This paper presents a switching strategy for a grid-connected voltage source inverter (VSI) using sliding mode control (SMC). The conventional SMC suffers from sliding losses due to the cross-coupling among controllers by the neutral point voltage expression. This issue can be addressed by using the switching technique to obtain the voltage and currents in a new reference frame through a non-linear transformation. In this frame, a decoupled non-linear model of the VSI is derived, and two sliding mode controllers are designed using hysteresis band comparators. The switching strategy not only avoids sliding losses but also increases the control range of the converter by introducing a third harmonic by the control signal. Simulation results using Matlab Simulink are provided to validate the robustness of the proposed controller.

This paper presents a model predictive control (MPC) for a grid-connected voltage source inverter (VSI) with current limitation. The control algorithm is performed in the dq frame to obtain the amplitude of the inverter currents. First, a state observer with a reduced model of the converter is used to estimate the inverter current and perform active damping. Then, an MPC algorithm is used to regulate the currents to a desired reference but with the advantage that these currents can be limited to a maximum value by introducing a constraint in the cost function instead of clipping the current of the inverter above a maximum current. This controller has been tested experimentally under a current reference step change and without a physical damping resistor.

This paper presents a hysteresis current control for single-phase single-stage buck-boost grid-connected inverters. The inverter topology employs four switches that are operated with the grid frequency and two bidirectional switches that are operated with high switching frequency. Hence, unlike the existing single-stage inverter topologies, the switching losses are minimized. Moreover, this inverter configuration has the capability to operate both in buck and boost modes and utilizes only a single inductor. The proposed hysteresis current control eliminates the need for designing a dedicated modulation technique for this inverter topology. An active damping technique is utilized to cope with the resonance damping problem without employing additional sensor. The reference current needed in the hysteresis controller is produced using a proportional-resonant (PR) controller whose input is the grid current error. The use of PR controller guarantees zero steady-state error in the grid current. The validity and superiority of the proposed control method are confirmed by MATLAB/Simulink simulations under various operating conditions which include buck mode, boost mode, transition from boost mode to buck mode, reference current change and virtual resistor variation. The simulation results show that the proposed control method is able to transfer the desired current into grid successfully under all operating conditions.

This paper presents a passivity-based control approach for four-switch buck-boost (FSBB) DC-DC converters. The state variables are selected as the inductor current and the capacitor voltage errors. The passivity based control is formulated that targets to drive the inductor current and capacitor voltage to their reference values. The reference of the inductor current is produced by a proportional-integral controller that operates on the capacitor voltage error. Two control input equations are defined for buck and boost operations due to the fact that FSBB converter contains separate switches for buck and boost stages. As a consequence of controlling each stage by the dedicated control input, the passivity based control method eliminates the need for using a mode detection algorithm. The validity and superiority of the proposed approach has been studied by Matlab/Simulink simulations under load step, reference voltage step and operation mode variations for buck and boost modes. The results reveal that the proposed control approach can regulate the output voltage under all cases.

This paper presents a networked control scheme for a photovoltaic-based industrial microgrid to adaptably operate in both grid-connected and islanded modes, and even to transfer smoothly between these two modes. The control scheme is mainly based on the droop method for active and reactive power sharing by means of voltage and frequency regulation. In addition, to get a smooth transfer between islanded and grid-connected modes, a phase-locked loop is also used in the control system. This loop is only activated during islanded mode to eliminate the phase deviation between the voltages in both sides of the point of common coupling switch. The output of this loop is send to all power units following a one-to-all communication scheme with low bandwidth. Finally, selected simulation results are reported in order to prove the effectiveness of the control scheme.

This paper presents a detailed analysis of a voltage source inverter with vector operation technique allowing to derive a transformation from natural-frame to a new frame called from heron γθ-frame. This transformation leads to obtain a dynamic model for the voltage source inverter in γθ-frame in order to apply an sliding mode control to the system. Due to the behavior of the vector operation, the switching losses of the system can be reduced. Also, the sliding mode control provides to the system a fast transient response against command reference changes and a good current tracking capability working at quasi-fixed switching frequency. Experimental results are provided using a fully-digital control system in order to validate the performance of the proposed system.

This paper presents an improved variable hysteresis-band current-control in natural frame for a three-phase shunt active power filter. The proposed control algorithm is based on three decoupled sliding-mode controllers combined with three independent Kalman filters. The use of Kalman filters instead of a non-adaptive state observer improves the quality of the estimated signals in presence of noise, increasing the immunity of the control loop in noisy environments and also reducing the THD of the current delivered to the grid. The overall control proposal has been fully integrated into a digital signal processor. Selected experimental results are introduced to validate the theoretical contributions of this paper.

