Digital Simulation of the Generalized Unified Power Flow Controller System with 60-Pulse GTO-Based Voltage Source Converter

 

ABSTRACT:

The Generalized Unified Power Flow Controller (GUPFC) is a Voltage Source Converter (VSC) based Flexible AC Transmission System (FACTS) controller for shunt and series compensation among the multiline transmission systems of a substation. The paper proposes a full model comprising of 60-pulse Gate Turn-Off thyristor VSC that is constructed becomes the GUPFC in digital simulation system and investigates the dynamic operation of control scheme for shunt and two series VSC for active and reactive power compensation and voltage stabilization of the electric grid network. The complete digital simulation of the shunt VSC operating as a Static Synchronous Compensator (STATCOM) controlling voltage at bus and two series VSC operating as a Static Synchronous Series Capacitor (SSSC) controlling injected voltage, while keeping injected voltage in quadrature with current within the power system is performed in the MATLAB/Simulink environment using the Power System Block set (PSB). The GUPFC, control system scheme and the electric grid network are modeled by specific electric blocks from the power system block set. The controllers for the shunt VSC and two series VSCs are presented in this paper based on the decoupled current control strategy. The performance of GUPFC scheme connected to the 500-kV grid is evaluated. The proposed GUPFC controller scheme is fully validated by digital simulation.

KEYWORDS:

60-Pulse GTO Thyristor Model VSC, UPFC, GUPFC,Active and Reactive Compensation, Voltage Stability

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

UPFC with 60-Pulse GTO-Based Voltage Source Converter

Figure 1. Three-bus system with the GUPFC at bus B5 and B2

EXPECTED SIMULATION RESULTS:

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 Figure 2. Sixty-pulse VSC output voltage

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Figure 3. Simulated results of the GUPFC .shunt converter operation for DC voltage with Qref = 0.3pu; 0.5 pu

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Figure 4. Simulated results of the GUPFC series converter operation Pref=8.7pu; 10pu, Qref=-0.6pu; 0.7pu

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Figure 5. Simulated results of the GUPFC series converter operation Pref=7.7pu; 9.0pu, Qref=-0.5pu; 0.9pu

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Figure 6. Digital simulation results for the decoupled current controller schemes for the shunt VSC in a weak power system

 CONCLUSION:

The paper presents and proposes a novel full 60-pulse GTO voltage source converter that it constructed becomes GUPFC FACTS devices. It comprises the full 60-pulse VSC-cascade models connected to the grid network through the coupling transformer. These full descriptive digital models are validated for voltage stabilization, active and reactive compensation and dynamically power flow control using three decoupled current control strategies. The control strategies implement decoupled current control switching technique to ensure accountability, minimum oscillatory behavior, minimum inherent phase locked loop time delay as well as system instability reduced impact due to a weak interconnected ac system and ensures full dynamic regulation of the bus voltage (VB), the series voltage injected and the dc link voltage Vdc. The 60-pulse VSC generates less harmonic distortion and reduces power quality problems in comparison to other converters such as (6,12,24 and 36) pulse. In the synchronous reference frame, a complete model of a GUPFC has been presented and control circuits for the shunt and two series converters have been described. The simulated results presented confirm that the performance of the proposed GUPFC is satisfactory for active and reactive power flow control and independent shunt reactive compensation.

 REFERENCES:

[1] K. K. Sen, “SSSC-static synchronous series compensator. Theory, modeling and application”, IEEE Transactions on Power Delivery, Vol. 13, No. 1, pp. 241-246, January 1998.

[2] B. Fardanesh, B. Shperling, E. Uzunovic, and S. Zelingher, “Multi-Converter FACTS Devices: The Generalized Unified Power Flow Controller (GUPFC),” in IEEE 2000 PES Summer Meeting, Seattle, USA, July 2000.

[3] N. G. Hingorani and L. Gyugyi, “Understanding FACTS, Concepts and Technology of Flexible AC Transmission Systems. Pscataway, NJ: IEEE Press. 2000.

[4] X. P. Zang, “Advanced Modeling of the Multicontrol Func-tional Static Synchronous Series Compensator (SSSC) in Newton Power Flow” , IEEE Transactions on Power Systems, Vol. 20, No. 4, pp. 1410-1416, November 2005,

[5] A. H. Norouzi and A. M. Sharaf, Two Control Schemes to Enhance the Dynamic Performance of the Statcom and Sssc”, IEEE Transactions on Power Delivery, Vol. 20, No. 1, pp. 435-442, January 2005.

