Self-powered energy management circuits make energy harvesting converters more efficient and more reliable. This paper presents an improvement of a Maximum Power Point Tracking (MPPT) technique applied on a Parallel Synchronized Switch Harvesting on Inductor (P-SSHI) technique for piezoelectric vibration converters. The aims are to detect the unstable vibrational state, optimize the output voltage and maximize the output power of the piezoelectric transducer. First, the P-SSHI technique is implemented without an MPPT technique. Then, an MPPT technique based on Fractional Open Circuit (FOC) voltage method is implemented. An improvement of the FOC method is proposed to enhance the capability of the Piezoelectric Energy Harvesting (PEH) system. The comparison between different simulation results shows that by using the same input parameters, the maximum efficiency for the PEH system based on the P-SSHI technique implemented without MPPT is 8.82 % whereas the maximum efficiency of the system based on the (FOC) voltage MPPT method is 13.77 %. A significant improvement of the PEH system is obtained by using the modified (FOC) method, where the efficiency reached 24.59 %.