Linear Generator System Research Articles

Rectification and converter control of the FPSLGs for energy storage applications

AbstractThis article presents two power converters with controllers attached to the Free‐Piston Stirling Linear Generator (FPSLG) and energy storage system (ESS). The rectifier uses hysteresis‐SVPWM current regulation and CB‐SPWM, while the buck‐boost converter utilizes the dual‐loop PI control method. The storage battery receives energy from a linear‐generator with a rectifier and converter. The FPSE and linear motors in the FPSLG convert thermal to electrical energy. A two‐level electrical energy conversion technique using a three‐phase AC signal to DC and DC‐DC converter has been devised to reduce output electrical energy oscillation as well as stabilize the generating system's DC power. Initially, the FPSE's nonlinear model and the three‐phase permanent magnet linear‐motor's linear mathematical model were created and followed by the ESS and control mechanism simulation. The simulation shows that the ESS system and control approach can give stable power to the storage battery using linear‐generator power. The PR controller replaces the PI controller in the position loop to improve frequency and displacement tracing. The control system design was simulated in MATLAB and the topology's feasibility and correctness were confirmed. Comparative analysis shows that, rectifier uses the H‐SVPWM's unity power factor of AC and stability controllability of the DC‐side voltage is better than the CB‐SPWM approach.

Heat Transfer Enhancement Analysis of Collector Tube in LFR-CSP

The heat transfer characteristics of the collector tube is one of the cores of a linear Fresnel reflector-solar thermal power generation system (LFR-CSP). In this paper, the heat transfer model of reflective linear Fresnel single-tube compound parabolic collector (CPC) is established. In light of the normal operating conditions during the day, it is found that the direct normal irradiation (DNI) and loop length exert significant effects on the heat collection and thermal loss performance of the linear Fresnel reflector. With the increase of DNI and unit length, the outlet temperature and heat collection capacity of the collector loop increase significantly. Because of the increase of DNI, the increase of collector heat is higher than that of thermal loss. However, the thermal loss per unit length increases correspondingly with the increase in loop length, and the heat collection efficiency decreases. Ambient temperature and wind velocity are not the main factors affecting the heat collection and thermal loss performance of the linear Fresnel reflector under the prerequisite of a good vacuum degree of the collector tube.

Control of Free Piston Stirling Linear Generator system connected with dc/dc converter for energy storage applications based on SVPWM Rectification Method

Recently, the world has been facing several challenges in terms of environmental change, which is expected to increase in the coming periods. Further challenging is how to reduce the emissions of greenhouse gasses into the atmosphere. Such emissions pollute our atmosphere, resulting in global warming. However, the wide use of renewable energies can both help to fight against this phenomenon and reach long-term goals. Considering the growing global concern over the use of fossil fuels and environmental pollution. In this case, a Stirling engine with diversified heat sources and low pollution was developed, and the Free Piston Stirling Linear Generator (FPSLG), which can be directly connected to the Stirling engine and thus eliminate the need for an intermediate mechanical transmission mechanism, was used to create a power generation system with the Stirling engine and has been employed in a range of applications, including space power supply, solar energy generation, and others. This article models two sets of power converters, one of which is connected to the FPSLG and the other to the storage battery system. The Space Vector Pulse Width Modulation (SVPWM) control methods adaption to the AC/DC rectifier and the two-loop Proportional Integral (PI) control method adaption to the DC/DC converter used for renewable energy conversion is proposed. Furthermore, the traditional PI in the position loop is replaced by a Proportional Resonance (PR) controller to increase the frequency and displacement tracking performance. The linear generator’s control system is simulated, and the efficiency of the proposed control strategy is proven. The system was initially simulated in MATLAB/Simulink using the dq-PI current controller to produce the logic pattern for the Voltage Source Rectifier (VSR), and the resulting logic pattern was examined.

Starting Control of Free Piston Stirling Linear Generator System Based on FOC

Aiming at the problem of poor system dynamic performance caused by low parameter matching in the coordinated control of Stirling engine and linear generator in the starting stage control of free piston Stirling linear generator system, a joint control method of free piston Stirling permanent magnet synchronous linear generator system based on field orientation control is proposed, based on the theoretical derivation of the mathematical model of the system and the principle of controller parameters setting, the simulation experiments of the system starting stage under several Stirling engine working conditions are carried out under simulation. The experimental results show that the stability and rapidity of the system are improved, and the dynamic response speed of generator parameters under different working conditions is accelerated, what fully verifies the correctness and effectiveness of the method. It provides an effective way to improve the control performance of the system and stabilize the power generation operation.

