analysis
Voltage Source Inverter Common mode voltage Analysis
Voltage Source Inverter Common mode voltage Analysis
Voltage Source Inverter Effect of Blanking time S1 g,ideal S2 g,ideal V an,ideal S1 g,actual S2 g,actual V an,actual V error = V an,ideal V an,actual
Voltage Source Inverter Effect of Blanking time Problem 8.12 page 246 Ref: Y. Murai, etal Waveform distortion and correction circuit for PWM inverters with switching lag-times, IEEE Transactions on Industry Applications, Sep/Oct 1987
Mathematical Modeling of Blanking Time Effect
Mathematical Modeling of Blanking Time Effect
Current Source Inverter Operation 11
Current Source Inverter Operation Advantages & Disadvantages CSI is a boost type converter Load voltage and current are sinusoidal (v.low THD) & no dv/dt issues. Reverse voltage blocking switches are needed Can tolerate short circuits No load operation / open circuit of the load is not possible Applicable for single or dedicated load Only two switches are on at any given instant Reference: P. Enjeti, P.D. Ziogas, J.F. Lindsay, A current source PWM inverter with instantaneous current control capability, IEEE Transactions on Industry Applications, May/June 1991, pp 582-588 12
Comparison of Current Source Inverter & Voltage Source Inverter Current source inverter with symmetrical gated commutated thyristors(sgcts) Voltage source inverter with NPC inverter and IGBT devices Ref: A.V. Meulen, J. Mauin Current source inverter vsvoltage source inverter Topology, Eaton Corp, Technical data TD02004004E, Aug 2010 13
Comparison of Current Source Inverter & Voltage Source Inverter
Further Reading Available Online Via http://libcat.tamu.edu http://onlinelibrary.wiley.com/book/10.1002/0471773719;jsess ionid=be7eb55c85968f44a70290a287d9a702.d04t01
Z Source Inverter Advantages & Disadvantages Z source inverter is a buck-boost type converter ac output voltage can be boosted and exceed the dc voltage source Z source inverter can be short circuited the shoot through time T 0 is used to boost the output voltage The PWM operation of the Z source Inverter is identical to a conventional VSI. Three switches are on at any given instant Dc voltage source current is discontinuous (similar to a buck-boost converter) Presence of stray inductance between the inverter and the Z-source (dc-link) causes voltage spikes and affects performance Equivalent resistance of the inductors limits the boost gain and also lowers the efficiency 16
Z Source Inverter - Analysis 17
Z Source Inverter - Analysis 18
Z Source Inverter - Analysis 19
Z Source Inverter PWM Operation 20
Z Source Inverter PWM Operation
Quazi- Z Source Inverters VSI with a boost converter