The compressed air energy storage system traditionally used in thermal power plants generally has a scale of megawatts, and is mainly used to adjust the power load, stabilize the network voltage fluctuation, and improve the utilization rate of renewable energy power generation. In 1978, Huntorf, Germany, established the first application-type 290 MW compressed air energy storage plant. In 1991, McIntosh in the United States built a 110MW, a 26h compressed air storage power station. In 2009, the US Department of Energy's special fund supported a $400 million planned 300MW compressed air energy storage power station in Kern, California. In the same year, a compressed air storage power plant project with a designed capacity of 2,700 MW was put into operation in Norton, Ohio. In 2010, the department again supported a plan to build a 150 MW compressed air energy storage project for renewable energy generation in Watkins Glen, New York, for $30 million. In 2011, Gaines, Texas, USA began construction of a 2MW wind power compressed air energy storage supporting system, which was completed at the end of 2012 with a storage capacity of 500MW.h, becoming the world's third application case for CAES power generation. In 2013, Germany plans to build the first adiabatic compressed air energy storage power plant, ADELE, with a design capacity of 200 MW. The Iowa Energy Storage Park project in the United States has designed a compressed air energy storage system with a capacity of 2,300 MW. It is expected to start production in 2015. Texas is planning to build a 317 MW power plant by 2016, in which the compressed air energy storage capacity is 1/4. The large-scale compressed air energy storage of China Electrical Engineering Journal has become characterized by its high reliability, economy and environmental friendliness. A promising storage method is receiving more and more attention. On the other hand, the application of large-scale compressed air energy storage is subject to many conditions, including unique geographical location, high upfront costs, and efficiency degradation due to limited storage pressure. The small-scale compressed air storage can expand the storage volume, increase the gas pressure, improve the conversion efficiency, etc., and make better use of the technical characteristics of CAES to expand the application space.
The liquid-gas compressed air energy storage technology utilizes the concept of a liquid piston to achieve space gas compression through liquid injection. The processing and utilization of thermal energy during air compression release is critical to the system's operating efficiency and energy conversion efficiency. Compared to reciprocating compressors, screw pumps and vane pumps for air compression release, liquid gas compression has higher heat transfer efficiency. Liquid-gas compression also solves problems such as gas leakage and friction loss that cannot be overcome in direct air compression technology, and improves the efficiency of the system from another aspect. Liquid-gas compression technologies include closed-air liquid-gas compression and open-air liquid-gas compression. The liquid-gas hybrid compression system has a simple structure and flexible control mode, but the storage energy is limited, and the volume of the injected liquid has high requirements. The liquid-gas cycle compression technology utilizes multiple small chambers for gas compression and cycle accumulation to achieve the final compression index. This technology guarantees a high energy density and is independent of liquid volume and is suitable for different environments. However, the system structure is complex, the work efficiency is not as good as the mixed liquid gas compression technology, and the control requirements are high.
This paper proposes a new type of mechanical full-bridge liquid-gas circulating compressed air energy storage scheme. The liquid valve control is realized by the single-chamber liquid piston technology with the single-chamber liquid piston technology. Through the modeling and simulation of macro energy flow representation of the system, the overall working characteristics of the system are analyzed. The system control is studied to improve the compression efficiency of the system.
1 Mechanical full-bridge liquid-gas circulation compressed air energy storage working characteristics 1.1 System structure Mechanical full-bridge liquid-gas circulation compressed air energy storage system consists of two parts: electrical drive and thermodynamic conversion. The electric drive section includes the motor, converter, liquid pump, solenoid valve and associated electrical detection and control unit. The thermodynamic conversion section includes a hydraulic line, a gas line, a high pressure liquid storage tank, a liquid container, a high pressure gas storage tank, and a valve and heat exchanger unit. For the system structure, wherein: 1, T2, T3, T4 are electromagnetic liquid valves; Gal, Ga2, Ga3, Ga4 are electromagnetic gas valves; Mf is a liquid level sensor; Mp is a pressure sensor.
High-pressure gas tank liquid-gas circulation compressed air energy storage system 1.2 Working process When compressing the energy storage working state, the control converter makes the motor run electrically, and drives the liquid chest to inject the liquid in the Ca tank into the Cb to compress the gas in the CB. Ga2 is turned off and Ga3 is turned on to ensure that the gas is poured into the high pressure gas. Liquid valve 1, T4 is open, T2, T3 is closed, and a certain volume of liquid is injected. This process is called a compression process. After Ga3 is turned off, Ga2 is turned on to ensure that the CB tank is maintained at normal pressure. The liquid valve 1, T4 is closed, T2, T3 is turned on, and the liquid pump draws the liquid in the CB into the CA. This process is called a pre-compression process. During the liquid valve opening and closing transition, the dead time should also be set to prevent the pump load from being impacted. The whole process is similar to full-bridge circuit PWM control. The compression process controls the valve to work as intended.
When working in the energy release state, the high pressure gas is released to drive, and the liquid in the CB tank is driven to flow to the CA, and the hydraulic motor is rotated to make the motor generate electricity and control the converter to maintain the output voltage. Similarly, there are expansion processes and pre-expansion processes. The only difference from the compression process is the addition of Gal control, which maintains a certain pressure on the CA to ensure the return of liquid during the pre-expansion process. Valve control as shown in the expansion release.
