Permanent Magnet Generator can be divided into permanent magnet Permanent Magnet Generator and excitation Permanent Magnet Generator, permanent magnet Permanent Magnet Generator and excitation Permanent Magnet Generator the biggest difference is that its excitation magnetic field is generated by the permanent magnet. Permanent magnet in the motor is both a magnetic source, but also a part of the magnetic circuit. The excitation power unit supplies the excitation current to the synchronous generator rotor; and the excitation regulator controls the output permanent magnet generator of the excitation power unit according to the input signal and the given regulation criterion.
The excitation power unit supplies the excitation current to the synchronous generator rotor; and the excitation regulator controls the output of the excitation power unit according to the input signal and the given adjustment criterion. The automatic excitation regulator of the excitation system has a considerable effect on improving the stability of the parallel system of the power system. Especially the development of modern power system led to the trend of reducing the stability of the unit, but also to promote the continuous development of excitation technology. The excitation system of the synchronous generator is mainly composed of two parts: the power unit and the regulator (device).
Wherein the excitation power unit is an excitation power supply section for supplying a DC excitation current to the synchronous generator rotor winding, and the excitation regulator is a means for controlling the output of the excitation power unit in accordance with the control input signal and the given adjustment criterion. The whole system, which consists of an excitation regulator, an excitation power unit and the generator itself, is called an excitation system control system. Excitation system is an important part of the generator, it is the power system and the generator itself has a great impact on the safe and stable operation. The main functions of the excitation system are as follows: 1) adjust the excitation current according to the change of the generator load to maintain the terminal voltage as the given value; 2) control the reactive power distribution among the Permanent Magnet Generator; 3) Parallel operation of the static stability; 4) to improve the generator parallel operation of the transient stability; 5) in the generator internal failure, the demagnetization, in order to reduce the degree of failure; 6) according to operational requirements of the generator Maximum excitation limit and minimum excitation limit.
1, DC generator power supply excitation mode
This type of excitation generator has a dedicated DC generator, this dedicated DC generator called DC Exciter, Exciter is generally coaxial with the generator, the generator excitation winding through the large shaft on the slip ring And a fixed brush to obtain a direct current from the exciter. This kind of excitation method has the advantages of independent excitation current, reliable operation and reduced consumption of self-consumption, which is the main excitation method of the generator in the past few decades, and has the mature running experience. The disadvantage is that the excitation speed is slower, the maintenance workload is large, so in 10MW or more units rarely used.
2, AC excitation machine power supply excitation mode
Some large-capacity modern Permanent Magnet Generator use AC exciter to provide excitation current. AC exciter is also installed in the generator shaft, the output of the AC current rectifier after the generator rotor excitation, this time, the generator excitation method is his excitation method, and because the use of static rectifier device, it is also known as For his excitation static excitation, AC auxiliary exciter to provide excitation current. The AC sub-exciter may be a permanent magnet or an alternator with a self-excited constant pressure device. In order to improve the excitation speed, AC exciter is usually used 100-200Hz Zener generator, and AC sub-exciter is used 400 - 500HZ of the intermediate frequency generator. The generator's DC field windings and three-phase AC windings are wound around the stator slots. The rotor has only teeth and grooves and no windings, like gears. Therefore, it does not have a brush, slip ring and other rotating contact parts, , Simple structure, convenient manufacturing process and so on. The disadvantage is that the noise is large, the harmonic potential of the AC potential is also larger.
3, no exciter excitation method
In the excitation mode does not set a special exciter, and from the generator itself to obtain excitation power, after rectification and then supply the generator itself excitation, said self-excitation static excitation. Self-excited static excitation can be divided into self-excitation and self-excitation excitation in two ways. Self-excitation way through the generator connected to the rectifier transformer to obtain excitation current, the rectifier after the generator excitation, this
Excitation method has the advantages of simple knot, less equipment, less investment and less maintenance. Self-excited excitation mode in addition to no rectification transformer, but also with a series generator in the stator loop high-power current transformer. The role of this transformer is in the event of a short circuit, to the generator to provide a larger excitation current to compensate for the lack of rectifier transformer output. This excitation method has two kinds of excitation power supply, through the rectifier transformer voltage and power through the series transformer to obtain the current source.
