Vector Control for an AC Drive with a Multilevel Frequency Converter Based on an Н-Bridge

Abstract

Using multilevel topologies for a stand-alone inverter, which is a part of induction or synchronous ac drives, makes it possible to achieve their operation under some fault conditions related to, for example, the failure of any element in a power circuit or short-term blackout in operation of distribution line of centralized power supply system. In the last case, due to switching the speed loop into the mode of voltage control of capacitor filters, it turns out during short-term interval to maintain at the set level the magnetic condition and mechanical coordinates of electrical machine without direct disconnection of converter by corresponding signal feeding from a security unit. The work considers the design formulas for synthesis of special algorithms of vector control by an ac actuating motor under the absence of power supply based on the set distribution of the roots of characteristic polynomial on the complex plane. As well as the reduction of logarithmic amplitude–phase–frequency characteristic of the loop in open condition to the normalized form is presented in the work. Within the framework of these formulas, the regeneration of electric energy in the stand-alone inverter with series-connected H-bridges is carried out to stabilizing the voltage of capacitor bank in each power module owing to when workability recovery of three-phase network, the ac drive returns to normal operation without significant degradation of quality of processes by rotor rotational speed.