The invention relates to a control system (1) and a method for controlling of a rectifier (2). The control system (1) enables to configure and to adopt the operating of a rectifier due to changing operating conditions and to operate the rectifier (2) in an optimal operating range in a simpler and faster way. The control system (1) for controlling a rectifier (2) comprising at least one reactor (6) per phase connected to the rectifier (2) for providing an input signal to the rectifier (2), means (7) for providing a bias current for controlling the reactor (6), means (8) for providing a control current for controlling the reactor (6). The bias current is fixed to a predefined value which is taken as an input signal for the means (8) for providing a control current for controlling the reactor (6), whereas means (8) for providing a control current for controlling the reactor (6) compensates the difference between the predefined value of the bias current and a start value defining a start point of the linear operating range of the reactor (6). A further object of the present invention is to find the minimum and maximum values of the optimal operating range of a rectifier (2) in a more efficient way by using an improved method for controlling a rectifier (2) which is controlled by at least one reactor (6) per phase connected to the rectifier (2) comprising the steps: setting a bias current value as a predefined value by means (7) for controlling the reactor (6); finding a start value defining a start point of a linear operating range within a control curve of the reactor (6) by compensating the difference between the predefined value of the bias current which is taken as an input signal for means (8) providing a control current for controlling the reactor (6) and the start value; finding an end value defining the end point of the linear operating range of said reactor (6), whereas the start point and end point define the linear operating range within the control curve of said reactor (6).