Optical Efficiency Analysis of Primary Mirror in LFR-CSP

The linear Fresnel solar thermal power generation system is one of the most representative forms of solar thermal power generation system at present. The primary mirror, as the main mirror, plays a key role in the photothermic conversion process of the collector tube. In this paper, the solar position and the optical efficiency of the primary mirror in LFR-CSP are modeled and analyzed. The light reflection process of primary mirror by solar position through four dimensions of solar declination angle, solar time angle, altitude angle and azimuth angle is studied, and the distribution law of solar position parameters in different seasons and different times throughout the year is analyzed. It is found that the variation range of chord efficiency of a single mirror element in the whole day is 75 %-93 %. The position of a mirror element in winter solstice has the greatest impact on the end loss of more than 1 %, but the summer solstice has no effect.

LINEAR GENERATOR PROTOTYPE WITH VERTICAL CONFIGURATION OF SEA WAVE POWER PLANT

There are three types of potential energy sources in the sea: ocean wave energy, tidal energy, and ocean heat energy. Ocean wave energy is a source of considerable energy. Sea waves are an up and down movement of seawater where the energy of sea waves is generated through the effect of air pressure movement due to fluctuations in ocean wave movements. The Ocean Wave Power Plant can use ocean wave energy to convert it into electrical energy. A linear generator is a device that can convert the mechanical energy of linear motion into electrical energy. The application of the ocean wave energy conversion technology, a linear generator system is an electrical machine that functions to convert the mechanical energy of linear motion into electrical energy using the principle of electromagnetic induction. Wave Energy Converter (WEC) technology has been developed with various methods. From the various existing concepts and designs, in general, WEC technology can be classified into three main types, namely Attenuator (horizontal configuration), Point Absorber (linear configuration), Terminator (damping configuration).

Control of linear generator based on hysteresis‐SVPWM current rectification and bidirectional buck/boost converter used for energy storage

The free-piston Stirling linear generation system has tremendous applications in space power supply, biomass generation, solar thermal generation, factory waste heat generation, and other industrial fields. However, the free-piston Stirling linear generation system suffered from the disadvantages of fluctuation of output electric energy and self-starting. To solve the aforesaid problems, a two-level electric energy conversion control mode which combines three-phase AC/DC and bidirectional buck/boost DC to DC converter is proposed in this paper to make the generation system with stable output DC power. Then, both the linear and non-linear mathematical model of the free-piston Stirling engine are established. Additionally, to improve the performance of frequency and displacement tracking, the traditional proportional-integral (PI) in the position loop is replaced by Proportional Resonance (PR) controller. Moreover, the Hysteresis-SVPWM current control strategy with high robustness and dynamic response is applied to the rectifier to realize the unit power factor control of the AC side of the generator and the stability and controllability of the DC side voltage. Finally, the three-phase voltage Source Rectifier (VSR) and Bi-directional DC/DC with an appropriate inductance and capacitance for energy storage are modelled. The effectiveness of the proposed system is validated using theoretical analysis and simulations in Matlab.

Experimental research and performance analysis of a free piston expander–linear generator coupled with a driving motor

This paper establishes a test bench for a free piston expander–linear generator (FPE–LG) system coupled with the drive motor (DM) to promote the application of FPE–LG on vehicle. Firstly, it discusses the operating characteristics and output performance of the FPE–LG under the simulated operation conditions of vehicle. Meanwhile, it investigates the operating characteristics of FPE–LG under different torques and expansion times. Finally, this paper analyzes the influence of different torques and expansion times on the operating frequency of FPE–LG. The experimental results show that the operating frequency of FPE–LG is related to the expansion time and torque. The power output of the DM decreases as the torque increases, the power output of the DM increases first and then decreases as the expansion time increases. Therefore, the selection of suitable expansion time under different intake pressure plays an important role in improving the power output of the DM. The maximum of the peak power output of DM is about 25.8 W, when the intake pressure is 4 bar, the expansion time is 30 ms and the torque is 0.00571 N m.

