CN114484901A - Photovoltaic photo-thermal experimental system based on nanofluid frequency division and control method - Google Patents
Photovoltaic photo-thermal experimental system based on nanofluid frequency division and control method Download PDFInfo
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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Abstract
A photovoltaic photo-thermal experimental system based on nanofluid frequency division and a control method thereof comprise a double-temperature control device, an ultrasonic water bath instrument, a cooler and a vacuum pump; the outlet of the heat exchanger is connected with the ultrasonic water bath instrument, and the inlet of the heat exchanger is connected with the outlet of the first vacuum pump; the heating instrument is connected with a second vacuum pump; the outlet of the heating instrument is connected to the inlet end of the flow channel of the photovoltaic photo-thermal module; the inlet of the ultrasonic water bath instrument is connected with the outlet of the cooler; the outlet of the ultrasonic water bath instrument is connected with the inlet of the cooler; thermal resistors are arranged at the outlet of the heat exchanger and the outlet of the ultrasonic water bath instrument. The invention realizes accurate control of the temperature of the circulating fluid through the double-temperature control system; for the property of easy agglomeration of the nanofluid, the ultrasonic combination is added to reduce the agglomeration of the nanofluid, so that the cyclic utilization rate of the nanofluid is improved, the experiment cost is reduced, the experiment error is reduced, and the stability of the experiment effect is ensured; the system is more flexible, various testing working conditions can be realized only by controlling the valve, and the system is easy to operate, simple and feasible.
Description
Technical Field
The invention relates to the field of solar photovoltaic photo-thermal power generation (PV/T), in particular to a frequency division type photovoltaic photo-thermal experimental system, which is designed and established by reasonably planning and arranging a set of novel photovoltaic photo-thermal experimental table based on nano-fluid frequency division mainly aiming at the aspects of flexibility of connection of experimental devices, accuracy of fluid temperature control, stability of testing performance and the like, and is used for accurately testing the electrical output and thermal output performance of the PV/T experimental system.
Background
The photovoltaic photo-thermal system stands out from a plurality of energy utilization systems due to the advantages of sustainable development, no noise, no pollution and the like. In a traditional photovoltaic power generation system, after sunlight is incident on the surface of a photovoltaic cell panel, only part of solar energy can be converted into electric energy, and unused solar spectrum energy is directly converted into heat, so that the problems of cell temperature rise and cell efficiency reduction are caused.
The frequency division type photovoltaic photo-thermal system can effectively solve the problem. In the whole solar spectrum range, part of solar energy is converted into electric energy by the photovoltaic cell, and the rest of solar energy is reflected or absorbed by the frequency division material before reaching the surface of the cell, so that the temperature rise of the cell can be effectively avoided. The nano fluid is a fluid in which metal or nonmetal particles with certain concentration and particle size of tens to hundreds of nanometers are suspended in fluid such as water or heat conduction oil, obvious absorption peak to solar radiation can be generated after the fluid is added with the nanoparticles, and the absorption performance of the nano fluid to sunlight can be changed by adjusting and combining parameters such as material, shape, size, concentration and the like of the nanoparticles.
Meanwhile, the frequency division type photovoltaic photo-thermal system utilizes forced circulation fluid (such as water or heat conduction oil) to cool the back plate of the cell panel, so that the operation temperature of the cell can be reduced, the cell can operate under an ideal working condition, and meanwhile, the waste heat is also recovered, thereby achieving the dual purposes and realizing the maximization utilization of energy.
In the practical application process, according to the needs, a frequency division flow channel is added above the battery plate, a cooling flow channel is added below the battery backboard, and different nano particles and base fluid are simultaneously selected or combined to modulate the frequency division characteristic, so that more flexible system control can be realized. At present, in a photovoltaic photo-thermal system in engineering application and experimental research, water or an air cooling battery panel is adopted, the research on the photovoltaic photo-thermal system based on nano fluid frequency division is less, and the discussion on the problems of circulating fluid temperature control, device layout, frequency division liquid stability and the like in a frequency division type photovoltaic photo-thermal system is still solved:
1. the circulating fluid temperature control is not accurate:
in the fluid circulation process, the cooling liquid is heated after absorbing the heat of the solar panel, and the frequency division fluid is also heated due to the absorption of solar energy. a. In order to achieve a better heat absorption effect, the cooling liquid should be cooled to a certain inlet temperature, but the cooling process is often inaccurate, and the inlet temperature of the cooling liquid required by the system cannot be achieved. b. The nano fluid used as the frequency division liquid has the frequency division effect related to the temperature, and in the experimental process, the system performance in each temperature interval needs to be tested, and the temperature control is particularly important.
