Direct Power Control of Series Converter of Unified Power-Flow Controller With Three-Level Neutral Point Clamped Converter

 

ABSTRACT:

A unified power-flow controller (UPFC) can enforce unnatural power flows in a transmission grid, to maximize the power flow while maintaining stability. Theoretically, active and reactive power flow can be controlled without overshoot or cross coupling. This paper develops direct power control, based on instantaneous power theory, to apply the full potential of the power converter. Simulation and experimental results of a full three-phase model with nonideal transformers, series multilevel converter, and load confirm minimal control delay, no overshoot nor cross coupling. A comparison with other controllers demonstrates better response under balanced and unbalanced conditions. Direct power control is a valuable control technique for a UPFC, and the presented controller can be used with any topology of voltage-source converters. In this paper, the direct power control is demonstrated in detail for a third-level neutral point clamped converter.

KEYWORDS:

  1. Direct power control
  2. Flexible ac transmission control (FACTS)
  3. Multilevel converter
  4. Sliding mode control
  5. Unified power-flow controller (UPFC)

 SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Fig. 1. One-wire schematic of the transmission line with UPFC.

 EXPECTED SIMULATION RESULTS:

 Fig. 2. UPFC series converter controlling power flow under balanced conditions, 2.5-s view during stepwise changes of active and reactive power flow reference Pref , Qref. (a) Simulation ( P 948 Wpu, Q 948 VArpu) ( ia,ib ,ic 2.38 Apu). (b) Experimental (CH1: P 40 W/V, CH2: Q 40 VAr/V, 5 V/div) (CH3, CH4: ia,ib 0.22 A/V, 5 V/div). (c) Simulation ( P 948 Wpu, Q 948 VArpu) ( ia, ib,ic 2.38 Apu). (d) Experimental (CH1:P  40W/V, CH2: Q 40 VAr/V, 5 V/div) (CH3,CH4: ia,ib 0.22 A/V, 5 V/div).

Fig. 3. UPFC series converter controlling the power flow under balanced conditions, 250-ms view during stepwise change of active and reactive power flow reference Pref, Qref. (a) Simulation ( P 948Wpu, Q 948 VArpu) ( USa,USb ,USc 230 Vpu) ( ia, ib, ic2.38 Apu). (b) Experimental, (CH1: P 40 W/V, CH2: Q 40 VAr/V, 5 V/div)(CH3,CH4:ia , ib 0.22 A/V, 5 V/div). (c) Simulation ( P 948Wpu, Q 948 VArpu) (USa ,USb ,USc 230 Vpu) ( ia,ib ,ic 2.38 Apu). (d) Experimental, (CH1: P 40 W/V, CH2: Q 40 VAr/V, 5 V/div) (CH3,CH4: ia,ib 0.22 A/V, 5 V/div).

F ig. 4. UPFC series converter controlling power flow, comparison between controllers DPC (-) ADC(- -) [5] DIC (-.) [21]. (a) Simulation under balanced conditions, simultaneous step in active and reactive power references Pref, ,Qref 250-ms view ( P 948Wpu, Q 948 VArpu). (b) Simulation under balanced conditions, simultaneous step in active and reactive power references Pref, ,Qref, 6 ms view ( P 948 Wpu, Q 948 VArpu). (c) Simulation under unbalanced conditions, 70% single-phase voltage sag at 0.125 s, 250-ms overview (P 948 Wpu, Q 948 VArpu) ( USa, USb, USc 230 Vpu).

CONCLUSION:

The DPC technique was applied to a UPFC to control the power flow on a transmission line. The technique has been described in detail and applied to a three-level NPC converter. The main benefits of the control technique are fast dynamic control behavior with no cross coupling or overshoot, with a simple controller, independent of nodal voltage changes. The realization was demonstrated by simulation and experimental results on a scaled model of a transmission line. The controller was compared to two other controllers under balanced and unbalanced conditions, and demonstrated better performance, with shorter settling times, no overshoot, and indifference to voltage unbalance. We conclude that direct power control is an effective method that can be used with UPFC. It is readily adaptable to other converter types than the three-level converter demonstrated in this paper.

