Improved Transformerless PV Inverter for Wide Input-Voltage Range

Voltage-source inverters are widely used in solar applications. However, when the voltage of the PV array is less than the peak output voltage of the inverter under shading condition (SC), they should be shut down. Therefore, a boost converter should be inserted between the PV array and the PV inverter (PVI) to boost the voltage of the PV array under SC, but it sustains the full power of the PVI under normal conditions (NCs). To address the problem, an improved transformerless PVI with a minimum power processing unit (MPPU) is proposed. The MPPU is composed of a minimum voltage compensation unit (MVCU) parallelled with a diode. The MVCU does not work under NC, while it only works under SC. The output voltage of the MVCU is the differential voltage between the absolute value of the output voltage of the inverter and the voltage of the PV array under SC, so it sustains the minimum power under SC and can operate in a wide input-voltage range. The inverter is a single-stage system, so efficiency of the system is high. The operating principle of the system is illustrated. A cooperative control strategy of the PVI is depicted. Design guidelines and example are given. Finally, experimental results verify the theoretical analysis.