Design And Implementation Of Improved H7 Inverter For Leakage Current Suppression

In recent years,photovoltaic power generation has attracted extensive attention at home and abroad because of its advantages of no pollution and no depletion.The traditional photovoltaic inverter has high power loss due to the large volume,heavy weight and high cost of the transformer.However,the inverter system without isolation transformer lacks electrical isolation,so there is a large amount of leakage current.High leakage current will cause electromagnetic interference and affect the performance of the system.Therefore,how to suppress the leakage current of non isolated photovoltaic inverter has become a hot issue in the current research.To solve this problem,an improved H7 inverter topology for leakage current suppression is proposed to suppress the leakage current in transformer free photovoltaic power generation system.Based on the topology of H7 inverter,a clamping circuit is added to construct an improved topology of H7 inverter.The clamping circuit is composed of three voltage dividing capacitors with equal capacitance and three clamping switches.The voltage dividing capacitor divides the DC input side voltage upv into four potential points,namely 0、U_PV/3、2U_PV/3 and U_PV.Two clamping switches are connected between the 2U_PV/3 potential point and the drain common point of the upper bridge arm switch,and one clamping switch is connected between the U_PV/3 potential point and the drain common point of the upper bridge arm switch,so that the inverter can,The common mode voltage can be clamped on U_PV/3 or 2U_PV/3.In addition,the clamping circuit can also keep the common mode voltage of the inverter stable in the freewheeling state.Then,according to the different conduction modes of clamp switches,a common mode voltage high frequency control scheme is proposed.It means that the common mode voltage in the freewheeling state is inconsistent with the common mode voltage in the previous state.The frequency of the common mode voltage is three times the switching frequency.On the basis of ensuring that the voltage at the clamping point is U_PV/3 or 2U_PV/3,the frequency of the common mode voltage is increased,and the common mode loop impedance of the circuit is correspondingly increased.The common mode characteristics of the system are optimized and the suppression effect of leakage current is better.Finally,according to the technical indexes of the inverter,the relevant parameters of the main circuit and control circuit are designed.Firstly,the correctness of the theoretical analysis and the feasibility of the design scheme are confirmed through the simulation results of saber,and then a principle prototype with an output of200W per phase is built.Through the comparative analysis of the relevant experimental waveforms of H7 inverter and improved H7 inverter,it is confirmed that the improved H7 inverter has better leakage current suppression effect than H7 inverter,and the correctness of the design scheme in this paper is also verified.