Continuous conduction mode (CCM) is desired to maintain a high efficiency while delivering the constant current required for the string inverter. When the input voltage range, output voltage, and load current are defined, this leaves the inductor value as the design parameter to maintain CCM.

Put simply, define the desired ripple current (ΔI) for the converter. Normally ΔI is 0.2–0.4 times the output current (I_O). A value of 0.4 is selected as the coefficient of ripple current.

Considering 18A maximum output current, and ignoring the voltage drop on the FETs and resistance of the inductor gives:

The output voltage at an 18A, 600W condition is about 33.3V, the input voltage can be considered 43V at the maximum power point of the PV panel, then, the output inductance can be derived, 3.48μH. At half load, considering output voltage at an 18A, 300W condition is about 16.7V, the input voltage is also 43V since the MPP voltage at half irradiation is similar with the MPP voltage at full irradiation, the output inductance is about 4.7μH.

In the case of the same size, an inductor with smaller inductance can have a larger saturation current. Finally, a 3.6μH inductor is chosen to make the design compact.