This chapter contains the following examples:
Application example of the Feed Forward function
With a heat exchanger, the temperature PV2 should be regulated at the output of the secondary circulation. A PID controller controls the inflow valve for warm air depending on PV2 and the setpoint SP. The cold water temperature is regarded as a measurable disturbance variable in this control process.
The feed forward function means a reaction can occur as soon as the cold water temperature changes without waiting for PV2 to decrease.
Presentation of the servo loop:
The following hypotheses are accepted:
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The condenser output temperature (cold water temperature) varies between 5 °C and 25 °C, with a mean value of 15 °C.
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A DT temperature change has a full effect on the output temperature of the heat exchanger.
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To compensate for a temperature increase (or decrease) by 5 C at the output of the heat exchanger, the steam control valve must be closed (or opened) by 10 %.
The feed forward input parameters should be adjusted so that the cold water temperature has the following effect on the steam control valve:
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Temperature range
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Effects
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15 °C
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no effect
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10% per 5 °C between 5 and 25 °C
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Adjustments to be preset
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Element
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Value
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ff_sup
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25 °C
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ff_inf
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5 °C
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otff_sup
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10 %
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otff_inf
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- 10 %
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Example of the cascaded arrangement of two controllers
A representation of the function map, part 1, follows:
A representation of the function map, part 2, follows:
Example of cascade-like control
A representation of the function map follows:
