Performance Analysis of Shunt Active Filter under different loading and Distorted Voltage condition 4/22/2016 1 Prof. Parikshit G. Jamdade Department of Electrical Engineering, PVG’s College of Engineering & Technology, Pune Prof. Shrinivas G. Jamdade Department of Physics, Nowrosjee Wadia College, Pune Shri. Santosh Patil PG Student, Department of Electrical Engineering, PVG’s College of Engineering & Technology, Pune Power Quality issues 1] Voltage swells 2] Voltage sags 3] Voltage interruption 4] Frequency variation 5] Voltage unbalance 6] Harmonics Harmonics Sources in Electrical Systems 1] Fluorescent Lamps (3 th ,5 th ,7 th ,9 th ) 2] SMPS used in computer systems 3] Electrical furnace (5 th & 7 th ) 4] HVDC systems 12h ± 1 (11 th & 13 th ) 5] Adjustable speed drives (ASDs) 6] 5 th &7 th order harmonics are high. 7] AC/DC converters and Inverters Mitigation Techniques 1] Passive filters 2] Active filters Series active filter, Shunt active filter, Hybrid filter
Transcript
Performance Analysis of Shunt Active Filter under different loading and Distorted Voltage condition
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Prof. Parikshit G. JamdadeDepartment of Electrical Engineering, PVG’s College of Engineering & Technology, Pune Prof. Shrinivas G. JamdadeDepartment of Physics, Nowrosjee Wadia College, Pune Shri. Santosh PatilPG Student, Department of Electrical Engineering, PVG’s College of Engineering & Technology, Pune
Power Quality issues 1] Voltage swells 2] Voltage sags3] Voltage interruption 4] Frequency variation 5] Voltage unbalance 6] Harmonics Harmonics Sources in Electrical Systems1] Fluorescent Lamps (3th ,5th ,7th ,9th ) 2] SMPS used in computer systems3] Electrical furnace (5th & 7th ) 4] HVDC systems 12h ± 1 (11th & 13th )5] Adjustable speed drives (ASDs) 6] 5th &7th order harmonics are high.7] AC/DC converters and InvertersMitigation Techniques 1] Passive filters 2] Active filters
Series active filter, Shunt active filter, Hybrid filter
Principle of Shunt Current Compensation
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The principle of the shunt filter is to
produce harmonic currents equal in
magnitude but opposite in-phase to the
harmonics that are present in power
system. This compensating harmonic
current can be produced, when
I(comp) = I(load) - I(source)
Instantaneous Real and Reactive Power (p & q) Theorysource voltage and load currents are transformed into Clerk’s components (α-β-0) while instantaneous real & reactive powers (p & q) are calculated in α-β frame of reference. These components are used get reference currents for compensation of reactive power and oscillatory component of instantaneous active power. To compensate the oscillating component of instantaneous active power, a low pass filter (LPF) is used and reactive power is compensated by equating it to zero (q=0). The hysteresis current controller receives these reference currents and generates switching signals for the voltage source inverter to generate compensating currents. Figure shows the block diagram for Instantaneous Reactive Power scheme. To regulate the dc input capacitor voltage fed to VSI, a PI regulator is used. The error between reference dc capacitor voltage and actual capacitor voltage is fed to the PI regulator. Output of PI controller, which accounts for loss component [8], is added with averaged real power in α-β reference frame for maintaining dc capacitor voltage at its reference value.
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Reference Current CalculationBy using Clarke Transformation, phase voltages abc are transformed into
Here, 3 phase, 3 wire supply system is used, so that zero sequence component is consider to be zero. Similarly for the phase currents,
Where, α and β , axes are the orthogonal coordinates.Instantaneous real and reactive powers are given as
Instantaneous active and reactive powers p and q can be decomposed into an average (dc) and anoscillatory component as follows
p = Mean of Instantaneous real power that is transferred from source to load through a-b-c coordinates.͠p = Alternating value of instantaneous real power which is exchanged between power source and load.͞q = Mean of instantaneous imaginary power exchanged between source and load.͠q = Alternating component of instantaneous reactive power exchanged between source and load.
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To compensate the Instantaneous Reactive power value of ‘q’ taken as zero. (q=0)To compensate Oscillatory component of the instantaneous active power, LPF connected. Therefore, the reference source currents i*α and i* β in α–β coordinate are expressed as
Inverse Clarke Transformation implemented to covert α-β quantities into a-b-c quantities,
AdvantagesEasily implementable. Excellent steady-state performance with ideal supply voltage.Disadvantages Large number of voltage and current transducers are required. This method is poor in compensation of harmonic current if source voltages are not symmetrical.Delay in compensation.
Synchronous Reference Frame (d-q) THEORYSRF theory is based on the transformation of currents in synchronously rotating d–q frame. Current components in d-q coordinates are generated by using Park’s Transformation and ‘θ’ as a transformation angle is obtained by phase locked loop.
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Reference Current GenerationSRF theory is based on the transformation of currents in synchronously rotating d–q frame using Park’s Transformation as follows,
These currents in d-q are decomposed into average current and oscillatory Current.
A low pass filter is used to bypass the oscillatory component of d-q frames and reference currents in
terms of d-q frames are as follows filter is,
Inverse Parks transformation is taken to convert reference current from d-q frame to a-b-c coordinates,
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Advantage The reference currents are derived directly from the real load currents without using source
voltages in the calculation. Reference current calculations are accurate under unbalanced or distorted voltage conditions. Satisfactorily work under unbalanced and distorted voltage condition as compared to p-q theory.
hence increasing the robustness and performance.Disadvantages Large number of voltage and current sensors are required. Delay in compensation. (Low pass filter and PLL)DC bus Voltage ControlThere are two main purposes of DC capacitor used, To maintain constant DC voltageIt serves as energy storage device to supply real power difference between source and load. • When Vdc > Vref active filter required to inject the power.• When Vdc < Vref active filter required to absorb the power.
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Hysteresis Current Control TechniqueUpper switch off and lower switch on : (Iact-Iref) ≥ HBLower switch off and upper switch on : (Iact-Iref) ≤ - HB
AdvantagesFixed hysteresis band is very simple and easy to implement.Excellent dynamic performance.Fast response.Inherent peak current limiting capability.Good accuracy. DisadvantagesThe switching frequency varies during fundamental period.Due to variable switching frequency, switching losses are increases
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Power factor of the system under different conditions
Input Power Factor Cos ϕ Before compensation After compensation
IRP Theory SRF Theory
Case 1 0.9484 lag 0.9987 lag 0.9992 lag
Case 2 0.9473 lag 0.9991 lag 0.9948 lag
Case 3 0.9678 lag 0.9990 lag 0.9932 lag
Active Power and Reactive power of the system under different conditions
System under Before Compensation After compensation
Balanced Loading condition Unbalanced Loading condition Distorted Voltage condition
SRF Theory
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Balanced Loading condition Unbalanced Loading condition Distorted Voltage condition
References
1] Sudhakar kothuru, Appala Naidu.k, Suresh. Y, J Kotturu, “Investigation on Shunt Active Filter with P-QTheory” International Conference on Circuits, Power and Computing Technologies, IEEE, 2013
2] Kakoli Bhattacharjee, “Harmonic Mitigation by SRF Theory Based Active Power Filter using AdaptiveHysteresis Control” IEEE Power and Energy Systems: Towards Sustainable Energy, 2014.
3] Jamdade P. G., Jamdade S. G. and S. V. Patil, “ Assessment of Power Coefficient of an Offline WindTurbine Generator System”, Electronic Journal of Energy and Environment, Vol. 1, No. 3, December2013.
