Development of an ocean wave energy harvester with a built‐in frequency conversion function

The research develops a novel harvester associated with a built‐in frequency conversion device to harness energy from ocean waves based on the piezoelectric effect. The developed harvester consists of 2 generators driven by rotational motions converted from vertical motions by a rack and pinion actuator. The generator has a rotator with a magnetic bar attached to its blade tips and a stator. By this innovative design, the harvester is capable of converting ocean waves with low frequencies to mechanical vibrations with higher excitation frequencies of the piezoelectric transducer for increasing its energy conversion efficiency. A corresponding mathematical model for the harvester is developed to evaluate the generated power. The simulation results show that the generated power increases with increases in the ocean wave height, number of magnetic bars and decreases in the wave period, the distance between 2 opposite magnetic bars, and harvester's submerged part height. The power output is realized up to 260 W with the height, length, and width of the harvester being 1m × 1m × 1m, at the ocean wave height and period being 2 m and 7 seconds, respectively.     

Design,modeling, and analysis of a high performance piezoelectric energy harvester for intelligent tires

Basic parameters affecting vehicle safety and performance such as pressure, temperature, friction coefficient, and contact‐patch dimensions are measured in intelligent tires via sensors that require electric power for operation and wireless communication to be synchronized to the vehicle monitoring and control system. Piezoelectric energy harvesters (PEHs) can extract a fraction of energy that is wasted as a result of deflection during rolling of tires, and this extracted energy can be used to power up sensors embedded in intelligent tires. A new design of PEH inspired from Cymbal PEHs is introduced, and its performance is evaluated in this paper. Cymbal PEHs are proven to be useful in vibration energy harvesting, and in this paper, for the first time, the modified shape of Cymbal energy harvester is used as strain‐based energy harvester for the tire application. The shape of the harvester is adjusted in a way that it can be safely embedded on the inner surface of tires. In addition to the high performance, ease of manufacturing is another advantage of this new design. A multiphysics model is developed and validated to determine the output voltage, power, and energy of the designed PEH. The modeling results indicated that the maximum output voltage, the maximum electric power, and the accumulated harvested energy are about 3.5 V, 2.8 mW, and 24 mJ/rev, respectively, which are sufficient to power two sensors. In addition, the possibility is shown to supply power to five sensors by increase in piezoelectric material thickness. The effect of rolling tire temperature on the performance of the proposed PEH is also studied.     

Performance analysis of axisymmetric floating energy harvesters and influences of parameters and shape variation

This paper presents a novel axisymmetric floating energy harvester associated with hydraulic cylinders and gear rack mechanism to harness wave energy. The harvester collects energy in surge, heave, and pitch modes. The mathematical models for the harvester are developed to analyze the performance and the harvested power. The Pierson‐Moskowitz two‐parameter spectrum was utilized to model the incident waves. The retardation function for the radiation force and the added mass curve are fitted based on the least squares method. The irregular exciting force, the displacement, the velocity, and the power harvesting of the axisymmetric floating energy harvesters in three motion modes with irregular waves are simulated. The effects of harvester design parameters and the geometry shape variation of the submerged part on the wave‐exciting force, the displacement, the velocity, the harvested power, and the harvesting efficiency are investigated. Under the same output damping and the same parameters with the radius of 4 m, the submerged height of 4 m, the above‐water height of 2 m, and the center of mass of ?1 m, the cylinder wave‐exciting force in surge is highest among three shapes, the cone wave‐exciting force is highest among three shapes in heave and pitch modes, and the total harvested power and the efficiency of the cylinder‐shaped harvester are the highest among three different axisymmetric shapes, which are 40.521 kW and 62.96%, respectively. The harvested power and the efficiency differences between the cylinder and the cone are 1.571 kW and 2.4%, and the differences between the cylinder and the halfsphere are 8.543 kW and 13.28%. For the cylinder‐shaped harvester with the submerged height of 4 m, the above‐water height of 2 m, and the center of mass of ?1 m, when the radius increases from 3 m to 5 m, under the optimal output damping, the total harvested power and the harvesting efficiency increase by 38.811 kW and 35.83%, respectively. For the cylinder‐shaped harvester with the radius of 4 m and the above‐water height of 2 m, as the submerged part height increases from 2 to 4 m, the total harvested power and the harvesting efficiency increase by 15.776 kW and 24.51%, respectively. For the cylinder‐shaped harvester with the radius of 4 m, the submerged height of 4 m, and the above‐water height of 2 m, as the center of mass is reduced from 0 to ?1 m, the total harvested power and the harvesting efficiency rise by 15.153 kW and 23.54%, respectively.     

