Asmany power quality specialists offer regard for tackling power quality issues,these issues are raised up because of the use of reactive loads and non-linearloads. This load makes reactive power burden and harmonic issue. This harmonicpollution deteriorates the quality of power at transmission side anddistribution side. Typically the term power quality imply keeping up asinusoidal waveform of bus voltages at evaluated voltage and frequency.Electric power quality phenomenon basically incorporate unbalance voltage andcurrent flicker, harmonics, voltage sag, swell, and power interruption1, 2. One of the mainresponsibilities of a utility system is to supply electric power in the form ofsinusoidal voltage and currents with appropriate magnitudes and frequency forthe customers at the points of common coupling (PCC). Although the generatedvoltage of synchronous machines in power plants are almost sinusoidal, someunsighted conditions such as lightning and short circuit faults and non linearloads cause steady state error or transient voltages and current disturbances.
For example, electric arc furnaces, ASDs, etc causes voltage fluctuations,power electronic converters generate current harmonics and distort voltagewaveforms, and short circuits faults result in voltage sags and swells 3-6. On the other hand mostcustomer loads such as office equipments, PLCs, microcontrollers, motorstarting, power electronics converters, and other industrial non linear and sensitiveloads are sensitive and unprotected to power quality disturbances and theirproper operation depends on the quality of the voltage that is supplied tothem.Tomitigate voltage and current related problems various types of custom powerdevices can be used.
All custom power devices such as DynamicVoltage Regulator (DVR), Distribution Static Compensator (DSTATCOM), and UPQCcan mitigate voltage sag/swell, while compensation capability of UPQC is best.The UPQC is a combination of series and shunt compensators, which are composedof IGBT based VSIs act as active connected in cascade via a common DC linkcapacitor. Both converters are fired by gating signals from PWM generator. Thegate pulses are generated by a dq0 based PWM control technique.
It is thecontrol strategy which decides the efficiency of a particular system. Byusing a unified power quality conditioner (UPQC) 1, it is possible to mitigate both the voltage quality relatedproblems and current quality issues by using the series and shunt compensatorsfor the load and from the utility grid respectively. The main purpose of a UPQC is to compensatefor supply voltage and current related problems. The device UPQC has two activepower filters; series active power filter and shunt active power filter tomitigate voltage and current related problems respectively. It has to be connectedin such a manner at the point of common coupling (PCC). These APFs are powerelectronic devices based on IGBT based VSIs which are used to replace thedistorted wave coming from the load by injecting negative harmonics to thenetwork.
The series active power filter can applied under non-sinusoidal supplyvoltage at the PCC due to harmonics caused by non-linear loads. The shuntactive power filter is implemented to compensate harmonic current at supply andload side and reactive power supportUPQCcan absorb active power or inject active power. The shunt APF can replace/ balancethe source currents by injecting negative and zero sequence components andcontrol the power factor by injecting the required reactive current. The seriesconnected APFF can replace/ balance the voltages at the load bus by injectingnegative and zero sequence voltages and maintain the magnitude of the load busvoltage by injecting the required active and reactive components.Thispaper deals with the effectiveness of UPQC for distribution network withnonlinear load under normal and faulted conditions.
The proposed controltechnique has been evaluated under different load conditions using MATLABsoftware.