Development and Research Status of Tidal Current Power Generation Systems in China

Considering the depletion of oil, coal, gas and other fossil energy, and the increasingly serious environmental pollution, all countries in the world are developing clean and renewable energy, such as wind energy, water energy, solar energy, etc., to alleviate the current energy crisis. Tidal current energy belongs to the marine renewable energy. It is clean, pollution-free, and abundant, with a good prospect of development due to its similarity with wind energy. This paper firstly analyses the reserves and distribution of tidal current energy in China. Then the early exploration of Tidal Current Power Generation System (TCPGS) in China is briefly introduced. Subsequently, it gives the details of the devices and experimental platforms of TCPGS that were researched and developed by various universities, research institutes and enterprises in China. The information mainly includes: the size and the capacity of the system, the support structure, turbine type, the selection of generator, and some river and offshore test information, etc. Finally, it discusses the similarities and differences between China and other countries in tidal current power generation technology, and summaries the current development status and gives the prospect of the TCPGS technology in China.

Tides and Tidal Currents—Guidelines for Site and Energy Resource Assessment

The main aim of this paper was to classify and to analyze the expeditious resource assessment procedure to help energy planners and system designers dealing with tides and tidal currents. Depending on the geographical features of the site to be evaluated, this paper reported the easiest methods to adopt for later working plans, crucial for preliminary considerations but to be supported by in situ measurements and by a more complex and detailed modelling. While tide trends are predictable by using Laplace equations and Fourier series, tidal currents velocities prediction is not easy, requiring suitable methods or hydraulic applications. Natural and artificial sites were analyzed and the best method for each type of them was presented. The latter together highlighting the minimum set of required information was discussed and provided as a toolkit for assessing tides and tidal current energy potential.

Bi-Directional Impulse Turbine with Spiral Flow Collector for Tidal Energy Conversion

In order to make use of ocean renewable energy, a combination system of a bi-directional impulse turbine and a bi-directional flow collector for tidal current energy conversion is investigated in this paper. It is the advantage that this turbine system does not need an operation of orientation change according to the reversal of regular tidal orientation when fixed on the seabed. The experimental investigations by using both a circulating water tank and a towing tank showed that the turbine power output could be increased by adopting the flow collector proposed in this study. Then the flow collector with fixed spiral vane named spiral flow collector was investigated by both a circulating water tank test and CFD analysis. The experimental result of the spiral flow collector showed that the performance improvement was found on the increase of axial velocity in the turbine which contributed to the increase of the turbine power output. The results of CFD analysis showed that 180 deg of the skew angle of the fixed spiral vane was suitable in view of the angular moment at the turbine inlet in this case.

Research on the Blade Motion of a Bidirectional Energy-Generating Turbine under Integrated Wave and Tidal Current Action

An integrated wave-tidal current power turbine is affected by both wave and tidal current forces, and its energy efficiency is closely related to the velocity and direction of the two forces. To improve the probability of the horizontal axis turbine reaching maximum energy efficiency under real-time changing sea conditions, we performed the following investigations in this study. Based on the actual application scenario of Lianyungang port, a time series prediction model of tidal current (velocity and flow direction) and wave (mean wave direction, mean wave period, and significant wave height) data for the past year was established. The changes in waves and tidal currents within 24 h after the cutoff point of the existing data were predicted. The integrated wave-tidal current mechanism was studied, and the superposition of wave energy and tidal current energy was transformed into the equivalent velocity vector of wave-tidal current integration. The conversion coefficient between waves and equivalent flows was determined by a numerical wave flume simulation. According to the historical wave and tidal current data, the equivalent velocity range of the integrated action of waves and tidal currents in Lianyungang was determined. The influence of different blade motions on the energy harvesting efficiency of the turbine under the corresponding flow conditions was studied using the Computational Fluid Dynamics (CFD) method to determine the blade motion law of the turbine. The blade motion law of the prototype was verified in a sea trial experiment. The experimental results were basically consistent with the simulation results for the blade motion law designed according to the wave and tidal current prediction law. This design scheme can provide a reference for engineering design for the development and utilization of new marine energy.

