Determination of flux density produced by multilevel inverters in CM voltage filter
Purpose - The purpose of this paper is to evaluate the conditions in which a saturation of the common mode (CM) choke might appear to be essential for proper design of the CM voltage filters. This paper presents a method for the determination of a CM choke flux density produced by multilevel inverters with carrier-based modulations. Design/methodology/approach - The proposed combination of secant and tangent methods allows efficient and high-resolution determination of the CM voltage waveforms produced at the output of the multilevel inverters with commonly used carrier-based modulations. Findings - The presented results show that the application of a five-level inverter with specific modulation causes a decrease of the maximum flux density, down to 15 per cent of the maximum level of the flux density reached in a two-level inverter. The proposed, dedicated approximation method provides an accuracy of the root estimation better by about three orders for a comparable number of the function calls in comparison with Brent's method. Practical implications - The presented theoretical evaluations make possible the determination of the maximum expected value of the flux density produced by multilevel inverters with various types of carrier-based modulations, which allows a reduction in dimensions, weight and cost of CM chokes applied in CM voltage compensators. Originality/value - In the paper, the new formulas that describe the placement of triangular carrier functions for commonly used multilevel inverters have been presented. In order to avoid accumulation of the estimation error, during determination of the CM voltage time integral, a dedicated, efficient method of roots approximation has been developed.
flux density voltage electromagnetism electric filters