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A thermal analysis of an interior permanent magnet machine using a lumped parameter model is presented, with the objective to evaluate several rotor cooling techniques for electric vehicle applications which are needed in order to achieve higher power densities. Two of the selected rotor cooling techniques involve cooling of the shaft by pumping a liquid through a channel in the shaft and by implementing a rotating heat pipe. The third selected rotor cooling technique is accomplished by pointing liquid jets towards the hub of the rotor. The lumped parameter model and implementation of these newly modeled cooling techniques are described. From the temperature distributions of the electrical machine resulting from water jacket cooling in combination with the different rotor cooling techniques, it was revealed that when the rotor of an electrical motor contains a hub, shaft cooling methods are ineffective. Rotor jet cooling however resulted in the most effective cooling approach to minimize permanent magnet temperatures.

An electrical variable transmission (EVT) is an electromagnetic power-split device with two mechanical and two electrical ports. It can be used in hybrid electric vehicles to split the power to the wheels in a part coming from the combustion engine and a part exchanged with the battery. Although crucial for the EVT design and evaluation, no papers are found to give a detailed overview of the different loss components in such a machine and how they can be calculated and measured. In contrast to conventional electrical machines, this machine has more degrees of freedom, which can be exploited to measure the different loss contributions separately. This paper proposes a methodology to identify and measure the different loss components in this kind of machines. The proposed method is able to identify the iron losses in stator and inner rotor, the copper losses, bearing losses, and slip ring friction losses separately. To this end, measurements of both torque and speed sensors in different operating points are combined. The methods are applied to identify the different loss contributions in a prototype permanent magnet assisted EVT, both in no-load operation as under load where its functionality as power-split device is evaluated.

In most applications where a variable transmission is required, either an EVT or a CVT would be viable options. In order to obtain a justified decision between both variable transmissions, the operating range and efficiency should be known better. To be able to pinpoint the pros and cons based on efficiency and operating range, a detailed comparison is necessary. However, to the knowledge of the authors there is no such study reported in literature so far. In this paper a permanent magnet Electrical Variable Transmission (EVT) is benchmarked against a half toroidal Continuously Variable Transmission (CVT) and this during steady state conditions. This paper provides the constraints for the comparison and results based on detailed models of both technologies. Two comparative studies are carried out: on one hand a study based on equal maximum output torque and on the other hand a study based on equal rated power. The outcome of the study shows that the CVT is in favor for high input torques and that the EVT is dominant for high input speeds.

An electrical variable transmission (EVT) is an electrical machine consisting of a stator and two concentric rotors. It is a competitive alternative for power split devices used in current series–parallel hybrid electric vehicles (HEVs). Although tending to have high power densities, permanent magnet (PM) machines suffer from no-load iron losses. Since the torque interaction between stator and outer rotor is low during large time intervals, the EVT in this paper possesses a flux bridge with dc-field winding to modulate the stator field, while maintaining the inner rotor flux linkage. In this paper, a torque controller is proposed that optimally combines the stator, dc-field, and inner rotor currents in order to minimize the copper and iron losses in every operating point of torque and speed on both rotors. Also the electromagnetic coupling between both rotors is considered. It turns out that there are two optimal load angles for the stator currents, of which one of the two is dominant depending on speed and torque. The control is tested on a 120 kW prototype EVT, and measurement results are given to illustrate the optimal performance obtained with the proposed torque control. In addition, efficiencies are measured in order to support the statements made concerning the proposed method.

The Electrical Variable Transmission is a complex device of which the electromagnetic behavior is typically studied based on FEM calculations. As the computational effort of these FEM calculations is high, it is a challenging task to investigate the impact of design changes on the performance of the device. To solve this, a Magnetic Equivalent Circuit model is presented. This study shows that the suggested model yields torque values, throughout a major part of the EVT operating range, which are within 10% of torque values obtained via FEM calculations but at a much lower computational effort. As the Magnetic Equivalent Circuit is solely based on known sources, material properties and the parametrized geometry of the EVT, it can, later on, directly be used for design optimization strategies.

This article presents a comparative study of a standard PI controller with three more advanced predictive current control schemes, applied to a surface mounted permanent magnet synchronous machine fed by a two-level voltage source inverter. The three predictive current controllers are: finite-set model based predictive control, deadbeat control, and a combination of both previous algorithms. Key performance indicators concerning control- and voltage quality, dynamic performance and parameter sensitivity, enable a quantitative comparison of the four controllers. The indicators are not only obtained from simulation results, they are also experimentally validated on a 4 kW axial flux permanent magnet synchronous machine with yokeless and segmented armature topology. A general conclusion is that the PI controller excels when it comes to control quality: only the deadbeat controller can compete with its low torque ripple. The predictive controllers on the other hand show superior dynamic performance.

