The present article is to select the key parameters of a shunt active filter in the conditions of centralized and distributed power supply systems. The main equations which reflect the dependences of shunt active filter key parameters with network and load characteristics are presented. A mathematical model of a generalized industrial electric network with a variable value of internal impedance with a nonlinear load and shunt active filter was developed by means of the Matlab Simulink software environment. During simulation the generalized dependences of shunt active filter key parameters from the value of internal network impedance were obtained which allow to select and properly tune the mentioned filter key parameters according to the power supply mode defined by the type of a source: centralized or distributed. The obtained results also allow to maintain the required level of power quality and electromagnetic compatibility by means of a shunt active filter during emergency power supply modes when switching from a centralized to a distributed power supply source.