Search Results (88)

This paper presents a case study demonstrating the power quality improvements in a 24 kV distribution system at a liquefied natural gas (LNG) industrial plant with variable speed drives (VSDs), the conventional capacitor bank, and a rooftop solar photovoltaic system. Solar photovoltaic (PV) inverters can supply harmonic currents to the grid, potentially affecting the system and causing maloperation of sensitive equipment in both the utility systems and neighboring industries connected to it. Therefore, the installation of shunt active power filters (APFs) in a 400 V system was proposed in this study. The installed locations were varied, and the corresponding power qualities were analyzed. The results were examined in terms of design and harmonic elimination. Simulations were conducted using the PSCAD/EMTDC software version 4.5. The power quality simulation and field measurement results after the APF installation were compared to demonstrate the effectiveness of the proposed solutions. The addition of APFs was found to improve the power quality. In addition to the mechanism analysis, the economic feasibility of the proposed approach was investigated. The costs of APF installation in various locations were analyzed. The results show that the proposed method can improve the power supply at a reasonable price. This work contributes to sustainable industrial energy systems by improving the reliability and power quality of photovoltaic-integrated electrical networks, thereby supporting higher penetration of renewable energy resources and stable low-carbon industrial operation. Full article

Large-scale wind integration introduces significant harmonic degradation and resonance risks. Traditional strategies primarily targeting Total Harmonic Distortion (THD) often struggle with individual node violations and high investment costs. To address these challenges, this paper proposes a two-stage sequential coordination strategy for Passive Power Filters (PPFs) and Active Power Filters (APFs). First, stochastic harmonic emission and frequency-domain power flow models are developed to characterize wind-induced harmonic propagation. Second, a sequential optimization framework is established to minimize Life Cycle Cost (LCC). In the first stage, PPF siting and sizing are optimized for cost-effective, system-wide mitigation of low-order harmonics while ensuring THD compliance. The second stage utilizes targeted APF deployment to precisely suppress residual high-order violations and localized resonance. Chance-constrained programming is incorporated to manage wind power uncertainty, enhancing the scheme’s robustness. Simulations on an IEEE 17-bus system demonstrate that the proposed method effectively balances harmonic suppression performance with economic efficiency, providing a robust and cost-effective solution for wind farm power quality management. Full article

This paper reviews circuit topologies in the literature that aim to suppress submodule (SM) capacitor-voltage ripple of modular multilevel converters (MMCs), since this low-frequency ripple largely determines the required SM capacitance and thus the overall converter volume, cost, and reliability. The circuit topologies covered in this review include high-frequency (HF) magnetic or switched power channels, transformerless active channel or bridging cells with mid-cell connections, hybrid-MMC and DC-bus management options, SM-level active power decoupling (APD) and active power filters (APF), and structural modifications. Physical power-channel topologies (HF magnetic or switched auxiliary paths) suppress the $2\omega$ capacitor-voltage ripple by transferring the associated low-frequency ripple power to an auxiliary high-frequency path. Hybrid-MMC and direct-current (DC) bus management reduce the required capacitance with only a modest increase in hardware requirements. SM-level APD and APF cells transfer the ripple power into auxiliary storage. Structural and topological arrangements modify the converter architecture itself, leading to architectural simplification, passive attenuation, and a reduced need for measurement or balancing. The reviewed topologies are then compared in terms of ripple reduction, hardware complexity, additional components, cost, and control complexity, and the resulting evidence is synthesised into application-driven design trade-offs and selection guidelines. In addition, DC–DC MMC topologies are discussed separately in a contextual overview. Full article

To improve the reliability and precision of shunt active power filters (APFs) under disturbances, this paper proposes an enhanced direct deadbeat control strategy requiring only grid-side current sensors. To this end, a sensor-lean yet robust framework is established by integrating PLL-less voltage estimation with online inductance identification. Specifically, the need for AC voltage sensors is eliminated by reconstructing the grid voltage from inverter outputs and consecutive current samples, while a load current feedforward mechanism further obviates the load current sensors. From an algorithmic perspective, the strategy utilizes the grid-side current as the direct controlled variable to minimize error propagation, while an online identification algorithm is incorporated to counteract parameter drift induced by magnetic saturation. Furthermore, system stability is rigorously guaranteed via Lyapunov theory. Validation through both simulation and experiments reveals that the grid current THD is reduced to 2.90% and 3.3%, respectively, with a dynamic response time within 20 ms. Ultimately, these findings confirm that the proposed scheme minimizes hardware dependency without compromising harmonic suppression or transient robustness. Full article

With the evolution of new power systems, harmonic sources in distribution networks have become increasingly dispersed, thus requiring lower-cost harmonic mitigation devices suitable for large-scale deployment. With its simple control architecture, the one-cycle controlled active power filter (APF) is better adapted to meet the aforementioned requirements. That said, under non-ideal voltage conditions like voltage distortion or unbalance, the compensating target current of the APF that relies on traditional one-cycle control (OCC) will undergo distortion as well, resulting in a substantial reduction in the compensation effect. This paper introduces a modified OCC method based on a positive-sequence filter, which allows for the control of a reduced-switch three-phase APF. This control method eliminates the negative sequence and harmonic components in the target current of the APF, and makes the compensated current maintain a good sinusoidal waveform. A one-cycle control equation applied to the reduced-switch APF was derived. The modified one-cycle control method allows the active filter to retain a favorable compensation effect when operating under non-ideal voltage conditions. Meanwhile, it preserves the inherent advantages of traditional one-cycle control, including the elimination of a phase-locked loop (PLL), a fixed switching frequency, and a straightforward control structure. Finally, an APF simulation model and a dSPACE-based APF experimental circuit were built to verify the proposed control method. In simulation, with the adoption of the modified OCC, the THD of the current was reduced from 8.25% before improvement to 3.79% after improvement. In experiments, according to the spectrum analysis function of the oscilloscope, the third-order current harmonic caused by voltage distortion was decreased from 500 mA to 100 mA, representing a reduction of 80%. Both simulation and experimental results verify that the proposed modified one-cycle control method can effectively solve the problem that control performance is susceptible to voltage quality. Full article

The widespread adoption of nonlinear loads in industry has introduced significant power quality issues in electric power distribution grids. The integration of these nonlinear loads has led to the proliferation of serious power quality problems such as the generation of harmonics and reactive power that negatively impact the quality and stability of the electrical grid. In addition to eliminating current harmonics, a shunt active power filter (APF) can also provide reactive power compensation. By dynamically adjusting the reactive power injection, these APFs can improve the power factor of the system and maintain the desired voltage regulation. The proposed control leverages the differential flatness property of the SAPF system, allowing for exact linearization and simplified tracking control without requiring complex modulation techniques. In this paper, a flatness-based control scheme is proposed for a three-phase three-level Neutral Point Clamped (NPC) APF. The main objectives of this work are twofold. The first objective is to mitigate current harmonics and compensate the reactive power drawn by nonlinear loads. The second objective focuses on maintaining a stable DC-link capacitor voltage of the active power filter (APF). To meet these requirements, a cascaded control structure is used, where the external loop regulates the DC-link voltage, while the inner loop is responsible for harmonic current compensation. The effectiveness of the proposed control strategy is validated through simulation results obtained using the MATLAB/Simulink R2024a environment. Full article

Power quality is a critical concern for large-scale industrial operations, necessitating advanced power conditioning equipment to maintain optimal performance and efficiency. Shunt active power filters (APFs) have gained significant attention for their profound impact on power quality, being valued for their system applicability, efficiency, and eco-friendliness. This study investigates the performance of an APF module connected upstream of a wide spectrum passive filter, the Advanced Universal Harmonic Filter (AUHF). The hybrid connection aims to reduce current total harmonic distortion (THDi) more effectively than using either the AUHF or the APF alone. Tests conducted under half-load and full-load conditions evaluate the performance of passive filters, active filters, and a hybrid configuration combining both. Results show that the hybrid configuration offers superior harmonic mitigation compared to individual filters. At full-load test, the combination of APF and AUHF reduced THDi to 1.2%, compared with 3.4% for the APF and 6.3% for the AUHF, demonstrating the enhanced performance of the hybrid setup. At half-load test, the THDi was reduced to 1.8%, compared with 7.2% for the APF and 8% for the AUHF, confirming the hybrid connection’s superior performance over the AUHF alone. Practical experiments corroborate these findings, demonstrating that the hybrid filter configuration not only meets but exceeds even the most stringent industrial power quality requirements. To further validate the experimental results, each test case was also simulated using Mirus SOLV v6.6.4b12 software. Comprehensive data underscores the hybrid filter’s potential as the optimal solution for significant power quality improvements. This research supports the adoption of hybrid filtering solutions, offering a reliable, efficient, and environmentally friendly approach to power quality management in industrial power systems. Full article

