Synchronous Machine Models

This page describes the most common synchronous machine models used in stability studies.

Nomenclature

The standard machine parameters are defined as follows:

• $R_{a}\,$ is the armature resistance (pu)
• $X_{a}\,$ is the armature reactance (pu)
• $X_{d}\,$ is the d-axis synchronous reactance (pu)
• $X_{q}\,$ is the q-axis synchronous reactance (pu)
• $X'_{d}\,$ is the d-axis transient reactance (pu)
• $X'_{q}\,$ is the q-axis transient reactance (pu)
• $X''_{d}\,$ is the d-axis subtransient reactance (pu)
• $X''_{q}\,$ is the q-axis subtransient reactance (pu)
• $T'_{d0}\,$ is the d-axis transient open loop time constant (s)
• $T'_{q0}\,$ is the q-axis transient open loop time constant (s)
• $T''_{d0}\,$ is the d-axis subtransient open loop time constant (s)
• $T''_{q0}\,$ is the q-axis subtransient open loop time constant (s)
• $H\,$ is the machine inertia constant (MWs/MVA)
• $D\,$ is an additional damping constant (pu)

Note that per-unit values are usually expressed on the machine's MVA base.

6th Order (Sauer-Pai) Model

6th order synchronous machine model based on the book:

Sauer, P.W., Pai, M. A., "Power System Dynamics and Stability", Stipes Publishing, 2006

Stator magnetic equations:

${\dot {E'_{q}}}={\frac {1}{T'_{d0}}}\left[V_{fd}-E'_{q}-(X_{d}-X'_{d})\left(I_{d}-\gamma _{d2}\psi ''_{d}-(1-\gamma _{d1})I_{d}+\gamma _{d2}E'_{q}\right)\right]\,$

${\dot {E'_{d}}}={\frac {1}{T'_{q0}}}\left[-E'_{q}-(X_{q}-X'_{q})\left(I_{q}-\gamma _{q2}\psi ''_{q}-(1-\gamma _{q1})I_{q}-\gamma _{q2}E'_{d}\right)\right]\,$

${\dot {\psi ''_{d}}}={\frac {1}{T''_{d0}}}\left[E'_{q}-\psi ''_{d}-(X'_{d}-X_{a})I_{d}\right]\,$

${\dot {\psi ''_{q}}}={\frac {1}{T''_{q0}}}\left[-E'_{d}-\psi ''_{q}-(X'_{q}-X_{a})I_{q}\right]\,$

$\psi _{d}=-X''_{d}I_{d}+\gamma _{d1}E'_{q}+(1-\gamma _{d1})\psi ''_{d}\,$

$\psi _{q}=-X''_{q}I_{q}-\gamma _{q1}E'_{d}+(1-\gamma _{q1})\psi ''_{q}\,$

where $\gamma _{d1}={\frac {X''_{d}-X_{a}}{X'_{d}-X_{a}}}\,$

$\gamma _{q1}={\frac {X''_{q}-X_{a}}{X'_{q}-X_{a}}}\,$

$\gamma _{d2}={\frac {1-\gamma _{d1}}{X'_{d}-X_{a}}}\,$

$\gamma _{q2}={\frac {1-\gamma _{q1}}{X'_{q}-X_{a}}}\,$

Stator electrical equations (neglecting electromagnetic transients):

$V_{d}=-\omega \psi _{q}-R_{a}I_{d}\,$

$V_{q}=\omega \psi _{d}-R_{a}I_{q}\,$

Equations of motion:

${\dot {\omega }}={\frac {1}{2H}}\left[P_{m}-P_{e}-D(\omega -\omega _{s})\right]\,$

${\dot {\delta }}=\Omega _{s}(\omega -\omega _{s})\,$

Initialisation:

${\boldsymbol {E}}_{q0}={\boldsymbol {V}}_{t0}+(R_{a}+jX_{q})\times {\boldsymbol {I}}_{a0}\,$

