Research On Inductive Power Transfer Technology Based On Multi-level And Multi-receiver

In recent years,high power inductive power transfer(IPT)technology has made rapid progress as the the development of power electronics technology.One of the most promising inductive power transfer applications is the wireless power supply for locomotives which may cancel pantographs.Due to capacity constraints of power electronic devices and the power demand for some railway applications rises up to the Megawatt level,it is a huge challenge for the traditional IPT system to get enough power.Therefore,it is necessary to improve the power capacity and working efficiency of IPT system.Generally,power capacity and working efficiency are two technical indexes of IPT systems.To improve the power capacity of IPT system,both of the input power capacity of inverter and output power capacity of magnetic coupler should be increased.However,the limitation of semiconductor devices capacity makes the traditional IPT system hard to meet the demand of high power load.Therefore,multiple-level inverter and multiple-pickup approach may be one of the promising solutions to meet the high power demands of locomotives charging applications.In addition,the optimal resistance of the IPT system changes as the mutual inductances between transmitter and pick-up coils.Therefore,it is necessary to find a new method to optimize the efficiency of dynamic IPT power supply system,which changes with the equivalent resistance.1.For the purpose of achieving high power,a diode-clamped five-level inverter is applies to be the alternating current source for IPT system.However,the low harmonic content of the output voltage will affect the stability and efficiency of the IPT system.The harmonic content of the inverter output voltage is directed with the pulse width and phase shift angle of control signal.Threrefore,according to the Fourier series expression of five level inverter output voltage,the relationship between the harmonics and the phase shift angle,pulse width is established.Then using the phase shift control technology could effectively control the harmonic content of five level inverter output voltage.In this way,the third harmonic,fifth harmonic and its odd harmonic of the five level inverter output voltage can be eliminated.2.In order to increase output power of the pickup structure,an IPT system based on multi-pickup coil parallel technology is propsosed.The cross coupling between pickup coils is analyzed via the electromagnetic coupling theory.However,the cross coupling between between the pickup coils can unbalance the output power of each pickup coil,suppress total output power,decrease working efficiency and its resonant characteristic.When the mutual inductances between the transmitter coil and the pickup coils are equal,the induced voltages of pickup coils are the same.The influence of the cross coupling between the pickup coils on the IPT system can be effectively eliminated by using the capacitance compensation method.When the mutual inductances between transmitting coil and pickup coils are different,the induced voltages coils are different.Applying active rectifier for each pickup coil to controling the pickup coils currents be same and combined with capacitance compensation method could effectively eliminate the influence of the cross coupling between pickup coils on the IPT system.3.When IPT system serves for rail locomotive,the optimal resistance of IPT system changes as the variation of mutual inductance between transmitter and pick-up coils caused by the motion of locomotive.The equivalent resistance of the IPT system changes as the power requirement of rail locomotive under acceleration,deceleration and other different working conditions.However,working efficiency of the IPT system is directly related to quivalent resistance.Then an optimal resistance point tracking control scheme based on the perturbance and observation approach is applied to optimize the efficiency of the IPT system.The experimental results show that the high frequency inverter with clamped five level technology can effectively improve the input power of IPT system and phase shift control method can eliminate the third harmonic,fifth harmonic and its odd harmonic of the five level inverter output voltage.Pickup struct based on multi-pickup coil could significant improve the output power of IPT system.The influence of the cross coupling between pickup coils is eliminated by adapting the currents of pickup coils to be same and compensed capacitor.Finally,a maximum efficiency point tracking control scheme based on the perturbance and observation approach is proposed to increase the IPT system efficiency.