當(dāng)穩(wěn)態(tài)優(yōu)化返回一個非零的失衡時，DMCplus動作計算給出一個與失衡相同的設(shè)定值，設(shè)定值由延伸到未來的且斜率等于穩(wěn)態(tài)失衡計算的線指定（如下圖25所示）。如果當(dāng)前值在操作限之間，則線起始于當(dāng)前值;如果當(dāng)前值超出操作限，線起始于違反操作限處。這保證了穩(wěn)態(tài)優(yōu)化和DMCplus動作計算之間的數(shù)學(xué)一致性。
圖25：失衡斜坡的DMCplus設(shè)定值
對于一失衡傳統(tǒng)斜坡，穩(wěn)態(tài)優(yōu)化總是試圖平衡斜坡。如果結(jié)果可以被平衡，上一節(jié)的未失衡傳統(tǒng)斜坡已經(jīng)描述了基于RAMPSP和RAMPRT的斜坡設(shè)定點計算。
然而如果穩(wěn)態(tài)優(yōu)化不能平衡斜坡并且用戶設(shè)定MXMIMB>0（指定斜坡允許失衡的最大控制周期數(shù)目），則對失衡量進(jìn)行檢查以確保它不是太大。
如果失衡不是太大，控制器被允許保持'MXNIMB'個連續(xù)斜坡失衡控制周期。如果被發(fā)現(xiàn)失衡太大，或者'MXNIMB+1'個連續(xù)失衡周期后，控制器將關(guān)閉。
當(dāng)穩(wěn)態(tài)優(yōu)化允許計算一個失衡方案時，斜坡將趨于驅(qū)動向操作限兩端。由于斜坡將更可能處于操作限附近，通過實施安全區(qū)確保斜坡值不被驅(qū)動到太接近儀表限制。
安全區(qū)等于操作限制之差的10％。這個區(qū)域作為操作限制的有效緩沖被施加在操作區(qū)域的兩端。詳情參見圖26.
若要設(shè)置允許的失衡限制，可通過用戶輸入的參數(shù)RHORIZ定義時域，它乘以穩(wěn)態(tài)時間即得到域。
根據(jù)失衡值與安全區(qū)域的相對關(guān)系存在三種不同的方式定義失衡限制。
如果失衡斜坡當(dāng)前值處于安全區(qū)域之間，允許失衡高線以當(dāng)前值為起點，上安全區(qū)域與時域交點為終點，兩點間的連線組成。這條線的斜率為高允許失衡。
如圖26所示，允許失衡低線以類似的方式構(gòu)成。穩(wěn)態(tài)計算失衡（DMCplus設(shè)定點線斜率）必須在允許失衡高低線之間（允許失衡高低線斜率）。當(dāng)斜坡當(dāng)前值接近一安全區(qū)域時，相應(yīng)的允許失衡值幅度減小，直到當(dāng)前值到達(dá)安全區(qū)域（允許失衡變?yōu)?）。
DMCplus動作計算設(shè)定點是一條起始于當(dāng)前值，如前所述斜率等于穩(wěn)態(tài)計算失衡的延伸向未來的線，詳見圖27。
圖26：操作限制間的失衡斜坡
圖27：操作限制間的DMCplus失衡斜坡設(shè)定點
附原文：
When the steady-state optimization returns a non-zero imbalance, the DMCplus move calculation is given a setpoint consistent with the imbalance, by specifying the setpoint as a line extending into the future with slope equal to the steady-state calculated imbalance (see Figure 25). If the current value is between the operating limits, the line starts at the current value; if the value is outside an operating limit, the line starts at the violated operating limit. This ensures mathematical consistency between the steady-state optimization and DMCplus move calculation.
For a Traditional Ramp with Imbalance, the steady-state optimization attempts to balance the ramp. If the event can be balanced, the previous section on Traditional Ramps with No Imbalance describes how the ramp setpoint is calculated, based on RAMPSP and RAMPRT.
If, however, the steady-state optimization cannot balance the ramp and the user has set MXMIMB>0(specifying the maximum number of control cycles the ramp is allowed to be out of balance), then the amount of imbalance is checked to be sure it is not too large.
If the imbalance is not too large, the controller is allowed to remain on for 'MXNIMB' consecutive control cycles with the ramp out of balance. If the imbalance is found to be too large,or after 'MXNIMB+1' consecutive cycles out of balance, the controller is turned off.
Whenever the steady-state optimization is allowed to calculate an imbalanced solution, the ramp will tend to be driven toward one side of the operating limits or the other. Since the ramp will be more likely to be near an operating limit, safety zones are implemented to ensure that the value of the ramp is not driven too near the instrument limits.
The Safety Zone is equal to 10% of the difference between the operating limits. This zone is applied at both ends of the operating region and effectively buffer the operating limits. See Figure 26.
To set the allowed imbalance limits, a time Horizon is specified by the user-entered parameter RHORIZ, which is multiplied by the steady-state time to give this Horizon.
There are three different ways in which the imbalance limits are determined depending on where the current value of the imbalanced ramp is relative to the Safety Zones.
If the current value of an imbalanced ramp is between the Safety Zones, the upper allowed imbalance line is constructed by drawing a line from the current value to intersect with the upper Safety Zone at the end of the Horizon. The slope of this line is the upper allowed imbalance.
A lower allowed imbalance line is constructed in a similar manner as shown in Figure 26.The steady-state calculated imbalance (slope of the DMCplus setpoint line) must be between the upper and lower allowed imbalance limits (slopes of the upper and lower allowed imbalance lines). As the current value of the ramp approaches one of the Safety Zones, the corresponding allowed imbalance decreases in magnitude until the current value reaches the safety zone, where that allowed imbalance becomes zero.
The DMCplus Move Calculation setpoint is a line starting at the current value, and extending into the future with a slope equal to the steady-state calculated imbalance as described previously. See Figure 27.
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