Sustainable Energy, Grids and Networks 16 (2018) 145–155 Contents lists available at ScienceDirect Sustainable Energy, Grids and Networks journal homepage: www.elsevier.com/locate/segan Digital single voltage loop control of a VSI with LC output filter Igor D.N. de Souza a , Pedro M. de Almeida a, *, Pedro G. Barbosa a , Carlos A. Duque a , Paulo F. Ribeiro b a Power Electronics and Automation Group, Electrical Engineering Program, Federal University of Juiz de Fora, Juiz de Fora, MG 36.036-900, Brazil b Electrical Engineering Institute, Federal University of Itajubá, Itajubá, MG 37500903, Brazil article info Article history: Received 8 January 2018 Received in revised form 18 June 2018 Accepted 7 July 2018 Available online 18 July 2018 Keywords: Voltage source inverter Active damping Single voltage loop and modified digital resonant controller abstract This paper deals with the output voltage control problem of a three-phase three-wire voltage source Inverter (VSI) with LC output filter. A novel discrete-time active damping technique is proposed in order to damp the filter resonance without the need of current feedback. The method is based on an inner voltage feedback with digital lead compensator on the feedback path. A modified digital resonant controller is also proposed to reject the current harmonic disturbance drawn by nonlinear loads. The resonant controllers are connected in series and the design is based on its zeros damping. Results from a small scale experimental setup are used to validate the proposed control strategy. © 2018 Elsevier Ltd. All rights reserved. 1. Introduction The Voltage-Source Inverter (VSI) with an LC output filter have been widely used to achieve high power quality indexes stable ac voltage. The aforementioned attributes are really important when dealing with uninterruptible power supply (UPS), in order to supply emergency power in case of utility power failures [1– 6]; AC microgrid, to integrate all kinds of distributed generators as a utility-friendly customer [7–15] and other high-performance ac power sources, e.g. grid emulators [16–18]. These applications required clean power and high reliability, regardless of electric power failures, distorted utility supply voltage and load conditions. In the last years, several control strategies has been devel- oped and applied to regulate the VSI output voltage. It can be cited, for instance, a conventional PI controller which presents the feature of easy implementation. However, under nonlinear-load condition the output voltage total harmonic distortion (THD) is high [19]. An adaptive control method with low THD and load current observer is proposed in [20]. Nevertheless, there is still a risk of divergence if the controller gains are not correctly selected. A H ∞ loop-shaping control scheme is applied to a single-phase inverter in [21] ensuring robustness against parametric variations. Deadbeat control scheme allied to state estimator and current observers is proposed in [22]. Deadbeat controllers provides fast convergence time, although its performance is deteriorated under parametric uncertainty. In [23] the repetitive control is used to reach a output voltage with high waveform-quality. Usually, this * Corresponding author. E-mail address: pedro.machado@ufjf.edu.br (P.M. de Almeida). control technique has a slow transient response. A model predic- tive control method with current observer for UPS system is de- scribed in [24]. Nonetheless, besides the cumbersome cost function calculation, the simulation and experimental results do not show good performance indexes in terms of THD and steady-state error. Nonlinear techniques, as sliding-mode control [25,26], are also employed, although it presents a well-known chattering problem. The multivariable FLC method suggested in [27] considers the nonlinearity of the system to achieve low THD under nonlinear load. However, it is not easy to carry out due to the computation complexities. The aforementioned nonlinear controllers present good performance, although the implementation is not easy due to the relatively complicated controllers. On the other hand, linear controllers are simpler, nevertheless the performance may be not satisfactory under nonlinear load. Double-loop linear control is one of the most used technique. It includes an inner current regulation feedback loop based on feeding back the LC-filter inductor or capacitor-current, and an outer voltage loop for controlling the filter capacitor voltage. It has been demonstrated that the internal loop is capable of actively damp the resonance due the fact that it behaves as a virtual impedance [28,29]. According to [2], the filter capacitor current feedback scheme achieves the best performance. Though, a larger phase shift at the operating frequency will occur if the controller gains are not correctly selected [30]. Furthermore, it has been shown that the aforementioned approach only presents good re- sults when the intrinsic delay regarding digital implementation has negligible phase lag effect [31,32]. For frequencies higher than one-sixth of the sampling fre- quency (f s /6), the virtual impedance exhibits a negative real part. https://doi.org/10.1016/j.segan.2018.07.004 2352-4677/© 2018 Elsevier Ltd. All rights reserved.