Electrical Variable Transmission Research Articles

Torque Analysis on a Double Rotor Electrical Variable Transmission With Hybrid Excitation

An electrical variable transmission (EVT) can be used as a power splitting device in hybrid electrical vehicles. The EVT analyzed in this paper is a rotating field electrical machine having two concentric rotors. On the outer rotor, permanent magnets (PMs) are combined with a dc-field winding, being the first implementation of its kind. The magnetic field in the machine as well as the electromagnetic torque on both rotors are a function of the q - and d -axis currents of the stator and inner rotor, as well as the dc-field current. To describe and fully understand this multiple-input multiple-output machine, this paper gives an overview of the influence of the different current inputs on the flux linkage and torque on both rotors. Focus is given to the hybrid excitation in the d -axis by combining the dc-field current and the alternating currents. This has the advantage compared to other EVT topologies that unwanted stator torque can be avoided without stator d -axis current flux weakening. Results of the analysis are presented by means of the torque to current characteristics of a double rotor PM-assisted EVT, as well as the torque to current ratios. The machine characteristics are finally experimentally verified on a prototype machine.

Global Optimized Design of an Electric Variable Transmission for HEVs

A way to improve existing hybrid vehicles is by globally optimizing the design of their components in relation to their actual use. This paper proposes a global optimal design method for power-split hybrid electric vehicles (PS-HEVs) equipped with an electric variable transmission (EVT). A genetic algorithm is used to optimize system parameters. The process includes discrete dynamic programming (DDP) for optimal energy management. The optimization focuses on minimizing fuel consumption and the number of battery cells. Pareto fronts are depicted and compared for different drive cycles, and they show the existence of a possible tradeoff between fuel consumption and battery size.

Field-Oriented Control for an Induction-Machine-Based Electrical Variable Transmission

An electrical variable transmission (EVT) is an electromagnetic device with dual mechanical and electrical ports. In hybrid electric vehicles (HEVs), it is used to split the power to the wheels in a part coming from the combustion engine and a part exchanged with the battery. The most important feature is that the power splitting is done in an electromagnetic way. This has the advantage over mechanical power splitting devices of reduced maintenance, high efficiency, and inherent overload protection. This paper gives a conceptual framework on how the torque on both rotors of the EVT can be simultaneously controlled by using a field-oriented control (FOC) scheme. It describes an induction-machine-based EVT model in which no permanent magnets are required, based on classical machine theory. By use of a predictive current controller to track the calculated current reference values, a fast and accurate torque control can be achieved. By selecting an appropriate value for the flux coupled with the squirrel-cage interrotor, the torque can be controlled in various operating points of power split, generation, and pure electric mode. The conclusions are supported by simulations and transient finite-element calculations.

Design and Optimization of Electric Continuous Variable Transmission System for Wind Power Generation

A novel brushless electric continuous variable transmission (E-CVT) system is presented and optimized. The proposed system offers an alternative solution for a variable-speed constant-frequency operation of the wind turbine application. The key is to eliminate the gearbox and brushes in the machine and this E-CVT system comprises of two rotors and two stators within one machine. This design inherits and integrates the merits of the direct-drive permanent magnet generator and the doubly fed induction generator with the additional benefit of the improved torque density and the need for a low-cost partial-scale converter. The structure, operation principle, and performance are analyzed. Genetic algorithm is employed to optimize the parameters for maximizing its power density. Time-stepping finite-element method is used to analyze the dynamic performance of the proposed system.

Comparison of different power-split hybrid architectures using a global optimisation design method

Power-split hybrid electric vehicles (PS-HEV) are the most efficient solution to reduce fuel consumption using electric hybridisation of vehicles. However, different architectures exist or can be developed and it is difficult to perform a fair comparison between these solutions. A global design approach, optimising the size of the components and using optimal energy management can be a good way to compare different PS-HEV architectures. This paper presents a method to size and design HEV in an optimal manner and to compare this vehicle on different objectives: fuel consumption, battery size, and global volume of the system. The method is then applied to four SP-HEV based on existing architectures (Toyota Hybrid System, Opel Ampera) and on alternative solutions (electrical variable transmission and serial-parallel architecture).

