Optimization Design Of MPPT Chip And Controller Used For Solar Panel

In the 21st century,the reserve of traditional fossil fuels available reduces year by year and global climate change and environment issues are becoming significant problems.In this case that the idea of green development is rooted in the public mind,developing renewable resources has been an inevitable trend.Therefore,as a clean resource with mature technology and high industrialization,the Solar Photovoltaic(PV)Generation is concerned significantly in many countries.To implement the PV generation,in addition to the research in material science,the power conversion circuit is a key aspect.Actually,the output of PV panels should not be connected to the grid or load directly,because the output power will change greatly from 0 watt to the theoretical maximum value according to different loads.As a result,a circuit with the function of maximum power point tracking(MPPT)is required to guarantee the maximum output power of PV panels.A MPPT controller consists of two modules:DC/DC converter as the architecture and MPPT chip as the control center.The research presented in this paper includes both modules.The main work and innovation of this paper are:(1)Based on the Buck topology,the model of MPPT controller is established.According to the model,the loop transfer function is derived and system stability is analyzed.Finally,the typeⅢ compensation work is adopted to guarantee the MPPT controller operates stably in Discontinuous Current Mode and Continuous Current Mode.The bode diagram shows the loop bandwidth can satisfy the requirement of Switching Mode Power Supply design.(2)Based on the Buck topology,the loss model of MPPT controller is built and the power dissipation equation of every device in the system is derived.Based on the loss model,the power conversion efficiency is optimized from 80%to 91.9%.Although the loss model is derived from Buck topology,it can be used in the efficiency optimization of Boost topology.(3)The optimization of analog circuits in MPPT chip.The circuits include voltage sampling circuit,current sensing circuit,voltage and current bias circuits.The work in this paper greatly improves the PVT performance and sampling precision of the circuits from 18%to 3%,which make the precise tracking of maximum power point of PV panels possible.(4)The design and implementation of a new MPPT algorithm circuit.In the traditional MPPT chip based on an analog comparator,the tracking precision and power range is lowered by the limited input voltage and system or random offset existing.It is complex to implement a mixed-signal MPPT chip by using an ADC.The common method is to charge a capactitor with current proportional to PV power and counter the periods of a clock in the charging time t.However,the tracking precision will become poor with PV power increasing.To solve the issues,the MPPT chip presented in this paper converses a current inversely proportional to PV power to digital values and implements the functions of calculating,memorizing and comparing with only a counter.As a result,the maximum tracking power range is from 1W to 40W(42%)and tracking precision 1%-2%(from 98%to larger than 99%)with the equivalent circuit complexity.(5)The design and implementation of inverse operation circuit.The circuit implements the function of calculating out the output power of PV panels according to the input signals from voltage and current sensing modules and then inversing it.The output of the module is the inverse of PV output power.What’s more,by adopting the complementary principle,the inverse operation circuit is designed to be insensitive to PVT variation.The output offset is lower than 1%at the same input voltage and current.