Fix flow computation of HVDC connected at only one side

src/main/java/com/powsybl/openloadflow/ac/equations/AcEquationSystemCreator.java

@@ -930,7 +930,7 @@ static void updateBranchEquations(LfBranch branch) {
     private static void createHvdcAcEmulationEquations(LfHvdc hvdc, EquationSystem<AcVariableType, AcEquationType> equationSystem) {
         EquationTerm<AcVariableType, AcEquationType> p1 = null;
         EquationTerm<AcVariableType, AcEquationType> p2 = null;
-        if (hvdc.getBus1() != null && hvdc.getBus2() != null) {
+        if (hvdc.getBus1() != null && hvdc.getBus2() != null && hvdc.isAcEmulation()) {
             p1 = new HvdcAcEmulationSide1ActiveFlowEquationTerm(hvdc, hvdc.getBus1(), hvdc.getBus2(), equationSystem.getVariableSet());
             p2 = new HvdcAcEmulationSide2ActiveFlowEquationTerm(hvdc, hvdc.getBus1(), hvdc.getBus2(), equationSystem.getVariableSet());
         } else {

src/main/java/com/powsybl/openloadflow/network/HvdcState.java

@@ -11,11 +11,20 @@
  */
 public class HvdcState extends ElementState<LfHvdc> {
 
+    private boolean acEmulation;
+
     public HvdcState(LfHvdc hvdc) {
         super(hvdc);
+        this.acEmulation = hvdc.isAcEmulation();
     }
 
     public static HvdcState save(LfHvdc hvdc) {
         return new HvdcState(hvdc);
     }
+
+    @Override
+    public void restore() {
+        super.restore();
+        element.setAcEmulation(acEmulation);
+    }
 }

src/main/java/com/powsybl/openloadflow/network/LfAction.java

@@ -365,9 +365,10 @@ public void apply(LfNetworkParameters networkParameters) {
         }
 
         if (hvdc != null) {
-            hvdc.setDisabled(true);
-            hvdc.getConverterStation1().setTargetP(-hvdc.getP1().eval());
-            hvdc.getConverterStation2().setTargetP(-hvdc.getP2().eval());
+            hvdc.setAcEmulation(false);
+            hvdc.setDisabled(true); // for equations only, but should be hidden
+            hvdc.getConverterStation1().setTargetP(-hvdc.getP1().eval()); // override
+            hvdc.getConverterStation2().setTargetP(-hvdc.getP2().eval()); // override
         }
     }
 }

src/main/java/com/powsybl/openloadflow/network/LfBus.java

@@ -149,6 +149,8 @@ default double getHighVoltageLimit() {
 
     void addBranch(LfBranch branch);
 
+    List<LfHvdc> getHvdcs();
+
     void addHvdc(LfHvdc hvdc);
 
     void updateState(LfNetworkStateUpdateParameters parameters);

src/main/java/com/powsybl/openloadflow/network/LfContingency.java

@@ -41,15 +41,18 @@ public class LfContingency {
 
     private final Set<String> disconnectedElementIds;
 
+    private final Set<LfHvdc> hvdcsWithoutPower;
+
     public LfContingency(String id, int index, int createdSynchronousComponentsCount, DisabledNetwork disabledNetwork, Map<LfShunt, AdmittanceShift> shuntsShift,
-                         Map<LfLoad, LfLostLoad> lostLoads, Set<LfGenerator> lostGenerators) {
+                         Map<LfLoad, LfLostLoad> lostLoads, Set<LfGenerator> lostGenerators, Set<LfHvdc> hvdcsWithoutPower) {
         this.id = Objects.requireNonNull(id);
         this.index = index;
         this.createdSynchronousComponentsCount = createdSynchronousComponentsCount;
         this.disabledNetwork = Objects.requireNonNull(disabledNetwork);
         this.shuntsShift = Objects.requireNonNull(shuntsShift);
         this.lostLoads = Objects.requireNonNull(lostLoads);
         this.lostGenerators = Objects.requireNonNull(lostGenerators);
+        this.hvdcsWithoutPower = Objects.requireNonNull(hvdcsWithoutPower);
         this.disconnectedLoadActivePower = 0.0;
         this.disconnectedGenerationActivePower = 0.0;
         this.disconnectedElementIds = new HashSet<>();
@@ -179,6 +182,10 @@ public void apply(LoadFlowParameters.BalanceType balanceType) {
                 bus.setGeneratorReactivePowerControlEnabled(false);
             }
         }
+        for (LfHvdc hvdc : hvdcsWithoutPower) {
+            hvdc.getConverterStation1().setTargetP(0.0);
+            hvdc.getConverterStation2().setTargetP(0.0);
+        }
     }
 
