| In recent years，energy crisis and environmental pollution problems havehighlighted and become an inevitable issue. Nowadays people focus their attentionupon renewable energy especially solar energy for incomparable advantages such asabundant storage, using safely, developing clean, available employing local materials.As a green new energy supply, solar photovoltaic power has been more and morespread.Electric bicycles become more and more popular as a means of transportationbecause of its characteristics, for example, lightweight, fast, economy, environmentalprotection and so on. But batteries in use process still remain pollution, inconvenientcharging and halfway off.In this paper, a solar electric bicycle based on the electric bicycle technologycombining with a photovoltaic technology was designed. The batteries can becharged at any time in the sunlight, effectively overcoming the widespreaddisadvantages such as charging too long, too often, and short line continuationmileage. It further improve the environmental protection of electric bicycles.The paper mainly completed the following several aspects:(1)Considering the power requirements of electric bicycles we chose solar cellsof which the maximum output power is300W as power supply. The mathematicalmodel of the solar cell has been set up by matlab to get its output characteristic. Alsoa kind of control methods was proposed combining the constant voltage method withperturbation and observation method with variable step, by analyzing the feature ofthe maximum power point tracking (MPPT) methods. The simulation results showthat the method cut the time of reaching the maximum power point in half, the outputpower volatility at the maximum power point reduced to1.4W from4W compared tothe conventional perturbation and observation method, so it reduced the power loss.(2)The charging and discharging characteristics of li-ion batteries in electricbicycles were studied. In terms of solar cells, a limited source, a control method forcharging lithium batteries was proposed.(3)The DC-DC converter was studied and the SEPIC converter was chosen for the system. To get its frequency characteristics the small AC signal modeling ofSEPIC converter was established. According to the need of the subject SEPICconverter was designed and tested. The turn off peak voltage of the power switchtube is less than10%. The ripple of the output voltage is0.6%. So, the requirementof the system was met.(4)The overall design hybrid power supply system of solar electric bicycles wasfinished from two aspects of hardware and software. To save and display real-timesystem data, analyze the system for further improvement, the PC program was design.Finally, a solar electric bike prototype was made.(5)The charging state and running condition of the solar electric bike weretested and analyzed in different time, light intensity and illumination angle.The experiments show that the lithium-ion battery of10Ah can be full chargedwith the fixed solar cells in six hours when the maximum light intensity is46872luxand the20Ah can be full charged with the solar cells witch is perpendicular to thesun in six hours when the maximum light intensity is58612lux. The output powercan reach210W and the speed can reach19.8Km/h only the solar cells as powersupply. But the speed decreased rapidly when the solar cells come into the shadow.The output power of solar cells is about120W and the speed can be25.2Km/h whenboth the solar cells and the lithium-ion battery work directly as parallel power supply.The speed does not decrease rapidly when the solar cells come into the shadow. Butthe output power of the solar cells is unstable. The total output power increases to278W and the speed can be25.7Km/h which reduces to21Km/h in the shadow whenthe solar cells work with the lithium-ion battery by DC-DC converter. The outputpower of solar cells is stable and with adjustable working point the MPPT can beachieved. |
