Mats Alaküla

Grid-Connected Integrated Battery Chargers in Vehicle Applications: Review and New Solution

For vehicles using grid power to charge the battery, traction circuit components are not engaged during the charging time, so there is a possibility to use them in the charger circuit to have an onboard integrated charger. The battery charger can be galvanically isolated or nonisolated from the grid. Different examples of isolated or nonisolated integrated chargers are reviewed and explained. Moreover, a novel isolated-high-power three-phase battery charger based on a split-phase permanent-magnet motor and its winding configuration is presented in this paper. The proposed charger is a bidirectional high-power charger with a unity power factor operation capability that has high efficiency.

An Isolated High-Power Integrated Charger in Electrified-Vehicle Applications

For electric and hybrid vehicles that use grid power to charge the battery, traction circuit components are not normally engaged during the charging time; hence, there is a possibility of using the traction circuit components in the charger circuit to have an onboard integrated charger. An isolated high-power integrated charger based on a special electrical machine with a double set of stator windings is described. Through the reconfiguration of the motor stator windings in the charging mode, a six-terminal machine is achieved. The so-called motor/generator acts as an isolated three-phase power source after synchronization with the utility grid in the charging mode. This rotary isolated power source constitutes a three-phase boost rectifier (battery charger) with full utilization of the inverter. The motor windings are reconfigured by a relay-based switching device for the charging and traction modes. This paper presents the mathematical model of the motor/generator and explains the systems functionality for the traction and charging modes. Furthermore, the charger grid synchronization and charge control are described. Finally, the simulation results are presented for a practically designed system with a traction power of 25 kW and a possible charge power of 12.5 kW.

Field-oriented control of saturated induction machines

A nonlinear, field-oriented model is described for saturated induction machines. The model is an extended version of the rotor-flux-oriented dynamic model developed by W. Leonhard (1985), which is valid under linear magnetic conditions and is used in a wide range of applications. The effects of main flux saturation are discussed. The theory is applied to an induction machine subjected to field-oriented control which operates in the field-weakening region where the changes of saturation level play an important role in the dynamic behavior. It is also shown that, with the implemented current control, the control response is seriously distorted by the effects of variable saturation during field weakening. >

An Integrated 20-kW Motor Drive and Isolated Battery Charger for Plug-In Vehicles

For vehicles using grid power to charge the battery, traction circuit components are not normally engaged during the charging time, so there is a possibility to use them in the charger circuit to have an on-board integrated motor drive and battery charger. An isolated high-power three-phase integrated motor drive and charger based on a split-phase permanent magnet motor is presented in this paper. The motor winding connections are reversible by a relay-based switching device for traction and battery charging. In traction mode, the motor is a classical three-phase motor, but in charging mode it is a rotating isolating transformer providing a three-phase voltage source for the inverter to charge the battery. A mathematical model of the motor with six stator windings is presented for an arbitrary phase shift in windings. For the charging mode, the split-phase motor grid synchronization process and charge control are explained including the developed controller. A 20 -kW system is designed and implemented to verify the proper operation of the proposed system. Simulation and practical results are provided to show the system performance in terms of functionality, dynamic response, and efficiency. Moreover, some discussions, recommendations, and limitations are provided to give more practical insights.

Direct oil cooling of traction motors in hybrid drives

This paper presents comparisons of utilizing direct oil cooling approaches and conventional indirect cooling approaches for electrical motors which are mounted in HEVs or ZEVs. Both finite volume Computational Fluid Dynamic (CFD) model by FLUENT and finite element electromagnetic model by JMAG are applied to make the simulation accurate and comprehensive. Average temperature over the stator back, pressure drop between inlet and outlet and average heat transfer coefficient over the cooling duct are evaluated under identical flow rate, velocity and pressure drop for different cooling approaches. In addition, the influences on torque and power performances by the cooling ducts made in the housing or stator back are evaluated by JMAG model. The directly cooled motors show lower temperature rises at the stator back since the direct contact between coolant and stator back can avoid the unnecessary thermal contact resistances between the stator back and housing, meanwhile make the coolant more close to the heat sources, and thus improve the cooling efficiency.