In a conventional research, for example, patent application No. CN201410298252 is named as a solar photo-thermal photoelectric frequency division utilization system, semiconductor nanofluid is used as a frequency division fluid, the nanofluid flows from a photoelectric unit to a photo-thermal unit, the nanofluid exchanges heat with cooling water through a heat exchanger, and the cooled nanofluid is sent to an aluminum pipe. The temperature of the nanofluid is not accurately regulated and controlled in the process, the temperature of the nanofluid before the nanofluid is sent into the aluminum pipe has great influence on an experimental test result, repeated measurement can not be achieved for many times if the accurate control of the temperature of the nanofluid is not carried out, and variable working condition testing can not be flexibly carried out.
2. The connection and layout of the device is inflexible:
the research on the photovoltaic photo-thermal system is not limited to the test of a single photovoltaic photo-thermal module, the photovoltaic photo-thermal system is often tested by adopting a plurality of photovoltaic photo-thermal modules, on the basis, the condition that the photovoltaic photo-thermal modules work together is considered, the practical engineering application condition is better met, and meanwhile, the problem of connection layout among different modules is also considered, so that the photovoltaic photo-thermal system is more comprehensively developed. When a plurality of photovoltaic photo-thermal modules are researched, the connection among the photovoltaic photo-thermal modules is not flexible, and the system performance needs to be tested by connecting the photovoltaic photo-thermal modules in series/parallel/mixed in the experimental process.
For example, the system connection in the case of a single photovoltaic and thermal module is only studied in the name of PV/T system based on photovoltaic cells in patent application No. 201010610205.3 and the system connection in the case of a solar photothermal and photoelectric frequency division utilization system in patent application No. CN201410298252, and the multi-module system and the connection layout thereof are not considered.
3. The properties of the nanofluid are unstable: \ u
Particles in the nanofluid are easy to agglomerate and precipitate, and the performance of the nanofluid is affected, so that the frequency division effect and the system performance are affected. For the experiment process needing to be carried out for many times, due to particle agglomeration, the nanofluid needs to be prepared again, the time cost is increased, the economic cost is increased, and due to the difference of each preparation, the nanofluid used each time cannot be guaranteed to have the same property, and the experiment error is increased when the experiment effect is compared.
For example, the name of patent application No. CN201410298252 is that the stability problem of the nanofluid is not considered yet in a solar photo-thermal photoelectric frequency division utilization system, the nanofluid is prone to aggregate and deposit along with time migration, the performance of the aggregated nanofluid is reduced, and the system performance is greatly influenced.
Disclosure of Invention
In order to solve the defects in the prior art, the invention discloses a novel photovoltaic photo-thermal experimental system based on nano-fluid frequency division, which has the following technical scheme:
the photovoltaic photo-thermal experimental system based on nanofluid frequency division comprises a photovoltaic photo-thermal module, a dual-temperature control device, an ultrasonic water bath instrument, a cooler, a first vacuum pump and a second vacuum pump; it is characterized in that: the dual-temperature control device comprises a heat exchanger and a heating instrument; an inlet on the cooling water side of the heat exchanger is connected with an outlet of the cooler; the outlet of the cooling water side of the heat exchanger is connected with the inlet of the cooler; an outlet at the working medium side of the heat exchanger is connected with an ultrasonic water bath instrument; an inlet on the working medium side of the heat exchanger is connected with an outlet of the first vacuum pump; the inlet of the first vacuum pump is connected with the water tank; the inlet of the heating instrument is connected with the outlet of the second vacuum pump; the outlet of the heating instrument is connected to the inlet end of the flow channel of the photovoltaic photo-thermal module; a working medium side outlet of the ultrasonic water bath instrument is connected with an inlet of the second vacuum pump, and a water bath side inlet of the ultrasonic water bath instrument is connected with an outlet of the cooler; an outlet at the water bath side in the ultrasonic water bath instrument is connected with an inlet of the cooler; and a cooling water side outlet of the heat exchanger and a water bath side outlet of the ultrasonic water bath instrument are provided with thermal resistors for measuring temperature, transmitting a temperature signal to the data acquisition system 7 and storing and analyzing data through a computer PC.
The invention also discloses a control method of the photovoltaic photo-thermal experimental system based on the nano-fluid frequency division.
Has the advantages that:
(1) the circulating fluid temperature control is accurate through the double-temperature control system.
