Panha Soth

Grid-following inverters play a vital role in integrating renewable energy systems into modern power grids. However, their performance deteriorates under grid voltage unbalance and uncertain grid impedance, resulting in current distortion and double-frequency active-power oscillations. This paper proposes a robust dual-sequence current control strategy for a three-phase grid-following inverter operating under these adverse conditions. The inverter model explicitly incorporates grid impedance uncertainty and is represented using a polytopic uncertainty model. Positive- and negative-sequence current controllers are independently designed based on a state-feedback integral structure, where the control gains are synthesized using linear matrix inequality (LMI) optimization to guarantee robust stability over the entire uncertainty range. In addition, sequence-based reference-current generation is employed to suppress the negative-sequence current and eliminate double-frequency power oscillations under unbalanced grid voltages. The effectiveness of the proposed approach is evaluated through simulation studies and compared with a previous robust power controller. The results suggest that the proposed controller significantly suppresses the 120 Hz active-power oscillation despite the presence of grid voltage unbalance and impedance uncertainty. Compared with a previous controller, the magnitude of the 120 Hz component is reduced by approximately 91%, demonstrating improved power-quality performance under grid voltage unbalance and impedance uncertainty.

Grid impedance variation has the possibility of leading to voltage oscillation and control instability, which poses a serious problem to electric vehicle (EV) charger design. In response to this problem, this paper proposes a robust control approach that is capable of dealing with grid impedance variation and system uncertainties. The proposed dual-loop control strategy is composed of an outer-loop proportional–integral (PI) controller and an inner-loop robust state feedback controller with integral action. The benefits of control are maximized according to linear matrix inequality (LMI) techniques. This paper aims to address the effects of grid impedance variation by including the uncertainty model considering the potential varying parameters in the control design process. Additionally, the uncertainty model considers sixteen possible sets, which are described by variations in the four most important parameters: grid impedance, grid resistance, filter impedance, and filter resistance. The simulations suggest that the proposed controller maintains stable current regulation for uncertainty factors as high as γ = 3.3, where all closed-loop poles remain within the unit circle. For all the tested uncertainty levels, the grid-current tracks the reference of 10 A with a faster settling time at γ = 1.1 and no overshoot for higher uncertainty levels.

This paper presents an approach for power balancing in grid-linked inverters within the context of smart grids, addressing the challenge of unbalanced grid voltage conditions. The proposed method employs a paralleled current control strategy, utilizing state feedback integral control to regulate both positive and negative sequence currents. This approach ensures resilient performance under grid voltage imbalances, which are a common problem in smart grid environments. The control gains are optimized through a linear matrix inequality-based method, enhancing the system's stability and responsiveness to fluctuating grid conditions. Simulations conducted using MATLAB and PSIM demonstrate the effectiveness of this control strategy in maintaining power balance and achieving a unity power factor despite unbalanced grid voltages. This study aims to contribute to the improvement of smart grid technologies by offering a dependable and efficient solution for power balancing in grid-connected inverter systems.

High grid impedance may lead to voltage fluctuations, resulting in disturbances to sensitive electrical equipment and machinery. The study proposes an optimal stabilizing control method with robust performance for a single-phase grid-connected inverter, taking into account uncertainties in both the system and grid impedance. This controller ensures system stability despite parameter variations within a specified uncertainty range. The proposed approach combines integral control and state feedback control to achieve offset-free performance for the output grid-current. The stabilizing gain of this proposed controller is determined by addressing an optimization problem utilizing linear matrix inequality. In addition, this proposed method discusses performances using different selections of the uncertainty range of both the AC grid and the inverter system.

The paper presents a systematic control design for a three-phase electric vehicle charger, considering an unbalanced voltage supply. During unbalanced voltage situations, the charging DC voltage oscillates because of the asymmetrical properties of the grid current. To reduce the oscillation of the DC voltage, parallel current control is utilized for both sequences of symmetrical components. The current flow from the grid to the battery is regulated using positive sequence current control. To address the unbalanced grid current, a negative sequence compensator is employed. This ensures a constant DC charging voltage. Both controllers utilize state feedback control along with integral action to provide offset-free performance. Furthermore, a controller gain is determined using an approach based on linear matrix inequalities, considering Lyapunov's stability. The simulation study emphasizes the benefits of the proposed control in comparison to those lacking negative sequence control. The simulation study highlights the advantages of proposed control compared to those without negative sequence control.