Vibration energy harvesting in vehicles by gear segmentation and a virtual displacement filtering algorithm

In this study, vibration straight‐line displacements occurring during electric vehicle operations are changed into reversely rotating displacements and divided into small segments by a gear unit. Piezoelectric bending elements are used to form a cantilever beam–based energy feedback mechanism for converting vibration energy into electrical power within an allowable displacement range. A virtual vibration displacement filtering algorithm is proposed to effectively filter virtual displacements that cannot excite the energy harvester and generate electrical power. The average speed of the gear exciting the bender has an accuracy 30%, which is increased using this algorithm compared with 2 other algorithms and directly affects the accuracy of calculating the average power generated by the calculation of piezoelectric bending elements. Theoretical and experimental analyses are conducted for the impact of gear pitch on the regeneration power value by changing the gear pitch at a fixed driving speed. Experiments show that when a vehicle is operated at a fixed speed, the proposed method can be used to obtain the maximum average power of a single piezoelectric bending element through determination of a rational gear pitch. Specifically, when the test vehicle operated at 20 and 60 km/h, the gear pitch should have been 7 and 10 mm.     

New architecture and SCADA for stand‐alone hybrid (medium‐sized asynchronous wind turbine + UPS with battery + photovoltaic array) power system without diesel generator

In general, the commercialized medium‐sized asynchronous wind turbines are fully automated facilities designed to operate in parallel connection to the grid; in case of isolated operation, they need to be combined with diesel generator. This paper aims at studying the method of producing electricity of maximal quality with the wind, by constructing a new stand‐alone hybrid (medium‐sized asynchronous wind turbines, UPS with battery, and photovoltaic array) power system without diesel generator. This paper proposes a new architecture of stand‐alone hybrid power system that consists of medium‐sized asynchronous wind turbine, UPS, current limiter (reactor), photovoltaic array, and consumer and dump loads; accordingly, a supervisory control and data acquisition (SCADA) for this system is suggested along with the operation strategies depending on the output power of the UPS and wind turbine, consumer load, and the battery voltage of UPS. The case study was confirmed through the simulation results of the operation of a new stand‐alone hybrid (two 110 kW of asynchronous wind turbines, 250 kVA of UPS with battery, reactor, 36 kW of photovoltaic array, and consumer and dump loads) power system. The results of the simulation showed that the system frequency change of the new stand‐alone hybrid power system was 60 ± 0.5 Hz, and the one of the wind + diesel stand‐alone hybrid system was 60 ± 1 Hz, for the sudden change of consumer load and gust. This new system can be eligible as a standardizing option for the architecture of nondiesel stand‐alone hybrid system and its SCADA system.     

Energy management of a fuel cell hybrid ultra-energy efficient vehicle

This paper focuses on energy management in an ultra-energy efficient vehicle powered by a hydrogen fuel cell with rated power of 1 kW. The vehicle is especially developed for the student competition Shell Eco-marathon in the Urban Concept category. In order to minimize the driving energy consumption a simulation model of the vehicle and the electric propulsion is developed. The model is based on vehicle dynamics and real motor efficiency as constant DC/DC, motor controllers and transmission efficiency were considered. Based on that model five propulsion schemes and driving strategies were evaluated. The fuel cell output parameters were experimentally determined. Then, the driving energy demand and hydrogen consumption was estimated for each of the propulsion schemes. Finally, an experimental study on fuel cell output power and hydrogen consumption was conducted for two propulsion schemes in case of hybrid and non-hybrid power source. In the hybrid propulsion scheme, supercapacitors were used as energy storage as they were charged from the fuel cell with constant current of 10 A.     

