Variable Frequency Converter: The Design Functional Parameters

2024-08-22

As an essential control device in modern industry, the design function parameters of a variable frequency converter directly affect the performance and application outcomes of the equipment. This article will provide a detailed introduction to the main design function parameters of variable frequency converters and explore how to choose the appropriate control mode and parameter settings based on different requirements.

Control Mode Selection for Variable Frequency Converters

The choice of control mode is crucial in the design of variable frequency converters. Common control modes include V/F control, vector control, and Direct Torque Control (DTC). Different control modes are suitable for different applications:

V/F Control

This is the most commonly used control mode, suitable for general applications such as fans and pumps. V/F control meets the requirements of constant torque loads through simple speed adjustments. Manufacturers usually preset a constant torque V/F mode, which is suitable for most application scenarios.

Vector Control

This mode is suitable for equipment requiring high-precision speed and torque control, such as rewinding and unwinding machines, and cranes. Vector control can provide higher torque precision and dynamic response. Some variable frequency converters even support encoder-based closed-loop vector control to further enhance control accuracy.

Direct Torque Control (DTC)

This control mode is typically used in scenarios that require precise torque control, such as crane operations. DTC provides rapid torque response and efficient dynamic performance, making it suitable for high-demand industrial applications.

Voltage and Frequency Design of Variable Frequency Converters

The voltage and frequency design of a variable frequency converter directly impacts its performance and applicability. The following are key considerations in the design of these parameters:

Power Supply Voltage

The standard power supply voltage in most markets is typically three-phase 380/660 volts, so most variable frequency converters are designed for 1AC/3AC 220V±15%, 3AC 380V±15%, and 3AC 660V±15%. This design ensures compatibility with most industrial motors and meets the common power frequency requirements.

Frequency Settings

Frequency settings in a variable frequency converter include maximum frequency, start frequency, and minimum frequency. These settings determine the operational range and adjustment flexibility of the motor. For example, some equipment like spinning machines may require a swing frequency function to adjust the frequency as needed.

Resonance Issues

In certain specialized equipment, variable frequency converters need to be preset with a skip frequency function to avoid resonance problems. This function sets skip frequency points to ensure that resonance does not occur during operation, thus protecting the equipment from damage.

Start, Stop, and Speed Regulation Functions of Variable Frequency Converters

The start, stop, and speed regulation functions are among the basic operational functions of a variable frequency converter. Below are detailed explanations of these functions:

Start and Stop Functions

Most variable frequency converters provide panel operation for start and stop functions and allow users to set frequency values. In practical applications, users can choose to operate the converter via terminal control or other communication methods to meet different control needs.

Speed Regulation Function

Variable frequency converters typically have multi-level speed settings, allowing users to set different frequency values through various I/O signals. This function supports multi-speed time control and is suitable for applications requiring flexible speed adjustment.

Interlock Function

Many variable frequency converters have built-in simple PLC functions for basic logic control. For example, in a system with two converters, one can act as the start controller, while the other operates based on the start signal. Some setups also include PID functions for process closed-loop control, such as in constant pressure water supply systems.