DC Component Suppression of Grid-Connected Z-Source Inverter Based on Disturbance Observer

Abstract

Regarding the problems of resonance and direct current (DC) components when the Z-source inverter (ZSI) without an isolation transformer is connected to the grid through an LCL filter, this paper proposes a novel DC component suppression strategy for a grid-connected ZSI based on the split capacitor method of disturbance observer (DOB). The split capacitor method is utilized to convert a third-order LCL filter into a first-order one to eliminate the resonance problem. The DC component of the inverter output voltage is regarded as an external disturbance, and the employed DOB is used to observe it, which is fed forward to suppress the DC disturbance component. Various comparison results of the simulation and experiment show that the proposed control strategy can effectively reduce grid-connected DC components injected into the grid at less than 0.5%, which decreases the DC component from 1.8% to 0.1%.

Aliasing Suppression Method for a Three-Phase Grid-Connected Photovoltaic Inverter Based on Multi-Sampling and Mean Filtering

“…The performance of different harmonic suppression methods is shown in Table 3 at rated power. Some harmonic suppression methods are provided in [7][8][9][10][11][12][13], especially in [8,10], but the ability of aliasing suppression is not analyzed. The total harmonic distortion (THD), 5th harmonic, and 7th harmonic can be reduced by less than 0.1% by the harmonic and aliasing suppression method in [18], while the method has not been further experimentally verified.…”

“…Method in [7] 0.481% 0.844% 1.690% Method in [8] <0.100% <0.100% 0.940% Method in [9] ≈0.250% ≈0.190% 2.840% Method in [10] <0.100% <0.100% 0.510% Method in [11] ≈0.200% ≈0.160% 0.730% Method in [18] <0.100% <0.100% 0.090% Method in [25] ≈0.200% ≈0.400% 1.100% Method in [26] <0.100% <0.100% 2.230% Method in [27] ≈1.700% ≈0.400% 2.460% Method in this paper 0.041% 0.046% 1.124%…”

“…With the rapid development of new energy sources, a large number of power electronic devices are connected to the power grid, so power quality problems (especially gridconnected current harmonics) are becoming a concern for power systems [1]. In the research related to digitally controlled inverters, some advanced control methods have been proposed to reduce the steady state error and improve the total harmonic distortion (THD) of the output current, such as deadbeat control [2], repetitive control [3], proportional resonant [4], state observer [5], hysteresis droop controller [6], and others [7][8][9][10][11][12][13]. However, the high-frequency operation of the switching device interferes with the sampling of the signal, causing the sampled signal to carry high-frequency harmonic components.…”

Linear, Nonlinear, and Distributed-Parameter Observers Used for (Renewable) Energy Processes and Systems—An Overview

“…Reference [196] presents the use of observers for DC-DC converters. Several recent papers have dealt with the emerging issues in observer design: observers were used to solve various aspects of gridconnected inverters [197][198][199][200], in a neutral-point clamped (NPC) converter that acts as an interface between the grid and many energy systems [201], as well as in microgrids, as demonstrated in papers [202,203], where linear discrete-time (digital) Luenberger observers were used. The most recent advances and potential challenges in the use of nonlinear observers for energy systems were nicely discussed in a very recent dissertation [204] published in 2023.…”