An energy conversion system comprises a generator which generates electrical power in response to movement, wherein the generator comprises first and second elements which generate energy in an energy generation mode. In some examples, these can be brought into and out of contact with each other by a drive mechanism so that the energy conversion system has an (e.g.) intermittent charging mode in which the first and second 5 elements are brought into contact by the drive mechanism and an energy generation mode in which the first and second elements are out of contact. The relative speed, the spacing between, or the relative orientations or positions of the first and second elements are controlled during the energy generation mode to decrease the variation in output power or voltage of the generator. This system controls the physical positions or the motion of the 10 elements of the generator during the energy generation mode in order to implement a more constant power or voltage generation. This enables any required power conversion circuitry to be simplified.