The nonideal generalized amplitude integrator (NGAI): interpretation, implementation and applications

Conventional integrators for DC signals and the so-formed PI controllers are classic concepts in converter control. While these integrators offer satisfactory performance in DC control system, they cause steady state error in AC control system. Major controllers, such as the hysteresis controller, the predictive controller and the synchronous frame controller have evolved in the past decade. The synchronous frame controller, in particular, has been regarded the standard solution in most three phase applications. Digital implementation of the synchronous frame controller involves the calculation of the trigonometric functions which is a time-consuming task. For an unbalanced system, a second frame is needed, the computation task is therefore doubled. This task is further multiplied for a multiple frequency system due to the need for multiple frames in such a system. The controller also does not apply to single phase applications. An interesting solution has been introduced, the so called resonant controller which works on the single phase basis with reduced computation. This paper clarifies that the resonant element in the resonant controller is actually a nonideal generalized amplitude integrator (NGAI) for AC signal. And the resonant controller is actually an H control for an AC control system. Digital implementation of the NGAI and signal prediction using the NGAI are discussed. Applications of the NGAI in converter current control and signal processing are presented.