3.1 PWM Modulation

Figure 3 shows a simplified, single-phase diagram of the Vienna rectifier. To control this rectifier, the duty cycle is controlled such that it regulates the voltage v_xiNdirectly. That is, if the software variable Duty is set to 1, it makes v_xiN the largest voltage possible by never turning on Q1 and Q2 switches and letting the inductor connect to the DC bus though the bridge diode. Similarly when Duty is set to 0, PWM is modulated such that Q1 and Q2 always conduct making v_xiN connect to the midpoint of the DC bus (which is zero), which makes it the lowest possible voltage for the switching cycle.

Figure 3. Single Phase Diagram of Vienna Rectifier

Figure 4 shows the detailed PWM configuration.

Figure 4. Vienna Rectifier Detailed PWM Modulation Scheme