The Coupling Problem Research Of Four Ports Electromechanical Energy Converter For Hev Application

With the development of Hybrid Electric Vehicles (HEV), a new structure of the electrical Continuously Variable Transmission (CVT) device - Four Ports Electromechanical Converter which owns two mechanical ports and two electrical ports, thus result in flexible electromechanical energy coupling modes was proposed. When utilized in vehicle's transmission system, it can not only replace traditional mechanical power transmission equipment to achieve efficient power coupling as a continuously variable transmission, but also can substitute for starter/generator and driving motor to achieve all functions of compound hybrid electric vehicle system, the vehicle's fuel efficiency will be improved significantly, while the transmission structure is more simplified and the control system is easier to achieve. Additionally, the device can also be used in other fields need variable speed transmission and energy transformation, such as wind power generation, underwater propulsion and mining equipment, which revealing great application potential. However, the complex coupling within this device has challenged in electromagnetic design and system control.This paper researched the coupling problems of induction machine based four ports electromechanical converter for HEV applications, including the mode of energy coupling, relations of electromagnetic coupling and decoupling control, mechanical coupling and decoupling methods..To analyze the feasibility of four ports electromechanical converter as a substitution of mechanical transmission device to achieve HEV functions, energy coupling modes was studied for HEV application system firstly, and hybrid power control system with different power flows was proposed. For different control strategies, the method of external characteristic parameters for the two motors which composing four ports electromechanical converter was confirmed, and simulated the instances of passenger car with CVT mode power tracking control strategies and city bus with Plug-in control strategies. Various structures and types of prototypes were designed according to obtained indexes, comparison and optimization design was proceeded to achieve feasible projects.Because there are two different coupling fields in the internal four ports electromechanical converter, to analyze the coupling relationships between two fields and its influence, the Finite Element Method (FEM) simulation and experimental methods were employed respectively to study the influence of the system output characteristics in different states of the inner and outer coupling fields as well as the varying characteristics of the main parameters. The stator side based "T"-shaped equivalent circuit and d, q-axis decoupling model was deduced. Constant parameters simulation model based on magnetic circuit calculation and variable parameters model based on finite FEM were established respectively. Simulation results indicated that the inductance parameters of the four ports electromechanical converter changed significantly with excitation currents and phase angle difference between inner and outer motor. The exact results corresponding to experiment were obtained with the model based on variable parameters.To achieve vector control of inner motor, the speed difference must be obtained quickly and accurately. This paper designed the speed decoupling method which can directly measuring the speed difference based on variable reluctance resolver, the number of resolvers was reduced with this project, another advantage is it can directly measure the dual rotor's speed difference with a conventional Resolve-to-Digital Converter (RDC) board with excellent real-time property. However, the difficulty is that its lead-in and output signals were depend on annular resolver or brush-slip ring group so was with poor reliability. Therefore, indirect measurement of two shafts' speed difference was proposed, which can directly decouple using coordinate transformation and Phase Lock Loop (PLL) decoding technology, there is no of external difference lag.Finally, an HEV system test bench based on four ports electromechanical converter was built. In the system, two 40kW induction motors were used to simulated the engine and road load respectively, Speed control of EM1 and torque control of EM2 were applied on the two motors constitute four ports electromechanical converter. The upper control program was based on MATLAB/ Simulink procedure, and implemented through dSPACE real-time control software and hardware platform. The main parameters and external characteristic of an integrated four ports electromechanical converter was measured on the test bench. Compared with split prototype, different control methods were validated in the same mode, the power flows and efficiencies were analyzed. Multi-mode dynamic switching custom cycle was made, the experiment was proceeded based on split type bench, which validates the feasibility and superiority of using four ports electromechanical converter to achieve HEV's functions.