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For utility-scale photovoltaic (PV) power plants, the trend goes towards larger installations with reduced levelized costs of electricity. Further cost reductions can be achieved by modular and redundant inverter topologies, which enable higher reliabilities and a better overall system availability. In this paper, a comparative evaluation of selected three-phase single-and multi-stage voltage source inverters with rated power of 50kW for modular utility-scale PV plants is presented. Based on detailed loss, volume and thermal models, the inverter systems are designed according to a variety of constraints and standards covering a wide range of practical issues, such as grid codes, EMI requirements and lifetime considerations. Finally, for different operational switching frequencies, the optimal topologies are identified by means of an analysis regarding achievable efficiencies, power density and required semiconductor chip areas.