Patent ID: 6422263
Filing Date: 2002-07-23
Classification: G05D,Y10T

Abstract:
In a liquid flow system comprising a plurality of reservoirs connected in series by pipelines or open channels including at least one first reservoir (V1) and a last reservoir (VOUT) downstream from said at least one first reservoir, said at least one first reservoir including a level sensor, at least one inflow and at least one outflow, each said inflow and outflow including a flow manipulation device and a flow measuring device, said last reservoir (VOUT) including a level sensor and at least one outflow having a flow measuring device, the improvement comprising a nested and cascaded variable bias feedforward and feedback flow and level control system for maintaining liquid levels in said reservoirs while substantially eliminating flow and level oscillations, said control system comprising the following:(a) a parenthetical control module comprising: (i) a proportional only level controller for maintaining a desired level of liquid in the last reservoir (VOUT), said proportional only level controller in electrical communication with the level sensor of said last reservoir (Vout), and (ii) a PID flow controller adapted to control the flow manipulation device of the at least one first reservoir inflow (FIN), â€ƒwherein said proportional only level controller is adapted to respond to the level sensor of said last reservoir and a calculated bias value resulting from the total outflow from the last reservoir to produce an output signal that is cascaded to the PID flow controller to become a set point thereof; and (b) a nested control module comprising: (i) a proportional only level controller for maintaining a desired liquid in the at least one first reservoir (V1), said proportional only level controller in electrical communication with the level sensor of said at least one first reservoir (V1), and (ii) a PID flow controller adapted to control the flow manipulation device of the at least one first reservoir outflow (F1), â€ƒwherein said nested control module proportional only level controller is adapted to respond to the level sensor of said at least one first reservoir (V1) and a calculated bias value resulting from the total inflow to said at least one first reservoir (V1) to produce an output signal that is cascaded to the nested control module PID flow controller to become a set point thereof.