The biggest difference between a permanent magnet generator and an excitation generator is that its excitation magnetic field is generated by a permanent magnet. Permanent magnet is not only a magnetic source, but also a part of motor magnetic circuit. The magnetism of the permanent magnet is not only related to the manufacturing process in the factory, but also related to the shape and size of the permanent magnet, the capacity of the magnetizer and the magnetizing method. The specific performance data are very discrete. Moreover, the magnetic flux and magnetomotive force provided by the permanent magnets in the motor also change with the material properties, dimensions and running state of the motor of the rest of the magnetic circuit. In addition, the magnetic circuit structure of permanent magnet generator is diverse, the leakage magnetic circuit is very complex and the leakage flux ratio is large, the ferromagnetic material is partially saturated, and the permeability is nonlinear. All these increase the complexity of electromagnetic calculation of permanent magnet generators, and make the accuracy of calculation results lower than that of electrically excited generators. Therefore, it is necessary to establish a new design concept, re-analyze and improve the magnetic circuit structure and control system; It is necessary to apply modern design methods and study new analysis and calculation methods to improve the accuracy of design and calculation; It is necessary to study and adopt advanced testing methods and manufacturing processes.
1.2 control problem
The permanent magnet generator can keep its magnetic field without external energy, but it also makes it extremely difficult to adjust and control its magnetic field from the outside. All these make the application range of permanent magnet generators limited. However, with the rapid development of control technology of power electronic devices such as MOSFET and IGBTT, permanent magnet generators only control the motor output, and there is no magnetic field control. The design needs the combination of NdFeB materials, power electronic devices and microcomputer control, so that the permanent magnet generator can run under brand-new working conditions.
Irreversible demagnetization of 1.3
If it is not designed and used properly, the permanent magnet generator may produce irreversible demagnetization or demagnetization when the temperature is too high (NdFeB permanent magnet) or too low (ferrite permanent magnet), under the armature reaction caused by pulse current, or under severe mechanical vibration, which will reduce the performance of the motor or even make it unusable. Therefore, it is necessary to research and develop methods and devices suitable for motor manufacturing enterprises, check the thermal stability of permanent magnet materials, and analyze the demagnetization resistance of various structural forms, so as to take corresponding measures in design and manufacture to ensure that permanent magnet generators will not lose their magnetism.
1.4 cost problem
Because the price of rare earth permanent magnet materials is still relatively expensive at present, the cost of rare earth permanent magnet generators is generally higher than that of electrically excited generators, but this achievement will be better compensated for the high performance and operation of the motors. In the future design, the performance and price will be compared according to the specific use occasions and requirements, and structural innovation and design optimization will be carried out to reduce manufacturing costs. Undeniably, the cost price of the product under development is slightly higher than that of the current general generator, but we believe that with the further improvement of the product, the cost problem will be well solved. The head of the technical department of Delphi company in the United States believes: "The customer is concerned about the cost of watts per kilometer." His statement fully shows that the market prospect of AC permanent magnet generators will not be troubled by cost problems.
1.5 characteristics of permanent magnet rotor;
Structure 1:
Parallel magnetic field structure; Made by casting and pressing, embedded with permanent magnets, it has the advantages of large energy, light weight, small volume, solid and reliable overall structure, and the maximum working speed is greater than 15000 rpm.
Patent number; ZL96 2 47776. 1
Structure 2:
Series magnetic field structure; The rotor is made of steel structure, and permanent magnets are embedded in the surface in turn. The rotor surface has strong magnetic flux, light weight, small volume, solid and reliable overall structure, and the maximum working speed is greater than 15000 rpm.
PatentNo.: ZL98 2 33864.3
Characteristics of the whole machine voltage stabilizing system:
The semi-controlled bridge rectifier circuit consists of thyristor and diode. The voltage stabilizing system is a chopper modulation voltage stabilizing device, and the voltage stabilizing accuracy is 0.1v. Therefore, the generator has the characteristics of being able to withstand large current instantly, being reliable and durable. The SCR can be automatically turned off by directly using the reverse voltage of alternating current generated by the generator, without adding a turn-off circuit, and the circuit structure is simple and reliable.
2. Advantages of permanent magnet generators
2. 1 has simple structure and high reliability.
The permanent magnet generator omits the excitation winding, carbon brush and slip ring structure of the excitation generator, and the structure of the whole machine is simple, which avoids the easy burning of the excitation winding, carbon brush and slip ring structure and greatly improves the reliability.
