Abstract : This paper introduces the topology of a cascaded multilevel high-voltage frequency converter, elucidates the basic principle of phase-shift carrier modulation technology, and conducts simulation analysis on a seven-level frequency converter.
Keywords : multilevel; high-voltage frequency converter; cascading; phase-shift carrier
1 Introduction
With the development of electrical drive technology, especially variable frequency speed control technology, high-voltage variable frequency speed control technology, particularly for large-capacity applications, has been widely adopted. High-voltage motors can achieve stepless speed regulation using high-voltage frequency converters, meeting the speed control requirements of production processes, improving product quality and output, and significantly saving energy and reducing production costs. However, due to the significant gap between my country's power electronics technology and that of advanced industrial countries, most users in my country currently rely on imported high-voltage frequency converters. As one of the key technology industries strongly supported by the state, high-voltage frequency converters are receiving increasing attention, and the pulse width modulation (PWM) method for high-voltage frequency converters is one of the most challenging and core aspects of variable frequency speed control technology. Therefore, this paper focuses on the analysis and simulation of the PWM method for high-voltage frequency converters.
2. Structure and Implementation Method of High Voltage Frequency Converter
Based on existing products, high-voltage frequency converters mainly have the following two structures:
2.1 High-Low-High Mode
The high-low-high method, also known as the indirect high-voltage method, involves stepping down the input high voltage to a low voltage of 380V via a step-down transformer, then using a conventional frequency converter to convert the frequency, and finally stepping up the voltage back to high voltage via a step-up transformer. This method is easy to implement and simple to control, but it is bulky, costly, inefficient, has difficulties in energy transmission at low frequencies, and requires special design for both the step-down and step-up transformers.
For detailed information, please click: Analysis of Pulse Width Modulation Methods for Cascaded Multilevel High-Voltage Frequency Converters
