The common-mode leakage current should be carefully considered when designing a transformer-less photovoltaic (PV) inverter since the leakage current can cause the output current distortion and increase the operational risk. The unipolar SPWM of traditional H-bridge inverter can produce the superior output performance but will cause a high-frequency fluctuated common-mode voltage and consequently the non-negligible leakage current. To attenuate the fluctuation phenomena of common-mode voltage,

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... ew neutral-point-clamped circuits have been designed to clamp the neutral point voltage and maintain the common mode voltage constant. This paper analyzes the equivalent common mode circuit of single-phase inverters and proposes a generalized design principle of multi-terminal neutral-point-clamped circuits, whose unidirectional and bidirectional variations are fully analyzed respectively. Subsequently, two types of single-phase PV inverters with the neutral-point-clamped circuits are proposed, respectively. Also, the operational losses and component counts are compared between the proposed topologies and the traditional NPC inverters. The experimental results verified the theoretical findings. Index Terms -Photovoltaic inverter, neutral-point-clamped circuit, common-mode voltage, single-phase inverter. 1