This model is based on the IEEE std 421.5 type PSS4B multi-band power system stabilizer model.

Model Overview

The PSS4B structure is based on separate bands targeting the low-, intermediate-, and high-frequency modes of oscillations. Each of the three bands is made of a differential band pass filter, a gain, and a limiter as shown below, and the outputs of the three bands are summed and passed through a final limiter producing the stabilizer output VST.

Input/Output

The model’s inputs and outputs are described in the following table:

I/O Name	Type (unit)	Description
dw	Input (pu)	Speed deviation
VST	Output (pu)	Stabilizer output

Parameters

Expanding the PSS4B diagram displays the block diagram shown below.

PSS4B has two modes: Detailed mode – which considers all the lead-lag blocks given in the Figure 1 with detailed time constant and gain inputs specified by the user; simplified mode – which considers only the first lead-lag block of the complete structure as shown in dotted part of Figure 1. Figure 2 shows the block diagram for simplified mode only. The value of R (=T2/T1) is taken as 1.2 (2).

Figure 1. PSS4B Complete Block Diagram

Figure 2. PSS4B Simplified mode diagram

Name	Unit	Description
KL1, KL2, KL	pu	Gains of the positive and negative branches of the differential filter in the low-frequency band and the overall gain K_L of the low-frequency band,
TL1 to TL12, KL11, KL17	s	Low frequency time constants of positive and negative lead-lag blocks and associated gains
KI1, KI2, KI	pu	Positive and negative branches gains of the differential filter of intermediate frequency band and the overall gain KI of intermediate band
TI1 to TI12, KI11, KI17	s	Intermediate frequency time constants of positive and negative lead-lag blocks and associated gains
KH1, KH2, KH	pu	Positive and negative branches gains of the differential filter of the high frequency band and the overall gain KH
TH1 to TH12, KH11, KH17	s	High frequency time constants of positive and negative lead-lag blocks and associated gains
FH, FI, FL	Hz	High, Intermediate, Low frequency bands. (applicable only for simplified model).
Detailed		1: Detailed model; 0- Simplified model
LIM_VH, LIM_VI, LIM_VL, LIM_VS	pu	Limits on output of high frequency, intermediate frequency, low frequency, and stabilizer output

Reference

"IEEE Recommended Practice for Excitation System Models for Power System Stability Studies," in IEEE Std 421.5-2005"
Grondin, R., I. Kamwa, L. Soulieres, J. Potvin, and R. Champagne, “An approach to PSS design for transient stability improvement through supplementary damping of the common low frequency,” IEEE Transactions on Power Systems, 8(3), August 1993, pp. 954-963.

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