Revista Eletrônica de Potência (Brazilian Journal of Power Electronics)

Title: Control system for multi-inverter parallel operation in uninterruptible power systems

Keywords: CAN, Parallel, PLL, VSI

Abstract

This paper proposes a network communication system applied in a control strategy for parallel-connected multi-inverters, which is based on a distributed control system and a redundant communication system. The control system is produced by a Phased-Locked Loop (PLL) synchronism algorithm, a voltage controller and a parallelism controller. All control systems are based on instantaneous values and in the parallelism control the inverters share a single voltage reference signal. The communication system, which is the main focus of the paper, is based on two buses: one analog, which is a measurement taken from the electrical grid; and one digital, comprised of a Controller Area Network (CAN). The former allows the reference voltage of all inverters to be in synchronism and the latter keeps the reference voltage in synchronism even during a grid power outage. There is a PLL algorithm in each Voltage Source Inverter (VSI), which ensures the synchronism between the internal reference and external signal received from the grid or from the CAN. The proposed networked control system was verified in three 5 kVA three-phase VSIs operating in parallel. Experimental results with static and dynamic tests and with electrical grid interruption and return, were obtained. The networked control system is redundant and it provides increased reliability, thus it can be applied in the parallel operation of an on-line Uninterruptible Power Supply (UPS).

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