# Traditional Ramps with No Imbalance 未失衡的传统斜坡

DMCplus斜坡设定值（见DMCplus动作发生器）是基于斜坡变量当前值，操作员输入的斜坡变量设定点，以及斜坡率并根据下列简单公式计算的。

Figure 21: Traditional Ramp with No Imbalance, value between limits, RAMPRT=0

图21：未失衡传统斜坡，值位于限制之间，RAMPRT=0

Figure 22: Traditional Ramp with No Imbalance, value outside limits, RAMPRT=0

图22：未失衡传统斜坡，值位于限制之外，RAMPRT=0

RAMPRT= 0与0<RAMPRT<=1的关键区别是后者在限制间存在优选值。RAMPSP的值是由用户指定的，并且必须是操作限之间。如果斜坡当前值处于操作限之间，RAMPRT指定了当前值与用于DMCplus动作计算设定值的RAMPSP距离分数。

Figure 23: Traditional Ramp with No Imbalance, value between limits, RAMPRT=0.25

图23：未失衡传统斜坡，值位于限制之间，RAMPRT=0.25

Figure 24: Traditional Ramp with No Imbalance, value outside limits, RAMPRT=0.25

图24：未失衡传统斜坡，值超出限制，RAMPRT=0.25

Normally, it is advantageous to make use of the surge capacity within a system for "smoothing"process disturbances. DMCplus achieves this goal while most regulatory controllers do not.

For each ramp variable, there is a high limit, a low limit, a setpoint, and a tuning parameter called the ramp rate. The high and low limits correspond to the maximum and minimum surge limits that can be reached after a major disturbance.

The ramp setpoint and ramp rate (tunable parameter) enable the controller to move the ramp variable gradually to a position between the high and low limits, in anticipation of the next major disturbance. (The ramp setpoint must be set between the high and low limits failing which the DMCplus interface will reset to the nearest limit).

The DMCplus value of the ramp setpoint (seen by the DMCplus move generator) is calculated based on the current value of the ramp variable, the operator-entered ramp variable setpoint, and the ramp rate according to the following simple formula.

If current value is at or between operating limits, then:

Actual internal ramp setpoint =current value + ramp rate * (operator entered ramp setpoint - current value)

If current value is above upper operating limit, then:

Actual internal ramp setpoint= upper operating limit + ramp rate *( operator entered ramp setpoint - upper operating limit)

If current value is below lower operating limit, then:

Actual internal ramp setpoint= lower operating limit + ramp rate * (operator entered ramp setpoint - lower operating limit )

The value of the ramp rate must be set between 0 and 1. For a ramp rate of 1.0, the internal ramp setpointis always the operator value.For a ramp rate of0.0, the ramp setpoint drifts between the lower and upper limit. Thus, the ramp rate can be seen as a kind of forcing function that drives the ramp variable value back towards the operator-entered ramp setpoint. This feature allows the DMCplus controller to keep level within a reasonable range without being overly aggressive about enforcing its setpoint.

For the Traditional Ramp with No Imbalance and RAMPRT=0, the steady-state optimization finds a steady-state solution that balances the ramp (eliminates steady-state imbalance). The setpoint for the ramp in the DMCplus move calculation is determined from the current value of the ramp. If the current value is between the operating limits, the setpoint is the current value (see Figure 21).

If the current value is outside the operating limits, the setpoint takes on the value of the violated limit(see Figure 22). For this type of ramp, there is no preferred value between the limits; the value is allowed to drift between limits. If the two operating limits are pinched to the same value, the ramp is controlled to a fixed value setpoint. In the event that the steady-state optimization is unable to balance the ramp, then DMCplus control is aborted.

The traditional ramp also supports averaging level control, specified by giving RAMPRT a value greater than zero(0) but not greater than one(1). The steady-state optimization finds a steady-state solution that balances the ramp.

The key difference between RAMPRT=0 and 0<RAMPRT<=1 is that a preferred value exists between the limits.This value, RAMPSP,is user-specified, and must be between the operating limits. If the current value of the ramp is between the operating limits then RAMPRT specifies the fraction of the distance from the current value back toward RAMPSP to be used as the setpoint for the DMCplus move calculation.

For example, if the current value is 60.0, RAMPSP=40.0 and RAMPRT=0.25, then the setpoint is60.0+0.25*(40.0-60.0)=55.0 (see Figure 23) The smaller RAMPRT is set, the less effort the controller makes in trying to get to RAMPSP. RAMPRT=0 means that RAMPSP is ignored, and RAMPRT=1 is equivalent to pinching both operating limits to the single value RAMPSP.

If the current value is violating an operating limit, the setpoint for the DMCplus move calculation is set at the fraction (specified by RAMPRT) of the distance back from the violated limit toward RAMPSP.

For example, if Upper Oper.Limit=80.0, the current value is greater than 80.0, RAMPSP=40.0, and RAMPRT=0.25, the setpoint for the DMCplus move calculation is 80.0+0.25*(40.0-80.0)=70.0 (see Figure 24). Again, if the steady-state optimization is unable to balance the ramp, DMCplus control is aborted.

2015.10.3