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Diverting surplus PV Power, by Robin Emley

9: Different Versions of the Software Sketch

All versions of the Mk2 PV Router sketch (apart from the phase-angle variant) will work with the original hardware. The difference between them is simply their efficiency. Mk2i offers substantially better performance than the original Mk2. It may therefore be a better choice for an application where additional workload is to be placed on the processor. Having said which, all versions can be relied on to heat up a tankful of water in similar times. Every version that has been posted to date is included in the list at https://openenergymonitor.org/emon/node/1757

Note that the phase-angle variant of the Mk2 sketch requires slightly different hardware. These differences are given in the associated post which accompanies that particular version.

A summary of the operation of the Mk2_PV_Router_mini.ino version now follows. The line numbers are as shown in the editor that forms part of the Arduino’s IDE.

Line Nos. Content
1 - 74 Global definitions
77 - 102 setup() which includes:
- initialisation of the Serial interface
- pin definitions for outputs
105 - 241 - loop(), which is executed for each per pair of V & I samples (~ 400 µS)
108 - update the # of samples, for the calculation of average power
111 - 113 - copy values from previous loop, to avoid them being overwritten
117 - 118 - get the next pair of voltage and current samples
121 - 122 - subtract the known DC offset (assumes a shared 2.5V reference)
125 - update the HPF for voltage (used with a LPF to find the DC offset)
128 - 132 - determine the polarity of the latest voltage sample
135 - 227 - if the polarity now is positive:
138 - 195 - if this is the first positive sample of a new mains cycle:
144 - 145 - update the LP filter with the net sum of ±deltas from last cycle
149 - 150 - calculate the energy content of the previous mains cycle
153 - 163 - a convenient place to display data, if required
165 - 187 - if the system has had time to settle since start-up:
169 - update the "energy bucket" with the latest contribution
170 - update a parallel bucket for LED use (this one has no limits)
174 - adjust the energy bucket's level by any desired safety margin
177 - 180 - apply upper and lower limits to the bucket's level
189 - set a flag to show that the trigger needs to be armed
192 - 194 - clear the per-cycle accumulators
198 - 226 - if the trigger needs to be armed:
201 - 225 - if the voltage is OK for arming the trigger (>20V typical)
208 - 217 - if bucket is at least half full, the trigger is to be 'on', else 'off'
220 - write this decision to the pin for the external trigger
223 - clear the flag (the trigger is armed only once per mains cycle)
235 - 236 - apply the phasecal algorithm to correct for phase-shift between V and I
237 - determine the instantaneous power (using P = V × I)
238 - add this latest contribution to the accumulated total for this mains cycle
240 - update the per-cycle accumulator for ±deltas
241 - end of loop(), and end of the main code
246 - 306 checkLedStatus(). This is an optional function which allows LED events at the
supply meter to be monitored. By displaying the value of energyInBucket_4led,
the operation of the measurement system can be compared directly with the
operation of the supply meter.

Help and Assistance

When building a Mk2 PV Router for the first time, the OpenEnergyMonitor community forum is a valuable resource. The OpenEnergyMonitor is an open-source project and most constructors are only too happy to provide assistance to anyone whose project has yet to get off the ground.