     private static double getUpdatedLoadP0(LfLoad load, LoadFlowParameters.BalanceType balanceType, double initialP0, double initialVariableActivePower) {

src/main/java/com/powsybl/openloadflow/network/LfHvdc.java

@@ -17,6 +17,8 @@ public interface LfHvdc extends LfElement {
 
     LfBus getBus2();
 
+    LfBus getOtherBus(LfBus bus);
+
     void setP1(Evaluable p1);
 
     Evaluable getP1();
@@ -29,6 +31,10 @@ public interface LfHvdc extends LfElement {
 
     double getP0();
 
+    boolean isAcEmulation();
+
+    void setAcEmulation(boolean acEmulation);
+
     LfVscConverterStation getConverterStation1();
 
     LfVscConverterStation getConverterStation2();

src/main/java/com/powsybl/openloadflow/network/impl/AbstractLfBus.java

@@ -10,6 +10,7 @@
 import com.powsybl.iidm.network.*;
 import com.powsybl.openloadflow.network.*;
 import com.powsybl.openloadflow.util.Evaluable;
+import com.powsybl.openloadflow.util.LfHvdcUtils;
 import com.powsybl.openloadflow.util.PerUnit;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -285,7 +286,11 @@ void addLoad(Load load, LfNetworkParameters parameters) {
     }
 
     void addLccConverterStation(LccConverterStation lccCs, LfNetworkParameters parameters) {
-        getOrCreateLfLoad(null, parameters).add(lccCs, parameters);
+        if (!LfHvdcUtils.isHvdcDandlingInIdm(lccCs, null)) {
+            // Note: Load is determined statically - contingencies or actions that change an LCC Station connectivity
+            // will continue to give incorrect result
+            getOrCreateLfLoad(null, parameters).add(lccCs, parameters);
+        }
     }
 
     protected void add(LfGenerator generator) {
@@ -482,6 +487,11 @@ public void addBranch(LfBranch branch) {
         branches.add(Objects.requireNonNull(branch));
     }
 
+    @Override
+    public List<LfHvdc> getHvdcs() {
+        return hvdcs;
+    }
+
     @Override
     public void addHvdc(LfHvdc hvdc) {
         hvdcs.add(Objects.requireNonNull(hvdc));
@@ -711,6 +721,14 @@ public void setDisabled(boolean disabled) {
         if (controllerShunt != null) {
             controllerShunt.setDisabled(disabled);
         }
+        for (LfHvdc hvdc : hvdcs) {
+            if (disabled) {
+                hvdc.setDisabled(true);
+            } else if (!hvdc.getOtherBus(this).isDisabled()) {
+                // if both buses enabled only
+                hvdc.setDisabled(false);
+            }
+        }
     }
 
     @Override

src/main/java/com/powsybl/openloadflow/network/impl/LfHvdcImpl.java

@@ -30,22 +30,27 @@ public class LfHvdcImpl extends AbstractElement implements LfHvdc {
 
     private Evaluable p2 = NAN;
 
-    private final double droop;
+    private double droop = Double.NaN;
 
-    private final double p0;
+    private double p0 = Double.NaN;
 
     private LfVscConverterStation converterStation1;
 
     private LfVscConverterStation converterStation2;
 
-    public LfHvdcImpl(String id, LfBus bus1, LfBus bus2, LfNetwork network, HvdcAngleDroopActivePowerControl control) {
+    private boolean acEmulation;
+
+    public LfHvdcImpl(String id, LfBus bus1, LfBus bus2, LfNetwork network, HvdcAngleDroopActivePowerControl control,
+                      boolean acEmulation) {
         super(network);
         this.id = Objects.requireNonNull(id);
         this.bus1 = bus1;
         this.bus2 = bus2;
-        Objects.requireNonNull(control);
-        droop = control.getDroop();
-        p0 = control.getP0();
+        this.acEmulation = acEmulation && control != null && control.isEnabled();
+        if (this.acEmulation) {
+            droop = control.getDroop();
+            p0 = control.getP0();
+        }
     }
 
