A method for energy harvesting using a voltage converter system (20) for converting input power into output power and for charging at least a first (50) and a second (60) rechargeable storage device, said method comprises:
- coupling a first power input path (31a) between an energy harvester (70) and the voltage converter system (20) for transferring input power from the energy harvester (70) to the voltage converter system,
- monitoring a parameter VBatt1 and a parameter VBatt2 indicative of a charging level of respectively said first rechargeable storage device (50) and said second rechargeable storage device (60),
- coupling the first rechargeable storage device (50) to an application load (90) such that the first rechargeable storage device when charged can supply power to the application load (90),
- coordinating charging of the first (50) and the second (60) rechargeable storage device by repetitively performing sub-steps of:
- 1a) coupling a first power output path (32a) between the voltage converter system (20) and the first rechargeable storage device (50) for transferring output power from the voltage converter system to the first rechargeable storage device (50),
- 2a) operating the voltage converter system (20) for transferring charges from the energy harvester (70) to the first rechargeable storage device (50) so as to charge the first rechargeable storage device (50) with energy from the energy harvester (70), and operating the voltage converter system for charging the first rechargeable storage device until the parameter VBatt1 has reached an upper threshold value VBatt1-up,
- 3a) if VBatt1 has reached said upper threshold value VBatt1-up and if VBatt2 is below an upper threshold value VBatt2-max then
- i) decoupling the first power output path (32a) and coupling a second power output path (32b) between the voltage converter system (20) and the second rechargeable storage device (60) for transferring output power from the voltage converter system to the second rechargeable storage device (60), and
- ii) operating the voltage converter system (20) for transferring charges from the energy harvester (70) to the second rechargeable storage device (60) so as to charge the second rechargeable storage device (60) with energy from the energy harvester (70),
- 4a) if during the charging of the second (60) rechargeable storage device the parameter VBatt1 has subsequently decreased from the upper threshold value VBatt1-up down to a lower threshold value VBatt1-low, with VBatt1-low<VBatt1-up, then decoupling the second power output path (32b) and restart at step 1a),
- transferring energy from the second rechargeable storage device (60) to the first rechargeable storage device (50) if i) the parameter VBatt1 of the first rechargeable storage device (50) has dropped below a critical threshold value VBatt1-SW, with VBatt1-SW<VBatt1-low, and if ii) the parameter VBatt2 is equal or above a predefined threshold value VBatt2-low, said transferring energy comprises sub-steps of:
- 1b) decoupling the first power input path (31a),
- 2b) coupling a second power input path (31b) between the second rechargeable storage device (60) and the voltage converter system (20) for transferring input power from the second rechargeable storage device (60) to the voltage converter system (20), and
- 3b) operating the voltage converter system (20) for charging the first rechargeable storage device (50) with energy from the second rechargeable storage device (60) until the parameter VBatt1 of the first rechargeable storage device (50) has reached said upper threshold value VBatt1-up.