July 2005, Issue 180

Solar-Powered Water Pump Controller
Cypress PSoC High Integration Challenge 2004 Contest Winner

FAULT MONITORING

In addition to basic motor control, a number of fault-monitoring tasks operate in the background and monitor the system for abnormal conditions. If a fault is detected, the system will shut down. If the fault subsequently disappears, the controller will automatically restart after a timed interval.

The first fault condition will occur if there’s insufficient solar power to drive the pump. This condition will be noticeable if the DC voltage is less than 39 V (for a 48-VNOMINAL DC bus).

A fault known as a dry run will occur if the water supply disappears and the pump dries. This can cause the pump to overheat because of the absence of cooling water.If the pump is lightly loaded, the DC voltage will remain high even though the closed-loop regulator will be increasing the motor speed.

The third type of fault occurs when the power stage draws an excessive amount of current. This can indicate a short circuit in the power electronics and pump. You can monitor this with the over-current pulse accumulator, which will overflow if too many switching current spikes are detected from the power stage in a given line cycle. If an overflow doesn’t occur, the pulse accumulator will reset for the subsequent line cycle.

The fourth fault condition occurs when the temperature inside the cabinet is too high. A cheap way to do this in a closed cabinet is to monitor the internal IC temperature.