Modular Online Uninterruptible Power System Plug‘n’Play Control and Stability Analysis

Abstract

Abstract-in this paper, a plug'n'play control strategy proposed for modular online UPS system is presented, which allows to plug the UPS modules in or out randomly. This provides a lower difficulty for the maintenance of the whole system. A two level control scheme was proposed, including local controllers to achieve active and reactive power sharing and central controllers to maintain synchronization capability, which allows the online UPS modular system having faster dynamic performance according to the standard IEC 62040-3. A detailed small signal mathematical model was developed in order to analyze the proposed modular online UPS system. Experimental results and data are presented to validate the stability analysis and support the proposed plug'n'play control feasibility.Index Terms-modular online UPS system, phase control, stability analysis. NOMENCLATURE

An enhanced control scheme for uninterruptible power supply

“…It is noted that the reactive power sharing with the droop control strategy should be always accurate in steady state in UPS system as the frequency is a global parameter for all UPS modules. Hence, by combining (6) and 7, it is seen that the active power sharing error is expressed as: (8) It can be observed from (8) that the active power sharing error is related with two factors that include the total resistance difference ( ) of the two UPS system and the voltage magnitude difference ( ). If the active power sharing error is caused by the output voltage difference between output voltages ( ) or line resistance mismatching ( ), the best way to mitigate the active power sharing error is to adjust each UPS's virtual resistance (…”

“…However, the droop control is a load dependent strategy that can not recover the frequency and voltage deviation caused by the load. Consequently, secondary control strategy such as consensus [8] based distributed controller has been employed to compensate the frequency and voltage amplitude deviation. However, the consensus control strategy may generate large overshoot for the frequency and voltage amplitude during compensation process, which may be harmful to the sensitive load.…”

Control System for Multi-Inverter Parallel Operation in Uninterruptible Power Systems

“…Also the system becomes complex, what can decrease its reliability. Interesting strategies to minimize these disadvantages have been reported [3]- [14], as the virtual impedance concept [3], [4], stability analysis [5], robust droop control [7], universal droop control [9], and improvements of virtual impedance and droop controls for different applications of VSI [13], [14]. Some works also integrate to the droop control a level of communication, which improves its performance [10], [11].…”

Modelagem de Pequenos Sinais no Espaço de Estados para Estruturas de Controle Hierárquico em Eixos Síncronos Aplicado ao Paralelismo de UPS Trifásicas

“…As fontes ininterruptas de energia (UPS -Uninterruptible Power Supplies) são equipamentos utilizados para proteger cargas críticas, como é o caso de sistemas de telecomunicações, data center e computação em nuvem, contra distúrbios que ocorrem na tensão fornecida pelas concessionárias de energia [1], [2]. Podem ser classificadas como off-line, interativa ou dupla conversão, sendo esta última reconhecida por apresentar o melhor desempenho dentre os tipos citados, alimentando a carga independentemente das condições da rede pública [1].…”