Application of PI500 frequency converter in vacuum pumps
ApplicationofPI500frequencyconverterinvacuumpump
Ding Yunfei, Tung Chee-hwa
(Dalian Puchuan Technology Co., Ltd., Dalian, Liaoning, 116023)
Abstract: This article provides a brief introduction to the application of Dalian Puchuan Technology's PI9000 series frequency converters in vacuum pumps. The control system integrates frequency conversion technology and control technology, fully leveraging the superior control performance of the Puchuan Technology PI9000 series frequency converters to effectively meet the requirements of vacuum pumps, such as low-speed high starting torque and high speed accuracy, thus significantly improving equipment performance.
Keywords: PI500; vacuum pump;
1. Overview
A vacuum pump is a rotary variable displacement vacuum pump that requires a backing pump for operation. It operates over a wide pressure range, has a high pumping speed, and is insensitive to dust and water vapor in the pumped gas. It is widely used in metallurgy, chemical, food, and electronic coating industries. Vacuum pumps are widely classified, including models such as WLW series vacuum pumps, W-type vacuum pumps, 2X-type vacuum pumps, ZJ-type vacuum pumps, SL-type Roots blowers, JZJX-type vacuum pumps, JZJS-type vacuum pumps, JZJWLW-type vacuum pumps, JZJP-type vacuum pumps, RPP-type vacuum pumps, and 2XZ-type vacuum pumps.
Vacuum pumps are widely used in plastic machinery, pesticide and chemical industry, dye and chemical industry, brick and tile machinery, cryogenic equipment, papermaking machinery, pharmaceutical and chemical industry, food machinery, industrial electric furnace, electronics industry, vacuum equipment, fertilizer, metallurgy, petroleum, mining, foundation treatment and other fields.
The function of a vacuum pump is to extract gas molecules from a vacuum chamber, reduce the gas pressure inside the chamber, and achieve the required vacuum level.
China has many vacuum pump manufacturers, with annual sales of approximately 150 million yuan, but this is only equivalent to the annual sales of a single vacuum pump company, Kinney, in the United States. Analysis of the global vacuum pump market shows that the market and application areas for various types of vacuum pumps are constantly changing and developing. China's vacuum pump manufacturing industry has a long history and a solid foundation. Domestically produced vacuum pumps have been applied and validated in various fields, and some pumps have even been exported overseas, gaining recognition and praise from foreign users. It should be said that China's vacuum pump manufacturing industry still has enormous room for development in both domestic and international markets.
2. Control problems of traditional vacuum pumps
The load on a vacuum pump decreases as the vacuum level increases. When the air resistance inside the container is high, the vacuum pump often operates under overload conditions. As the vacuum level increases, the current decreases, and the motor operates normally. When the container is properly sealed, the motor operates under overload conditions for a short time, preventing motor burnout. However, when the container seal deteriorates, the motor operates under overload conditions for a longer period, sometimes leading to motor burnout.
Traditionally, the following methods have been used to solve the problem of pump overload:
1) A mechanical automatic pressure regulating bypass valve is adopted.
A bypass valve is installed on the main pipeline between the inlet and outlet of the Roots vacuum pump. This valve controls the pressure difference between the pump inlet and outlet to ensure it does not exceed the rated value. When the pressure difference reaches the rated value, the valve automatically opens due to the pressure difference, connecting the outlet and inlet of the Roots vacuum pump and rapidly reducing the pressure difference. At this point, the Roots vacuum pump operates under almost zero pressure difference. When the pressure difference falls below the rated value, the valve automatically closes, and the gas is drawn away by the backing pump through the Roots vacuum pump. Roots vacuum pumps with bypass relief valves can be started simultaneously with the backing pump, simplifying unit operation.
(2) Use hydraulic coupling
The use of a hydraulic coupling also prevents pump overload, allowing the pump to operate under high pressure differentials. The hydraulic coupling is installed between the pump and the motor. Under normal operating conditions, the hydraulic coupling transmits rated torque from the motor end to the pump. The maximum pressure differential of the Roots vacuum pump is determined by the maximum torque transmitted by the hydraulic coupling, which in turn is regulated by the amount of liquid within it. When the pump operates under high pressure differentials or when the backing pump starts simultaneously, a speed difference (slippage) is generated within the hydraulic coupling, transmitting only a certain torque to slow the pump down. As pumping continues, the gas load decreases, and the Roots vacuum pump gradually accelerates to its rated speed.
(3) Vacuum electrical components are used to control the pump inlet pressure.
A pressure-sensitive component, such as a vacuum diaphragm relay or electrical contact vacuum pressure sensor, is installed at the inlet line of the Roots vacuum pump. After the vacuum system starts, when the pressure at the Roots vacuum pump inlet is lower than the given value (the pump's allowable starting pressure), the pressure-sensitive component sends a signal, which, via the electrical control system, starts the Roots vacuum pump (if the vacuum system has a Roots vacuum pump bypass line, the bypass line valve is simultaneously closed). If the pump inlet pressure is higher than the specified value, the Roots vacuum pump automatically shuts down (or simultaneously opens the pump bypass line valve), thus ensuring the reliable operation of the Roots vacuum pump.
Clearly, the above methods are complex in structure, costly, have poor control precision, and result in serious energy waste, and are no longer suitable for the requirements of equipment development.
3. Common frequency converter application solutions
To protect the motor, some vacuum pump manufacturers use frequency converters. They use current transformers and current transmitters to detect the actual current of the motor, and then input the converted analog signal into the frequency converter, which performs PID calculations to control the motor current and speed, ultimately protecting the motor.
As shown in the diagram above, its control loop is complex. Although the frequency converter can achieve closed-loop PID control of the current, the control accuracy is not high, and the switching is complicated. It cannot distinguish between the motor stall current and the normal load current, which may cause the motor to operate in a stall state for a long time, resulting in motor burnout. The control effect is not ideal.
4. Characteristics of Dalian Puchuan PI500 frequency converter in vacuum pump applications
The Dalian Puchuan PI500 vector frequency converter adopts a globally leading sensorless vector control algorithm, which decomposes the motor stator current into torque current, airflow, and excitation current components through coordinate transformation, thereby achieving precise torque control. Compared with the V/F control algorithm, it has advantages such as better low-frequency torque characteristics, better dynamic response characteristics, and higher speed control accuracy.
The Dalian Puchuan PI500 vector frequency converter vacuum pump solution does not require any external equipment; the frequency converter itself can achieve precise control of motor current and speed.
Regardless of the container's sealing performance, the Dalian Puchuan PI500 vector frequency converter can control the motor current within its rated value without any external auxiliary equipment. Furthermore, the control range is adjustable, achieving a control accuracy of ±1%. Based on this, the vacuum pump operates at maximum efficiency, reaching the set vacuum level as quickly as possible.
Meanwhile, the Dalian Puchuan PI500 vector frequency converter can also quickly identify the vacuum pump's stall current and load current. When the vacuum pump stalls due to mechanical reasons, it can immediately identify the problem, trigger an alarm, and stop the machine, preventing the fault from escalating further.
5. Parameter Settings
6. Conclusion
The Dalian Puchuan PI500 pump-specific solution not only solves the control problems of vacuum pumps and eliminates the need for traditional mechanical overload protection devices, but also simplifies the frequency converter control circuit, significantly improving overall efficiency. In practical use, it has received unanimous praise from vacuum pump manufacturers.
Author: Ding Yunfei, senior engineer, Bachelor of Engineering, has been engaged in R&D project management and quality management of high-end CNC machine tools, all-digital bus CNC systems and servo drives.