Development of a thermoelectric battery-charger with microcontroller-based maximum power point tracking technique

This article describes a battery charger, which is powered by thermoelectric (TE) power modules. This system uses TE devices that directly convert heat energy to electricity to charge a battery. The characteristics of the TE module were tested at different temperatures. A SEPIC dc–dc converter was applied and controlled by a microcontroller with the maximum power point tracking (MPPT) feature. The proposed system has a maximum charging power of 7.99 W: that is better than direct charging by approximately 15%. The objectives are to study the principle of TE power generation and to design and develop a TE battery charger that uses waste heat or another heat source as the direct input power.     

Enhanced novel dual effect isotope batteries: Optimization of material and structure

Materials and structures of radio‐voltaic/radio‐photovoltaic (RV/RPV) dual effect isotope batteries were optimized in this paper. The response relationship between different types of volt layer and the dual effect was studied. The GaAs volt layer with a high band gap can easily obtain a higher voltage output than the Si volt layer. Dual effect multilevel isotope batteries achieved better output performance by using the CsI scintillator due to its high photon yield. The CsI scintillator combined with the GaAs volt layer showed good spectral matching property, which is conducive to improve the RV/RPV dual effect isotope batteries. The overall scale of the multilevel structure was designed by performing Particle and Heavy Ion Transport code System (PHITS) calculation. When its overall scale reached 20 cm, the deposition rate of ⁶⁰Co gamma (γ) rays exceeded 90%. The response relationship between the thickness of each level of the CsI scintillator and the battery performance was analyzed by MCNP5. The total performance came up to the maximum when the CsI thickness in each level reached 2 cm. Finally, the multilevel isotope batteries were prepared. The output performance of the multilevel isotope batteries was characterized under ⁶⁰Co γ source at a dose rate of 0.103 kGy/hr. The multilevel isotope battery in series obtained open circuit voltage of 7.77 V, short circuit current of 1.69 μA, maximum output power of 7.98 μW, and energy conversion efficiency of 0.15%. These isotope batteries showed great potential for the power supply of electronic equipment in many special fields.     

Efficient study of a coarse structure number on the bluff body during the harvesting of wind energy

In the present study, an energy harvester with coarse passive turbulence control (PTC) structure is represented to harvest piezoelectric wind energy. Wind tunnel experiments are conducted to investigate the influence of the PTC on the vibrational amplitude of the vortex-induced vibration and piezoelectric power output. Parametric studies of the PTC numbers and sizes are presented to determine the optimized PTC structure to enhance the efficiency of piezoelectric energy harvesting. The experimental results show that the specific parameters of θ= 60^° and W = 8 mm are the most efficient PTC group for designing a vortex-induced vibration-based energy harvester with the coarse surface device.     

Effect of energy storage systems on automatic generation control of interconnected traditional and restructured energy systems

