TIDUFB1 December 2024
To understand the current loop model, first closely look at the inductor current. In Figure 2-4 the duty cycle D is provided to the PWM modulator, which is connected to the switches Q1 and Q2. Remembering this, see Equation 1:
When D is set to 1, all the switches are off, and when D is 0, all switches are on, which connect the inductor to the point to M.
To modulate the current through the inductor, the voltage vxiN is regulated using the duty cycle control of the Q1 and Q2 switches. Assuming the direction of current is positive in the direction from the AC line into the rectifier and using the DC bus feedforward, the input AC voltage feedforward along with the assumption that the grid is fairly stiff. The current loop can be simplified as shown in Figure 2-4, and the current loop plant model can be written as in Equation 2.
where
The negative sign on the reference is in place because the current loop is thought to be regulating the voltage vxiN. To increase the current, vxiN must be reduced and thus, the opposite sign for reference and feedback in Figure 2-4. This current loop model is used to tune the current compensator. A simple proportional controller is used for the current loop. The gain of the proportional gain is adjusted to make sure the system is stable.