FILTER REGENERATION SYSTEM FOR INTERNAL COMBUSTION ENGINE AND FILTER REGENERATION METHOD FOR INTERNAL COMBUSTION ENGINE

A filter regeneration system for an internal combustion engine, the filter regeneration system including: a calculation unit configured to calculate a minimum oxygen concentration and a minimum nitrogen dioxide concentration at which a passive regeneration reaction, in which carbon in PM accumulated on a filter arranged in an exhaust gas passage of the internal combustion engine reacts with nitrogen dioxide and oxygen to generate carbon dioxide and nitrogen monoxide, occurs based on an amount of the PM accumulated on the filter; and an exhaust gas temperature control unit configured to, in a case where an oxygen concentration and a nitrogen dioxide concentration in exhaust gas on an upstream of the filter are equal to or higher than the minimum oxygen concentration and the minimum nitrogen dioxide concentration, respectively, control a temperature of exhaust gas flowing into the filter within a temperature range in which the passive regeneration reaction occurs preferentially.