14-02-2013, 04:34 PM
Single phase Active harmonic filters for Harmonic elimination and Power Factor correction for Distributed loads
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Abstract:
With advancement in technology,
there has been an increase in usage of power
electronic converters/loads for various industrial
applications and process automation. Power
electronic loads inject harmonic currents into the
utility causing overheating of power transformers and
neutral wires, unpredictable performance of
protection systems etc. In addition, electric
resonances in such loads can also cause other
undesirable phenomena like voltage fluctuations,
radio frequency interference (RFI) etc. To mitigate
these undesirable effects, a new generation of power
electronics converter (Active Filters) is being
considered. Technical review of recent trends in the
area of active filters is presented in this paper.
Finally, this paper discusses the trends in the design
of active filters and the factors affecting them.
Introduction:
Technology advancement in last three decades has
led to increase in usage for power electronic
converters for various industrial, commercial and
residential applications. These static converters draw
non sinusoidal currents and hence polluting the utility
supply due to the characteristics and noncharacteristic
harmonics generated by them.
Harmonics have adverse effect on the power system
network and result in
Overheating of neutral conductors, bus bar, lug
connections, motor control and switchgear,
which may affect current interrupting capabilities
Circuit breaker nuisance tripping, malfunction of
on-board breaker electronics, excessive arcing,
improper fuse operation or nuisance blown fuse
interruption (artificial heating, or “skin effect”)
AC motor torque pulsation, voltage sags,
notching; DC adjustable speed drives creating
high inrush currents
Overheating in transformers and cable systems,
insulation (dielectric) breakdown
Power factor capacitors becoming overloaded,
potential for resonance conditions
Control scheme for Single Phase AHF
IGBT based full bridge voltage source inverter
with a DC capacitor and a coupling inverter is
used as single phase active power filter. Fig 4
shows a single phase active power filter
connected in shunt to AC mains. For the
calculation of reactive and harmonic components
of the AC mains current, the load current is
sensed using a current transformer.
Experimental Implementation.
For the proof of concept an IGBT based 10 kVA
model is developed. The control is developed using
both analog and digital processor based approach.
Analog multiplier IC AD633JN is used along with
another operational amplifiers to generate the
compensating signals. This approach is simple but
the control circuit becomes complex with usage of
more components. Hence a Microchip based
microcontroller is used to generate the PWM pulses
for firing of IGBTs. Active harmonic filter is tested
for all the combinations of loads that is lagging load,
leading load, harmonics loads and composite loads.
For the harmonics loads, the voltage is also
intentionally made distorted (by introducing a variac
to supply the load) to show the effectiveness of AHF
in distorted voltages environment.
Conclusion
In this paper a single-phase active power filter
employed to correct the power factor of groups of
loads is presented. The full-bridge voltage source
inverter controlled through the sensor of the AC load
current is used as the active filter. Sine multiplication
theory is implemented using microcontroller.