The reactive compensation capacitor in the system can change the impedance characteristics of the power grid

thereby match with the impedance of active power filters at certain frequencies

causing resonance and leading to system instability. Aiming at this problem in this paper and with the active power filter based on cascade H-bridge topology as the application object

the synergy control strategy considering both filtering and reactive power compensation is proposed which

at the time of filtering

replace the shunt capacitor for reactive power compensation so to assure stable operation of the system. In order to compensate the harmonic current by the control strategy

a quasi-proportional resonance controller is introduced into the current inner loop in the decoupling control of the rotating coordinate system. For reactive power compensation

the PI controller is adopted to generate the q-axis fundamental current

which is achieved by superimposing on the q-axis harmonic current. Finally

the system stability analysis is performed on the basis of considering the network impedance of shunt capacitors and filter impedance

and the necessity of replacing shunt capacitors with active power filters for reactive power compensation is demonstrated in accordance with the impedance stability theory so to ensure system stability. The effectiveness and feasibility of the proposed control strategy are indicated by the simulation results based on PSCAD/EMTDC.