Research On Key Technologies In Drive System For Minitype Hybrid Electric Vehicle

Automotive industry has been the mainstay industry for a country, but the problem between need of fossil fuel and environmental pollution is becoming more and more serious, because of motor vehicle in life using. The one effective mean to resolve this contradiction must be found now. Fortunately, new energy vehicle, specially hybird electric vehicle(HEV) has been proven a kind of practical and fast-developing vehicle in the latest years. Based on the power electronics being the core part for HEV technology development, this dissertation focuses on the key technologies of electric drive equipment in the minitype HEV system.These are three aspects to research as follows.(1) The power structure of minitype HEV's prototype is proposed by the comparion between different power structures, likely series HEV, parallel HEV and combined HEV. Based on the selected structrue, the lead-acid battery mixed with super capacitor is adopted as hybrid electric engergy storage mode. Because this mixture can exert the advantages of lead-acid battery and super capacitor. In the proposed minitype HEV's electrical structrue, the lead-acid battery, super capacitor and BLDCM's inverter are cascaded by two bi-directional DC/DC converters. This electrical structure has some characteristics:flexibility, rationality and overall efficiency. Aimed to realize proposed electrical structure efficiently under different minitype HEV's operating modes, this dissertation have compared the seven topologies with bi-directional DC/DC converter fuction, mainly through number of the devices, electrical stress of active and passive devices, volume and dissipation of devices.Then as requirement of different minitype HEV's operating modes, it gives the selection basis and characteristic of bi-directional DC/DC converter used in minitype HEV.(2) This dissertation focuses on the most important aspects of the bi-directional DC/DC converter in the minitype hybrid electric vehicle for the project applications.The different operating modes of converter are introduced under all HEV's work conditions. Based on summarization, the demerits including low efficiency at light load and the uncontrolled discontinuous current are derivated. Through theoretical and mathematical analysis, a new algorithm of average current controlling and digital control method in discontinuous synchronous rectifier mode with a single current sensor resistance are proposed to realize the multi-mode bi-directional cascade Buck-boost DC/DC converter. At the same time, the prototype using proposed technology is implemented to verify the operational principles and advantages that improved synchronous rectifier inverse-boost converter light load efficiency. And then, a new kind bi-directional DC/DC converter with the characteristics of soft-switching based on "3-L" structure is proposed to use in minitype HEV. This bi-directional DC/DC converter has many advantages:low electrical stress of active devices, high efficiency, simple structure and so on.(3) Aimed to improve the drive performance and comfort. Firstly, the actual BLDCM's mathematical model and mechanical characteristic are analyed based on pratical DC/AC inverter with power MOSFET and anti-parallel diode. This dissertation presents a comprehensive research on torque ripples of brushless dc motor drive in conduction region and commutation region.The phenomenon of torque ripples of conduction exists because of diode freewheeling happened under the conventional PWM schemes.Through new proposed energy unit theoretical analysis, a new method for reducing the torque ripple in brushless dc motor with a single current sensor has been proposed under the minitype HEV's electrical sturcture. So in such drives, torque ripples are theoretically eliminated in conduction region. For torque ripple in the commutation region, a series of new methods are proposed and analyed to reduce this kind torque ripple, including of single-stage and two-stage modulation strategy. Effectiveness and feasibility of the proposed control method are verified through experiments.Nowadays, the key technologies of HEV have been mastered by several great automobile manufacturers, likely Toyota, Ford, GM, Honda and so on. But if our motherland wants to belong to first group in new energy vehicle, the key technologies of HEV must be researched and mastered as soon as possible. So this dissertation has been finished with this background and prospect. Although the all kinds of new methods are realized on minitype HEV's prototype, the proposed system analysis and method implementation are valuable for project application and design.