Small-scale wind turbines often utilise permanent magnet generators that supply power via an uncontrolled diode rectifier. In such systems, a custom generator design is required to optimise the aerodynamic and electromechanical performance; therefore the phase number of the generator is not restricted. This study assesses and compares the performance of prototype 700 W five- and three-phase permanent magnet generators connected to a diode bridge rectifier and their performance under open-circuit fault conditions. The simulation and experimental results demonstrate that the five-phase system can utilise a smaller DC-link capacitor and develops lower shaft torque ripple compared to the three-phase system. The three-phase generator can only tolerate one single-phase open-circuit failure. However, three possible open-circuit phase failure modes are considered in the five-phase machine: a single open-circuit phase and two open-circuit phases, where the two phases can be adjacent or non-adjacent. It is shown that the shaft torque ripple and output power are superior in the five-phase system with both the single-phase failure mode and the non-adjacent phase failure mode compared to the three-phase system with a single-phase failure. However, the adjacent phase failure mode is more extreme and generates less output power than the three-phase system. Simulation and finite-element analysis results are verified by experiments on the prototype 30-slot, four-pole, double-layer, surface-mounted permanent magnet generator.

A simple, direct mathematical model is developed for steady-state analysis of salient-pole, self-excited synchronous reluctance generators. The model does not require either the power consumed by the load or the ratio of the load to excitation current to be estimated which are prerequisite assumptions of previous analysis techniques. The model is verified by experiment which includes assessment of critical speed, excitation capacitance, no-load terminal voltage and voltage regulation on load. The experiments are performed using a prototype synchronous reluctance generator. The analysis technique is then used to investigate the effect that saliency, stator resistance and power factor have on the performance of the self-excited system.

For the majority of proposed wave- and tidal current-driven power generation applications, the electrical generators are submerged in sea water, frequently at many metres of depth. The environment places significant stress on the rotating or translating seals between the driven shaft and the electrical generator leading to reduced reliability and lifetime. A potential solution is to eliminate the seal, thereby flooding the generator and allowing sea water to circulate around the shaft, windings and rotor of the machine. The impact of immersing the windings of the machine in sea water is assessed here. Specifically, the impact that the insulation has on the leakage capacitance as well as the consequent impact the leakage capacitance has on current and voltage oscillations in the switching converter used to excite the winding is assessed. Thermal tests are conducted to assess the impact of the insulation on the thermal conductance of the coil–insulation system. Experimental evidence is provided.

The majority of electrical generators in wave and tidal power plants are face harsh environmental conditions. Particularly the seals between the moving shaft and the stationary generator as these are mechanically stressed under pressure of the sea water. Flooding the electrical generator and the air gap respectively is a possible solution that would overcome seal failure. With this proposal, the strains on the seals can be reduced as they would have to seal non-moving parts against the sea water only. The lifetime of seals could be prolonged with this measure. On the other hand, this will also result in changes to the electrical behavior of the windings and the electrical machine respectively. This is the subject of this paper. Mainly, these are changes to the winding capacitances. They result in a different transient behavior, for example when the machine is operated with switched inverters. The performance of six different insulation materials for the submersion in sea water are studied and the results are compared to the standard operation in air. Furthermore, with the changed sealing methods the thermal characteristics are altered, which will be also analyzed within this work.

This paper discusses the benefits of five-phase technology for applications including wind turbine generators. The performances of three-phase and five-phase permanent magnet generator (PMG) systems that use diode rectifier circuits are discussed. Investigations proved that the five-phase topology harnesses some specific and important benefits that are not provided by three-phase systems. The benefits include improved fault tolerance and reliability, and reduced voltage and torque ripple and size of DC link capacitor. These are general improvements that are sought after in many applications including renewable energy applications. The paper also discusses the design of a novel five-phase wind turbine generator which was optimised to make use of the key competitive advantages of our five-phase technology in renewable energy sector. Finite element (FE) and Matlab / Simulink are used in the investigations. Test results are also presented in this paper and used to validate simulations where possible.

In this paper, performance of three- and five-phase permanent magnet generators (PMG) feeding a rectifier system are compared for small-scale wind generator systems. The volume and rated speeds of the two generators are kept equal and determined using FEM 2D. No-load induced voltage, self and mutual inductances and resistance are calculated and used to simulate the performance of the 3-phase and 5-phase generators coupled to a dc link through a diode bridge rectifier. Generator mathematical models are developed and simulated. The simulations show that five-phase system has torque ripple that is a factor of 7 lower than the three-phase system with an almost identical efficiency figure.