Overview

With the development of frequency conversion technology and the continuous improvement of people's requirements for the quality of drinking water, frequency conversion constant pressure water supply systems are widely used in multi story residential communities and high-rise buildings for their environmental protection, energy saving, and high-quality water supply. The speed regulation system of variable frequency constant pressure water supply can achieve stepless speed regulation of the water pump motor, automatically adjust the operating parameters of the system according to changes in water consumption, and maintain constant water pressure to meet water requirements when water consumption changes. This is currently the case Advanced and reasonable energy-saving water supply system. How to fully utilize the various functions built-in in dedicated frequency converters in practical applications is of great significance for the rational design of variable frequency constant pressure water supply equipment, cost reduction, and product quality assurance. Compared with previous water towers, high-level water tanks, and pneumatic water supply methods, the variable frequency constant pressure water supply method has incomparable advantages in terms of equipment investment, operational economy, system stability, reliability, automation level, and significant energy-saving effects. At present, the variable frequency constant pressure water supply system is developing towards high reliability, fully digital microcomputer control, and multi variety serialization. The pursuit of high intelligence, serialization, and standardization is an inevitable trend for future water supply equipment to adapt to the requirements of large-scale development, intelligent buildings, network water supply scheduling, and overall planning in urban construction.

System Composition

The variable frequency speed regulation constant pressure water supply system consists of an actuator, signal detection, control system, human-machine interface, and alarm device.

1. Executing Agency

The actuator is composed of a set of water pumps, which are used to supply water to the user's pipeline network. The water pumps are divided into two types:

Variable speed pump: It is a water pump controlled by a frequency converter and can be adjusted by frequency conversion. It is used to change the speed of the motor according to changes in water consumption, in order to maintain a constant water pressure in the pipeline network.

Constant speed pump: The water pump operates only in the power frequency state, with a constant speed. They are used for regulating pumps with increased water consumption When the large water supply capacity is insufficient, quantitative supplementation of water supply should be carried out.

2. Signal detection

In the system control process, the signals that need to be detected include the tap water pressure signal and the alarm signal:

① Water pressure signal: It reflects the water pressure value of the user's pipeline network and is the main feedback signal for constant pressure water supply control.

② Alarm signal: It reflects whether the system is operating normally, whether the water pump motor is overloaded, and whether the frequency converter is abnormal. This signal is a switch signal.

3. Control system

The water supply control system is generally installed in the water supply control cabinet, including three parts: the water supply controller (PLC system), the frequency converter, and the electrical control equipment.

① Water supply controller: It is the core of the entire variable frequency constant pressure water supply control system. The water supply controller directly collects the working conditions, pressure, and alarm signals in the system, analyzes the data information from the human-machine interface and communication interface, implements control algorithms, and obtains a control scheme for the actuator. The actuator (i.e. water pump) is controlled through a frequency converter and contactor.

② Inverter: It is the unit that controls the speed of the water pump. The frequency converter tracks the control signal sent by the water supply controller to change the operating frequency of the speed regulating pump, completing the speed control of the speed regulating pump.

③ Electric control equipment: It is composed of a set of electrical components such as contactors, protective relays, and transfer switches. Used to complete the switching of water pumps, manual/automatic switching, etc. under the control of the water supply controller.

4. Human computer interface

The human-machine interface is a place where people and machines exchange information. Through the human-machine interface, users can change the set pressure and modify some system settings to meet the needs of different processes. At the same time, users can also learn about the operation status of the system and the working status of the equipment from the human-machine interface. The human-machine interface can also monitor the operation process of the system and display alarms.

5. Communication interface

The communication interface is an important component of this system. Through this interface, the system can exchange data with configuration software and other industrial monitoring systems. At the same time, modern advanced network technology can be applied to this system through the communication interface, such as remote diagnosis and maintenance of the system.

6. Alarm device

As a control system, alarms are an essential and important component. Due to the adaptability of this system to different water supply fields, in order to ensure the safe, reliable, and smooth operation of the system, and prevent faults caused by motor overload, frequency converter alarms, excessive fluctuations in the power grid, interruption of water supply sources, overpressure of effluent, overflow in pump stations, etc., the system must monitor various alarm quantities, determine the alarm category by PLC, display and protect action control to avoid unnecessary losses.

System Features

1. The control object of the water supply system is the water pressure of the user's pipeline network, which is a process control quantity. Like other process control quantities (such as temperature, flow rate, concentration, etc.), it has a lag response to the control effect. The frequency converter used for water pump speed control also has a certain lag effect.

2. Due to factors such as pipe resistance and water hammer in the user's pipeline network, as well as some inherent characteristics of the water pump itself, the change in pump speed is proportional to the change in pipeline pressure. Therefore, the variable frequency speed regulation constant pressure water supply system is a linear system.

3. The variable frequency speed regulation constant pressure water supply system should have wide universality and be applicable to various water supply systems. However, there are significant differences in the pipe network structure, water consumption, and head of different water supply systems, so the model of its control object has strong variability.

4. In the variable frequency speed regulation constant pressure water supply system, due to the addition of a quantitative pump for control, the control of the quantitative pump (including the stop and operation of the quantitative spring) occurs constantly. At the same time, the operating status of the quantitative pump directly affects the model parameters of the water supply system, causing them to change unpredictably. Therefore, it can be considered that the control object of the variable frequency speed regulation constant pressure water supply system is constantly changing.

5. When unexpected situations occur (such as sudden water or power outages, pump, frequency converter or soft starter failures, etc.), the system can automatically switch based on the status of the pump, frequency converter or soft starter, power grid conditions, water source level, pipeline pressure and other operating points to ensure constant pressure in the pipeline. When a malfunction occurs, execute specialized fault procedures to ensure that water supply can still be provided in emergency situations.

6. The electrical control cabinet of the water pump has remote and local control functions and data communication interfaces, which can be connected to control signals or control software, and can transmit real-time data related to water supply for display, monitoring, and report printing functions.

7. By using a frequency converter for speed regulation and a combination of regulating and fixed pumps for constant pressure water supply, the energy-saving effect is significant. Each water pump is soft started, and the starting current can be reduced from zero to the rated current of the motor, reducing the impact of starting current on the power grid and the speed impact of starting inertia on the large inertia of the equipment, thus extending the service life of the equipment.