Fluid heating system with combustion trim learning
A fluid heating system including a burner unit is operated based on feedback control loops. The fluid heating system comprises a burner unit configured to heat a fluid, a sensor configured to sense a characteristic of the appliance, and a controller coupled to the burner unit and the sensor. The controller includes an electronic processor and a memory. The controller is configured to receive a first signal corresponding to the characteristic from the sensor, determine, based on the first signal, a first feedback loop control, control combustion of the burner unit based on the first feedback loop control, determine, based on the first feedback loop control, a second feedback loop control, and control combustion of the burner unit based on the second feedback loop control.
1 . A method for controlling a fluid heating system comprising:
receiving, at a first control loop, a sensor value indicative of a characteristic of the fluid heating system during a first operation;
determining, at the first control loop, a first trim value based on the sensor value;
determining, at a second control loop, a second trim value based on (i) a deviation of the first trim value from a reference value and (ii) an operational parameter of the fluid heating system; and
controlling a second operation of the fluid heating system based on the second trim value.
2 . The method of claim 1 , wherein the first control loop determines the first trim value to drive the sensor value towards a reference sensor value.
3 . The method of claim 2 , wherein the second control loop determines the second trim value to drive the first trim value towards a reference trim value.
4 . The method of claim 1 , wherein the second control loop determines the second trim value by reverse-interpolating the operational parameter into a trim table.
5 . The method of claim 4 , wherein the trim table comprises one or more trim points and the operational parameter is used to interpolate between the one or more trim points.
6 . The method of claim 1 , wherein the second control loop comprises retrieving one or more trim points from a trim table.
7 . The method of claim 6 , wherein the second control loop comprises adjusting the one or more trim points based on the deviation.
8 . The method of claim 7 , wherein the second control loop comprises computing the second trim value based on the adjusted one or more trim points.
9 . The method of claim 6 , wherein the one or more trim points correspond to at least one of a modulation percentage, a firing rate, an air damper angle, and a blower speed.
10 . The method of claim 1 , wherein the first control loop comprises:
determining whether the sensor value is within a valid range;
in response to determining that the first sensor value is within the valid range, adding the sensor value to a first buffer.
11 . The method of claim 1 , wherein controlling the second operation of the fluid heating system based on the second trim value comprises adjusting a combustion property of the fluid heating system based on the second trim value.
12 . The method of claim 11 , wherein the combustion property is at least one of an air-to-fuel ratio, a nitrogen oxides concentration, a carbon monoxide concentration, a combustion oscillation, a combustion noise, and a flame characteristic.
13 . The method of claim 1 , wherein the sensor value is at least one of an oxygen concentration and a nitrogen oxides concentration.
14 . The method of claim 1 , wherein the operational parameter is at least one of a modulation percentage and a firing rate.
15 . The method of claim 1 , wherein the first trim value is at least one of (i) a ratio of a reference barometric pressure and an actual air pressure and (ii) a ratio of an actual premix temperature and a reference premix temperature.
16 . A method for controlling a fluid heating system, comprising:
receiving, at a first control loop, a sensor value indicative of a characteristic of the fluid heating system during a first operation;
determining, at the first control loop, a first trim value based on the sensor value;
determining, at a second control loop, a second trim value based on the first trim value and an operational parameter of the fluid heating system; and
controlling a second operation of the fluid heating system based on the second trim value;
wherein the first control loop comprises:
adding the first trim value to a first buffer,
determining whether the sensor value is within a defined deviation of an average value of the first buffer,
in response to determining that the sensor value is within the defined deviation of the average value of the first buffer, determine an error between the sensor value and a reference sensor value, and
adding the error to a second buffer.
17 . The method of claim 16 , wherein the first trim value is determined based on an average value of the second buffer.
18 . A fluid heating system comprising:
a controller configured to receive a sensor value from a sensor, the sensor value indicative of a characteristic of the fluid heating system during a first operation;
wherein the controller is configured to:
determine, at a first control loop, a first trim value based on the sensor value;
determine, at a second control loop, a second trim value based on (i) a deviation of the first trim value from a reference trim value and (ii) an operational parameter of the fluid heating system; and
control a second operation of the fluid heating system based on the second trim value.
19 . The fluid heating system of claim 18 , wherein the controller is configured to determine the first trim value to drive the sensor value toward a reference sensor value.
20 . The fluid heating system of claim 19 , wherein the controller is configured to determine the second trim value to drive the first trim value toward the reference trim value.
21 . The fluid heating system of claim 18 , wherein the controller is configured to determine the second trim value by reverse-interpolating the operational parameter into a trim table.
22 . The fluid heating system of claim 18 , wherein the controller is configured to, at the second control loop, retrieve one or more trim points from a trim table and adjust the one or more trim points based on the deviation.
23 . The fluid heating system of claim 22 , wherein the one or more trim points correspond to at least one of a modulation percentage, a firing rate, an air damper angle, and a blower speed.
24 . The fluid heating system of claim 18 , wherein the controller is configured to control the second operation by adjusting a combustion property of the fluid heating system based on the second trim value, wherein the combustion property is at least one of an air-to-fuel ratio, a nitrogen oxides concentration, a carbon monoxide concentration, a combustion oscillation, a combustion noise, and a flame characteristic.
25 . The fluid heating system of claim 18 , wherein the sensor value is at least one of an oxygen concentration and a nitrogen oxides concentration.
26 . The fluid heating system of claim 18 , wherein the operational parameter is at least one of a modulation percentage and a firing rate.
27 . The fluid heating system of claim 18 , wherein the first trim value is at least one of (i) a ratio of a reference barometric pressure and an actual air pressure and (ii) a ratio of an actual premix temperature and a reference premix temperature.