rus
Issue #4/2016
I.Vasiliev, A.Chuprin
Development of a piezoelectric energy harvester for navigation support of railway transport
Development of a piezoelectric energy harvester for navigation support of railway transport
Investigation of vibration parameters of the freight cars is presented. Several designs of piezoelectric energy harvester are proposed for the efficient conversion of mechanical vibrations into electrical power. Based on experimental studies a comparison of different types and designs of energy harvester is performed. The amount of energy required for wireless transceiver for monitoring location of a vehicle is evaluated. Obtained data can be used for development of production technology of the piezoelectric energy harvester to provide autonomous power supply for freight cars.
Теги: energy conversion piezoelectric element piezoelectric energy harvester renewable energy возобновляемые источники энергии преобразование энергии пьезоэлектрический генератор тока пьезоэлемент
In order to optimize the operation of the railway system it’s necessary to create a unified information system that will provide:
•implementation of automated control of the trains, as well as a reduction in staff controlling the train;
•introduction of paperless information technology;
•increase the reliability and efficiency of reporting on the car and locomotive fleet;
•high level of information services in domestic and international transit traffic.
To achieve this it’s necessary to equip each mobile unit of railway transport with a set of sensors, which can monitor the required parameters and send their to the data center. The main problem for implementation of this idea is the lack of power supply system on freight cars. Application of electric cables or galvanic cells is a complex and costly solution to the problem [1]. Thus one of the promising directions is the use of alternative sources of energy based on solar, wind, thermal or mechanical energy [2]. The main requirement to the system used as an autonomous power source, is the ability to work under railway transport conditions. In spite of the simple structure of solar cells, their main disadvantage is the reduction of the accumulated energy in the dark as well as the degradation of the optical characteristics due surface contamination of the element [3]. Thermoelectric generators produce electricity based on temperature difference, and have small volumes and long service life. However, their efficient operation requires a large temperature difference [4]. Wind turbine converts the energy of airflow into electric energy. Its main drawback is the complexity of the design and, as a result, performance degradation with decreasing of the turbine size [5]. Autonomous power generators based on the piezoelectric effect can satisfy strength requirements, operate effectively in a wide temperature range and presence of moisture, withstand vibration and mechanical shock arising during the motion of the train [6–9].
In this project for the most efficient conversion of mechanical energy to electricity the vibration parameters of freight cars were studied and the frequency band with the highest values of accelerations is determined. Experimental study and comparison of various types of piezoelectric generators demonstrate the possibility of creating an autonomous source of power for navigation support of railway transport.
Study of the vibration parameters of freight cars
The studies were conducted at different parts of the Moscow railway on following types of cars:
•tank car with the bogie model 18-100. This type of car chosen due to its high center of gravity and the most unfavorable dynamic behavior.
•gondola car with the bogie model 18-9855. This type of car was chosen as the most popular type of rolling stock. Gondola cars are designed to carry a large range of goods that don’t require protection from the weather.
Equipment recording the dynamic performance of the car located in the car-laboratory which is the part of the train; equipment recording the impact indicators of the car on track and turnouts located in the measuring units installed near measuring sections of rail.
The main measuring device for recording data is a strain gauge amplifier Spider-8 (HBM, Germany). Data recording was performed using computer with specialized data collection and processing program. For acceleration measurement used accelerometers B12/500 with measuring range ± 100g. Digitization conducted with a frequency of 200 Hz and a low pass filter of 20 Hz. All measuring and recording equipment is certified by technology adopted in Russian Federation.
As can be seen from Fig.1, vertical accelerations depend on the type of rolling stock (type and design of bogie) as well as load. Acceleration level of the loaded tank car greater than the empty, and the opposite situation observed for gondola. The minimum vertical acceleration equal to 0.015g at a speed of 10 km/h (corresponding to shunting speed), but when the train passing through turnouts single acceleration peaks occur, which exceed the basic level in more than 3 times. At operational speed (80 km/h) minimum acceleration level equal to 0.054g and maximum level is 0.22g. Single peaks of acceleration arising from the joints and track defects can reach more than 0.8g.
The oscillation frequencies of freight cars are in the range of 1.5–18 Hz. Some frequencies directly related to train speed (interaction of the wheel and the rail, spring oscillation). For example, the peak amplitude at 60 km/h is 5.6 Hz and at 135 km/h – 12.1 Hz.
