Modeling and stability analysis in multi-converter systems including positive feedforward control

A positive feedforward control technique is proposed to improve phase margin in multi-converter applications without physical hardware modification and with little reduction of system bandwidth. The positive feedforward control is realized by combining it with the conventional negative feedback control. The positive feedforward controller acts like an active filter presenting an impedance with positive real part at high frequencies while at low frequencies the negative feedback controller provides tight output voltage control. To provide controller design criteria, small-signal models by g-parameter representation are presented. Stability of the whole system with interactions between subsystems is analyzed based on the impedance criterion. As an illustrative example, the stability improvement by the positive feedforward control of a buck converter with an input filter is demonstrated by simulation in frequency domain. Experimental results including a constant power load connected in parallel to the input filter are also presented.