SMOCPro中的阀门饱和处理—dSPdV
SMOCPro dSPdV简介
SMOCPro通过调整传递到内核的“可实现的”操作变量设定点（SP）限制来处理阀门饱和问题。这个过程发生在预处理模块中。
在设定点控制模式（SPC）下MV的操作范围由设定点高低限(SPHi和SPLo)和输出高低限(OPHi和OPLo)所决定。因此，无论是SP或OP限被触碰到，MV操作范围都将受到限制。然而，鉴于SMOCPro直接操作MV设定点，只有SPHi和SPLo限可以在SPC模式下绝对强制执行。在这种情况下，OP值是PID闭环控制计算的结果，因此其不能保证留在（OPHi，OPLo）范围内，除非这些限制对应于终端控制元件的物理限制。
如果用户指定的OP限比物理限更严格（例如，OPHi 限是90％的阀位），并希望由SMOCPro严格执行此OP限，那么MV模式必须设置为直接数字控制（DDC），而不是SPC。
SMOCPro dSPdV说明
让我们通过一个例子来解释这个概念。考虑OP限是期望值而不是物理限的情况。此处应将MV设置为SPC模式，且由SMOCPro确定可实现的PV限。
在控制器每次执行时，算法计算当前OP值可达到的最大（CalcSPHi）和最小（CalcSPLo）PV。该过程包括以下三个步骤（见图1的图形解释）：
1.用户指定了两个增益，分别为dSPdVHi和dSPdVLo（dSP = delta SP，dV = 阀位‘OP’ 变化），它们分别代表了设定点和输出在OPHi和OPLo的预期增益。在这两个增益之间，如果实际OP处于OPLo和OPHi范围之间，单个增益dSPdV则基于此计算。如果阀位（OP）值小于或等于用户指定的OPLo限，增益被夹紧在dSPdVLo值。类似地，如果阀位（OP）大于或等于用户指定的OPHi限，增益被夹紧在dSPdVHi值。
2.计算“内部”MV设定点限IntCalcSPLo和IntCalcSPHi。此计算通过考虑两件事完成：1）当前OP值和OP限之间的距离; 2）步骤1计算出的当前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
