This invention provides a modular, efficient and self-feedback/balance, fluid-powered actuation system. This system comprises two basic modules; actuation module and positioning module, which are directly connected to each other. The actuation modules can be constructed as a triple acting actuator having a novel balanced linear-rotary mechanism converter or a double acting actuator with two novel balance guide bars. The positioning module is constructed as a two-staged, self-feedback/balance positioner with position as a variable for controlling positions of an output shaft of the actuation modules. An input shaft in the positioning module is operated by three types input signals. This system also provides a rotary force to actuate and control different rotary valves with lighter weight, superior seal and high accuracy and can be used for quick cycle, high vibration applications or other critical services.