Allow optionally forcing power requests (frequenz-floss#365)

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).

Fixes frequenz-floss#321

Author: daniel-zullo-frequenz

RELEASE_NOTES.md

@@ -24,6 +24,8 @@ This release drops support for Python versions older than 3.11.
   soc_rx = battery_pool.soc.new_receiver()    # new
   ```
 
+* A power request can now be forced by setting the `include_broken` 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 `include_broken` 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

@@ -15,18 +15,12 @@
 
 import asyncio
 import logging
+import time
 from asyncio.tasks import ALL_COMPLETED
 from dataclasses import dataclass, replace
+from datetime import timedelta
 from math import isnan
-from typing import (  # pylint: disable=unused-import
-    Any,
-    Dict,
-    Iterable,
-    List,
-    Optional,
-    Set,
-    Tuple,
-)
+from typing import Any, Dict, Iterable, List, Optional, Self, Set, Tuple
 
 import grpc
 from frequenz.channels import Bidirectional, Peekable, Receiver, Sender
@@ -62,6 +56,40 @@ 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."""
+
+    expiry_time: int
+    """The expiration time (taken from the monotonic clock) of the cache entry."""
+
+    @classmethod
+    def from_ttl(
+        cls, inv_bat_pair: InvBatPair, ttl: timedelta = timedelta(hours=2.5)
+    ) -> Self:
+        """Initialize a CacheEntry instance from a TTL (Time-To-Live).
+
+        Args:
+            inv_bat_pair: the inverter and adjacent battery data pair to cache.
+            ttl: the time a cache entry is kept alive.
+
+        Returns:
+            this class instance.
+        """
+        return cls(inv_bat_pair, time.monotonic_ns() + int(ttl.total_seconds() * 1e9))
+
+    def has_expired(self) -> bool:
+        """Check whether the cache entry has expired.
+
+        Returns:
+            whether the cache entry has expired.
+        """
+        return time.monotonic_ns() >= self.expiry_time
+
+
 @actor
 class PowerDistributingActor:
     # pylint: disable=too-many-instance-attributes
@@ -211,6 +239,10 @@ 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 +256,45 @@ 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], include_broken: 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
+            include_broken: whether all batteries in the batteries set in the
+                request must be used regardless the status.
 
         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, include_broken
+        )
         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], include_broken: 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
+            include_broken: whether all batteries in the batteries set in the
+                request must be used regardless the status.
 
         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, include_broken
+        )
         return sum(
             max(battery.power_lower_bound, inverter.active_power_lower_bound)
             for battery, inverter in pairs_data
@@ -282,21 +322,19 @@ async def run(self) -> None:
 
             try:
                 pairs_data: List[InvBatPair] = self._get_components_data(
-                    request.batteries
+                    request.batteries, request.include_broken
                 )
             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.include_broken:
                 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 +417,44 @@ 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.
+        """
+        available_bat_ids = {battery.component_id for battery, _ in inv_bat_pairs}
+        unavailable_bat_ids = request.batteries - available_bat_ids
+        unavailable_inv_ids = {
+            self._bat_inv_map[battery_id] for battery_id in unavailable_bat_ids
+        }
+
+        if request.include_broken and not available_bat_ids:
+            return self.distribution_algorithm.distribute_power_equally(
+                request.power, unavailable_inv_ids
+            )
+
+        result = self.distribution_algorithm.distribute_power(
+            request.power, inv_bat_pairs
+        )
+
+        if request.include_broken and unavailable_inv_ids:
+            additional_result = self.distribution_algorithm.distribute_power_equally(
+                result.remaining_power, unavailable_inv_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.
 
@@ -388,6 +464,9 @@ def _check_request(self, request: Request) -> Optional[Result]:
         Returns:
             Result for the user if the request is wrong, None otherwise.
         """
+        if not request.batteries:
+            return Error(request=request, msg="Empty battery IDs in the request")
+
         for battery in request.batteries:
             if battery not in self._battery_receivers:
                 msg = (
@@ -398,11 +477,11 @@ 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.include_broken)
                 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.include_broken)
                 if request.power > bound:
                     return OutOfBound(request=request, bound=bound)
 
@@ -551,29 +630,15 @@ def _get_components_pairs(
 
         return bat_inv_map, inv_bat_map
 
-    def _get_working_batteries(self, batteries: Set[int]) -> Set[int]:
-        """Get subset with working batteries.
-
-        If none of the given batteries are working, then treat all of them
-        as working.
-
-        Args:
-            batteries: requested batteries
-
-        Returns:
-            Subset with working batteries or input set if none of the given batteries
-                are working.
-        """
-        working_batteries = self._all_battery_status.get_working_batteries(batteries)
-        if len(working_batteries) == 0:
-            return batteries
-        return working_batteries
-
-    def _get_components_data(self, batteries: Set[int]) -> List[InvBatPair]:
+    def _get_components_data(
+        self, batteries: Set[int], include_broken: bool
+    ) -> List[InvBatPair]:
         """Get data for the given batteries and adjacent inverters.
 
         Args:
             batteries: Batteries that needs data.
+            include_broken: whether all batteries in the batteries set in the
+                request must be used regardless the status.
 
         Raises:
             KeyError: If any battery in the given list doesn't exists in microgrid.
@@ -582,7 +647,11 @@ def _get_components_data(self, batteries: Set[int]) -> List[InvBatPair]:
             Pairs of battery and adjacent inverter data.
         """
         pairs_data: List[InvBatPair] = []
-        working_batteries = self._get_working_batteries(batteries)
+        working_batteries = (
+            batteries
+            if include_broken
+            else self._all_battery_status.get_working_batteries(batteries)
+        )
 
         for battery_id in working_batteries:
             if battery_id not in self._battery_receivers:
@@ -594,6 +663,12 @@ 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 include_broken:
+                cached_entry = self._cached_metrics[battery_id]
+                if cached_entry and not cached_entry.has_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.",
@@ -661,7 +736,9 @@ 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.from_ttl(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.
@@ -683,10 +760,12 @@ 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.from_ttl(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 +29,14 @@ class Request:
     If `False` and the power is outside the batteries' bounds, the request will
     fail and be replied to with an `OutOfBound` result.
     """
+
+    include_broken: bool = False
+    """Whether to use all batteries included in the batteries set regardless the status.
+
+    if `True`, the remaining power after distributing between working batteries
+    will be distributed equally between broken batteries. Also if all batteries
+    in the batteries set are broken then the power is distributed equally between
+    broken batteries.
+
+    if `False`, the power will be only distributed between the working batteries.
+    """

src/frequenz/sdk/power/_distribution_algorithm.py

@@ -423,6 +423,27 @@ def _greedy_distribute_remaining_power(
 
         return DistributionResult(new_distribution, remaining_power)
 
+    def distribute_power_equally(
+        self, power: float, inverters: set[int]
+    ) -> DistributionResult:
+        """Distribute the power equally between the inverters in the set.
+
+        This function is mainly useful to set the power for components that are
+        broken or have no metrics available.
+
+        Args:
+            power: the power to distribute.
+            inverters: the inverters to set the power to.
+
+        Returns:
+            the power distribution result.
+        """
+        power_per_inverter = power / len(inverters)
+        return DistributionResult(
+            distribution={id: power_per_inverter for id in inverters},
+            remaining_power=0.0,
+        )
+
     def distribute_power(
         self, power: float, components: List[InvBatPair]
     ) -> DistributionResult: