Research On A Combined Three-Phase Leakage-Free Photovoltaic Inverter With Flying Capacitor

With the introduction of the dual carbon target,the global demand for renewable energy is increasing.As solar power system is an important part of renewable energy,the performance of PV inverter such as efficiency,reliability and cost is especially important.Compared with traditional isolated PV inverters,non-isolated PV inverters have the advantages of small size,lightweight,high efficiency and low cost,and their applications are promising and expected to become one of the important technical means to promote the achievement of the dual carbon goal.However,due to the lack of electrical isolation of the transformer,its existence of the leakage current problem will have adverse effects on the system and even endanger the personal safety of the practitioners.Therefore,solving the leakage current problem has become a research hotspot.This paper first gives an overview of PV inverter development and grid-connected standards,and introduces several representative non-isolated PV inverter topologies.Then,the mechanism of leakage current generation is analyzed,and the mathematical model of non-isolated PV inverter is established,and the means of leakage current suppression or elimination are analyzed and derived.In this paper,a combined three-phase non-leakage current PV inverter topology with flying span capacitor is proposed based on the new single-phase H5 inverter topology,which can achieve the effect of completely eliminating leakage current by directly connecting the negative end of the PV panel to the ground and short-circuiting the parasitic capacitance of the PV panel to the ground,stabilizing the common-mode voltage;each phase of this topology operates independently of each other,and the working states do not affect each other,which is easy to realize the decoupling control of three phases,and the inverter has a strong ability to carry asymmetric loads.The working principle and working mode of the circuit topology are analyzed in detail,a three-phase SPWM closed-loop control scheme is given,simulation experiments are conducted,and a complete hardware circuit selection and PCB schematic design are carried out according to the requirements,and the system is divided into two parts: the main circuit and the control circuit.Finally,a prototype inverter with 200 W output per phase is built and the relevant experimental measurements are performed according to the given parameters.The simulation and physical experimental results are consistent with the theoretical analysis,which verifies the correctness and validity of the theoretical analysis.