Hi everyone,
I am new into using three phase inverters.
I understand that there are two possible modes of operation for 3Phase Inverters: 180 degree or 120 degree.
My doubt is that which mode of conduction is generally used when we have SPWM control and SVM control.
Is it possible to use SPWM in 120 degree conduction mode as well as 180 degree conduction mode ?
Thank you every one in advance for your help and time taken to answer my doubts.
Kind regards,
Silpa
Hi Silpa Baburajan
----In SVM and SPWM algorithms, it is hard to find the switching duration. Because switching will happen at very high switching frequencies compared to fundamental Modulating wave.
----Modulating wave is of sinusoidal fashion in SPWM and SVM can say 180 degree is the operating mode.
----It can also be verified by comparing the wave shape of Phase and line voltages. In 180 degree mode phase voltage wave follows six steps and line voltage of two level. Can observe wave forms similar to the theoretical analysis of 180 degree mode.
----For 120 degree conduction, Modulating wave has to be changed in SPWM to trapezoidal with required conduction period.
https://www.tntech.edu/engineering/pdf/cesr/ojo/asuri/Chapter4.pdf
https://www.ijert.org/research/three-phase-150-degree-mode-of-conduction-voltage-source-inverter-using-arduino-IJERTV5IS120210.pdf
The Pulse Width Modulation (PWM) techniques consist in generating, with each inverter leg, an output voltage consisting in a sequence of rectangular pulses with fixed height and variable width. The rectangular pulses are generated with a modulation frequency which is typically very high if compared to the desired output fundamental frequency (e.g. 10 kHz against 50 Hz) and this is one major difference with respect to the 120° and 180° conduction mode (six-step mode) you mentioned.
The switching instants are commonly found by comparing a modulating signal (which is proportional to the reference leg voltage at the fundamental frequency) with a carrier signal (which is typically a sawtooth or triangular signal at the modulation frequency).
In SPWM approaches, the modulating signals for the three inverter legs are proportional to the sinusoidal waveforms desired at the output. In SVM approaches, a common mode voltage is superimposed to these sinusoidal waveforms in a way to maximize the overall DC-bus voltage utilization. This is automatically achieved through the space vector approach (hence the name of the SVM) and allows to increase the linear modulation region of the inverter of about 15% with respect to standard SPWM approaches.
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