Design And Control Of Dual-Channel Bidirectional Chargers For Plug-in Electric Vehicles

With the increasing environmental pollution and oil energy crisis,especially caused by the carbon emission and other harmful substances such as vehicle exhaust,plug-in electric vehicles has become an research focus and guides the development of global automotive industry.The energy storage module is the ’power heart’ of electric vehicles,which not only depends on the device itself but also is closely related to the chargers.The current chargers are divided into two kinds,namely on-board chargers and charging stations.With the increasing amount of electric vehicles,more charging stations have to be built and the cost will be much higher.Instead of off-board charging stations,on-board chargers can be applied almost everywhere as long as there is an electrical plug.However,with the increase of charging capacity,the volume,weight and cost will become crucial obstacles restricting the electric vehicles’ development.Firstly,this thesis introduces domestic and overseas research background and review including the development history of on-board chargers and the concept of vehicle-to-grid.Some conventional and classical topologies about dc-dc conversion and dc-ac conversion are also displayed in the first section.Through comparing their advantages and disadvantages and considering the actual industrial requirements,a dual-channel isolated magnetically integrated power circuit is proposed which can be used in both single-phase and three-phase charging system or to send power to the grid if change the converter’s working direction.Besides,when separating from the external grid plug,this kind of power converter can also be utilized to drive the electric motor.In detail,each channel is composed of one bidirectional dual-active-bridge dc/dc converter and one bidirectional three-phase half-bridge converter,and the two of these are linked by a dc bus stretching across an electrolytic capacitor.The two channels are also paralleled on the battery pack side and the grid side.Especially,the grid filtering inductance is substituted by the wind inductances of two three-phase permanent magnet synchronous motors,which means that one motor is magnetically integrated in one channel.Secondly,detailed study of the forestage dual-active-bridge dc/dc converter is explained including power equations,soft-switching range and ten operating modals in one switching period.What’s more,based on the conventional phase-shifted control strategy,an interleaved control technology is introduced in the paralleled dc/dc converters which can reduce the charging or discharging current ripple by half.Then some experimental waveforms are given to verify the validity.Thirdly,paralleled voltage-source converters on the grid side are analyzed in detail in the third section.This section are divided into two parts:single-phase grid and three-phase grid.Equivalent circuits and different control strategies are demonstrated at first in the single-phase grid.Then carrier-shifted sinusoidal pulse width modulation is adopted to reduce the grid current harmonic.The actual working waveforms are given in the end of first part.When the converter is connected with three-phase grid,the reasons and solutions of circulating current are analyzed at first.Next,the space vector modulation based direct power control strategy and phase-shifted space vector pulse width modulation are introduced,and finally experimental results are given to verify the theoretical derivation.Fourthly,based on the previous control strategies and harmonic improving methods,systematic experiments are conducted including single-phase and three-phase operation modes.Especially,when working in the three-phase grid,the neutralize of two reverse torques between the two motors is shown with waveforms of torque ripples and furthermore,the compared shaking waveforms of the motor spindle in one-channel and two-channel system are also revealed to verify the actual effects.Fifthly,the chaotic modulation is introduced to reduce the electro-magnetic interference.This section detailedly explains why the chaotic modulation can improve the spectrum character and how to generate chaotic series through rigorous mathematical derivation.Then this kind of modulation is applied in the proposed single-phase and three-phase structures.Relative waveforms are displayed to prove that the chaotic modulation can improve the harmonic character and keep the stable working working performance constant.