This study introduces a sliding mode control (SMC) strategy for three-phase dynamic voltage restorers (DVRs) with 12-switch voltage source inverter (VSI). The compensating voltage references needed in the SMC strategy are generated by an adaptive notch filter (ANF) which exhibits excellent performance under grid voltage anomalies such as voltage sags, swells, unbalanced and distorted grid voltage conditions. The consequence of using ANF eliminates the use of phase lock loop (PLL) or frequency lock loop (FLL) and low pass filter (LPF) which makes it distinguishable from the existing reference signal generation solutions. In addition, the use of SMC strategy with its attractive properties makes the control implementation simple. Theoretical results are supported by simulation results as well as real-time laboratory results over a range of grid voltage anomalies. These results show that the proposed control strategy not only offers an excellent dynamic response independent from the parameter variations and disturbances, but also compensates the voltage sags, swells and harmonics on the load terminals under the defined limits of the IEEE-519 standard.

This paper presents an indirect sliding mode control (SMC) for single-ended primary-inductor converters (SEPIC). Unlike the conventional SMC methods, the proposed SMC method employs a sliding surface function based on the input current error only. The use of such sliding surface function not only simplifies the implementation, but also reduces the cost of implementation. It is shown that the output voltage control can be achieved indirectly. The input current reference is generated by proportional-integral (PI) regulator. The existence condition and region of the closed-loop system are determined for all possibilities of the PI gains. The performance of the proposed SMC method is investigated on a laboratory prototype converter, operated in buck and boost modes, in terms of the voltage regulation ability under abrupt changes in the input voltage and load resistance. The experimental results are presented and discussed.

This paper presents a model predictive control (MPC) method for DC-DC single-ended primary-inductor converters (SEPIC) with auto-tuning weighting factor capability. The conventional MPC requires retuning of the weighting factor when the operating condition of the converter is changed. The effect of this change is observed as inability of the controller in maintaining the switching frequency constant. The weighting factor avoids excessive switching frequency in the DC-DC converters. Based on the relation between the inductor current ripple and switching frequency, an auto-tuning weighting factor based MPC is proposed. The effect of the weighting factor on the switching frequency is investigated. The proposed MPC eliminates the need for retuning the weighting factor when the operating point of the converter is changed. The proposed control strategy is verified experimentally under input voltage, load, and parameter variations. The results obtained from conventional and proposed MPC methods are compared. It is shown that the proposed MPC method controls the average switching frequency when the operating mode of the converter is changed. Furthermore, parameter mismatch results are presented for both conventional and proposed MPC methods.

This paper presents a super twisting sliding mode control (ST-SMC) for single-phase dynamic voltage restorers (DVRs). Unlike the conventional first-order sliding mode controller, the proposed ST-SMC technique eliminates the need for differentiating the compensation voltage in the sliding surface function while keeping the merits of first-order SMC. As a consequence of employing ST-SMC, a continuous control signal is achieved from which the pulse width modulation (PWM) signals can be generated. In this case, the inverter operates at constant switching frequency. The stability analysis of ST-SMC is also presented. The reference compensation voltage needed in ST-SMC is estimated by using Brockett oscillator based frequency-locked loop. Theoretical considerations are verified through experimental results under ideal and distorted grid voltage conditions. The obtained results show that the ST-SMC has good dynamic performance and can maintain the load voltage at desired level under voltage sag, swell and harmonically distorted grid voltages.

In this context of grid synchronization, estimating the phase and frequency of the grid voltage signal is an interesting problem. Out of various techniques available in the literature, Linear Kalman Filter (LKF) is one of the most popular one. In this paper, we propose an alternative implementation of the LKF for grid synchronization application. The proposed implementation uses a linear parametric model of the grid voltage signal including DC offset. It does not involve any quadrature signal generation, rather it works by estimating the phase angle. This helps to estimate the unknown grid frequency directly from the phase angle. This clearly differentiates the proposed alternative implementation with respect to the existing implementations. Performance improvement by the proposed technique is verified extensively through comparative numerical simulation and experimental studies. Comparative results demonstrate the suitability of the proposed technique with respect to other state-of-the-art techniques namely SOGI-PLL and EPLL.

In this study, a two-stage grid-connected inverter is proposed for photovoltaic (PV) systems. The proposed system consist of a single-ended primary-inductor converter (SEPIC) converter which tracks the maximum power point of the PV system and a three-phase voltage source inverter (VSI) with LCL filter to export the PV supplied energy to the grid. The incremental conductance (IC) method with novel variable step algorithm is used as maximum power point tracking algorithm. Thus, tracking speed and accuracy is improved. A sliding-mode control (SMC) strategy is used to control the inverter stage. Obtained simulation results show that proposed system tracks the maximum power point of the PV system and injects sinusoidal currents to the grid.