$\delta _{0}=\angle {\boldsymbol {E}}_{q0}\,$

$\psi _{0}=\angle {\boldsymbol {I}}_{a0}\,$

$I_{d0}=|{\boldsymbol {I}}_{a0}|\sin(\delta _{0}-\psi _{0})\,$

$I_{q0}=|{\boldsymbol {I}}_{a0}|\cos(\delta _{0}-\psi _{0})\,$

$V_{d0}=|{\boldsymbol {V}}_{t0}|\sin(\delta _{0}-\theta _{0})\,$

$V_{q0}=|{\boldsymbol {V}}_{t0}|\cos(\delta _{0}-\theta _{0})\,$

$E'_{d0}=V_{d}-X''_{q}I_{q0}+R_{a}I_{d0}-(1-\gamma _{q1})(X'_{q}-X_{a})I_{q0}\,$

$E'_{q0}=V_{q}+X''_{d}I_{d0}+R_{a}I_{q0}+(1-\gamma _{d1})(X'_{d}-X_{a})I_{d0}\,$

$\psi ''_{d0}=E'_{q0}-(X'_{d}-X_{a})I_{d0}\,$

$\psi ''_{q0}=-E'_{d0}-(X'_{q}-X_{a})I_{q0}\,$

$V_{fd0}=E'_{q0}+(X_{d}-X'_{d})\left(I_{d0}-\gamma _{d2}\psi ''_{d0}-(1-\gamma _{d1})I_{d0}+\gamma _{d2}E'_{q0}\right)\,$

$P_{m}=P_{e0}=(V_{d0}+R_{a}I_{d0})I_{d0}+(V_{q0}+R_{a}I_{q0})I_{q0}\,$

$\omega _{0}=\omega _{s}\,$

6th Order (Anderson-Fouad) Model

6th order synchronous machine model based on the book:

Anderson, P. M., Fouad, A. A., "Power System Control and Stability", Wiley-IEEE Press, New York, 2002

Stator magnetic equations:

${\dot {E'_{q}}}={\frac {1}{T'_{d0}}}\left[V_{fd}-(X_{d}-X'_{d})I_{d}-E'_{q}\right]\,$

${\dot {E'_{d}}}={\frac {1}{T'_{q0}}}\left[(X_{q}-X'_{q})I_{q}-E'_{d}\right]\,$

${\dot {E''_{q}}}={\frac {1}{T''_{d0}}}\left[E'_{q}-(X'_{d}-X''_{d})-E''_{q}\right]\,$

${\dot {E''_{d}}}={\frac {1}{T''_{q0}}}\left[E'_{d}-(X'_{q}-X''_{q})-E''_{d}\right]\,$

$E''_{q}-V_{q}=R_{a}I_{q}+X''_{d}I_{d}\,$

$E''_{d}-V_{d}=R_{a}I_{d}-X''_{q}I_{q}\,$

$\psi _{d}=E''_{q}-X''_{d}I_{d}\,$

$\psi _{q}=-E''_{d}-X''_{q}I_{q}\,$

Stator electrical equations (neglecting electromagnetic transients):

$V_{d}=-\omega \psi _{q}-R_{a}I_{d}\,$

$V_{q}=\omega \psi _{d}-R_{a}I_{q}\,$

Equations of motion:

${\dot {\omega }}={\frac {1}{2H}}\left[P_{m}-P_{e}-D(\omega -\omega _{s})\right]\,$

${\dot {\delta }}=\Omega _{s}(\omega -\omega _{s})\,$

Initialisation:

${\boldsymbol {E}}_{q0}={\boldsymbol {V}}_{t0}+(R_{a}+jX_{q})\times {\boldsymbol {I}}_{a0}\,$

$\delta _{0}=\angle {\boldsymbol {E}}_{q0}\,$

$\phi _{0}=\angle {\boldsymbol {I}}_{a0}\,$

$I_{d0}=|{\boldsymbol {I}}_{a0}|\sin(\delta _{0}-\phi _{0})\,$

$I_{q0}=|{\boldsymbol {I}}_{a0}|\cos(\delta _{0}-\phi _{0})\,$

$V_{fd0}=|{\boldsymbol {E}}_{q0}|+(X_{d}-X_{q})I_{d0}\,$

$E'_{q0}=V_{fd0}-(X_{d}-X'_{d})I_{d0}\,$

$E''_{q0}=E'_{q0}-(X'_{d}-X''_{d})I_{d0}\,$

$E'_{d0}=(X_{q}-X'_{q})I_{q0}\,$

$E''_{d0}=E'_{d0}+(X'_{q}-X''_{q})I_{q0}\,$

$V_{d0}=E''_{d0}+X''_{q}I_{q0}-R_{a}I_{d0}\,$

$V_{q0}=E''_{q0}-X''_{d}I_{d0}-R_{a}I_{q0}\,$

$P_{m}=P_{e0}=(V_{d0}+R_{a}I_{d0})I_{d0}+(V_{q0}+R_{a}I_{q0})I_{q0}\,$

$\omega _{0}=\omega _{s}\,$

4th Order (Two-Axis) Model

Stator magnetic equations:

