ORNL · lukelowry · Jun 5, 2026
diff --git a/GridKit/Model/PhasorDynamics/Governor/Tgov1/README.md b/GridKit/Model/PhasorDynamics/Governor/Tgov1/README.md
@@ -14,6 +14,7 @@ Standard model of the stream turbine
 
 Symbol      | Units  | Description                       | Typical Value | Note
 ------------|--------|-----------------------------------|---------------| ------
+$T_{\mathrm{rate}}$ | [MW] | Turbine rating                    | 100.0 |
 $R$         | [p.u.] | Droop Constant                    | 0.05 |
 $T_1$       | [sec]  | Valve Time Delay                  | 0.5  |
 $T_2$       | [sec]  | Turbine Numerator Time Constant   | 2.5  |
@@ -52,53 +53,60 @@ $P_{ref}$       | [p.u.] | Reference Power                   | Either a constant
 
 ## Model Equations
 
-### Differential Equations
-The TGOV1 differential equations, as derived from the model diagram. Define the pre-limit derivative of $P_v$
-
+For readability, define:
 ```math
-f = \dfrac{1}{T_1}\left[-P_v + \dfrac{1}{R}(P_{ref} - \omega)\right]
+f = -P_v + \dfrac{1}{R}(P_{ref} - \omega)
 ```
 
-so that $\dot P_v$ can be written in piecewise form compactly.
+### Differential Equations
+The TGOV1 differential equations, as derived from the model diagram.
+
 ```math
 \begin{aligned}
-   \dot P_{tx}   &= P_v - \dfrac{1}{T_3}(P_{tx}+T_2P_v) \\
-   \dot P_v      &=
-   \begin{cases}
-      f
-         &  \text{if } (P_v^{\min} < P_v < P_v^{\max}) & \lor \\
-         &  \quad (P_v \leq P_v^{\min} \land f>0)       & \lor \\
-         &  \quad(P_v \geq P_v^{\max} \land f<0)            \\
-      0  
-         &  \text{else}
-   \end{cases}
+   0 &= -T_3 \dot P_{tx} - P_{tx} + (T_3 - T_2)P_v \\
+   0 &= -T_1 \dot P_v
+        + \text{antiwindup}(
+            P_v,
+            f,
+            P_v^{\min},
+            P_v^{\max}
+          )
 \end{aligned}
 ```
 
+CommonMath defines the [Anti-Windup](../../../../CommonMath.md#anti-windup-indicator)
+target and smooth approximation.
+
 ### Algebraic Equations
 The algebraic equation dictating the mechnical power output.
 ```math
 \begin{aligned}
-   P_m &= \dfrac{1}{T_3}(P_{tx}+T_2P_v) - D_t \omega \\
+   0 &= -\dfrac{S_{\mathrm{sys}}}{T_{\mathrm{rate}}} P_m
+        + \dfrac{1}{T_3}(P_{tx}+T_2P_v) - D_t \omega \\
 \end{aligned}
 ```
 
-In simulation the piecewise form above is replaced with a smooth approximation where $\phi$ is GridKit's smooth anti-windup indicator. See [CommonMath: Anti-Windup Indicator](../../../../CommonMath.md#anti-windup-indicator) for its definition, behavior, and design rationale.
-
 ## Initialization
-At steady state we assume that $P_v$ is at or within its limits. This implies the initial conditions are a function of $P_m$ which is equal to the electric torque.
+At steady state we assume that $P_v$ is at or within its limits. This implies the initial conditions are a function of the initial mechanical power converted to the TGOV1 component base.
 ```math
 \begin{aligned}
-   P_{tx}  &= (T_3-T_2) P_m\\
-   P_v     &= P_m\\
-   \dot P_{tx} &=0\\
-   \dot P_v    &=0\\
+   P^{\mathrm{tgov1}}_{m,0}
+      &= \dfrac{S_{\mathrm{sys}}}{T_{\mathrm{rate}}}P_{m,0} \\
+   P_{tx,0}
+      &= (T_3 - T_2)P^{\mathrm{tgov1}}_{m,0} \\
+   P_{v,0}
+      &= P^{\mathrm{tgov1}}_{m,0} \\
+   \dot P_{tx,0}
+      &= 0 \\
+   \dot P_{v,0}
+      &= 0
 \end{aligned}
 ```
 