 

 

Adaptive PI Control of STATCOM for Voltage Regulation

ABSTRACT:

STATCOM can provide fast and efficient reactive power support to maintain power system voltage stability. In the literature, various STATCOM control methods have been discussed including many applications of proportional-integral (PI) controllers. However, these previous works obtain the PI gains via a trial-and-error approach or extensive studies with a tradeoff of performance and applicability. Hence, control parameters for the optimal performance at a given operating point may not be effective at a different operating point. This paper proposes a new control model based on adaptive PI control, which can self-adjust the control gains during a disturbance such that the performance always matches a desired response, regardless of the change of operating condition. Since the adjustment is autonomous, this gives the plug-and-play capability for STATCOM operation. In the simulation test, the adaptive PI control shows consistent excellence under various operating conditions, such as different initial control gains, different load levels, change of transmission network, consecutive disturbances, and a severe disturbance. In contrast, the conventional STATCOM control with tuned, fixed PI gains usually perform fine in the original system, but may not perform as efficient as the proposed control method when there is a change of system conditions.

KEYWORDS:
1. Adaptive control
2. Plug and play
3. Proportional-integral (PI) control
4. Reactive power compensation
5. STATCOM
6. Voltage stability.

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:
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Figure 1 Studied system

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Fig.2 Results of (a) voltages and (b) output reactive power using the same network and loads as in the original system.
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Fig.3 Results of using the same network and loads as in the original system.
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Fig. 4. Results of (a) voltages and (b) output reactive power with changed PI control gains
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Fig. 5. Results of (a) voltages and (b) output reactive power with a change of load
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Fig. 6. Results of with changed PI control gains.
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Fig. 7. Results of α with a change of load.
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Fig. 8. Results of α(a) voltages and (b) output reactive power with a change of transmission network.
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Fig. 9. Results of α with a change of transmission network.
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Fig. 10. Results of α (a) voltages and (b) output reactive power with two consecutive disturbances.
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Fig. 11. Results of α with two consecutive disturbances.

CONCLUSION:
In the literature, various STATCOM control methods have been discussed including many applications of PI controllers. However, these previous works obtain the PI gains via a trialand- error approach or extensive studies with a tradeoff of performance and applicability. Hence, control parameters for the optimal performance at a given operating point may not always be effective at a different operating point. To address the challenge, this paper proposes a new control model based on adaptive PI control, which can self-adjust the control gains dynamically during disturbances so that the performance always matches a desired response, regardless of the change of operating condition. Since the adjustment is autonomous, this gives the “plug-and-play” capability for STATCOM operation.
In the simulation study, the proposed adaptive PI control for STATCOMis compared with the conventional STATCOM control with pretuned fixed PI gains to verify the advantages of the proposed method. The results show that the adaptive PI control gives consistently excellent performance under various operating conditions, such as different initial control gains, different load levels, change of the transmission network, consecutive disturbances, and a severe disturbance. In contrast, the conventional STATCOM control with fixed PI gains has acceptable performance in the original system, but may not perform as efficient as the proposed control method when there is a change of system conditions.
Future work may lie in the investigation of multiple STATCOMs since the interaction among different STATCOMs may affect each other. Also, the extension to other power system control problems can be explored.

REFERENCES:
[1] F. Li, J. D. Kueck, D. T. Rizy, and T. King, “A preliminary analysis of the economics of using distributed energy as a source of reactive power supply,” Oak Ridge, TN, USA, First Quart. Rep. Fiscal Year, Apr. 2006, Oak Ridge Nat. Lab.
[2] A. Jain, K. Joshi, A. Behal, and N. Mohan, “Voltage regulation with STATCOMs:Modeling, control and results,” IEEE Trans. Power Del., vol. 21, no. 2, pp. 726–735, Apr. 2006.
[3] D. Soto and R. Pena, “Nonlinear control strategies for cascaded multilevel STATCOMs,” IEEE Trans. Power Del., vol. 19, no. 4, pp. 1919–1927, Oct. 2004.
[4] F. Liu, S. Mei, Q. Lu, Y. Ni, F. F. Wu, and A. Yokoyama, “The nonlinear internal control of STATCOM: Theory and application,” Int. J. Elect. Power Energy Syst., vol. 25, no. 6, pp. 421–430, 2003.
[5] C. Hochgraf and R. H. Lasseter, “STATCOM controls for operation with unbalanced voltage,” IEEE Trans. Power Del., vol. 13, no. 2, pp. 538–544, Apr. 1998.