| At present,more and more electric motors are used as power sources in the small horsepower micro-cultivator,and with the electric micro-cultivator the electric tools became more widely used,like electric pump,electric tree trimmer and so on.However,the battery capacity of micro-cultivator blocks its endurance capacity currently.Research results show that the capacity issue can be solved by Solar Micro-cultivator,which is,however,rarely studied in China.Therefore,it is significant to research and developSolar Micro-cultivator studying the design theory of its’ driving system and photovoltaic controller,studying driving characteristics and control strategy.A Wheel driving system was designed and manufactured based on the requirements of working and driving characteristics of Solar Micro-cultivator,combining the current research achievements on its driving system home and abroad.Besides,A Solar Micro-cultivator driven by hub-motor and mainly provided by lithium battery pack which is assisted by photovoltaic module.The completed work and conclusions are as follows:1.DesigningTheory and calculation for driving system.Based on the working characteristics and features of solar cultivator,a new approach of wheel driving system and the calculation method of its main parameters were proposed and a theoretical model of main components was established in this paper.The evaluation indexes and calculation formulas of dynamic property and economic efficiency were established and applied to analyze the designed solar cultivator.The results show that the solar cultivator works well by providing enough tractive force for ploughing operation in low speed and by keeping high efficiency in transit.When the PV module is placed horizontally,the average daily power gotten by the solar cultivator reaches a peak at June and a lowest point at January.The solar cultivator with different speed,weight and slope working under 4 different conditions including horizontal transport,ramp transport,horizontal ploughing and ramp ploughing has different working hours.The lighter working load is,the more the cumulative daily working hour.The faster the cultivator runs,the less the cumulative daily working hour.The heavier the use weight is,the less the cumulative daily working hour.The bigger ramp slope is,the less the cumulative daily working hour.2.Simulation of dynamic characteristics of Solar Micro-cultivator,The model of each component of Solar Micro-cultivator was established by SimulationXTM and MATLABTM.The simulation system for Solar Micro-cultivator was applied to simulate dynamic characteristics of PV module and dynamic property of cultivator under no-load transporting and ploughing situation.Moreover,the biaxial optimization control method for Solar Micro-cultivator was also proposed.The research results show that light intensity has a great effect on short-circuit current and output power of photovoltaic battery,while tiny effect on open circuit voltage.Ambient temperature impacts the open circuit voltage a lot,while hardly the short-circuit current.The largest power of photovoltaic battery and its corresponding output voltage decreases with the increase of temperature.In a particular time of a day,there is a slope anglewhere photovoltaic battery can get the largest total solar radiation,and at a particular slope angle,photovoltaic batterycan get the largest total solar radiation at noon hour.In a particular time of a day,incident light intensity increases with the number of day,and then decreases gradually.Annual incident light intensitychanges obviously periodically.The best slope angle of photovoltaic battery is significantly different from month to month in Nanjing area.The light intensity gotten by photovoltaic battery is greatly impacted by its slope angle and direction angle in different area,which consequently impacts the energy gotten by the Solar Micro-cultivator.Driving torque of the Solar Micro-cultivator increases with the increase of working load.The driving torque is constant when working in a uniform speed,while increases or decreases according to inertial force when accelerating or decelerating.When ploughing in a uniform speed,the output torque of each component of the Solar Micro-cultivatordiffers greatly under different soil conditions.The output torques is greater than those under no-load transporting,which means every component’s output torque increases with the increase of working load,and so does the total tractive force.In a particular working condition,the total tractive force is constant when working in a uniform speed,while has a certain fluctuate when accelerating or decelerating.The tractive efficiency differs a lot under different working load and speed.3.Overall design scheme of photovoltaic controller of Solar Micro-cultivator was proposed,including hardware and software.The hardware design of controller includes the selection of micro-controller,parameters’calculation for inductances,capacitances,and switch tubes in BUCK main circuit,and the design of sampling module,driver module,power supply module,etc.The software design includes