Steel sheet temperature control device and temperature control method

1. A steel sheet temperature control device, comprising:

a sheet temperature measurement unit that measures temperature of a steel sheet at an inlet side and an outlet side of a heating furnace including a plurality of heating zones disposed along a conveyance direction of the steel sheet;

a furnace temperature measurement unit that measures furnace temperature of each of the heating zones; and

a process computer configured to execute a process, the process including:

calculating an influence coefficient representing temperature change of the steel sheet at the outlet side of the heating furnace in response to temperature change of the steel sheet at the inlet side of the heating furnace, and an influence coefficient representing temperature change of the steel sheet at the outlet side of the heating furnace in response to change in the furnace temperature of each of the heating zones, using a heating model equation capable of calculating the temperature of the steel sheet in the heating furnace, by inputting a set value of the temperature of the steel sheet at the inlet side of the heating furnace, and set values of the furnace temperature of each of the heating zones and sheet passing speed;

setting a control model by inputting a furnace temperature change command value and outputting the furnace temperature of each of the heating zones and the temperature of the steel sheet at the outlet side of the heating furnace, by using the calculated influence coefficient, transfer time of the steel sheet until influence of furnace temperature change in each of the heating zones appears on the temperature of the steel sheet at the outlet side of the heating furnace, a time constant from when the furnace temperature change command value of each of the heating zones is output to when the furnace temperature is actually changed, and a variable representing unknown temperature disturbance to be applied to the temperature of the steel sheet at the outlet side of the heating furnace;

estimating values of a state variable and a temperature disturbance variable of the control model at the same time, by inputting a deviation between an actual value of the temperature of the steel sheet at the inlet side of the heating furnace measured by the sheet temperature measurement unit and a set value, a deviation between an actual value of the temperature of the steel sheet at the outlet side of the heating furnace measured by the sheet temperature measurement unit and a set value, and a deviation between an actual value of the furnace temperature of each of the heating zones measured by the furnace temperature measurement unit and an initial set value;

calculating a furnace temperature change amount of each of the heating zones under a constraint condition such that square sum of a deviation between a target value and the actual value of the temperature of the steel sheet at the outlet side of the heating furnace becomes minimum, by using the estimated values of the state variable and the temperature disturbance variable of the control model; and

controlling a fuel flow rate used in each of the heating zones to achieve the calculated furnace temperature change amount.

2. The steel sheet temperature control device according to claim 1 , wherein calculating the furnace temperature change amount includes at least one of constraint condition relating to upper and lower limit values of the furnace temperature, constraint condition relating to the furnace temperature change amount per unit time, constraint condition relating to upper and lower limit values of the fuel flow rate, and condition relating to the fuel flow rate change amount per unit time, as the constraint condition.

3. The steel sheet temperature control device according to claim 1 , wherein the calculating of the influence coefficient, the setting, the estimating, and the calculating of the furnace temperature change amount are performed for each set value of a plurality of sheet passing speeds assumable during an actual operation, and the controlling includes controlling a fuel flow rate used in each of the heating zones to achieve the furnace temperature change amount calculated from the set value of the sheet passing speed close to actual sheet passing speed.

4. A steel sheet temperature control method, comprising:

smeasuring temperature of a steel sheet at an inlet side and an outlet side of a heating furnace including a plurality of heating zones disposed along a conveyance direction of the steel sheet;

measuring furnace temperature of each of the heating zones;

calculating a first influence coefficient representing temperature change of the steel sheet at the outlet side of the heating furnace in response to temperature change of the steel sheet at the inlet side of the heating furnace, and a second influence coefficient representing temperature change of the steel sheet at the outlet side of the heating furnace in response to change in the furnace temperature of each of the heating zones, using a heating model equation capable of calculating the temperature of the steel sheet in the heating furnace, by inputting a set value of the temperature of the steel sheet at the inlet side of the heating furnace, and set values of the furnace temperature of each of the heating zones and sheet passing speed;

setting a control model by inputting a furnace temperature change command value and outputting the furnace temperature of each of the heating zones and the temperature of the steel sheet at the outlet side of the heating furnace, by using the first influence coefficient and the second influence coefficient, transfer time of the steel sheet until influence of furnace temperature change in each of the heating zones appears on the temperature of the steel sheet at the outlet side of the heating furnace, a time constant from when the furnace temperature change command value of each of the heating zones is output to when the furnace temperature is actually changed, and a variable representing unknown temperature disturbance to be applied to the temperature of the steel sheet at the outlet side of the heating furnace;

estimating values of a state variable and a temperature disturbance variable of the control model at the same time, by inputting a deviation between an actual value of the measured temperature of the steel sheet at the inlet side of the heating furnace and a set value, a deviation between an actual value of the measured temperature of the steel sheet at the outlet side of the heating furnace and a set value, and a deviation between an actual value of the measured furnace temperature of each of the heating zones and an initial set value;

calculating a furnace temperature change amount of each of the heating zones under a constraint condition such that square sum of a deviation between a target value and the actual value of the temperature of the steel sheet at the outlet side of the heating furnace becomes minimum, by using the estimated values of the state variable and the temperature disturbance variable of the control model; and

controlling a fuel flow rate used in each of the heating zones to achieve the calculated furnace temperature change amount.

5. The steel sheet temperature control device according to claim 2 , wherein calculating of the influence coefficient, the setting, the estimating, and the calculating of the furnace temperature change amount are performed for each set value of a plurality of sheet passing speeds assumable during an actual operation, and the controlling includes controlling a fuel flow rate used in each of the heating zones to achieve the furnace temperature change amount calculated from the set value of the sheet passing speed close to actual sheet passing speed.