During major disturbances in electric power system (PS) penetrated with renewable energy sources, primary and supplementary automatic generation control (AGC) strategies usually show inefficiency in mitigating the frequency and power oscillations because of sluggish control action. The frequency and power deviations should be controlled to retain the generation‐demand balance, which reinforce the quality and stability of overall PS. The fast‐acting energy storage systems (ESSs) having very small time constants like capacitive energy storage (CES) and redox flow battery (RFB) are utilised in this study to improve these dynamic responses. To conduct the analysis, initially, a two‐area nonreheat thermal PS with extra generations from wind turbine system (WTS) and dish‐stirling solar thermal system (DSTS) is explored extensively, and then to validate the efficacy of the method, the approach is tested on two‐area nonreheat thermal system having governor deadband (GDB) nonlinearity, reheat thermal, and restructured multisource thermal gas systems. An imperialist competition algorithm (ICA) optimised fuzzy PID‐filter‐(1 + PI) controller named as FPIDF‐(1 + PI) is utilised as supplementary controller, and its performance with CES/CES‐RFB is compared with ICA‐optimised FPIDF with/without CES and existing optimal PI/PID/PIDF/FPID controller without CES. Investigation of dynamic responses for sudden variation in power demand unveils the superiority of the control approach compared with others regarding settling time, peak undershoot, and performance index. Analysing the impact of ESSs on the responses divulges that the amalgamation of CES‐RFB in PS imparts better system dynamics. The robustness analysis suggests that ICA‐optimised controller with ESSs performs excellently and robustly for ±25% variation in PS parameters, random load disturbances, and nonlinearities.     

Fuel-cell power conversion system based on double dual topologies

This article describes (and demonstrates through experiments) the feasible implementation of a power conversion system designed for a Fuel Cell (FC) application in renewable energy generation. The system is designed to be powered by an FC stack, which output is a low (in amplitude) non-regulated dc voltage, with a relatively wide range of variation. The system must boost the voltage from the power source to an internal 200 V dc bus, while the final output voltage (after the inversion) must be provided at a level of 120 V ac. The main feature of the described system is that it is based on double-dual converters, a family of converters with several advantages such as automatic power balance and large voltage gain; this leads to a good performance and power quality. The system is based on a double dual boost converter to increase and regulate the dc-voltage, and a double dual buck converter, to invert the dc-voltage and provide an ac-voltage as output. The article shows the system's feasibility through theoretical analysis and provides experimental results with an FC stack. Experimental results are provided to demonstrate the feasibility of the proposed system.     

Fully-integrated micro PEM fuel cell system with NaBH4 hydrogen generator

A fully-integrated micro PEM fuel cell system with a NaBH₄ hydrogen generator was developed. The micro fuel cell system contained a micro PEM fuel cell and a NaBH₄ hydrogen generator. The hydrogen generator comprised a NaBH₄ reacting chamber and a hydrogen separating chamber. Photosensitive glass wafers were used to fabricate a lightweight and corrosion-resistant micro fuel cell and hydrogen generator. All of the BOP such as a NaBH₄ cartridge, a micropump, and an auxiliary battery were fully integrated. In order to generate stable power output, a hybrid power management operating with a micro fuel cell and battery was designed. The integrated performance of the micro PEM fuel cell with NaBH₄ hydrogen generator was evaluated under various operating conditions. The hybrid power output was stably provided by the micro PEM fuel cell and auxiliary battery. The maximum power output and specific energy density of the micro PEM fuel cell system were 250 mW and 111.2 W h/kg, respectively.     

Non-isolated multiphase boost converter for a fuel cell with battery backup power system

This work describes a step-up non-isolated DC/DC converter aimed for fuel cell stand-alone power systems. The proposed converter has the following features: simple structure based on the basic boost topology that reduces the number of components; it uses the interleaving technique in order to reduce the current ripple at the input and output sides, reduction of the inductors size, higher frequency that reduce the output filter capacitor and easier power losses management. In addition, the use of an inner current control loop in the input side assures power sharing and easy module parallelization. The converter feeds a backup battery that maintains a DC voltage level at the main bus. An outer battery-charging loop controls the converter. Experimental validation is given for a four-phases 1 kW prototype at 100 kHz PWM switching frequency connected to a Nexa Ballard (1.2 kW-46 A) PEM fuel cell.     

