What Is a Permanent Magnet Synchronous Generator?

Permanent magnet synchronous motor is a synchronous motor that generates a synchronous rotating magnetic field by the excitation of a permanent magnet. The permanent magnet generates a rotating magnetic field as a rotor. The three-phase stator windings react under the action of the rotating magnetic field to induce a three-phase symmetrical current.

1. Several ways for the generator to obtain the excitation current 1) Excitation method powered by a DC generator This type of excitation generator has a dedicated DC generator. This dedicated DC generator is called a DC exciter, and the exciter is generally Coaxial with the generator, the generator's field winding receives a DC current from the exciter through a slip ring and fixed brushes mounted on the large shaft. This excitation method has the advantages of independent excitation current, more reliable operation and reduced consumption of self-use electricity. It is the main excitation method for generators in the past few decades and has mature operating experience. The disadvantage is that the excitation adjustment speed is slow, and the maintenance workload is large, so it is rarely used in units with more than 10MW.

2) Excitation method powered by AC exciter Some modern large-capacity generators use AC exciter to provide excitation current. The AC exciter is also installed on the big shaft of the generator.

The permanent magnet synchronous motor can be integrally installed on the wheel axle to form an integrated direct drive system, that is, one wheel axle is a drive unit, and a gear box is omitted. The characteristics of permanent magnet synchronous motors are as follows:

(1) PMSM itself has high power efficiency and high power factor;

(2) PMSM generates less heat, so the motor cooling system has a simple structure, small size, and low noise;

(3) The system adopts a fully enclosed structure, no transmission gear wear, no transmission gear noise, no lubricant, no maintenance;

(4) The overload current allowed by PMSM is large, and the reliability is significantly improved;

(5) The entire transmission system is light in weight, and the unsprung weight is lighter than the traditional wheel and axle drive, and the power per unit weight is large;

(6) Since there is no gear box, the bogie system can be designed at will: such as flexible bogies and single-axle bogies, which greatly improves the train's dynamic performance. ^[2]

In changing the excitation current of the generator, it is generally not carried out directly in the rotor circuit, because the current in the circuit is large, and it is not convenient to directly adjust it. The usual method is to change the excitation current of the exciter to adjust the generator. Purpose of rotor current. Common methods include changing the resistance of the exciter's excitation circuit, changing the additional excitation current of the exciter, and changing

SCR's conduction angle, etc. Here, the method of changing the conduction angle of the thyristor is mainly described. It is based on the change of the generator voltage, current or power factor, and changes accordingly.

The components that automatically adjust the excitation include organic voltage transformers, machine-side current transformers, and excitation transformers; the excitation device needs to provide the following currents, factory AC380v, factory DC220v control power. Factory DC220v closing power supply; the following empty contacts are required , Automatic start, automatic stop, grid connection (one normally open, one normally closed) increase and decrease; the following analog signals need to be provided: generator terminal voltage 100V, generator terminal current 5A, bus voltage 100V, excitation device output below Relay contact signal; over-excitation, de-excitation, abnormal excitation device, etc.

The excitation control, protection and signal loop is composed of de-excitation switch, magnetic-assisting circuit, fan, de-excitation switch stealing, over-excitation change, regulator failure, abnormal generator working condition, power transmitter, etc. When the internal fault of the synchronous generator has to be eliminated, it must also be demagnetized. The magnetic field of the rotor should be reduced to a minimum as soon as possible to ensure that the demagnetization time is shortened as much as possible when the rotor is not over. Features. According to the magnitude of the rated excitation voltage, it can be divided into linear resistance demagnetization and nonlinear resistance demagnetization.

In the past ten years, due to the emergence and use of new technologies, new processes and new devices, the excitation method of generators has been continuously developed and improved. In the field of automatic adjustment of excitation devices, many new types of adjustment devices have also been developed and promoted. Due to the significant advantages of using a microcomputer computer software to automatically adjust the excitation device, many countries are currently developing and testing microcomputer computers with digital external adjustment excitation devices composed of corresponding external equipment. This type of adjustment device will be able to achieve self-adjustment. Adapt to the best adjustment.

