Highly Efficient Multilevel Frequency Converters of Metallurgical Production Facilities

Abstract

A comparative analysis of traditional and multilevel low-voltage frequency converters was performed. Calculation methods were proposed that make it possible to evaluate the technical and economic indices of multilevel semiconductor devices. The attractive qualities of low-voltage multilevel frequency converters as compared with high-voltage (with rated voltage exceeding 1 kV) multilevel semiconductor devices were distinguished. In low-voltage multilevel converters, the loss in semiconductor rectifiers was reduced by about 1.5 times, the effect of overvoltage in the load was decreased, and the operating speed of the active rectifier was increased. A method of estimation of the loss in semiconductor converters with two-level standalone inverters based on mathematical models and experimental studies is proposed, which made it possible to clarify the parameters of analytical equations. It is stated that using the three-level bridge inverters (rectifiers) in active rectifiers makes it possible to shorten the durability of transient process of the system in the regeneration mode because of a reduced level of switching overvoltages. A method of choosing the optimal number of phases of semiconductor multilevel low-voltage frequency converters for metallurgical production facilities according to the criterion of maximum probability of failure-free operation was developed.