Dynamic evaluation of the overloading potential of a convection cooled permanent magnet synchronous motor

In order to obtain the maximum efficiency from a hybrid driveline it is crucial to optimize the power distribution between the electric drive and the internal combustion engine. An accurate estimation of how much electric power can be delivered at any instant of time is therefore of great interest. Such estimation is dependent on several factors, as the state of charge of the battery, the temperature and the cooling conditions of the motor and the power electronics at that particular moment. This article proposes a method for evaluating the overloading potential of the electric drive dynamically at any time, based on a previously developed thermal model. Alternative modelling techniques are discussed and the resulting thermal model is validated against experimental measurements.

Dynamic Thermal Modeling and Application of Electrical Machine in Hybrid Drives

This paper presents a holistic view of thermal modeling for an electrical machine used in a Hybrid Electrical Vehicle (HEV). This interconnected system model focuses on the thermal assessment of an electrical machine in a HEV application and estimates the time to failure of the machine depending on the construction of the insulation system and the exploitation of the machine. A transient thermal model of the machine is made as a Lumped Parameter Model (LPM) based on dimensions, material properties and Finite Element Analysis (FEA) determining the power loss model and Computational Fluid Dynamics (CFD) cooling model. The LPM thermal model is compared to measurements and later used in a vehicle powertrain model. Based on the verified thermal model, the estimation of the winding temperature in the machine over different driving cycles is used to predict the thermal degradations of the main insulation and the thermal lifetime of the machine.

Impact of Soft Magnetic Material on Construction of Radial Flux Electrical Machines

Electrical machines with distributed concentrated windings are challenging the selection of the soft magnetic materials due to stator design and power conversion efficiency. A shorter magnetization path and relatively high magnetization frequency is beneficial for low-permeability soft magnetic materials with low power losses in the core. In this paper, a three-phase machine with laminated and iron powder cores is analyzed with focus on a modular winding design, the torque capability, and the stator energy conversion efficiency. Different iron powder cores are compared to a laminated core using 2-D finite element analysis (FEA). The three-phase machine torque is compared among a conventional distributed concentrated winding, an axially distributed wave-winding, and a number of circumferentially distributed wave-winding segments. According to 3-D FEA, the conventional coils are preferred if the permeability of the core is low.

Dynamic Testing characterization of a synchronous reluctance machine

The dynamic testing method (DTM) has been shown to accurately characterize the electromagnetic model of permanent magnet synchronous machines by describing the relationship between the phase currents and the linked magnetic flux with minimal amount of test equipment as compared with traditional methods. Within this paper, a performance evaluation of the DTM applied to a synchronous reluctance machine is presented. This paper discusses the challenges of a dynamic test of a nonlinear synchronous machine and suggests a fuzzy proportional, derivative and integral controller (PD + I) controller for improved control performance and measurements. Finally, the DTM measurements are compared with the results of the constant speed method (CSM). The CSM measurements of flux linkage and torque curves confirm the validity of the DTM measurements for this machine.

Heat transfer analysis of a traction machine with directly cooled laminated windings

A directly enhanced cooled winding in an electrical traction machine has the potential to extend the operation range, which is in particular attractive for a traction application when operating near peak power for extended periods of time. This paper presents the heat transfer analysis of a modular machine segment with a laminated winding. The laminated winding has a great potential when it comes to production of the winding and the thermal management of the excessive power losses in the winding. The prototype is built and assessed based on experimental measurements and finite element analysis. The results indicate some practical challenges of integrating the combined heat exchanger and winding and controlling the coolant flow through the machine construction. The prototype machine shows a limited enhanced cooling capability mostly due to flow leakage while the results from the simulation models indicate the great potential of direct cooled windings.