Add RPC to set reactive power (#60)

A new RPC, named `SetPowerReactive` has been added to set reactive power
for inverters, and other components that support it. Also, the
parameters to the RPC can be sent using the message
`SetPowerReactiveParam`.

Author: tiyash-basu-frequenz

RELEASE_NOTES.md

@@ -50,6 +50,12 @@
 
   A new inverter component states have been added: `Unknown`
 
+* [Added RPC to set reactive power](https://github.com/frequenz-floss/frequenz-api-microgrid/pull/60)
+
+  A new RPC, named `SetPowerReactive` has been added to set reactive power for
+  inverters, and other components that support it. Also, the parameters to the
+  RPC can be sent using the message `SetPowerReactiveParam`.
+
 ## Bug Fixes
 
 <!-- Here goes notable bug fixes that are worth a special mention or explanation -->

proto/frequenz/api/microgrid/microgrid.proto

@@ -179,7 +179,7 @@ service Microgrid {
   // ==== vales here are allowed and will be accepted
   rpc AddInclusionBounds(SetBoundsParam) returns (google.protobuf.Timestamp);
 
-  // Sets the power output of a component with a given ID, provided the
+  // Sets the active power output of a component with a given ID, provided the
   // component supports it.
   //
   // Note that the target component may have a resolution of more than 1 W.
@@ -198,6 +198,19 @@ service Microgrid {
     };
   }
 
+  // Sets the reactive power output of a component with a given ID, provided the
+  // component supports it.
+  //
+  // Note that the target component may have a resolution of more than 1 VAr.
+  // E.g., an inverter may have a resolution of 88 VAr.
+  // In such cases, the magnitude of power will be floored to the nearest
+  // multiple of the resolution.
+  rpc SetPowerReactive(SetPowerReactiveParam) returns (google.protobuf.Empty) {
+    option (google.api.http) = {
+      get : "/v1/components/{component_id}/setPowerReactive/{power}"
+    };
+  }
+
   // Starts the component, and brings it into a state where it is immediately
   // operational.
   //
@@ -368,6 +381,18 @@ message SetPowerActiveParam {
   float power = 2;
 }
 
+// Parameters for setting the reactive power of an appropriate component using
+// the `SetPowerReactive` RPC.
+message SetPowerReactiveParam {
+  // The ID of the component to set the output reactive power of.
+  uint64 component_id = 1;
+
+  // The output reactive power level, in VAr.
+  // -ve values are for inductive (lagging) power , and +ve values are for
+  //  capacitive (leading) power.
+  float power = 2;
+}
+
 // Parameters for setting bounds of a given metric of a given component.
 message SetBoundsParam {
   // An enumerated list of metrics whose bounds can be set.