Multi‐objective design optimization for mini‐channel cooling battery thermal management system in an electric vehicle

Lithium‐ion battery packs have been generally used as the power source for electric vehicles. Heat generated during discharge and limited space in the battery pack may bring safety issues and negative effect on the battery pack. Battery thermal management system is indispensable since it can effectively moderate the temperature rise by using a simple system, thereby improving the safety of battery packs. However, the comprehensive investigation on the optimal design of battery thermal management system with liquid cooling is still rare. This article develops a comprehensive methodology to design an efficient mini‐channel cooling system, which comprises thermodynamics, fluid dynamics, and structural analysis. The developed methodology mainly contains four steps: the design of the mini‐channel cooling system and computational fluid dynamics analysis, the design of experiments and selection of surrogate models, formulation of optimization model, and multi‐objective optimization for selection of the optimum scheme for mini‐channel cooling battery thermal management system. The findings in the study display that the temperature difference decreases from 8.0878 to 7.6267 K by 5.70%, the standard temperature deviation decreases from 2.1346 to 2.1172 K by 0.82%, and the pressure drop decreases from 302.14 to 167.60 Pa by 44.53%. The developed methodology could be extended for industrial battery pack design process to enhance cooling effect thermal performance and decrease power consumption.     

Fuel cell-battery hybrid powered light electric vehicle (golf cart): Influence of fuel cell on the driving performance

A light electric vehicle (golf cart, 5 kW nominal motor power) was integrated with a commercial 1.2 kW PEM fuel cell system, and fuelled by compressed hydrogen (two composite cylinders, 6.8 L/300 bar each). Comparative driving tests in the battery and hybrid (battery + fuel cell) powering modes were performed. The introduction of the fuel cell was shown to result in extending the driving range by 63–110%, when the amount of the stored H₂ fuel varied within 55–100% of the maximum capacity. The operation in the hybrid mode resulted in more stable driving performances, as well as in the increase of the total energy both withdrawn by the vehicle and returned to the vehicle battery during the driving. Statistical analysis of the power patterns taken during the driving in the battery and hybrid-powering modes showed that the latter provided stable operation in a wider power range, including higher frequency and higher average values of the peak power.     

Performance comparison of two fuel cell hybrid buses with different powertrain and energy management strategies

In order to assess the influences of different powertrain structures and energy management strategies on the performance of hybrid fuel cell buses (FCB), two buses (FCB A and FCB B) were constructed with a “energy hybrid structure” and “power hybrid structure”, respectively. Different energy management strategies were investigated based on analysis of the two systems. And the two buses were compared with each other in a bus cycle and constant speed testing. The Polymer Electrolyte Membrane Fuel Cell (PEMFC) in FCB A showed an advantage in fuel economy for it worked usually in the high efficient range of the PEMFC engine. The hydrogen consumption rate in the cycle testing was 7.9 kg/100 km and 9.8 kg/100 km for FCB A and FCB B, and in the 40 kmph constant speed testing it was 3.3 kg/100 km and 4.0 kg/100 km, respectively. The fuel economy could be improved when the hydrogen and air supply subsystems are optimized and controlled with an advanced algorithm. It could also benefit from a braking energy regeneration system. Compared with FCB A, the PEMFC in FCB B worked under unfavorable operation conditions because its working range was comparatively wide, and the power changing rate was relatively large from a statistical point of view, which resulted in performance recession of the PEMFC in FCB B. After a mileage of 7000 km, the output power of the PEMFC in FCB B was reduced by 10%, compared with 2.4% in FCB A. An advanced energy management strategy is necessary to split the power between the PEMFC and a battery suitable for long durability of a PEMFC.     

Off-grid solar-hydrogen generation by passive electrolysis

A novel embodiment of a polymer electrolyte membrane (PEM) electrolyser is presented as a means for producing hydrogen off-grid by the efficient absorption of the time-varying power output of a solar photovoltaic (PV) panel or array. The balance-of-plant power load was minimised using passive design principles to ensure efficient operation under cloudy, sunset and wintry conditions. Heat generated during the electrolysis process is stored when appropriate to significantly enhance the efficiency of hydrogen production after a period of darkness. A prototype field trial demonstrated the electrolyser's ability to track closely the highly variable output of the PV year-round under a wide range of operating conditions. Hydrogen yields for various geographical locations were estimated to vary from 25 to 65 kg p.a. for a 1.6 kW electrolyser with fixed-tilt PV panels depending on local levels of solar insolation. This could be increased to over 100 kg p.a. by employing a PV panel of greater capacity and a battery for absorbing the peak generation and then discharging it overnight to the electrolyser.     

