Detailed explanation of PLC cascade PID control (temperature control of furnace and central air conditioning system)

About PID For other theoretical knowledge, please refer to other articles in the column , Here we mainly talk about cascade PID And the mathematical model of double tank, the differential equation of liquid level and its Bernoulli equation are derived , If cascade is used for liquid level control of double tank PID, Our outer ring PID The target value is the flow F1, stay F1 The position needs to add a flow sensor , Outer ring PID Output value Pout1 To inner ring PID Complete the liquid level h2 The control of .

single PID The loop control system can meet the requirements of production process and work stably in many occasions , But our process object system has a large capacity lag , The load changes greatly or other disturbances are violent , In this case, the single loop control system will not be able to achieve a good control effect , When the production process requirements are very high, it will be difficult to meet the requirements .

Cascade PID The essence of is that the existence of inner loop significantly reduces its phase lag , The dynamic quality of the outer loop can be appropriately improved , Therefore, the suppression ability of load side disturbance is also improved .

1、 Cascade PID

 2、 Double tank

 3、 Physical quantity related to water tank

 4、 Differential equations

5、 Differential equations