(2) The PID control double-temperature control system based on the particle swarm algorithm enables the fluid temperature to be controlled more accurately, more quickly and more stably, can well achieve the purpose required by experimental testing, can ensure that the temperature control of the cooling fluid and the frequency division fluid is more accurate, and achieves better experimental effect.
(3) For the property of easy agglomeration of the nanofluid, the ultrasonic combination is added to reduce the agglomeration of the nanofluid, so that the cyclic utilization rate of the nanofluid is improved, the experiment cost is reduced, and the experiment error is reduced. In the ultrasonic oscillation process of the ultrasonic water bath instrument on the nanofluid, the temperature of the water bath rises along with the increase of ultrasonic time, and the temperature rise can cause improper ultrasonic, so that the agglomeration phenomenon of the nanofluid is aggravated. The temperature monitoring and the timely cooling of the water in the ultrasonic water bath instrument also ensure the stability of the experimental effect.
(4) The design of device and pipe connection for the system is more nimble, only needs control valve just can realize multiple test operating mode, easy operation and simple feasible.
Drawings
Fig. 1 is a schematic structural diagram of a photovoltaic photo-thermal experimental system based on nanofluid frequency division.
FIG. 2 is a block diagram of a hardware system of the temperature control section of the present invention.
FIG. 3 is a diagram of an adaptive PID control system based on particle swarm optimization.
FIG. 4 is a graph comparing the temperature output curve after particle swarm optimization and the temperature output curve without particle swarm optimization.
In the drawings, each reference numeral is
Wherein: 1-water tank, 2-first vacuum pump, 2' -second vacuum pump, 3-heat exchanger, 4-ultrasonic water bath instrument, 5-flowmeter, 6-heater, 7-data acquisition system, 8-computer PC, 9-direct current load, 10-cooler, 11-radiometer, 12-environmental thermometer, 13-anemometer, 14-photosensitive element, 15-double-shaft tracking system and a-q-valve.
Detailed Description
The invention discloses a photovoltaic photo-thermal experimental system based on nanofluid frequency division, which comprises a photovoltaic photo-thermal module, a dual-temperature control device, an ultrasonic water bath instrument 4, a cooler 10, a first vacuum pump 2 and a second vacuum pump 2'; it is characterized in that: the double-temperature control device comprises a heat exchanger 3 and a heater 6; the inlet of the cooling water side of the heat exchanger 3 is connected with the outlet of the cooler 10; the outlet of the cooling water side of the heat exchanger 3 is connected with the inlet of the cooler 10; an outlet at the working medium side of the heat exchanger 3 is connected with the ultrasonic water bath instrument 4; an inlet at the working medium side of the heat exchanger 3 is connected with an outlet of the first vacuum pump 2; the inlet of the first vacuum pump 2 is connected with the water tank 1; the inlet of the heating instrument 6 is connected with the outlet of the second vacuum pump 2'; the outlet of the heating instrument 6 is connected to the inlet end of the flow channel of the photovoltaic photo-thermal module; a working medium side outlet of the ultrasonic water bath instrument 4 is connected with an inlet of the second vacuum pump 2', and a water bath side inlet in the ultrasonic water bath instrument 4 is connected with an outlet of the cooler 10; the outlet of the water bath side in the ultrasonic water bath instrument 4 is connected with the inlet of the cooler 10; and a cooling water side outlet of the heat exchanger 3 and a water bath side outlet of the ultrasonic water bath instrument 4 are provided with thermal resistors for measuring temperature, transmitting temperature signals to the data acquisition system 7 and storing and analyzing data through a computer PC 8.
In the fluid circulation process, the cooling liquid is heated after absorbing the heat of the solar panel, and the frequency division fluid is also heated due to the absorption of solar energy; a. in order to achieve a better heat absorption effect, the cooling liquid is cooled to a certain inlet temperature, but the cooling process is not accurate and cannot achieve the inlet temperature of the cooling liquid required by the system; b. the nano fluid used as the frequency division liquid has the frequency division effect related to the temperature, and in the experimental process, the system performance in each temperature interval needs to be tested, and the temperature control is particularly important. Therefore, the accuracy of the temperature control of the circulating fluid is essential.
The following detailed description will explain the technical means and reasons taken by the present invention to solve the deficiencies in the prior art:
dual-temperature control system
The technical scheme is mainly realized through two devices, namely a heat exchanger 3 and a heating instrument 6, and the control strategy uses the self-adaptive PID control of particle swarm optimization to achieve the purpose that a cooling working fluid and a frequency division working fluid in a control system enter a photovoltaic photo-thermal module to be tested at a target temperature.
