Abstract: This paper analyzes the structure, technical performance, control method and applicable operating conditions of high-power frequency converters, and discusses their engineering implementation and reasonable selection.
Keywords: high voltage frequency converter, three-level frequency converter, unit series multilevel
0 Introduction
With increasing awareness of the superior performance of frequency converters and the growing need for energy conservation and emission reduction in industrial and mining enterprises, frequency converter technology is developing towards higher voltage, greater power, and superior performance. Although various high-voltage frequency converters are constantly emerging, they do not yet have a nearly unified topology like low-voltage frequency converters, and engineers' understanding of them is gradually maturing. Therefore, to select and use high-power, high-voltage frequency converters effectively, a systematic analysis of their control methods, technical performance, and applicable operating conditions is essential.
1. Topology of a high-power frequency converter
Commonly used high-power frequency converters can be classified into "high-low-high" and "high-low" type frequency converters according to their main circuit topology. Both "high-low-high" and "high-low-high" type frequency converters use low-voltage converters. The "high-low-high" type, also known as an indirect high-voltage frequency converter, reduces the high-voltage power supply voltage to a level permissible by a standard low-voltage frequency converter. After passing through the low-voltage converter, the voltage is then boosted by an output transformer to supply the high-voltage motor. While this structure is relatively simple to control, it requires large transformers on both sides, and the two voltage transformations increase losses and result in a large equipment size. Because the magnetic coupling capability of the output transformer weakens at low frequencies, the load capacity of the frequency converter system decreases during startup. Although a 12-pulse rectification is used, the generated harmonics still exceed the standard. These significant drawbacks limit its application.
For details, please click: Engineering Applications of High-Power Frequency Inverters
