In recent years, non-isolated inverters have gained widespread attention in commercial and residential PV grid-connected systems due to their cost, efficiency, and flexibility advantages. However, in practical applications, the output voltage of the PV panel is generally low. Due to the loss of the electrical isolation of the transformer, the high-frequency switching action of the conventional inverter may produce a common mode voltage applied to the parasitic capacitance between the PV array and the ground, resulting in a common mode leakage current, which affects the safe operation of the system. This paper proposes a non-isolated five-level Boost inverter with no leakage current and its dual-mode modulation strategy to enhance the applicability and practicability of the inverter.

Firstly, the circuit structure combines the dual-output Boost converter with the five-level inverter to create a five-level Boost inverter topology. The Boost capability is expanded, suitable for PV power generation applications with low DC voltage on the input side. Secondly, the dual-mode modulation strategy of unipolar carrier level shifted is studied, providing five-level output capability and increasing the equivalent switching frequency under the same carrier frequency. By comparing the PV panel’s DC output voltage and the grid voltage’s absolute value, two working modes of Boost voltage and buck voltage are realized, and the energy transmission efficiency of the converter is improved. In addition, a five-level voltage is output on the side of the bridge arm, and more levels make the output voltage closer to the sine wave, which is conducive to improving the quality of incoming current. Furthermore, the negative polarity of the DC side of the topology is directly connected to the voltage neutral of the AC side to eliminate the common mode leakage current of the stray capacitor to the ground. Finally, the working principle of the inverter circuit and the realization method of the specific modulation strategy are provided, and the key parameters are designed.

An experimental prototype was built. The experimental results show that: (1) The inverter’s two working modes overcome the limitation that the traditional multilevel inverter can only step down, making it suitable for a wide range of input voltage changes. (2) The common ground structure can effectively inhibit leakage current. (3) The output voltage V_AB of the bridge arm presents five voltage levels, and the energy storage capacitor can be charged and discharged at a high switching frequency, ensuring the stationarity of the output voltage of each level. Hence, the output voltage waveform is symmetrical in the positive and negative half cycles. At the same time, the incoming current i_g can accurately track the phase of the grid voltage V_g, producing a smooth output waveform with little distortion, which meets the requirements for grid-connected current quality. (4) The proposed inverter can output reactive power output, which meets the requirements of non-unit power factor operation in IEEE grid-connected standards.