Zero Ripple Current with Coupled Inductors in Continuous Conduction Mode under PWM Signals

This paper presents a generalized analysis to explain current ripple of an m windings coupled inductor with a given coupling factor kij for each pair of windings and then studies more in detail its use in continuous conduction mode and with pulsewidth modulated signals. To determine the current ripple, a generalized expression of the equivalent inductance of each winding is calculated including the influence of voltage unbalance. In the ideal case, the equivalent inductance shows that the current ripple can only become m times smaller than with uncoupled inductors. But in the unbalanced case, some divergences of the equivalent inductance appear that are responsible for zero ripple current. The proposed generalized expressions of the equivalent inductance also describes the current ripple of the new appearing intervals due to out-of-phase signals. An easy to design condition is proposed that achieves zero current ripple in all windings but one. Experimental results are provided that validate the presented theoretical expressions under the given conditions.