Active damping of LCL resonance with minimum sensor effort by means of a digital infinite impulse response filter

This paper presents a concept for active damping of an LCL filter connecting a digitally controlled PWM converter to the grid. Active damping is performed by means of a digital Infinite Impulse Response (IIR) filter. Digital filters, being well known in digital signal analysis, can easily be implemented when using digital controllers and require very low computational effort. In contrast to active damping solutions found in literature, no extra quantities except the controlled current must be sensed. This functionality is proven via experimental results. After a short introduction of the problem and an overview of solutions found in literature, the implemented fundamental procedure for active damping is described. Subsequently, the main idea of using an IIR filter for active damping, being an approximation to a derivative function, is qualified and the design procedure is presented. In this paper it is stated that with this method the sensors are minimized and that due to the approximation of the derivative function the damping performance is lower compared to solutions found in literature. However, the damping effect by using an IIR filter is proven. The use of IIR filters and the reduction of sensor effort for active damping of EMI filters with multiple passives looks promising also for other applications with a known load.