For cooling the working fluid, it is necessary to accurately control its inlet temperature into the photovoltaic photothermal module. In the operation process, the temperature of the working fluid coming out of the photovoltaic photo-thermal system rises, the outlet temperature of the photovoltaic photo-thermal module is measured by using a thermal resistor at the outlet of the photovoltaic photo-thermal module, the flow of cooling water entering the heat exchanger 6 is determined according to the opening degree of the temperature control valve q, the working fluid is subjected to heat exchange with the cooling water through the heat exchanger 3 for cooling, and the working fluid is cooled to 3-5 ℃ below the required temperature due to the fact that the cooling is not easy to accurately control. Before entering the photovoltaic photothermal module, the temperature is measured and then heated to the actually required working temperature by using the heating instrument 6. On the one hand, the accurate control of the temperature can be realized, on the other hand, the heating is carried out before the inlet, and the temperature loss caused by insufficient heat preservation of the pipeline before the fluid enters the system is reduced.
For the frequency-divided fluid, it is also necessary to control its temperature into the photovoltaic optothermal module. The temperature of the circulated frequency division fluid rises, the outlet temperature of the frequency division fluid is fed back to a computer, the cooling effect is controlled according to the opening degree of the temperature control valve p, the working fluid is primarily cooled by the heat exchanger 3, and the temperature interval is between dozens of and hundreds of degrees because the experiment needs to test the influence of the frequency division fluid at different temperatures, so that the frequency division fluid is heated by the heating instrument 6 until the required temperature is reached.
And a self-adaptive PID control system optimized by particle swarm is selected for temperature control. The invention emphasizes that: because the traditional PID control mode often has the problems of larger delay and larger inertia, even obvious time-varying property and nonlinearity are shown for some working conditions, the control result can not well solve the automatic control problem of the temperature, if the better control effect is to be achieved, the control rule and parameters must be continuously adjusted, the PID control combined with the intelligent algorithm has good overcoming and adaptive capacity for various interferences in the control process, and based on the defects of the traditional PID control mode, the inventor proves that the traditional PID control strategy can not be suitable for the invention through numerous experiments, so the invention adopts the PID control strategy of the particle swarm optimization algorithm, thereby improving the control performance and stability, and leading the temperature control in the experimental test process to be more sensitive and accurate.
The particle swarm algorithm simulates the process of finding food by a bird swarm. Assume that a flock of birds is randomly distributed in an area where only one food item is in the area and experiences constant information transfer between individuals looking for food. The individual does not know the specific position of the food, but the individual can continuously adjust the searching speed by tracking the individual with the best current position, the individual with the best current position is determined according to the distance between the individual and the food, and after the individual searches the food, the searching work of the whole bird group is completed. In the particle swarm optimization, the particles correspond to birds, and the particle optimization process corresponds to a process of searching food for a bird swarm. The particle swarm algorithm is widely applied as an intelligent algorithm, self-adaptive PID control optimized by the particle swarm algorithm has a good effect on parameter setting, and the system has the characteristics of rapidity and stability and well controls the temperature in the system.
The specific algorithm of the self-adaptive PID control strategy of the double-temperature-controlled particle swarm optimization is as follows:
according to an analog control algorithm:
the digital control algorithms used by the computer include position control algorithms, incremental algorithms and velocity algorithms. With the incremental algorithm, the relationship between the error and the controlled variable is as follows:
△u(k)＝Kp[e(k)-e(k-1)]+Kie(k)+Kd[e(k)-2e(k-1)+e(k-2)]
u(k)＝u(k-1)+△u(k)
PID control based on particle swarm optimization is to perform K pairs through the particle swarm optimization in each sampling periodp、Ki、KdAnd (6) setting. As shown in figure 3, the PID control system based on the particle swarm algorithm performs multiple iterations at a sampling moment k according to error values at the moments k, k-1 and k-2, calculates a control quantity corresponding to particles in each iteration, calculates corresponding output and adaptive values, selects historical optimal particles and global optimal particles according to the adaptive values, and takes the obtained global optimal particles as PID parameters at the next moment k +1 after the iteration is finished. Thus, the PID parameters will change continuously with the change of the system status. And adopting the absolute value of the error, the error change rate and the control quantity as adaptive functions. The adaptive function expression of the ith particle at the kth sampling time is:
F(i)＝α|error(i)|+β|derror(i)|+γ|u(i)|
where error (i) is the position error derror (i) of the ith particle at the kth sampling time, and the position error change rate of the ith particle at the kth sampling time; u (i) is a control quantity which is the position of the ith particle at the kth sampling time. To reflect the effect of these three terms in the fitness function, the three terms are multiplied by weights α, β, γ, respectively.