Processing and analysis of the obtained data fully confirm the theoretical concepts of oscillatory processes in the system car-track and can be summarized as:
•oscillation frequency and acceleration increase with increasing of car speed;
•difference between load and empty car is not essential as the total car weight varies no more than twice.
Research and development of peizoelectric energy harvester
Based on the vibration parameters of the rolling stock, beam and membrane types of piezoelectric elements were selected which provide the most efficient conversion of mechanical energy into electrical oscillations. In experimental studies V25W beam piezoelectric element from Mide Technology Corp. and PB 100 × 0.51 membrane piezoelectric elements were used (Fig.2) [10]. To adjust the natural frequency to the frequency of the exciting force additional loads of different mass were installed to the piezoelectric element. Rectifying of the electrical signal from the piezoelectric element was performed with the help of the electronic circuit shown in Fig.3.
The measurements were executed on an electrodynamic vibration system V650 HPAK-CE. A special rig was made for each type of piezoelectric elements for the deflection of piezo element during the action of external vibrations.
Experimental studies of beam piezoelectric energy harvester were carried out at parameters of exciting force, given in Table. Output voltage and power of piezo generator were measured for a number of resistors with electric resistance in the range 10–1 000 Ohm (Fig.6).
In order to evaluate the possibility of using piezoelectric generator as an autonomous power supply to provide navigation support for railway transport, the amount of energy required for operation of the transceiver was calculated. The transceiver consist of GPS module Jupiter SE868-AS [11] and GSM/GPRS module GL865-DUAL [12] from Telit Company. It was assumed that each car has piezo generator consisting of 100 piezoelectric beam elements. Based on experimental data the output power of each piezo element is assumed to be 3.5 mW. Location tracking of the car is constantly monitored during movement of the train, and GPS module works in a periodic mode (asleep for 12 s, then awake 3 s) during parking. Data are transmitted from the cars to a service center for GSM / GPRS channel once every 5 minutes during movement of rolling stock and once every 15 minutes during parking. Taking into account the possible loss in the conversion of energy from the piezoelectric element, during charging and self-discharge of the battery, the proportion of useful energy was assumed to be 60% of the energy initially obtained from the piezoelectric element. According to the results of analysis, in the worst case, when the car is idle 80% of the total time, beam piezoelectric generator able to harvest 104% of the amount of energy required for operation of the transceiver.
To increase the output power a special design of beam piezo generator is proposed, which allows accumulate energy not only from vertical but also from horizontal vibration of the car. Piezoelectric elements placed on a special holder in three spatial dimensions (Fig.4). Additional features of this design are more compact arrangement and, as a consequence, increase the power density of piezo generator [13].
The parameters of exciting force during the experimental studies of the membrane piezoelectric energy harvester are shown in Table. To reduce the initially high natural frequency of the piezoelectric element (500 Hz) a special design was used (Fig.5). The presence of the spring between the piezoelectric element and the load can significantly reduce the natural frequency of the whole system depending on the stiffness coefficient and geometric dimensions of the spring. Furthermore, this design allows registering both vertical and horizontal mechanical vibrations. The measurement results for the different springs are shown in Fig.5. For comparison, measurements of loaded piezoelectric element without the spring were made. As seen from the graphs, the output power of the membrane piezo generator increases with the use of springs with a low stiffness coefficient (spring number 1, 2), and decrease with the high stiffness coefficient (spring number 3, 4). With the increasing of spring stiffness coefficient the output power of piezo generator is reduced to the value obtained in the absence of the spring.
Low output power of the membrane piezo generator compared to the beam piezo generator caused by features of the membrane piezoelectric elements (rigid metal base, single layer of piezoelectric ceramic). However, the obtained data allow to qualitatively compare the effectiveness of different designs piezoelectric energy harvesters.
Conclusions
To date, the use of satellite technology to provide navigation support for railway transport is complicated due to the lack of power supply of freight cars. In this paper investigated the vibration parameters of the rolling stock and proposed designs of the beam and membrane piezoelectric energy harvesters for the most efficient conversion of mechanical vibrations into electrical energy. Based on the data analysis, the freight cars are experiencing fluctuations in the frequency range 1.5–18 Hz and the average values of the acceleration are 0.015–0.27g. The maximum output power of the investigated piezoelectric energy harvester is 3.5 mW per one piezo element. In case of placement on each car 100 piezoelectric elements the generated energy obtained by moving of the car is sufficient for operation of the transceiver, even if 80% of the total time the car is idle. Presented results confirm the possibility of using the piezoelectric energy harvester as an autonomous power supply for freight cars. ■
The project supported by Ministry of Education and Science of the Russian Federation (agreement No. 14.579.21.0086 dated 11.21.2014).
