This paper presents a hybrid methodology to analyze the commercial measures of changing stator windings and adjusting air gap length to upgrade efficiency of typical three-phase direct-on-line induction motors with die-cast copper rotor (DCR). The calculation is carried out through combining the time-stepping and time-harmonic finite element analysis (FEA) and the circuit equivalent circuit model. Typical full-load performance of stator windings with different air gap lengths are computed by MATLAB invoking the 2D transient and eddy current field analysis in ANSYS/MAXWELL. Then, MATLAB scripts about post-processing of the FEA results are used to obtain the full-load running performance including the loss distribution and circulating current. The MATLAB scripts of circuit model built based on the FEA results is used to compare the overload and starting performance. After that, four stators with the four windings and three DCRs with different air gap of an 11 kW motor are fabricated and tested to validate the calculations. By comparing results from both calculations and measurements, it is shown that the factors of stator windings and air gap length can effectively improve the efficiency of the 11 kW DCR induction motor without the addition of extra materials. The motor with the 11/12 pitch Y-Δ series winding and 0.6 mm air gap has the best performance, in terms of efficiency, overloading capability and starting performance. Its efficiency can increase from 90% to the highest 92.35% by sole adjustment of stator winding and air gap length.

Currently, the ocean energy strategy is rapidly developing, and a high proportionate tidal current energy grid connection presents significant obstacles to the planning and secure and stable operation of an island microgrid. For an island microgrid with high proportion tidal current energy access and demand response resources, this research suggests a multiple time scales rolling coordinative dispatching method. An MPPT control based on Q-Learning algorithm is first developed for real-time maximum power tracking of tidal current energy generation after the island microgrid’s topology has been examined. Following that, a multiple time scales rolling coordinative dispatching’s fundamental architecture and implementation method are provided, with equal time intervals coordinated in a step-by-step recursive way. In the example analysis of an island microgrid, we consider the rigid demand load that does not participate in the demand side response, and the ship load and controllable load that participate in the demand side response. On sea islands, ship loads on the long timeframe achieve traffic and energy interaction, and dispatchable loads on the short timescale participate in supply and demand balancing. This is due to the multiple time scales properties of demand response resources. In addition, a multiple time scales rolling coordinative dispatching model for an island microgrid is developed. It includes day-ahead, intraday, and real-time components. Finally, example analysis is used to confirm the dispatching method’s usefulness and advancement, and we conclude that the tidal current energy consumption rate of the island microgrid is increased by 17.08%.

Wave energy, a high-quality renewable energy, is abundant in reserves and relatively stable. However, the wave energy power of the same sea area varies greatly in different seasons. The traditional linear generator cannot work efficiently in such a wide power range. This paper presents a segmented permanent-magnet linear generator structure, which is especially designed for the wave energy converter. This type of linear generator can match the wave energy power by increasing or decreasing the specific primary unit, making the generator more efficient over a wider range of wave power than the traditional type. This paper verifies the correctness by finite element analysis.

Wind power is one of the most attractive renewable clean energies under development at present. On a global scale, wind power generation development was very rapid in recent years. As the wind power generation tends to develop toward large-scale and offshore, the traditional cooling methods gradually expose their own shortcomings. As the large wind turbine installation tower is high, and the installation site is dispersed, the installation and maintenance of wind turbine generator are difficult. So, the generator is required to have a small weight and less maintenance. Self-circulation inner evaporative cooling system (SCIECS) has the following advantages: self-circulation without pump, high cooling efficiency, safe and reliable operation, and basically maintain-free, etc. The self-circulation of cooling system can be realized by the 35 between wind turbine generator and the horizontal direction, and it is very suitable for being used in a large-scale wind power generator. Owing to the intrinsic nonlinearity of two-phase self-circulation system, changes of operation condition and circuit topology in a large range may lead to an instability of the cooling system, causing the system parameters to severly change. The instability of the cooling system can cause the local overheating and even burning of the generator, which provides a huge security risk for the cooling system, thus threatening the safe and stable operation of the generator. The stability of SCIECS is very important for the safe operation of wind turbine. In this paper, static stability of the SCIECS in wind power generator is studied based on the nonlinear bifurcation analysis theory and its numerical continuation method. System static bifurcation diagram is obtained to analyze the evolution characteristics of the SCIECS. Parameter effect of the system static bifurcation is analyzed at the same time. In order to verify the theoretical prediction of the static bifurcation of the small-angle two-phase natural circulation, an experimental platform is built. Static bifurcation of the SCIECS is observed experimentally. The experimental results show that the static bifurcation phenomenon exists in the natural circulation two-phase flow of small angle, and the theoretically predicted m-Q bifurcation curves are in good agreement with the experimental curves, which verifies the correctness of the theoretical analysis.

Tidal power generation technology has advanced quickly in recent years. In this study, the Hilbert-Huang transform (HHT) was used to examine the electrical energy distribution law of tidal power generation according to the time periods of days, months, and years based on observed data for tidal power generation. Our analysis summarized the tidal power generation law as follows: in the span of one day, the motor ran for 14 h before shutting off for 10 h. The frequency was 28 Hz, and the maximum voltage was 259 V. The tidal power generation swung twice a month, reaching its peak in the middle of the month and its trough at the beginning. The tidal power output fluctuated twice a year, reaching its peak in August, September, and October and its trough in February, March, and April. In the investigation of tidal power generation patterns, the HHT transformation’s precision and potency were confirmed.

With the development of large-scale hydro-generators, large hydro-generator cooling technology is increasingly demanded. Different cooling method will not only affect the structure of hydro-generators, also it will affect the energy consumption and reliability of the generators. The commonly large-scale hydro-generator cooling method includes: air cooling, water cooling, and evaporative cooling methods. This paper analyzes the principle of the three cooling methods and describes qualitatively the advantages and disadvantages of them. The air cooling hydro-generator structure is simple, but the generator operating temperature is high; the water-cooling method has a certain superior in cooling performance, but it requires more auxiliary equipments, and has higher equipment failure rates. The evaporative cooling method is a recently developed cooling technique. It not only has a remarkable cooling effect, but also can decrease the equipment failure rates and the cost of maintenance. In order to build a comprehensive model to assess the three hydro-generator cooling methods, this paper proposes a comprehensive evaluation method based on AHP. The method includes 11 indexes of resource consumption, energy consumption and reliability to assess the influence of cooling ways. The energy saving influence of all the 11 indicators are calculated by using the AHP comprehensive evaluation. Finally, comparison between a 400 MW air cooling and an evaporative cooling hydro-generators at Lijiaxia hydropower Station are made using the proposed method. Evaluation results indicate that in terms of daily operation, the energy saving of the evaporative cooling hydro-generator can be more than 300 tons standard coal equivalent per year as compared with that of air cooling generator. In terms of maintenance, the evaporative cooling method can save more than 5000 tons of standard coal equivalent per year. The comprehensive evaluation results show that the evaporative cooling method is significantly better than the air cooling. It can be seen that the proposed evaluation method may quantitatively calculate the merits of hydro-generator caused by cooling method, which provides guidance to select and improve cooling method of hydro-generator.