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According to the characteristics of the hydraulic power generation system (HPGS), HPGS can be directly fed into a DC nano grid through using an uncontrolled rectifier. However, determined only by the DC voltage, the motor speed of the HPGS is a constant rather than an optimal speed, whose curve is unknown yet during the whole power generation process. In order to realize the control of the HPGS's motor speed and reduce the armature current harmonics, a pulse width modulation (PWM) rectifier topology is introduced to replace the uncontrolled rectifier. First, the principle of the PWM rectifier is studied. Second, a control structure of this PWM rectifier is established, including a current decoupling control in the inner loop and a speed feedback control in the outer loop. After this, a maximum efficiency converting control strategy is adopted. Based on the above, the simulation model of the PWM rectifier which was fed into DC nano grid was established and a series of experiments were carried out. The experimental results show that the armature current waveform is sine wave and its rectification is flexible. Furthermore, the maximum efficiency converting control strategy is realized with HPGS's always working at the optimal speed curve.

Both Backward Bent Duct Buoy (BBDB) and Japanese “Mighty Whale” are offshore floating Oscillating Water Column (OWC) type wave power devices. The investment of “Mighty Whale” is comparatively huge and its wave-to-wire efficiency is about 5.3%. Based on the reports of model experiments and over-3-year sea trials of “Mighty Whale”, recent progress of air turbines and the studies of BBDB and air turbine in Guangzhou Institute of Energy Conversion (GIEC), Chinese Academy of Sciences (CAS), the cost-performance ratio of wave power boat based on the BBDB principle is evaluated. According to the RMB purchasing power in 2014, if the incident wave power density is 16 kW/m, the boat lifespan is 15 years, and the air turbine efficiency is high enough to make the wave-to-wire conversion efficiency reach 30%, the cost of electricity generated by this boat can drop to below 1 CNY/kWh. If the incident wave density or the wave-to-wire efficiency is higher, this cost will decrease further. And, the mobility of the self-propelled wave power boat solves the underwater residue problem caused by the complex mooring of traditional wave energy converter; also, it helps the wave power boat in moving to a port to avoid typhoons and adjusting to the wave direction. Therefore, the BBDB wave power boat technology has broad prospects for developments.

To find an efficient and economic way to convert wave energy, a one-base multi-buoy offshore floating wave energy converter Sharp Eagle Wanshan is designed, consisting of four absorbing buoys, one semi submersible barge, and other components. The working principle of the device is described in this paper. An experiment of a 1:13.78 model machine was carried out to test the hydrodynamic performance of the device and make an initial evaluation for the design The influence of wave period, wave height, work load and wave direction was tested. After construction, two-stage open sea tests have been finished in the waters near Wanshan Islands from November 2015 to June 2016. The device showed great power generation capacity with total generated output of 30530.57 kWh, and largest daily generation of 1847.09 kWh. During the open sea tests, the energy conversion efficiency was measured, and results show that capture width ratio of Wanshan remains higher than 20% in the wave period between 4 and 6.5 s and wave height range of 0.6-1.8 m. After operating in a wide range of conditions, including a tropical storm on May 27, amounts of tests data, experiences and lessons have been obtained and will be summed up and presented in the paper. (C) 2017 Elsevier Ltd. All rights reserved.

Metallic cobalt/carbon composites were synthesized by metal-organic framework as precursor via a facile method in the paper. The obtained cobalt nanoparticles are 5–10 nm in size and anchor on carbon homogeneously. The results indicate that metallic cobalt particles have excellent dispersion feature on the surface of carbon. The electrochemical performance of metallic cobalt/carbon composites was characterized by Cyclic voltammetry (CV) and galvanostatic charge/discharge tests. The specific capacitance of the composite material is up to 144.5 F g −1 at current density of 0.5 A g −1 with a capacitance retention rate of 96.5% at current density of 2 A g −1 . The results suggest that synergistic performance can be achieved by combining metallic cobalt and carbon, which inherits the overall system with enhanced electrochemical performance.

Co3O4nanoparticles were prepared from cobalt nitrate that was accommodated in the pores of a metal-organic framework (MOF) ZIF-8 (Zn(MeIM)2, MeIM = 2-methylimidazole) by using a simple liquid-phase method. Analysis by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that the obtained Co3O4was composed of separate nanoparticles with a mean size of 30 nm. The obtained Co3O4nanoparticles exhibited superior electrochemical property. Co3O4electrode exhibited a maximum specific capacitance of 189.1 F g−1at the specific current of 0.2 A g−1. Meanwhile, the Co3O4electrode possessed the high specific capacitance retention ratio at the current density ranging from 0.2 to 1.0 A g−1, thereby indicating that Co3O4electrode suited high-rate charge/discharge.