•implementation of automated control of the trains, as well as a reduction in staff controlling the train;
•introduction of paperless information technology;
•increase the reliability and efficiency of reporting on the car and locomotive fleet;
•high level of information services in domestic and international transit traffic.
To achieve this it’s necessary to equip each mobile unit of railway transport with a set of sensors, which can monitor the required parameters and send their to the data center. The main problem for implementation of this idea is the lack of power supply system on freight cars. Application of electric cables or galvanic cells is a complex and costly solution to the problem [1]. Thus one of the promising directions is the use of alternative sources of energy based on solar, wind, thermal or mechanical energy [2]. The main requirement to the system used as an autonomous power source, is the ability to work under railway transport conditions. In spite of the simple structure of solar cells, their main disadvantage is the reduction of the accumulated energy in the dark as well as the degradation of the optical characteristics due surface contamination of the element [3]. Thermoelectric generators produce electricity based on temperature difference, and have small volumes and long service life. However, their efficient operation requires a large temperature difference [4]. Wind turbine converts the energy of airflow into electric energy. Its main drawback is the complexity of the design and, as a result, performance degradation with decreasing of the turbine size [5]. Autonomous power generators based on the piezoelectric effect can satisfy strength requirements, operate effectively in a wide temperature range and presence of moisture, withstand vibration and mechanical shock arising during the motion of the train [6–9].
In this project for the most efficient conversion of mechanical energy to electricity the vibration parameters of freight cars were studied and the frequency band with the highest values of accelerations is determined. Experimental study and comparison of various types of piezoelectric generators demonstrate the possibility of creating an autonomous source of power for navigation support of railway transport.
Study of the vibration parameters of freight cars
The studies were conducted at different parts of the Moscow railway on following types of cars:
•tank car with the bogie model 18-100. This type of car chosen due to its high center of gravity and the most unfavorable dynamic behavior.
•gondola car with the bogie model 18-9855. This type of car was chosen as the most popular type of rolling stock. Gondola cars are designed to carry a large range of goods that don’t require protection from the weather.
Equipment recording the dynamic performance of the car located in the car-laboratory which is the part of the train; equipment recording the impact indicators of the car on track and turnouts located in the measuring units installed near measuring sections of rail.
The main measuring device for recording data is a strain gauge amplifier Spider-8 (HBM, Germany). Data recording was performed using computer with specialized data collection and processing program. For acceleration measurement used accelerometers B12/500 with measuring range ± 100g. Digitization conducted with a frequency of 200 Hz and a low pass filter of 20 Hz. All measuring and recording equipment is certified by technology adopted in Russian Federation.
As can be seen from Fig.1, vertical accelerations depend on the type of rolling stock (type and design of bogie) as well as load. Acceleration level of the loaded tank car greater than the empty, and the opposite situation observed for gondola. The minimum vertical acceleration equal to 0.015g at a speed of 10 km/h (corresponding to shunting speed), but when the train passing through turnouts single acceleration peaks occur, which exceed the basic level in more than 3 times. At operational speed (80 km/h) minimum acceleration level equal to 0.054g and maximum level is 0.22g. Single peaks of acceleration arising from the joints and track defects can reach more than 0.8g.
The oscillation frequencies of freight cars are in the range of 1.5–18 Hz. Some frequencies directly related to train speed (interaction of the wheel and the rail, spring oscillation). For example, the peak amplitude at 60 km/h is 5.6 Hz and at 135 km/h – 12.1 Hz.
Processing and analysis of the obtained data fully confirm the theoretical concepts of oscillatory processes in the system car-track and can be summarized as:
•oscillation frequency and acceleration increase with increasing of car speed;
•difference between load and empty car is not essential as the total car weight varies no more than twice.
