Power System Stabilizer (PSS2B)

IEEE 421.5 Type PSS2B dual-input power system stabilizer (the integral-of-accelerating-power stabilizer). The speed deviation (from the machine's speed output) and the electrical power Pe each pass two washouts and a transducer lag; the integrated power KS2/(1+sT7) is added to the speed signal, passed through a ramp-tracking filter [(1+sT8)/(1+sT9)^M]^N and subtracted again, which synthesizes an accelerating-power signal that does not respond to mechanical-power ramps. Gain KS1, three lead-lags and the [VSTMIN, VSTMAX] limit give VS for the exciter's VS input. The washouts keep VS = 0 in steady state. Wire speed and Pe from the synchronous machine. Pairs with the machine for load-flow initialization. Also known as PSS2A; equivalent to PSS2C with the fourth lead-lag and the output logic unused.

Category: Control / Excitation

Overview

The Type PSS2B power system stabilizer (IEEE Std 421.5) is the dual-input "integral of accelerating power" stabilizer, the most widely applied PSS structure. Like any stabilizer it adds damping torque to the electromechanical (0.1–2 Hz) rotor swings by modulating the voltage-regulator reference through VS.

A speed-only stabilizer (PSS1A) also reacts to genuine mechanical-power changes — a turbine ramp shows up as a speed deviation and the PSS fights it, swinging the terminal voltage. PSS2B instead synthesizes the accelerating power from speed and electrical power, then filters out the mechanical-power component with a ramp-tracking filter. The result responds to rotor swings but not to turbine ramps.

The 2016 edition of the standard supersedes PSS2B with PSS2C; PSS2B data is PSS2C data with the fourth lead-lag and the output logic unused, which is the structure implemented here.

Block diagram

IEEE 421.5 Type PSS2B block diagram: a speed channel and an electrical-power channel each pass washouts and a transducer lag; the power channel's integral is added before a ramp-tracking filter and subtracted after it; gain KS1, three lead-lags and an output limit give VS.

Block by block:

Speed channel. The speed deviation $Δ ω$ (speed minus 1 pu), limited to $[V_{S I 1 m i n}, V_{S I 1 m a x}]$ , passes two washouts $s T_{W 1} / (1 + s T_{W 1})$ , $s T_{W 2} / (1 + s T_{W 2})$ and a transducer lag $1 / (1 + s T_{6})$ .
Power channel. The electrical power, limited to $[V_{S I 2 m i n}, V_{S I 2 m a x}]$ , passes the washouts $s T_{W 3} / (1 + s T_{W 3})$ and $s T_{W 4} / (1 + s T_{W 4})$ (bypassed when $T_{W 4} = 0$ ), then $K_{S 2} / (1 + s T_{7})$ . With $K_{S 2} = T_{7} / (2 H)$ this is the integral of electrical power expressed as a speed change.
Accelerating power. The sum of the speed signal and $K_{S 3}$ times the power signal is an estimate of the integral of mechanical power. The ramp-tracking filter ${[(1 + s T_{8}) / (1 + s T_{9})^{M}]}^{N}$ removes torsional and noise content from it while tracking a ramp without steady error; subtracting the power signal again leaves the integral of accelerating power. Common choices are $M = 5, N = 1$ and $M = 2, N = 4$ ; $N = 0$ bypasses the filter.
Compensation and output. The gain $K_{S 1}$ and three lead-lags $(1 + s T_{1}) / (1 + s T_{2})$ , $(1 + s T_{3}) / (1 + s T_{4})$ , $(1 + s T_{10}) / (1 + s T_{11})$ provide the phase lead, and the output is limited to $[V_{S T m i n}, V_{S T m a x}]$ . Set a stage's lead and lag equal to bypass it.

Every washout bypasses itself when its time constant is 0, as the standard requires.

Initialization

All washouts remove the steady component, so VS = 0 at any steady operating point. The power-channel washout needs the machine's electrical power at $t = 0$ to start there instead of stepping from zero; the load-flow auto-initialization fills Pe(0) in from the machine that feeds the stabilizer. The first simulation step uses 1.0 pu speed and Pe(0) in place of the inputs.

The machine's electrical outputs carry a short transient right after $t = 0$ while its stator currents build up. The stabilizer responds to that transient like any other power swing; it washes out within a few seconds.

Wiring

speed (ω) ← the synchronous machine's speed output (pu).
Pe ← the synchronous machine's Pe output (pu on the machine base).
VS → the exciter's VS input (enable PSS input on the exciter's Aux Inputs tab).

Enable the monitors on the Monitoring tab to record VS and the synthesized accelerating-power signal.

Tuning notes

Pick $T_{W 1} = T_{W 2} = T_{W 3} = T_{7}$ in the 2–10 s range and $K_{S 2} = T_{7} / (2 H)$ with the machine's inertia constant $H$ .
Tune the lead-lags for the phase lag of the exciter and field at the local-mode frequency, then raise $K_{S 1}$ until the mode is well damped and back off for margin.
Keep the output band small (a few percent up, less down) so the stabilizer cannot dominate the regulator.

