The use of high power multi-level converters as an interface for renewable energy sources allows modern power grids to achieve a higher flexibility and reliability. Cascaded H-Bridge Converters (CHB) are particularly suitable in these applications but more advanced control techniques are required. In particular Dead-Beat current control methods are a promising solution for high-power CHB. However in high-power applications, a reduced switching frequency is required to ensure high efficiency operation and the performance of the control, in term of quality of the AC side current, may be reduced. As a result a more accurate approximation of the derivative, used in the discretised control law, may be required to ensure accurate operation. In this paper three different methods for the discretisation of the converter model are analysed and compared. The most suitable one is then chosen to implement an improved Dead-Beat current control for AC current regulation of a 7-level, CHB active rectifier.