A Brushless Double Mechanical Port Permanent Magnet Motor for Plug-In HEVs

This paper proposes a new brushless double mechanical port flux-switching permanent magnet (BDMP-FSPM) motor for plug-in hybrid electric vehicles applications. The key is to highly integrate two rotors and single stator into one motor frame, which is based on the concept of incorporating the double-rotor motor into a stator-permanent-magnet motor. In addition, by combining the non-contact magnetic planetary gear with the proposed motor, the new resulting electric continuous variable transmission system can not only realize the required speed and torque transmission, but also manage the power split and combination in various driving cycles. The electromagnetic performances of the proposed motor are analyzed by using the finite-element method, such as magnetic field distribution, coupled back-EMF, torque performances, torque-speed curves, and power-speed curves. Experimental results of the BDMP-FSPM prototype are also given to verify the validity.

An objective analysis of drivability for two wheeler powertrain with control oriented dynamic model

The objective of this work is to estimate drivability characteristics parameters of two wheeler powertrain with control oriented powertrain model. The evaluation is essential for defining drivability characteristics for a future electric variable transmission (EVT) powertrain. The mathematical model for the complete powertrain is developed using suitable modeling approaches for the different sub-modules of the complete system. The Spark Ignition (SI) engine model used for this work is developed from mean value model approach and experimentally validated with test data from TVS Motor Company, India. The model is integrated with two types of transmission models, Continuous Variable Transmission (CVT) and Manual Transmission (MT). It simulates dynamic power-flow from the engine to wheel for analyzing longitudinal drivability of the vehicle for both powertrain configurations. It is proposed that the drivability can be measured with certain parameters which show good correlation with subjective assessments for vehicle launch as well as tip in condition. The objective assessment of both types of powertrains is performed using the above mentioned powertrain models. The results of the simulation for drivability tests are discussed in this paper.

A New Hybrid-Excited Electric Continuous Variable Transmission System

A New Hybrid-Excited Electric Continuous Variable Transmission System

Research on the Power Management Strategy of Hybrid Electric Vehicles Based on Electric Variable Transmissions

Electric variable transmission is a new electromechanical energy conversion device structure, which is especially suitable as the driving force distribution device for hybrid electric vehicles. This paper focuses on the power management strategy of hybrid electric vehicles based on an electric variable transmission, and a kind of hierarchical control ideology is proposed. The control strategy is composed of four control levels, namely analysis of force requirement, operation mode switching, force distribution and coordinate control, which are designed respectively in this paper. Then a simulation model is built based on the notion of energetic macroscopic representation, and an experimental test bench is built. The simulation and experiment results demonstrate the feasibility of the proposed strategy, and it can be taken as a new theory and method for the study of hybrid electric vehicle based on electric variable transmission.

Application and simulation of dual-mechanical-port machine in hybrid electric vehicles

Summary There are growing interests in electric and hybrid electric vehicles (HEVs) because of environmental concerns. Recent efforts are directed toward developing an improved propulsion system for electric and HEVs applications. In a conventional series–parallel HEV, a planetary gear is used to integrate the power of internal combustion engine and two electric machines into the drive train so that the engine can always operate with the highest efficiency while the vehicle runs at any desired speed and torque. However, two electric machines and associated power inverters along with a planetary gear make the HEV drive train much more complicated and bulky in size. Dual-mechanical-port electrical machine (DMPM) is a new breed of energy conversion device with more compact and integrated structure that can potentially realize an efficient electrical variable transmission for HEV applications. This machine can replace the planetary gear and two electric machines of conventional structure in order to make their structures much simpler. Applying a proper power management and control strategy to have a good driving performance for a series–parallel HEV based on DMPM are the main contributions of this paper. Because Toyota Prius II (Toyota Motor Sales, U.S.A., Inc., Torrance, CA, USA) is a well-known series–parallel HEV, the parameters of this vehicle are chosen as a practical example in simulation results. Copyright © 2014 John Wiley & Sons, Ltd.

Research on the Split Electric Variable Transmission for Hybrid Electric Vehicle

This paper introduced an advanced electric variable transmission used in hybrid electric vehicle, and analyzed the operating mode in hybrid electric vehicle. For the strong flux coupling of EVT, a kind of split electric variable transmission used in hybrid electric vehicle was expatiated, and the parameters of split electric variable transmission were designed. The simulation model of HEV using the split electric variable transmission was completed using Matlab/Simulink, and the experiment test bench was built. The simulation and experiment results demonstrate the feasibility of the proposed method, and it can be taken as a new theory and method for the study of hybrid electric vehicle.

