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.