 And if the reference power is a constant parameter, we can determine the value by solving the steady state equations.
 ```math
 \begin{aligned}
-   P_{ref}  &= R P_m\\
+   P_{ref,0}
+      &= R P^{\mathrm{tgov1}}_{m,0}
 \end{aligned}
 ```
diff --git a/GridKit/Model/PhasorDynamics/Governor/Tgov1/Tgov1.hpp b/GridKit/Model/PhasorDynamics/Governor/Tgov1/Tgov1.hpp
@@ -73,6 +73,7 @@ namespace GridKit
         using Component<scalar_type, index_type>::J_rows_buffer_;
         using Component<scalar_type, index_type>::J_cols_buffer_;
         using Component<scalar_type, index_type>::J_vals_buffer_;
+        using Component<scalar_type, index_type>::va_system_base_;
         using Component<scalar_type, index_type>::variable_indices_;
         using Component<scalar_type, index_type>::residual_indices_;
 
@@ -113,6 +114,7 @@ namespace GridKit
 
       private:
         // Input parameters
+        RealT Trate_{0};
         RealT R_{0};
         RealT Pvmin_{0};
         RealT Pvmax_{0};
@@ -121,14 +123,20 @@ namespace GridKit
         RealT T3_{0};
         RealT Dt_{0};
 
+        // Derived parameters
+        RealT va_component_base_{0};
+
         // Input States (which can be parameters)
         ScalarT pref_{0};
 
         /// Component signal extension
         ComponentSignals<ScalarT, IdxT, Tgov1InternalVariables, Tgov1ExternalVariables> signals_;
 
         // Parameter initialization function
-        void initializeParameters(const ModelDataT& data);
+        void    initializeParameters(const ModelDataT& data);
+        void    setDerivedParams();
+        ScalarT toComponentBase(ScalarT value) const;
+        ScalarT toSystemBase(ScalarT value) const;
 
         /* Local copies of signal variables */
         std::vector<ScalarT> ws_;

diff --git a/GridKit/Model/PhasorDynamics/Governor/Tgov1/Tgov1Data.hpp b/GridKit/Model/PhasorDynamics/Governor/Tgov1/Tgov1Data.hpp
@@ -22,6 +22,7 @@ namespace GridKit
        */
       enum class Tgov1Parameters
       {
+        Trate, ///< Turbine-rating power base
         R,     ///< Droop Constant
         T1,    ///< Valve Time Delay
         T2,    ///< Turbine Numerator Time Constant

diff --git a/GridKit/Model/PhasorDynamics/Governor/Tgov1/Tgov1Impl.hpp b/GridKit/Model/PhasorDynamics/Governor/Tgov1/Tgov1Impl.hpp
@@ -32,8 +32,10 @@ namespace GridKit
        */
       template <typename scalar_type, typename index_type>
       Tgov1<scalar_type, index_type>::Tgov1()
+        : Trate_(100.0)
       {
         size_ = 3;
+        setDerivedParams();
       }
 
       /**
@@ -44,7 +46,8 @@ namespace GridKit
        */
       template <typename scalar_type, typename index_type>
       Tgov1<scalar_type, index_type>::Tgov1(SignalT* pmech, SignalT* omega)
-        : R_(0.05),
+        : Trate_(100.0),
+          R_(0.05),
           Pvmin_(0),
           Pvmax_(1),
           T1_(HALF<RealT>),
@@ -57,6 +60,7 @@ namespace GridKit
 
         // 3 internal variables
         size_ = 3;
+        setDerivedParams();
       }
 
       /**
@@ -69,6 +73,7 @@ namespace GridKit
       {
         initializeParameters(data);
         size_ = 3;
+        setDerivedParams();
       }
 
       /**
@@ -82,6 +87,11 @@ namespace GridKit
       template <typename scalar_type, typename index_type>
       void Tgov1<scalar_type, index_type>::initializeParameters(const ModelDataT& data)
       {
+        if (data.parameters.contains(ModelDataT::Parameters::Trate))
+        {
+          Trate_ = std::get<RealT>(data.parameters.at(ModelDataT::Parameters::Trate));
+        }
+
         if (data.parameters.contains(ModelDataT::Parameters::R))
         {
           R_ = std::get<RealT>(data.parameters.at(ModelDataT::Parameters::R));
@@ -118,6 +128,24 @@ namespace GridKit
         }
       }
 
+      template <typename scalar_type, typename index_type>
+      void Tgov1<scalar_type, index_type>::setDerivedParams()
+      {
+        va_component_base_ = Trate_ * static_cast<RealT>(1.0e6);
+      }
+
+      template <typename scalar_type, typename index_type>
+      scalar_type Tgov1<scalar_type, index_type>::toComponentBase(scalar_type value) const
+      {
+        return value * va_system_base_ / va_component_base_;
+      }
+
+      template <typename scalar_type, typename index_type>
+      scalar_type Tgov1<scalar_type, index_type>::toSystemBase(scalar_type value) const
+      {
+        return value / toComponentBase(static_cast<scalar_type>(ONE<RealT>));
+      }
+
       /**
        * @brief Set the component ID
        */
@@ -199,7 +227,7 @@ namespace GridKit
         // Initial mechanical = initial electric torque
         if (signals_.template isAssigned<Tgov1InternalVariables::PM>())
         {
-          p0 = y_[2]; ///<- generator needs to be initialized first
+          p0 = toComponentBase(y_[2]); ///<- generator needs to be initialized first
         }
 
