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

Innovative Grid-Connected Photovoltaic Systems Control Based on Complex-Vector-Filter

The research presented in this paper explains how the complex-vector-filter (CVF) method can help in minimizing the current harmonic of a grid-tied photovoltaic system. In fact, the harmonic-free positive sequence (HFPS) load current is used to produce referential sinusoidal currents. This control stabilizes the grid’s currents under unbalanced load currents, as well as mitigates undesirable harmonic load currents, while feeding clean active power to the grid. Thanks to the proposed controller, the performance, such as robustness, as well as the stability and dynamics of the CVF are more effective compared to the proportional-integral (PI) with phase-locked-loop (PLL) controller. Moreover, the CVF ensures robustness and stability during the synchronization between the photovoltaic (PV) generator and the utility grid system. The PI&PLL control presents higher active and reactive power fluctuations during synchronization. On the other hand, the CVF ensures the elimination of the reactive power fluctuations during synchronization. The performance of the proposed CVF is validated by simulation through MATLAB software. Under all conditions, the grid current, considering harmonics, is within the limits set by the IEEE-519 power quality standard, where a total harmonic distortion (THD) of 1.56% was achieved in the case of feeding a non-linear load

Energy Storage as Enabling Technology for Smart Grid

Awareness about human impact on mighty climatic changes is radically changing our concept of energy. The thoughtless use of energy slowly leaves our habits and good use of energy is certain the way of a better future. CO2 emission reduction and carbon fossil fuel limitation are the main targets of governmental actions: this is possible thanks to technology improvement as efficient generation from renewable sources and good management of the electricity network. In recent years distributed generation, also of small size, grew up causing new management problems, indeed production from renewable energy sources (RES) is intermittent and unprogrammable. Energy storage systems can be a solution to these problems and pave the way to completely active users, grid parity and smart grid, moreover can be an useful tool to increase electricity access in rural areas. Research on energy storage is intrinsically a multidisciplinary field: storage types, power stages, technologies, topologies, weather, forecast, control algorithms, regulatory, safety and business cases to mention the most importants. In the present work is described the whole design of an energy storage system. First chapters are dedicated to a description of energy storage context, chapters 1 and 2; indeed, it is a matter of fact that in the last years, energy storage became more and more interesting from explicit mention as a tool against climatic changes to first options on the market. The general approach was the realization of a modular energy storage system for residential application, hardware and software design steps are deeply described in chapters 3 and 4. Simulations and tests on the prototype are reported in chapter 5. Finally conclusion and future works are given. At the end of the document some appendices are included to cover specific aspects touched during the work thesis

Power-quality improvement of a stand-alone induction generator using a STATCOM with battery energy storage system

This paper presents a STATCOM with a self-oscillating bidirectional dc-dc converter for interfacing battery energy storage in a stand-alone induction generator system. The self-oscillation mode is based on relay feedback control with hysteresis. To reduce the output current ripple, an LCL filter is connected between the half bridge of this dc-dc converter and the energy storage system. The other side of bidirectional converter is coupled with a voltage-source converter. The proposed control allows that the previous electronic converters, with an additional resistive dump load, compensate all disturbances in a self-excited induction generator due to three-phase four-wire loads and an improvement of system efficiency. The simulated results show good performance of the stand-alone power system under different loading conditions.Postprint (published version

Sliding Mode Control of Photovoltaic Energy Conversion Systems

Increasing interest and investment in renewable energy give rise to rapid development of high penetration solar energy. The focus has been on the power electronic converters which are typically used as interface between the dc output of the photo voltaic (PV) panels and the terminals of the ac utility network. In the dual-stage grid-connected PV (GPV) system, the dc dc stage plays a significant role in converting dc power from PV panel at low voltage to high dc bus voltage. However, the output of solar arrays varies due to change in solar irradiation and weather conditions. More importantly, high initial cost and limited lifespan of PV panels make it more critical to extract as much power from them as possible. It is, therefore, necessary one to employ the maximum power point tracking (MPPT) techniques in order to operate PV array at its maximum power point (MPP). A fast-and-robust analog-MPP tracker is thus proposed by using the concepts of Utkin’s equivalent control theory and fast-scale stability analysis. Analytical demonstration has also been presented to show the effectiveness of the proposed MPPT control technique. After the dc stage, the dc-ac inverter stage is employed to convert dc power into ac power and feed the power into the utility grid. The dc-ac stage is realized through the conventional full-bridge voltage source inverter (VSI) topologies. A fixed frequency hysteresis current (FFHC) controller, as well as an ellipsoidal switching surface based sliding mode control (SMC) technique are developed to improve the steady state and dynamic response under sudden load fluctuation. Such a control strategy is used not only maintains good voltage regulation, but also exhibits fast dynamic response under sudden load variation .Moreover, VSI can be synchronized with the ac utility grid. The current injected into the ac grid obeys the regulations standards (IEEE Std 519 and IEEE Std 1547)and ful fills the maximum allowable amount of injected current harmonics. Apart from that, controlling issues of stand-alone and grid-connected operation PV have also been discussed. A typical stand-alone PV system comprises a solar array and battery which is used as a backup source for power management between the source and the load .A control approach is developed for a 1-_ dual-stage transformer less inverter system to achieve voltage regulation with low steady state error and low total harmonic distortion (THD) and fast transient response under various load disturbances. The SMC technique is employed to address the power quality issues. A control technique for battery charging and discharging is also presented to keep the dc-link voltage constant during change in load demand or source power. This battery controller is employed for bidirectional power flow between battery and dc-link through a buck-boost converter in order to keep the input dc voltage constant. The robust stability of the closed-loop system is also analyzed. Finally, modeling and control of a 1-_ dual-stage GPV system has been analyzed. A small-signal average model has been developed for a 1-_ bridge inverter. The proposed controller has three cascaded control loops. The simulation results and theoretical analysis indicate that the proposed controller improves the efficiency of the system by reducing the THD of the injected current to the grid and increases the robustness of the system against uncertainties