The structure of the device in the system of the control method is shown in figure 2, a temperature measuring module consisting of a plurality of thermal resistors simultaneously collects the temperature of the working fluid of the controlled object and the heat exchanger 3 of the heat exchange module, and inputs the temperature signal to a main control module computer 8, and the main control module controls the output temperature signal of an output module. And the opening degree of a cooling water side valve q of the heat exchanger 3 is driven by the output module, so that the temperature of the working fluid of the controlled object is regulated. In an experimental system, the thermometry module needs to measure the temperature at several points: the outlet temperature of the fluid after the fluid comes out of the photovoltaic photo-thermal module, the inlet temperature of the fluid before the fluid enters the 3-heat exchanger, the inlet temperature of the fluid before the fluid enters the heating instrument, the outlet temperature of the fluid after the fluid comes out of the heating instrument, and the fluid flow measured by a 5-flow meter in the system. And (3) sending the signals into a main control module, performing self-adaptive PID control of particle swarm optimization, outputting a valve position size signal of a heat exchanger 3-cooling water side valve q through a control system, preliminarily adjusting the temperature, and simultaneously adjusting the heating temperature of a heater 6-to ensure that the fluid temperature at the outlet of the heater is the inlet temperature required by a set experiment.
Connection and layout:
the research on the photovoltaic photo-thermal system is not limited to the test of a single photovoltaic photo-thermal module, when a plurality of photovoltaic photo-thermal modules are researched, the connection among the photovoltaic photo-thermal modules is not flexible, and the system performance needs to be tested by connecting the photovoltaic photo-thermal modules in series/parallel/mixed in the experimental process. Therefore, flexibility in connection and layout of hardware devices of the photovoltaic and photothermal system is required.
In the experimental system, in order to realize the flexibility of connection and layout, four branch flow channels are connected on a main flow channel from a heater 6 to an inlet of a water tank 1, the four branch flow channels are respectively connected to inlets of four photovoltaic photo-thermal modules, valves e, f, g and h are respectively installed on the four branch flow channels to control the on-off and the opening degree of the branch flow channels, a valve a is added on the main flow channel between a first branch flow and a second branch flow, a valve b is added on the main flow channel between the second branch flow and a third branch flow, a valve c is added on the main flow channel between the third branch flow and a fourth branch flow, and a valve d is added on the flow channel between the fourth branch flow and the water tank 1. Valves l, i, j and k are respectively added to outlet branch runners of the four photovoltaic photo-thermal modules to control the on-off and the opening of the branches, and valves m, n and o are added to a connecting trunk from the outlet runners of the photovoltaic photo-thermal modules to the water tank 1.
In the experimentation, need test the output of experimental system under the different operating modes, added valve a to o between the connection of four photovoltaic light and heat modules in figure 1, through the switch of controlling different valves, can realize following function: on one hand, the number of modules used in the experiment can be controlled, only part of the modules can be used, and the four modules can be tested together. On the other hand, the connection mode between different modules is controlled, and the different modules can be connected in series, in parallel or in a mixed manner. The multifunctional flexibility test of the photovoltaic photo-thermal system of the nanofluid frequency division is realized by switching and combining the valves.
Ultrasonic combination:
particles in the nanofluid are easy to agglomerate and precipitate, and the performance of the nanofluid is affected, so that the frequency division effect and the system performance are affected. For the experiment process needing to be carried out for many times, due to particle agglomeration, the nanofluid needs to be prepared again, the time cost is increased, the economic cost is increased, and due to the difference of each preparation, the nanofluid used each time cannot be guaranteed to have the same property, and the experiment error is increased when the experiment effect is compared. Therefore, it is also essential to keep the properties of the nanofluid stable. An ultrasonic water bath apparatus 4 is added in the experimental system, and the agglomeration of the nanofluid can be reduced by ultrasonic oscillation, so that the working stability of the nanofluid is ensured. And the water in the ultrasonic water bath instrument 4 is heated due to the long working time of the instrument, the property of the nanofluid is affected even more seriously due to improper ultrasound caused by the heating, and the agglomeration of the nanofluid is even more serious, so that the temperature of the water in the ultrasonic water bath instrument 4 is monitored, and the water in the 4-ultrasonic water bath instrument is cooled by using the cooler 10, so that the ultrasonic water bath instrument 4 is ensured to work at a stable temperature.
The invention is further described below with reference to the accompanying drawings and specific embodiments.
