3.6 Arbitration Routine

This routine takes the results from the MPPT state machine (MPPT) and the charger state machine (CSM) to determine how to best modify the operating point of the converter. This routine is abstracted from the actual hardware and is only able to request more or less power.

Battery safety is paramount, so the CSM is always given priority over the MPPT in the delivery of power. When the CSM requests more power, it calls the arbiter with this request. The arbiter looks at the MPPT routine’s result register to determine if lowering or raising the panel voltage will increase the power. Ninety-nine percent of the time when in Constant-Current mode, the MPPT result register will indicate 'none', meaning the ideal operating point has already been found and no additional power can be obtained from the panel. When in a Constant-Voltage mode, it is possible that the MPPT will have found more power, but the CSM is slowly reducing the current into the battery to keep the voltage constant.

When the CSM requests lower power, the default operation is simply to raise the panel voltage. This might have the wrong result if the result register is currently 'higher', meaning that raising the panel voltage will increase power. This will be temporary as the arbiter routine is updated numerous times per second. The routine will quickly lower the current as requested by increasing the voltage enough so that the operating point will move past the maximum power point (MPP), resulting in lower output power as required.