REFERENCES:

[1] L. Gyugyi, “Unified power-flow control concept for flexible ac transmission systems,” Proc. Inst. Elect. Eng., Gen., Transm. Distrib., vol. 139, no. 4, pp. 323–331, Jul. 1992.

[2] L. Gyugyi, C. Schauder, S.Williams, T. Rietman, D. Torgerson, and A. Edris, “The unified power flow controller: A new approach to power transmission control,” IEEE Trans. Power Del., vol. 10, no. 2, pp. 1085–1097, Apr. 1995.

[3] X. Lombard and P. Therond, “Control of unified power flow controller: Comparison of methods on the basis of a detailed numerical model,” IEEE Trans. Power Syst., vol. 12, no. 2, pp. 824–830, May 1997.

[4] H. Wang, M. Jazaeri, and Y. Cao, “Operating modes and control interaction analysis of unified power flow controllers,” Proc. Inst. Elect. Eng., Gen., Transm. Distrib., vol. 152, no. 2, pp. 264–270, Mar. 2005.

[5] H. Fujita, H. Akagi, and Y. Watanabe, “Dynamic control and performance of a unified power flow controller for stabilizing an ac transmission system,” IEEE Trans. Power Electron., vol. 21, no. 4, pp. 1013–1020, Jul. 2006.

Operation of Series and Shunt Converters with 48-pulse Series Connected three-level NPC Converter for UPFC

 

ABSTRACT:

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.

 KEYWORDS:

  1. 48-pulse converter
  2. Neutral Point Clamped (NPC) converter
  3. Angle control
  4. Unified Power Flow Controller (UPFC)

 SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

image001

Fig. 1. 48-pulse VSC based +100 MVA UPFC in a 3-bus power system

EXPECTED SIMULATION RESULTS:
image002

Fig.2 Line real power (top) and reactive power (bottom) references (MVA)

image003

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 ).

image004

Fig.4 Shunt converter output voltage (blue), Line voltage (green) and shunt converter current (red) (5.42s-5.48s)

image005

Fig.5 Shunt converter real power (blue, p.u.), reactive power (green, p.u.).

image006

Fig.6 Current (p.u.) of transmission line L1.

image007

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)

image008

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 )

CONCLUSION:

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.

REFERENCES:

[1] 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.

[2] N. G. Hingorani and L. Gyugyi, Understanding FACTS: concepts and technology of flexible AC transmission systems: IEEE Press, 2000.

[3] L. Gyugyi, “Dynamic compensation of AC transmission lines by solid-state synchronous voltage sources,” IEEE Transactions on Power Delivery, vol. 9, pp. 904, 1994.

[4] 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.

[5] 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.

Operation of Series and Shunt Converters with 48-pulse Series Connected Three-level NPC Converter for UPFC

ABSTRACT:

 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.

KEYWORDS:

  1. 48-pulse converter
  2. Neutral Point Clamped (NPC) converter
  3. Angle control
  4. Unified Power Flow Controller (UPFC)

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

 image002

Fig.1 Schematic of Unified Power Flow Controller (UPFC)

image004

Fig. 2. 48-pulse VSC based +100 MVA UPFC in a 3-bus power system

EXPECTED SIMULATION RESULTS:

 image006

 Fig.3 Line real power (top) and reactive power (bottom) references (MVA)

image008

Fig. 4 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 ).

image010

Fig.5 Shunt converter output voltage (blue), Line voltage (green) and shunt converter current (red) (5.42s-5.48s)

image012

Fig.6 Shunt converter real power (blue, p.u.), reactive power (green, p.u.).

image014

Fig.7 Current (p.u.) of transmission line L1.

image016

Fig.8 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)

image018

Fig.9 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 )

CONCLUSION:

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.

REFERENCES:

[1] 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.

[2] N. G. Hingorani and L. Gyugyi, Understanding FACTS: concepts and technology of flexible AC transmission systems: IEEE Press, 2000.

[3] L. Gyugyi, “Dynamic compensation of AC transmission lines by solid-state synchronous voltage sources,” IEEE Transactions on Power Delivery, vol. 9, pp. 904, 1994.

[4] 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.

[5] 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.