Single-phase Grid-connected Voltage Source Inverter Research Articles

2DOF-based current controller for single-phase grid-connected voltage source inverter applications

This paper presents the design of a discrete-time control scheme for the current injected into the grid by a single-phase voltage source inverter (VSI). The VSI is connected to the grid by means of an LCL filter that attenuates the switching harmonics present in the output waveform of the inverter. The current control is based on a resonant regulator implemented in a Two-Degrees-Of-Freedom (2DOF) scheme that allows the location of all the poles to be defined in the closed loop of the system without the need for observers and measuring only the current injected into the grid. This control scheme, therefore, allows the attenuation of the resonance frequency of the LCL filter and requires no additional damping methods with which to mitigate the resonance phenomenon. The design parameters can be obtained using a fairly straightforward mathematical approach that involves only operations with real numbers. The simulation and experimental results obtained show that the control scheme performs correctly even considering changes in the grid inductance.

Sliding Mode Control for Single-Phase Grid-Connected Voltage Source Inverter with L and LCL Filters

This paper presents an analysis of the sliding mode control (SMC) method applied to a single-phase grid-connected voltage source inverter (VSI) with L and LCL filters. First, simulation results were presented for the L filter, and then, after some adjustments, the same theory was applied to the LCL VSI with active damping. To improve the obtained results for the SMC control, we adopted the hyperbolic tangent function and the explicit establishment of the modulation index m in the mathematical procedure to help reduce the chattering phenomena; later on, the same function was replaced by the usage of a proportional plus resonant controller to continuously improve the control system responses.

Design and implementation of nonlinear integral backstepping control strategy for single-phase grid-connected VSI

This paper presents the design and the implementation of a nonlinear integral backstepping control strategy for a single-phase grid-connected voltage source inverter (VSI). The proposed control strategy aims to resolve the problem of the sinusoidal reference current tracking, to have a rapid transient response needed to deal with the transient incident such as grid voltage drops and to generate into the grid a current with fewer harmonics. These properties are verified by seeking the direction, the amplitude and the transient response of the injected grid current. An experimental VSI prototype is used to validate the effectiveness of the proposed controller, basing on a digital signal processor DSP microcontroller. The achieved results show that the well- obtained properties satisfy the grid current injection conditions.

Comparative study on Lyapunov‐function‐based control schemes for single‐phase grid‐connected voltage‐source inverter with LCL filter

This study deals with various Lyapunov-function-based control (LFBC) schemes proposed for a single-phase grid-connected voltage source inverter with LCL filter. Use of LCL filter causes resonance which may adversely affect the controller's stability. The conventional (CLFBC) scheme employing the inverter-side current guarantees the asymptotic global stability, but it is not able to damp the resonance. As a remedy to the poor resonance damping, the adoption of grid-current and capacitor-voltage feedback schemes have been investigated. Although the former offers a globally asymptotically stable system, it cannot improve the poor resonance damping. However, the CLFBC with capacitor-voltage feedback scheme not only preserves the global stability, but also improves the resonance damping substantially. The analytical equations of the closed-loop poles for each control scheme are provided which can be used to compute the pole positions and the damping ratio needed for a desired response. Furthermore, the effect of changing controller gains on the loci of closed-loop poles is also studied. Simulation and experimental results obtained from 3.3 kW system demonstrate that the CLFBC with capacitor-voltage feedback scheme not only offers a global stability, but also leads to good quality sinusoidal grid current with reasonable total harmonic distortion and fast dynamic response.

Lyapunov-Function and Proportional-Resonant-Based Control Strategy for Single-Phase Grid-Connected VSI With LCL Filter

This paper presents a new control strategy based on Lyapunov-function and proportional-resonant (PR) controller for single-phase grid-connected LCL-filtered voltage-source inverters (VSIs). While Lyapunov-function-based control guarantees the global stability of the system, the PR controller is employed to process the grid current error and determine the inverter current reference. However, it is shown that the conventional Lyapunov-function-based control (CLFBC) together with the PR control cannot damp the inherent resonance of the LCL filter. Therefore, this control approach is modified by adding a capacitor voltage loop so as to achieve the desired resonance damping. In addition, a transfer function from the reference grid current to actual grid current is formulated in terms of the LCL-filter parameters and their possible variations in the proposed control strategy. An important consequence of using the PR controller is that the need for performing first and second derivative operations in the generation of inverter current reference is eliminated. Also, a zero steady-state error in the grid current is guaranteed in the case of variations in the LCL-filter parameters. The computer simulations and experimental results obtained from a 3.3-kW system show that the proposed control strategy exhibits a good performance in achieving the required control objectives such as fast dynamic response, zero steady-state error, global stability, and sinusoidal grid current with low total harmonic distortion (THD).

A Sliding-Mode Controller With Multiresonant Sliding Surface for Single-Phase Grid-Connected VSI With an LCL Filter

This paper presents a sliding-mode control (SMC) scheme via multiresonant sliding surface for single-phase grid-connected voltage source inverter with an LCL filter to eliminate the grid current tracking error as well as suppress its total harmonic distortion (THD). In general, the design of SMC leads to a sliding surface that is a linear combination of the system state variables and the generated references. The sliding surface would drift while the system parameters change or external disturbance exists, which affects the tracking error and THD of system output seriously. Moreover, for ac tracking system, integral SMC can reduce, but not fully alleviate the sinusoidal tracking error and has limited ability to suppress the grid current harmonics, especially for high-order harmonics. In order to fully eliminate the grid current tracking error and suppress its THD effectively, multiple resonant terms of the grid current error are added to the sliding function. It is used for the first time in the SMC. This method can be used for an arbitrary ac tracking system. Simulation and experimental results on a 5-kVA single-phase grid-connected inverter prototype show the effectiveness of the proposed control strategy. The tracking precision of the grid current is about 0.91% and the THD of the grid current is 0.76%.

Development of a FPGA Based Real-Time Power Analysis and Control for Distributed Generation Interface

Energy coming from renewable sources has become very important nowadays, mainly because of their negligible contribution to greenhouse gas generation. A problem that then arises is how to integrate these new sources into a traditional power grid, in such a manner as to maximize the efficiency and reliability of this new distributed generation (DG) system. The hardware to do that is generally a voltage source inverter (VSI) that supplies a common load, as in single-phase residential and commercial applications. The optimizing process requires, of course, the usual power analysis. This paper presents the development and the experimental evaluation of a power control system for a single-phase grid-connected VSI including the power analysis using as processor for the control implementation a field-programmable gate array (FPGA) circuit. New hardware structures of adaptive linear neural networks (ADALINE) allow the implementation of power control algorithms and have also permitted the real-time analysis of the high-order harmonics without increasing the implementation area of the FPGA circuit. These features are ideal for novel DG power electronics interfaces that could be used not only for active power dispatch but also for harmonics and reactive power compensation. Simulation and experimental results of the proposed fixed and variable frequency schemes are included to confirm their validity.