I am looking for optimum Carrier frequency for sinusoidal pulse width modulation for reducing THD?Does selection of frequency convert SPWM into SHE-PWM?
Dear Ranvir,
The more you will increase the carrier frequency the less will be the THD if there is a filter connected to the output.
So the optimum is the maximum your system can generate if your only aim is to reduce THD. However, the adverse effect is the switching loss will be very high.
Selection of frequency does not convert directly SPWM to SHE-PWM although it helps to make the switching frequency band of harmonics move far past the fundamental. This makes filtering easy.
I am simulating for 2 level SPWM with IGBT's. How Much maximum Switching frequency i can select .What is optimum value?
Dear Ranvir,
The ideal, as mentioned by Mr. Arpan, is to use the maximum switching frequency possible in order to reduce the harmonics.
However, the limitation is the temperature of the semiconductors switches. Higher switching frequencies mean higher switching losses. You'll have to estimate the total losses (switching and conduction ones) and semiconductor junction temperatures according to the information provided in the switches data sheet (Eon, Eoff, Erec, VCEsat, Vf, Rthj-c, Rthc-s) and the heatsink and cooling system you are intended to use (Rths-a).Then you'll be able to compare with the maximum allowed operation temperature of the junction (Tvj, usually 125 ºC).
The process is iterative, but a simple MATLAB script should solve your problem.
I hope this information can help you in your design.
Ideally THD is reducing while we are increasing switching frequency but lower order harmonics are boosting at high rate at low modulation indices with increase in switching frequency.
Good morning everybody, it cuts both ways actually. While it is true you achieve a better quality of the output voltage waveform by increasing switching frequency, this involves additional stresses on the downstream cables and motor. It reminds me of a project we had in Denizli, Turkey where existing deep-well pumps stations were to be refurbished by installing power inverters to drive the existing submerged pump motors. We were advised by the supplier of the inverters not to operate with switching frequencies above 2 to 4 kHz so as not to damage the motor insulation.
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