Three-Level 48-Pulse STATCOM with Pulse Width Modulation

ABSTRACT:

 In this paper, a new control strategy of a three level 48-pulse static synchronous compensator (STATCOM) is proposed with a constant dc link voltage and pulse width modulation at fundamental frequency switching. The proposed STATCOM is realized using eight units of three-level voltage source converters (VSCs) to form a three-level 48-pulse STATCOM. The conduction angle of each three-level VSC is modulated to control the ac converter output voltage, which controls the reactive power of the STATCOM. A fuzzy logic controller is used to control the STATCOM. The dynamic performance of the STATCOM is studied for the control of the reference reactive power, the reference terminal voltage and under the switching of inductive and capacitive loads.

KEYWORDS:

  1. Fuzzy logic control (FLC)
  2. Static synchronous compensator (STATCOM)
  3. Voltage source converter (VSC)
  4. Flexible ac transmission system (FACTS)
  5. Power frequency switching (PFS)

 SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1 System configuration for simulation

 EXPECTED SIMULATION RESULTS:

 

 Fig. 2 a Dynamic performance of STATCOM for varying the reference reactive power. b Zoomed-in waveforms of the STATCOM ac current as well the dc current during a floating, b capacitive and c inductive operations

 

Fig. 3 Dynamic performance of STATCOM for varying the reference terminal voltage

Fig. 4 Dynamic performance of STATCOM by switching on inductive and capacitive loads

Fig. 5 a ac terminal voltage without STATCOM on switching non-linear load. b Dynamic performance of STATCOM and ac terminal voltage by switching on switching non-linear load

Fig. 6 Dynamic performance of STATCOM by switching on large value of apparent power

Fig. 7 Dynamic performance of STATCOM under short circuit of the upper half of the dc bus capacitance

Fig. 8 Dynamic performance of STATCOM under short circuit of the complete dc bus capacitance

Fig. 9 a Variation of the dc voltage with sudden load change using a PI and an FLC. b Variation of the ac terminal voltage with sudden load change using a PI and an FLC

CONCLUSION:

A new control strategy of a three-level 48-pulse STATCOM has been proposed with a constant dc link voltage and pulse width modulation at fundamental frequency switching. Its performance has been validated using MATLAB/Simulink. Simulation results have validated the satisfactory dynamic and steady performances of the proposed STATCOM operation. The harmonic content of the STATCOM current is found well below 5 % as per IEEE 519 standard [27].

 REFERENCES:

  1. T. Johns, A. Ter-Gazarian, D.F. Warne, Flexible ac transmission systems (FACTS), IEE Power Energy Series, the Institute of Electrical Engineers, London, UK, 1999
  2. N.G. Hingorani, L. Gyugyi, Understanding FACTS: Concepts and Technology of Flexible ac Transmission Systems (IEEE Press, 2000)
  3. R.M. Mathur, R.K. Verma, Thyristor-Based FACTS Controllers for Electrical Transmission Systems (Wiley-IEEE Press, 2002)
  4. K.R. Padiyar, FACTS Controllers in Power Transmission and Distribution (New Age International (P) Limited Publishers, India, 2007)
  5. K.K. Sen, Introduction to FACTS Controllers: Theory, Modeling and Applications (Wiley-IEEE Press, 2009)

 

Flexible AC transmission system (FACTS)

flexible alternating current transmission system (FACTS) is a system composed of static equipment used for the AC transmission of electrical energy. It is meant to enhance controll ability and increase power transfer capability of the network. It is generally a power electronics-based system.

FACTS is defined by the IEEE as “a power electronic based system and other static equipment that provide control of one or more AC transmission system parameters to enhance controll ability and increase power transfer capability.”

According to Siemens “FACTS Increase the reliability of AC grids and reduce power delivery costs. They improve transmission quality and efficiency of power

transmission by supplying inductive or reactive power to the grid.

In shunt compensation, power system is connected in shunt (parallel) with the FACTS. It works as a controllable current source. Shunt compensation is of two types:

Shunt capacitive compensation
This method is used to improve the power factor. Whenever an inductive load is connected to the transmission line, power factor lags because of lagging load current. To compensate, a shunt capacitor is connected which draws current leading the source voltage. The net result is improvement in power factor.
Shunt inductive compensation
This method is used either when charging the transmission line, or, when there is very low load at the receiving end. Due to very low, or no load – very low current flows through the transmission line. Shunt capacitance in the transmission line causes voltage amplification (Ferranti effect). The receiving end voltage may become double the sending end voltage (generally in case of very long transmission lines). To compensate, shunt inductors are connected across the transmission line. The power transfer capability is thereby increased depending upon the power equation