This paper presents a novel approach to reduce harmonic distortion and mitigate zero-sequence circulating current (ZSCC) in parallel active power filters (APFs). By employing Dual-Comparison One-Cycle Control (DC-OCC), this method effectively reduces harmonics. Carrier asynchronization among inverter modules in parallel configurations leads to the generation of ZSCC, which distorts output waveforms and reduces system efficiency. A mathematical model is developed to decompose ZSCC into low-, medium-, and high-frequency components, revealing how these components are influenced by carrier-phase deviations. Based on this model, a ZSCC extraction and compensation scheme is proposed. This method enables effective suppression of ZSCC without requiring additional components, communication links, or sensors. Simulation and experimental results demonstrate that the proposed approach achieves significant harmonic suppression, improved power factor, and a peak efficiency of 98.7%, confirming the effectiveness of the control strategy in practical applications. Full article

The proliferation of power converters in modern energy production systems has led to increased harmonic content due to the commutation of active switching devices. This increase in harmonics contributes to lower system efficiency, reduced power factor, and consequently, a higher reactive power requirement. To address these issues, this paper presents both simulation and experimental results of various control strategies implemented on Parallel Voltage Source Inverters (PVSI) for harmonic mitigation. The proposed control strategies are categorized into direct and indirect control methods. The direct control techniques implemented include the instantaneous power method (PQ), the synchronous algorithm (DQ), the maximum principle method (MAX), the algorithm based on synchronization of current with the voltage positive-sequence component (SEC-POZ), and two methods employing the separating polluting components approach using a band-stop filter and a low-pass filter. The main innovation in these active power filter (APF) control strategies, compared to traditional or existing technologies, is the real-time digital implementation on high-speed platforms, specifically FPGAs. Unlike slower microcontroller-based systems with limited processing capabilities, FPGA-based implementations allow parallel processing and high-speed computation, enabling the execution of complex control algorithms with minimal latency. Additionally, the enhanced reference current generation achieved through the seven applied methods provides precise harmonic compensation under highly distorted and nonlinear load conditions. Another key advancement is the integration with Smart Grid functionalities, allowing IoT connectivity and remote diagnostics, which enhances system monitoring and operational flexibility. Following validation on an experimental test bench, these algorithms were implemented and tested on industrial APF prototypes powered by a standardized three-phase network supply. All control strategies demonstrated an effective reduction in total harmonic distortion (THD) and improvement in power factor. Experimental findings were used to provide recommendations for choosing the most effective control solution, focusing on minimizing THD and enhancing system performance. Full article

The authors of this paper highlight the creation of an experimental system for the implementation and testing of active low-voltage electronic power filters of the parallel type, with applicability in a wide range of electrical parameters. In this paper, the authors present the results obtained on an experimental test bench for power quality purposes. The experimental test bench is one of the results of a technology transfer project. One of the specific objectives of the project was to carry out industrial research and experimental development activities in order to develop a competitive, technical and economic solution for an intelligent power system, Active Power Filter (APF). Thus, this paper presents the experimental test bench for the design, implementation and testing of algorithms for current harmonics mitigation. The conceptual theoretical frame bases of both direct and indirect control have been presented by the authors. As a case study, both the simulation and experimental results of the indirect control strategy implemented on the test bench are provided. The indirect control method is chosen due to simplicity, no complex calculus requirements, and the use of a minimum number of transducers. By features comparison with modern control strategies, this study underlines the supremacy of the indirect control in active harmonics control. Full article

Aiming at the significant challenges faced by active power filters (APFs) in suppressing low-order harmonic currents (such as second and fourth), this paper proposes a rarefaction suppression method based on quasi-proportional resonance (QPR) control. Firstly, the harmonic mathematical model of APFs in a synchronous, rotating coordinate system is established to reveal the inherent defects of traditional proportional–integral (PI) control in low-order harmonic suppression. Theoretical analysis shows that although the proportional resonant (PR) controller can achieve zero-steady-state-error tracking of specific frequency harmonics, its narrow bandwidth and low robustness may easily lead to system oscillation. Therefore, the QPR control strategy is introduced. By superimposing a low-pass filter with an adjustable cut-off frequency on the resonant link, the bandwidth is significantly broadened and the anti-frequency disturbance ability of the system is enhanced. In addition, the stability of QPR control parameters is analyzed. Finally, the verification based on the experimental platform demonstrates that the proposed method reduces the total harmonic distortion (THD) of the 380 V bus current from 82.18% to 3.45%, and the low-order harmonic current suppression performance is significantly better than the traditional scheme. This research provides an effective solution for the synergistic suppression of low-order harmonic currents. Full article

