Expose 3-phase power through the grid

The 3-phase power is needed to calculate the power factor
of the microgrid. The power factor is not available through
the microgrid API in the current version used in the SDK.

So the 3-phase power is temporary exposed through the grid
until the migration to the latest version is completed.
Then the 3-phase power factor can be fetched and streamed
through the microgrid.

Signed-off-by: Daniel Zullo <[email protected]>

Author: daniel-zullo-frequenz

src/frequenz/sdk/timeseries/grid.py

@@ -21,7 +21,11 @@
 from ._quantities import Current, Power
 from .formula_engine import FormulaEngine, FormulaEngine3Phase
 from .formula_engine._formula_engine_pool import FormulaEnginePool
-from .formula_engine._formula_generators import GridCurrentFormula, GridPowerFormula
+from .formula_engine._formula_generators import (
+    GridCurrentFormula,
+    GridPower3PhaseFormula,
+    GridPowerFormula,
+)
 
 if TYPE_CHECKING:
     # Break circular import
@@ -95,6 +99,24 @@ def power(self) -> FormulaEngine[Power]:
         assert isinstance(engine, FormulaEngine)
         return engine
 
+    @property
+    def _power_3_phase(self) -> FormulaEngine3Phase[Power]:
+        """Fetch the grid 3-phase power for the microgrid.
+
+        This formula produces values that are in the Passive Sign Convention (PSC).
+
+        A receiver from the formula engine can be created using the
+        `new_receiver`method.
+
+        Returns:
+            A FormulaEngine that will calculate and stream grid 3-phase power.
+        """
+        engine = self._formula_pool.from_power_3_phase_formula_generator(
+            "grid_power_3_phase", GridPower3PhaseFormula
+        )
+        assert isinstance(engine, FormulaEngine3Phase)
+        return engine
+
     @property
     def current(self) -> FormulaEngine3Phase[Current]:
         """Fetch the grid current for the microgrid.