Optimized Desien Methodology Research Of The Zero-voltage Switching Grid-connected 3-phase Inverter

With the development of the society and improvement of the living condition,the energy consumption,especially the electrical energy consumption,has been sustainably growing.Traditional fossil energy resources face several issues such as limited reserves,environmental pollution and greenhouse gases emission.In contrast,renewable energies including solar energy and wind energy have the advantages as almost unlimited reserves,environmental friendly and wide distribution.Consequently,renewable energy generation systems,especially solar generation system,have drawn more and more attentions and expectations.In the solar generation system,grid-connected inverter plays as an interface between photovoltaic panel and grid.Its power conversion efficiency and power density are two crucial performance indicators.Compared to the traditional hard-switching inverter,soft-switching inverter has lower switching loss,which makes it more likely to achieve both high efficiency and high power density.Among all of the reported soft-switching inverters,compound active clamped(CAC)inverter has several merits such as simple auxiliary circuit,low voltage stress and high conversion efficiency.The design of the parameters needs to meet the requirements of the grid power quality,realization of the soft switching,temperature rise and achieve efficiency and power density goals simultaneously.Utilizing traditional design methodology,it is difficult to achieve a global optimum result of considerable amounts of parameters coupled with each other.On the other hand,the idea that transfers the power electronics converter design issue into solving an optimization problem has been reported.The design goal such as system loss or dimensions is described as a target function of several design parameters.With optimization algorithm,the global optimum result can be achieved.Similar methodology has been utilized in designing several hard-switching converters.Utilizing optimization methodology to design soft-switching inverter,however,has not been reported yet.In view of the situation,this paper proposes a design methodology of the CAC soft-switching inverter.The detailed contents include:The zero-voltage turn-off loss models of different IGBT modules are obtained through experimental test under different buffer capacitance and current conditions.The core loss of the resonant inductor is tested and modeled under PWM stimulation condition.Besides,the loss models of the resonant inductor windings and filter inductor,the dimensional models of the resonant inductor,filter inductor,clamping capacitor and heat sink are also introduced.The total loss of the inverter and the volume of the key components are described as the target functions.The design requirements,such as current THD and temperature rise,are set to be the constrained conditions.Subsequently,the design process is transferred into solving the constrained nonlinear optimization problem.With the optimization algorithm,Pareto front on efficiency vs.power density of the soft-switching inverter can be obtained.The design parameters are chosen according to the target of high efficiency and high power density.The resonant inductor operates with current of high frequency and high amplitude.The design target is to achieve high efficiency and miniaturization.Based on the design parameters obtained from the global optimization,the detailed design is proceeded with the help of the finite element analysis(FEA).Aiming to minimize the power dissipation,barrel structure windings and flat structure windings are analyzed.The optimum winding position,foil thickness are chosen.And the experimental results show that the performance of the prototype meets all the design requirements.According to the characteristics of the soft-switching inverter,the crucial loop which is sensitive to the parasitic parameters is analyzed.Utilization of the bus bar with laminate structure and proper arrangement of the key components reduce the perimeter and the area of the crucial loop.Consequently,the stray inductance of the crucial loop is distinctively reduced.Both FEA results and experimental results reveal the improvement.A 30kW soft-switching inverter prototype is built according to the designed parameters.The experimental results shows that all of performance indicators including current THD,temperature rise of the resonant inductor and heat sink meet the design requirements.The highest efficiency and the efficiency at the full load power condition is 98.3%and 98.1%respectively.The proposed soft-switching inverter has the highest efficiency in all of reported soft-switching inverters using IGBT devices.The proposed soft-switching inverter has a distinct advantage of the efficiency over hard-switching inverter and the soft-switching inverter designed by traditional method.Moreover,prominent volume reductions of resonant inductor,filter inductor and clamping capacitor have been achieved with the proposed design methodology.Both measured efficiency and power density meets the theoretical design target well.