Research On Power Management In Drive System Of Hybrid Electric Vehicle

Hybrid electric vehicle (HEV) becomes a kind of new, fast-developing vehicle in the latest years, which has the best future as a green vehicle, along with the problems of energy and environment becoming more and more serious in the 21st century. To being the core part of HEV system, the power drive equipment mainly involves power conversion of the storage energy cell, motor drive and so on. This dissertation aims at the key technologies of power drive equipment, and researches into the following several aspects: economic performance of the storage energy system and special charging technology, bidirectional high power DC-DC converter and soft-switching scheme, current control strategy and circuit loss analysis, brushless DC motor drive topology and control strategy.First, this dissertation enumerates characteristics of each kind of battery cell and ultra-capacitor. According to the supplementarity performance of battery and ultra-capacitor, it introduces a hybrid storage mode, and it analyzes capacity design principia of each kind of storage energy part which aiming at the power pulsant load. In view of the actual application example, this dissertation also analyzes independent storage energy system and hybrid storage energy system quantitatively. At the same time, it investigates the smallest charging electromotive force during the normal charge process with the actual charging circuit. Then, as request of HEV system, it gives the digital control scheme of intermittent current and the fast charging method on electricity quantity control.Second, this dissertation compares three circuit topologies which have the bidirectional functions of buck and boost, mainly through electrical stress of active device, volume and electrical stress of passive element, and so on. Moreover, basing on the conventional ZCT circuit, it analyzes two kinds of improved ZCT topologies to reduce the current stress of primary switching device effectively. Also, aiming at the current sampling problem, the dissertation proposes an improved current sampling strategy and a concept about the highest sampling frequency of the digital control system. After studying the relationship between IGBT switching loss and the freewheeling diode switching characteristics, it points out that both devices have restriction mutually, and can not reduce switching loss by quickening up switching speed. Then, in allusion to the constant frequency and variable frequency control strategy, it researches circuit loss respectively, and proposes the method of constant current ripple control.Third, the dissertation studies two kinds of drive topologies of brushless DC motor, and mainly compares the control strategy, inductor loss, torque ripple and system efficiency. Then, it proposes a two-stage modulation strategy to eliminate torque ripple during motor commutation process of seven switching drive topology. Simultaneously, it uses the current predictive control to suppress LC resonance phenomenon. Moreover, this dissertation calculates the commutation angle on the whole speed range of brushless DC motor, and puts forward a concept of the best commutation phase point. The commutation torque decrease phenomenon can be restrained by the best commutation phase point control on the whole speed range. In view of the two control methods of constant power for the brushless DC motor, it analyzes the phase inductor influence to different control strategies, and proposes the concept about constant power speed strategy choose based on phase inductor. Considering on the circuit cost, this dissertation proposes a novel converter named seven switching current converter. This circuit combines with characteristics of all-controlled device IGBT and half-controlled device SCR, and it can simultaneously satisfy the request of the constant torque and constant power.Fourth, this dissertation proposes two kinds of motor faults, namely over-current fault during motor reverse braking and motor phase-sequence fault. The primary causation for the problem that phase current during reverse braking out of control is a short loop by the back electromotive force, and it proposes a double switching modulation scheme that can control braking current effectively. Moreover, aiming at phase-sequence fault, this dissertation analyzes the average torque of motor start-up, and proposes a self-recovering strategy.Fifth, this dissertation develops a 50kW power converter of HEV system, does lots of experiments, and obtains approving results.Researching on the power drive technology of HEV system can promote power electronics, and can resolve the problems on system efficiency, topology choice, control strategy of the high power transformation equipment. Also, it can provide relative design instruction for HEV system in the practical application, and solve the actual problem during power transformation process.