Abstract
This work presents the design of a control law based on the average model of a shunt active power filter considering an H-bridge neutral point clamped topology and its experimental validation. Therefore, the proposed controller is formed by three control loops, namely current (inner), regulation (outer), and balance control loops. The current loop aims to compensate both the displacement power factor and the harmonic distortion produced by nonlinear loads connected to the point of common coupling. To deal with harmonic current distortion, the current loop involves an adaptive mechanism based on a bank of resonant filters tuned at odd harmonics of the fundamental grid frequency. The regulation and balance loops are aimed to maintain the voltage of the capacitors forming the DC-link at a desired constant level. For this, proportional-integral controllers are designed. The design of all three loops considers the average model of the system. The performance of the proposed multi-loop control law is evaluated through numerical results and real-time experimental implementation, both considering a 2 kW academic benchmark with a constant switching frequency of 7 kHz. In order to provide harmonic distortion, a nonlinear load based on an uncontrolled diode bridge rectifier is considered. Additionally, step-load changes from 0.5 kW to 1 kW are considered for the nonlinear load. As a result, a suitable current tracking, voltage regulation, and balance are observed despite parametric uncertainties, load variations, and harmonic distortion. As a consequence, in steady state, simulation results indicate that the compensated grid current THD is 1.75%; meanwhile, the nonlinear load current THD is 52.5%. Experimental results indicate that the compensated grid current THD is 2.32%; meanwhile, the nonlinear load current THD is 53.8%.
Highlights
The ever increasing connection of non-linear loads (NLL) to the grid has produced power quality problems in sensitive electrical distribution systems
Shunt active power filters (SAPF) can compensate both the harmonics generated by NLL and the reactive power produced by non-resistive linear loads to ensure a power factor (PF) close to unity according to international power quality standards, such as IEEE-519 [4]
The performance of the SAPF based on the 5L-HB-neutral point clamped (NPC) inverter under the proposed controller was experimentally tested in a 2 kW prototype with a constant switching frequency of 7 kHz
Summary
The ever increasing connection of non-linear loads (NLL) to the grid has produced power quality problems in sensitive electrical distribution systems. The work in [28] described in detail the modeling and control design for a three-level half-bridge NPC converter used as an SAPF, whereas, in [29], a control scheme for the cascaded H-bridge topology was proposed. According to the best of the authors knowledge, there is no similar work in the literature regarding the experimental validation of the proposed control scheme applied to a five-level HB-NPC topology for an SAPF of 2 kW academic prototype with a constant switching frequency of 7 kHz. The rest of the paper is organized as follows: In Section 2, the model of the system is obtained, and the control objectives together with the main assumptions are presented.
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