How is the power losses varies of AC-DC, DC-AC, DC-DC power converter of rating (2 KVA- 5 MVA)?
The main power losses are resistive i.e I^2R and switching losses.
For the resistive relationship with current, use Ohm's law.
There are a number of places where resistive losses occurs. Some of the significant ones can be:
1) Transformers / Inductors,
2) The switches e.g. BJT's, IGBT, FET's etc.
3) Electrolytic capacitors
Losses in busbars, cabling, terminations and connectors are usually low, if properly sized.
For the switching loss , the transition area where devices are partially on, it's the product of the instantaneous on state voltage and current. Most power electronics handbooks cover the topic.
Switching losses are generally ignored for FET's under 100kHz, but are significant for IGBT's and BJT's.
losses in converters during steady state operation of converter are directly proportional to load current and can be divided into two categories 1. when switch is in ON state, during this condition it is I2R where R is on state resistance of switch or forward resistance of switch. 2. during transition i.e when switch is turning ON or OFF. During this time both current and voltage are simultaneously present across the switch thus power loss is reasonably high compared to ON state and can be found out by product of instantaneous voltage across and current through the switch.
Thank you very my Prof. NitinLanger and Prof. David Johnson. Can you help me to find the literature for AC-DC, DC-AC converter at 5kVA to 5MVA level. I will be thankful to you gays.
Hello Rajeev
You can look at the Interactive Power Electronics Seminar here: http://www.ipes.ethz.ch/
There is a good freely downloadable ebook available (full of advertisements, but they pay for the book) on power electronics here:
http://bookboon.com/en/introduction-to-power-electronics-ebook
My favourite book is still "Power Electronics: Converters, Applications, and Design"
by Ned Mohan (Author), Tore M. Undeland (Author), William P. Robbins (Author), though a bit dated, but really good on theory and practical aspects of power electronics.
There are extensive academic works in the different journals e.g. IEEE, Wiley, Elsivier etc.
Hi,
Please see page 884 of the following paper for power loss calculation:
M. R. Islam, Y. G. Guo, and J. G. Zhu, “A multilevel medium-voltage inverter for step-up-transformer-less grid connection of photovoltaic power plants,” IEEE Journal of Photovoltaics, vol. 4, no. 3, pp. 881-889, May 2014.
I rather disagree with the first three statements: also switching losses of mosfets can be relevant, even below 10kHzcompared to the conduction losses. The losses are mainly induced by the recovery of diodes, especially in bridge configurations. Some IGBTs may even show lower losses than mosfets as they may have better freewheel diodes. Conduction losses are more than proportional with current^2 in mosfets due to the temperature effect. The conduction losses are less than proportional with current^2 for IGBTs. The recovery losses of diodes (switching) is highly temperature dependent with silicon components, and much less with SiC. It is necessary to consult each time the data sheets. Inductors have not only I^2*R but also iron or ferrite losses and eddy currents in the conductors. These effects get even dominant for larger sizes, see also my book "Inductors and transformers for power electronics". The finging field around the air gap causes high local losses in the conductors, and can increase these eddy current losses easily a factor 6 higher than a corresponding transformer winding.
if you choose soft switching control ZCS or ZVS, the switching losses decreased very well. you must consider the series resistance in the electrolyte capacitors that use in the out put filter. if the out put current have a bad THD or big ripple, this resistance can decrease the circuit efficiency. indeed current ripple decrease efficiency because that crosses from all electrical elements ( capacitor, switches, diodes ) and make the additional losses on this devices. You must consider reverse recovery speed in diodes because the low speed diodes in the high current converters have a big losses in snuff time.
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