Modeling of stored charge in metallized biaxially oriented polypropylene film capacitors based on charging current measurement. 
Metallized biaxially oriented polypropylene film (BOPP) capacitors are widely used in pulsed power systems.  When the capacitor is used as the energy storage equipment under high electric field, more charges should be provided to maintain the voltage of the capacitor.  This should be ascribed to the completion of the slow polarization which may take several hours or even longer.  This paper focuses on the stored charge in metallized BOPP film capacitors.  The modeling of the stored charge by the equivalent conversion of circuits is conducted to analyse the slow polarization in the BOPP film.  The 3-RC network is proposed to represent the time-dependent charge stored in the capacitor.  A charging current measurement system is established to investigate the charge storage property of the capacitor.  The measurement system can measure the long time charging current with a sampling rate of 300 Hz.  The total charge calculated by the charging current indicates that the stored charge in the capacitor under the electric field of 400 V/μm is 13.5% larger than the product of the voltage and the capacitance measured by the AC bridge.  The nonlinear effect of the electric field on the slow polarization charge is also demonstrated.  And the simulation of charge storage based on the 3-RC network can match well with the trend of the stored charge increasing with the time.