Fix non impedant phase shifter with active power flow control activated

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

@@ -518,6 +518,11 @@ public void fix(boolean minImpedance, double lowImpedanceThreshold) {
             for (LfBranch branch : branches) {
                 branch.setMinZ(lowImpedanceThreshold);
             }
+        } else {
+            // zero impedance controller phase shifter is not supported
+            branches.stream()
+                    .filter(LfBranch::isPhaseController)
+                    .forEach(branch -> branch.setMinZ(lowImpedanceThreshold));
         }
     }
 

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

@@ -266,15 +266,14 @@ public boolean isConnectedAtBothSides() {
 
     @Override
     public void setMinZ(double lowImpedanceThreshold) {
-        if (piModel.setMinZ(lowImpedanceThreshold, true)) {
-            LOGGER.trace("Branch {} has a low impedance in DC, set to min {}", getId(), lowImpedanceThreshold);
-            dcZeroImpedance = false;
-
-        }
         if (piModel.setMinZ(lowImpedanceThreshold, false)) {
             LOGGER.trace("Branch {} has a low impedance in AC, set to min {}", getId(), lowImpedanceThreshold);
             acZeroImpedance = false;
         }
+        if (piModel.setMinZ(lowImpedanceThreshold, true)) {
+            LOGGER.trace("Branch {} has a low impedance in DC, set to min {}", getId(), lowImpedanceThreshold);
+            dcZeroImpedance = false;
+        }
     }
 
     private static boolean isZeroImpedanceBranch(PiModel piModel, boolean dc, double lowImpedanceThreshold) {

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

@@ -600,4 +600,34 @@ void incrementalPhaseShifterSensiTest() {
             assertEquals(-43.007011829925496, di2t12p, 0d);
         }
     }
+
+    @Test
+    void activePowerflowControlAndNonImpedantPhaseShifterTest() {
+        selectNetwork(PhaseControlFactory.createNetworkWithT2wt());
+        parameters.setPhaseShifterRegulationOn(true);
+        t2wt.setR(0).setX(0);
+        t2wt.getPhaseTapChanger().setRegulationMode(PhaseTapChanger.RegulationMode.ACTIVE_POWER_CONTROL)
+                .setTargetDeadband(1)
+                .setRegulating(true)
+                .setTapPosition(1)
+                .setRegulationTerminal(t2wt.getTerminal1())
+                .setRegulationValue(100);
+
+        LoadFlowResult result = loadFlowRunner.run(network, parameters);
+        assertTrue(result.isOk());
+        assertActivePowerEquals(112.197, line2.getTerminal1());
+        assertActivePowerEquals(-112.019, line2.getTerminal2());
+        assertEquals(2, t2wt.getPhaseTapChanger().getTapPosition());
+
+        line1.setR(0).setX(0);
+        t2wt.setR(2.0).setX(100.0);
+        t2wt.getPhaseTapChanger()
+                .setRegulationTerminal(line1.getTerminal1())
+                .setTapPosition(0);
+
+        assertTrue(result.isOk());
+        assertActivePowerEquals(-12.006, line1.getTerminal1());
+        assertActivePowerEquals(112.197, line2.getTerminal1());
+        assertEquals(0, t2wt.getPhaseTapChanger().getTapPosition());
+    }
 }