Single-stage Non-isolated Dual Cuk Inverter

With the rapid development of the new energy industries, high-performance grid-connected inverter is attracted more and more attention. However, the traditional step-down voltage-source-inverter(VSI) is not suitable for new energy system with a wide range of DC input voltage. In order to stabilize the input voltage, the high-performance step-up or step-down DC-DC converter is widely used in the new energy system as the front-end stage of the VSI. However, the front-end converter not only complicates the system, but also shortens the system life because of the additional DC bus electrolytic capacitor for reduction of ripple voltage.Firstly, aiming at the shortcomings of the traditional VSI, this paper on the basis of reading a lot of domestic and foreign literature combined with combined inverter structure method, presents a novel single-stage non-isolated dual Cuk inverter, whose output voltage could higher or lower than the input voltage. The traditional DC-DC combined inverters are composed of two identical DC converters, in which the number of passive devices is two times of the single converter. Acorrding to the characteristics of Cuk converter, this paper presents a novel single-stage non-isolated dual Cuk inverter, whose passive device numbers are as the same as the Cuk converter, only the half of that in the traditional DC-DC combined inverters.Thus, the power desinity is improved. In addition,the output voltage of the novel inverter could hogher or lower than the input voltage because of the ability to buck/boost voltage of Cuk DCconverter. Furthermore, according to the nolinear feature of the Cuk converter, a nolinear PWM scheme is used. The invernal capacitor value is decreased by using the nolinear PWM scheme, thus the dual Cuk inverter doesn’t need electrolytic capacitor any more, increases its life and reliability.Lastly the mathematical model based on the nplinear PWM scheme is deduced and the closed loop control is studied.Simulation results indicate that the dual Cuk inverter has the ability to Buck/Boost input voltage, which is fit for the occasion with wide range fluctuating input voltage, and restraints the input and load abrupt disturbance.To verify the theroretical analysis and simulations, a 500V·A prototype is buildt andthe grid-off and grid-connected experiments are performed. The experimental results have proved that the theroretical analysis and simulations are correct.