DAVIC: A New Distributed Adaptive Virtual Impedance Control for Parallel-Connected Voltage Source Inverters in Modular UPS System

Abstract

In this paper, an average active power sharing control strategy based on distributed concept for the parallel operation of voltage source inverters (VSIs) is proposed to be applied to the modular uninterruptible power supply (UPS) systems. The presented method is named distributed adaptive virtual impedance control (DAVIC), which is coordinated with the droop control method. Low bandwidth CAN-based communication is used for the requirement of data sharing of the proposed method in the real modular UPS system. Unlike the conventional virtual impedance control techniques, the virtual impedance of a converter module is adjusted automatically by using global information when DAVIC is applied, further to tune the output impedance of the power modules. The adaptive virtual impedance is calculated by using the difference between the active power of a local module and the average active power of all the modules in a modular UPS. The DAVIC overcomes the drawback of conventional virtual impedance control since an accurate value of the real output impedances of different converter modules is not required. Simulations using PLECS and experiments on a real commercial modular UPS are developed to verify the effectiveness of the proposed control methodology. These results shown a superior power sharing performance is obtained when using the proposed method.Index Terms-droop control; adaptive virtual impedance; modular uninterruptible power supply system; power sharing; circulating current.Baoze Wei (S'15, M'18) received the B.S. degree in electrical engineering, the M.S. degree in power electronics and power drives from Yanshan University,

Distributed Control Strategies for Microgrids: An Overview

“…For compensating these variations, adaptive virtual impedance loops have been proposed in the literature, which modifies (on-line) the values of the virtual resistances and inductances. For instance, to decouple the active and reactive power supply in MGs, which are not strongly inductive, adaptive distributed approaches have been proposed in [120], [195]- [197].…”

“…An alternative method, based on the same principle that [195], [196], but using active power, is proposed in [197]. The virtual impedance value is adjusted by a PI controller that regulates the deviation of local active power to achieve power consensus of parallel converters of a modular Uninterruptible Power Source (UPS).…”

Adaptive Droop Control Method for Suppressing Circulating Currents in DC Microgrids

“…Although this method results in an accurate load sharing, it suffers from the huge computational effort. Authors of [14] propose a new virtual parameter by passing the converter's power to a low pass filter. Utilizing a low pass filter adds latency and complexity to the design stage.…”

Enhanced Circular Chain Control for Parallel Operation of Inverters in UPS Systems

“…If the parallel inverters are of the same power rating, the load current must be equally shared between them. However, if their ratings are different, the load current should be shared in proportion with each inverter's power rating [3]. To avoid circulating current, the output voltages of the parallel inverters should be synchronized in terms of amplitude and phase, and obviously, the frequency of the output voltages should be the same [4].…”

“…To avoid circulating current, the output voltages of the parallel inverters should be synchronized in terms of amplitude and phase, and obviously, the frequency of the output voltages should be the same [4]. In addition, voltage limits of the dc-link capacitors have to be considered in case input rectifiers are unidirectional, which may face excessive voltages due to active power absorption by some inverters because of circulating currents [3,5].…”