26-10-2010, 06:24 PM
StatComs With Capacitive Energy Storage for Reduction of Voltage Phase Jumps in Weak Networks
Presented By
JOYAL K RAJ
Roll No. 119
EEE
College Of Engineering, Trivandrum
2007-11 Batch
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Questionnaire
What is StatCom?
What is weak network?
What is PCC?
What is voltage dip?
What is phase jump?
Contents
Load variation problems in weak networks
Previous methods
New method-A brief introduction
Working
Overview and inner control loop
Outer control loop
DC voltage control
Active power compensation scheme
Simulation and experimental result
Conclusions
References
Load variation problems
Tripping of motor drives in paper mill, steel mill etc.
Poor regulation
Change in power factor
Increase in production losses
Decrease in overall efficiency of the system
Previous methods and its limitations
Reactive power compensation
Limitation :- No solution for phase jump
Series voltage injection technique
Limitation :- Used only for particularly protected load
New method-A brief description
Active power compensation technique of StatCom is used in addition to reactive power compensation
Large capacitor bank connected on dc side of StatCom
StatCom control magnitude and phase angle of voltage
Total apparent power remains constant
Working
I) Overview and Inner Control Loop
VSC connected to the PCC through a phase reactor
The measured bus flux is resolved into a positive sequence , negative sequence, and an offset component using low pass filter method with a PLL operating on the positive sequence component
The converter current is also separated into the same three components using the angle from the PLL
The deadbeat current control loop calculates the flux change for next sampling interval that is required to get the desired current.
The flux modulator block generates the switching patterns that will deliver the required flux change
2)Outer Control Loop
The references for the offset components of the converter current are set to zero
Bus flux is controlled in this work instead of the bus voltage
For the negative sequence, both the d and q components of the bus flux are controlled to zero respectively by two PI controllers
The magnitude of the positive sequence bus flux is controlled close to the nominal value by another PI controller
The controller output provides the reference for the positive sequence reactive current
The output gives the reference for the positive sequence active current
Active Power Compensation
The connection and disconnection of the resistive load may represent the switching of large loads or large time-varying loads
The converter can keep the voltage magnitude deviation within a certain range by reactive power support
Connect an energy storage capacitor bank on the dc side
The active power compensation takes the active load as a feed-forward signal
Simulation and experimental result
Conclusion
Phase jumps and magnitude fluctuations of the voltage at the PCC can be reduced significantly with the additional active power
Beneficial to phase-sensitive loads,connected in a weak network with large time-varying loads
Simulation and experimental results verify that this scheme is fruitful.
Even though initial cost is high if the potential benefits are considered it is still an attractive solution
References
[1] Hailian Xie , Lennart Ängquist and Hans-Peter Nee,” Investigation of StatComs With Capacitive Energy Storage for Reduction of Voltage Phase Jumps in Weak Networks,” in IEEE Trans. Power Del., vol. 24, no. 1, pp. 217-225, Feb. 2009.
[2] J. D. Li, S. S. Choi, and D. M. Vilathgamuwa, “Impact of voltage phase jump on loads and its mitigation,” in Proc. 4th Int. Power Electronics and Motion Control Conf., 2004, pp. 1762–1766.
[3] J. E. R. Collins and A. Mansoor, “Effects of voltage sags on AC motor drives,” in Proc. IEEE Annual Textile, Fiber, and Film Industry Technical Conf., 1997.
[4] A. Sannino, M. Miller, and M. Bollen, “Overview of voltage sag mitigation,” in Proc. IEEE Power Eng. Soc. Winter Meeting, 2000, pp. 2872–2878.
Thank you
