Hysteretic control of grid-side current for a single-phase LCL grid-connected voltage source converter

© 2016. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/This paper proposes a new approach to control the grid-side current of LCL-grid connected voltage source converters using hysteretic relay feedback controllers. The closed loop system is stabilized by designing a local feedback around the relay element. The compensator allows the use of relay feedback controllers by making the controlled plant almost strictly positive real. The article proposes the use of the locus of the perturbed relay system as analysis and design tool and studies orbital stability for several plant and controller conditions. The approach is validated by means of simulation testing.Postprint (author's final draft

Optimization and analysis of the current control loop of VSCs connected to uncertain grids through LCL filters

Premio Extraordinario de Doctorado 2011This thesis focuses on the design and analysis of the control of voltage source converters connected to the grid through LCL filters. Particularly it is centered on grids presenting uncertainty in their intrinsic dynamic parameters and their influence over the inner control loop of a grid converter: the current control. To that end, the thesis follows a three-fold discussion. Firstly, the thesis studies the grid model, its uncertain parameters and presents a proposal to recursively estimate them. The estimation is based on a recursive least-squares optimization procedure applied to the current and voltage measurements, performed in the point of common coupling, expressed in a synchronous reference frame. The synchronization and the reference frame transformation process is specially designed for the proposed system. The optimization process is complemented with an estimation evaluation block that gives a real-time measure of the estimation quality. The influence of those uncertain parameters over the stability of the current control loop of grid converters is the second topic of this thesis. For the case of linear controllers, the analysis is performed by applying the structured singular value mu theory to a parametric uncertainty model that is described in the document. The proposed method extracts safe grid parameters ranges from a previously defined controller and plant model. Special attention is payed to important practical considerations as pure real uncertainty and sampled-data systems analysis. To test the method performance and illustrate its behavior, this dissertation discusses the robustness of three particular examples: a SISO control approach, a MIMO servo-controller approach and a robust H_inf design. For the case of non-linear controllers, the thesis focuses on hysteresis controllers and presents some practical conclusions. After that analysis, the thesis deals with the complementary problem: the design of a robust controller for grid converters connected through LCL filters to grids whose parameters range between known values. As a prior stage, the thesis presents an LQ servo-controller design procedure that may be complemented with the use of state estimators. The control is faced in a synchronous reference frame and directly controls the grid injected current. Once the framework is settled, the thesis proposes a design technique based on a robust Loop-shaping H_inf design procedure complemented with the nu-gap analysis tool. The final part of this dissertation describes the experimental set-up used for testing the presented proposals. After this, a summary of experimental results and waveforms is presented

Hysteretic control of grid-side current for a single-phase LCL grid-connected VSC

Postprint (published version

Hysteretic control of grid-side current for a single-phase LCL grid-connected voltage source converter

© 2016. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/This paper proposes a new approach to control the grid-side current of LCL-grid connected voltage source converters using hysteretic relay feedback controllers. The closed loop system is stabilized by designing a local feedback around the relay element. The compensator allows the use of relay feedback controllers by making the controlled plant almost strictly positive real. The article proposes the use of the locus of the perturbed relay system as analysis and design tool and studies orbital stability for several plant and controller conditions. The approach is validated by means of simulation testing

Admittance-shaped Hinf current controller for grid-connected VSC

This paper introduces an H8 current controller that allows the shaping of power converters’ input admittance in frequency domain, allowing to define not only its magnitude but also its phase. In addition to admittance shaping, some current tracking specification are also introduced to the algorithm demonstrating that both admittance shaping and tracking performance are possible, but not at the same frequencies. The correct performance (both in time and frequency domain) of the proposed method is demonstrated in an L-filter grid-connected single-phase VSC.Postprint (published version

Admittance-shaped Hinf current controller for grid-connected VSC

This paper introduces an H8 current controller that allows the shaping of power converters’ input admittance in frequency domain, allowing to define not only its magnitude but also its phase. In addition to admittance shaping, some current tracking specification are also introduced to the algorithm demonstrating that both admittance shaping and tracking performance are possible, but not at the same frequencies. The correct performance (both in time and frequency domain) of the proposed method is demonstrated in an L-filter grid-connected single-phase VSC

Hinf current controller for input admittance shaping of VSC-based grid applications

© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other workThis paper presents a current controller that shapes, in the frequency domain, the input admittance of voltage-source converters connected to the grid. The controller is obtained by means of a H8 synthesis procedure, which minimizes the difference between the application closed-loop input admittance and a model-reference defined by the designer. This formulation achieves good accuracy in both modulus and phase. The proposed methodology allows the fulfilment of other current control objectives, such as current tracking, by defining frequency regions where each objective is desired. Experimental results show the good response of the proposed controller, both in frequency and time domain

Hinf current controller for input admittance shaping of VSC-based grid applications

© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other workThis paper presents a current controller that shapes, in the frequency domain, the input admittance of voltage-source converters connected to the grid. The controller is obtained by means of a H8 synthesis procedure, which minimizes the difference between the application closed-loop input admittance and a model-reference defined by the designer. This formulation achieves good accuracy in both modulus and phase. The proposed methodology allows the fulfilment of other current control objectives, such as current tracking, by defining frequency regions where each objective is desired. Experimental results show the good response of the proposed controller, both in frequency and time domainAccepted versio

Hinf simultaneous admittance and tracking current controller of three-phase active grid front-ends

This paper proposes an H8 current controller that allows power converter input admittance shaping, both in modulus and in phase, in a three phase voltage source converter to grid connection through an L filter. In addition to this new feature, controller allows grid current tracking. Proposed controller tries to solve then trade-off problem between stand-alone converter performance (current tracking) and its influence on global stability (admittance control) by an intuitive controller design. Time and frequency domain simulated results demonstrate the good performance of the proposed method.Postprint (author's final draft