This paper presents a control delay compensation method for an LLCL-type active power filter (APF), aimed at improving performance in digital control systems. The proposed strategy is directly integrated into the inner-loop current controller, requiring no additional compensation modules, predictor structures, or capacitor current feedback, which simplifies the control structure and increases flexibility. The method uses real-time internal state responses of the controller to actively compensate for the phase lag caused by digital control delay, effectively maintaining current control accuracy and overall system dynamic stability. Simulation studies based on a 5.5 kW APF system are conducted to verify the effectiveness of the approach. The results show improved current tracking accuracy, stable dynamic behavior under various load conditions. The simulation-based results indicate the potential of the proposed method for improving control accuracy and stability in digitally controlled APF systems. Moreover, very few studies have addressed control delay compensation specifically for LLCL-based APF systems, making this work a valuable contribution to the field. Full article

Focusing on the common problems of phase-locked loop dependence, multiple current sensor requirements, a large number of controllers, and complex settings in traditional parallel active power filter (APF) control methods, this paper proposes a harmonic compensation control strategy based on an improved proportional resonant (PR) controller. The proposed method introduces an instantaneous power theory to construct a reference current model, which relies solely on grid voltage and current signals, does not require load-side current detection and phase-locked loop modules, and effectively simplifies the sensor configuration and system structure. At the same time, compared with the traditional solution that requires PR modules to be configured for each order of harmonics, this study only uses one set of PR controllers for fundamental current tracking, which has advantages in terms of compactness and computing resource occupation. To guide the controller parameter setting, this paper systematically discusses the influence of changes in K_p and K_r on pole distribution and dynamic performance based on discrete domain modeling and root locus analysis methods. The results were verified on the MATLAB/Simulink simulation platform and the 1 kVA experimental platform and compared with the traditional control method that requires the use of phase-locked loops (PLLs), load current sensors, and multiple PR controllers. The simulation and experimental results show that the proposed method has achieved a certain degree of optimization in terms of harmonic suppression effect, dynamic response performance, and system structure complexity. Full article

Grid-forming converters (GFMCs) have gained significant attention for their functionality in grid voltage formation and grid-supportive services. However, managing harmonic distortions caused by nonlinear loads remains a critical challenge in weak grids. This paper presents a novel grid-forming active power filter (GFMC APF) that integrates voltage and frequency regulation with effective harmonic control. The proposed control method generates harmonic voltage commands by detecting voltage at the point of common coupling. The GFMC APF compensates harmonic voltages by creating a near short-circuit impedance path for harmonics, thereby preventing harmonic currents from propagating into the grid. In addition to improving harmonic performances, the system enhances grid stability by enhancing inertia, damping, and short-circuit capacity while suppressing wide-frequency oscillations. The proposed method avoids complex parameter tuning, ensuring simplicity and scalability. Simulation results validate the effectiveness of the GFMC APF in delivering precise harmonic control, improved power quality, and enhanced grid-forming capabilities. Full article

Shunt active power filters (SAPFs) have been around for a long time. They improve the quality of a current drawn from the grid when feeding non-linear loads formed by old-fashioned power electronic converters such as uncontrolled and controlled rectifiers. Most SAPFs are implemented using the well-known six-switch three-phase inverter (SSTPI) topology. This paper investigates the capability of adopting the four-switch three-phase inverter (FSTPI) scheme to develop low-cost SAPFs, mainly for low-power ranges. The performance of the proposed SAPF using the FSTPI topology is compared with the conventional scheme of an SAPF formed by the six-switch three-phase inverter (SSTPI) topology. Qualitative and quantitative analyses are conducted. The performance of the proposed FSTPI-based SAPF is investigated under different loading conditions. The obtained results indicate the validity and effectiveness of the FSTPI scheme in improving the quality of currents drawn from the AC grid. The SAPF scheme investigated is also feasible and results in cost reduction when the SAPF power circuit is constructed with modern WBG devices, such as SiC-based MOSFETs, which are relatively expensive (approximately three times the price of the equivalent Si IGBTs). Full article