Solar Drive Overcurrent Limiting Setup
Requirement:
In certain scenarios, when pumping water (due to pressure changes in the system), it could cause motors to draw high currents when running at full speed until the pressure stabilises as expected. This typically happens in areas where pivot irrigation systems are located on steep up and downhill slopes, and also happens in scenarios where irrigation systems are being adjusted (changing or opening additional irrigation sections causing sudden drops in pressure etc.). Running at these high currents is obviously not desired and could damage the motors. Normal drive overcurrent protection features will assist in stopping the motor when the current is too high (for too long), but this will stop the motor and the drive will show an error. Ideally in these scenarios one would rather prefer the drive to slow the motor down (reduce the running frequency to a speed where the current returns to an acceptable value) while pressure builds up and then speeds up again.
Solution/s:
- Solar Drives do not offer the same current limiting features as VSDs (see FAQ entry HERE), but as a workaround for Solar Drives, the motor running current (as measured by the Solar Drive) can be used as an Analog Input, with this input used as feedback to compare with a Target Value (Motor Rated Amps) and then adjusting the motor speed if the Amps are higher/lower than the target Amps (motor rated current). This thus works similarly to a Constant Water Pressure Setup, but instead of attempting to maintain a constant water pressure (using a PID as feedback), the Solar Drive will attempt to maintain a constant motor running current.
- For scenarios where a PID is used for constant water pressure setup this solution can however not be implemented since the PID feature is then already in use, but in such a scenario one could consider setting the PID Initial Value parameter FA-21 (set target Hz as % of the upper limit frequency) and the PID Initial Value Holding Time parameter FA-22 to limit the frequency for a period of time before speeding up (to give the pipe time to fill up and pressure to rise before speeding up). This typically only helps for scenarios where the high current issue occurs during initial start-up (not for scenarios where the current rises during full speed operation such as when changing or opening additional irrigation sections causing sudden drops in pressure or pivot systems operating on steep up and downhill slopes).
- For scenarios where the issue only occurs during initial start-up, one could also consider using the Simple PLC feature to control the start-up procedure. Please see the FAQ page regarding this for Solar Drives HERE.
Current Limiting Explained:
Wiring:
- Connect AO1 to AI1
Parameters:
- F0-03 = 8 (Frequency Source = PID Control)
- F1-03 = Motor Rated Current
- F5-07 = 2 (to set AO1 output as the motor current x 2)
- FA-01 = 50% (to set the target current as a % of the feedback current F5-07 above which is double the running current, thus the target should be 50%)
- FA-02 = 0 (PID feedback Source = AI1)
- FA-04 = 1000 (PID range)
Explanation:
When the output current exceeds the value set in F1-03 (Motor Rated Current), the output frequency will start to drop until the output current drops to the target current (motor rated current) – if the running current is lower than the target current (motor rated current), the frequency will start to rise until it reaches the target current (motor rated current).
