1. Energy Saving through Frequency Conversion
The energy-saving benefits of AC drives are primarily evident in applications involving fans and pumps. After adopting variable-frequency speed regulation for fan and pump loads, the power saving rate ranges from 20% to 60%. This is because the actual power consumption of fan and pump loads is essentially proportional to the cube of the speed. When the required average flow is relatively low, using variable-frequency speed regulation to reduce the speed of fans and pumps results in significant energy savings. In contrast, traditional methods for flow regulation in fans and pumps involve dampers or valves, with the motor speed remaining largely unchanged and little variation in power consumption. According to statistics, electricity consumption by fan and pump motors accounts for 31% of the national total and 50% of industrial electricity consumption. Therefore, implementing variable-frequency speed regulation devices for such loads is of great importance. Currently, successful applications include constant-pressure water supply, various types of fans, central air conditioning, and hydraulic pumps.
2. Applications in Automation Systems
Due to their built-in 32-bit or 16-bit microprocessors, AC drives possess various arithmetic logic operations and intelligent control functions, offering output frequency accuracy of 0.1% to 0.01%. Equipped with comprehensive detection and protection mechanisms, they are widely used in automation systems. Examples include winding, stretching, metering, and thread guiding in the chemical fiber industry; annealing furnaces for flat glass, glass kiln stirring, edge rollers, and bottle-making machines in the glass industry; automatic feeding and batching systems for electric arc furnaces; and intelligent control of elevators. AC drives are also applied in CNC machine tool control, automotive production lines, papermaking, and elevator systems.
3. Improving Process Levels and Product Quality
AC drives are extensively used in the control of various mechanical equipment, such as conveyors, cranes, extruders, and machine tools. They enhance process levels and product quality, reduce mechanical impact and noise, and extend equipment service life. With variable-frequency speed control, mechanical systems are simplified, and operation and control become more convenient. In some cases, existing process standards can even be improved, thereby enhancing the overall functionality of the equipment. For example, in setting machines used in the textile and other industries, internal temperature is regulated by adjusting the amount of hot air delivered. Typically, circulating fans are used to deliver hot air. Since fan speed remains constant, the amount of hot air is adjusted only by dampers. If dampers malfunction or are improperly adjusted, the setting machine may become uncontrollable, affecting product quality. Additionally, high-speed starting of circulating fans causes significant wear between drive belts and bearings, making belts consumable items. With variable-frequency speed regulation, temperature adjustment can be achieved by automatically controlling fan speed through the AC drive, addressing product quality issues. Furthermore, AC drives enable fans to start smoothly at low frequencies and speeds, reducing wear on drive belts and bearings, extending equipment service life, and achieving up to 40% energy savings.
4. Soft Start for Motors
Hard starting of motors not only causes severe grid impacts but also imposes high demands on grid capacity. The high starting current and vibrations significantly damage dampers and valves, adversely affecting the service life of equipment and pipelines. By using AC drives, the soft start function allows the starting current to increase gradually from zero, with its maximum not exceeding the rated current. This reduces grid impact and the demand for power supply capacity, extends the service life of equipment and valves, and lowers maintenance costs.
Working Principle
An AC drive mainly consists of a rectifier (converting AC to DC), a filter, an inverter (converting DC to AC), a braking unit, a drive unit, a detection unit, and a microprocessing unit. The AC drive adjusts the output voltage and frequency by controlling the switching of internal IGBTs, providing the motor with the required voltage based on its actual needs, thereby achieving energy savings and speed regulation. Additionally, AC drives offer various protection functions, such as overcurrent, overvoltage, and overload protection. With the continuous advancement of industrial automation, AC drives have become widely adopted.
Main Circuit
The main circuit supplies the asynchronous motor with a voltage and frequency-regulated power source. It can be broadly categorized into two types: voltage-source inverters, which convert DC voltage sources to AC (with capacitors for DC circuit filtering), and current-source inverters, which convert DC current sources to AC (with inductors for DC circuit filtering). The main circuit comprises three parts: the "rectifier," which converts AC power to DC power; the smoothing circuit, which absorbs voltage ripples generated by the converter and inverter; and other essential components.
