125 research outputs found

    Low order harmonics mitigation in grid connected, parallel PV inverters

    Get PDF
    PhD ThesisThis research is concerned with the problem of network power quality when grid connected systems are used to feed the network distribution grid. A parallel connection of photovoltaic (PV) system is the main interest of study for this research. This type of PV system uses power electronic components such as inverter and current controller that produce harmonics which adversely affect the power quality of the distribution network. Development and simulation of current controller using the proportional resonance (PR) scheme is considered to overcome the harmonic problems in single and parallel PV inverters. This scheme eliminates specific harmonic in the low order part. The control parameter randomisation technique is added to the scheme to produce a more efficient current controller system. Thus, the inverter harmonic performance (inverter output current) is improved. This concept is extended to parallel inverter based systems, where opportunities for harmonic cancellation improve the inverter harmonic performance further. Experimental hardware setup using TMS320F2812 is also developed to verify the promising simulation results

    Adaptive proportional resonant controller for single-phase grid-connected PV inverter based on grid impedance estimation technique

    Get PDF
    Ph. D ThesisPhotovoltaic PV systems have shown a significant growth in recent years driven by the increased efficiency and reductions in the cost of PV modules. Today, distribution generation based PV systems have a major contribution to the total electricity production worldwide. However, in areas with high penetration of PV system connected to the grid, interaction may arise between the grid and PV system. This research focuses on the effect of grid operating conditions on the performance of grid-connected PV inverter systems. A simulation model of the system under investigation has been developed to evaluate the impact of frequency deviation, grid voltage distortion and grid impedance variation on the harmonic performance of the injected current as well as the voltage at the point of the common coupler. Proportional resonance PR controller is employed to regulate the current produced from the PV inverter due to its reputation in tracking sinusoidal signals. The obtained simulation results demonstrate that the harmonic performance of the grid current and PCC voltage can be significantly influenced by the change of grid operating conditions. In particular, grid impedance variation can result in a shift in the system resonance frequency leading to distortion in network current and voltage. To adapt the PR controller to the grid impedance variation, a novel adaptive PR controller which takes into account the change in grid impedance is proposed. The adaptive consists of a high-order digital band-pass filter and chain of statistical signal processing technique. Simulation results show that the harmonic performance of grid current and PCC voltage can be enhanced and the proposed APR controller is robust against impedance variation. Finally, the proposed control method is experimentally implemented and the obtained results validate the effectiveness of the proposed control structure.Libyan Ministry of Higher Education and Scientific Research, and the general electricity company of Libya (GECOL

    Performance Enhancement of Active Power Filter using Robust Control Strategies

    Get PDF
    The prime focus of this thesis is to report control strategies to improve the performance of single phase shunt Active Power Filter (APF). Basically, Sliding Mode (SM) control strategy and Feedback Linearization based control strategy have been applied considering their ease of implementation and robustness under external disturbances. An low cost analog SM controller is presented to reduce the steady state current error. In this method a band pass filter is used for calculating the reference source current which makes source current Total Harmonic Distortion (THD) independent of source voltage THD. Multisim based simulation method and results are presented to report the method of low cost analog implementation. To overcome the drawbacks caused by varying switching frequency, a fixed switching frequency SM controller is presented, in which Artificial Neural Network (ANN) is used to generate the reference source current. In this control strategy, a proper combination of fixed frequency sliding mode current control, ANN based fundamental source current extraction circuit and unipolar PWM increases the dynamic response of APF system and makes it adaptive under variable load and source conditions. As feedback linearization based controller improves the performance of the power electronic systems by analysing stability of the complete system, a straight forward Partial Feedback Linearization (PFL) based control strategy is presented to reduce the source current THD of single phase shunt APF. The nonlinear system dynamics of the APF has been partially feedback linearized using its average dynamic model. New control input to the linearized system is obtained considering the stability of the complete APF system. After that, control input to APF is derived by nonlinear transformation. Stability of the internal dynamics of the system is analysed considering zero dynamics of the system. A prototype of the APF system is built and the proposed controller is implemented using dSPACE 1104. Both experimental and simulation results of the PFL based control strategy are compared with exact feedback linearization of APF via SM control for validation of performance improvement. Finally the application of PFL based control strategy is extended to three phase APF by considering it as Multiple Input Multiple Output (MIMO) system and MATLAB/Simulink based simulation results are presented to validate the theory

    High Power Density, High Efficiency Single Phase Transformer-less Photovoltaic String Inverters