intelligent charging program,PWM program,AD sampling program and MPPT algorithm program.The tracking algorithm for the largest power point was analyzed theoretically.The bidirectional perturbation method was proposed to verify the tracking algorithm.4.Driving system platform which is consisted of 5 independent modules was developed according to the test requirements of Solar Micro-cultivator.After designing the photovoltaic module,the power system module,the load simulation module and the data acquisition module,light intensity sensors,current and voltage sensors were calibrated,and velocity and torque sensors were calibrated statically.5 Dynamic characteristicstests are held,among which,charging testsinclude light intensity,charging voltage and power of lithium battery pack and the charging efficiency characteristic of photovoltaic controller,dynamic characteristic testsinclude running speed,output power of driving wheel,as well as output characteristic and tractive efficiency characteristic of lithium battery pack,and working simulation test includestractive performance simulation test,starting-with-load simulation test andsudden-load simulation test.The research results show that the change of daily light intensity was similar to normal distribution.When the photovoltaic controller opens,it can track the largest power point of photovoltaic module well.In charging process,terminal voltage of lithium battery pack increases gradually,especially obviously in the starting phase.The changing tendency of output current of lithium battery pack is identical with the one ofcharging current of photovoltaic module.The charging current of lithium battery pack increases or decreases with the increase or decrease of the output current of photovoltaic module,which increases or decreases with the increase of light intensity.The proposed photovoltaic controller can operate MPPT algorithm well to charge the lithium battery pack.The velocities of both the left and right driving wheels have the same changing tendency with the change of electric accelerator pedal and loading torque.In a particular loading torque,the velocities increase with the increase of the pedal’s open angle.In a particular open angle,the velocitiesdecrease with the increase of the driving wheel’s load,the power of driving wheel is in proportion to the loading torque,and the voltage of lithium battery pack is inversely proportional tothe loading torque.When the loading torque is constant,the voltage decreases slowly with the increase of the open angle.When the open angle is constant,the current of motor is proportional to the loading torque,and the larger the open angle is,the more obviously the current increases.In a particular velocity and loading torque,the tractive efficiencies of both the left and right wheels have the same changing tendency.In tractive test,the Solar Micro-cultivator is capable to work for deeperploughing operation.The output power increases with the increase of load,while the velocity decreases.The output voltage of lithium battery pack increases or decreases with the decrease or increase of the output power of driving wheel,and its output current is proportional to the loading torque.In starting-with-load simulation test,the cultivator can run quickly with larger load.The input currents of both hub motors have a spike because of large instantaneous starting load,while the voltage of battery pack shows a large drop.After the system is stable,both current and voltages keep stable,which means the cultivator has good ability to start with load.In sudden-load simulation test,when the voltage fluctuates lightly resulting from the sudden change of load,while the currents of both motors fluctuate obviously,and the larger the load is,the more obviously the currents fluctuate,which means the cultivator has good ability to resist impact load.6.The control strategy distinguishing driving patterns and building the strategy model of deciding ald switching for those patternswas developed in Lab ViewTM.The strategy was verified combining with the driving system platform.The test results show that when the open angle of acceleration pedal is up to its 10%,the driving system is in starting pattern to analyze the pedal’s position and changing rate.Under starting pattern,the driving system can understand well the drivers’ intention,and have a good starting quality.Under working pattern,the driving system can adjust driving motor according to the change of load to work with best efficiency characteristic.Under transition pattern,the driving system can response swiftly and then be stable.Under energy limited pattern,the driving system can response swiftly and be stable at the half of rated power.In the pattern switching test,the driving system can switch its working pattern smoothly and have a good switching quality.The proposed model and the switching control strategy are proved to be effective,which can improve working efficiency and prolong working hours.The research can provide theoretical basis and technical support for the development of driving and control system of Solar Micro-cultivator. |
