A power conversion system, comprising: an active rectifier circuit comprising a plurality of rectifier switching devices (S1-S6) coupled to receive AC input power from an external power source and operative to provide a DC output according to a plurality of rectifier switching control signals , wherein the AC input of the active rectifier circuit is connected to three AC input phase terminals of the external power source through an LCL input filter circuit ; and a controller operative to: generate the rectifier switching control signals to operate the rectifier switching devices (S1-S6); at the LCL input filter circuit, measure a first AC input voltage signal associated with a first AC input phase, a second AC input voltage signal associated with a second AC input phase, and a third AC input voltage signal associated with a third AC input phase; using current measurements at the LCL input filter circuit, determine a first grid current signal (Ir), a second grid current signal (Is), and a third grid current signal (It); if the active rectifier circuit is not in a switching mode, identify a suspected AC input phase loss condition if two of the AC input voltage signals are in phase with one another; and if the active rectifier circuit is in the switching mode, identify the suspected AC input phase loss condition if an absolute value of a sum of any two of the grid current signals is less than a predetermined non-zero threshold. an active rectifier circuit comprising a plurality of rectifier switching devices (S1-S6) coupled to receive AC input power from an external power source and operative to provide a DC output according to a plurality of rectifier switching control signals , wherein the AC input of the active rectifier circuit is connected to three AC input phase terminals of the external power source through an LCL input filter circuit ; and a controller operative to: generate the rectifier switching control signals to operate the rectifier switching devices (S1-S6); at the LCL input filter circuit, measure a first AC input voltage signal associated with a first AC input phase, a second AC input voltage signal associated with a second AC input phase, and a third AC input voltage signal associated with a third AC input phase; using current measurements at the LCL input filter circuit, determine a first grid current signal (Ir), a second grid current signal (Is), and a third grid current signal (It); if the active rectifier circuit is not in a switching mode, identify a suspected AC input phase loss condition if two of the AC input voltage signals are in phase with one another; and if the active rectifier circuit is in the switching mode, identify the suspected AC input phase loss condition if an absolute value of a sum of any two of the grid current signals is less than a predetermined non-zero threshold. generate the rectifier switching control signals to operate the rectifier switching devices (S1-S6); at the LCL input filter circuit, measure a first AC input voltage signal associated with a first AC input phase, a second AC input voltage signal associated with a second AC input phase, and a third AC input voltage signal associated with a third AC input phase; using current measurements at the LCL input filter circuit, determine a first grid current signal (Ir), a second grid current signal (Is), and a third grid current signal (It); if the active rectifier circuit is not in a switching mode, identify a suspected AC input phase loss condition if two of the AC input voltage signals are in phase with one another; and if the active rectifier circuit is in the switching mode, identify the suspected AC input phase loss condition if an absolute value of a sum of any two of the grid current signals is less than a predetermined non-zero threshold. <EOS>