Overview
The entire PWM modulation process is a process of AC-DC-AC. First, a three-phase full-bridge rectifier circuit is used and then a large capacitor is used to obtain a DC power supply with a smaller ripple. Then use this power supply as the inverter circuit power supply, and generate pulse control IGBT three-phase bridge by comparing three standard sine waves and triangle waves. Finally, the waveform of the PWM modulation is obtained.
Rectifying part
The thyristor full bridge used in this part. Note that the initial phase unit of this three-phase power supply is degrees, not radians. Just set the bridge to a thyristor.
Subsystem: Pulse generation
Here, in order to obtain a larger DC power supply, the conduction angle alpha=0°, the pulse width 80° (double narrow pulses can also be used), and the interval 60° (from top to bottom). As for why, it is because when the two-phase voltage is subtracted, although it is greater than 0, one of the phases is already less than zero. At this time, turning on the other thyristor will not form a loop. Therefore, it is necessary to ensure that the first pulse comes when the second pulse comes. The pulse is still there.It must be noted that the pulse width of this pulse module is to write a percentage, so it must be multiplied by 100! This oscilloscope is used to see the control pulse.
Inverter part
Pulse modulation subsystem:
The difference between the sine wave generator here and the sine generator in powerlib is that its initial phase is usedradianTo show it! A fcn module is used here, and the content inside is roughly to compare x with s1, s2, and s3. If it is smaller, set the respective output to 1, otherwise it is 0.
Modulation comparison:
control pulse;
there are three complementary pulses.
Overall block diagram and results
The unevenness here is because when each bridge arm is turned on, three of the lower bridge arms may be turned on, the other two or one of them may be turned on, so that 1/3Ud and 2/3Ud will appear.