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This paper deals with the performance of unified power quality conditioner (UPQC) based on current source converter (CSC) topology. UPQC is used to mitigate the power quality problems like harmonics and sag. The shunt and series active filter performs the simultaneous elimination of current and voltage problems. The power fed is linked through common DC link and maintains constant real power exchange. The DC link is connected through the reactor. The real power supply is given by the photovoltaic system for the compensation of power quality problems. The reference current and voltage generation for shunt and series converter is based on phase locked loop and synchronous reference frame theory. The proposed UPQC-CSC design has superior performance for mitigating the power quality problems.

The main impact in the power distribution system is the quality of power, which causes more distortion in the source due to using nonlinear loads (power electronics loads). The main cause for distortion is harmonics, notching, and interharmonics. Distortion is that the fundamental frequency sine wave is represented as super position of all harmonic frequency sine waves on fundamental sine wave. The usage of power electronics loads is increased day by day, while considering that industries power electronics drives are used for the automation of the industries. To compensate the distortion in the system, passive filters were used and while using the passive filters particular harmonic range is only eliminated. In order to overcome the drawbacks of passive filter, for the elimination of power quality problems, active filters were used.

Power quality problems are harmonics, sag, and swell which are mitigated by the active filters by the configuration of dynamic voltage restorer (DVR), distribution-static synchronous compensator (D-STATCOM), and unified power quality conditioner (UPQC) [

The unified power quality conditioner is commonly called UPQC. The design configuration is based on the connection of series and shunt inverters. In this, the design configuration is right series and left shunt with the current source converter (CSC) [

It reduces the harmonics in the supply current, so that it can improve utility current quality for nonlinear loads.

UPQC provides the VAR requirement of the load, so that the supply voltage and current are always in phase; therefore, no additional power factor correction equipment is required.

UPQC maintains load end voltage at the rated value even in the presence of supply voltage sag.

The design configuration of UPQC-CSC [

The design configuration of UPQC-CSC.

The control strategy for the unified power quality conditioner is based on the synchronous reference frame (SRF) [

Control block diagram.

The control strategy of the series controller is achieved through the synchronous reference frame theory. In this, the series controller gets the reference signal for the generation of pulse for the three-phase converter, by comparing the source voltage with distortion and constant voltage. The source voltage

Simulation of synchronous reference frame theory based series controller.

The shunt converter has the function of compensating the current related problems. Along with the shunt controller, DC link voltage is maintained. The

Simulation of shunt controller.

The direct current link controller has the PI controller in which the constant voltage is given as the set point and the measured voltage is given for the comparison to maintain the constant voltage. The PV array is attached with the DC link for injection. The DC link controller is shown in Figure

DC link controller.

The UPQC-CSC has the reactor as the DC link for the series and shunt converter and is controlled by the synchronous reference frame (SRF) theory and the pulse is generated by the hysteresis band controller. The shunt and series converters have the function of compensating current and voltage problems, respectively. The simulation of UPQC-CSC is shown in Figure

UPQC-CSC simulation diagram.

Output of source voltage and current and load voltage and current waveform.

PCC voltage with sag, compensating voltage and voltage after compensation.

Shunt injection for THD compensation.

Series injection for sag compensation.

Consider

source voltage: 415 V, 50 Hz;

load parameters:

resistive load: 10 KΩ;

inductive load: 2 mH;

RLC load: 10 KW;

shunt inverter side:

LC filter: 3.5 mH, 5 Ω, and 10

series inverter side:

LC filter: 12

DC link reactor:

for UPQC-CSC: 200 mH;

solar voltage: 727.1 V.

Figure

The compensation of the voltage related problems is done by the series active filter to maintain the system voltage 1 P.U. By using the SRF theory even a minor disturbance in the system is sensed and compensation is done; Figure

Total harmonics distortion (THD in %).

Current source converter | |||
---|---|---|---|

H |
Source voltage |
Load voltage |
Load current |

H | 0.97 | 0.99 | 0.04 |

H3 | 0.28 | 0.08 | 0.08 |

H5 | 0.09 | 0.05 | 0.06 |

H7 | 0.03 | 0.06 | 0.02 |

H9 | 0.03 | 0.04 | 0.04 |

H11 | 0.02 | 0.03 | 0.06 |

THD | 0.89 | 0.45 | 0.17 |

The Fourier fast transform analysis graph for the source voltage THD of about 0.89% is shown in Figure

Source voltage THD graph.

The Fourier fast transform analysis graph for the load voltage with the nonlinear loading conditions of about 0.45% is shown in Figure

Load voltage THD graph.

The Fourier fast transform analysis graph for the load current with the nonlinear loading conditions of about 0.17% is shown in Figure

Load current THD graph.

In this paper, synchronous reference frame theory based control method is implemented to control the working of unified power quality conditioner based on current source converter topology. The simulation results show that the device is capable of compensating the current harmonics under unbalanced and nonlinear load conditions, simultaneously mitigating voltage sag and swell. The proposed UPQC-CSC design has superior performance for mitigating the power quality problems. The series converter is capable of mitigating the voltage related problems and shunt converter is capable of mitigating the harmonics.

The authors declare that there is no conflict of interests regarding the publication of this paper.