**ABSTRACT**

The growing installation of distributed
generation (DG) units in low voltage distribution systems has popularized the
concept of nonlinear load harmonic current compensation using multi functional
DG interfacing converters. It is analyzed in this paper that the compensation
of local load harmonic current using a single DG interfacing converter may
cause the amplification of supply voltage harmonics to sensitive loads,
particularly when the main grid voltage is highly distorted. To address this
limitation, unlike the operation of conventional unified power quality
conditioners (UPQC) with series converter, a new simultaneous supply voltage
and grid current harmonic compensation strategy is proposed using coordinated
control of two shunt interfacing converters. Specifically, the first converter
is responsible for local load supply voltage harmonic suppression. The second
converter is used to mitigate the harmonic current produced by the interaction
between the first interfacing converter and the local nonlinear load. To
realize a simple control of parallel converters, a modified hybrid voltage and
current controller is also developed in the paper. By using this proposed
controller, the grid voltage phase-locked loop and the detection of the load
current and the supply voltage harmonics are unnecessary for both interfacing
converters. Thus, the computational load of interfacing converters can be
significantly reduced. Simulated and experimental results are captured to
validate the performance of the proposed topology and the control strategy.

**KEYWORDS:**

1.
Parallel converters

2.
Active power
filter

3.
Dynamic
voltage restorer

4.
LCL filter

5.
Resonance;
power quality

6.
Harmonic
detection

7.
Phase-locked
loop.

**SOFTWARE:**MATLAB/SIMULINK

**CIRCUIT DIAGRAM:**

Fig. 1. Diagram of the proposed
topology.

**EXPECTED SIMULATION RESULTS:**

Fig. 2. Only the local
load harmonic current is compensated. (From upper to lower: π

_{π π’ππππ¦}, πΌ_{π}, πΌ_{2}, πΌ_{πΏπππ})
Fig. 3. The harmonic
spectrum of grid current πΌ

_{π}in Fig. 11.
Fig. 4. The harmonic
spectrum of supply voltage π

_{π π’ππππ¦}in Fig. 11.
Fig. 5. Only the supply
voltage harmonic component is compensated. (From upper to lower: π

_{π π’ππππ¦}, πΌ_{π}, πΌ_{2}, πΌ_{πΏπππ})
Fig. 6. The harmonic
spectrum of grid current πΌ

_{π}in Fig. 14.
Fig. 7. The harmonic
spectrum of supply voltage π

_{π π’ππππ¦}in Fig. 14.**CONCLUSION**

When a single multi-functional
interfacing converter is adopted to compensate the harmonic current from local
nonlinear loads, the quality of supply voltage to local load can hardly be
improved at the same time, particular when the main grid voltage is distorted.
This paper discusses a novel coordinated voltage and current controller for
dual-converter system in which the local load is directly connected to the
shunt capacitor of the first converter. With the configuration, the quality of
supply voltage can be enhanced via a direct closed-loop harmonic voltage
control of filter capacitor voltage. At the same time, the harmonic current
caused by the nonlinear load and the first converter is compensated by the
second converter. Thus, the quality of the grid current and the supply voltage
are both significantly improved. To reduce the computational load of DG
interfacing converter, the coordinated voltage and current control without
using load current/supply voltage harmonic extractions or phase-lock loops is
developed to realize to coordinated control of parallel converters.

**REFERENCES**

.

[1]
B. Singh, K. AI-Haddad, A. Chandra, “A review of
active filters for power quality improvement,”

*IEEE Trans. Ind. Electron*., vol. 46, no. 5, pp. 960 - 971, May. 1999.
[2]
P. Acuna,
L. Moran, M. Rivera, J. Dixon, and J. Rodriguez, “Improved active power filter
performance for renewable power generation systems,”

*IEEE Trans*.*Power Electron*., vol. 29, no.2, pp. 687-694, Feb. 2013.
[3]
Y. W. Li, F. Blaabjerg, D. M. Vilathgamuwa, and
P. C. Loh, “Design and Comparison of High Performance Stationary-Frame
Controllers for DVR Implementation,”

*IEEE Trans. Power Electron*., vol. 22, pp. 602-612, Mar. 2007.
[4]
C. Meyer, R. W. DeDoncker, Y. W. Li, and F.
Blaabjerg, “Optimized Control Strategy for a Medium-Voltage DVR – Theoretical
Investigations and Experimental Results,”

*IEEE Trans. Power Electron.*, vol. 23, pp. 2746-2754, Nov. 2008.
[5]
F.
Blaabjerg, Z. Chen, and S. B. Kjaer, “Power electronics as efficient interface
in dispersed power generation systems,”

*IEEE Trans*.*Power Electron*., vol. 19, pp. 1184-1194, Sep. 2004.