Abstract
The three-phase three-wire neutral-point-clamped shunt active power filter (NPC-SAPF), which most adopts classical closed-loop feedback control methods such as proportional-integral (PI), proportional-resonant (PR) and repetitive control, can only output 1st–25th harmonic currents with 10–20 kHz switching frequency. The reason for this is that the controller design must make a compromise between system stability and harmonic current compensation ability under the condition of less than 20 kHz switching frequency. To broaden the bandwidth of the compensation current, a Lyapunov stability theory-based control strategy is presented in this paper for NPC-SAPF. The proposed control law is obtained by constructing the switching function on the basis of the mathematical model and the Lyapunov candidate function, which can avoid introducing closed-loop feedback control and keep the system globally asymptotically stable. By means of the proposed method, the NPC-SAPF has compensation ability for the 1st–50th harmonic currents, the total harmonic distortion (THD) and each harmonic content of grid currents satisfy the requirements of IEEE Standard 519-2014. In order to verify the superiority of the proposed control strategy, stability conditions of the proposed strategy and the representative PR controllers are compared. The simulation results in MATLAB/Simulink (MathWorks, Natick, MA, USA) and the experimental results obtained on a 6.6 kVA NPC-SAPF laboratory prototype validate the proposed control strategy.
Highlights
The increased application of power electronicscauses serious harmonic pollution in power systems [1,2]
An LCL-filter-based shunt active power filter (SAPF) with PR controllers is proposed in [4], and the grid current spectrum shows that it has good compensation performance below the 25th harmonics but poor performance on eliminating switching frequency harmonics
The proposed control strategy based on Lyapunov stability theory is simulated in MATLAB/Simulink
Summary
The increased application of power electronics (variable frequency drives, AC-DC converters, etc.)causes serious harmonic pollution in power systems [1,2]. The active power filter (APF) is considered an effective solution for harmonic elimination of nonlinear loads [3,4,5,6,7,8,9,10,11,12,13,14,15]. An LCL-filter-based SAPF with PR controllers is proposed in [4], and the grid current spectrum shows that it has good compensation performance below the 25th harmonics but poor performance on eliminating switching frequency harmonics. A sensorless control strategy with multiple quasi-resonant compensators for SAPF was presented in [5], which is able to track an unknown grid frequency, reducing its sensitivity to this variable.
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