Fixed PST Flow Regulation on non impedant branch causing exception

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

@@ -481,9 +481,9 @@ public void fix(boolean minImpedance, double lowImpedanceThreshold) {
                 branch.setMinZ(lowImpedanceThreshold);
             }
         } else {
-            // zero impedance controller phase shifter is not supported
+            // zero impedance phase shifter controller or controlled branch is not supported
             branches.stream()
-                    .filter(LfBranch::isPhaseController)
+                    .filter(b -> b.isPhaseController() || b.isPhaseControlled())
                     .forEach(branch -> branch.setMinZ(lowImpedanceThreshold));
         }
     }

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

@@ -278,7 +278,10 @@ public boolean isConnectedAtBothSides() {
     @Override
     public void setMinZ(double lowImpedanceThreshold) {
         for (LoadFlowModel loadFlowModel : List.of(LoadFlowModel.AC, LoadFlowModel.DC)) {
-            if (piModel.setMinZ(lowImpedanceThreshold, loadFlowModel)) {
+            if (piModel.setMinZ(lowImpedanceThreshold, loadFlowModel) ||
+                    (LoadFlowModel.DC.equals(loadFlowModel) && isZeroImpedance(loadFlowModel))) {
+                // Note: For DC load flow model, the min impedance has already been set by AC load flow model but
+                //       the zero impedance field must still be updated.
                 LOGGER.trace("Branch {} has a low impedance in {}, set to min {}", getId(), loadFlowModel, lowImpedanceThreshold);
                 zeroImpedanceContextByModel.get(loadFlowModel).zeroImpedance = false;
             }

src/test/java/com/powsybl/openloadflow/ac/AcLoadFlowPhaseShifterTest.java

@@ -621,15 +621,16 @@ void activePowerflowControlAndNonImpedantPhaseShifterTest() {
         assertActivePowerEquals(-112.019, line2.getTerminal2());
         assertEquals(2, t2wt.getPhaseTapChanger().getTapPosition());
 
-        line1.setR(0).setX(0);
+        line1.setR(0.0).setX(0.0);
         t2wt.setR(2.0).setX(100.0);
         t2wt.getPhaseTapChanger()
                 .setRegulationTerminal(line1.getTerminal1())
                 .setTapPosition(0);
+        LoadFlowResult result2 = loadFlowRunner.run(network, parameters);
 
-        assertTrue(result.isOk());
-        assertActivePowerEquals(-12.006, line1.getTerminal1());
-        assertActivePowerEquals(112.197, line2.getTerminal1());
-        assertEquals(0, t2wt.getPhaseTapChanger().getTapPosition());
+        assertTrue(result2.isOk());
+        assertActivePowerEquals(100.0, line1.getTerminal1());
+        assertActivePowerEquals(0.0, line2.getTerminal1());
+        assertEquals(1, t2wt.getPhaseTapChanger().getTapPosition());
     }
 }

src/test/java/com/powsybl/openloadflow/network/impl/LfNetworkLoaderImplTest.java

@@ -204,4 +204,17 @@ void validationLevelTest5() {
         PowsyblException e = assertThrows(PowsyblException.class, () -> Networks.load(network, new FirstSlackBusSelector()));
         assertEquals("Only STEADY STATE HYPOTHESIS validation level of the network is supported", e.getMessage());
     }
+
+    @Test
+    void testMinImpedance() {
+        network = EurostagTutorialExample1Factory.create();
+        network.getLine("NHV1_NHV2_1").setR(0.0).setX(0.0).setB1(0.0).setB2(0.0).setG1(0.0).setG2(0.0);
+        List<LfNetwork> lfNetworks = Networks.load(network, new FirstSlackBusSelector());
+        LfBranch line = lfNetworks.get(0).getBranchById("NHV1_NHV2_1");
+        assertTrue(line.isZeroImpedance(LoadFlowModel.AC));
+        assertTrue(line.isZeroImpedance(LoadFlowModel.DC));
+        line.setMinZ(10); // for both AC and DC load flow model
+        assertFalse(line.isZeroImpedance(LoadFlowModel.AC));
+        assertFalse(line.isZeroImpedance(LoadFlowModel.DC));
+    }
 }