Renovation of Sunwoele VFD (Variable-frequency Drive) in Guangxi Sugar Factory

I. Overview

In the field of industrial control, in addition to hydraulic and pneumatic controls, the vast majority of controls are electric control systems, and most of their final control objects and actuators are motors. In the past, DC speed control systems were used in speed control systems that required fast response and high precision. It once occupied a dominant position in electric transmission. Its disadvantages are high cost, poor reliability, and troublesome maintenance. The induction motor has a simple structure, is strong and reliable, and is low in cost, but it is difficult to control using traditional methods. With the advancement of science and technology, the development of high-power transistor electronic technology, the rapid advancement of large-scale integrated circuits and microprocessing technology, AC motor frequency conversion speed regulation technology has become increasingly perfect. As a result, AC transmission control systems represented by induction motors have largely replaced DC motor speed control systems and become the mainstream of electrical transmission control.

Variable frequency speed regulation is the most practical of many AC speed regulation methods. It does not need to replace the original induction motor in the application, and it has high efficiency, good mechanical properties, wide speed regulation range, small starting current, high control accuracy, and easy installation. With the advantages of convenient and simple operation, no pollution to the power grid, and energy saving, it is the best solution for AC drive control. It has perfect protection functions and is easy to control automatically. It plays an important role in improving the automation level of industry, improving labor productivity, product quality, greatly saving energy and raw materials, and reducing production costs.

In the sugar production process, most of the equipment is driven by AC motors. The energy consumption of the motors accounts for most of the total production energy consumption. However, many motors work at light load for a long time or part of the time. With traditional Methods such as voltage transformation control and mechanical energy consumption control cannot achieve good output torque and high power utilization. Variable-frequency logarithmic control cannot achieve continuous speed regulation. If VFD (Variable-frequency Drive) speed regulation control is used, it can not only meet the needs of system work, but also save energy greatly.

2. Functional characteristics of Sunwoele variable frequency speed regulator

In order to adapt to different control objects and usage environments, Sunwoele variable frequency speed regulators are equipped with rich functions for users to choose.

1. Flexible frequency control

The two basic outputs of the variable frequency speed regulator to control the motor are frequency and voltage, so the general general-purpose VFD (Variable-frequency Drive) is equipped with sufficient frequency setting function and frequency control interface. The frequency output of VFD (Variable-frequency Drive) can be set through the numeric keyboard on the device, such as: basic frequency and starting frequency. And the width of jump frequency, multi-stage operating frequency, maximum and minimum frequency, acceleration and deceleration slope, etc. At the same time, there are also functions such as rising and falling, starting and stopping on the keyboard to change the motor speed. There is also a PID automatic control system that can use the signal input port provided by VFD (Variable-frequency Drive) to control the operation of the motor. At this time, the operation of the motor can be controlled with 0~5V or 0~10V, or it can be set with a current signal of 4~20mA.

2. Reliable protection function

With the development of detectors and related technologies, the motor and the frequency converter itself can be reliably protected at the same time. The general protection functions are as follows: overcurrent protection, regenerative overvoltage protection, overvoltage and undervoltage protection, phase loss protection, overload protection, output short circuit protection, overheating protection, grounding protection and other functions. At the same time, there are memory anomaly detection, CPU anomaly detection, parameter error alarm, power switching device failure alarm, etc. These protection and alarm signals can provide reliable fault information to management and operators in a timely manner, making it easier for technicians to diagnose and repair control system faults. It is more conducive to the protection of equipment.

3. Energy-saving principles of Sunwoele VFD (Variable-frequency Drive) in fan and pump applications

The load that drives the fan and pump is a square torque load. This type of load is also called a fluid load. The main characteristics of this type of load are:

1.) The output frequency of VFD (Variable-frequency Drive) is below the basic frequency and this type of load is generally not allowed to operate above the basic frequency.

2.) From fluid mechanics, we know that the relationship between air volume flow, motor speed and motor power is as follows:

Q1/Q2=n1/n2 H1/H2=(n1/n2)2

P1/P2=(n1/n2)3

Q represents air volume flow, H represents wind pressure (pipe network water pressure), P represents shaft power, and n represents rotational speed. It can be seen from the above formula that when Q decreases, H and P decrease by square and cube respectively.

The torque of this type of load is proportional to the square of the rotational speed, and the shaft power output by the motor is proportional to the cube of the rotational speed. When dragging this type of load, as the rotational speed decreases, the required torque decreases in proportion to the square. The current is small and the motor will not overheat.