Improvement of an EVT-Based HEV Using Dynamic Programming

Automotive engineers and researchers have proposed different topologies for series-parallel hybrid electric vehicles (SP-HEVs). The Toyota Hybrid System (THS) is the best known SP-HEV-based vehicle, but alternative solutions, such as electric variable transmission (EVT), have been also proposed. An efficient comparison between these different solutions is a key point to estimate the added value of each topology. This paper presents the application of optimal control to two series-parallel hybrid architectures for efficiency assessment purposes. The dynamic programming method is applied to the THS and to a virtual hybrid vehicle with an EVT. The way to take into account the supplementary degree of freedom provided by the decoupling of the wheels and the engine in both topologies is presented. The optimal fuel consumption is then compared on different driving cycles and brings out an overconsumption of the EVT topology. Then, a parametric study shows that inserting an appropriate gear ratio on the internal-combustion-engine (ICE) shaft can improve the EVT efficiency that becomes close to the THS efficiency.

Field Weakening Control of a PM Electric Variable Transmission for HEV

This paper presents the control of a Permanent Magnet Electric Variable Transmission (PM-EVT) for Hybrid Electric Vehicles (HEVs). Consisting of two electric machines, the EVT realizes the power split function in an electromagnetic way rather than in a mechanical way. A specific PM-EVT has been designed for Toyota Prius II. The control scheme of the entire vehicle is deduced using the Energetic Macroscopic Representation methodology. The energy management strategy yields local control references. A specific attention is paid for the field weakening for wide speed range. Simulation results are provided to illustrate the EVT modeling and control.

Sensorless Control Strategy of Electrical Variable Transmission Machines for Wind Energy Conversion Systems

This paper focuses on the control for the dual power flow wind energy conversion system (DPF-WECS) based on the permanent magnet electrical variable transmission (PM-EVT) machine. The PM-EVT machine can be considered as two permanent magnet synchronous machines (PMSMs) by ignoring the magnetic field coupling between the inner rotor and stator windings. For the DPF-WECS, the speed of the inner rotor should be controlled precisely to generate the constant voltage and constant frequency electricity. However, the rotor position of the inner PMSM composed of the inner rotor and outer rotor is difficult to be measured exactly due to the rotational stator and rotor. Thus the inner PMSM is hardly to be controlled using vector control strategy with the measured rotor position. In this paper, a sensorless control strategy based on the model reference adaptive system (MRAS) for the PM-EVT machines with double layer permanent magnet outer rotor for the DPF-WECS is proposed and evaluated by simulation. The effectiveness of proposed control strategy is verified by experimental results.

Application of Electrical Variable Transmission in Wind Power Generation System

In the widely applied non-direct-driven wind power generation system, a gearbox is connected between the wind turbine and high-speed doubly fed induction generator so that the system can supply power with constant voltage and constant frequency as the wind turbine speed varies. However, the multilevel mechanical gearbox is rather vulnerable and poses many difficulties to maintain. Electrical variable transmission (EVT), an electrical continuous variable gearbox, is a very competitive alternative for the vulnerable constant speed-ratio mechanical gearbox. In this paper, the application of this machine in wind power generation system with its operational modes and control strategy is presented. The working principle of the EVT-based system is introduced, and the unique power conversion characteristics are investigated. A control algorithm with maximum power point tracking for the outer rotor is developed and implemented in a prototype machine. Both computer simulation and experimental results verify the working principle and the unique features of the EVT-based wind power generation system.

Thermal Analysis and Cooling System Design of Dual Mechanical Port Machine for Wind Power Application

Dual mechanical port (DMP) machine, a kind of electrical continuous variable transmission, is a very competitive alternative for vulnerable constant speed-ratio mechanical gearbox in wind power application and hybrid electrical vehicles. As the inner wound rotor is surrounded by the stator and the permanent magnet (PM) outer rotor, the DMP machine suffers from possible PM demagnetization and insulation failure under severe thermal condition. In this paper, thermal analysis and cooling system design of a DMP prototype machine are investigated. To predict the heat sources in actual operation, a transient cosimulation method is presented. Thermal parameters and the flow distribution in the cooling ducts are calculated in detail. Finite-element analysis of the thermal field is carried out to obtain the temperature distribution and two typical thermal contacts are considered. A robust fully forced-air cooling system with inner rotor teeth ducts is proposed for the DMP machine and a 10-kW DMP machine is prototyped. Experimental results at different working conditions are given to verify the theoretical analysis. Both simulation and experimental results reveal that the numerical approach and the proposed cooling system are not only more accurate and reliable, but can be referred to other electrical machine cooling system design.