     @Override
@@ -68,6 +73,21 @@ public LfBus getBus2() {
         return this.bus2;
     }
 
+    @Override
+    public LfBus getOtherBus(LfBus bus) {
+        return bus.equals(bus1) ? bus2 : bus1;
+    }
+
+    @Override
+    public void setDisabled(boolean disabled) {
+        super.setDisabled(disabled); // for AC emulation equations only.
+        if (!acEmulation && !disabled) {
+            // re-active power transmission to initial target values.
+            converterStation1.setTargetP(converterStation1.getInitialTargetP());
+            converterStation2.setTargetP(converterStation2.getInitialTargetP());
+        }
+    }
+
     @Override
     public void setP1(Evaluable p1) {
         this.p1 = Objects.requireNonNull(p1);
@@ -98,6 +118,16 @@ public double getP0() {
         return p0 / PerUnit.SB;
     }
 
+    @Override
+    public boolean isAcEmulation() {
+        return acEmulation;
+    }
+
+    @Override
+    public void setAcEmulation(boolean acEmulation) {
+        this.acEmulation = acEmulation;
+    }
+
     @Override
     public LfVscConverterStation getConverterStation1() {
         return converterStation1;
@@ -122,7 +152,9 @@ public void setConverterStation2(LfVscConverterStation converterStation2) {
 
     @Override
     public void updateState() {
-        ((LfVscConverterStationImpl) converterStation1).getStation().getTerminal().setP(p1.eval() * PerUnit.SB);
-        ((LfVscConverterStationImpl) converterStation2).getStation().getTerminal().setP(p2.eval() * PerUnit.SB);
+        if (acEmulation) {
+            ((LfVscConverterStationImpl) converterStation1).getStation().getTerminal().setP(p1.eval() * PerUnit.SB);
+            ((LfVscConverterStationImpl) converterStation2).getStation().getTerminal().setP(p2.eval() * PerUnit.SB);
+        }
     }
 }

src/main/java/com/powsybl/openloadflow/network/impl/LfNetworkLoaderImpl.java

@@ -482,23 +482,19 @@ private static void createBranches(List<LfBus> lfBuses, LfNetwork lfNetwork, LfT
             }
         }
 
-        if (parameters.isHvdcAcEmulation()) {
-            for (HvdcLine hvdcLine : loadingContext.hvdcLineSet) {
-                HvdcAngleDroopActivePowerControl control = hvdcLine.getExtension(HvdcAngleDroopActivePowerControl.class);
-                if (control != null && control.isEnabled()) {
-                    LfBus lfBus1 = getLfBus(hvdcLine.getConverterStation1().getTerminal(), lfNetwork, parameters.isBreakers());
-                    LfBus lfBus2 = getLfBus(hvdcLine.getConverterStation2().getTerminal(), lfNetwork, parameters.isBreakers());
-                    LfVscConverterStationImpl cs1 = (LfVscConverterStationImpl) lfNetwork.getGeneratorById(hvdcLine.getConverterStation1().getId());
-                    LfVscConverterStationImpl cs2 = (LfVscConverterStationImpl) lfNetwork.getGeneratorById(hvdcLine.getConverterStation2().getId());
-                    if (cs1 != null && cs2 != null) {
-                        LfHvdc lfHvdc = new LfHvdcImpl(hvdcLine.getId(), lfBus1, lfBus2, lfNetwork, control);
-                        lfHvdc.setConverterStation1((LfVscConverterStationImpl) lfNetwork.getGeneratorById(hvdcLine.getConverterStation1().getId()));
-                        lfHvdc.setConverterStation2((LfVscConverterStationImpl) lfNetwork.getGeneratorById(hvdcLine.getConverterStation2().getId()));
-                        lfNetwork.addHvdc(lfHvdc);
-                    } else {
-                        LOGGER.warn("Hvdc line '{}' in AC emulation but converter stations are not in the same synchronous component: operated using active set point.", hvdcLine.getId());
-                    }
-                }
+        for (HvdcLine hvdcLine : loadingContext.hvdcLineSet) {
+            LfBus lfBus1 = getLfBus(hvdcLine.getConverterStation1().getTerminal(), lfNetwork, parameters.isBreakers());
+            LfBus lfBus2 = getLfBus(hvdcLine.getConverterStation2().getTerminal(), lfNetwork, parameters.isBreakers());
+            LfVscConverterStationImpl cs1 = (LfVscConverterStationImpl) lfNetwork.getGeneratorById(hvdcLine.getConverterStation1().getId());
+            LfVscConverterStationImpl cs2 = (LfVscConverterStationImpl) lfNetwork.getGeneratorById(hvdcLine.getConverterStation2().getId());
+            HvdcAngleDroopActivePowerControl control = hvdcLine.getExtension(HvdcAngleDroopActivePowerControl.class);
+            if (cs1 != null && cs2 != null) {
+                LfHvdc lfHvdc = new LfHvdcImpl(hvdcLine.getId(), lfBus1, lfBus2, lfNetwork, control, parameters.isHvdcAcEmulation());
+                lfHvdc.setConverterStation1(cs1);
+                lfHvdc.setConverterStation2(cs2);
+                lfNetwork.addHvdc(lfHvdc);
+            } else {
+                LOGGER.warn("The converter stations of hvdc line {} are not in the same synchronous component: no hvdc link created to model active power flow.", hvdcLine.getId());
             }
         }
     }