As inverters are often used in critical applications, reliability is an important issue. In particular, the power electronic switches and gate drivers, the most essential components of the inverter, are vulnerable parts in real live operation. Therefore, this paper focuses on open-switch fault detection for multilevel inverters. When a single-switch open-circuit fault occurs in one of the power electronic switches, the algorithm can detect the fault and the switch that is causing it. The detection is worked out for both a linear resistive inductive load and an induction motor. The proposed algorithm is an extension of an already available finite-set model-based predictive control algorithm. Therefore, no extra hardware or measurements are required. This paper also discusses a suggested method for reconfiguration after fault detection. Computer simulation and experimental verifications validate the proposed methods.

This paper describes how an electrical variable transmission (EVT) can be used as an alternative for mechanical continuously variable transmission (CVT) systems. An EVT is an electromagnetic power split device having two mechanical and two electrical ports. The speed ratio between both mechanical ports (rotors) can be varied in a continuously variable way, so that this machine can be used as an electromagnetic alternative for the mechanical push-belt and half-toroidal CVT. Its operating principle is based on splitting the power into an electromagnetic direct path and an electrical path involving two inverters connected back to back. Its potential use as a CVT is investigated by comparing experimental data against toroidal and belt CVT data from literature having comparable power ratings. To this end, measurements are performed on a prototype $\text{120-kW}$ permanent magnet EVT.

An electrical variable transmission is a dual rotor electromagnetic device that can be used in hybrid electric vehicles to split the power to the wheels in a part coming from the combustion engine and a part exchanged with the battery. Since the power split is done in an electromagnetic way, no mechanical gears and corresponding friction losses are present. However the losses mainly originate from copper, iron, inverter and bearing losses. In this paper these loss contributions and their relative importance are calculated over a driving cycle, an analysis that can be used for further design optimizations. The loss models, that have previously been fitted on no-load measurements on a prototype machine, predict a mean EVT power split efficiency of 89% over the low power New European Driving Cycle. The main loss components and their origin are hereby discussed, and improvements are proposed.

In this article a control strategy for an induction machine (IM) based electric variable transmission (EVT) for hybrid electrical vehicles (HEV) is presented. Such electrical machines consists out of two rotors resulting in a power split and a decoupling of the internal combustion engine (ICE) speed and wheel speed. The proposed control method relies on a finite-set model based predictive control (FS-MBPC) algorithm to steer the torque of both rotors as well as the flux level within the machine. The advantage of this controller is the inherent feature of field weakening and strong reduction of Joule losses as a result of the optimisation routines within this controller using a cost function. As the focus of this paper is on the control method, simulation runs in Matlab/Simulink are performed to asses the feasibility and effectiveness of the proposed control method.

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.

International audience; Smart grid applications, renewable energy utilization and electric vehicles (EVs) are attracting researchers due to their importance nowadays as well as in the future. An efficient power electronic converter is a main and common topic for research in this area. In this paper, a prototype of the electrical part of a power-train for EVs using an advanced multilevel converter topology is introduced, discussed and analysed. A comparison between the advanced converter, two-level and conventional multilevel converter topology is discussed as well. A switch function model is derived and discussed for the proposed converter. A mathematical model for the converter supplied by a fuel-cell (FC) and boost-converter (BC) is implemented with Matlab/Simulink. The simulation results are analysed to evaluate the converter. The evaluation is based on the harmonic analysis and power loss calculations. The converters are tested at different switching frequencies to show the effect of this variable on the converter loss. The results indicate that the proposed converter is 1.32% more efficient compared to conventional five-level DCC. Moreover, the lowest harmonic content, for all of the studied converters, is the proposed one.

An electrical variable transmission (EVT) is an electromagnetic device with multiple rotors and multiple shafts. In hybrid electric vehicles 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. This paper summarizes how an induction machine based EVT can be modeled and controlled using field oriented control.

In a drive train a continuously variable transmission (CVT) has the advantage that the combustion engine can be driven in its optimal point along the requested power curve, which enhances overall efficiency. Moreover there is no power loss during shifting of gears which is often demanded in off highway applications. Several mechanical and hydraulic CVT's exist that have already proven their functionality, each having their pros and cons. This paper introduces the concept of an electromagnetic CVT which has some inherent advantages compared to mechanical systems being the absence of friction and the need for lubrication, only two moving parts and inherent overload protection. The machine can be seen as a conventional induction motor with two rotors. The rotors are arranged in a concentric way and are electromagnetically coupled. The working principle is explained, and an efficiency map is calculated for a scaled test case. It is concluded that with a smart choice of the interrotor flux a good efficiency can be achieved in a broad range of torque and flux of the interrotor.