Energy harvesting from sediment microbial fuel cell to supply uninterruptible regulated power for small devices

Sediment microbial fuel cell (SMFC) is a bio‐electrochemical device that generates direct current by microbes present in the soil. The main drawback of SMFC is the low voltage and fluctuations. Therefore, a suitable scheme is required to obtain sufficient voltage with insignificant fluctuation. This paper proposes an energy harvester power management system (PMS) to get rid of low voltage and fluctuation problem of SMFC. The proposed PMS is composed of a dc‐dc boost converter, switches, and super capacitors. The boost converter (using LTC3108 IC) successfully steps up the voltage up to 2.658 V and provides it to the load for 1.5 minutes. Four SMFCs connected with four individual super capacitors and a single boost converter has been used to implement this scheme. In this strategy, the charging and discharging time of the SMFCs are controlled in such a way that the continuous power will be supplied to the load with the optimum number of SMFCs. This scheme is tested on an experimental setup. It is found that the energy harvester PMS supplies a continuous voltage of 2.658 V with the efficiency of 85.46%, which is sufficient to power for small devices such as remote environment sensors, temperature sensors, LED lighting, and submersible ultrasonic receiver.     

Design and optimization of radioisotope sources for betavoltaic batteries

A Monte Carlo source model using PENELOPE was developed to investigate different tritiated metals in order to design a better radioisotope source for betavoltaic batteries. The source model takes into account the self‐absorption of beta particles in the source which is a major factor for an efficient source design. The average beta energy, beta flux, source power output, and source efficiency were estimated for various source thicknesses. The simulated results for titanium tritide with 0° and 90° angular distributions of beta particles were validated with experimental results. The importance of the backscattering effect due to isotropic particle emission was analyzed. The results showed that the normalized average beta energy increases with the source thickness, and it reaches peak energy depending on the density and the specific activity of the source. The beta flux and power output also increase with increasing source thickness. However, the incremental increase in beta flux and power output becomes minimal for higher thicknesses, as the source efficiency decreases significantly at higher thicknesses due to the self‐absorption effect. Thus, a saturation threshold is reached. A low‐density source material such as beryllium tritide provided a higher power output with higher efficiency. A maximum power output of approximately 4 mW/cm³ was obtained for beryllium tritide with SiC. A form factor approach was used to estimate the optimum source thickness. The optimum source thickness was found near the thickness where the peak beta particle average energy occurs.     

Hydrogen fuel cell hybrid scooter (HFCHS) with plug-in features on Birmingham campus

A commercially available ‘pure’ lead-acid battery electric scooter (GoPed) was converted to a hydrogen fuel cell battery hybrid scooter (HFCHS) in views of investigating the effect of hybridisation on driving duty cycles, range, performance, recharging times, well-to-wheel CO₂ footprint and overall running costs. The HFCHS with plug-in features consisted mainly of a 500 W hydrogen PEM Fuel Cell stack connected to four 12 V 9 Ah lead-acid batteries and two hydrogen metal-hydride canisters supplying pure hydrogen (99.999%) and also acting as heat sink (due to endothermic hydrogen desorption process). In this study, the HFCHS urban driving cycle was compared with that of a conventional petrol and ‘pure’ battery electric scooter. The energy consumed by the HFCHS was 0.11 kWh/km, with an associated running cost of £0.01/km, a well-to-wheel CO₂ of 9.37 g CO₂/km and a maximum range of 15 miles. It was shown that the HFCHS gave better energy efficiencies and speeds compared to battery and petrol powered GoPed scooters alone.