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Speed Control System Of The Permanent Magnet Synchronous Motor

1 Development of permanent magnet synchronous motor

Speed Control System Of The Permanent Magnet Synchronous Motor插图

The permanent magnet synchronous motor is a new type of synchronous motor. Due to its advantages of low energy loss, small size, and high efficiency, permanent magnet synchronous motors are used in various fields. With the development of science and technology and people’s in-depth research on permanent magnet motors, permanent magnet synchronous motors have attracted the interest of various countries and have been widely used due to their good magnetic properties, low cost, and abundant materials. As of 1990, NdFeB permanent magnet materials accounted for half of the world’s permanent magnet material market share and became the preferred permanent magnet material for permanent magnet synchronous motors. This made the research results of permanent magnet synchronous motor systems play a huge role in social development and technological innovation.

2. Application of permanent magnet synchronous motor

Speed Control System Of The Permanent Magnet Synchronous Motor插图1

Over the past few decades, due to the development of new materials, novel motor topologies, power electronics, microprocessors, and bearing technologies, high-speed motor drive systems have gained widespread attention in academia and industry due to their high power density and high efficiency. Applications such as blowers, centrifugal compressors, flywheel systems, microturbines, pumps, spindles, turbochargers, etc. One of the main advantages of high-speed motors is to reduce the size and mass of the system for a given power because the output power of the motor is directly proportional to the speed and volume. Another reason for using a high-speed machine is increased reliability due to the elimination of intermediate gears, belts, and other transmissions. Due to recent advances in power electronics and permanent magnet materials, a permanent magnet synchronous motor (PMSM) that is lighter, smaller, and more efficient than conventional induction motors has become a reality as a traction motor.

2.1 Development overview of variable speed permanent magnet synchronous motor

When the permanent magnet synchronous motor is loaded, the air gap magnetic field is jointly established by the permanent magnet magnetomotive force and the armature magnetomotive force. The armature magnetomotive force has an influence on the air gap magnetic field, the influence of the fundamental wave of the armature magnetomotive force on the air gap magnetic field is called the armature reaction.
With the emergence of alnico permanent magnets and ferrite permanent magnets, the performance indicators such as heat resistance and maximum magnetic energy of magnetic materials have been improved, and permanent magnet motors have flourished in the industrial field, with flexible and intuitive virtual parameterization.

With the development of prototype technology, the design theory of permanent magnet synchronous motor is becoming more and more perfect, the design methods are constantly enriched, the structure is more flexible, the types are more and more, the process has been greatly improved, and the application occasions are more and more extensive, involving aerospace and defense industries, industrial and agricultural production and family life.

With the implementation of China’s energy-saving projects and the improvement of the quality of life, the market demand for variable-speed permanent magnets will increase significantly.

Permanent magnet synchronous motors with different rotor structures have different operating power, control modes, and use possibilities.

2.2 The development status of the control strategy of the permanent magnet synchronous motor speed control system
Speed Control System Of The Permanent Magnet Synchronous Motor插图2

Permanent magnet synchronous motor has been widely used in industry because it has the advantages of high working efficiency, high power density, and wide constant power range compared with other motors on the market. All drives require a position sensor for vector control of the machine.

For high-performance field-oriented control, accurate rotor position information is essential, which is usually measured by a rotary encoder or resolver. However, the use of these sensors increases the cost, size, mass, and wiring complexity, reducing the mechanical robustness and reliability of the overall PMSM control system. Designers prefer to use signals generated by position sensors (as incremental encoders) to estimate velocity. This approach is usually limited by the computational precision and quantization error of the approximation methods used for velocity estimation.

The dynamic performance of the velocity loop requires higher gains compared to the external position loop. Velocity estimation methods are usually based on digital position information (number of pulses from a position sensor). Another method is to measure the pulse duration and calculate the speed of the motor by overlapping the pulse generated by the encoder with the high-frequency clock signal.

The velocity can be estimated by counting the clock signal from the encoder pulses since the count position length is a known fixed value. At low speeds, some estimation schemes provide poor results, and as a result, speed control can become unstable.

In general, the research on AC speed control systems of permanent magnet synchronous motors is mainly divided into two directions: system components and speed control system research: system components such as controllers, drives, sensors, and motor bodies, etc.; high-performance permanent magnet synchronous motors speed control system means that the system has the advantages of fast dynamic response, fault-free static tracking, and strong anti-interference ability.

The two control methods are vector control and direct torque control, and the applications are different in specific situations. The two control methods essentially control the motor torque by controlling the q-axis current. The superiority of this control can ensure that the dynamic and static characteristics of the system are improved. Looking back on the development of related technologies in recent years, the speed regulation scheme of permanent magnet synchronous motors has been upgraded under vector control and direct torque control.

The main upgrade is to use a new controller to replace the previously used PI controller. After the upgrade, the performance is further optimized, such as variable sliding mode control, adaptive control, back-off control, feedback linearization, etc. Some algorithms have directly changed the traditional double-closed-loop structure and achieved better control effects after finding another way.

These control methods include model-oriented control, intelligent control, and so on. Since the speed control system requires high precision of rotor position information, high-performance mechanical encoders have problems such as difficult installation, low-cost performance (such as absolute positioning), and unstable system operation.

Therefore, considering the system needs to be stable and comprehensive cost-effective factors, in the 1970s People began to study sensorless technology, and the research on this technology has achieved initial results, some speed control system products using the sensorless technology have appeared on the market.

The vector control technology needs to cooperate with high-precision hardware equipment in the specific implementation, and at the same time, it needs to use the algorithm to make reasonable compensation for the motor parameters.

3 Conclusion

Compared with other motor control systems, the permanent magnet synchronous motor control system has obvious advantages in terms of efficiency indicators such as work efficiency and torque power, control performance such as response speed and high-precision monitoring, design flexibility, and ease of application.

At the same time, it has broad application prospects in the field of high-performance servos and other occasions, as well as occasions with noise requirements such as automobiles, household appliances, and fans.

Under the development trend of economic globalization, the international market is more open, the market demand is growing rapidly, and the requirements for product performance are increasing day by day.

Therefore, the permanent magnet synchronous motor control system has many advantages and strong market competitiveness and has become a research hotspot in the field of AC speed regulation. It is of great significance to study the permanent magnet synchronous motor control system.

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