High voltage gain DC-DC converters are widely used in various applications like low voltage sustainable sources. In traditional boost converters, the voltage gain is limited by high voltage stress, high current ripple, and low efficiency due to employing a high duty cycle ratio. In this paper, we propose converters that are a combination of four sub-structures, namely active switched inductor, passive switched inductor, switched capacitor cell, as well as an auxiliary switch with non-isolated configuration. The proposed structures have high voltage gain compared to the conventional either switched inductor-based or switched capacitor-based ones in addition to a low duty cycle ratio. By adding an auxiliary switch, the efficiency is improved, particularly for high voltage gains. The principle of operation and steady-state analysis are discussed in detail. Also, simulation results from PSCAD/EMTDC software are validated by a prototype built for experimental examination. The results are demonstrated that the voltage gain and efficiency could be improved by utilizing the auxiliary switch.

Grid faults constitute the main challenge for distributed generation, especially permanent magnet synchronous generator (PMSG)-based wind turbines connected to the grid via back-to-back (BTB) converters. On the other hand, grid codes enforced wind turbines to aid network and accomplish low-voltage ride-through (LVRT) requirements during grid faults. DC-link overvoltage suppression without external devices and reactive current injection to the grid in symmetrical and asymmetrical faults were the main required subjects in different grid codes. Reactive current injection may lead to overcurrent in one or two phases during asymmetrical faults. This paper presents solutions to accomplish LVRT requirements during grid faults, including dc-link overvoltage suppression by improving BTB converter's controllers and the design of active power limitation to maintain the peak current of the grid side inverter in a safe range during different asymmetrical grid faults. In fact, by controlling generation of PMSG active power directly with grid side inverter, the peak current remained in the safe limit and required reactive current, including negative-sequence component can be injected to the grid. Furthermore, the grid side active power oscillation and dc-link voltage ripple can be suppressed by using the proposed controller. Simulation results showed the validity and efficiently of the proposed control approach in different conditions.

In recent years, the complexities of wind turbine control are raised while implementing grid codes in voltage sag conditions. In fact, wind turbines should stay connected to the grid and inject reactive power according to the new grid codes. Accordingly, this paper presents a new control algorithm based on super‐twisting sliding mode for a gearless wind turbine by a permanent magnet synchronous generator (PMSG). The PMSG is connected to the grid via the back‐to‐back converter. In the proposed method, the machine side converter regulates the DC‐link voltage. This strategy improves low‐voltage ride through (LVRT) capability. In addition, the grid side inverter provides the maximum power point tracking (MPPT) control. It should be noted that the super‐twisting sliding mode (STSM) control is implemented to effectively deal with nonlinear relationship between DC‐link voltage and the input control signal. The main features of the designed controller are being chattering‐free and its robustness against external disturbances such as grid fault conditions. Simulations are performed on the MATLAB/Simulink platform. This controller is compared with Proportional‐Integral (PI) and the first‐order sliding mode (FOSM) controllers to illustrate the DC‐link voltage regulation capability in the normal and grid fault conditions. Then, to show the MPPT implementation of the proposed controller, wind speed is changed with time. The simulation results show designed STSM controller better performance and robustness under different conditions.

The impact of grid-connected PV power plants (GCPPP) operation on the grid entails mandatory provision and conformable execution of futuristic grid-codes (GC) by GCPPP stakeholders. While standard GC-compliant reactive power injection occurs in the advent of voltage drops at the point of common coupling (PCC), weather-dependent active power delivery should also coincide. Hence, it is essential to derive the PV inverter current reference set-points meticulously and confine its current range. This paper proposes a novel control strategy for realization of enhanced LVRT operation in three-phase single-stage GCPPPs. The control scheme encompasses the following features: (a) PCC negative-sequence current reference set-points determination from its positive-sequence counterpart; as well as the analytical determination of PCC voltage sequence components, (b) GC-compliant reactive power injection, without causing second-order harmonic oscillations in the delivered active power to the grid during asymmetrical PCC faults, (c) utilization of a current limiter for immaculate regulation of the PV array output power. Simulation results reflect on the developed control scheme’s effectiveness in significantly improving GCPPP LVRT operation for a wide range of operating conditions.