Research On The Load Adaptability Of Off-Grid Micro-High Efficiency Inverter

With the excessive use of fossil fuels,the world is facing with the dual test of energy crisis and environmental pollution.The development and utilization of new energy is being a research hotspot around the world.And solar energy has the outstanding advantages of its abundance,safety and reliability in new energy.So photovoltaic power generation system has been attached importance to by a lot of countries.As a core component of photovoltaic power generation system,the performance of inverter plays a crucial role in the efficiency and stability of the whole system.In addition to photovoltaic inverter systems,inverters appear in many industrial and daily applications.Among them,off-grid inverter applications are: electric vehicles,on-board power supply,household photovoltaic inverter system.Off-grid inverters are directly loaded,which requires high load adaptability.Load adaptability is an important parameter to measure the performance of an inverter.The switching frequency of hysteresis current control is not fixed,which makes it difficult to design the filter and the output current spectrum is scattered.In this paper,several typical hysteresis current modulation modes are compared.The bipolar CCM mode is adaptive,insensitive to load,with good output waveform quality but high switching frequency.The switching frequency of unipolar CCM mode is low and the mode is adaptive,but the low frequency harmonic content is high.The inverter controlled by unipolar Boundary Current Mode(BCM)modulation has the characteristics of low cost and high power density,but the switching frequency controlled by unipolar control will reduce to zero when the load voltage passes zero.The BCM modulation is sensitive to the load current,and there is a large frequency distortion near the load current crossing zero for capacitive and inductive load.A unipolar-bipolar hybrid BCM modulation is proposed to eliminate the zero-crossing and high-frequency distortion of switching frequencies while maintaining the efficiency advantage of the unipolar BCM modulation.Finally,an experimental platform was set up for verification.The experimental results show that the proposed unipolar-bipolar hybrid BCM modulation has good load adaptability to frequency.