Abstract
This paper is concerned with the approximate controllability of Sobolev-type Hilfer fractional differential equations (FDEs) with control and Sobolev-type Hilfer fractional initial conditions in Hilbert spaces. By means of two operators and the probability density function, the definition of mild solutions for the studied problem was given. Then, via Hilfer fractional derivative and by combining the techniques of fractional calculus and the fixed point theorem, we analyzed the existence and uniqueness of mild solutions. With the help of a Cauchy sequence and approximate techniques, we established some sufficient conditions for the approximate controllability of the proposed control system. Finally, an example is presented for the demonstration of obtained results.