| Transportation electrification has received extensive research and development due to its contribution to energy structure transformation and the achievement of peak carbon dioxide emissions and carbon neutrality.Compared to the conventional wire-connected electrical transfer systems,the magnetic coupled inductive power transfer system has a broad application prospect for transportation electrification because of its advantages of safety,reliability,convenience and no influence of the environment and is gradually evolving towards high power,long-distance,and miniaturization requirements.However,the output characteristics and transmission efficiency of the IPT system are affected by different load types,and due to the arbitrary position of primary and secondary magnetic couplers,the relative position of primary and secondary magnetic couplers during the charging process will also affect the output characteristics and transmission efficiency of the system.Furthermore,in the cases of weak coupling and constraint magnetic coupler,high efficiency operation presents higher design requirements for high-power IPT systems.Therefore,this paper takes the high-power IPT system as the research object,and conducts research on high misalignment compatibility,minimizing resonant current and device stress,optimizing the entire operating range efficiency and maximizing system overall coupling for different load types.New implementation solutions and optimization methods for the high-power IPT system are provided.The main research contents of this paper are mainly divided into the following three parts:First,for constant voltage load types such as DC buses,this paper proposes an asymmetrical factor design method for the IPT system with high misalignment compatibility and constant voltage output.In order to improve constant voltage output IPT system performance over a wide misalignment and load range,the asymmetrical factor is introduced as a new design variable.By designing asymmetrical voltage factor and asymmetrical compensation factor,it can help to minimize the primary current and improve the entire operation range transmission efficiency.It is given for the first time that the IPT system can achieve the asymmetrical monotonic power characteristic over the entire switching frequency range and a constant voltage output over a wide load range by redistributing the zeros and poles of the power characteristics.By designing the frequency corresponding to the minimum input impedance angle,the input impedance angle can be insensitive to coupling and load.Based on the condition of minimizing the primary current over the entire operating range,the selection of the asymmetrical factor and the design produce of the system are given.Based on the proposed method,the primary current increases by only 15% over a 2:1 coupling coefficient variation range at rated load.Experimental results show that the proposed asymmetrical factor method in this paper uses the series-series compensation circuit without adding additional compensation components or converters and has the advantages of minimum primary current,low reactive power,low control and structural complexity,high misalignment compatibility and entire operating transmission efficiency optimization.Second,for constant power load types such as electric vehicle power battery,this paper proposes a high misalignment compatibility constant power output IPT system based on the detuned multifrequency compensation topology and multiband switching control strategy.When the primary side is detuned and the secondary side is tuned,the fundamental relationships between power variation and coupling range are established,and multiple intersecting power vs.coupling coefficient curves are constructed with multiple switching frequencies.The maximum output power of the system can be constant when the switching frequency and load resistance change.Based on the identity of reactive power and primary current range for each switching frequency,a multiband switching control strategy for the proposed multifrequency compensation topology is given to extend the misalignment range or reduce the output power variation range.According to the constraints of component parasitic parameters and component tolerance,the number of switching frequencies of the proposed detuned multifrequency compensation topology can be selected.The optimal parameter design method over multiple switching frequencies is given to minimize the device stress with misalignment.With the proposed system,a choice of two suitable switching frequencies changes output power by only 10% over a 2.5:1 coupling coefficient range,and three frequencies can support an output power range of 6.7%.Experimental results show that the proposed multifrequency IPT system without extra inverters or coils has the advantages of consistent output power,narrow primary current variation range and reactive power variation range,low control complexity,high misalignment adaptability and the entire operating range efficiency optimization.Finally,for constant current load types such as fast charging and weak coupling application,this paper proposes a weak coupling IPT system based on complex resonant threecoil structure.By adding the tertiary coil to the primary side and all resonant frequencies of the three resonant circuits,as extra degrees of freedom,are detuned,the detuned operation state of the proposed three-coil system can achieve an equivalent complex resonant operation state.Based on the three-coil circuit model and the criterion of eliminating independent variables,an equivalent two-coil circuit model is given,and the relationship between the system overall mutual inductance and overall coupling coefficient and the main mutual inductance and main coupling coefficient is established,which is helpful to provide accurate system output characteristics and resonant conditions.The formation mechanism of the coupling enhancement ability of the proposed three-coil system and the selection of the tertiary impedance are analyzed.The results show for the first time that not only the capacitive tertiary impedance can enhance the overall coupling,but also the inductive tertiary impedance can enhance the overall coupling of the system,thus achieving the objective of relatively low switching frequency or the magnetic coupler inductance compared to the two-coil system.Additionally,based on coil losses with different auxiliary coupling coefficients and coupling enhancement factors,an efficiency optimization strategy is given,which can maximize the system overall coupling coefficient and minimize the coil loss with the limited magnetic coupler size.The misalignment situation is analyzed and the optimization strategy is given.Compared to a two-coil system with the same main coupling coefficient,the proposed system dropped coil losses by 73% and enhanced overall coupling by a factor of three.Experimental results show that the proposed complex resonant three-coil structure IPT system only adds a tertiary coil on the primary side and limited in size and can achieve load-independent constant current output characteristics,zero input impedance angle of the compensation circuit,higher overall coupling coefficient,lower switching frequency and lower coil losses. |