Influence of the Number of Coil on the Accelerated-Type Wave Energy Generation System

This paper proposed a pulley-buoy accelerated type linear wave power generation system, and verifies its feasibility and effectiveness through experiments. Compared with traditional three-phase wave energy converter, the process of energy transfer was cancelled in the pulley-buoy accelerated type linear wave power generation system, wave energy was converted into electrical energy through the movement of float directly. In the system, the pulley assembly increased the velocity of the float and the generating capacity of the linear generation system, thereby increasing its conversion efficiency. In the experiment, an undersized pulley-buoy accelerated type linear wave power generation system and a swing wave-making system were built in the laboratory. The experiment explored the influence of the number of the stator coil on the power generation performance of the system, and results showed that within the scope of this research, increasing the stator coils to a certain extent could effectively raise the efficiency of wave energy conversion and improve the generation performance of the pulley-buoy accelerated type linear wave power generation system. This research provides valuable experience for the actual application and effective operation of wave energy conversion system.

Influence of Buoy Size on Accelerated Wave Power Generation Device

This paper proposed a pulley-buoy accelerated wave energy linear power generation system, and the feasibility and effectiveness of this system were verified through experimental research. Compared with the traditional wave energy power generation system with three-stage energy conversion links, the pulley-buoy accelerated wave energy linear power generation system omits the intermediate energy transfer and conversion link, and realizes the direct gain of electric energy from the buoy movement caused by wave, and by introducing the pulley combination, the movement speed of the buoy is enlarged, the power generation of the linear power generation system is increased, thereby the wave energy conversion efficiency of the system is improved. Under laboratory conditions, a small-size pulley-buoy accelerated wave energy linear power generation system prototype and a swing-plate wave-making system were built to explore the effects of different buoy sizes on the power generation performance of the system. The test results show that within the research scope of this paper, increasing the size of the buoy can effectively increase the wave energy conversion efficiency of the system and improve the power generation performance of the accelerated wave energy power generation system. The research results in this paper provide useful experience for the practical application and efficient operation of wave energy power generation systems.

Development of free piston engine linear generator system and a resonant pendulum type control method

A free piston engine linear generator, which has the potential of the compact physique, high brake efficiency and high flexibility for fuel, has been developed. The developed free piston engine linear generator consists of a two-stroke combustion unit, an air-bounce chamber and a linear generator. The key technologies to realize the continuous operation are the control method and lubricating and cooling strategies. The proposed structure is featured as a piston shape with two different diameters coaxially, called a “W-shape” piston, which has an empty space inside for the oil cooling path. The performance of the structure is evaluated by a one-dimensional cycle simulation. The result indicates the possible output power of 10 kW and thermal efficiency of 42% using premixed charge compression ignition combustion strategy. The control method is another challenge of the free piston engine linear generator. This work proposes two strategies of the position feedback control method and the resonant pendulum type control method. The first method has the function of the feedback loops for the piston position and velocity so that the piston motion follows the reference profile calculated in advance. The experimental results show the limited range of operation because the fixed profile does not absorb the deviation of the piston motion due to the combustion deviation. The second method is based on the speed control without a fixed reference profile of the piston motion. The experimental result shows the robustness to the change in operating parameters such as ignition position, amount of fuel and desired power output.

Electromagnetic Characteristics Analysis of a Tubular Moving Magnet Linear Generator System

As a new type of advanced electrical power generation system, free-piston engines can be applied to many fields, such as electric vehicles and communication base stations. In this paper, a novel tubular moving magnet linear generator system is designed for free-piston engines. A three-dimensional finite element model of the designed linear generator is presented using a transient computing method with a motion solver. The electromagnetic force, electromotive force, and generating efficiency of the designed linear generator are analyzed in detail. A prototype is manufactured and tested under laboratory conditions, and then the main performance of the prototype is evaluated using the validated finite element model. The electromagnetic analysis in this paper indicates that a generating efficiency of 91.4% can be obtained by the moving magnet linear generator under the rated working frequency of 50 Hz. Compared with the existing moving coil linear generator prototype, the power volume density and the power mass density of the new designed moving magnet linear generator prototype are increased by 150% and 35%.

