Enhanced controller for a four-leg inverter operating in a stand-alone microgrid with unbalanced loads

Abstract

<span lang="EN-US">Stand-alone low voltage (LV) microgrids supplying small local loads far from the utility grid are becoming an increasingly popular alternative to a total reliance on the centralized utility grid. In most of LV microgrids, three-phase four-wire distribution systems are used to supply both single- and three-phase loads. Unequal distribution of loads can result in voltage unbalance problems. The use of the four-leg inverter is one of the best solutions for providing a neutral current path and compensating unbalanced load conditions in stand-alone LV microgrids. This paper proposes a fast control technique to compensate unbalanced voltage conditions for a four-leg inverter operating in a stand-alone LV microgrid. The suggested technique provides the current controller’s orthogonal component without introducing any additional dynamics or distortions. The major benefits of the recommended per-phase control technique over conventional orthogonal signal generation (OSG) methods are enhanced steady-state and dynamic performances as well as independency to the system parameters. Several simulation results are provided to confirm the superior performance of the suggested methods.</span>

Sliding mode control of four‐leg inverters in a stand‐alone microgrid for unbalance, neutral to ground voltage, and harmonics compensation

“…In order to implement the proposed control technique, the test bench similar to Figure 2 is implemented. Detailed comparison of the proposed method with the existing literature [9,29] is presented to demonstrate the accuracy and validity of the suggested method. The considered test system including the four-leg inverter, LC filter, and loads is based on [9,29].The proposed control method in this paper is developed based on existing literature to compensate NGV and harmonic distortions in addition to voltage unbalance.…”

“…It is assumed that the single-phase PV inverter supplies the load in phase 'a' without the contribution of the four-leg inverter to generate the power in the test system. The PI controller that is used in the control section of the system was designed as described in [9]. In this simulation, the PV with its converter supplies a current of 460 A (peak) with a unity power factor and the load value are 0.43[Ω] in per phase as the same as the first condition in the previous simulation.…”

“…Comparison between the proposed method and the conventional method [9] in the steady-state condition.…”

“…For compensating power quality problems such as unbalanced load conditions as well as high NGV and harmonics distortions in stand-alone microgrids, many control techniques including linear and nonlinear ones have been proposed. One of the most conventional linear controllers is the proportionalintegral (PI) which is the simplicity to perform and good transient response [8,9]. However, the steady-state error does not tend to zero when faced with linear and nonlinear loads which is the weakness of the PI controller.…”

Simultaneous voltage unbalance compensation and neutral‐to‐ground voltage minimization for an islanded mini‐grid using model predictive control

“…In the aspect of the control method, several techniques for controlling the four-leg inverter in islanded mini-grids against unbalanced load conditions were previously proposed. One of the most common control methods is the proportional-integral (PI) technique [10,21]. Although this method has a simple structure, it does not perform perfectly under unbalanced load conditions.…”