Power management apparatus for energy harvesting

A power management apparatus comprising:

• a plurality of energy harvesting input channels each for connecting to an electrical energy harvesting source;
• a first energy storage element connection for connecting to an energy storage element;
• an inductor connection for connecting to an inductor;
• a switching circuit which is configured to selectively connect to the energy harvesting input channels, the inductor connection and the first energy storage element connection;
• and
• a controller which is configured to:
• operate the switching circuit to transfer energy between the energy harvesting input channels and the first energy storage element connection by a sequence of energy transfer cycles, each of the energy transfer cycles comprising:
• an energise phase in which energy is transferred from one of the plurality of energy harvesting input channels to the inductor connection for an energise time (tE) to transfer energy to the inductor and;
• a de-energise phase in which energy is transferred from the inductor connection to the first energy storage element connection for a de-energise time (tD),
• wherein each energy harvesting input channel is allocated a plurality of the energy transfer cycles, with a harvesting cycle period (tP) between start times of successive energy transfer cycles, and the plurality of energy harvesting input channels are connected to the inductor connection in a time-multiplexed manner;
• determine operating parameters for operating the switching circuit by:
• determining, for each of the energy harvesting input channels, maximum power operating parameters which transfer a maximum power from the electrical energy harvesting source connected to the energy harvesting input channel and a maximum power inductor utilisation factor representing a portion of time for which the inductor is required by that input channel to transfer the maximum power;
• determine a maximum inductor utilisation factor representing a total amount of time for which the inductor can be used to transfer energy between the energy harvesting input channels and the energy storage element;
• determine a sum of the inductor utilisation factors for the plurality of energy harvesting input channels;
• compare the sum of the inductor utilisation factors with the maximum inductor utilisation factor;
• and
• if the sum of the inductor utilisation factors is greater than the maximum inductor utilisation factor,
• determining a set of adjusted operating parameters for sharing use of the inductor between the plurality of energy harvesting input channels in the time-multiplexed manner, wherein at least one of the energy harvesting input channels is selected for an adjustment of the operating parameters from the maximum power operating parameters, the selection based on an effect of a change in the inductor utilisation factor and a corresponding change in power of the energy harvesting input channel, wherein the set of adjusted operating parameters (tE, tP) are determined such that a sum of adjusted inductor utilisation factors is less than the maximum inductor utilisation factor.