SMOCPro中的閥門飽和處理—dSPdV
SMOCPro dSPdV簡介
SMOCPro通過調整傳遞到內核的“可實現的”操作變量設定點（SP）限制來處理閥門飽和問題。這個過程發生在預處理模塊中。
在設定點控制模式（SPC）下MV的操作范圍由設定點高低限(SPHi和SPLo)和輸出高低限(OPHi和OPLo)所決定。因此，無論是SP或OP限被觸碰到，MV操作范圍都將受到限制。然而，鑒于SMOCPro直接操作MV設定點，只有SPHi和SPLo限可以在SPC模式下絕對強制執行。在這種情況下，OP值是PID閉環控制計算的結果，因此其不能保證留在（OPHi，OPLo）范圍內，除非這些限制對應于終端控制元件的物理限制。
如果用戶指定的OP限比物理限更嚴格（例如，OPHi 限是90％的閥位），并希望由SMOCPro嚴格執行此OP限，那么MV模式必須設置為直接數字控制（DDC），而不是SPC。
SMOCPro dSPdV說明
讓我們通過一個例子來解釋這個概念。考慮OP限是期望值而不是物理限的情況。此處應將MV設置為SPC模式，且由SMOCPro確定可實現的PV限。
在控制器每次執行時，算法計算當前OP值可達到的最大（CalcSPHi）和最小（CalcSPLo）PV。該過程包括以下三個步驟（見圖1的圖形解釋）：
1.用戶指定了兩個增益，分別為dSPdVHi和dSPdVLo（dSP = delta SP，dV = 閥位‘OP’ 變化），它們分別代表了設定點和輸出在OPHi和OPLo的預期增益。在這兩個增益之間，如果實際OP處于OPLo和OPHi范圍之間，單個增益dSPdV則基于此計算。如果閥位（OP）值小于或等于用戶指定的OPLo限，增益被夾緊在dSPdVLo值。類似地，如果閥位（OP）大于或等于用戶指定的OPHi限，增益被夾緊在dSPdVHi值。
2.計算“內部”MV設定點限IntCalcSPLo和IntCalcSPHi。此計算通過考慮兩件事完成：1）當前OP值和OP限之間的距離; 2）步驟1計算出的當前dSPdV值。
**Valve Saturation Handling in SMOCPro—dSPdV **
SMOCPro dSPdV Introduction
SMOCPro tackles the valve saturation problem by adjusting the “achievable” manipulated variable setpoint (SP) limits passed to the kernel. This process takes place in the pre-processing module.
The operating range of an MV under set point control mode (SPC) is defined by its setpoint high and low limits (SPHi and SPLo) and its output high and low limits (OPHi and OPLo). Therefore, the MV operating range will be limited by whichever of these is hit first, either an SP or OP limit.
However, only SPHi and SPLo limits can be absolutely enforced under SPC mode since SMOCPro manipulates the MV set point directly. In this case, the OP value is a result of the PID closed loop control scheme, hence it cannot be guaranteed to remain within the (OPHi,OPLo) range, unless these limits correspond to the physical limits of the final control element.
If a user specifies OP limits that are more restrictive than the physical limits (e.g. an OPHi limit of 90% for a valve) and would like this OP limit to be strictly enforced by SMOCPro, then the MV mode must be set to direct digital control (DDC) instead of SPC.
SMOCPro dSPdV Explanation
Let us present an example to explain the concept. Consider the case where the OP limits are desired values and not physical limits. Here it is advised to set the MV on SPC mode and let SMOCPro determine the achievable PV limits.
At every controller execution, the algorithm computes the maximum (CalcSPHi) and minimum (CalcSPLo) achievable PVs for the current OP value. The process consists of the following three steps (see Figure 1 below for a graphical explanation):
- The user specifies two gains, called dSPdVHi and dSPdVLo (dSP = change in SP, dV = change in valve position ‘OP’), which represent the expected gain relationship between the setpoint and output at OPHi and OPLo respectively. From these two gains, a single gain dSPdV is calculated based upon where the actual OP is within the range OPLo and OPHi. If the valve position (OP) value is less than or equal to the user-specified OPLo limit, then the gain is clamped to the dSPdVLo value. Similarly, if the valve position (OP) is greater than or equal to the user-specified OPHi limit, then the gain is clamped to the dSPdVHi value.
- Calculate “internal” MV set point limits IntCalcSPLo and IntCalcSPHi. This calculation is done by taking into account two things: 1) the distance between the current OP value and the OP limits; and, 2) the current dSPdV value calculated in step 1.
2016.7.2