High power density by combining of a double stator and an opposite-magnets linear generator in a dual-type free-piston engine generator

A linear generator system based on a free-piston engine is expected to be a highly efficient power-generation engine for series hybrid vehicles. However, the engine generator must produce in a limited installation space the very high power required to drive a car. Consequently, considering the car-mounting situation, higher power density is required by means of reduced generator size and higher efficiency. In this paper, a cylindrical double-stator linear synchronous generator with opposing permanent magnets is used for free-piston engine. The double stator realizes smaller size, and using opposing magnets achieves a larger thrust constant than that with a single stator. In a finite-element analysis, the high-efficiency area is expanded compared to a surface-magnet type of the same size. Furthermore, this paper clarifies the effectiveness for improved power density with maximum-generation control in a simulation of a dual-sided engine model.

Improving the constant‐volume degree of combustion considering generatable range at low speed in a free‐piston engine linear generator system

Series hybrid vehicles using free‐piston engine coupled with linear generator are expected for high‐efficiency energy conversion systems. Such engines do not have a crank mechanism, which greatly reduces the friction loss. In addition, the piston action can be controlled freely by the generation braking thrust by using an inverter control. In a conventional crank engine, past research has shown that delaying the piston motion after the combustion increases the maximum combustion pressure, and this delay brings a constant‐volume degree close to the Otto cycle. In the free‐piston system, a high braking thrust is needed at a low piston speed immediately after combustion. However, the highest braking thrust was limited in the low‐speed range because the back electromotive force of a permanent magnet synchronous generator was too small. This article shows the range that can be theoretically attained for a low‐speed generator. The delaying piston movement with only the braking thrust improved the effective work by 25% near the top dead center. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Performance characteristics of compressed air-driven free-piston linear generator (FPLG) system – A simulation study

The integrated model of the two-stroke free-piston engine system driven by compressed air is established using MATLAB/Simulink software and the relationship and the influence of the reciprocating motion, friction force, cylinder process and electromagnetic characteristics of permanent magnet linear generator are fully investigated. The piston displacement, velocity, acceleration, thrust, air pressure in cylinder and generator voltage and their relationship are simulated and analyzed, and the motion performance, the characteristics and interaction relationship of the system are obtained. The experimental platform of air driven free-piston linear expander system is tested. Simulation results are compared with experimental data and the whole model is validated. The developed model is then used to study the influence of piston assembly mass, the timing of air intake and exhaust on piston motion characteristics. The peak voltage output, voltage harmonic distortion and efficiency of permanent magnet linear generator under different air pressure and the output power and efficiency with pressure of FPLG under different loads are obtained. The results show change rules of piston displacement, velocity and frequency changes with air pressure, piston assembly mass. Finally from the simulation result, the air pressure and air intake position of highest efficiency of the linear generator are found.

Effect of Copper Loss Reduction with Output Dispersion in a Free-Piston Engine Linear Generator System

Effect of Copper Loss Reduction with Output Dispersion in a Free-Piston Engine Linear Generator System

Design of 100W Regenerative Vehicle Suspension to Harvest Energy from Road Surfaces

In this study, we considered structure of regenerative suspension which is combined with linear generator to re-use vibrations absorbed by the suspension when the vehicle is driving on road surfaces. Then we carried out the optimum design to develop high efficiency linear generator which is up to 250W power, average power 100 W by using the experimental plan method. Finally we carried out an electromagnetic simulation to verify the result of optimum design, and we confirm the maximum power and the average power were 586.43 Watt, 214.98 Watt respectively. The proposed linear power generation system in this study could help keep power supply and performance in the emerging hybrid vehicles in the high-tech automobile industry.

Operation Range of Generation Braking Force to Achieve High Efficiency Considering Combustion in a Free-Piston Engine Linear Generator System

Operation Range of Generation Braking Force to Achieve High Efficiency Considering Combustion in a Free-Piston Engine Linear Generator System

Design of a Linear Synchronous Generator and Examination of the Driving Range for a Free-Piston Engine Linear Generator System

Design of a Linear Synchronous Generator and Examination of the Driving Range for a Free-Piston Engine Linear Generator System

Effectiveness and Setting Operation Range of Resonant Output Distribution Control in Consideration of Spring Characteristics on a Free-Piston Engine Linear Generator System

Effectiveness and Setting Operation Range of Resonant Output Distribution Control in Consideration of Spring Characteristics on a Free-Piston Engine Linear Generator System