Control algorithms

Illustration of offset in simple algorithm

Sophisticated software installed on i2O's server is used to automatically generate and update the control algorithms on a daily basis.

When the system is first installed, P2 is set to a safe fixed level (similar to the level it would have been set to if the PRV outlet pressure had been fixed). At the end of the first 24 hour period, flow and pressure data from the controller and pressure data from the P3 sensor are sent to the server which then calculates the first control algorithm. At the next communication between controller and server, (usually after a further 24 hours) the control algorithm is uploaded to the controller. The controller then begins to use the control algorithm to set P2.

This first control algorithm is based on one day of data, thus P2 cannot be determined with high confidence. The algorithm therefore uses a large offset (margin of security) when setting P2 so that P2 is only varied within a very safe band. As the server collects more data it can more precisely update and improve the control algorithm while reducing the offset. P3 begins to track P3ref more closely, lowering the average pressure in the network and steadily increasing the leakage saving. The algorithm may continue to improve even after a period of several years as longer term factors, such as seasonality, take effect.

The offset may be different for different flow rates, for example higher at higher flow rates.  The offset is usually calculated so that the probability that P3 is above P3ref is 99.5% for any one 15 minute logged period. This probability can be varied depending on the trade off between leakage reduction and risk of a P3 value below P3ref. If there are changes in the DMA, such as new houses or a factory closure, the control algorithm automatically adjusts to the new demand pattern. A sudden change to the data caused by, for example, a large burst or boundary valve being opened would trigger an alarm and would not lead to a change in the control algorithm.