Summary of Asynchronized Synchronous Generator
Stability With the development of modern power systems, the voltage level of transmission lines has gradually increased, the lines have been lengthened, and the unevenness of the load curve has intensified. When the transmission line transmission power is lower than the natural power, the transmission line will have excess reactive power, which will cause the power frequency and overvoltage of the power plant and the line to continue, which will endanger the safe operation of the system and increase the loss of the line. The machine can't be side by side, and the appearance of the long line makes the generator and system stability problems more prominent. The traditional solution to the above problem is to add a reactor, a static var compensator or a camera to the synchronous generator's phase-in operation or power line. However, foreign practice has proved that these methods have some inherent technical and economic defects. Due to the abundant water resources in China, the conventional hydropower stations and the pumped storage power stations, which are one of the effective means of peak shaving and valley filling, have been greatly developed. However, many hydropower stations, especially those in the Yellow River Basin, have large head changes, low turbine efficiency, and serious cavitation and sediment wear. How to improve the operating conditions of the turbine and improve the efficiency of the turbine has become a concern. The practice in foreign countries has proved that the pumped storage power station is better to use the reversible unit. However, this type of unit requires high efficiency in both electric and power generation conditions due to the use of the water turbine as a water pump. Therefore, it is hoped that the unit can be used by the author. There is a rice enhancement from North China Electric Power University. Variable speed unit. The traditional electric-generator set uses a DC-excited synchronous generator, which is difficult to adjust and has poor characteristics. In addition, when the unit needs to be operated in an electric state, starting is difficult. In response to the above problems, domestic and foreign power workers are seeking economic and effective solutions. The following analysis of the basic principle, structure, performance, excitation control mode and development status of the asynchronous synchronous generator shows that the asynchronous synchronous generator is an effective way to solve the above problems. 1 The basic principle and structure of the asynchronous synchronous generator The stator of the synchronous generator is the same as the stator of the conventional synchronous generator, but the rotor is different. The rotor of the asynchronous synchronous generator has two-phase or three-phase controllable field windings, which can be AC-excited, so that the motor operates in a synchronous or controllable asynchronous state. When the rotor winding is connected to an alternating current of a certain frequency (f), a magnetic field is generated which is rotated relative to the rotor. The rotational speed is: where p is the pole pair. The actual speed of the rotor plus the rotational speed of the rotating magnetic field generated by the AC excitation (the direction can be the same or opposite) is equal to the synchronous speed. The synchronous rotating magnetic field formed in the air gap of the motor induces an induced potential of the synchronous frequency on the stator side. Viewed from the stator side, it is equivalent to the synchronous rotating magnetic field formed when the DC-excited rotor rotates at a synchronous speed. If the asynchronous generator or the synchronous generator is distinguished by whether the rotational speed of the motor rotor is consistent with the synchronous rotational speed, the asynchronous synchronous generator should be referred to as an asynchronous generator. However, in terms of performance, asynchronous synchronous generators are similar to synchronous generators in many places. For example, asynchronous generators absorb reactive excitation from the grid through the stator, and there is no independent excitation winding asynchronous generator and synchronous power generation. Like the machine, there are independent excitation windings that can absorb capacitive reactive power from the grid and provide lag reactive power to the grid. The speed of the asynchronous generator changes with the load. The asynchronous generator can be the same as the synchronous generator. When the load changes, the speed remains the same, so it is called asynchronous synchronous generator. Asynchronous synchronous generators, like traditional synchronous generators, are also composed of a motor body, an excitation power supply, and an automatic excitation regulator. Since the rotor of the asynchronous synchronous generator has two-phase or three-phase excitation windings, the frequency, magnitude and phase of the excitation voltage of the rotor are adjusted by the automatic excitation regulator to realize the controllable asynchronous operation of the generator. 