Hans Bernhoff

Electrical Motor Drivelines in Commercial All-Electric Vehicles: A Review

This paper presents a critical review of the drivelines in all-electric vehicles (EVs). The motor topologies that are the best candidates to be used in EVs are presented. The advantages and disadvantages of each electric motor type are discussed from a system perspective. A survey of the electric motors used in commercial EVs is presented. The survey shows that car manufacturers are very conservative when it comes to introducing new technologies. Most of the EVs on the market mount a single induction or permanent-magnet (PM) motor with a traditional mechanic driveline with a differential. This paper illustrates that comparisons between the different motors are difficult by the large number of parameters and the lack of a recommended test scheme. The authors propose that a standardized drive cycle be used to test and compare motors.

Multiphysics simulation of wave energy to electric energy conversion by permanent magnet linear generator

The possibility to use three-phase permanent magnet linear generators to convert sea wave energy into electric energy is investigated by multiphysics simulations. The results show a possibility, which needs to be further verified by experimental tests, for a future step toward a sustainable electric power production from ocean waves by using direct conversion. The results suggest that wave energy can have an impact on tomorrows new sustainable electricity production, not only for large units, but also for units ranging down to 10 kW. This gives wave power a larger economical potential than previously estimated. The study demonstrates the feasibility of computer simulations to give a broad, and in several aspects a detailed, understanding of the energy conversion. The simulation results also give a useful starting point for future experimental work.

Economical considerations of renewable electric energy production—especially development of wave energy

Investments in renewable energy plants normally only take standard economic key figures into account, such as installed rated power, the market price of energy and the interest rate. The authors propose that the degree of utilisation, i.e. the ratio of yearly produced energy in the installation to the installed power, must be included due to its significant impact on the present value of the investment. A site with a limited average wave height could be of economic interest if the utility factor for the installation is high, since the investment cost (associated with the power installed) can be better adjusted to conditions at the particular site. In the case of wave power from the Baltic Sea with its limited variation in wave height (and limited average wave height), this indicates that the economic potential is best for smaller units.

Catch the wave to electricity

The ocean are largely an untapped source of energy. However, compared to other energies, power fluctuations for ocean waves are small over longer periods of time. This paper present a grid-oriented approach to electricity production from ocean waves, utilizing a minimal amount of mechanical components.

Simulation of wave-energy converter with octagonal linear generator

To extract electrical energy from sea waves in a commercially and technologically acceptable manner, a number of issues have to be solved. Electricity generation by means of direct conversion of the oscillating gravitational potential energy of a floating buoy can be anticipated, provided a proper design of a generator could be made. This paper deals with the simulation of a novel design for a linear generator aimed for the extraction of energy from ocean waves. The ocean waves are modeled by 4-m-height sinusoidal waves with a characteristic period of 7 s. A wide range of the geometrical sizes, permanent magnets, stator winding, and spring forces acting on the buoy are possible. This paper presents simulations of octagonal three-phase linear generators in the 100-kW power range. The beneficial effects of a stator of octagonal shape are briefly investigated, but not studied in depth. The main emphases in the present study have been to decrease power fluctuations and suppress voltage harmonics. In conventional rotating machines, well-known measures are to use a fractional number of slots per pole and phase, and an additional method is to make the pole edges smoother. These methods are here simulated for the first time on a linear machine aimed for ocean wave-energy conversion and a substantial reduction in power fluctuations and voltage harmonics are predicted.

High-Speed Kinetic Energy Buffer: Optimization of Composite Shell and Magnetic Bearings

This paper presents the design and optimization of a high-speed (30 000 r/min) kinetic energy storage system. The purpose of the device is to function as an energy buffer storing up to 867 Wh, primarily for utility vehicles in urban traffic. The rotor comprises a solid composite shell of carbon and glass fibers in an epoxy matrix, constructed in one curing. The shell is optimized using a combined analytical and numerical approach. The radial stress in the shell is kept compressive by integrating the electric machine, thereby avoiding delamination. Radial centering is achieved through eight active electromagnetic actuators. The actuator geometry is optimized using a direct coupling between SolidWorks, Comsol, and Matlab for maximum force over resistive loss for a given current density. The optimization results in a system with 300% higher current stiffness than the reference geometry with constant flux area, at the expense of 33% higher power loss. The actuators are driven by semipassive H bridges and controlled by an FPGA. Current control at 20 kHz with a noise of less than 5 mA (95% CI) is achieved, allowing position control at 4 kHz to be implemented.