This paper presents an active damping method in natural frame for a three-phase voltage source inverter with LCL filter. The proposed method is based on the pole placement technique via Ackermann's formula. This approach is used to obtain the proper sliding surface vector coefficients to emulate a virtual resistor in series with the capacitor filter. Besides a well-known method in the literature have been used to obtain three decoupled controllers in natural frame. The stability is theoretically studied and experimental results shows the validity of this proposal.

This paper presents a sliding mode control for a three-phase grid-connected voltage source inverter with vector operation. The design of closed-loop system is based on the sliding-mode theory, and it is carried out with the help of a converter large-signal dynamic model. The closed-loop system improves the transient response and minimizes the steady-state error. Essentially, the contribution of this paper is as follows: the dynamic model for the tree-phase grid-connected inverter with vector operation and the proposed sliding-mode control scheme. Experimental results are provided using a fully-digital control system in order to validate the theoretical predictions.

This paper present a sliding mode control operating at fixed switching frequency for a three-phase unity power factor rectifier using the vector operation technique. The proposed method allows to find a large-signal converter dynamic model in order to transform a tree-phase system into two decoupled subsystems. With this technique only two sliding-mode controllers are needed and the neutral point voltage influence is removed from the controllers dynamics. A fast output-voltage control is used which avoids output-voltage variations when a sudden change in the load appears. Besides a variable hysteresis band control is used in order to fix the switching frequency of the sliding-mode controllers. Experimental results are provided using a fully-digital control system in order to validate the theoretical predictions.

Three-phase inverters are the mostly used converters for connecting distributed generation sources to the main grid. Conventionally, these renewable sources must inject only its generated active power. Recently, reactive power injection has been included in some national grid codes. In voltage regulation, the conventional PI control can not be used. The whole system tends to instability when PI controllers work distributively for voltage regulation in different connection points along the grid. The slope voltage controller seems to be the best option to avoid these instabilities. The parameters design of the slope voltage controller is normally carried out by trial and error methodology due to lack of a small-signal model of the complete system. With this widely used methodology, the dynamic behavior can not be determined by the designer. This work develops a closed-loop small signal model of a grid-connected distributed generation source with voltage regulation capabilities. The derived mathematical model predicts accurately the system behavior in the frequency range of interest. This model can be used in future research for tuning the controller parameters with the aim of achieve predefined design objectives. The model has been validated through simulation results.

Unbalanced voltages in three-phase power systems is a common perturbation propagated along the grid. Distributed Generation plants have gained widespread attention due to their capability to improve power quality in a distributed manner, including voltage unbalance mitigation. A conventional control strategy to command power plants during balanced grid voltages, is the use of power factor to inject/absorb reactive power depending on grid conditions. Advanced control strategies during unbalanced grid voltages can be selected prioritizing positive or negative sequence active and reactive power. This selection determines the voltage support service and therefore can improve the voltage profile, i.e. phase-voltages can be properly supported and voltage imbalance simultaneously corrected. Based on the definition of effective power factor in IEEE 1459 Standard, the reactive power needed for any control strategy is obtained and the resulting effects are described.

This paper proposes a new active damping method based on virtual resistors for three-phase grid connected voltage source inverters (VSI) with LCL filter. The use of this filters is a standard solution to provide the proper attenuation to the sideband voltage harmonics of the modulation signal. However these grid filters can introduce an unstable dynamics if a passive or active damping is not properly introduced. The passive damping solution causes a decrease of the overall efficiency due to the associated losses and reduces the filter effectiveness but in contrast no more extra sensors are needed. Active damping methods are more efficient because they don't introduce losses but suffers from control and system complexity because in some cases a high number of sensors are needed. The proposed strategy employs a nonlinear sliding mode control (SMC) scheme in natural frame in combination with a Kalman filter to emulate a resistor in the LCL filter which damps the system actively without the use of extra sensors. Two current controllers are designed in order to control the active and reactive power independently and a voltage controller is designed to control the neutral point which is fixed with a third harmonic voltage in order to increase the control dynamic range.

This paper presents a novel power sharing control strategy for islanded mode microgrids (MG). The goal is to enable renewable power sources connected to the point of common coupling (PCC) through three-phase three-wire inverters to cooperatively feed linear and non-linear local loads. The strategy contribution is two-fold. First, a centralized controller is designed to facilitate the power sharing capability of all inverters by means of data communications regardless of load changes and inverter faults. Second, a communication protocol is designed following an event-driven paradigm in such a way that the consumed bandwidth is reduced. Selected simulation results show the main features of the power sharing control strategy.