Allow optionally forcing power requests

A power request might need to be forced to implement
safety mechanisms, even when some components might be
seemingly failing (i.e. when there is not proper consumption
information, the user wants to slowly discharge batteries to
prevent potential peak breaches).

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

RELEASE_NOTES.md

@@ -16,6 +16,8 @@ This release drops support for Python versions older than 3.11.
 
 * Now `frequenz.sdk.timeseries.Sample` uses a more sensible comparison.  Before this release `Sample`s were compared only based on the `timestamp`.  This was due to a limitation in Python versions earlier than 3.10.  Now that the minimum supported version is 3.11 this hack is not needed anymore and `Sample`s are compared using both `timestamp` and `value` as most people probably expects.
 
+* A power request can now be forced by setting the `force` attribute. This is especially helpful as a safety measure when components appear to be failing, such as when battery metrics are unavailable. Note that applications previously relying on automatic fallback to all batteries when none of them was working will now require the force attribute to be explicitly set in the request.
+
 ## New Features
 
 <!-- Here goes the main new features and examples or instructions on how to use them -->

src/frequenz/sdk/actor/power_distributing/power_distributing.py

@@ -17,6 +17,7 @@
 import logging
 from asyncio.tasks import ALL_COMPLETED
 from dataclasses import dataclass, replace
+from datetime import datetime, timedelta, timezone
 from math import isnan
 from typing import (  # pylint: disable=unused-import
     Any,
@@ -62,6 +63,34 @@ class _User:
     """The bidirectional channel to communicate with the user."""
 
 
+@dataclass
+class _CacheEntry:
+    """Represents an entry in the cache with expiry time."""
+
+    inv_bat_pair: InvBatPair
+    """The inverter and adjacent battery data pair."""
+
+    def __init__(
+        self, inv_bat_pair: InvBatPair, duration: timedelta = timedelta(hours=2.5)
+    ) -> None:
+        """Initialize a CacheEntry instance.
+
+        Args:
+            inv_bat_pair: the inverter and adjacent battery data pair to cache.
+            duration: the duration of the cache entry.
+        """
+        self.inv_bat_pair = inv_bat_pair
+        self._expiry_time = datetime.now(tz=timezone.utc) + duration
+
+    def is_expired(self) -> bool:
+        """Check whether the cache entry has expired.
+
+        Returns:
+            whether the cache entry has expired.
+        """
+        return datetime.now(tz=timezone.utc) >= self._expiry_time
+
+
 @actor
 class PowerDistributingActor:
     # pylint: disable=too-many-instance-attributes
@@ -211,6 +240,10 @@ def __init__(
             max_data_age_sec=10.0,
         )
 
+        self._cached_metrics: dict[int, _CacheEntry | None] = {
+            bat_id: None for bat_id, _ in self._bat_inv_map.items()
+        }
+
     def _create_users_tasks(self) -> List[asyncio.Task[None]]:
         """For each user create a task to wait for request.
 
@@ -224,37 +257,43 @@ def _create_users_tasks(self) -> List[asyncio.Task[None]]:
             )
         return tasks
 
-    def _get_upper_bound(self, batteries: Set[int]) -> float:
+    def _get_upper_bound(self, batteries: Set[int], force_use_all: bool) -> float:
         """Get total upper bound of power to be set for given batteries.
 
         Note, output of that function doesn't guarantee that this bound will be
         the same when the request is processed.
 
         Args:
             batteries: List of batteries
+            force_use_all: whether all batteries in the power request must be used.
 
         Returns:
             Upper bound for `set_power` operation.
         """
-        pairs_data: List[InvBatPair] = self._get_components_data(batteries)
+        pairs_data: List[InvBatPair] = self._get_components_data(
+            batteries, force_use_all
+        )
         return sum(
             min(battery.power_upper_bound, inverter.active_power_upper_bound)
             for battery, inverter in pairs_data
         )
 
-    def _get_lower_bound(self, batteries: Set[int]) -> float:
+    def _get_lower_bound(self, batteries: Set[int], force_use_all: bool) -> float:
         """Get total lower bound of power to be set for given batteries.
 
         Note, output of that function doesn't guarantee that this bound will be
         the same when the request is processed.
 
         Args:
             batteries: List of batteries
+            force_use_all: whether all batteries in the power request must be used.
 
         Returns:
             Lower bound for `set_power` operation.
         """
-        pairs_data: List[InvBatPair] = self._get_components_data(batteries)
+        pairs_data: List[InvBatPair] = self._get_components_data(
+            batteries, force_use_all
+        )
         return sum(
             max(battery.power_lower_bound, inverter.active_power_lower_bound)
             for battery, inverter in pairs_data
@@ -282,21 +321,19 @@ async def run(self) -> None:
 
             try:
                 pairs_data: List[InvBatPair] = self._get_components_data(
-                    request.batteries
+                    request.batteries, request.force
                 )
             except KeyError as err:
                 await user.channel.send(Error(request=request, msg=str(err)))
                 continue
 
-            if len(pairs_data) == 0:
+            if not pairs_data and not request.force:
                 error_msg = f"No data for the given batteries {str(request.batteries)}"
                 await user.channel.send(Error(request=request, msg=str(error_msg)))
                 continue
 
             try:
-                distribution = self.distribution_algorithm.distribute_power(
-                    request.power, pairs_data
-                )
+                distribution = self._get_power_distribution(request, pairs_data)
             except ValueError as err:
                 error_msg = f"Couldn't distribute power, error: {str(err)}"
                 await user.channel.send(Error(request=request, msg=str(error_msg)))
@@ -379,6 +416,52 @@ async def _set_distributed_power(
 
         return self._parse_result(tasks, distribution.distribution, timeout_sec)
 