Sizing the traction motor for optimal fuel efficiency in vehicle electrification

This paper presents the traction motor sizing, by means of motor rated torque and speed, for optimal urban fuel economy in two mild and three strong hybridisation powertrains on front-wheel-drive vehicles. The two mild hybrids are belt-integrated-starter-generator and Crankshaft-Integrated-Starter- Generator (C-ISG) systems. The three strong hybrids include an electric machine attached to the front axle, strong C-ISG system where motor is placed between a starting clutch and transmission, and single-mode electric variable transmission. Using the vehicle performance data as constraints and the motor rated torque and speed as the design variables, the objective function is to maximise the urban fuel economy.

Control of the dual mechanical port electrical machine and its applications in hybrid electrical vehicle

AbstractThis paper deals with the control strategy of the dual mechanical port electrical machine (DMPEM) which is suitable for hybrid electrical vehicles. In particular, it discusses the power management algorithm of the electrical variable transmission (EVT) system based on DMPEM. Also an equivalent circuit of DMPEM has been proposed for the first time, which gives clear physical meanings to all components in the circuit. The power flow of DMPEM under different operating conditions is analyzed from the equivalent circuit. The proposed control strategy is validated on a simulated EVT experiment platform. The result proves its validity. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

A Fuzzy Logic Global Power Management Strategy for Hybrid Electric Vehicles Based on a Permanent Magnet Electric Variable Transmission

The major contribution of this paper is to propose a Fuzzy Logic Global Power Management Strategy for Hybrid Electric Vehicles (HEVs) that are driven by the PM-EVT (PM machine—Electric Variable Transmission) powertrain, such that the PM-EVT will have superior advantages over other types of powertrains, including the current Toyota Prius powertrain for series-parallel HEVs. This has been investigated throughout three aspects. The first is the optimum power splitting between the Internal Combustion Engine (ICE) and the PM-EVT. The second is maximizing the vehicle’s energy capture during the braking process. Finally, sustaining the State of Charge (SOC) of the battery is adopted by a robust ON/OFF controller of the ICE. These goals have been accomplished by developing three fuzzy logic (FL) controllers. The FL controllers are designed based on the state of charge of the battery, vehicle’s velocity, traction torque, and the vehicle’s requested power. The integration of the studied system is accomplished via the Energetic Macroscopic Representation (EMR) simulation model strategy based on the software Matlab/Simulink. The PM-EVT based HEV system with the proposed power management strategy is validated by comparing to the Toyota Prius HEV. The vehicle’s performances have been analyzed throughout a combined long-trip driving cycle that represents the normal and the worst operating conditions. The simulation results show that global control system is effective to control the engine’s operating points within the highest efficiency region, exploiting of EVT machines for capturing maximum braking energy, as well as to sustain the SOC of the battery while satisfy the drive ability. The proposed control strategy for the studied HEVs sounds interesting and feasible as supported by a large amount of simulation results.

Traction Motor Sizing for Optimal Fuel Economy in Propulsion Hybridization

This paper presents the traction motor sizing for optimal urban fuel economy in two mild and three strong hybridization propulsion on front-wheel-drive vehicles. The traction motor sizes, by means of motor rated torque and speed, are optimized for maximum urban fuel economy. The two mild hybrids are Belt-Integrated-Starter-Generator (B- ISG) and Crankshaft-Integrated-Starter-Generator (C-ISG) systems. The three strong hybrid configurations include a strong C-ISG system where motor is placed between a starting clutch and the transmission, one-mode Electric Variable Transmission (EVT), and two-mode EVT. Using the simulated vehicle performance data as constraints and the motor rated torque and speed as the design variables, the objective function is to maximize the urban fuel economy. The purpose of this study is to provide a design guideline for hybrid propulsion configurations and component sizing of the traction motors.