The method of obtaining the exciting current is called the exciting method. The current excitation methods are divided into two categories: one is a DC exciter excitation system that uses a DC generator as the excitation power source; the other is a rectifier excitation system that uses a silicon rectifier to convert AC to DC and supplies it for excitation. The description is as follows:

1 DC Exciter Excitation The DC exciter is usually coaxial with the synchronous generator and adopts the parallel excitation or other excitation connection method. In the alternative excitation method, the excitation current of the exciter is supplied by another coaxial DC generator called the secondary exciter. As shown in Figure 15.5.

2

1 Introduction

In recent years, with

According to the requirements of different industrial and agricultural production machinery, the motor drive is divided into three types: constant speed drive, speed control drive and precision control drive.

1. Constant speed drive

There are a large number of production machines in industrial and agricultural production that require continuous operation at a substantially constant speed in one direction, such as fans, pumps, compressors, ordinary machine tools, and the like. In the past, most of these machines were driven by three-phase or single-phase asynchronous motors. Asynchronous motor has lower cost, simple and reliable structure and convenient maintenance, which is very suitable for the driving of this type of machinery. However, asynchronous motors have low efficiency, low power factor, and large losses, and such motors are widely used, so a large amount of electrical energy is wasted in use. Secondly, the fans and pumps used in a large number of industries and agriculture often need to adjust their flow, which is usually done by adjusting dampers and valves, which wastes a lot of power. Since the 1970s, people have used inverters to adjust the speed of asynchronous motors in fans and pumps to adjust their flow rates, and they have achieved considerable energy savings. However, the cost of inverters has limited its use, and the low efficiency of asynchronous motors still exists.

For example, home air-conditioning compressors originally used single-phase asynchronous motors, which were switched on and off to control their operation. Noise and high temperature variations were their disadvantages. In the early 1990s, Toshiba Japan first adopted variable frequency speed regulation of asynchronous motors for compressor control. The advantages of variable frequency speed regulation promoted the development of variable frequency air conditioners. In recent years, Japan's Hitachi, Sanyo and other companies have started to use permanent magnet brushless motors to replace the variable frequency speed regulation of asynchronous motors, which has significantly improved efficiency, obtained better energy saving effects and further reduced noise. At the same rated power and rated speed Under the assumption that the volume and weight of the single-phase asynchronous electric motor are 100%, the volume of the permanent magnet brushless DC motor is 38.6%, the weight is 34.8%, the amount of copper is 20.9%, and the amount of iron is 36.5%, which improves the efficiency. More than 10%, and the speed is convenient, the price is equivalent to the asynchronous motor frequency control. The application of permanent magnet brushless DC motors in air conditioners has promoted the upgrading of air conditioners.

Another example is the cooling fans that are used extensively on equipment such as instruments. In the past, the driving method of the outer rotor structure of a single-phase asynchronous motor was used, which has a large volume and weight and low efficiency. In recent years it has been completely replaced by a brushless fan driven by a permanent magnet brushless DC motor. Modern fast-developing information devices such as computers use brushless fans without exception. In recent years, the use of brushless fans has formed a complete series, with many varieties and specifications. There are 12 types of frame sizes from 15mm to 120mm, 7 types of frame thicknesses from 6mm to 18mm, and voltage specifications are DC 1.5V, 3V, 5V, 12V, 24V, 48V, speed range from 2100rpm to 14000rpm, divided into 4 kinds of low speed, medium speed, high speed and ultra high speed, life is more than 30,000 hours, the motor is a permanent magnet brushless DC motor with outer rotor.

Practice in recent years shows that in the case of continuous operation with power not greater than 10 kW, in order to reduce volume, save materials, improve efficiency and reduce energy consumption, more and more asynchronous motors are being driven by permanent magnet brushless DC motors. Gradually replace. However, in the case of high power, due to the large cost and investment, in addition to the permanent magnet material, a power driver is required, so it is rarely used.

