• Energy Research

In this paper, the improved turbine power matching of passive wind energy systems for dc-connected battery storage applications with an impedance matching method is investigated. The passive system uses a direct-drive permanent magnet synchronous generator and is directly connected via a diode rectifier to the dc fixed-voltage battery storage. To improve power matching, an external inductance is added to the passive system between the generator and the diode rectifier. A static finite element based solution method is proposed to accurately calculate the necessary external inductance to achieve near maximum power point matching. It is shown that the proposed finite element based calculation method is computationally efficient and excellently suited for generator design optimization, which is critical for this application. It is also shown that by rewinding existing machines for the correct cut-in speed and adding the external inductance for improved power matching, existing machines can be effectively recycled for passive wind energy systems. The proposed static finite element solution method's accuracy and improved power matching are confirmed with measured results on a sub 5 kW power level.

This paper discusses nonlinear proportional-integral (PI) current control with anti-windup of reluctance synchronous machines (RSMs) for which the flux linkage maps are known (e.g. obtained by FEM analysis or measurements). Due to the nonlinear flux linkage, the current dynamics of RSMs are highly nonlinear and, so, to obtain an (almost) identical current closed-loop dynamics over the complete operation range, the controller parameters and the disturbance compensation terms must be adjusted online at each sampling instant. The model-based controller design is derived theoretically in state space. The theoretical results are illustrated and validated by simulation and measurement results.

Small-scale uncontrolled passive wind generator systems are an attractive solution for rural energy generation because of the system’s reliability and low cost. However, designing these uncontrolled wind generators for good power matching with the wind turbine is challenging and often requires external impedance matching. In this paper, permanent magnet generators with different stator and rotor structures were investigated and designed to increase the generator’s synchronous inductance for a natural impedance matching. For the design methodology, multi-objective optimisation was used to design the generators for near-maximum turbine power matching, whereby internal impedance matching was reached as much as possible. It was shown that altering the placement and orientation of the permanent magnets in the rotor is a viable method to achieve the desired impedance matching; however, these generators do not have the best performance. It was found that the surface-mounted permanent magnet generator with semi-closed slots was the optimum topology. An optimised generator prototype was tested for the experimental validation. All designs were verified by comparing the results of 2D and 3D finite-element analysis.

Energy storage is a crucial technology for facilitating the integration of renewable energy sources (RES), such as wind and solar energy, into the electrical grid. The challenge of maintaining a balance between incoming and outgoing grid power can be effectively addressed by integrating energy storage technologies with inherently intermittent RES. A range of viable options for storing energy from RES currently exists, among which the Linear Electric Machine Gravity Energy Storage System (LEM-GESS) stands out as a promising choice. The LEM-GESS stores energy in a shaft using piston masses based on the concept of gravity. This paper presents the performance and cost analysis of different linear machines employed as the main drive units in a dry gravity energy storage system. Specifically, linear permanent magnet flux switching machine demonstrates the best performance in terms of overall system cost when considering a 20MW/10MWh system and optimizing for the minimum levelized cost of storage (LCOS). Noteworthy findings reveal that the LEM-GESS cost is highly sensitive to system efficiency, with factors such as material cost and power factor also influencing the LCOS. Designs with modest secondary height, low usage of copper and magnet materials on the primary of the LEM, and a high power factor are preferred to minimize the LCOS. In conclusion, the LEM-GESS with a permanent magnet machine drive option is a highly promising and cost-effective technology for supporting the integration of RES into the grid.

It is believed that wind energy is growing at a very rapid rate, especially in the last few years. When compared with other sources of renewable energy in the energy portfolio, it becomes evident that the bulk is wind energy-based. However, there are some backlogs to full manifestation of this technology ranging from initial high cost to performance and reliability issues, among others. But in spite of these bottlenecks, new research trends have been assertive in seeking out a sustainable solution for harnessing wind energy for power generation – especially in the design and construction of wind generators. In order to motivate and prime a sustainable energy mix among stakeholders, this paper is a shot at appraising the theory of these innovative wind generators towards ecological sustainability, economy, efficiency, and employment creation.

In this paper a comparative study of the air-cored and iron-cored direct-drive permanent magnet wind generators is done. The comparative study is based on optimum designed air- and iron-cored wind generators on a 15 kW power level. With the generators designed to have the same power and efficiency performances, mainly mass difference is compared, but other aspects such as performance quality, per unit impedance and magnet demagnetisation, amongst other things, are also compared. Although a high amount of permanent magnet material is used in the air-cored generator, this generator is shown to have very attractive features for converter-fed direct-drive wind generator applications.

This paper presents an overview of various sensorless control methods, with a focus on dual three-phase permanent magnet synchronous machines (DTP-PMSM). Owing to the important role that DTP-PMSMs play in motion-control applications in industry, most academic researchers and industry activists seek to reduce costs and size while increasing the capability and efficiency of motion applications. This has led to an increase in the number of publications about multiphase machines in recent years. The purpose of this article is to review the most important sensorless control techniques, which are divided into two main categories, namely saliency-based control method for low-speed range and model-based control method for high-speed range. Both methods are subdivided into other categories, with a focus on DTP-PMSMs. The methods are compared with each other for the purpose of selecting the most suitable control technique for implementation in applications such as ship propulsion, wind turbines, and aerospace.

Field programmable gate arrays provide great flexibility to hardware designer. The novel control strategy can be realized by quickly modifying the FPGA module in case reducing the developed time of some prototypes. The control of six-phase induction machine control is still a confused subject affecting its industrial application. This motivates authors to start the research in this field. The appetence of the six-phase machine is due to the high reliability and good torque performance. But the control for this type machine is very complex to obtain drive performance superior to three-phase machine. So the authors propose a special current waveform suppling to every phase of six-phase machine. The control strategy of machine becomes flexible by using the principle proposed by authors. A chip of FPGA is used producing the six-phase current waveforms controlling six-full bridge inverter. And some control methods also are estimated by programming FPGA. Further some experiments have completed by the six-phase machine test bed. The results from the practice are shown the six-phase machine drive can be realized without complex setup due to the application of FPGA, and performance of the drive is superior to the three-phase machine drive.