This paper proposes a systematic control design for a single-phase LC-filtered inverter considering uncertain system parameters. One major difficulty in controlling single-phase power converters is the lack of a direct conversion method for transforming single-phase signals into dq-frame signals. By employing an all-pass filter in this proposed approach, it is possible to control the output voltage in terms of DC quantity or the dq-rotating frame. Furthermore, voltage stability and harmonic distortion (THD) minimization of the uninterruptible power supply (UPS) are major concerns in inverter design. Therefore, this controller uses integral action to get rid of steady-state errors and stabilize the closed-loop system by the state feedback control. In order to enlarge and guarantee the stability range in the presence of potential parameter fluctuations, an uncertainty model is being considered. In this context, the uncertainty models refer to the potential model with variations in the filter's inductance and capacitance caused by operating temperature, aging, and various external factors. The efficacy of the control approach is assessed through simulations and experiments, with the objective of comparing its results with those of the PI control using a control board featuring a TMS320F28335 digital signal processor. Consequently, the proposed approach offers lower THD at every load step with lesser afford in performance tuning in comparison to the PI method.

Uncertain grid impedance is often common in power distribution networks; therefore, it is crucial to design an efficient controller in this situation. An issue that frequently occurs is the problem of unpredictable grid impedance, which can cause voltage fluctuations, power quality problems, and potential damage to equipment. This work provides a systematic control strategy to tackle these issues by supplying well-regulated power from a DC source to an AC power grid. A linear matrix inequality (LMI)-based robust optimal control is proposed in this paper to provide stability to the inverter system without offset error at the output side. The convergence time to steady state is minimized by solving the LMI problem to maximize the eigen value of the closed-loop system with the inclusion of the uncertainty of the filter parameter and grid impedance. Furthermore, the uncertainties in this study include the potential variation of values for the filters and the grid's impedance. These uncertainties occur because the grid impedance can fluctuate fast in the event of a fault or termination of a transmission line, while the filter's impedance can also be affected by changes in operating temperature. The simulation study of this proposed control includes a comparison between wide and narrow uncertainty ranges, as well as a performance comparison under uncertain parameters. Furthermore, this approach exhibits a lower power ripple in comparison to existing PI control method.

A linear matrix inequality (LMI)-based robust stabilizing control is proposed in this paper for a three-phase grid-connected inverter (GCI) with L-filtered output. Previous research, such as MPC, required high computational power and precise modeling in order to obtain offset-free performance. Achieving optimal performance in the case of PI control poses a persistent chal-lenge in terms of gain tuning. This proposed control strategy effectively addresses the afore-mentioned issues by the utilization of systematic control design, incorporating integral action to mitigate the presence of offset error. The set of state feedback and integral gain is obtained by solving the LMI-based optimization problem to maximize the convergence rate to a steady state in the presence of uncertainty in the L-filter. The mentioned uncertainties are represent-ed by potential ranges of the inductor values. Output power delivery can be simply regulated by a computed reference state using a given power reference and measured grid current and voltage. The effectiveness of the proposed method is verified through simulations. The pro-posed robust control method demonstrates a significant decrease in ripple, with a reduction of 86.66% when compared to the conventional PI control approach.

This paper lays out a systematic control design for a three-phase PV-connected inverter with an output LC-filter. It mainly focuses on the inverter side to provide a well-regulated three-phase voltage, assuming that the DC voltage side is stable by using the DC-DC converter. This proposed controller is based on state feedback control with integral action to provide closed-loop stability to the system with zero steady-state error. To shorten the settling time to the steady state of the output three-phase voltage, the set of state feedback gain and integral gain is determined by solving an optimization problem using a linear matrix inequality approach. In addition, this control method is employed using a dq-rotating reference frame so that the controller can be driven on DC quantities. The space vector pulse width modulation (SVPWM) is also considered in this proposed inverter, using the control input obtained by the computed optimal gain to trigger the IGBT switches of the three-phase inverter. To verify the efficacy of this proposed PV-connected inverter, simulations are conducted using MATLAB to compute the optimal gain and PSIM to implement the control algorithm. To further verify the performance of this proposed controller, a comparison with the existing PI control method is studied in the simulation results. The experiment was conducted with the TMS320F28335 digital signal processor together with the inverter prototype.