A Kind Of Voltage Sharing Circuit For The DC Side Voltage Divider Capacitor Of Forward Clamp Type H10 Three-Phase Inverter

As a sustainable and environmentally friendly energy production method,photovoltaic power generation is the key direction of energy reform and plays an important role in the process of achieving the goal of carbon neutrality in China.Non-isolated three-phase inverter has become the key direction of inverter development with its higher conversion efficiency and smaller size,but the loss of isolation transformer will make the photovoltaic panel to the ground parasitic capacitance and the earth,the power grid form a loop,resulting in leakage current,excessive leakage current will not only affect power quality,but also endanger the safety of operators.Many improvements have been proposed for the leakage current problem,one of which is a forward clamp H10 three-phase inverter by adding a clamp switch tube and bus switch to make the common-mode voltage change between Ud/3 and 2Ud/3 to suppress leakage current.However,the parasitic capacitance of the clamp switch will make the voltage of the DC side divider capacitor uneven,which will affect the change of the common mode voltage of the system,which makes the effect of this improved topology in suppressing leakage current worse.This paper proposes a DC side voltage divider capacitor equalization circuit for forward clamp type H10 three-phase inverter,this voltage sharing topology includes four switching transistors and two voltage sharing inductors,which are divided into two parts with the same principle and structure,one part is used to equalize the voltage of the voltage divider capacitor C_dc2and C_dc3,and the other part is used to equalize the voltage of the series equivalent capacitor of the balance capacitor C_dc1and the remaining two voltage divider capacitors.Then,a control strategy for this voltage-sharing circuit is proposed,which uses the sampling circuit to compare the voltage divider capacitor voltage with the reference value to obtain a preliminary control signal.Then the preliminary control signal is cross-cut with the unilateral triangle wave to obtain the control signal of the corresponding switch tube to limit the current flowing through the switch tube.When the voltage of the voltage divider capacitor on the DC side is higher than the reference value,the corresponding switch is turned on,the excess energy is absorbed by the voltage-equalizing inductor,and the energy in the voltage-sharing inductor is transferred to the low-energy voltage-divider capacitor by freewheeling through the switching diode for the remainder of the duty cycle.On the basis of not affecting the working state of the forward clamp H10 three-phase inverter,this voltage-sharing scheme uses additional circuit structure to forcibly change the voltage of the voltage divider on the DC side to achieve the purpose of equalizing the voltage and improve the effect of this inverter in suppressing leakage current.Finally,the system parameters of the forward clamp H10 three-phase inverter and the device parameter design process of the voltage equalizing circuit are given,and the loss analysis of the switching devices in the voltage sharing circuit is carried out.Then,a system simulation and experimental platform is built,and the results show that the DC side voltage divider voltage of the H10 three-phase inverter can be suppressed by equalizing the forward clamp H10 three-phase inverter by the voltage-sharing circuit,so that the inverter has a better leakage current suppression effect,which is consistent with the theoretical analysis and verifies the correctness of the scheme.