Improving stability and response of control systems

A control system is disclosed in which an error signal (e), i.e. the difference between a required value (R) and a feedback value (F), is used to select a gain value (k) for use in a controller (4). Then the error signal (e) is multiplied by a selected gain signal (k). In order to reduce noise, the error signal (e) is filtered before being fed to a gain selection means. Additionally a disturbance compensation means comprising a lookup table and driven by another parameter of the controlled system is used to produce a compensated error signal (e') for selecting the gain. This is achieved by multiplying the error signal (e) is by a value read from the lookup table, depending on the value of the other parameter, for example temperature.