Cascaded Control of Multilevel Converter based STATCOM for Power System Compensation of Load Variation


The static synchronous compensator (STATCOM) is used in power system network for improving the voltage of a particular bus and compensate the reactive power.It can be connected to particular bus as compensating device to improve the voltage profile and reactive power compensation. In this paper, a multi function controller is proposed and discussed. The control concept is based on a linearization of the d-q components with cascaded controller methods. The fundamental parameters are controlled with using of proportional and integral controller. In closed loop method seven level cascaded multilevel converter (CMC) is proposed to ensure the stable operation for damping of power system oscillations and load variation.


  1. FACTS
  2. PWM
  3. CMC



 Figure 1.STATCOM network connection.


Figure 2. Load terminal dq0 Currents with Load variation

Figure 3. Source terminal dq0 Currents with Load variation.

Figure 4. Iqref output for load rejection.

Figure 5. Source Voltage for load rejection with AGC.

Figure 6. THD of output Voltage of Cascaded Multilevel converter.

Figure 7. THD of output Current of Cascaded Multilevel Converter

Figure 8.Source Active and Reactive power.

Figure 9. Power factor in Load and Source Bus

Figure 10.Three phase Supply Voltage of multilevel converter.


The cascaded controller is designed for seven level CMC based STATCOM. This control scheme regulates the capacitor voltage of the STATCOM and maintain rated supply voltage for any load variation with in the rated value. It has been shown that the CMC is able to reduce the THD values of output voltage and current effectively. The CMC based STATCOM ensures that compensate the reactive power and reduce the harmonics in output of STATCOM.


[1] N. Hingorani and L. Gyugyi, 2000, “Understanding FACTS: Concepts and Technology Flexible AC Transmission Systems”, New York: IEEE Press.

[2] P. Lehn and M. Iravani, Oct.1998, “Experimental evaluation of STATCOM closed loop dynamics”, IEEE Trans. Power Delivery, vol.13, pp.1378-1384.

[3] Mahesh K.Mishra and Arindam Ghosh, Jan 2003, ”Operation of a D-STATCOM in Voltage Control Mode”, IEEE Trans. Power Delivery, vol.18, pp.258-264.

[4] Arindam Ghosh, Avinash Joshi, Jan 2000, ”A New Approach to Load Balancing and Power Factor Correction in Power Distribution System”, IEEE Trans. Power Delivery, vol.15, No.1, pp. 417-422.

[5] Arindam Ghosh, Gerard Ledwich, Oct 2003,”Load Compensating DSTATCOM in Weak AC Systems”, IEEE Trans. Power Delivery, vol.18, No.4, pp.1302-1309.


Verification of New Family for Cascade Multilevel Inverters with Reduction of Components



This paper presents a new group for multilevel converter that operates as symmetric and asymmetric state. The proposed multilevel converter generates DC voltage levels similar to other topologies with less number of semiconductor switches. It results in the reduction of the number of switches, losses, installation area, and converter cost. To verify the voltage injection capabilities of the proposed inverter, the proposed topology is used in dynamic voltage restorer (DVR) to restore load voltage. The operation and performance of the proposed multilevel converters are verified by simulation using SIMULINK/MATLAB and experimental results.


  1. Cascaded multilevel converter,
  2. New topology
  3. Reduction of components
  4. DVR




Fig. 1. Proposed cascade topology

 Fig. 2. Proposed topology with four DC voltage sources.





Fig. 3. (a) Supply voltage, (b) DVR injection voltage, and (c) load voltage for the three-phase balanced voltage sag.


Fig. 4. Output phase voltage in fault (sag) time




Fig. 5. (a) Supply voltage, (b) DVR injection voltage, and (c) load voltage for the three-phase balanced voltage swell.


Fig. 6. Output phase voltage in fault (swell) time.


 In this paper, a novel topology was presented for multilevel converter, which has reduced number of switches. The suggested topology needs fewer switches for realizing voltages for the same levels of output voltages. This point reduces the installation area and the number of gate driver circuits. Therefore, the cost of the suggested topology is less than the conventional topology. Based on the presented switching algorithm, the multilevel inverter generates near sinusoidal output voltage, causing very low harmonic distortion. The suggested inverter used in DVR does not require any coupling series transformer and has lower cost, smaller size, and higher performance and efficiency. Simulation results verified the validity of the presented concept.


[1] Z. Pan, F.Z. Peng, “Harmonics optimization of the voltage balancing control for multilevel converter/ inverter systems”, IEEE Trans. Power Electronics, pp. 211-218, 2006.

[2] L.M. Tolbert, F. Z. Peng, T. Cunnyngham, J. N. Chiasson, “Charge Balance Control Schemes for Cascade Multilevel Converter in Hybrid Electric Vehicles,” IEEE Trans. Industrial Electronics, Vol. 49, No. 5, pp. 1058-1064, Oct. 2002.

[3] S. Mariethoz, A. Rufer, “New configurations for the three-phase asymmetrical multilevel inverter,” in Proceeding of the IEEE 39th Annual Industry Applications Conference, pp. 828-835, Oct. 2004.

[4] J.Rodriguez, J.S. Lai, F.Z. Peng, “Multilevel Inverter: A Survey of Topologies, Controls, and applications”, IEEE Trans. on Industrial Electronics, Vol. 49, No. 4, August. 2002.

[5] J.S. Lai, F.Z. Peng, “Multilevel Converters-A New Breed of power Converters”, IEEE Trans. Industry Application, Vol. 32, No. 3, pp. 509-517, MAY/JUNE.1996