Research On Voltage Balance Control Of Series Photovoltatic Modules With Different Power

With the widespread adoption of photovoltaic applications,there are still many problems in its development technology.For example,in order to output maximum power,how to cascade multiple photovoltaic modules with different powers.Under normal circumstances,the same modules are used for each photovoltaic panel to avoid the above situation in the system.However,in actual photovoltaic applications,certain phenomena inevitably occur,such as light occluded,voltage limited,etc.,leading to mismatch between photovoltaic modules.This means the output voltage of system is cascaded by photovoltaic modules with different power.So ultimately,it will cause power decrease of photovoltaic system,even more,electronic components destroyed.In view of this,the thesis proposes a control strategy of voltage balancing,which is suitable for small and medium-sized photovoltaic systems.At the same time,a voltage balancing controller is designed to verify the feasibility of the scheme.Firstly,through the analysis of actual cases,the thesis illustrates the impact and hann of the mismatched power generation system between photovoltaic modules.At the same time,the output characteristics and conditions which are at the maximum power point are studied in the distributed photovoltaic power generation system.This can prove the necessity of this study,and also prepare for the further research and model building about photovoltaic systems.Secondly,a new type of bidirectional isolated DC/DC voltage balancing circuit is proposed.In the design,on the one hand,a large capacity capacitor is introduced to ensure the voltages of transformers secondary side are balanced.On the other,a great deal of the effort has been paid in bidirectional power transfer,including deriving the transmission power expression as the theoretical support and determining the algorithm of phase-shift control,etc.In this way,fast response times can be achieved and the output voltage balancing will be guaranteed.Thirdly,Photovoltaic system models are built by PSIM simulation software,including max power point tracking with dual-loop PI control in Buck circuit,voltage balancing control by phase-shift and the work results of photovoltaic power generation system under mismatch condition.The simulation results verify the rationality of the design.Finally,a voltage balancing controller based on STM32F103C8T6 chip is designed,including a Buck circuit and an isolated half-bridge DC/DC circuit.In the design of hardware circuit,the main tasks include parameter calculation of components,such as transformer,inductor,capacitor,etc..Besides,there are various modular circuits designed,such as sampling of analog,signal processing,MOSFET drive circuits,auxiliary power and ARM minimum system.In the part of software design,major control program is designed.Configuration of PWM,AD conversion interrupt service routine and algorithm optimization are also included.Through experimental verification,the test results show that the photovoltaic integrated modules are able of working at the maximum power point,and not only ensure the voltage balancing control,but also meet the requirements in the overshoot and dynamic response.