Since the introduction of the sustainable development strategy in my country, many enterprises and institutions have been striving to achieve a low-carbon, energy-saving, and environmentally friendly lifestyle in the future. Energy conservation and emission reduction are important measures to achieve the sustainable development strategy. In the power system, this mainly involves implementing energy conservation and emission reduction measures for equipment such as fans, motors, and pumps.
To achieve this goal, vigorous development and research are needed in AC motor variable frequency speed control and energy-saving technology. In China's industry and agriculture, asynchronous AC motors are the most widely used. However, asynchronous motors suffer from significant drawbacks such as low power factor, poor speed control capability, and high energy consumption. Applying variable frequency energy-saving technology to asynchronous AC motors can effectively solve these problems. This can significantly contribute to energy conservation and emission reduction in asynchronous AC motors, thus supporting China's sustainable development strategy.
01. Analysis of the Principles and Characteristics of Motor Variable Frequency Control Technology
Variable frequency motors are a general term for motors driven by frequency converters, including both variable frequency induction motors and frequency converters. They can improve the working efficiency of motors and reduce energy consumption. Taking an AC generator as an example, its speed formula is as follows:
n1=60f/p . （1）
In equation (1): n1 — synchronous speed;
f — power supply frequency, 50Hz;
p — Number of pole pairs of the motor.
Motor slip can be expressed by the formula:
s = (n1 - Cn) / n1 . （2）
In equation (2): s — motor slip rate;
n — motor speed.
From equations (1) and (2), we can deduce that:
n = 60f(1-s)/p . (3)
Variable frequency drive (VFD) technology for motors allows for precise control of output frequency and voltage through a frequency converter, a significant advantage not found in other motor control systems. Furthermore, it features soft start and notification functions. Employing electromagnetic design reduces electronic and rotor resistance, enabling stepless speed regulation. It also boasts low energy consumption, fully embodying energy conservation and emission reduction characteristics.
02. Analysis of the Development and Application of Motor Variable Frequency Control
Initially, motors in my country used fixed frequencies, meaning they could only output a fixed amount of power and voltage. Therefore, the drive frequency of these motors remained constant during operation. However, the drive frequency required by the load was constantly changing. To meet this demand, the motor's rated drive frequency was generally higher than the required frequency. While this ensured sufficient drive frequency for normal operation, a significant portion of this drive frequency was wasted. This resulted in substantial waste of electrical energy, failing to utilize it effectively and contradicting my country's sustainable development strategy.
To achieve the goals of energy conservation and efficient power utilization, variable frequency drive (VFD) technology for motors has been developed. VFDs can adjust the motor's output power and voltage according to the drive frequency required by the load, ensuring no unnecessary drive is wasted and significantly improving energy efficiency, fully complying with my country's energy conservation and emission reduction requirements. As my country's requirements for energy conservation and emission reduction become increasingly stringent, the development and research of VFD energy-saving control systems are continuously improving and being widely adopted in more and more places.
1) The development process of motor frequency conversion technology
Most modern motor frequency conversion systems employ constant V/F control systems, characterized by their simple structure and low manufacturing cost. This system is widely used in large applications such as fans where the dynamic performance requirements of the frequency conversion system are not very high. This system is a typical open-loop control system, capable of meeting the smooth speed change requirements of most motors, but its dynamic and static adjustment performance is limited, making it unsuitable for applications with stringent dynamic and static performance requirements.
To achieve high performance in both dynamic and static regulation, a closed-loop control system is the only viable option. Therefore, some researchers have proposed a motor speed control method that controls the closed-loop slip frequency. This method can achieve high performance in both static and dynamic speed regulation. However, this system is only applicable to motors with relatively low speeds. At higher motor speeds, this system not only fails to save energy but also generates significant transient currents, causing instantaneous changes in motor torque. Therefore, to achieve high dynamic and static performance at higher speeds, the problem of transient current generation in the motor must be addressed first. Only by reasonably resolving this issue can we better develop motor frequency conversion energy-saving control technology.
2) Application of motor frequency conversion control
Approximately 70% of the energy consumption of motors is used in fan and pump loads. Therefore, variable frequency drive (VFD) technology can effectively save energy in these loads, achieving energy conservation and emission reduction. Take air conditioning as an example. Without a VFD control system, an air conditioner can only reduce the set temperature by closing the fan duct. However, the motor continues to run, and this drive power is completely wasted. But in an air conditioner with a VFD control system, when the set temperature is lowered, only the motor speed needs to be reduced, decreasing the output drive power. There's no need to close the fan duct, and the motor's drive frequency is not wasted, significantly improving energy efficiency.
03. Conclusion
In order to meet the requirements of the national sustainable development strategy, the power system has vigorously promoted the use of variable frequency drive (VFD) energy-saving control systems for motors. The application of this system has greatly alleviated the current shortage of electricity in my country. VFD energy-saving control systems can reduce unnecessary drive frequencies of motors, achieving the rational use of electricity.