src/main/java/com/powsybl/openloadflow/network/impl/LfVscConverterStationImpl.java

@@ -10,7 +10,13 @@
 import com.powsybl.iidm.network.ReactiveLimits;
 import com.powsybl.iidm.network.VscConverterStation;
 import com.powsybl.iidm.network.util.HvdcUtils;
-import com.powsybl.openloadflow.network.*;
+
+import com.powsybl.openloadflow.network.LfHvdc;
+import com.powsybl.openloadflow.network.LfNetwork;
+import com.powsybl.openloadflow.network.LfNetworkParameters;
+import com.powsybl.openloadflow.network.LfNetworkStateUpdateParameters;
+import com.powsybl.openloadflow.network.LfVscConverterStation;
+import com.powsybl.openloadflow.util.LfHvdcUtils;
 import com.powsybl.openloadflow.util.PerUnit;
 
 import java.util.Objects;
@@ -25,10 +31,13 @@ public class LfVscConverterStationImpl extends AbstractLfGenerator implements Lf
 
     private final double lossFactor;
 
-    private LfHvdc hvdc; // set only when AC emulation is activated
+    private LfHvdc hvdc;
+
+    private final boolean hvdcDandlingInIDM;
 
     public LfVscConverterStationImpl(VscConverterStation station, LfNetwork network, LfNetworkParameters parameters, LfNetworkLoadingReport report) {
         super(network, HvdcUtils.getConverterStationTargetP(station) / PerUnit.SB);
+        this.hvdcDandlingInIDM = LfHvdcUtils.isHvdcDandlingInIdm(station, network);
         this.stationRef = Ref.create(station, parameters.isCacheEnabled());
         this.lossFactor = station.getLossFactor();
 
@@ -55,8 +64,13 @@ public void setHvdc(LfHvdc hvdc) {
 
     @Override
     public double getTargetP() {
-        // because in case of AC emulation, active power is injected by HvdcAcEmulationSideXActiveFlowEquationTerm equations
-        return (hvdc == null || hvdc.isDisabled()) ? super.getTargetP() : 0;
+        if (hvdc == null) {
+            // Because in case one node is not in the LfNetwork, the connectivty of that node is given by IDM
+            return hvdcDandlingInIDM ? 0 : super.getTargetP();
+        } else {
+            // Because in case of AC emulation, active power is injected by HvdcAcEmulationSideXActiveFlowEquationTerm equationsn
+            return hvdc.isAcEmulation() ? 0 : super.getTargetP();
+        }
     }
 
     @Override
@@ -96,8 +110,8 @@ public void updateState(LfNetworkStateUpdateParameters parameters) {
         var station = getStation();
         station.getTerminal()
                 .setQ(Double.isNaN(calculatedQ) ? -station.getReactivePowerSetpoint() : -calculatedQ * PerUnit.SB);
-        if (hvdc == null) { // because when AC emulation is activated, update of p is done in LFHvdcImpl
-            station.getTerminal().setP(-targetP * PerUnit.SB);
+        if (hvdc == null || !hvdc.isAcEmulation()) { // because when AC emulation is activated, update of p is done in LFHvdcImpl
+            station.getTerminal().setP(-getTargetP() * PerUnit.SB);
         }
     }
 }