Research and development of peizoelectric energy harvester
Based on the vibration parameters of the rolling stock, beam and membrane types of piezoelectric elements were selected which provide the most efficient conversion of mechanical energy into electrical oscillations. In experimental studies V25W beam piezoelectric element from Mide Technology Corp. and PB 100 × 0.51 membrane piezoelectric elements were used (Fig.2) [10]. To adjust the natural frequency to the frequency of the exciting force additional loads of different mass were installed to the piezoelectric element. Rectifying of the electrical signal from the piezoelectric element was performed with the help of the electronic circuit shown in Fig.3.
The measurements were executed on an electrodynamic vibration system V650 HPAK-CE. A special rig was made for each type of piezoelectric elements for the deflection of piezo element during the action of external vibrations.
Experimental studies of beam piezoelectric energy harvester were carried out at parameters of exciting force, given in Table. Output voltage and power of piezo generator were measured for a number of resistors with electric resistance in the range 10–1 000 Ohm (Fig.6).
In order to evaluate the possibility of using piezoelectric generator as an autonomous power supply to provide navigation support for railway transport, the amount of energy required for operation of the transceiver was calculated. The transceiver consist of GPS module Jupiter SE868-AS [11] and GSM/GPRS module GL865-DUAL [12] from Telit Company. It was assumed that each car has piezo generator consisting of 100 piezoelectric beam elements. Based on experimental data the output power of each piezo element is assumed to be 3.5 mW. Location tracking of the car is constantly monitored during movement of the train, and GPS module works in a periodic mode (asleep for 12 s, then awake 3 s) during parking. Data are transmitted from the cars to a service center for GSM / GPRS channel once every 5 minutes during movement of rolling stock and once every 15 minutes during parking. Taking into account the possible loss in the conversion of energy from the piezoelectric element, during charging and self-discharge of the battery, the proportion of useful energy was assumed to be 60% of the energy initially obtained from the piezoelectric element. According to the results of analysis, in the worst case, when the car is idle 80% of the total time, beam piezoelectric generator able to harvest 104% of the amount of energy required for operation of the transceiver.
To increase the output power a special design of beam piezo generator is proposed, which allows accumulate energy not only from vertical but also from horizontal vibration of the car. Piezoelectric elements placed on a special holder in three spatial dimensions (Fig.4). Additional features of this design are more compact arrangement and, as a consequence, increase the power density of piezo generator [13].
The parameters of exciting force during the experimental studies of the membrane piezoelectric energy harvester are shown in Table. To reduce the initially high natural frequency of the piezoelectric element (500 Hz) a special design was used (Fig.5). The presence of the spring between the piezoelectric element and the load can significantly reduce the natural frequency of the whole system depending on the stiffness coefficient and geometric dimensions of the spring. Furthermore, this design allows registering both vertical and horizontal mechanical vibrations. The measurement results for the different springs are shown in Fig.5. For comparison, measurements of loaded piezoelectric element without the spring were made. As seen from the graphs, the output power of the membrane piezo generator increases with the use of springs with a low stiffness coefficient (spring number 1, 2), and decrease with the high stiffness coefficient (spring number 3, 4). With the increasing of spring stiffness coefficient the output power of piezo generator is reduced to the value obtained in the absence of the spring.
Low output power of the membrane piezo generator compared to the beam piezo generator caused by features of the membrane piezoelectric elements (rigid metal base, single layer of piezoelectric ceramic). However, the obtained data allow to qualitatively compare the effectiveness of different designs piezoelectric energy harvesters.
Conclusions
To date, the use of satellite technology to provide navigation support for railway transport is complicated due to the lack of power supply of freight cars. In this paper investigated the vibration parameters of the rolling stock and proposed designs of the beam and membrane piezoelectric energy harvesters for the most efficient conversion of mechanical vibrations into electrical energy. Based on the data analysis, the freight cars are experiencing fluctuations in the frequency range 1.5–18 Hz and the average values of the acceleration are 0.015–0.27g. The maximum output power of the investigated piezoelectric energy harvester is 3.5 mW per one piezo element. In case of placement on each car 100 piezoelectric elements the generated energy obtained by moving of the car is sufficient for operation of the transceiver, even if 80% of the total time the car is idle. Presented results confirm the possibility of using the piezoelectric energy harvester as an autonomous power supply for freight cars. ■
The project supported by Ministry of Education and Science of the Russian Federation (agreement No. 14.579.21.0086 dated 11.21.2014).
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