Control mode 4 is a control mode where the user can set two different set points to create a secure GAP, these references must be defined in the parameters RefkV and RefkV2. The only restriction when setting these values is that RefkV must be higher than RefkV2. 


The tolerance value will be applied to both set points in the same manner. In control mode 4, the UPFC will not perform control actions if the input voltage is within the GAP created with these set points. The voltages outside the GAP will be forced to stay near to the closest set point as shown in Figure 4.


In Figure 4, the lower set point (RefkV2) is 0.243, the higher set point (RefkV) is 0.2439 and the tolerance (Tol1) is 0.1%. Every voltage value within this GAP at the input of the UPFC will be the same at the output of the UPFC. On the other hand, if the voltage value at the input of the UPFC is higher than the higher set point, the output of the UPFC will be forced to stay within the limits of RefkV (RefkV+RefkV*Tol1 ≥ Vout ≥ RefkV-RefkV*Tol1). The same happens with RefkV2 when the input voltage is below this reference.



Figure 4. Voltage regulation in control mode 4, RefkV=243.9 and RefkV2=243


This control mode performs voltage regulation only (control mode 1). In Figure 5, the lower set point is set in RefkV2 = 0.236.


Figure 5. Voltage regulation in control mode 4, RefkV=243.9 and RefkV2=236