    Get PDF
    abstract: Two major challenges in the transformer-less, single-phase PV string inverters are common mode leakage currents and double-line-frequency power decoupling. In the proposed doubly-grounded inverter topology with innovative active-power-decoupling approach, both of these issues are simultaneously addressed. The topology allows the PV negative terminal to be directly connected to the neutral, thereby eliminating the common-mode ground-currents. The decoupling capacitance requirement is minimized by a dynamically-variable dc-link with large voltage swing, allowing an all-film-capacitor implementation. Furthermore, the use of wide-bandgap devices enables the converter operation at higher switching frequency, resulting in smaller magnetic components. The operating principles, design and optimization, and control methods are explained in detail, and compared with other transformer-less, active-decoupling topologies. A 3 kVA, 100 kHz single-phase hardware prototype at 400 V dc nominal input and 240 V ac output has been developed using SiC MOSFETs with only 45 μF/1100 V dc-link capacitance. The proposed doubly-grounded topology is then extended for split-phase PV inverter application which results in significant reduction in both the peak and RMS values of the boost stage inductor current and allows for easy design of zero voltage transition. A topological enhancement involving T-type dc-ac stage is also developed which takes advantage of the three-level switching states with reduced voltage stress on the main switches, lower switching loss and almost halved inductor current ripple. In addition, this thesis also proposed two new schemes to improve the efficiency of conventional H-bridge inverter topology. The first scheme is to add an auxiliary zero-voltage-transition (ZVT) circuit to realize zero-voltage-switching (ZVS) for all the main switches and inherent zero-current-switching (ZCS) for the auxiliary switches. The advantages include the provision to implement zero state modulation schemes to decrease the inductor current THD, naturally adaptive auxiliary inductor current and elimination of need for large balancing capacitors. The second proposed scheme improves the system efficiency while still meeting a given THD requirement by implementing variable instantaneous switching frequency within a line frequency cycle. This scheme aims at minimizing the combined switching loss and inductor core loss by including different characteristics of the losses relative to the instantaneous switching frequency in the optimization process.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

    Mitigation of DC Current Injection in Transformerless Grid-Connected Inverters

    Get PDF
    PhD ThesisWith a large number of small-scale PV plants being connected to the utility grid, there is increasing interest in the use of transformerless systems for grid-connected inverter photovoltaic applications. Compared to transformer-coupled solutions, transformerless systems offer a typical efficiency increase of 1-2%, reduced system size and weight, and reductions in cost. However, the removal of the transformer has technical implications. In addition to the loss of galvanic isolation, DC current injection into the grid is a potential risk. Whilst desirable, the complete mitigation of DC current injection via conventional current control methods is known to be particularly challenging, and there are remaining implementation issues in previous studies. For this reason, this thesis aims to minimize DC current injection in grid-connected transformerless PV inverter systems. The first part of the thesis reviews the technical challenges and implementation issues in published DC measurement techniques and suppression methods. Given mathematical models, the performance of conventional current controllers in terms of DC and harmonics mitigation is analyzed and further confirmed in simulations and experiments under different operating conditions. As a result, the second part of the thesis introduces two DC suppression methods, a DC voltage mitigation approach and a DC link current sensing technique. The former method uses a combination of a passive attenuation circuit and a software filter stage to extract the DC voltage component, which allows for further digital control and DC component mitigation at the inverter output. It is proven to be a simple and highly effective solution, applicable for any grid-connected PV inverter systems. The DC link sensing study then investigates a control-based solution in which the dc injection is firstly accurately determined via extraction of the line frequency component from the DC link current and then mitigated with a closed loop. With an output current reconstruction process, this technique provides robust current control and effective DC suppression based on DC link current measurement, eliminating the need for the conventional output current sensor. Results from rated simulation models and a laboratory grid-connected inverter system are presented to demonstrate the accurate and robust performance of the proposed techniques. This thesis makes a positive contribution in the area of power quality control in grid-connected inverters, specifically mitigating the impact of DC injection into the grid which has influences on the network operating conditions and the design and manufacture of the PV power converter itsel

    Peak Load Shaving and Power Quality Improvement for the Louis-Hippolyte-La Fontaine Tunnel in Montréal

    Get PDF
    The Louis-Hippolyte-La Fontaine Tunnel is one of the major access points to the island of Montreal, and in conjunction with the bridge, it is the longest underwater tunnel-bridge in Canada. Recent reports estimate that around 130,000 vehicles commute through the tunnel daily. High operational standards are required to ensure the safety of commuters. Hence, high-stress levels are reflected on the electrical grid. The high tension levels on electrical power grids and the expensive price of peak power demand have prompted both the consumer and the utility to adopt Energy Storage Systems (ESS) for peak load shaving. In this thesis, a Battery Energy Storage System (BESS) is sized and controlled to reduce the constraints imposed on the electrical grid by the Louis-Hippolyte-La Fontaine Tunnel by means of peak load shaving. The peak load reduction is attained through peak load shaving by utilizing a BESS, and also through energy and peak load shaving by using BESS in conjunction with Photovoltaics solar cells (PV). Also in this thesis, a control scheme is developed for Voltage Source Inverters (VSI) used in peak shaving applications. The developed control first allows the VSI to interface peak shaving systems with the grid reducing stress levels imposed on the grid, and secondly, play the role of power factor correction for reactive power compensation, and finally, to implement the capabilities of active harmonic filters and harmonic mitigation techniques to suppress the harmonic content in the line current

    Integration of an Active Filter and a Single-Phase AC/DC Converter with Reduced Capacitance Requirement and Component Count