The overall operation example of the invention: during operation of the experimental system, sunlight irradiates on the photovoltaic photo-thermal module, and the double-shaft tracking system 15 rotates to adjust the azimuth and the angle of the whole photovoltaic photo-thermal module according to the incident direction of sunlight rays measured by the photosensitive element 14, so that the sunlight is ensured to vertically irradiate on the photovoltaic photo-thermal module as far as possible. Under the irradiation of sunlight, the photovoltaic cells in the modules generate current and voltage, the current and voltage are measured by the direct current electronic load 9 and displayed on a screen, and the measured parameters such as the current and the voltage are transmitted to the computer 8 for recording and processing, so that the electrical output parameters of the photovoltaic photo-thermal module required by the test of the experiment table are obtained.
Meanwhile, in the photovoltaic photo-thermal module, water is selected as a base liquid for the frequency division fluid, spherical silver (Ag) with the concentration of 5ppm and the particle size of about 50nm is selected as nano particles, the nano fluid consisting of the water and the silver particles absorbs heat to raise the temperature, the outlet temperature of the nano fluid is measured by using a thermal resistor at the outlet of the photovoltaic photo-thermal module, the temperature is acquired by a 7-data acquisition system and is transmitted to an 8-computer for recording and storing, and therefore the heat output parameter-temperature of the photovoltaic photo-thermal module required to be measured in an experiment is obtained.
In order to control experimental variables, the fluid in the photovoltaic photo-thermal experimental system is recycled, and in order to ensure stable properties of the nano fluid, ultrasonic oscillation is needed to prevent agglomeration. The temperature of an inlet of the device needs to be accurately controlled for experimental tests, a particle swarm optimization adaptive PID control algorithm and a dual-temperature control strategy are applied to temperature control, and the heat exchanger 3 and the heater 6 are used for realizing temperature adjustment. Fluid entering water tank 1 that comes out at photovoltaic light and heat system heat transfer, under vacuum pump 2's effect, heat exchanger 3 is sent to the fluid, with the cooling water heat transfer that comes out in the cooler 10, carry out preliminary cooling, ultrasonic oscillation in the supersound water bathing appearance 4 is sent into to the fluid that the heat transfer was accomplished, fluid gets into flowmeter 5 and heating appearance 6 under vacuum pump 2 ''s effect afterwards, the fluid heats up to required operating temperature in heating appearance 6 accurate heating, the fluid that the heating was accomplished gets into and carries out the experiment test in the photovoltaic light and heat system.
The temperature control strategy of the working fluid is mainly realized by the method: the temperature of the working fluid at the outlet of the photovoltaic photothermal module is 313.15K measured by the thermal resistors, the temperature is adjusted by using a dual-temperature control system, the inlet temperature of the working fluid which is going to enter the photovoltaic photothermal module next time is 291.15K, and the temperature measurement module consisting of the multiple thermal resistors simultaneously collects the temperature of the working fluid of the controlled object and the heat exchanger 3 of the heat exchange module and inputs the temperature signals to the main control module computer 8.
In the double-temperature control system, a self-adaptive PID control strategy of particle swarm optimization is adopted, and a transfer function is
The controller adopts a PD controller, the sampling period is 1ms, the total sampling time is 300 times, and the time is 0.3 s. The particle group size is 25, the inertial weight is 0.9, the maximum search speed is 5, the initial value of Kp is set to be a randomly generated number within the range of 5-15, the initial value of Kd is set to be a randomly generated number within the range of 0-1, and the maximum search range is set to be 2. The fitness function is set to have alpha of 0.95, beta of 0.05 and gamma of 0.01, and the particles iterate for 50 generations at each moment. As shown in fig. 4, for example, a temperature output curve after particle swarm optimization and a temperature output curve without particle swarm optimization are compared, it can be seen that a gray curve is a working fluid temperature output curve before particle swarm optimization, a black curve is a working fluid temperature output curve after particle swarm optimization, and the temperatures of the two schemes are finally stabilized at a target temperature, but it can be seen that: the temperature output curve optimized by the particle swarm optimization has the characteristics of shorter rise time, smaller overshoot, shorter regulation time and small stable error, and has better control performance.
Therefore, the self-adaptive PID optimized particle swarm controls the output temperature signal of the output module. And driving the opening degree of a cooling water side valve q of the heat exchanger 3 by using an output module to enable the heat exchanger 3 to cool the working liquid to 288.15K, sending the working liquid into the heating instrument 6 to be heated and heated up after ultrasonic oscillation until the temperature reaches a target 313.15K, and carrying out next experimental test after the working liquid reaching the target temperature enters the photovoltaic thermal module.