2.Speed regulation drive

There are quite a lot of working machines whose running speed needs to be arbitrarily set and adjusted, but the speed control accuracy requirements are not very high. This type of drive system has a large number of applications in packaging machinery, food machinery, printing machinery, material handling machinery, textile machinery and transportation vehicles. The most widely used DC motor speed control system in this type of speed control application field initially. With the development of power electronics and control technology after the 1970s, the variable frequency speed control of asynchronous motors quickly penetrated into the original DC speed control system. . This is because, on the one hand, the performance and price of the asynchronous motor frequency conversion speed regulation system are completely comparable to the DC speed regulation system; on the other hand, compared with the DC motor, the asynchronous motor has a simple manufacturing process, high efficiency, less copper used in the same power motor, Easy maintenance and other advantages. Therefore, the variable frequency speed regulation of asynchronous motors has quickly replaced the DC speed regulation system in many occasions.

AC permanent magnet synchronous motor is a low-carbon motor in today's society due to its small size, light weight, high efficiency and energy saving. People have paid more and more attention to it because of the running characteristics of synchronous motors and their control technology is becoming more and more mature. Medium- and small-power DC motors and asynchronous motors are gradually being replaced by permanent magnet synchronous motor speed control systems. Elevator drive is a typical example. The elevator drive system has certain requirements for the acceleration, steady speed, braking, and positioning of the motor. In the early days, people used DC motor speed control systems, which had the disadvantages of low efficiency and difficult maintenance. In the 1970s, the frequency conversion technology developed maturely. The variable frequency speed regulation drive of asynchronous motors quickly replaced the DC speed regulation system in the elevator industry. The latest drive technology that has been gradually adopted in the elevator industry in the past decade is the permanent magnet synchronous motor speed regulation system, which is small in size, energy saving, good control performance, and easy to make low-speed direct drive, eliminating gear reduction devices; Floor accuracy and comfort are superior to previous drive systems, and they are also suitable for use in machine room-less elevators. Permanent magnet synchronous motor drive systems are quickly gaining favor in various industries, and a variety of inverter series products supporting it have been listed in many brands. It is foreseeable that in the case of speed regulation drive, it will be the world of permanent magnet synchronous motors. Japan's Fuji Corporation has launched a series of three-phase permanent magnet synchronous motor products and matching inverter controllers. The power is from 0.4kW to 750kW, and the volume is 1 or 2 smaller than the asynchronous motor of the same capacity. , Can be used for machine tools, pumps, compressors, lifting and transportation machinery, extrusion machinery, elevators and other occasions.

3. Precision control drive

High-precision servo control system

The servo motor plays a very important role in the operation control of the industrial automation field. The control performance requirements of the servo motor are different in different applications. In practical applications, servo motors have various control methods, such as torque control / current control, speed control, position control, and so on. Servo motor systems have also experienced DC servo systems, AC servo systems, stepper motor drive systems, and until recently the most noticeable permanent magnet motor AC servo systems. In recent years, the vast majority of imported various automatic equipment, automatic processing devices and robots use AC servo systems of permanent magnet synchronous motors.

Permanent magnet synchronous motor in information technology

Today's information technology is highly developed, and various computer peripherals and office automation equipment have also been highly developed. The key components supporting it, such as micromotors, have large demands, and precision and performance requirements have become higher and higher. The requirements for this type of micromotor are miniaturization, thinning, high speed, long life, high reliability, low noise and low vibration, and the accuracy requirements are particularly high. For example, the spindle drive motor for a hard disk drive is a permanent magnet brushless DC motor that drives the disc to rotate at a high speed of nearly 10,000 rpm. The magnetic head on the disc that performs data reading and writing functions is suspended at a distance of only 0.1 to 0.3 microns from the disc surface. One can imagine the high accuracy requirements. In the information technology, most of the driving motors used in printers, hard disk drives, optical disk drives, fax machines, copiers, etc. are permanent magnet brushless DC motors. Due to technical limitations, such micromotors cannot be manufactured in China at present, and some products are assembled in China.