The Research On Charging Strategy And Power Conversion Topology Of Power Battery For Electric Vehicle Applications

This paper focuses on the research on the optimal charging strategy of power battery and the soft switching technology of on-board charging device for electric vehicle.The research aims to optimize the power battery charging curves,improve the efficiency and power density of the power converter,improve the charging performance of the battery charging system,and enhance the safety and reliability of charging process.The main research and innovative achievements of the paper are summarized as follows:(1)Research on the optimization method of multi-stage constant current charging strategy based on Taguchi method.Due to the complexity of lithium-ion battery characteristics,the charging performance needs to be further improved.This paper proposes an optimization method for multi-stage constant current charging of lithium-ion batteries based on Taguchi method.The method divides the charging process into five constant-current stages,and the charging current in each stage is used as the control factor to optimize the charging process.At the same time,the charging capacity,time and efficiency are simultaneously adopted as indicators reflecting the charging performance,and each indicator is independent with each other,which avoids the limitations of single-objective charging optimization and the unreasonable weighting for different optimization objectives.Taguchi method,as an experiment-based optimization method,can effectively avoid the complex modeling process of lithium-ion batteries and greatly reduce the experimental cost.This work intuitively reveals the effect of the charging current in each stage on each charging indicator in the multi-stage constant current charging method,and provides the most reasonable basis for the selection of the optimal charging currents.Compared with the traditional constant current-constant voltage and multi-stage constant current charging methods,the effectiveness of the proposed method in improving the charging efficiency and reducing the temperature rise of the battery is verified.(2)Research on the optimal charging strategy based on complementary pulse current control.Aiming at the inherent defect in pulsed charging strategy that the pulsed AC component will cause additional charging losses and the charging time will be prolonged due to the pulse interval,an optimized charging strategy based on complementary pulse current control is proposed in this paper.Although the above two characteristics are also the main reasons for the pulse charging strategy to accelerate ion diffusion and eliminate polarization.Therefore,the purpose of the proposed optimized charging method is to reduce the negative effects of pulse current while retaining the excellent characteristics of pulse charging.First,in order to minimize the harm of the AC component of the pulse current,the minimum AC impedance frequency of the battery is obtained through the AC impedance spectrum to optimize the pulse frequency.Then,according to the internal resistance characteristics of the battery,the pulse amplitude is optimized by minimizing the ohmic losses during charging process.Finally,based on the proposed charging converter,the complementary characteristic of the pulsed current completely eliminates the prolongation of the charging time caused by the pulse interval.And balance between the charged batteries can be achieved through the pulse duty cycle control.This work reduces the charging losses caused by the pulse AC and DC components in the charging process,and completely eliminates the increase of the charging time caused by the pulse interval in the traditional method.Through comparative experiments,the correctness of the theoretical analysis of the proposed method is verified.(3)Research on the soft-switching topology of single-phase full-bridge converter based on coupled inductor.The on-board charging devices of electric vehicles has higher expectations for the lightweight and miniaturization of charging converter.Due to the hard switching characteristics of traditional single-phase converters,a soft-switching topology of single-phase full-bridge AC/DC converter based on coupled inductor is proposed in this paper.This topology integrates a small coupled inductor on the main filter inductor,and forms the ZVS auxiliary circuit by adding an auxiliary inductor and a bidirectional switch.Based on the proposed hybrid modulation strategy,the auxiliary inductor current is reversed during the commutation.The ZVS characteristics of all high-frequency switches are obtained,and the added bidirectional switch has excellent ZCS characteristics.Moreover,when the proposed hybrid modulation is adopted in this soft-switching topology,the voltage transfer characteristics of the converter are consistent with those of the traditional full-bridge converter using unipolar modulation.The operating principle,electrical modeling and parameter design of the converter are deduced and analyzed in the paper,and the correctness of the theoretical analysis is verified by experiments.The soft-switching characteristic can effectively improve the operating efficiency and switching frequency of the converter,and provide a basis for the miniaturization and lightweight of the pre-stage rectifier for on-board charging devices.(4)Research on the soft-switching topology of push-pull converter based on complementary active clamping.Aiming at the leakage inductor effect and hard-switching characteristics of traditional push-pull converters,a novel soft-switching topology based on complementary active clamping is proposed in this paper.This topology adds a clamping capacitor between the two active switches to absorb the energy stored in the transformer leakage inductors when the switch is turned-off,and the two power switches of the converter form an active clamp switch with each other.Compared with the traditional converter,the proposed soft-switching topology completely eliminates the leakage inductor effect,and the larger leakage inductors of the transformer can reduce the external inductor.Through the duty cycle and switching frequency modulation,the output voltage and transmission power of the converter can be flexibly controlled,and all power switches have excellent soft-switching characteristics.The rectifier diodes on the output side is naturally commutated without reverse recovery.The operating principle,electrical characteristics,optimal control and parameter design of the proposed converter are analyzed in the paper,and the validity of the theoretical analysis is verified by experiments.The excellent characteristics of the soft-switching topology make the push-pull converter suitable for high-frequency and high-power applications,and provide a solution for the high-frequency isolated DC/DC converter at the rear stage of the on-board charging devices.This paper conducts in-depth research on the optimal charging strategy of the power battery and the soft-switching technology of on-board charging converters for electric vehicles,proposes a variety of optimized charging strategies,and provides a set of soft-switching power conversion scheme for on-board charging devices.