2. An ultrasonic combination water bath temperature control strategy comprises the following steps:
in order to ensure the stable temperature of the water bath in the ultrasonic water bath instrument 5, the temperature of the water bath is measured by using a thermal resistor, and a measured temperature signal is sent to a computer 8 by a data acquisition system 7. Under the feedback action, if the temperature rises, the control valve p increases the opening, the cooling water flow increases, and the water bath temperature decreases.
3. Photovoltaic photo-thermal module connection and layout
Taking a system output experiment under the condition of measuring the parallel connection of the first three photovoltaic photo-thermal modules as an example. On the fluid side, the valves c, d, h, k are open, and the valves a, b, e, f, g, i, j, l, m, n, o are closed. On the electrical side, the last panel is disconnected from the dc electronic load 9, and the first three modules are connected in parallel.
On the basis of the traditional photovoltaic photo-thermal system based on nanofluid frequency division, the novel photovoltaic photo-thermal system based on nanofluid frequency division is optimized and established by combining practical problems in the operation process. Firstly, for the problem of inaccurate temperature control, from the practical and feasible point of view, a PID (proportion integration differentiation) controlled dual-temperature control system optimized by particle swarm is used, and through the optimization of the strategy, the temperature control is more accurate, the rise time of a temperature output curve is shorter, the overshoot is smaller, the stable error is small, and the better control performance is realized; secondly, aiming at the conditions that the properties of the nanofluid are unstable and easy to agglomerate, the ultrasonic water bath instrument is used for ultrasonic oscillation, and the temperature of the ultrasonic water bath instrument is monitored, regulated and controlled on the basis, so that the negative effects on the properties of the nanofluid caused by improper ultrasonic and overhigh water bath temperature are prevented, the cyclic utilization rate of the nanofluid is improved, the experiment cost is reduced, and the experiment errors are reduced; thirdly, the requirement of experimental test cannot be met only by using a single photovoltaic photo-thermal module for testing, and the invention establishes and connects a plurality of photovoltaic photo-thermal modules and considers the connection relation among the modules, so that the flexibility and operability of the experimental system are greatly improved. To sum up, the novel photovoltaic photo-thermal system based on nano-fluid frequency division that this patent was established has temperature control accuracy, and nano-fluid circulation stability is good, advantage such as overall arrangement is nimble, has solved the problem in the traditional system, has better feasibility and novelty.
The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are merely illustrative of the principles of the invention, but that various changes and modifications may be made without departing from the spirit and scope of the invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (8)
1. The photovoltaic photo-thermal experimental system based on nanofluid frequency division comprises a photovoltaic photo-thermal module, a dual-temperature control device, an ultrasonic water bath instrument, a cooler, a first vacuum pump and a second vacuum pump; the dual-temperature control device comprises a heat exchanger and a heating instrument; it is characterized in that: an inlet on the cooling water side of the heat exchanger is connected with an outlet of the cooler; the outlet of the cooling water side of the heat exchanger is connected with the inlet of the cooler; an outlet at the working medium side of the heat exchanger is connected with an ultrasonic water bath instrument; an inlet on the working medium side of the heat exchanger is connected with an outlet of the first vacuum pump; the inlet of the first vacuum pump is connected with the water tank; the inlet of the heating instrument is connected with the outlet of the second vacuum pump; the outlet of the heating instrument is connected to the inlet end of the flow channel of the photovoltaic photo-thermal module; a working medium side outlet of the ultrasonic water bath instrument is connected with an inlet of the second vacuum pump, and a water bath side inlet of the ultrasonic water bath instrument is connected with an outlet of the cooler; an outlet at the water bath side in the ultrasonic water bath instrument is connected with an inlet of the cooler; and a cooling water side outlet of the heat exchanger 3 and a water bath side outlet of the ultrasonic water bath instrument are provided with thermal resistors for measuring temperature, transmitting a temperature signal to the data acquisition system 7 and storing and analyzing data through a computer PC.
2. The photovoltaic photothermal experiment system based on nanofluid frequency division according to claim 1, wherein: and the outlet of the second vacuum pump is connected with the input end of the heating instrument through a flow meter.