+    def _get_power_distribution(
+        self, request: Request, inv_bat_pairs: List[InvBatPair]
+    ) -> DistributionResult:
+        """Get power distribution result for the batteries in the request.
+
+        Args:
+            request: the power request to process.
+            inv_bat_pairs: the battery and adjacent inverter data pairs.
+
+        Returns:
+            the power distribution result.
+        """
+
+        def distribute_power_equally(
+            power: float, batteries: set[int]
+        ) -> DistributionResult:
+            power_per_battery = power / len(batteries)
+            return DistributionResult(
+                distribution={
+                    self._bat_inv_map[battery_id]: power_per_battery
+                    for battery_id in batteries
+                },
+                remaining_power=0.0,
+            )
+
+        if request.force and not inv_bat_pairs:
+            return distribute_power_equally(request.power, request.batteries)
+
+        available_bat_ids = {battery.component_id for battery, _ in inv_bat_pairs}
+        unavailable_bat_ids = request.batteries - available_bat_ids
+
+        result = self.distribution_algorithm.distribute_power(
+            request.power, inv_bat_pairs
+        )
+
+        if request.force and unavailable_bat_ids:
+            additional_result = distribute_power_equally(
+                result.remaining_power, unavailable_bat_ids
+            )
+
+            for inv_id, power in additional_result.distribution.items():
+                result.distribution[inv_id] = power
+            result.remaining_power = 0.0
+
+        return result
+
     def _check_request(self, request: Request) -> Optional[Result]:
         """Check whether the given request if correct.
 
@@ -388,7 +471,7 @@ def _check_request(self, request: Request) -> Optional[Result]:
         Returns:
             Result for the user if the request is wrong, None otherwise.
         """
-        if len(request.batteries) == 0:
+        if not request.batteries:
             return Error(request=request, msg="Empty battery IDs in the request")
 
         for battery in request.batteries:
@@ -401,11 +484,11 @@ def _check_request(self, request: Request) -> Optional[Result]:
 
         if not request.adjust_power:
             if request.power < 0:
-                bound = self._get_lower_bound(request.batteries)
+                bound = self._get_lower_bound(request.batteries, request.force)
                 if request.power < bound:
                     return OutOfBound(request=request, bound=bound)
             else:
-                bound = self._get_upper_bound(request.batteries)
+                bound = self._get_upper_bound(request.batteries, request.force)
                 if request.power > bound:
                     return OutOfBound(request=request, bound=bound)
 
@@ -554,11 +637,14 @@ def _get_components_pairs(
 
         return bat_inv_map, inv_bat_map
 
-    def _get_components_data(self, batteries: Set[int]) -> List[InvBatPair]:
+    def _get_components_data(
+        self, batteries: Set[int], force_use_all: bool
+    ) -> List[InvBatPair]:
         """Get data for the given batteries and adjacent inverters.
 
         Args:
             batteries: Batteries that needs data.
+            force_use_all: whether all batteries in the power request must be used.
 
         Raises:
             KeyError: If any battery in the given list doesn't exists in microgrid.
@@ -568,7 +654,9 @@ def _get_components_data(self, batteries: Set[int]) -> List[InvBatPair]:
         """
         pairs_data: List[InvBatPair] = []
         working_batteries = (
-            self._all_battery_status.get_working_batteries(batteries) or batteries
+            batteries
+            if force_use_all
+            else self._all_battery_status.get_working_batteries(batteries)
         )
 
         for battery_id in working_batteries:
@@ -581,6 +669,12 @@ def _get_components_data(self, batteries: Set[int]) -> List[InvBatPair]:
             inverter_id: int = self._bat_inv_map[battery_id]
 
             data = self._get_battery_inverter_data(battery_id, inverter_id)
+            if not data and force_use_all:
+                cached_entry = self._cached_metrics[battery_id]
+                if cached_entry and not cached_entry.is_expired():
+                    data = cached_entry.inv_bat_pair
+                else:
+                    data = None
             if data is None:
                 _logger.warning(
                     "Skipping battery %d because its message isn't correct.",
@@ -648,7 +742,9 @@ def _get_battery_inverter_data(
 
         # If all values are ok then return them.
         if not any(map(isnan, replaceable_metrics)):
-            return InvBatPair(battery_data, inverter_data)
+            inv_bat_pair = InvBatPair(battery_data, inverter_data)
+            self._cached_metrics[battery_id] = _CacheEntry(inv_bat_pair)
+            return inv_bat_pair
 
         # Replace NaN with the corresponding value in the adjacent component.
         # If both metrics are None, return None to ignore this battery.
@@ -670,10 +766,12 @@ def _get_battery_inverter_data(
             elif isnan(inv_bound):
                 inverter_new_metrics[inv_attr] = bat_bound
 
-        return InvBatPair(
+        inv_bat_pair = InvBatPair(
             replace(battery_data, **battery_new_metrics),
             replace(inverter_data, **inverter_new_metrics),
         )
+        self._cached_metrics[battery_id] = _CacheEntry(inv_bat_pair)
+        return inv_bat_pair
 
     async def _create_channels(self) -> None:
         """Create channels to get data of components in microgrid."""

src/frequenz/sdk/actor/power_distributing/request.py

@@ -29,3 +29,6 @@ class Request:
     If `False` and the power is outside the batteries' bounds, the request will
     fail and be replied to with an `OutOfBound` result.
     """
+
+    force: bool = False
+    """Whether to force the power request regardless the status of components."""