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This paper introduces a power conversion technique based on active control for harvesting power from multiple piezoelectric transducers with higher efficiency than conventional passive approaches. The proposed scheme allows each source to operate efficiently, especially in case of irregular vibrations and heterogeneous transducers. A prototype system was developed and validated in realistic conditions: three 0.5 × 12.7 × 31.8 mm3 piezoelectric cantilevers with 18g tip masses were excited with the vibrations of a train passenger car. The converter harvested up to 142μW@0.22g-RMS and up to 90μW@0.11g-RMS. An implementation based on discrete components including passive startup and basic power management consumes a fraction of the extra harvested power as little as 5.5μW per source during operation. The structure is modular and the number of sources can be easily increased without affecting power consumption.