Due to the price and supply insecurities for rare earth metal-based permanent magnet (PM) materials, a search for new PM materials is ongoing. The properties of a new PM material are not known yet, but a span of likely parameters can be studied. This paper presents an investigation on how the remanence and recoil permeability of a PM material affect its usefulness in a low speed, multi-pole, and PM synchronous generator. Demagnetisation is also considered. The investigation is carried out by constrained optimisation of three different rotor topologies for maximum torque production for different PM material parameters and a fixed PM maximum energy. The rotor topologies used are surface mounted PM rotor, spoke type PM rotor and an interior PM rotor with radially magnetised PMs. The three different rotor topologies have their best performance for different kinds of materials. The spoke type PM rotor is the best at utilising low remanence materials as long as they are sufficiently resistant to demagnetisation. The surface mounted PM rotor works best with very demagnetisation resistant PM materials with a high remanence, while the radial interior PM rotor is preferable for high remanence materials with low demagnetisation resistance.

Low speed, high torque machines are used in wind turbines where the turbine rotor is directly connected to the generator. A permanent magnet synchronous generator using high-energy rare-earth permanent magnets (PMs) is one common choice for this application, but rare-earth PMs have supply insecurities and cost risks. A rare-earth free 32-pole PM generator, using ferrite PMs in a spoke-type rotor, for use in a 12 kW experimental wind turbine is built and tested. Voltages and currents at load and no load are measured, as well as the magnetic field in the end regions of the machine. The generator can deliver the required power at nominal speed and has low harmonic content in the output. The electrical measurements are compared to two-dimensional finite element design calculations and the experimental results are lower than expected from simulations. The measured voltage is lower than expected, requiring a higher current than calculated for the rated power. Three-dimensional magnetic field simulations show that there are leakage flux paths in the end-regions that the two-dimensional design calculations overlook, explaining the discrepancy between simulations and measurements.

The price of rare-earth metals used in neodymium-iron-boron (NdFeB) permanent magnets (PMs) has fluctuated greatly recently. Replacing the NdFeB PMs with more abundant ferrite PMs will avoid the cost insecurity and insecurity of supply. Ferrite PMs have lower performance than NdFeB PMs and for similar performance more PM material has to be used, requiring more support structure. Flux concentration is also necessary, for example, by a spoke-type rotor. In this paper the rotor of a 12 kW NdFeB PM generator was redesigned to use ferrite PMs, reusing the existing stator and experimental setup. Finite element simulations were used to calculate both electromagnetic and mechanical properties of the design. Focus was on mechanical design and feasibility of construction. The result was a design of a ferrite PM rotor to be used with the old stator with some small changes to the generator support structure. The new generator has the same output power at a slightly lower voltage level. It was concluded that it is possible to use the same stator with either a NdFeB PM rotor or a ferrite PM rotor. A ferrite PM generator might require a larger diameter than a NdFeB generator to generate the same voltage.

The increased focus on ferrite magnets makes it interesting to investigate their suitability in electrical machines such as generators for wind power and motors for electric cars. Efforts are currently being made to improve the magnetic properties of ferrites. A simulation method is used to investigate how different magnetic properties such as remanence, coercivity and intrinsic coercivity affect the performance of electrical machines, here quantified as output torque. It is also ensured that the magnet is not partly demagnetized during a short-circuit event. Simulations are performed through a two-dimensional finite-element-based simulation method. Not all combinations of magnetic properties will render a usable design and it is therefore investigated how high the required values are for different magnetic properties as well as how high an output torque can be achieved. It is concluded that increasing the remanence or the coercivity can be quantified as an improved energy product, whereas improvement of the intrinsic coercivity enables the magnet to have a more optimal shape and thereby have a working point where the energy product is maximized. In addition it is found that for a fixed available magnetic energy, the performance does not change significantly with increasing remanence.

Magnetocaloric effects of various materials are getting more and more interesting for the future, as they can significantly contribute towards improving the efficiency of many energy intensive applications such as refrigeration, heating, and air conditioning. Accurate characterization of magnetocaloric effects, exhibited by various materials, is an important process for further studies and development of the suitable magnetocaloric heating and cooling solutions. The conventional test facilities have plenty of limitations, as they focus only on the thermodynamic side and use magnetic machines with moving bed of magnetocaloric material or magnet. In this work an entirely new approach for characterization of the magnetocaloric materials is presented, with the main focus on a flexible and efficient power electronic based excitation and a completely static test platform. It can generate a periodically varying magnetic field using superposition of an ac and a dc magnetic field. The scale down prototype uses a customized single phase H-bridge inverter with essential protections and an electromagnet load as actuator. The preliminary simulation and experimental results show good agreement and support the usage of the power electronic test platform for characterizing magnetocaloric materials.

This study challenges current design flow rate practices for instantaneous preparation of domestic hot water volume in Swedish residential buildings. Two research questions are addressed: (i) What design hot water flow rates should be used? (ii) What is a feasible threshold for peak flow coverage? The dataset comprises 21.5 million one-minute measurements with a resolution of 1 litre from 648 apartments, collected over 22 or 24 days in winter/spring. Based on these measurements, random sampling generated 10 000 multi-family buildings for each size from 2 to 100 apartments. Coverage thresholds according to the upper percentiles (98.5th, 99.5th, 99.9th) and the maximum were evaluated, with the 99.5th percentile selected for further analysis. The results show that current Swedish and European design principles substantially overestimate domestic hot water flow demands, leading to potential oversizing of components for hot water preparation. Our recommendation is to lower the current design flow rates by approximately 30% in residential buildings with more than 30 apartments. The flow reductions are somewhat lower in buildings with fewer than 30 apartments. Our proposal for new design flow rates reflects simultaneity effects more accurately, enabling reduced design flows with negligible risk of noticeable loss of comfort.