The 48-pulse series connected 3-level Neutral Point Clamped (NPC) converter approach has been used in Unified Power Flow Controller (UPFC) application due to its near sinusoidal voltage quality. This paper investigates the control and operation of series and shunt converters with 48-pulse Voltage Source Converters (VSC) for UPFC application. A novel controller for series converter is designed based on the “angle control” of the 48-pulse voltage source converter. The complete simulation model of shunt and series converters for UPFC application is implemented in Matlab/Simulink. The practical real and reactive power operation boundary of UPFC in a 3-bus power system is specifically investigated. The performance of UPFC connected to the 500-kV grid with the proposed controller is evaluated. The simulation results validate the proposed control scheme under both steady state and dynamic operating conditions.
- 48-pulse converter
- Neutral Point Clamped (NPC) converter
- Angle control
- Unified Power Flow Controller (UPFC)
Fig. 1. 48-pulse VSC based +100 MVA UPFC in a 3-bus power system
EXPECTED SIMULATION RESULTS:
Fig.2 Line real power (top) and reactive power (bottom) references (MVA)
Fig. 3 Measured real and reactive power, DC link voltage and converter angles (Top trace: measured line real power (MW); second top trace: measured line reactive power, (MVar); third top trace: DC bus voltage; fourth top trace: shunt converter angle α ; fifth top trace: series converter angle α ; bottom trace: series converter angle σ ).
Fig.4 Shunt converter output voltage (blue), Line voltage (green) and shunt converter current (red) (5.42s-5.48s)
Fig.5 Shunt converter real power (blue, p.u.), reactive power (green, p.u.).
Fig.6 Current (p.u.) of transmission line L1.
Fig.7 Series converter 48 pulse converter voltage (blue, p.u.) and current (black, p.u.) during time 2~2.03s (when real power reference is increased)
Fig. 8 Series converter angle σ vs. DC bus voltage (Top trace: line real power and reactive power; second top trace: shunt converter injected reactive power; third top trace: DC bus voltage; bottom trace: series converter angle σ )
In this paper, the control and operation of series and shunt converters with 48-pulse series connected 3-level NPC converter for UPFC application are investigated. A new angle controller for 48-pulse series converter is proposed to control the series injection voltage, and therefore the real and reactive power flow on the compensated line. The practical UPFC real and reactive power operation boundary in a 3-bus system is investigated; this provides a benchmark to set the system P and Q references. The simulation of UPFC connected to the 500-kV grid verifies the proposed controller and the independent real power and reactive power control of UPFC with series connected transformer based 48-pulse converter.
 N. G. Hingorani, “Power electronics in electric utilities: role of power electronics in future power systems,” Proceedings of the IEEE, vol. 76, pp. 481, 1988.
 N. G. Hingorani and L. Gyugyi, Understanding FACTS: concepts and technology of flexible AC transmission systems: IEEE Press, 2000.
 L. Gyugyi, “Dynamic compensation of AC transmission lines by solid-state synchronous voltage sources,” IEEE Transactions on Power Delivery, vol. 9, pp. 904, 1994.
 C. D. Schauder, L. Gyugyi etc. “Operation of the unified power flow controller (UPFC) under practical constraints,” IEEE Transactions on Power Delivery, vol. 13, pp. 630-639, April 1998.
 L. Gyugyi. “Unified power-flow control concept for flexible AC transmission systems,” IEE Proceedings – Generation, Transmission and Distribution, vo. 139, pp. 323-331, July 1992.