    Get PDF
    Existing methods of incorporating an active filter into an AC/DC converter for eliminating electrolytic capacitors usually require extra power switches. This inevitably leads to an increased system cost and degraded energy efficiency. In this paper, a concept of active-filter integration for single-phase AC/DC converters is reported. The resultant converters can provide simultaneous functions of power factor correction, DC voltage regulation, and active power decoupling for mitigating the low-frequency DC voltage ripple, without an electrolytic capacitor and extra power switch. To complement the operation, two closed-loop voltage-ripple-based reference generation methods are developed for controlling the energy storage components to achieve active power decoupling. Both simulation and experiment have confirmed the eligibility of the proposed concept and control methods in a 210-W rectification system comprising an H-bridge converter with a half-bridge active filter. Interestingly, the end converters (Type I and Type II) can be readily available using a conventional H-bridge converter with minor hardware modification. A stable DC output with merely 1.1% ripple is realized with two 50-μF film capacitors. For the same ripple performance, a 900-μF capacitor is required in conventional converters without an active filter. Moreover, it is found out that the active-filter integration concept might even improve the efficiency performance of the end converters as compared with the original AC/DC converter without integration

    Switching Pattern Improvement for One-Cycle Zero-Integral-Error Current Controller

    Get PDF
    The one-cycle current control is a non-linear technique based on the cycle-by-cycle calculation of the ON time of the power converter switches. Its application is not common in tracking fast-changing reference currents, due to the necessity of fast and accurate measurements, and high-speed computing. In a previous study, a one-cycle digital current controller based on the minimization of the integral error of the current was developed and applied to the control of a three-phase shunt active power filter. In the present work, the one-cycle controller has been improved by proposing a new switching pattern. It allows an easy implementation that reduces the critical computational cost and avoids the main drawbacks of the previous implementation. The controller has been applied in a three-leg four-wire shunt active power filter, including a stability analysis considering the proposed switching pattern. Simulated and experimental results are presented to validate the proposed controller

    Switching Pattern Improvement for One-Cycle Zero-Integral-Error Current Controller

    Full text link
    [EN] The one-cycle current control is a non-linear technique based on the cycle-by-cycle calculation of the ON time of the power converter switches. Its application is not common in tracking fast-changing reference currents, due to the necessity of fast and accurate measurements, and high-speed computing. In a previous study, a one-cycle digital current controller based on the minimization of the integral error of the current was developed and applied to the control of a three-phase shunt active power filter. In the present work, the one-cycle controller has been improved by proposing a new switching pattern. It allows an easy implementation that reduces the critical computational cost and avoids the main drawbacks of the previous implementation. The controller has been applied in a three-leg four-wire shunt active power filter, including a stability analysis considering the proposed switching pattern. Simulated and experimental results are presented to validate the proposed controller.Orts-Grau, S.; Balaguer-Herrero, P.; Alfonso-Gil, JC.; Martínez-Márquez, CI.; Martínez-Navarro, G.; Gimeno Sales, FJ.; Segui-Chilet, S. (2022). Switching Pattern Improvement for One-Cycle Zero-Integral-Error Current Controller. IEEE Access. 10:158-167. https://doi.org/10.1109/ACCESS.2021.31377581581671

    Performance Enhancement of Active Power Filter using Robust Control Strategies

    Get PDF
    The prime focus of this thesis is to report control strategies to improve the performance of single phase shunt Active Power Filter (APF). Basically, Sliding Mode (SM) control strategy and Feedback Linearization based control strategy have been applied considering their ease of implementation and robustness under external disturbances. An low cost analog SM controller is presented to reduce the steady state current error. In this method a band pass filter is used for calculating the reference source current which makes source current Total Harmonic Distortion (THD) independent of source voltage THD. Multisim based simulation method and results are presented to report the method of low cost analog implementation. To overcome the drawbacks caused by varying switching frequency, a fixed switching frequency SM controller is presented, in which Artificial Neural Network (ANN) is used to generate the reference source current. In this control strategy, a proper combination of fixed frequency sliding mode current control, ANN based fundamental source current extraction circuit and unipolar PWM increases the dynamic response of APF system and makes it adaptive under variable load and source conditions. As feedback linearization based controller improves the performance of the power electronic systems by analysing stability of the complete system, a straight forward Partial Feedback Linearization (PFL) based control strategy is presented to reduce the source current THD of single phase shunt APF. The nonlinear system dynamics of the APF has been partially feedback linearized using its average dynamic model. New control input to the linearized system is obtained considering the stability of the complete APF system. After that, control input to APF is derived by nonlinear transformation. Stability of the internal dynamics of the system is analysed considering zero dynamics of the system. A prototype of the APF system is built and the proposed controller is implemented using dSPACE 1104. Both experimental and simulation results of the PFL based control strategy are compared with exact feedback linearization of APF via SM control for validation of performance improvement. Finally the application of PFL based control strategy is extended to three phase APF by considering it as Multiple Input Multiple Output (MIMO) system and MATLAB/Simulink based simulation results are presented to validate the theory
    corecore