Frequency Converter Basics and Applications

Author: Chief Editor: Yuan Kui et al
Publisher:
Publish Date: 2004-02-01
Features:
Book Introduction
Chapter 1 briefly introduces the development history of frequency converter technology, the main characteristics and application scope of frequency converters, the advantages of frequency converter drive systems, and the development trends of frequency converter technology.
Chapter 2 introduces various basic knowledge related to frequency converters, including the basic principles of frequency conversion speed regulation, the classification of frequency converters, control methods and basic principles of frequency converters, and semiconductor devices in frequency converters.
Chapter 3 introduces the basic hardware structure of frequency converters, the basic functions of each circuit, and the various main functions of frequency converters.
Chapter 4 introduces how to design frequency converter drive systems, including the introduction of common load mechanical characteristics, the selection of motor types and capacities, the selection of frequency converter types and capacities, how to understand frequency converter performance from manufacturer samples, and various matters to be aware of when designing frequency converter drive systems.
Chapter 5 introduces various peripheral devices of frequency converters and how to select these devices based on system requirements when designing frequency converter drive systems.
Chapter 6 introduces the various matters to be noted when installing, commissioning, and maintaining frequency converters.
Chapter 7 introduces the various abnormal situations that may occur when using frequency converters and corresponding countermeasures.
The book also provides technical data for several typical universal frequency converters and wiring diagrams for the typical applications of one frequency converter in the appendix.
This book is suitable for engineering and technical personnel engaged in AC speed regulation, as well as for teachers and students of electromechanical and automatic control majors in universities and colleges.
Excerpt:
Chapter 1 Introduction
1.1 Development History of Frequency Converter Technology
DC motor drives and AC motor drives were born successively in the 19th century and have a history of over 100 years, becoming the main driving devices of power machinery. However, due to technical reasons, in a long period of time, non-variable speed drives accounting for about 80% of the entire power drive system adopted AC motors (including asynchronous and synchronous motors), while DC motors were primarily used in speed control systems. However, as is well known, due to structural reasons, DC motors have the following shortcomings:
(1) Brushes and commutators need to be replaced regularly, making maintenance difficult and the lifespan short;
(2) Due to the presence of commutation sparks in DC motors, they are difficult to apply in harsh environments with flammable and explosive gases;
(3) Complex structure, making it difficult to manufacture large-capacity, high-speed, and high-voltage DC motors.
In contrast to DC motors, AC motors have the following advantages:
(1) Robust structure, reliable operation, and easy maintenance;
(2) No commutation sparks, making them applicable in harsh environments with flammable and explosive gases;
(3) Easy to manufacture large-capacity, high-speed, and high-voltage AC motors.
Therefore, for a long time, people have hoped to replace DC motors with adjustable-speed AC motors in many cases and have conducted extensive research and development on the speed control of AC motors. However, until the 1970s, the research and development of AC speed regulation systems had not achieved truly satisfactory results, which also limited the popularization and application of AC speed regulation systems.
For this very reason, in industrial production, such power drive systems as fans and pumps requiring speed control were forced to use vanes and valves to adjust wind speed and flow. This approach not only increased the complexity of the system but also led to energy waste.
After the second oil crisis in the mid-1970s, people fully recognized the importance of energy conservation and further emphasized and strengthened the research and development of AC speed regulation technology.
With the simultaneous development of power electronic technology during this period, the frequency converter technology, as the core of AC speed regulation systems, also developed significantly and gradually entered the practical stage.
Although the initial purpose of developing frequency converter drive technology was mainly for energy saving, with the development of power electronic technology, microelectronics technology, and control theory, the performance of power semiconductor devices and microprocessors has been continuously improving, and frequency converter drive technology has also developed significantly.
With the application of various complex control technologies in frequency converter technology, the performance of frequency converters has been continuously improved, and their application scope has also become broader.
Currently, frequency converters are not only widely used in traditional power drive systems but have also expanded to almost all fields of industrial production and are widely used in home appliances such as air conditioners, washing machines, and refrigerators.
Frequency converter technology is an interdisciplinary technology that is based on control technology, power electronic technology, microelectronics technology, and computer technology, and it continues to develop with the advancement of these foundational technologies.
Table 1-1 provides an overview of the basic development process of frequency converter technology in recent years.
1.2 Advantages of Frequency Converter Speed Control Systems
Compared to traditional AC drive systems, AC motor speed control systems using frequency converters have many advantages, such as energy saving, easy realization of speed control for existing motors, achieving high-efficiency continuous speed control over a wide range, easy realization of motor forward and reverse switching, high-frequency start and stop operations, electrical braking, high-speed motor driving, adaptability to various working environments, controlling multiple motors with a single frequency converter, high power factor of the power supply, small required power supply capacity, and the ability to form high-performance control systems, etc.