Mats Leksell

Integrated chargers for EV's and PHEV's: examples and new solutions

The battery is an important component in an electric vehicle (EV) or a plug-in hybrid electric vehicle (PHEV) and it should be charged from the grid in a cost efficient, preferably fast and definitely safe way. The charger could be an on board or an off board charger. For an on board charger it is possible to use available hardware of the traction system, mainly the inverter and the electric motor, in the charger circuit. This is called an integrated charger. In this paper, different examples of integrated chargers are reviewed and explained. Additionally, other possible solutions of integrated chargers are described.

Thermal Analysis of a PMaSRM Using Partial FEA and Lumped Parameter Modeling

This paper presents an advanced lumped parameter (LP) thermal model for a permanent-magnet assisted synchronous reluctance machine (PMaSRM) developed for propulsion in a hybrid electric vehicle. Particular focus is put on the stator winding and a thermal model is proposed that divides the stator slot into a number of elliptical copper and impregnation layers. The model is enabled by the derivation of an approximate analytical expression for the thermal resistance of an elliptical cylinder with constant thickness. The approach is attractive due to its simplicity and the fact that it closely models the actual temperature distribution for common slot geometries. Additionally, an analysis, using results from a proposed simplified thermal finite element model representing only one slot of the stator and its corresponding end winding, is presented in which the number of layers and the proper connection between the parts of the LP thermal model representing the end winding and the active part of winding is determined. The presented thermal model is evaluated experimentally on a PMaSRM equipped with a water cooling jacket, and a good correspondence between the predicted and measured temperatures is obtained.

Synchronization at startup and stable rotation reversal of sensorless nonsalient PMSM drives

In this paper, a variant of the well-known voltage model is applied to rotor position estimation for sensorless control of nonsalient permanent-magnet synchronous motors (PMSMs). Particular focus is on a low-speed operation. It is shown that a guaranteed synchronization from any initial rotor position and stable reversal of rotation can be accomplished, in both cases under load. Stable rotation reversal is accomplished by making the estimator insensitive to the stator resistance. It is also shown that the closed-loop speed dynamics are similar to those of a sensored drive for speeds above approximately 0.1 per unit, provided that the model stator inductance is underestimated. Experimental results support the theory.

An integrated charger for plug-in hybrid electric vehicles based on a special interior permanent magnet motor

For a plug-in hybrid electric vehicle (PHEV), the battery needs to be charged from the grid while the vehicle is parked. The traction system components are normally not engaged during the charging time so there is a possibility to use them in the charger system to develop an integrated charger. An innovative high power isolated three-phase bi-directional integrated charger with unit power factor operation is introduced for PHEVs based on a special configuration of the ac motor. The winding of the machine is re-arranged in charging mode to have a three-phase boost based high power battery charger. The system configuration, the device model (machine with multiple windings), traction and charging system functionality and charger control are presented in this paper.

Thermal Modeling of Directly Cooled Electric Machines Using Lumped Parameter and Limited CFD Analysis

This paper presents a practical approach to model thermal effects in directly cooled electric machines. The main focus is put on modeling the heat transfer in the stator winding and to the cooling system, which are the two critical parts of the studied machines from a thermal point of view. A multisegment structure is proposed that divides the stator, winding, and cooling system into a number of angular segments. Thereby, the circumferential temperature variation due to the nonuniform distribution of the coolant in the cooling channels can be predicted. Additionally, partial computational fluid dynamics (CFD) simulations are carried out to model the coolant flow in the cooling channels and also on the outer surface of the end winding bodies. The CFD simulation results are used as input to the analytical models describing the convective heat transfer to the coolant. The modeling approach is attractive due to its simplicity since CFD simulations of the complete machine are avoided. The proposed thermal model is evaluated experimentally on two directly cooled induction machines where the stator winding is impregnated using varnish and epoxy, respectively. A good correspondence between the predicted and measured temperatures under different cooling conditions and loss levels is obtained.

Design and performance analysis of a permanent-magnet assisted synchronous reluctance machine for an integrated charger application

In a plug-in hybrid electric vehicle equipped with an integrated charger, the electric machine and the inverter, which in traction mode are used to propel the vehicle and recover energy during braking, are also used to charge the battery from the grid while the vehicle is at rest [1]. This paper studies the design and performance of a permanent-magnet assisted synchronous reluctance machine (PMaSynRM) both in traction and charging mode. Designing a PMaSynRM in order to obtain optimal reluctance and magnetic torque components is a complex task since rotor dimensioning for one torque component (magnet or reluctance torque) limits the possibility to optimize the other torque component. This paper identifies and relates the design parameters that influence these torque components and the performance of the machine using simulations based on the finite element method. The results are compared based on developed torque, torque ripple and relative values of the resulting magnet and reluctance torque.

Machine design considerations for an MHF/SPB-converter based electric drive

This paper identifies suitable phase/slot/pole combinations for fractional-slot concentrated winding (FSCW) permanent-magnet machines when forming an integrated electric drive together with a modular high frequency (MHF) converter or a stacked polyphase bridge (SPB) converter.

Minimizing power pulsations in a free piston energy converter

A free piston energy converter (FPEC) is a combination of a linear combustion engine and a linear electrical machine. This type of converter has many potential advantages like high efficiency, low fuel consumption and low emissions, which make it suitable for a series hybrid vehicle. However, the generated power pulsates due to the reciprocating motion of the translator. This paper presents a comparative study on how different generator force profiles affect the electric power pulsations produced by the FPEC. In addition, the influence of these profiles on translator motion and the needed power converter current is investigated. A dynamic free piston model is used for the investigation. Results show that the generator force profile has a major impact on the power pulsation amplitude and peak current demand. Thus the chosen force profile affects dimensioning of power converter, electrical machine and energy storage. Furthermore, loading the translator heavily in the beginning or end of the stroke seems to affect the peak translator velocity more than evenly distributed load profiles

Direct sensorless speed control of PM-motors-a simple and effective sensorless method

This paper presents a method for sensorless speed control of nonsalient permanent magnet synchronous motors (PMSM). Special attention is put on the startup and synchronization of the motor, which are crucial for good performance of the drive system. The method merges both estimation and control of speed into one combined algorithm. Good performance is verified theoretically and experimentally.

Performance of a Series Hybrid Electric Vehicle with a Free-Piston Energy Converter

The free-piston energy converter (FPEC), consists of an internal combustion engine and a linear electrical machine. It is characterised by high efficiency and rapid transient response, which makes it suitable for hybrid electric vehicles. In this paper we investigate the performance gain of utilising the FPEC in a medium sized series hybrid electric vehicle (SHEV), compared to a conventional diesel-generator. First, we utilise optimisation to find a lower limit on the SHEVs fuel consumption for a given drive cycle. In addition, we develop a control strategy based on the ideas of an equivalent consumption minimisation (ECM) proposed earlier in the literature. The results show a potential decrease in fuel consumption of up to 19% compared to a diesel-generator SHEV. The ECM control strategy behaves as desired, and a 13% reduction of fuel consumption compared to a traditional load-following strategy is achieved