**ABSTRACT:**** **

This paper deals with an implementation of a new control algorithm for a three-phase shunt active filter to regulate load terminal voltage, eliminate harmonics, correct supply power-factor, and balance the nonlinear unbalanced loads. A three-phase insulated gate bipolar transistor (IGBT) based current controlled voltage source inverter (CC-VSI) with a dc bus capacitor is used as an active filter (AF). The control algorithm of the AF uses two closed loop PI controllers.

The dc bus voltage of the AF and three-phase supply voltages are used as feed back signals in the PI controllers. The control algorithm of the AF provides three-phase reference supply currents. A carrier wave pulse width modulation (PWM) current controller is employed over the reference and sensed supply currents to generate gating pulses of IGBT’s of the AF. Test results are presented and discussed to demonstrate the voltage regulation, harmonic elimination, power-factor correction and load balancing capabilities of the AF system.

**KEYWORDS:**

- Active filter
- Harmonic compensation
- Load balancing
- Power-factor correction
- Voltage regulation

** ****SOFTWARE:** MATLAB/SIMULINK

**BLOCK DIAGRAM:**

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Fig. 1. Fundamental building block of the active filter.

** ****EXPECTED SIMULATION RESULTS:**

** **Fig. 2. Performance of the AF system under switch IN and steady state conditions with a three-phase nonlinear load.

Fig. 3. Steady state response of the AF for voltage rgulation and harmonic elimination with a three-phase nonlinear load.

Fig. 4. Steady state response of the AF for voltage regulation, harmonic elimination, and load balancing with a single-phase nonlinear load.

Fig. 5. Switch IN response of the AF for voltage regulation, harmonic elimination with a three-phase nonlinear load.

Fig. 6. Switch IN response of the AF for voltage regulation, harmonic elimination and load balancing with a single-phase nonlinear load.

Fig. 7. Dynamic response of the AF for voltage regulation, harmonic elimination, and load balancing under the load change from three-phase to single-phase.

Fig. 8. Dynamic response of the AF for voltage regulation, harmonic elimination, and load balancing under the load change from single-phase to three-phase.

Fig. 9. Steady state response of the AF for power-factor correction, harmonic elimination with a three-phase nonlinear load.

Fig. 10. Steady state response of the AF for power-factor correction, harmonic elimination, and load balancing with a single-phase nonlinear load.

Fig. 11. Switch IN response of the AF for power-factor correction and harmonic elimination with a three-phase nonlinear load.

Fig. 12. Switch IN response of the AF for power-factor correction, harmonic elimination, and load balancing with a single-phase nonlinear load.

** ****CONCLUSION:**

** **An improved control algorithm of the AF system has been implemented on a DSP system for voltage regulation/power-factor correction, harmonic elimination and load balancing of nonlinear loads. Dynamic and steady state performances of the AF system have been observed under different operating conditions of the load. The performance of the AF system has been found to be excellent. The AF system has been found capable of improving the power quality, voltage profile, power-factor correction, harmonic elimination and balancing the nonlinear loads.

The proposed control algorithm of the AF has an inherent property to provide a self-supporting dc bus and requires less number of current sensors resulting in an over all cost reduction. It has been found that for voltage regulation and power-factor correction to unity are two different things and can not be achieved simultaneously.

However, a proper weight-age to in-phase and quadrature components of the supply current can provide a reasonably good level of performance and voltage at PCC can be regulated with a leading power-factor near to unity. It has been found that the AF system reduces harmonics in the voltage at PCC and the supply currents well below the mark of 5% specified in IEEE-519 standard.

**REFERENCES:**

[1] L. Gyugyi and E. C. Strycula, “Active AC power filters,” in *Proc.IEEE-IAS Annu. Meeting Record*, 1976, pp. 529–535.

[2] T. J. E. Miller, *Reactive Power Control in Electric Systems*. Toronto,Ont., Canada: Wiley, 1982.

[3] J. F. Tremayne, “Impedance and phase balancing of main-frequency induction furnaces,” *Proc. Inst. Elect. Eng. B*, pt. B, vol. 130, no. 3, pp. 161–170, May 1983.

[4] H. Akagi, Y. Kanazawa, and A. Nabae, “Instantaneous reactive power compensators comprising switching devices without energy storage components,” *IEEE Trans. Ind. Applicat.*, vol. IA-20, pp. 625–630, May/June 1984.

[5] T. A. Kneschki, “Control of utility system unbalance caused by single-phase electric traction,” *IEEE Trans. Ind. Applicat.*, vol. IA-21, pp. 1559–1570, Nov./Dec. 1985.