Hydrodynamic Model and Tidal Current Energy Potential in Lepar Strait, Indonesia

Previous studies have shown the abundance of tidal energy resources in Indonesia. However, some sites have yet to be considered. The Lepar Strait, for example, is located between Bangka and Lepar Islands. This paper describes a field survey and numerical modelling conducted in the Lepar Strait. The modelling was performed using Delft3D, with the aim of determining potential sites for harvesting tidal current energy and estimate the generated power. In the modelling, the domain decomposition method was employed for model downscaling, allowing grid resolution reaching 130 x 130 m2, which is sufficient to represent the narrow gaps between tiny islands in the area of interest. The National Bathymetric (Batnas) from the Geospatial Information Agency (BIG) and the International Hydrographic Organization (IHO) tide constituents were applied for the bathymetry and tide elevation boundaries. The comparison between the surveyed and modelled data showed a good agreement. The RMSE and r for water level are > 0.95 and < 0.15, and the RMSE for velocity was <0.19. Furthermore, an energetic flow reaching 1.5 m/s was found at the Northern part of Lepar Strait, situated at the narrow gaps. The Gorlov Helical Turbine was selected in this study due to shallow water and low mean velocity. In the 2019 model, the power density and power output at the best potential sites were 2,436.94 kWh/m2 and 1,870.41 kWh, respectively. This number is higher than those previously found in Kelabat Bay. Nonetheless, it is still far below the currently promising project in Larantuka and Lombok Straits. Future research is recommended, to conduct a detailed field measurement campaign and assess the impact of energy extraction in more detail.

Research on Blade Design of Lift–Drag-Composite Tidal-Energy Turbine at Low Flow Velocity

The research on tidal-current energy-capture technology mainly focuses on the conditions of high flow velocity, focusing on the use of differential pressure lift, while the average flow velocity in most sea areas of China is less than 1.5 m/s, especially in the marine aquaculture area, where tidal-current energy is needed to provide green energy locally. Due to the low flow velocity of this type of sea area, it seriously affects the effect of differential pressure lift, which is conducive to exerting the effect of impact resistance. In this regard, the coupling effect of the differential pressure lift and the impact resistance on the blade torque is comprehensively considered, this research puts forward the design method of the lift-–drag-composite thin-plate arc turbine blade. Based on the blade element momentum (BEM) theory and Bernoulli’s principle, the turbine dynamic model was established, and the nonlinear optimization method was used to solve the shape parameters of the turbine blades, and the thin-plate arc and NACA airfoil blade turbines were trial-produced under the same conditions. A model experiment was carried out in the experimental pool, and the Xiangshan sea area in Ningbo, East China Sea was taken as the experimental sea area. The results of the two experiments showed the same trend, indicating that the energy-harvesting performance of the lift–drag-composite blade was significantly better than that of the lift blade under the conditions of low flow velocity and small radius, which verified the correctness of the blade design method, and can promote the research and development of tidal energy under the conditions of low flow velocity and small radius.

An FTC Design via Multiple SOGIs with Suppression of Harmonic Disturbances for Five-Phase PMSG-Based Tidal Current Applications

This paper firstly adopts a fault accommodation structure, a five-phase permanent magnet synchronous generator (PMSG) with trapezoidal back-electromagnetic forces, in order to enhance the fault tolerance of tidal current energy conversion systems. Meanwhile, a fault-tolerant control (FTC) method is proposed using multiple second-order generalized integrators (multiple SOGIs) to further improve the systematic fault tolerance. Then, additional harmonic disturbances from phase current or back-electromagnetic forces in original and Park’s frames are characterized under a single-phase open condition. Relying on a classical field-oriented vector control scheme, fault-tolerant composite controllers are then reconfigured using multiple SOGIs by compensating q-axis control commands. Finally, a real power-scale simulation setup with a gearless back-to-back tidal current energy conversion chain and a small power-scale laboratory prototype in machine side are established to comprehensively validate feasibility and fault tolerance of the proposed method. Simulation results show that the proposed method is able to suppress the main harmonic disturbances and maintain a satisfactory fault tolerance when third harmonic flux varies. Experimental results reveal that the proposed model-free fault-tolerant design is simple to implement, which contributes to better fault-tolerant behaviors, higher power quality and lower copper losses. The main advantage of the multiple SOGIs lies in convenient online implementation and efficient multi-harmonic extractions, without considering system’s model parameters. The proposed FTC design provides a model-free fault-tolerant solution to the energy harvested process of actual tidal current energy conversion systems under different working conditions.