Variable Structure Control for Three-Phase LCL-Filtered Inverters Using a Reduced Converter Model

Abstract

Abstract-This paper presents a new concept in active damping techniques using a reduced model of a LCLfiltered grid connected inverter. The presence of the LCL filter complicates the design of the inverter control scheme, particularly when uncertainties in the system parameters, especially in the grid inductance, are considered. The proposed control algorithm is addressed to overcome such difficulties using a reduced model of the inverter in a state observer. In this proposal, two of the three state variables of the system are obviated from the physical inverter model and only the inverter side current is considered. Therefore, the inverter side current can be estimated emulating the case of an inverter with only one inductor, thus eliminating the resonance problem produced by the LCL filter. Besides, in the case of a distorted grid, the method allows to estimate the voltages at the point of common coupling free of noise and distortion without using any PLL-based synchronization algorithm. This proposal provides the following features to the closed-loop system: 1) robust and simple active damping control under system parameters deviation, 2) robustness against grid voltage unbalance and distortion, and 3) an important reduction in the computational load of the control algorithm which allows to increase the switching frequency. To complete the control scheme, a theoretical stability analysis is developed considering the effect of the observer, the system discretization and the system parameters deviation. Experimental and comparative evaluation results are presented to validate the effectiveness of the proposed control scheme.

Complex-Based Controller for a Three-Phase Inverter With an <italic>LCL</italic> Filter Connected to Unbalanced Grids

“…For a practical implementation, where a switched action is required, a frequency analysis is necessary to avoid resonance phenomena due to the switching frequency. From (17) we can deduce,…”

“…Also, nonlinear techniques have been used for LCL inverters. Examples include Sliding Mode Control [16] [17], nonlinear feedback and Poincaré analysis [18].…”

Discrete sliding mode control strategy for a three‐phase Boost‐type VIENNA rectifier with the CB‐PWM

“…CB‐PWM will be discussed in the subsequent sections. In the CB‐PWM modulation method for the VIENNA rectifier, three‐phase sinusoidal reference voltages ( V a,ref , V b,ref , V c,ref ) are used and expressed as: …”

“…Although the three-level SVPWM can be realized by a simplified two-level SVPWM, to avoid the large number of calculations and maintaining the advantages of conventional SVPWM, a simplified SVPWM algorithm, injecting a particular zero-sequence component into the three-phase sinusoidal duty cycles, which has been discussed in detail in Refs. [29,30] The CB-PWM waveforms before and after the injection of common-mode component are shown in Fig. 4.…”

“…CB-PWM will be discussed in the subsequent sections. [29,30] In the CB-PWM modulation method for the VIENNA rectifier, three-phase sinusoidal reference voltages…”