2.2 Small size, light weight and high specific power.
Using permanent magnet rotor structure, the internal structure design of the generator is very compact, and the volume and weight are greatly reduced. The simplification of the permanent magnet rotor structure also reduces the rotor inertia moment, improves the practical speed and reaches a very high specific power (that is, the ratio of power to volume).
2.3 Good low and medium speed power generation performance.
Under the same power level, the output power of the permanent magnet generator is twice that of the excitation generator at no load, that is, the actual excitation generator with the same power level of the permanent magnet generator.
2.4 It can significantly prolong the service life of the battery and reduce the maintenance workload of the battery.
The main reason is that the permanent magnet generator adopts switching rectifier and voltage stabilization mode, which has high voltage stabilization accuracy and good charging effect. Avoid battery life shortening caused by over-current charging. The starting rectification output of the permanent magnet generator charges the battery with small current pulses, and the same charging current has better charging effect, thus prolonging the service life of the battery.
high-effect
Permanent magnet generator is an energy-saving product. The structure of permanent magnet rotor eliminates the excitation power needed to generate rotor magnetic field and the mechanical loss caused by friction between carbon brush and slip ring, which greatly improves the efficiency of permanent magnet generator. In the speed range of 1500 rpm ~ 6000 rpm, the average efficiency of ordinary excitation generator is only 45% ~ 55%, while that of permanent magnet generator is as high as 75% ~ 80%.
2.6 Self-starting regulator is adopted.
No external excitation power supply is needed. The generator can generate electricity as long as it rotates. When the battery is damaged, the car charging system can still work normally as long as the engine is running. If the car has no battery, it can be ignited by shaking or sliding.
2.7 It is especially suitable for working in a humid or dusty environment.
2.8 No radio interference
The permanent magnet generator structure without carbon brush and slip ring eliminates the radio interference caused by the friction between carbon brush and slip ring; The electric spark is eliminated, which is especially suitable for working in an environment with high explosion risk, and also reduces the requirements of the generator for environmental temperature.
3. Comparison of structural characteristics
3. 1 permanent magnet generator:
The permanent magnet generator has simple structure, large rotor magnetic field, no excitation winding, no carbon brush, no slip ring, large air gap and no contact. The only worn part of the whole machine is the bearing. The reliability of the product is improved, no external regulator is needed, the spacing of magnetizer materials is optimized, the magnetic leakage is reduced, the no-load performance of the generator is good, and the circuit is sufficient.
Excitation generator:
The performance of excitation generator at idle speed is poor, and the battery is easy to discharge; When the generator speed is 1500-6000 rpm, the efficiency is only 40%-50%, and the efficiency is low. Due to the excitation coil in the rotor, the temperature of the whole machine rises. Excitation generators are also prone to problems such as damage of carbon brushes and slip rings.
3.2 Performance comparison (taking 28V, 36A and 1000W generators as examples)
generator
type
electric current
(1)
Full load speed
(rpm)
Average efficiency
(1500-6000 rpm)
Regulating voltage
㈤
load characteristic
㈤
speed performance
㈤
Excitation type
nine
3500
0.45
28 0.3
|△U|≤0.8
|△U|≤0.5
Permanent magnet type
18
2800
0.8
28 0.2
|△U|≤0.3
|△U|≤0.2
3.3 Comparison of Volume Temperature Rise
Generator type
Outside diameter (mm)
Length (mm)
Temperature rise (k)
Weight (kg)
Excitation type
Φ 142
180
75
6.5
Permanent magnet type
Φ 128
165
50
four
From the comparison of the above performance, structure and volume, the permanent magnet generator is simpler in structure, smaller in size, lighter in weight, superior in performance and sufficient for low-speed power generation.
Comparison table of bulk density between JFYJ permanent magnet generator (3000W) and ordinary excitation generator (3000W)
type
Outside diameter (mm)
Length (mm)
Weight (kg)
Permanent magnet type
Φ 17 1
265
12
Excitation type
Φ200
3 10
24
4, the charm of rare earth NdFeB
NdFeB, the crown of rare earth, is a unique rare substance. Because of its powerful magnetic bearing function, it will become the darling of the industrial revolution in 2 1 century. The revolution of automobile industry triggered by it has become a great concern of automobile experts all over the world. According to industry experts' prediction, the motor in 2 1 century will be dominated by permanent magnets.
As a big country of rare earths, China has 80% of the world's reserves, but the utilization and development of rare earths are not ideal. On the contrary, some developed countries have fully realized the potential value of rare earths and are conducting in-depth research. China should develop its own unique rare earth resources and give full play to this resource advantage, just as South Africans exploit diamonds and Middle Easterners exploit oil. At present, we have found a breakthrough in the deep development and utilization of rare earths in wind power projects.