3. The photovoltaic photothermal experiment system based on nanofluid frequency division according to claim 1, wherein: an outlet flow channel of the photovoltaic photo-thermal module is connected with the water tank through a connecting pipeline; a plurality of controllable switch valves are arranged on the connecting pipeline; connecting four branch runners on a main runner from a heater to an inlet of a water tank, respectively connecting the four branches to inlets of four photovoltaic photo-thermal modules, respectively installing valves e, f, g and h on the four branch runners to control the on-off and the opening of the branches, adding a valve a on the main runner between a first branch and a second branch, adding a valve b on the main runner between the second branch and a third branch, adding a valve c on the main runner between the third branch and a fourth branch, and adding a valve d on the fourth branch and a runner of the water tank 1; valves l, i, j and k are respectively added to outlet branch runners of the four photovoltaic photo-thermal modules to control the on-off and the opening of the branches, and valves m, n and o are added to a connecting trunk from the outlet runners of the photovoltaic photo-thermal modules to the water tank 1.
4. The photovoltaic photo-thermal experimental system based on nanofluid frequency division according to claim 3, wherein: the outlet of the outlet runner of the photovoltaic photo-thermal module is provided with a thermal resistor for measuring temperature, and a temperature signal is transmitted to a data acquisition system and then is connected to a computer PC for storing and analyzing data.
5. The photovoltaic photothermal experiment system based on nanofluid frequency division according to claim 1, wherein: the device also comprises an irradiation meter, an environmental thermometer and an anemometer, and is used for measuring the surrounding environment of the experiment table.
6. The photovoltaic photothermal experiment system based on nanofluid frequency division according to claim 1, wherein: still include photosensitive element and rather than the biax tracker who is connected, biax tracker is used for rotating the position and the angle of adjusting whole photovoltaic light and heat module.
7. The control method of the photovoltaic photo-thermal experimental system based on the nano-fluid frequency division comprises the photovoltaic photo-thermal experimental system based on the nano-fluid frequency division of any one of claims 1 to 6, and is characterized in that: the method comprises the following steps:
step 1: according to the incident direction of the sunlight measured by the photosensitive element, the double-shaft tracking system rotates to adjust the direction and the angle of the whole photovoltaic photo-thermal module so as to ensure that the sunlight vertically irradiates on the photovoltaic photo-thermal module;
step 2: under the irradiation of sunlight, a photovoltaic cell in the photovoltaic photo-thermal module generates current and voltage, the current and the voltage are measured by a direct current electronic load and displayed on a screen, and parameters such as the measured current and voltage are transmitted to a computer for recording and processing, so that electrical output parameters of short-circuit current and open-circuit voltage of the photovoltaic photo-thermal module required by the test of the experiment table are obtained;
and step 3: in the photovoltaic photo-thermal module, water is selected as a base liquid for the frequency division fluid, spherical silver with a certain concentration and a particle size of about 50nm is used as nano particles, the nano fluid formed by the water and the silver particles absorbs heat to heat, the outlet temperature of the nano fluid is measured by using a thermal resistor at the outlet of the photovoltaic photo-thermal module, the temperature is acquired by a data acquisition system and is transmitted to a computer PC to be recorded and stored, and therefore the temperature-thermal output parameter of the photovoltaic photo-thermal module required to be measured in an experiment is obtained;
and 4, step 4: after the working fluid used in the photovoltaic photo-thermal module comes out of the outlet of the module, the working fluid enters the water tank 1 for storage; before the next cycle experiment, a first vacuum pump is used for sending working fluid into a heat exchanger for heat exchange and cooling, then the working fluid enters an ultrasonic water bath instrument for ultrasonic oscillation, the oscillated working fluid is sent to a heating instrument by a second vacuum pump to be heated to a set temperature, and then the working fluid enters a photovoltaic photo-thermal module again for the next test;
and 5: and 4, measuring the temperature of the water bath of the ultrasonic water bath instrument and the temperature of the photovoltaic photo-thermal module by using the thermal resistor while working in the step 4, and controlling the opening degrees of the valves p and q by using a self-adaptive PID control strategy optimized by a particle swarm after a measurement result is transmitted to a computer PC (personal computer) so as to ensure that the water bath temperature of the ultrasonic water bath instrument is constant and the expected heat exchange effect of the heat exchanger is achieved.
8. The photovoltaic photo-thermal experimental system control method based on nanofluid frequency division as claimed in claim 7, wherein: the step 3 further comprises: the thermal resistance in the photovoltaic photo-thermal experimental system needs to measure the temperature of the following points: the outlet temperature of the fluid after the fluid comes out of the photovoltaic photo-thermal module, the inlet temperature of the fluid before the fluid enters the heat exchanger, the inlet temperature of the fluid before the fluid enters the heating instrument, and the outlet temperature of the fluid after the fluid comes out of the heating instrument.
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