Trouble Understanding Shunt active power filter using instantaneous power theory

Question

I have a demo Simulink model of a shunt active power filter using instantaneous power theory (Source, unbalanced none linear load and the filter, a very sample one, that i am using to understand the concept). Here is the model :

Here is a look inside the Filter :

Now, I understood that the all idea of an active filter in general is to measure the disturbance (current harmonics content), and generate the same opposite signal, and inject it in the main line, so that the injected current will cancel the harmonic signal only and leave the fundamental in the PCC.

In my model, the universal bridge (blue box) is the one generating the compensation current right (the red arrow) ? (based on the triggers of the hysteresis control block), but from what i know on the universal bridge (and power converters in general) is that they need a source of power to convert from, in our case a DC source right ? i don't see any DC source in the other side of the Bridge (Yellow arrow).

My questions :

1- am i right about my understanding ?

2- am i right about the sens of the compensation current (red arrow) ?

3- most importantly : where does the Universal bridge get its power from in order to generate the compensation current ?

Answer 1

look let me tell u that u are right! but the APF filter take its power from Utility and when the nonliner load wana to consume oscilliting power,the APF will feed it,so its like some one take from u money to protect u,the money is the Power that APF need to inject Opposite Current...

Hope it help u if u have any question mail me because i work about this subject too

Answer 2

Role of DC side capacitor : DC side capacitor serves two main purposes

1. it maintains a de voltage with small ripple in steady state,
2. Serves as an energy storage element to supply real power difference between load and source during transient period. In steady state the real power supplied by the source should be equal to the real power demand of the load plus a small power to compensate the losses in the active filter. Thus, the de capacitor voltage can be maintained at a reference value.

Source : Design Simulation and Experimental Investigations, on a Shunt Active Power Filter for Harmonics, and Reactive Power Compensation , by S.JAIN and P.AGARWAL. [Journal : Electric Power Components and Systems, 2003 / DOI : 10.1080/15325000390203674]

(Link to the paper here <=======)