2 Asynchronous Synchronous Generator Excitation Control Mode Asynchronous Synchronous Generator Rotor uses three-phase (or two-phase) symmetrical winding windings, so AC excitation can be used. Compared with the synchronous generator with DC excitation (the adjustable amount of synchronous generator excitation is only one, that is, the amplitude of the DC excitation current, so the synchronous generator excitation can only adjust the reactive power), using AC excitation Asynchronized synchronous generator, the adjustable amount of excitation has the frequency and phase of the excitation current in addition to the amplitude of the excitation current. By changing the excitation current frequency to change the speed of the generator to achieve the purpose of speed regulation, adjust the generator operating power according to the optimal operation mode, and change the no-load potential of the generator to the system voltage vector by changing the phase of the excitation current. The relative position of the generator, thereby changing the power angle of the generator. Therefore, the AC excitation generator can adjust the excitation current, not only can adjust the reactive power of the generator, but also can adjust the active power of the generator, that is, the reason why the asynchronous synchronous generator has the advantage over the traditional synchronous generator (good regulation) Characteristics, operational flexibility and reliability), in addition to its electrical structure compared with traditional synchronous generators, multi-phase rotor symmetrical AC excitation, the key is that asynchronous synchronous generators have a set of excitation control that can fully exert the characteristics of motor operation system. The excitation control method commonly used in asynchronous synchronous generators is similar to the dual-channel multi-variable feedback excitation control method of asynchronous turbine generators. This excitation control method uses the decoupling relationship between the active and reactive power of the asynchronous synchronous generator and the d-axis and q-axis current under the synchronous coordinate axis to establish the control equation, and realizes the independent control of active and reactive power based on the synchronous motor frequency control. The excitation control method proposed by vector control is based on the excitation control method proposed by the multi-scalar model of AC motor. 3 Asynchronous synchronous generator performance characteristics (1) Adjust the excitation current of the asynchronous synchronous generator, not only can control the output of the generator reactive power, but also control the output of the generator active power. The DC-excited synchronous generator can only adjust the amplitude of the excitation current. Therefore, the excitation current of the synchronous generator can only adjust the reactive power. The asynchronous generator can adjust the amplitude of the excitation current due to AC excitation. Value, frequency and phase, therefore, not only can the output of the reactive power of the generator be controlled, but also the output of the active power of the generator can be controlled when the excitation current is adjusted. Therefore, when the asynchronous synchronous generator is connected to the grid, it will be able to automatically adjust the frequency of the grid as a frequency-modulated generator. (2) The asynchronous synchronous generator can realize variable speed operation, so it is called a variable speed generator. When used in a pumped storage power station, the turbine efficiency can be changed. Especially when the load is not rated, it can control the pumping volume by changing the speed. It can also control the residual power in the power system at night. This is the conventional pumping storage. Can not be done by the power station. (3) Asynchronous synchronous generators can achieve deep phase ingress operation. The asynchronous synchronous generator overcomes the shortcoming of the DC excitation generator's phase-in operation mainly limited by the static stability limit value, and is limited only by the allowable value of the generator stator current, so that the generator can be deeply phase-introduced to solve the ultra-high voltage power. The problem of power frequency overvoltage caused by excessive system reactive power has found the most economical and effective way. (4) Asynchronized synchronous generators have high stable operation capability. The static stability of an asynchronous synchronous generator is determined by the selected control method and control law. By adjusting the excitation regulation system, the voltage regulation process is a pure electromagnetic adjustment process, which is independent of the rotor position and does not affect the rotor motion condition, that is, independent of the electromechanical process. Similarly, active regulation does not cause reactive disturbances, only limited by the winding heating conditions. Theoretical and experimental analysis indicates that the above adjustment process is stable within the allowable limits of the stator and rotor currents. The dynamic characteristics of asynchronous synchronous generators are also limited by the structure of the automatic excitation regulation system. The analysis shows that the characteristics of the transient process remain constant over the entire allowable range, so the asynchronous synchronous generator has higher transient stability. 