         // Input Variables (Parameter for now)
@@ -208,7 +236,7 @@ namespace GridKit
         // Internal States
         y_[0] = (T3_ - T2_) * p0; // y0 - Ptx (Turbine Power )
         y_[1] = p0;               // y1 - Pv  (Valve Position)
-        y_[2] = p0;               // y2 - Pm  (Mech Power)
+        y_[2] = toSystemBase(p0); // y2 - Pm  (Mech Power)
 
         // D.V. Derivative
         yp_[0] = 0.0; // Ptx
@@ -256,15 +284,15 @@ namespace GridKit
         // Set signal variable aliases
         ScalarT omega = ws[0];
 
-        // The 'pre-limit' derivative of Pv
-        ScalarT func = (-pv + (pref_ - omega) / R_) / T1_;
+        // The 'pre-limit' target of Pv
+        ScalarT func = -pv + (pref_ - omega) / R_;
 
         // Internal Differential Equations
-        f[0] = -ptx_dot + pv - (ptx + T2_ * pv) / T3_;
-        f[1] = -pv_dot + Math::antiwindup(pv, func, Pvmin_, Pvmax_);
+        f[0] = -T3_ * ptx_dot - ptx + (T3_ - T2_) * pv;
+        f[1] = -T1_ * pv_dot + Math::antiwindup(pv, func, Pvmin_, Pvmax_);
 
         // Internal Algebraic Equations
-        f[2] = -pmech + (ptx + T2_ * pv) / T3_ - (Dt_ * omega);
+        f[2] = -toComponentBase(pmech) + (ptx + T2_ * pv) / T3_ - (Dt_ * omega);
 
         return 0;
       }

diff --git a/GridKit/Model/PhasorDynamics/INPUT_FORMAT.md b/GridKit/Model/PhasorDynamics/INPUT_FORMAT.md
@@ -144,7 +144,7 @@ are specified:
   `Genrou`             | 6th order machine model                              | `bus`, `pmech`\*, `speed`\*, `efd`\*    | `p0`, `q0`, `H`, `D`, `Ra`, `Tdop`, `Tdopp`, `Tqop`, `Tqopp`, `Xd`, `Xdp`, `Xdpp`, `Xq`, `Xqp`, `Xqpp`, `Xl`, `S10`, `S12`, `mva`  | `ir`, `ii`, `p`, `q`, `delta`, `omega`, `speed`
   `Gensal`             | 5th order salient-pole machine model                 | `bus`, `pmech`\*, `speed`\*, `efd`\*    | `p0`, `q0`, `H`, `D`, `Ra`, `Tdop`, `Tdopp`, `Tqopp`, `Xd`, `Xdp`, `Xdpp`, `Xq`, `Xl`, `S10`, `S12`, `mva`  | `ir`, `ii`, `p`, `q`, `delta`, `omega`, `speed`, `Eqp`, `psidp`, `psiqpp`, `psidpp`, `vd`, `vq`, `te`, `id`, `iq`
   `GenClassical`       | the classical machine model                          | `bus`, `pmech`\*, `speed`\*, `efd`\*  | `p0`, `q0`, `H`, `D`, `Ra`, `Xdp`, `mva` | `ir`, `ii`, `p`, `q`, `delta`, `omega`
-  `Tgov1 `             | the TGOV1 governor model                             | `pmech`, `speed`                 | `R`, `T1`, `T2`, `T3`, `Pvmax`, `Pvmin`, `Dt` | `none`
+  `Tgov1 `             | the TGOV1 governor model                             | `pmech`, `speed`                 | `Trate`, `R`, `T1`, `T2`, `T3`, `Pvmax`, `Pvmin`, `Dt` | `none`
   `Ieeet1`             | the IEEET1 exciter model                             | `bus`, `speed`, `efd`, `vs`\*    | `Tr`, `Ka`, `Ta`, `Ke`, `Te`, `Kf`, `Tf`, `Vrmin`, `Vrmax`, `E1`, `E2`, `Se1`, `Se2`, `Ispdlim` | `efd`, `ksat`
   `SexsPti`            | the SEXS-PTI simplified exciter model                | `bus`, `efd`, `vs`\*             | `Ta`, `Tb`, `Te`, `K`, `Efdmax`, `Efdmin` | `efd`
   `Ieeest`      | the IEEEST stabilizer model                          | `input`, `output`                | `A1`, `A2`, `A3`, `A4`, `A5`, `A6`, `T1`, `T2`, `T3`, `T4`, `T5`, `T6`, `Ks`, `Lsmin`, `Lsmax`, `Vcl`, `Vcu`, `Tdelay` | `vss`
@@ -184,7 +184,7 @@ side for off-nominal transformer branches.
    "devices": [
        { "class": "Branch", "ports": {"bus1":1, "bus2":2}, "id": "BR1", "params": {"R":0.0, "X":0.1, "G":0.0, "B":0.0} },
        { "class": "Genrou", "ports": {"bus":1, "speed": 1, "pmech":2, "efd":3}, "id": "DV1", "params": {"p0":1.0, "q0":0.05013, "H":3.0, "D":0.0, "Ra":0.0, "Tdop":7.0, "Tdopp":0.04, "Tqopp":0.05, "Tqop":0.75, "Xd":2.1, "Xdp":0.2, "Xdpp":0.18, "Xq":0.5, "Xqp": 0.0, "Xqpp":0.18, "Xl":0.15, "S10":0.0, "S12":0.0}, "mon": ["delta", "omega"] },
-       { "class": "Tgov1", "ports": {"bus":1, "speed": 1, "pmech":2}, "id": "DV2", "params": {"R":0.05, "T1":0.5,"T2":2.5, "T3":7.5, "Pvmax":0, "Pvmin":1, "Dt":0}},
+       { "class": "Tgov1", "ports": {"bus":1, "speed": 1, "pmech":2}, "id": "DV2", "params": {"Trate":100.0, "R":0.05, "T1":0.5,"T2":2.5, "T3":7.5, "Pvmax":0, "Pvmin":1, "Dt":0}},
        { "class": "Ieeet1", "ports": {"bus":1, "speed": 1, "efd":3}, "id": "DV3", "params": {"Tr":0.001, "Ka":50.0, "Ta":0.04, "Ke":-0.06, "Te":0.6, "Kf":0.09, "Tf":1.46, "Vrmin":-1, "Vrmax":1, "E1":2.8, "E2":3.373, "Se1":0.04, "Se2":0.33, "Ispdlim":0}},
        { "class": "BusFault", "ports": {"bus":1}, "id": "EVT1", "params": {"state0": false, "R":0.0, "X":1e-3} }
    ]

