This paper proposes a Kalman filter (KF) based H∞ control scheme for a three phase shunt active power filter (SAPF) system. For the current control loop, a H∞ controller is designed with a mixed sensitivity approach for achieving stability and high disturbance rejection in the SAPF system. A new current reference scheme is also proposed that employs KF to avoid synchronization circuit and proportional integral (PI) controller loop resulting in a reliable and cost-effective SAPF system. This reference scheme can self-regulate the dc-link voltage by a fast and adaptive estimation of the source reference current with power system perturbations raised in source or load sides. The efficacy of the proposed KF-H∞ control algorithm is evaluated through comparison with an existing PI and PI plus vector PI (PI-PIVPI) algorithm and then validated with experimental studies pursued using a dSPACE1104. From the obtained experimental results, it is observed that the proposed SAPF significantly outperforms the existing PI-PIVPI in terms of exhibiting robustness to modeling uncertainties and insensitivity to grid perturbations such as harmonics, measurement noise and phase angle jump. Thus, the power quality improvement is achieved in terms of perfect current harmonics cancellation as well as power factor improvement.

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Performance Enhancement of Shunt Active Power
filter using a Kalman Filter based H∞ Control
Strategy
ABSTRACT
This paper proposes a Kalman filter (KF) based H∞ control scheme for a three phase shunt
active power filter (SAPF) system. For the current control loop, a H∞ controller is designed with
a mixed sensitivity approach for achieving stability and high disturbance rejection in the SAPF
system. A new current reference scheme is also proposed that employs KF to avoid
synchronization circuit and proportional integral (PI) controller loop resulting in a reliable and
cost-effective SAPF system. This reference scheme can self-regulate the dc-link voltage by a fast
and adaptive estimation of the source reference current with power system perturbations raised in
source or load sides. The efficacy of the proposed KF-H∞ control algorithm is evaluated through
comparison with an existing PI and PI plus vector PI (PI-PIVPI) algorithm and then validated
with experimental studies pursued using a dSPACE1104. From the obtained experimental
results, it is observed that the proposed SAPF significantly outperforms the existing PI-PIVPI in
terms of exhibiting robustness to modeling uncertainties and insensitivity to grid perturbations
such as harmonics, measurement noise and phase angle jump. Thus, the power quality
improvement is achieved in terms of perfect current harmonics cancellation as well as power
factor improvement.
KEYWORDS:
1. Active power filter
2. Self-regulate
3. Robustness
4. Power quality
5. Harmonics cancellation
6. Power factor improvement

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SOFTWARE: MATLAB/SIMULINK
CIRCUIT DIAGRAM:
Fig.1 Proposed SAPF Control Scheme
EXPECTED SIMULATION RESULTS:
Fig.2 Test Case-1:(a) three-phase supply voltages, (b) three-phase load currents

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Fig.3 Test Case-1:(a) three-phase source reference currents in proposed
method, (b) three-phase compensating currents in proposed method, (c) dclink
voltage in proposed method
Fig.4. Test Case-1: Harmonic spectra of (a) phase-a load current, (b) phase a
source current in the Proposed method, and (c) phase-a source current in the
Existing method
Fig.5.Test Case-2: Waveforms of three phase source currents, (i) Proposed
Method, (ii) Existing Method

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Fig. 6. Test Case-2: Harmonic spectra of (a) phase-a source current in
Proposed Method, and (b) phase-a source current in Existing Method
Fig.7.Test Case -3: (a) three phase load currents, (b) dc-link voltage in
proposed method
Fig. 8 Test Case -3: (a) Waveforms of three phase compensating currents,
(b) Waveforms of three phase source currents , (i) Proposed Method, (ii)
Existing Method

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Fig. 9 Test Case-3: Harmonic spectra of (a) phase-a load current, (b)
phase-a source current in Proposed Method, and (c) phase-a source current in
Existing Method
Fig. 10.Test Case-4: (a) Three phase supply voltages, (b) Three phase load
currents, (c) Three phase compensating currents in Proposed Method
Fig. 11. Case-4: Waveforms of three phase source currents and dc-link
voltage, (i) Proposed Method, (ii) Existing Method

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Fig. 12. Test Case-4: Harmonics spectra of (a) phase-a load current, (b) phasea
source current in Proposed Method, and (c) phase-a source current in
Existing Method
Fig. 13. Test Case-5: Harmonics spectra of (a) phase-a load current, (b) phasea
source current in Proposed Method, and (c) phase-a source current in
Existing Method
CONCLUSION
In this paper, a H∞ controller with a new reference current estimation scheme based on KF has
been proposed for a SAPF. This reference generation scheme is simple yet reliable and self
regulator of dc-link voltage without having a PI controller. Only source current sensors are
sufficient to determine the reference current, which decreases the effective cost of SAPF
implementation. Further, H∞ current controller is designed with a proper selection of weighting
functions to specify the robustness, control effort performance and error tracking performance of
SAPF. Finally, the effectiveness of the proposed KF-H∞ control strategy was verified through
various experimental tests, where the proposed control strategy presented good steady state as
well as dynamic performance against supply or load variations. Generally power line

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uncertainties such as fluctuation of load, variation of system parameter, sudden failure of power
system components and sensor nonlinearities degrade the reliability and efficiency of the SAPF
system. Moreover, grid perturbations such as harmonics, measurement noise and phase angle
jump are responsible for power quality deterioration. Hence, the objective of designing a robust
control strategy in SAPF is achieved by accommodating all the possible perturbations occurring
in the power system. From the experimental results, it is also observed that the proposed KF-H∞
control approach to design a SAPF is found to be robust in face parametric uncertainties due to
grid perturbations yielding improvement in power quality more effectively in terms of tracking
error reduction and efficient current harmonics mitigation.
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