Power generation and grid stability have become key issues in the last decade. The high penetration of large capacity wind generation into the electric power grid has led to serious concerns about its influence on the dynamic behavior of power systems. The low-voltage ride-through (LVRT) capability of wind turbines during grid faults is one of the core requirements to ensure stability in the power grid during transient conditions. The doubly-fed induction generators (DFIGs) offer several advantages when utilized in wind turbines, but discussions about their LVRT capabilities are limited. This paper presents a comprehensive study of the LVRT of grid-connected DFIG-based wind turbines. It provides a detailed investigation of the transient characteristics and the dynamic behavior of DFIGs during symmetrical and asymmetrical grid voltage sags. A detailed theoretical study supported by computer simulations is provided. This paper also provides a new rotor-side control scheme for DFIG-based wind turbines to enhance its LVRT capability during severe grid voltage sags. The proposed control strategy focuses on mitigating the rotor-side voltage and current transients during abnormal grid conditions, without any additional cost or reliability issues. As a result, the DFIG performance is improved and utility company standards are fulfilled. Computer simulations are used to verify the expanded ride-through capability of the novel strategy and its effective performance compared to the conventional control schemes.

This paper presents the short-circuit behavior and degradation of 650-V/60-A E-mode GaN HEMTs under various test conditions. First, the paper introduces the basic information of device, test method, and platform. Subsequently, single pulse, 10 $\mu$ s short-circuit tests are performed from 50 V to 400 V to extract the typical behavior of devices. Both short-circuit current self-regulation phenomenon and quick failure have been observed. Simultaneously, the device short-circuit behavior at various gate drive voltages and temperatures have been explored to identify the protection condition. Then, repetitive short-circuit tests have been performed to reveal device degradation trends. As a result, their output current reduction and gate-to-source threshold voltage shift have occurred. This work shows the critical need to improve the robustness of this type of GaN HEMT from the device and circuit perspectives.

In recent years, a lot of research efforts have been devoted to the application of sliding mode control (SMC) techniques to power electronic equipment and electrical drives. Hundreds of technical papers have been published in this research field. The tendency stems from the nature of sliding mode with discontinuous control actions and due to its potential for circumventing parameter variation effects along with low implementation complexity. This paper presents a control design procedure for DC/DC power converters. It develops SMC algorithms for several types of DC/DC converters with different control objectives, complete and incomplete information about system states. A chattering reduction approach for power converters based on the idea of multi-phase converters is also proposed. A wide range of MATLAB/SIMULINK computer simulations along with experimental results are provided to demonstrate the effectiveness of the proposed control design.

Sliding-Mode Control (SMC) has been widely utilised to control nonlinear systems with uncertain dynamics. This is due to its order reduction properties, low sensitivity to disturbances, great dynamic performance and ability to reduce the complexity of feedback control design by decoupling the system into independent lower dimensional subsystems. Therefore, significant research has been dedicated to the application of SMC techniques to power electronic equipment and electrical drives. This paper presents a comprehensive control design procedure for AC/DC converters and DC/AC inverters based on SMC. It develops SMC algorithms for several types of power electronic equipment with different control objectives, complete and incomplete information about system states. A wide range of MATLAB/SIMULINK computer simulations are provided to demonstrate the effectiveness of the proposed control design.

Solar photovoltaic (PV) energy sources are rapidly becoming more popular. The PV system output power relies on the applied current or voltage nonlinearity and there exist a unique point called the maximum power point (MPP). For effective energy extraction from the PV system, this paper presents a new controller design strategy to track the MPP of a PV system using a sliding mode control method of self-optimization. The proposed controller design offers fast and accurate convergence to the MPP in steady state and during varying environmental conditions. A DC/DC boost converter is utilized as a control actuator for the MPP tracking using PWM control. Simulation and experimental results are provided to demonstrate the validity of the proposed controller design.