diff --git a/GridKit/Model/PhasorDynamics/SynchronousMachine/GENROUwS/GenrouImpl.hpp b/GridKit/Model/PhasorDynamics/SynchronousMachine/GENROUwS/GenrouImpl.hpp
@@ -490,10 +490,10 @@ namespace GridKit
                + G_ * (vd * -std::cos(delta) + vq * std::sin(delta));
 
       ScalarT Te = y_[12];
-      pmech_set_ = Te;
+      pmech_set_ = toSystemBase(Te);
       if (signals_.template isAttached<GenrouExternalVariables::PM>())
       {
-        signals_.template writeExternalVariable<GenrouExternalVariables::PM>(Te);
+        signals_.template writeExternalVariable<GenrouExternalVariables::PM>(pmech_set_);
       }
 
       efd_set_ = Eqp + Xd1_ * (id + Xd3_ * (Eqp - psidp - Xd2_ * id)) + psidpp * ksat;
@@ -569,7 +569,7 @@ namespace GridKit
       ScalarT vi = wb[1];
 
       // Set signal variable aliases
-      ScalarT pmech = ws[0];
+      ScalarT pmech = toMachineBase(ws[0]);
       ScalarT efd   = ws[1];
 
       /* 6 Genrou differential equations */

diff --git a/GridKit/Model/PhasorDynamics/SynchronousMachine/GENSALwS/GensalImpl.hpp b/GridKit/Model/PhasorDynamics/SynchronousMachine/GENSALwS/GensalImpl.hpp
@@ -313,10 +313,10 @@ namespace GridKit
       y_[15] = B_ * (vd * std::sin(delta) + vq * std::cos(delta))
                + G_ * (vd * -std::cos(delta) + vq * std::sin(delta));
 
-      pmech_set_ = Te;
+      pmech_set_ = toSystemBase(Te);
       if (signals_.template isAttached<GensalExternalVariables::PM>())
       {
-        signals_.template writeExternalVariable<GensalExternalVariables::PM>(Te);
+        signals_.template writeExternalVariable<GensalExternalVariables::PM>(pmech_set_);
       }
 
       efd_set_ = Eqp + Xd1_ * (id + Xd3_ * (Eqp - psidp - Xd2_ * id)) + ksat;
@@ -388,7 +388,7 @@ namespace GridKit
       ScalarT vi = wb[1];
 
       // Set signal variable aliases
-      ScalarT pmech = ws[0];
+      ScalarT pmech = toMachineBase(ws[0]);
       ScalarT efd   = ws[1];
 
       /* 5 Gensal differential equations */