fix(core): Avoid flickering between charge/discharge due to PID filter

Before this change the PID filter implementation eventually caused the behavior to switch from charging to discharing, eventhough the system wanted to (a) charge with a lower value than before (b) set active power to 0. This was due to the fact, that the PID filter overshoots its target.
By detecting if the system wants charge/discharge/no current flow the battery, it now dynamically adjusts the limits of the battery so it does not overshoot in the unwanted area. This reduces stress on the battery. It also improves the controller that are using this filter (e.g. self consumption optimization, peak load shaving). Sometimes they showed behavior where they wildly flicker between charging/discharging.

Author: Felix Remmel

io.openems.edge.ess.api/src/io/openems/edge/ess/api/ActivePowerConstraintWithPid.java

@@ -0,0 +1,40 @@
+package io.openems.edge.ess.api;
+
+import io.openems.common.exceptions.OpenemsError.OpenemsNamedException;
+import io.openems.common.function.ThrowingBiConsumer;
+import io.openems.edge.ess.power.api.Phase;
+import io.openems.edge.ess.power.api.Pwr;
+
+public final class ActivePowerConstraintWithPid implements ThrowingBiConsumer<ManagedSymmetricEss, Integer, OpenemsNamedException> {
+
+	@Override
+	public void accept(ManagedSymmetricEss ess, Integer value) throws OpenemsNamedException {
+		if (value != null) {
+			var power = ess.getPower();
+			var pidFilter = power.getPidFilter();
+
+			// configure PID filter
+			var minPower = power.getMinPower(ess, Phase.ALL, Pwr.ACTIVE);
+			var maxPower = power.getMaxPower(ess, Phase.ALL, Pwr.ACTIVE);
+			if (maxPower < minPower) {
+				maxPower = minPower; // avoid rounding error
+			}
+
+			int currentActivePower = ess.getActivePower().orElse(0);
+			
+			if (value <= 0 && currentActivePower <= 0 && minPower < 0 && maxPower > 0) {
+				// Prevent PID filter to overshoot and flicker from charging to discharging
+				pidFilter.setLimits(minPower, 0);
+			} else if (value >= 0 && currentActivePower >= 0 && minPower < 0 && maxPower > 0) {
+				pidFilter.setLimits(0, maxPower);
+			} else {
+				// changing between charging/discharging is intended behavior, so we allow it.
+				pidFilter.setLimits(minPower, maxPower);
+			}
+			
+			var pidOutput = pidFilter.applyPidFilter(currentActivePower, value);
+
+			ess.setActivePowerEquals(pidOutput);
+		}
+	}
+}

io.openems.edge.ess.api/src/io/openems/edge/ess/api/ManagedSymmetricEss.java

@@ -85,28 +85,7 @@ public enum ChannelId implements io.openems.edge.common.channel.ChannelId {
 				.unit(Unit.WATT) //
 				.accessMode(AccessMode.WRITE_ONLY) //
 				.onChannelSetNextWrite(
-						new PowerConstraint("SetActivePowerEqualsWithPid", Phase.ALL, Pwr.ACTIVE, Relationship.EQUALS) {
-							@Override
-							public void accept(ManagedSymmetricEss ess, Integer value) throws OpenemsNamedException {
-								if (value != null) {
-									var power = ess.getPower();
-									var pidFilter = power.getPidFilter();
-
-									// configure PID filter
-									var minPower = power.getMinPower(ess, Phase.ALL, Pwr.ACTIVE);
-									var maxPower = power.getMaxPower(ess, Phase.ALL, Pwr.ACTIVE);
-									if (maxPower < minPower) {
-										maxPower = minPower; // avoid rounding error
-									}
-									pidFilter.setLimits(minPower, maxPower);
-
-									int currentActivePower = ess.getActivePower().orElse(0);
-									var pidOutput = pidFilter.applyPidFilter(currentActivePower, value);
-
-									ess.setActivePowerEquals(pidOutput);
-								}
-							}
-						})),
+						new ActivePowerConstraintWithPid())),
 		/**
 		 * Sets a fixed Reactive Power.
 		 *