Mitigating Circulating Common-Mode Currents Between Parallel Soft-Switched Drive Systems

Abstract

A mathematical model that is developed for a generalized drive system, including common-mode passive and active elements, is used to explore the issues of paralleling soft-switched resonant dc-link drive systems. Differences between the modulation pattern for each drive system cause common voltage disturbances, which lead to significant circulating currents between the drive systems. Control methods for actively compensating for common-mode circulating currents or reducing the commonmode voltage disturbances are investigated. Practical modifications to the drive system controls are implemented to reduce the circulating currents between paralleled systems.Index Terms-Component, drive system modeling, electromagnetic interference (EMI), paralleling power converters, softswitched power converters.

A Circulating-Current Suppression Method for Parallel-Connected Voltage-Source Inverters With Common DC and AC Buses

“…Gcd1 is the controller in the d-axis circulating-current control loop. Then, by substituting (8) into (14), one can obtain the new reference current Idr1* for the VSI1. Being Idr1 is the original daxis reference current.…”

“…The calculation results from (8) and (10) will be Ide1<0, Ide2>0. Substituting (8) into (14), and (10) into (16), the new d-axis reference current Idr1* will be subtracted from Idr1, and Idr2* will be increased from Idr2, which indicates the correct compensation direction. So that, with proper design of the circulating-current controllers, the cross and the zero-sequence circulating-currents can be effectively suppressed.…”

A Coordinate Control Strategy for Circulating Current Suppression in Multiparalleled Three-Phase Inverters

“…Consequently, the zero-sequence circulating current will be generated when there are mismatches among the paralleled converters, which distorts the output current quality, increases the power loss, and degrades the overall performance. [14], [15].…”

A Comparative study of Conventional & Proposed Drive System

“…For the power capability, reliability, efficiency, and redundancy improvement the parallel converters have been used. Parallel converter techniques can be employed to improve the performance of active power filters [4]- [6], uninterruptible power supplies (UPS) [7]- [8], fault tolerance of doubly fed induction generators [9], and three-phase drives [10], [11]. Usually the operation of converters in parallel requires a transformer for isolation.…”