Stabilised Control of Converter Interfaced DERs for Reliable Operation of Microgrid and Microgrid Clusters

This thesis aims to achieve a stabilised control of converter interfaced DER for the reliable and resilient operation of microgrid and microgrid clusters. The suitability of voltage and current control for VSCs is evaluated and corrective measures are proposed to stabilise converter operation. Furthermore, the accurate power demand distribution in islanded MGs and interconnected MGs are ensured by advanced control strategies. The proposal presented in the thesis is verified both through simulation and experimental work

Application of sliding mode controller in DC/AC and DC-DC power converter system

Maintaining good voltage regulation at output and having fast dynamic response under sudden load fluctuation are extremely important in distributed generation (DG) as well as uninterrupted power supply (UPS) systems. This work presents a fixed frequency hysteresis current (FFHC) controller, which is implemented on the basis of sliding mode control (SMC) technique and fixed frequency current controller with a hysteresis band. The controller have the benefit of hysteretic current control having fast dynamic responses and reduces the disadvantages of the variable switching frequency. For this work elliptical sliding surface was taken.These have been verified and compared with the carrier based pulse width modulated (PWM) voltage controller under the same load fluctuation. The proposed method is then applied to islanded single phase - voltage source inverter (VSI) system. The results show that the dynamic response is quite faster than that of widely used PWM-controlled inverter systems. The DC voltage that is required for the inverter input is supposed to given from the output of PV panel with buck converter.In PV system sliding mode control is used to track the maximum power point .Here inverter and buck converter connected to PV array are taken separately

Design of a hysteresis predictive control strategy with engineering application cases

Aplicat embargament des de la data de defensa fins al 31 de juliol de 2022This doctoral thesis exposes the development of a redesigned Predictive Control strategy that uses hysteresis to improve the performance of the controlled systems in different fields of application. The approach may use one of the three hysteresis models presented in this thesis. Moreover, the hysteresis may be used as a modulation stage or as a reference trajectory generator. The first step in the methodology of this research will be to validate the hysteresis dynamic model that will be used within the control scheme. Due to the three exposed hysteresis models have the same constitution , it is assumed that the test of one is enough to guarantee the validation of the other two hysteresis systems. This validation consists on implementing the hysteresis model in an experimental platform to confirm that the model is indeed feasible. Later, it will be seen that this application is within the scope of renewable energies. Once the hysteresis model is validated, the proposed strategy is developed. This is an Adaptive-Predictive control scheme with a modulation stage for the control signal. This stage employs hysteresis to improve the functioning of the adaptive phase and in general the entire closed-loop performance. lt will be shown how the use of this modulation scenario salves the parametric drift problem commonly present in some adaptive based controlled systems. Additionally, a fault detection system within the Adaptive-Predictive control scheme is also proposed and validated through a numerical simulation. Furthermore, it will be seen how the hysteresis also can be used as a model to generate the reference trajectory needed to accomplish the control objective. Finally, the proposed strategy is implemented in a varied set of control systems to validate it. These control systems are: a nonlinear Van der Poi oscillator, a nonlinear base-isolated system, a DC-DC buck converter, and a single-phase inverter.Esta tesis doctoral expone el desarrollo de una estrategia de Control Predictivo rediseñada que utiliza histéresis para mejorar el rendimiento de los sistemas controlados en diferentes campos de aplicación. Este esquema de control puede utilizar uno de los tres sistemas de histéresis presentados en esta tesis. Además, la histéresis se puede utilizar como etapa de modulación o como generador de trayectorias de referencia. El primer paso en la metodología de esta investigación será validar el modelo dinámico de histéresis que se utilizará dentro del esquema de control. Debido a que los tres modelos de histéresis expuestos tienen la misma constitución, se asume que la prueba de uno es suficiente para garantizar la validación de los otros dos modelos de histéresis. Esta validación consiste en implementar el modelo de histéresis en una plataforma experimental para confirmar que este es realmente factible. Posteriormente, se verá que esta aplicación está dentro del ámbito de las energias renovables. Una vez validado el modelo de histéresis, se desarrolla la estrategia propuesta. Es decir, un esquema de control Adaptativo-Predictivo con una etapa de modulación para la señal de control. Esta etapa emplea histéresis para mejorar el funcionamiento de la fase adaptativa y, en general, de todo el rendimiento del sistema en lazo cerrado. Se mostrará cómo el uso de este etapa de modulación resuelve el problema de la deriva paramétrica comúnmente presente en algunos sistemas basados en control adaptativo. Adicionalmente, también se propone y valida un sistema de detección de fallos dentro del esquema de control Adaptativo-Predictivo mediante una simulación numérica. Además, se verá cómo la histéresis también se puede utilitzar como modelo para generar la trayectoria de referencia necesaria para lograr el objetivo de control. Finalmente, la estrategia propuesta se implementa en un conjunto variado de sistemas de control para validarla. Estos sistemes de control son: un oscilador Van der Poi no lineal, un sistema no lineal de base aisladora, un convertidor Buck DC-DC y un inversor monofásico.Postprint (published version