IEEE (2005) ST7B Model<br /></p><p><br /></p><p>The model ST7B is representative of static potential-source excitation systems. In this system,<br /></p><p>the AVR consists of a PI voltage regulator. A phase lead-lag filter in series allows introduction of a<br /></p><p>derivative function, typically used with brushless excitation systems. In that case, the regulator is of the PID type. In addition, the terminal voltage channel includes a phase lead-lag filter. The AVR includes the appropriate inputs on its reference for overexcitation limiter (OEL1), underexcitation limiter (UEL), stator current limiter (SCL), and current compensator (DROOP). All these limitations, when they work at voltage reference level, keep the PSS (VS signal from Type PSS1A, PSS2A, or PSS2B) in<br /></p><p>operation. However, the UEL limitation can also be transferred to the high value (HV) gate acting on the<br /></p><p>output signal. In addition, the output signal passes through a low value (LV) gate for a ceiling overexcitation<br /></p><p>limiter (OEL2).<br /></p>