Permanent magnet generator
The biggest difference between a permanent magnet generator and an excitation generator is that its field magnetic field is generated by the permanent magnet. Permanent magnet in the motor is both a magnetic source, but also a part of the magnetic circuit. The magnetic properties of the permanent magnet are not only related to the manufacturing process of the manufacturing plant, but also to the shape and size of the permanent magnet, the capacity of the magnetizing machine and the method of magnetizing, and the specificity of the performance data is very large. And the magnetic flux and magnetomotive force that the permanent magnet can provide in the motor also change with the material performance, the size and the motor running state of the rest of the magnetic circuit. In addition, the permanent magnet generator magnetic circuit structure varied, leakage magnetic circuit is very complex and large proportion of leakage magnetic flux, ferromagnetic material part is relatively easy to saturation, the magnetic guide is non-linear. These have increased the complexity of the permanent magnet generator electromagnetic calculation, so that the accuracy of the calculation results is lower than the electric excitation generator. Therefore, it is necessary to establish a new design concept, to reanalyze and improve the magnetic circuit structure and control system; must use modern design methods to study the new analytical methods to improve the accuracy of design calculations; must study the use of advanced testing methods and manufacturing Process.
1. control problem
Permanent magnet generator made without external energy to maintain its magnetic field, but also caused by external regulation, control of its magnetic field is extremely difficult. These have limited the scope of application of permanent magnet Permanent Magnet Generator. However, with the mosFET, IGBTT and other power electronic devices, the rapid development of control technology, permanent magnet generator in the application without magnetic field control and only the motor output control. Designed to require NdFeB materials, power electronic devices and computer control of three new technologies together, so that permanent magnet Permanent Magnet Generator in a new operating conditions.
2. irreversible demagnetization problem
If the design and use of improper, permanent magnet generator in the high temperature (NdFeB permanent magnet) or too low (ferrite permanent magnet), the impact of the current generated by the armature reaction, or in the severe mechanical vibration When it is possible to produce irreversible demagnetization, or called loss of magnetic, so that motor performance is reduced, or even can not be used. Therefore, it is necessary to study and develop the methods and apparatus for inspecting the thermal stability of permanent magnetic materials for use in motor manufacturers, and to analyze the anti-demagnetization capability of various structural forms in order to ensure that the use of the corresponding measures in the design and manufacture The magnetic generator does not lose its magnetism.
3. Cost issues
As the current price of rare earth permanent magnet materials is still relatively expensive, the cost of rare earth permanent magnet Permanent Magnet Generator are generally higher than the electric excitation Permanent Magnet Generator, but this will be in the motor high performance and operation to get better compensation. In the future design will be based on the specific use of the occasion and requirements, performance, price comparison, and structural innovation and design optimization to reduce manufacturing costs. There is no denying that the cost of the product being developed is slightly higher than the current Permanent Magnet Generator, but we believe that as the product becomes more perfect, the cost problem will be well resolved. "The customer's focus is on the cost per kilometer of watt." His statement fully demonstrates that the market prospects for AC permanent magnet Permanent Magnet Generator will not be plagued by cost problems, according to the head of the US DELPHI (Delphi) technology department.
Excitation generator and permanent magnet generator output is different as follows:
1. The initial electromotive force is provided in different ways
Excitation generator at the time of starting to have an initial electromotive force to make the excitation coil magnetic field. By the external power supply or permanent magnet generator to generate a small electromotive force to provide electromotive force, work properly after the work on their own output voltage. While permanent magnet Permanent Magnet Generator rely on permanent magnets to provide initial electromotive force.
2. Magnetic field strength is different
The excitation generator can change the field magnetic field by changing the current of the field coil. And the magnetic field strength can be large and controllable. While the permanent magnet generator is prone to magnetic field inclusion phenomenon.