${\dot {E'_{q}}}={\frac {1}{T'_{d0}}}\left[V_{fd}-(X_{d}-X'_{d})I_{d}-E'_{q}\right]\,$

${\dot {E'_{d}}}={\frac {1}{T'_{q0}}}\left[(X_{q}-X'_{q})I_{q}-E'_{d}\right]\,$

$E'_{q}-V_{q}=R_{a}I_{q}+X'_{d}I_{d}\,$

$E'_{d}-V_{d}=R_{a}I_{d}-X'_{q}I_{q}\,$

$\psi _{d}=E'_{q}-X'_{d}I_{d}\,$

$\psi _{q}=-E'_{d}-X'_{q}I_{q}\,$

Stator electrical equations (neglecting electromagnetic transients):

$V_{d}=-\omega \psi _{q}-R_{a}I_{d}\,$

$V_{q}=\omega \psi _{d}-R_{a}I_{q}\,$

Equations of motion:

${\dot {\omega }}={\frac {1}{2H}}\left[P_{m}-P_{e}-D(\omega -\omega _{s})\right]\,$

${\dot {\delta }}=\Omega _{s}(\omega -\omega _{s})\,$

Initialisation:

${\boldsymbol {E}}_{q0}={\boldsymbol {V}}_{t0}+(R_{a}+jX_{q})\times {\boldsymbol {I}}_{a0}\,$

$\delta _{0}=\angle {\boldsymbol {E}}_{q0}\,$

$\phi _{0}=\angle {\boldsymbol {I}}_{a0}\,$

$\theta _{0}=\angle {\boldsymbol {V}}_{t0}\,$

$I_{d0}=|{\boldsymbol {I}}_{a0}|\sin(\delta _{0}-\phi _{0})\,$

$I_{q0}=|{\boldsymbol {I}}_{a0}|\cos(\delta _{0}-\phi _{0})\,$

$V_{d0}=|{\boldsymbol {V}}_{t0}|\sin(\delta _{0}-\theta _{0})\,$

$V_{q0}=|{\boldsymbol {V}}_{t0}|\cos(\delta _{0}-\theta _{0})\,$

$E'_{q0}=V_{q0}+R_{a}I_{q0}+X'_{d}I_{d0}\,$

$E'_{d0}=V_{d0}+R_{a}I_{d0}-X'_{q}I_{q0}\,$

$V_{fd0}=E'_{q0}+(X_{d}-X'_{d})I_{d0}\,$

$P_{m}=P_{e0}=(V_{d0}+R_{a}I_{d0})I_{d0}+(V_{q0}+R_{a}I_{q0})I_{q0}\,$

$\omega _{0}=\omega _{s}\,$

2nd Order (Classical) Model

Stator equations:

$E'_{q}-V_{q}=R_{a}I_{q}+X'_{d}I_{d}\,$

$V_{d}=X'_{d}I_{q}-R_{a}I_{d}\,$

Equations of motion:

${\dot {\omega }}={\frac {1}{2H}}\left[P_{m}-P_{e}-D(\omega -\omega _{s})\right]\,$

${\dot {\delta }}=\Omega _{s}(\omega -\omega _{s})\,$

Initialisation:

${\boldsymbol {E}}_{q0}={\boldsymbol {V}}_{t0}+(R_{a}+jX'_{d})\times {\boldsymbol {I}}_{a0}\,$

$\delta _{0}=\angle {\boldsymbol {E}}_{q0}\,$

$\theta _{0}=\angle {\boldsymbol {V}}_{t0}\,$

$P_{m}=P_{e0}=\left({\frac {1}{R_{a}+jX'_{d}}}\right)|{\boldsymbol {V}}_{t0}||{\boldsymbol {E}}_{q0}|\sin(\delta _{0}-\theta _{0})\,$

$\omega _{0}=\omega _{s}\,$