Hi
I am designing a 250w sine pwm inverter(H-Bridge). The dc link voltage will be 400V volts. And output required is 230Vrms.
I am driving the inverter using IR2110 and the switches used are IRFPE50PBF. The pwm frequency is 50kHz. However on runnning the devices gets heated within a minute. I tried simple square pwm with 50% duty ratio ,50Khz. This time no heating was observed. I wanted to know what could be the cause of heating, whether its due to conduction loss (Rdson=1.2 ohm) or whether its due to anti parallel diode(trr=980ns). I put a dead band of 1micro second.How do i reduce the heating.Is reducing the switching frquency the only method to reduce the heating .
, are there better devcies rated for 50kHz, and 1kW operation.
thanking you.
It's due to switching loss. When switching frequency increases, switching loss increases as well. And remember that, as frequency increases, current required to turn the MOSFET fully on increases, as the gate must be charged in a smaller time. So, maybe, the problem lies in MOSFET gate drive section. What is the value of the gate current-limiting resistor? What voltage are you using to drive the MOSFETs?
Hi
I havent got answers for heating of switch at 50khz, at extreme duty cycles as compared to 50% duty cycle. Can i get some references regarding the solution to this problem..
Thanking you.
First point, no, second point, yes. Tahmid is referring to incomplete bootstrap capacitor charge which is a different problem.at higher duty cycles more gate charge is required from driver than at 50%, and also it increases with the switching frequency
Did you notice that the original post reports a dead time of 1 us? That's already quite a lot for MOSFETs.I think that you have problems because you dont have delay circuit.
When you say the load is 216ohms, is that after the LC filter, or is the resistive load connected directly to the bridge outputs? From the shape of the current waveforms, I'm assuming that you are still using the LC filter. That means that the bridge diodes will conduct current during the dead time, which may contribute to heating. As FvM stated above, finding out if your dissipation is extraordinary or not requires that you give specific information about the load (including any LC filters used), and how the FETs are cooled (we'll want an estimate of thermal impedance to ambient, and a rough estimate of the case temperature). You might as well post a decent schematic as well.Hi
@fvm
The loading in both 50% and 90% duty ratio is 216 ohms ,the dc link voltage being 400. I am posting the waveforms, the load current waveform is not square wave (dont know why). I have used LEM LA55-P current sensor.
I am using complementary pwm scheme given in texas 28335 microcontroller, with active high complementary
@mtwieg
The above mentioned inverter is also used in sine-pwm mode with an L-C filter connected to it. In this sine pwm ,diodes of one diagonal will conduct during one half cycle of pwm
One possibility is that, at higher duty cycles, the MOSFET is not being fully turned on. You may need to use a larger bootstrap capacitor. What is the value of the bootstrap capacitor you are using now?
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