A hybrid SS-CAES system with a battery

Abstract— Renewable energy sources such as wind and solar play a significant role in generating the electricity for rural areas in developing country. However, they are intermittent, which can result in the instability of the electrical power system. This paper investigates a hybrid energy storage system (HESS) based on a small scale compressed air energy storage (SS-CAES) system including a battery, which is used to store excess energy for later use. The SS-CAES system is connected to a boost converter and a small battery through a bidirectional buckboost converter. The boost converter’s output current is controlled such that the speed of the air motor is set by a maximum power tracking controller. The battery’s bidirectional dc/dc converter controls the dc link voltage: it charges the battery if the CAES power is greater than the load; and it discharges if the load demand is greater than the CAES supply. This paper discusses the design of such system. Simulation results show acceptable performanc

Control and sizing of a hybrid battery and compressed air energy storage system

—This paper discusses the sizing and control of a hybrid energy storage system comprising a battery and a compressed air energy storage (CAES) system. The CAES system is connected to the load through a boost converter that controls the air motor’s speed to achieve maximum power point tracking (MPPT). A bidirectional converter is used to connect a battery to the load and maintain the output voltage constant. The air motor and battery sizes are estimated for a typical house in the Southern region of the UK. The battery is sized to buffer load fluctuations. All system models have been simulated using MATLAB/Simulink. Two scenarios are considered: a CAES only system controlled in constant voltage mode and a hybrid system comprising CAES with an MPPT controller and a battery with a voltage controller. The results demonstrate that the power rate of air motor is estimated properly by considering the difference between the generated power and demand power. The power difference called energy deficit is used to size the battery. The performance of CAES system is improved by hybridizing with a battery; the system maintains constant voltage when the CAES operates at maximum power point (MPP). The air motor in hybrid system controlled in MPPT mode has approximately 47% greater efficiency than that of air motor controlled in voltage mode

Adaptive inertia tuning of an energy harvester for increasing its operational bandwidth

A rotational energy harvesting system comprises a sprung mass coupled to an electrical generator through a motion transmission system such as a ball screw. In this paper, the operational bandwidth of a rotational energy harvester is expanded by varying its moment of inertia and load resistance of the generator. It is shown that the resulting tuneable device produces significantly higher amounts of harvested power. In addition to mass and stiffness, the natural frequency of a rotational device is defined by its moment of inertia, an additional design parameter that enables implementing the approach presented here. This parameter also determines the apparent mass (inertance) of the device, an important factor that allows a small additional mass to increase the apparent mass hugely and hence increase the overall power density of the harvester.It is shown that the system with variable load resistance shows a good performance at frequencies around the natural frequency of the device whereas away from resonance frequencies the system with variable moment of inertia produces more power. The approach described in this paper is a first step in the direction of having an autonomous energy harvester with a wide operational bandwidth. One of the advantages of the presented method is that, unlike some other methods, changing the adjustable parameters (i.e., moment of inertia and load resistance) can be conducted intermittently. In other words, this approach only consumes power during the tuning operations and does not use energy once the harvester is tuned at its optimum conditions.These tuneable rotational systems should be used where the excitation frequency varies slowly (e.g., in marine environment) as any sudden changes in frequency would result in an instantaneous change in the apparent mass and the device may even stall. To implement the device effectively, some kind of predictive control may need to be used that can detect frequency variations fast enough for the inertia to change in a timely manner. This aspect that is outside the scope of this paper is currently under investigation.<br/

Design of near-periodic struts for helicopter gearbox vibration isolation using multicell optimization

The structure-borne tones generated by the main gearbox are the primary components of helicopter interior noise. Recently, a kind of periodic strut has been designed to isolate the multispectral vibration from transmitting to the cabin, for their specific stop-band characteristics. Using multicell optimization, the disorders are designed into the strut to obtain better vibration and noise reduction effect. The dynamic model of the periodic strut is firstly established by combining the spectral element method and the transfer matrix method. On this basis, a multi-objective multivariable genetic algorithm is adopted to optimize the geometry by taking the maximum attenuation as the performance objective function. Then, a near-periodic structure is achieved. Compared with the perfect periodic strut, the optimal one has a much wider and deeper stop band, which is critical for a better vibration and noise attenuation effect. In addition, a method is presented to analyze the wave propagation to explore the increase of width and depth of the bandgaps more closely. Experimental investigations are then carried out on a pair of original and optimal struts to validate the improvements. It is shown that 26.22% more attenuation is achieved through this structural optimization

Low cost rotary to linear magnetic gear

-A rotary-to-linear PM (permanent magnet) gear is introduced. The topology is initially derived based on the operating principle of a transverse flux machine. It is shown that when the number of poles on all three members, rotor, translator and stationary ferromagnetic pieces are the same, it essentially behaves like that of a magnetic screw gear with helical magnets with the added advantages of ease of manufacture and low cost. Using different number of poles and iron pieces enables the adjustment of the gear ratio, which provides another design variable. The paper describes the design and construction of a demonstrator gear and presents performance results obtained from finite element analysis and experiments

Investigation of a monostable nonlinear vibration isolator with the inertia-elastic boundary

This paper proposes a new monostable nonlinear vibration isolator with the inertia-elastic boundary (IEB-MVI), and thoroughly investigates its performance and nonlinear dynamic behaviors. The theoretical model of IEB-MVI for vibration isolation is derived and experimentally validated. To show the vibration isolation performance improvement, the comparison study is performed between the IEB-MVI, a linear isolator and a monostable isolator without the inertia-elastic boundary (IEB). Results show that the IEB-MVI can abate the resonant vibration response by 4.93 dB in the low-frequency band and widen the effective isolation bandwidth by 35.2 % compared to the monostable isolator without the IEB; both the IEB-MVI and the monostable counterpart achieve the same broadband vibration isolation performance in the high-frequency band, which is significantly better than that achieved by the linear isolator. This indicates the benefit of the IEB for performance improvement of the monostable isolator. Next, the influence of the different IEB parameters on the performance is comprehensively studied. Finally, the study analyzes the bifurcation characteristics of the IEB-MVI, which develops insight into the isolator's nonlinear dynamic behaviors

Characterization of New PEEK/HA Composites with 3D HA Network Fabricated by Extrusion Freeforming

Addition of bioactive materials such as calcium phosphates or Bioglass, and incorporation of porosity into polyetheretherketone (PEEK) has been identified as an effective approach to improve bone-implant interfaces and osseointegration of PEEK-based devices. In this paper, a novel production technique based on the extrusion freeforming method is proposed that yields a bioactive PEEK/hydroxyapatite (PEEK/HA) composite with a unique configuration in which the bioactive phase (i.e., HA) distribution is computer-controlled within a PEEK matrix. The 100% interconnectivity of the HA network in the biocomposite confers an advantage over alternative forms of other microstructural configurations. Moreover, the technique can be employed to produce porous PEEK structures with controlled pore size and distribution, facilitating greater cellular infiltration and biological integration of PEEK composites within patient tissue. The results of unconfined, uniaxial compressive tests on these new PEEK/HA biocomposites with 40% HA under both static and cyclic mode were promising, showing the composites possess yield and compressive strength within the range of human cortical bone suitable for load bearing applications. In addition, preliminary evidence supporting initial biological safety of the new technique developed is demonstrated in this paper. Sufficient cell attachment, sustained viability in contact with the sample over a seven-day period, evidence of cell bridging and matrix deposition all confirmed excellent biocompatibility.status: publishe