A master and slave control strategy for parallel operation of three-phase UPS systems with different ratings

Parallel operation of UPS system has been used to increase power capacity of the system or to secure reliable supply of power to critical loads. During parallel operation, load sharing control to maintain the current balance is critical for reliable operation, since load sharing is very sensitive to differences in components of each module such as amplitude /phase difference, line impedance, and output LC filters. To solve these problems various control algorithms have been researched. However, these methods cannot be applied to UPS systems with different ratings. For this case, master and slave control algorithms for parallel operation is adequate. If the ratings of UPS systems are different, the value of passive LC filters will be different, and it will affect current sharing. This paper presents the general problems associated with parallel operation of UPS systems, and control strategy for parallel operation with different ratings. The validity of the proposed control strategy is investigated through simulation and experiment with two UPS systems.

[1]  T. Kawabata,et al.  Parallel Operation of Voltage Source Inverters , 1986, 1986 Annual Meeting Industry Applications Society.

[2]  Tore Undeland,et al.  Power Electronics: Converters, Applications and Design , 1989 .

[3]  Joachim Holtz,et al.  Multi-inverter UPS system with redundant load sharing control , 1989, 15th Annual Conference of IEEE Industrial Electronics Society.

[4]  Ching-Lung Chu,et al.  Combination voltage-controlled and current-controlled PWM inverters for UPS parallel operation , 1995 .

[5]  Jaeho Choi,et al.  Improved digital control scheme of three phase UPS inverter using double control strategy , 1997, Proceedings of APEC 97 - Applied Power Electronics Conference.

[6]  K. Mauch,et al.  Parallel operation of single phase inverter modules with no control interconnections , 1997, Proceedings of APEC 97 - Applied Power Electronics Conference.

[7]  K. Mauch,et al.  Control of parallel inverters in distributed AC power systems with consideration of the line impedance effect , 1998, APEC '98 Thirteenth Annual Applied Power Electronics Conference and Exposition.

[8]  Chen Jian,et al.  Parallel operation control technique of voltage source inverters in UPS , 1999, Proceedings of the IEEE 1999 International Conference on Power Electronics and Drive Systems. PEDS'99 (Cat. No.99TH8475).

[9]  T. G. Koo,et al.  Wireless parallel operation control of a two-module UPS system for equivalent load sharing , 2000, 2000 26th Annual Conference of the IEEE Industrial Electronics Society. IECON 2000. 2000 IEEE International Conference on Industrial Electronics, Control and Instrumentation. 21st Century Technologies.