Research On THD And Efficiency Optimization Variable Frequency Control Strategy In GaN-based Full-bridge Inverter

With the increasingly severe global energy consumption and environmental pollution,the renewable energy power generation technology represented by photovoltaic power generation has become a new research hotspot.The inverter is an important part of the photovoltaic power generation system.To improve its power density and efficiency,it has become a new trend to apply the third generation wide bandgap semiconductor device GaN to inverters.The characteristic of GaN devices is suitable for high frequency operation,so GaN-based inverter can maintain high efficiency under high switching frequency while achieving higher power density and lower THD.Working characteristics of GaN-based inverter under the continuous current mode(CCM)and boundary current mode(BCM)are analyzed mainly from two aspects:efficiency,THD carries on the discussion and comparison.According to their respective problems,three new control strategy is adopted,and the corresponding simulation and experiment proved that they can achieve a better control effect.Firstly,this paper analyzes the operation characteristics of GaN-based inverter under traditional CCM control.Switches of the inverter under CCM control are worked with hard-switching.Because switches of GaN-based inverter are worked at high frequency,the switching loss of the inverter increases,which leads to the reduction of the efficiency of the whole machine.Therefore,a new variable frequency control strategy is adopted in this paper,which can reduce the switching loss of the whole machine on the premise of ensuring THD requirements,and a 150 W test prototype is built for experimental verification.Secondly,this paper analyzes the operation characteristics of the inverter under traditional BCM control.Under the traditional BCM control,the switches of the GaN-based inverter are worked with soft-switching,which makes it maintain high efficiency at the high switching frequency.But the traditional BCM control has the problem that the output voltage has distortion at the zero-crossing point.In this paper,the problem is analyzed and the cause of distortion is summarized.The existing method to improve the output voltage zero-crossing distortion problem is to adopt the SHCM control strategy,but this control strategy does not completely solve the distortion problem.Therefore,this paper adopts a new variable frequency control strategy,unipolar frequency doubling SHCM control strategy,which to some extent solves the problem,and a 150 W test prototype is built for experimental verification.Finally,the working characteristics of the inverter under the hybrid control are analyzed,and a new hybrid control strategy is adopted.Using the SHCM control strategy,although the output voltage zero-crossing distortion problem can be solved,the efficiency of the whole machine still needs to be improved.In this chapter,the characteristics of hybrid unipolar and bipolar CBCM control strategy,hybrid unipolar and unipolar frequency doubling SHCM control strategy,hybrid unipolar SHCM and unipolar CBCM control strategy are analyzed,and on these bases,the hybrid unipolar SHCM and bipolar CBCM control strategy is adopted.A more efficient hybrid control strategy is realized to solve the problem of output voltage zero-crossing distortion.The strategy is verified by simulation and experiment.