It is required for a three-phase three-wire shunt active power filter（SAPF） to control the positive

negative and zero sequence components respectively when the power grid is not balanced

therefore

taking the mid-point capacitor three-phase four-wire SAPF as the research object

we proposed a nonlinear passivity-based control（PBC） strategy based on port-controlled hamilton with dissipation（PCHD） model by using its passivity.Firstly

according to the mathematical model of the controlled object in the dq0 coordinate system

the PCHD model was obtained. Then

the passive controller of SAPF was designed by an interconnection and damping assignment（IDA） method. Finally

the outer-loop voltage controller of SAPF based on PI control was obtained according to the close connection between the total and differential voltages of the DC side and compensating current. Simulation and experimental results show that the mid-point capacitor three-phase four-wire SAPF based on PCHD model designed in this paper can realize low harmonic current

DC side voltage stability and neutral-point voltage balance on the condition of balanced or unbalanced grid;compared to the traditional PI control

the proposed control method has a better compensation effect and faster response speed.