Ports

Port	Kind	Signal
`speed`	Control input	Real
`Pe`	Control input	Real
`VS`	Control output	Real

Parameters

Inputs

Parameter	Type	Default	Units	Description	ID
VSI1MAX	Number	`2`	—	Upper limit on the speed-deviation input VSI1 (pu).	`VSI1MAX`
VSI1MIN	Number	`-2`	—	Lower limit on the speed-deviation input VSI1 (pu).	`VSI1MIN`
TW1	Number	`10`	s (also ms)	Washout time constant of sTW1/(1+sTW1). 0 bypasses the washout.	`TW1`
TW2	Number	`10`	s (also ms)	Washout time constant of sTW2/(1+sTW2). 0 bypasses the washout.	`TW2`
T6	Number	`0`	s (also ms)	Transducer time constant 1/(1+sT6) of the speed channel. 0 bypasses it.	`T6`
VSI2MAX	Number	`2`	—	Upper limit on the electrical-power input VSI2 (pu).	`VSI2MAX`
VSI2MIN	Number	`-2`	—	Lower limit on the electrical-power input VSI2 (pu).	`VSI2MIN`
TW3	Number	`10`	s (also ms)	Washout time constant of sTW3/(1+sTW3). 0 bypasses the washout.	`TW3`
TW4	Number	`0`	s (also ms)	Washout time constant of sTW4/(1+sTW4). 0 bypasses the washout.	`TW4`
KS2	Number	`1.43`	—	Gain of the power channel KS2/(1+sT7). For an integral-of-accelerating-power stabilizer KS2 = T7/(2H).	`KS2`
T7	Number	`10`	s (also ms)	Time constant of KS2/(1+sT7), which integrates the electrical power. Normally equal to TW2.	`T7`
KS3	Number	`1`	—	Gain of the power signal added ahead of the ramp-tracking filter. Normally 1.	`KS3`

Filter

Parameter	Type	Default	Units	Description	ID
T8	Number	`0.3`	s (also ms)	Lead time constant of the ramp-tracking filter [(1+sT8)/(1+sT9)^M]^N.	`T8`
T9	Number	`0.15`	s (also ms)	Lag time constant of the ramp-tracking filter.	`T9`
M	Choice: 0 / 1 / 2 / 3 / 4 / 5	2	—	Lag order M of the ramp-tracking filter (common: M = 5 with N = 1, or M = 2 with N = 4).	`M`
N	Choice: 0 / 1 / 2 / 3 / 4	4	—	Number of cascaded ramp-tracking sections N. 0 bypasses the filter.	`N`

Compensation

Parameter	Type	Default	Units	Description	ID
KS1	Number	`20`	—	Stabilizer gain applied after the ramp-tracking filter.	`KS1`
T1	Number	`0.16`	s (also ms)	First lead-lag lead time constant of (1+sT1)/(1+sT2).	`T1`
T2	Number	`0.02`	s (also ms)	First lead-lag lag time constant.	`T2`
T3	Number	`0.16`	s (also ms)	Second lead-lag lead time constant of (1+sT3)/(1+sT4).	`T3`
T4	Number	`0.02`	s (also ms)	Second lead-lag lag time constant.	`T4`
T10	Number	`1`	s (also ms)	Third lead-lag lead time constant of (1+sT10)/(1+sT11). Equal to T11 bypasses the stage.	`T10`
T11	Number	`1`	s (also ms)	Third lead-lag lag time constant.	`T11`
VSTMAX	Number	`0.2`	—	Upper limit on the stabilizer output VS (pu).	`VSTMAX`
VSTMIN	Number	`-0.066`	—	Lower limit on the stabilizer output VS (pu).	`VSTMIN`

Monitoring

Parameter	Type	Default	Units	Description	ID
Monitor VS	Choice: Off / On	Off	—	Record the stabilizer output VS (pu) sent to the exciter's VS input, after the [VSTMIN, VSTMAX] limit as a named observable.	`measure_vs`
Monitor accelerating power	Choice: Off / On	Off	—	Record the synthesized accelerating-power signal (pu) entering the KS1 gain: the ramp-tracking filter output minus the integrated electrical power as a named observable.	`measure_vacc`

Signal Names

Parameter	Type	Default	Units	Description	ID
VS name	Text	(empty)	—	Observable name for VS. Blank = skip.	`vs_name`
accelerating power name	Text	(empty)	—	Observable name for accelerating power. Blank = skip.	`vacc_name`

Initialization

Parameter	Type	Default	Units	Description	ID
Pe(0)	Number	`0`	—	Initial electrical power (pu on the machine base). Seeds the power-channel washout and stands in for Pe on the first step. Normally set by the load-flow auto-initialization.	`p_init`

Observables

Default name	Kind	Recorded when	Description	ID
set by VS name	Signal	Monitor VS is on	The stabilizer output VS (pu) sent to the exciter's VS input, after the [VSTMIN, VSTMAX] limit.	`VS`
set by accelerating power name	Signal	Monitor accelerating power is on	The synthesized accelerating-power signal (pu) entering the KS1 gain: the ramp-tracking filter output minus the integrated electrical power.	`vacc`

Power System Stabilizer (PSS2B) ​

Overview ​

Block diagram ​

Initialization ​

Wiring ​

Tuning notes ​

Ports ​

Parameters ​

Inputs ​

Filter ​

Compensation ​

Monitoring ​

Signal Names ​

Initialization ​

Observables ​

Power System Stabilizer (PSS2B)

Overview

Block diagram

Initialization

Wiring

Tuning notes

Ports

Parameters

Inputs

Filter

Compensation

Monitoring

Signal Names

Initialization

Observables