Method by a drive system for a DC-motor comprising an inverter and a multiple phase synchronous machine with a permanent magnet rotor and provided with a rotor position detecting means for detecting in order to generate a rotation dependent logic position signal or signals. Digital technique is used to displace the commutation points individually to an intended angle referred to said rotation dependent logic position signal or signals (POS 1,POS 2, POS 3). In a first step said position signal is supplied to a pulse detector (101) which creates a pulse train (T₀ - T₅) corresponding to the commutation reference points of time. In a second step every pulse in said pulse train gives a counting of a number of reference clock pulses (N₁,N₂,..N₆) in a counter (108) and in a third step corresponding binary numbers are stored in a register to be transmitted to a multiplier (111) in which multiplication takes place with a digital constant (k₁) from a constant memory (110).