A 225 kW Direct Driven PM Generator Adapted to a Vertical Axis Wind Turbine

A unique direct driven permanent magnet synchronous generator has been designed and constructed. Results from simulations as well as from the first experimental tests are presented. The generator has been specifically designed to be directly driven by a vertical axis wind turbine and has an unusually low reactance. Generators for wind turbines with full variable speed should maintain a high efficiency for the whole operational regime. Furthermore, for this application, requirements are placed on high generator torque capability for the whole operational regime. These issues are elaborated in the paper and studied through simulations. It is shown that the generator fulfils the expectations. An electrical control can effectively substitute a mechanical pitch control. Furthermore, results from measurements of magnetic flux density in the airgap and no load voltage coincide with simulations. The electromagnetic simulations of the generator are performed by using an electromagnetic model solved in a finite element environment.

Injection dependent long carrier lifetimes in high quality CVD diamond

Abstract In this paper we report an experimental study of photocurrent mobility×lifetime products and free carrier lifetimes in CVD grown polycrystalline diamond of various qualities. The investigated samples are low impurity samples, nitrogen content ∼10 15 cm −3 , with an average grain size ranging from 25 μm up to 110 μm. This large difference in average grain size makes it possible to distinguish effects due to lifetime limiting trapping and recombination defect centers inside the grains from effects caused by defect centers at grain boundaries. At low carrier densities, 13 cm −3 , the effective free carrier lifetime is in the sub-nanosecond to nanosecond range in all samples due to intra-grain trapping and recombination centers. At high carrier densities, >10 13 cm −3 , the intra-grain centers becomes saturated and the effective lifetime becomes predominately given by carrier diffusion to and recombination at the defects related to the grain boundaries. Hence, the effective lifetime at high carrier densities is strongly related to the average grain size and increases up to several tens of nanoseconds, in samples with a large average grain size, whereas it remains in the nanosecond range for samples with small average grain size. In addition, we observe a lower mobility×lifetime product and decay constant with increasing nitrogen content, clearly showing the negative influence of nitrogen and nitrogen-related defects on these important material parameters.

Simulation of cogging in a 100 kW permanent magnet octagonal linear generator for ocean wave conversion

Fluctuations in the torque acting on the rotor in a rotating electric generator i.e., cogging, gives unstable rotor motion and can venture reliable operation of the machine. Cogging also gives a similar fluctuation in the output power. This paper presents a study of the cogging force in a linear permanent magnet generator. A constant output power is possible in a rotating machine with three phases winding. In a linear generator, due to the reciprocate piston motion, power fluctuations on the slow time scale of the piston bounce period cannot be avoided. Associated with power variations on a time scale shorter than the piston bounce motion is fluctuations on the force (torque) acting on the piston, i.e., cogging. Cogging is not less dangerous in linear generators compared to rotation machines and the problem requires investigation. The paper investigates means to reduce cogging by improving the geometrical design of the stator. In particular, rational number of the slots per pole and phase reduce the cogging by one order of magnitude

FEM simulations and experiments of different loading conditions for a 12 kW direct driven PM synchronous generator for wind power

Results from experiments on a direct driven permanent magnet synchronous generator are presented. Dynamic simulations have been performed using the finite element method in order to study the generator. The simulations are performed by using an electromagnetic model, which is described by a combined field and circuit equation model and is solved in a finite element environment. The stator winding of the generator consists of circular cables and the rotor has surface-mounted, arched, permanent magnets. A complete experimental setup has been used consisting of a motor, a frequency converter, a gearbox and electrical loads. The generator is connected to a purely resistive load. Measurements have been performed for different rotational speeds and different loads. Furthermore, the generator has been studied for the realistic wind turbine loading conditions for operation at the optimum tip speed ratio. The variable speed operation in a wind turbine is evaluated and discussed. The agreement between experimental results and simulations based on finite element calculations is high, indicating precise simulations. The measurement errors are calculated and discussed. Furthermore, other sources of error are suggested and discussed that could explain the differences between the simulations and the measured data.