A Study on the Wireless Parallel Operation of a Three-phase Modular UPS Inverter Seon – Tae Kim Department of Electrical Communication System Engineering Graduate School of Soonchunhyang University Asan, Korea

A Study on the Wireless Parallel Operation of a Three-phase Modular UPS Inverter Seon – Tae Kim Department of Electrical Communication System Engineering Graduate School of Soonchunhyang University Asan, Korea (Supervised by Professor Jun–Keun Ji) 

 This paper proposes a wireless parallel operation method of three-phase modular UPS inverter using resistive droop control. Control schemes for the parallel operation of UPS inverters can be classified into two types depending on the presence or absence of the communication line. In this paper, the wireless droop control method is used to overcome the disadvantages of the parallel operation method using communication line. Line impedance of low voltage grid such as parallel UPS inverter system is predominantly resistive. Hence, this paper uses resistive droop control method. And it uses the method holding the system frequency on 60  by applying Q-f(reactive power-phase angle) droop control that takes phase angle instead of frequency of output voltage. Furthermore, it applies a virtual resistor to droop control so that the output impedance of UPS inverter gets closer to resistive. It makes resistive droop control effective. This paper considers modular UPS using three-phase four-wire three-level NPC inverter. Because of symmetry of the circuit configuration, it can be modeled as a separate single-phase three-level inverter. From this, PR voltage controller with excellent control characteristics in single-phase inverter and PI current controller is used. The simulation using PSIM was performed in order to verify the validity of proposed algorithm. After consisting two-parallel system with three-phase modular UPS inverter, the experiment according to resistive load was conducted. It demonstrated the performance of current sharing and power sharing.