Huang Advanced et al.: Modeling of liquid-gas cycle compressed air energy storage system and optimization of compression efficiency 1.3 Compression process Energy conversion characteristics The compression and release of liquid-gas cycle compressed air energy storage system is analyzed according to the ideal gas constant temperature process. According to the ideal gas state equation: constant, 287J / (molK); left is the number of moles of gas, mol; 7 is the temperature, K. The relationship between pressure and volume during constant temperature is defined as the liquid volume of the CB tank according to the Boyle hyperbolic curve. Fu, and keep 6 = heart relationship. After the first (secondary compression, the external work is the surface height difference; / is the number of compressions; "for the gas tank liquid filling volume multiple.
The actual work is described by equation (4). The table does not calculate the work efficiency of the compressed gas through the equations (7)-(9). The motor efficiency is 7me., the converter efficiency is 7mv, and the pump works. The efficiency is /7pum. The compression efficiency of the external work of the whole compression energy storage process can be expressed as 2 macro energy flow representation system modeling set from the initial state (Fi, eight, T!) to the destination state (Ff, Pf, compression process Work done is expressed according to the first law of thermodynamics, the heat generated by the compressed air must be completely transferred to reach the temperature. In actual work, this complete heat exchange is difficult to achieve, so the constant temperature compression process can not be realized. In fact, the use A method of reducing the compression ratio, increasing the number of compressions, and ensuring good heat exchange, using adiabatic compression and isovolumic cooling to achieve quasi-temperature compression.
For the adiabatic compression process, the gas state equation is rewritten by introducing adiabatic index to obtain the work of adiabatic compression process. The relationship describing the compression efficiency is 2.1. The macroscopic energy flow representation is characterized by the transmission of energy as the main line of control. The constituent units of the system are described as an active model of the excitation-reaction. For electrical systems, energy can be reflected by voltage and current. The interaction between voltage and current is the ultimate performance of the excitation-reaction. For thermodynamic systems, energy can be described by pressure and volume. For mechanical systems, energy can be described by torque and speed. With EMR modeling, intuitive energy flow control of complex energy source systems can be realized, and it is widely used in hybrid electric vehicles, wind power generation, industrial automation, and the like.
The liquid-gas circulating compressed air energy storage system contains the transfer and conversion of different energy states such as electrical, mechanical and thermodynamics. The simulation modeling using EMR can simplify system control and improve design and development efficiency. An example of the EMR base model library.
2.2 Liquid-gas cycle Compressed air energy storage EMR model According to the system structure diagram, the energy path of the corresponding energy storage system is described as shown in the following, divided into three parts: electrical system, mechanical system and thermodynamic system. EMR modeling is performed separately in accordance with the three parts. The electrical part consists of a DC voltage source, a filter capacitor and a full bridge converter. For the DC bus, the constraint condition is that the volume of the high-pressure gas storage tank is Fs, and the constraint condition of each compression injection connection point is the heart of the Chinese Journal of Electrical Engineering. For the chopper output. The DC motor constraint is the hydraulic I system energy path. Here, the electromechanical energy conversion is realized by a four-quadrant chopper and a DC motor. The chopper constraint is the macroscopic energy flow representation model.
The coupling is used to transmit mechanical energy. The constraint condition is that the liquid pump is the key to the thermal energy conversion of the compressed gas mechanical energy. The bidirectional fixed hydraulic pump is used, the constraint condition is /2 for the rotational speed; the pump volume; A:leak is the leakage coefficient. iHP is the Haber coefficient; it is pumping efficiency; it is known as pump efficiency; vF is fluid movement viscosity; it is liquid density; it is pump rated pressure; / is pump rated speed: it is rated fluid movement viscosity.
A valve is a switch that has no energy accumulation and belongs to a mechanical energy converter. The action of the valve will only affect the flow and pressure of the output liquid. The constraint condition is to control the design input and output "5 plant sub-model ~\yrJ/). The inverse function of the inverse function is based on the working characteristics of the liquid pump, and the input flow value gPmref is input. The joint detection quantity gPmm, ftm+m, introduces the PI controller Cv(1) to realize the inversion control: the coupling is an energy storage EMR model, and a speed controller (1) is introduced, which can be realized by PI control. According to formula (15), two observations are introduced to realize the inversion control: according to the motor equation (14), the current signal /ranref can be directly inverted by the torque rdcrcf or can be realized by PI control. Through the stator current and the detection voltage and current, the converter output voltage is determined as the converter inversion control (13), and the observed voltage and the given voltage are determined as the off control. The inversion control block diagram of the whole system is as shown.
3 Compression efficiency optimization control Through the EMR modeling and IBC control, the liquid-gas circulating compressed air energy storage system can work, but the working efficiency cannot be guaranteed. In order to improve the efficiency of energy storage compression, the market prospect of compression efficiency optimization controller Escn. compressed air energy storage power station is introduced. China Energy Storage Network, 2011-1-23 (8).
Chen Huanhuan, the application of compressed air energy storage has broad prospects. Chinese Journal of Science, 2011-4-11 (7).
Zhang Liying, Ye Tinglu, Xin Yaozhong, et al. Issues and measures related to large-scale wind power access to the power grid. Chinese Journal of Electrical Engineering, 2010, Xu Yujie, Chen Haisheng, Tan Chunqing, et al. Characteristic analysis of integrated wind and solar energy storage and power generation systems. China Electrical Engineering Journal, 2012, T Huang Advanced (1980), male, lecturer, the main research direction is the vehicle power system, power converter technology, Hao Ruixiang (1977), male, associate professor, the main research direction is the converter technology and Special Power Supply; Zhang Liwei (1977), male, associate professor, the main research direction is the use of carrier tools and system integration.
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