It is known that a constant power load connected to DC electrical network may lead to instability problems on the DC-link variables. This paper addresses this problem of instability. To do this, a supercapacitor which is an energy storage element connected to the network is used to stabilize. To achieve this goal, a nonlinear control law based on backstepping approach is synthesised and robustness tests relatively to parameters variation have been realized. Simulation results confirm the good performances and robustness of the using approach.