ABSTRACT:
This study presents a new reference
current estimation method using proposed robust extended complex Kalman filter (RECKF)
together with model predictive current (MPC) control strategy in the
development of a three-phase shunt active power filter (SAPF). A new
exponential function embedded into the RECKF algorithm helps in the estimation
of in phase fundamental component of voltage (vh) at the point of common
coupling considering grid perturbations such as distorted voltage, measurement noise
and phase angle jump and also for the estimation of fundamental amplitude of
the load current (ih). The estimation of these two variables (vh, ih) is used
to generate reference signals for MPC. The proposed RECKF-MPC needs less number
of voltage sensors and resolves the difficulty of gain tuning of proportional–integral
(PI) controller. The proposed RECKF-MPC approach is implemented using
MATLAB/SIMULINK and also Opal-RT was used to obtain the real-time results. The
results obtained using the proposed RECKF together with different variants of
Kalman filters (Kalman filter (KF), extended KF (EKF) and extended complex KF
(ECKF)) and PI controller are analysed both in the steady state as well as
transient state conditions. From the above experimentation, it was observed
that the proposed RECKF-MPC control strategy outperforms over PI controller and
other variants of Kalman filtering approaches in terms of reference tracking
error, power factor distortion and percentage total harmonic distortion in the
SAPF system.
SOFTWARE: MATLAB/SIMULINK
Fig.1a
Proposed RECKF-MPC-based SAPF
Fig.2 Capacitor voltage response in SAPF in steady state for KF, EKF, ECKF, RECKF and PI with
a MATLAB
b Real-time Opal-RT (voltage scale: 100 V/div, time scale: 10 ms/div),
compensating current response in SAPF in steady state for KF, EKF, ECKF, RECKF
and PI with c MATLAB d Real-time Opal-RT (current scale: 15 A/div, time scale:
10 ms/div)
scale:
10 ms/div)
Fig. 6 Continued
Fig. 7 Transient state response in SAPF system for PI and RECKF with MATLAB
a Load
current
b Capacitor
voltage
c Compensating
current
d Source
voltage and source current
Fig. 8 Transient state response in SAPF system for PI and RECKF with real-time Opal-RT
a Load
current b Capacitor voltage c Compensating current d Source voltage and source
current (for (a), (c) and (d), current scale: 25 A/div and for (b), voltage
scale: 125 V/div, time scale: 20 ms/div)
In this paper, a model predictive-based
SAPF with a new reference current estimation scheme has been presented. This
scheme exploits the estimation of in phase fundamental component of distorted
PCC voltage along with the estimation of fundamental amplitude of load current
using KF, EKF, ECKF and proposed RECKF algorithms. The proposed RECKF algorithm
is based on applying a new weighted exponential function as a factor to limit
the variation of innovation vector, to restrain the unusual measured value and
to enhance the estimated accuracy with consideration of grid perturbations such
as voltage distortion, measurement noise and phase angle jump. MPC strategy
presented in this paper is very simple and powerful and advantageously
considers the discrete nature of power converters. In addition, it is not necessary
to include any type of modulator and the drive signals for the IGBTs are generated
directly by this control. The proposed RECKF-MPC control strategy avoids the
use of external linear and non-linear controllers; hence a cheaper control strategy
can be implemented while high performance is maintained. The performances of
the proposed RECKF-MPC-based SAPF have been verified both in steady state and
transient state conditions. The proposed RECKF approach overcomes difficulties
encountered with the fixed-gain PI controller, such as flexibility and robustness
over stabilisation of capacitor voltage when changing loads.
Determination of current reference and
current controller for SAPF is one of the most important issues in improvement
of power quality. From the real-time and simulation results, it is observed
that RECKF-MPC exhibits excellent tracking performance thus is a better control
approach to SAPF design in steady state as well as transient state condition
which improves power quality more effectively in terms of efficient harmonics
mitigation, power factor improvement and tracking error reduction in presence of
above all grid perturbations.
REFERENCES:
2 Heydt, G.T.: ‘Electric power quality’ (Stars
in a Circle, West Lafayette, IN, 1991)
3 Clark, J.W.: ‘AC power conditioners – design,
applications’ (Academic, San Diego, CA, 1990)
4 Rastogi, M., Mohan, N., Edris, A.A.: ‘Hybrid-active
filtering of harmonic currents in power systems’, IEEE Trans. Power Deliv., 1995,
10, pp. 1994–2000
5 Akagi, H., Kanazawa, Y., Nabae, A.: ‘Instantaneous
reactive power compensators comprising switching devices without energy storage
components’, IEEE Trans. Ind. Appl., 1984, IA-20, pp. 625–630
