Power Quality Improvement of Unbalanced Power System with Distributed Generation Units

Power Quality Improvement of Unbalanced Power System with

Distributed Generation Units

ABSTRACT:

This paper presents a power electronic system for improving the power quality of the unbalanced distributed generation units in three-phase four-wire system. In the system, small renewable power generation units, such as small PV generator, small wind turbines may be configured as single phase generation units. The random nature of renewable power sources may result in significant unbalance in the power network and affect the power quality. An electronic converter system is proposed to correct the system unbalance and harmonics so as to deal with the power quality problems. The operation and control of the converter are described. Simulation results have demonstrated that the system can effectively correct the unbalance and enhance the system power quality.

KEYWORDS:

1.      Component

2.      Distributed generation

3.      Voltage source converter

4.      Power Quality Compensator

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig.1. Instantaneous power relationship in a system and a parallel connected compensator with energy storage system

Fig.2.The connection of VSC in a three-phase four-wire system

EXPECTED SIMULATION RESULTS:

Fig.3. Feeder 1 currents and power

 

Fig.4. Feeder 2 currents and power

Fig.5. Grid currents and power

                      

Fig.6. Compensator currents and power

                     

Fig.7. Grid current fundamental component

CONCLUSION:

This paper presents a study of using a voltage source converter (VSC) based compensator to deal with the unbalance and harmonic distortion issue in the low voltage system with embedded single phase DG units. The VSC performs the functions of an interface for an energy storage system as well. The VSC is connected in parallel with the system to control the energy storage system, correct the system unbalance, remove the harmonic components and minimize the neutral current of the supply system.

REFERENCES:

[1] G..Strbac, “Impact of dispersed generation on distribution systems: a European perspective” Power Engineering Society Winter Meeting, 2002. IEEE, vol. 1, . 2002, pp. 118 –120.

[2] M. Dussart, P. Lauwers, S. Magnus, Y. Laperches, “Connection requirements for dispersed generation: evolutions of existing requirements and need for further standardization” Electricity Distribution, 2001. Part 1: Contributions. CIRED2001, Conference Publication No. 482, © IEE2001

[3] J.A.P. Lopes, “Integration of dispersed generation on distribution networks-impact studies” Power Engineering Society Winter Meeting, 2002. IEEE, vol. 1, 2002, pp. 323 –328.

[4] F. Blaabjerg, Z. Chen, S. B Kjaer, “Power Electronics as Efficient Interface in Dispersed Power Generation Systems”, IEEE Transactions on Power Electronics, vol. 19, Issue: 5, Sept. 2004, pp.1184- 1194.

[5] Z. Chen, “Three Phase Four Wire System Power Redistribution Using A Power Electronic Converter”, Power Engineering Letters, IEEE Power Eng. Rev. October, 2000, pp. 47-49.

Transient Stability Enhancement by DSSC with Fuzzy Supplementary Controller

Transient Stability Enhancement by DSSC with

Fuzzy Supplementary Controller

ABSTRACT

 The distributed flexible alternative current transmission system (D-FACTS) is a recently developed FACTS technology. Distributed Static Series Compensator (DSSC) is one example of DFACTS devices. DSSC functions in the same way as a Static Synchronous Series Compensator (SSSC), but is smaller in size, lower in price, and possesses more capabilities. Likewise, DSSC lies in transmission lines in a distributed manner. In this work, we designed a fuzzy logic controller to use the DSSC for enhancing transient stability in a two-machine, two-area power system. The parameters of the fuzzy logic controller are varied widely by a suitable choice of membership function and parameters in the rule base. Simulation results demonstrate the effectiveness of the fuzzy controller for transient stability enhancement by DSSC.

KEYWORDS

1.      D-FACTS

2.       Simulation model

3.       DSSC

4.       Transient stability Fuzzy logic controller

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Fig. 1. Simulation model of two-machine system for transient stability study with DSSC.

Fig. 2. D-FACTS deployed on the power line.

Fig. 3. Circuit schematic of a DSSC module.

EXPECTED SIMULATION RESULTS:

Fig. 4. Changing the rotor angle difference (d_theta1_2) when the DSSCs entered the circuit.

             

Fig. 5. Changing the rotor angle difference (d_theta1_2) after the fault with DSSC (without supplementary fuzzy logic damping controller) and without DSSC.

 Fig. 6. Changing the angular speed of the machines after the fault with DSSC (without supplementary fuzzy logic damping controller) and without DSSC.

Fig.7. Rotor angle difference (d_theta1_2) deviation after the fault with FLC and classic controller.

Fig. 8. Machine voltage variation after the fault with FLC and classic controller.

Fig. 9. Rotor angle difference (d_theta1_2) deviation after the fault with FLC and classic damping controller and without damping controller.

Fig. 10. Machine voltage variation after the fault with FLC and classic damping controller and without damping controller.

Fig. 11. Variation of FLC output signal after the fault.

CONCLUSION:

In this study, we introduced a graphical-based simulation model of the DSSC. DSSC was placed in a sample two machine power system to increase transient stability. Simulation studies presented in the paper showed that when the DSSCs were out of service, the rotor angle between the machines (d_theta1_2) increased rapidly and two machines fell out of synchronism after fault clearing. However, when the DSSCs were in circuit, DSSCs stabilized the system even without specific controller. Subsequently, an FLC was added to the main control system of the DSSC in order to improve the transient stability margin of the system. The simulation results show that specific to this case, DSSC can stabilize the system under severe fault. Moreover, a comparative study between the FLC and conventional classic controller shows that the proposed FLC has better performance and influence in transient stability enhancement and oscillation damping

REFERENCES:

[1] Yi Guo, David J. Hil and Youyi Wang, “Global Transient Stability and Voltage Regulation for Power System,” IEEE Transaction On Power System, Vol. 16, No. 4, Nov. 2001.

[2] L. Gyugyi, “Dynamic compensation of ac transmission lines by solid-state synchronous voltage sources,” IEEE Trans. Power Delivery, 19(2), 1994, pp.904-911.

[3] P. Rao, M.L. Crow and Z.Young, “STATCOM control for power system voltage control application,” IEEE Trans. Power Delivery, 15, 2000, pp.1311-1317.

[4] H. Wang and F.Li, “Multivariable sampled regulators for the coordinated control of STATCOM ac and dc voltage,” IEE Proc. Gen. Tran. Dist., 147(2), 2000, pp. 93-98.

[5] A.H.M.A Rahim and M.F.Kandlawala, “Robust STATCOM voltage controller design using loop shaping technique,” Electric Power System Research, 68, 2004, pp.61-74.