ABSTRACT:
In
order to improve the harmonic compensation performance of active power filter
(APF) in distribution network, based on deadbeat control theory, the command
current prediction algorithm and current tracking control strategy are
optimized in this article. Firstly, the command current repetitive prediction
in abc coordinate system is transferred to dq for improving its accuracy in
lead compensation, and the equivalent for fractional delay beat is achieved by
Lagrange Interpolation Polynomial to solve the problem of inaccurate prediction
caused by grid frequency fluctuation. Then, considering the inherent half-sampling-period
delay of sinusoidal PWM (SPWM), an improved deadbeat control strategy for
current tracking is proposed by estimating the output current of next sampling
period. Because the output current in next sampling period is replaced by that
in current sampling period with traditional deadbeat control strategy, this
estimation could make up for the defect of low control precision caused by that
replacement. After that, adding error repetitive correction into the improved
deadbeat control channel to reduce the periodic tracking error of output
current. Finally, the stability and accuracy of the improved control system are
analyzed theoretically, and its feasibility and effectiveness are verified by
the simulation and hardware-in-the-loop (HIL) experiments.
KEYWORDS:
1. Deadbeat
control
2. Frequency
fluctuation
3. Harmonic
compensation
4. Lagrange
interpolation polynomial
5. Error
repetitive correction
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Figure 1. Three-Phase Apf Topology And Overall Control Structure.
EXPECTED SIMULATION REUSLTS:
Figure 3. Simulation Results For The Improved Deadbeat Control Strategy With Traditional Or Proposed Repetitive Prediction. (A) With Traditional Prediction At Grid Frequency Of 50.5hz. (B) With Proposed Prediction At Grid Frequency Of 50.5hz (C) With Traditional Prediction At Grid Frequency Of 49.5hz. (D) With Proposed Prediction At Grid Frequency Of 49.5hz.
Figure 4. Power Grid Voltage And Nonlinear Load
Current. (A) Power Grid
Voltage.
(B) Nonlinear Load Current.
Figure 5. Grid-Side Current And Output Current Of
Phase A With Traditional Or Improved Deadbeat Control Strategy. (A) Traditional
Deadbeat. (B) Improved Deadbeat (Krc D
0).
Figure 6. Grid-Side Current And Output Current Of
Phase A With Different Value Of Krc.
(A) Krc D 0:15. (B) Krc D 0:30. (C) Krc D 0:45.
CONCLUSION:
In order to improve the harmonic compensation performance of APF, command current prediction algorithm and dead-beat control strategy for current tracking are optimized in this article. The feasibility and effectiveness of the proposed method are verified by theoretical analysis, simulation, and experiment. The conclusions are as follows:
(1)
The accuracy of command current prediction is the pre- requisite for optimizing
the current tracking control strategy. Compared with the traditional command
current repetitive prediction algorithm, the proposed one exhibits higher
prediction accuracy and stronger adaptability to the fluctuation of grid
frequency.
(2)
Compared with the traditional deadbeat control, because the APF output current
in the next sampling period has been estimated, the effective controlled
frequency band of the control system is enlarged on the premise of ensuring system
stability.
(3)
When current tracking error repetitive correction is added into the improved deadbeat
control channel, the periodic tracking error could be reduced to some extent,
and the control accuracy is increased as well.
(4)
The simulation and experiment results demonstrate that the proposed control
method has a fine steady-state performance to grid frequency fluctuation and a
satisfactory dynamic response to the sudden change of load current.
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