4 Asynchronous Synchronous Generator Research Status at Home and Abroad Many countries are working on the development of asynchronous synchronous generator sets, but the depth of research and the breadth of research in the former Soviet Union are in a leading position. In the early Soviet Union, the development of asynchronous generator sets was carried out in the early 1950s. After decades of unremitting efforts, the theoretical analysis, structural design and excitation control of asynchronous synchronous generator sets have achieved remarkable achievements. It has entered the industrial practical stage, designing asynchronous wind turbines as small as several hundred kW and asynchronous steam turbine generators as large as 800 MW. At present, foreign research on asynchronous synchronous generators mainly includes the following aspects: (1) Performance analysis of asynchronous synchronous generators such as motor state change model and dynamic characteristic flow analysis and efficiency optimization active and reactive control motors in three Transient analysis under phase short circuit is used as performance analysis of wind turbines. (2) Excitation control of asynchronous synchronous generators) Analysis of transient stability of asynchronous generators controlled by PLL Control of stability of asynchronous generators with PLL control Digital for asynchronous generators The ideal controller (AC/DC/AC) has vector control and fuzzy logic control of the asynchronous synchronous generator of DSP (Digital Signal Processor). (3) Other researches such as asynchronous parallel operation of synchronous generators and power systems, and dynamic performance analysis of asynchronous generators in power system applications. At present, China's research on asynchronous synchronous generators is still in its infancy. Only Chongqing University, North China Electric Power University and other universities in China have carried out this work. Due to various factors such as funds, it is basically limited to theoretical research, computer simulation and dynamic model experiments. With the development of China's energy construction, the domestic motor industry should catch up and meet the needs. The development trend of foreign large motors in this respect should cause us to pay full attention. 5 Conclusion Asynchronous synchronous generator is a new type of motor developed by combining the advantages of asynchronous generator and synchronous generator. It has good running performance, but at the same time, there are still many technical problems to be solved. (1) In terms of motor theory: it is necessary to further clarify the characteristics and operational characteristics of asynchronous synchronous generators, and propose accurate equivalent circuits and temporary and steady-state mathematical models to study the measures to reduce the excitation capacity and expand the operating range to optimize the motor parameters. (2) In terms of motor structure: The research on the type of insulation structure and end fixing structure of the asynchronous winding of the asynchronous generator should be studied to deal with the high voltage, large current collector ring, effective rotor ventilation system and ventilation method. (3) In terms of excitation control: research should be conducted on the matching of excitation circuit parameters, reduction of excitation capacity and loss, and reasonable selection of frequency conversion devices. Discuss how to improve the static stability of the unit and the bearing capacity of the motor under abnormal operation mode. [4] A review of the application research of asynchronous generators in the former Soviet Union. AC excitation control method for asynchronous synchronous generators. North China Electric Power University [6] AC excitation generator excitation control. Chinese Electrical Engineering Journal, 1998, Equations. Due to the limited space, the mathematical model for establishing the trend, the determination of the calculation method (the three methods can be optional), the preparation of the calculation program, etc. are omitted. The above only illustrates the function of the program (see Figures 2 to 7). 3 Conclusion The teaching software for power system analysis is developed as an auxiliary tool for teaching and training of power systems. It has the following characteristics: (1) The system has a friendly human-machine interface, flexible operation, and the same interface style as the Windows style. It is fully compatible with the mainstream operating system and provides multiple shortcut keys to enable each module function. (2) The input mode of the graphic is fast and intuitive. All the input information can be clicked through the pop-up dialog box by the mouse prompt, which avoids the previous form of inputting data according to a specific format, and greatly improves the efficiency and accuracy of the input. (3) All data and information of the trend calculation result can be displayed directly on the system diagram, and the information of only interest can be displayed. Data editing is powerful. (4) The software has strong practicability, fully taking into account the computing teaching and training applications under various operating modes of the power system. The program has a better modular design. In summary, the software uses the most advanced computer programming technology, and has achieved a number of indicators such as stable operation, accurate operation, and ease of use. It can enhance the students' understanding of the teaching content, create conditions for improving the quality of teaching, and allow users to have a deeper impression of what they have learned. The software can be used for daily professional teaching in schools, on-the-job training for in-service personnel, and analysis and calculation of actual systems. EPT specialize in Rapid Vacuum Casting (also referred to as room temperature vulcanization/RTV) to create short run quantities of production-like parts at low cost to the customer. Abs Like,Abs Like Prototype,Vacuum Molding Plastic,Vacuum Forming Plastic Ningbo Expert Mould Plastic Co., Ltd. , https://www.prototypesmaker.com
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