This paper investigates robust control strategies for wind energy conversion systems with variable-speed permanent magnet synchronous generators, which are integrated into the grid to provide reliable, secure, and efficient electrical power. A three-phase grid-side converter without a grid transformer is connected to the grid using an LCL filter with low resistive losses. In these working conditions, an instantaneous power PI controller for the outer voltage-loop in the grid-side converter is used to regulate the DC-link voltage and generate the required currents for the inner current-loop in the grid-side converter. Two integral-type terminal sliding-mode (TSM) controllers are proposed to control the active and reactive powers exchanged between the converter and the grid. The switching signals in the controllers are softened to attenuate chattering. The time-varying gains in the controllers are constructed to reduce control energy wastage and avoid overestimation of the boundaries of system uncertainties. Simulated and experimental results validate the proposed method.

For unbalanced three‐phase grid voltage, the traditional Virtual Synchronous Generator (VSG) control cannot overcome the distortion of output current. For this reason, a new control method is proposed in this study. The additional positive‐sequence current adjuster to the traditional VSG control allows the reference current to track the positive‐sequence current, and inhibit the negative‐sequence components. Meanwhile, the oscillations in the power system are decreased. The proposed method has been simulated using Matlab/Simulink and verified experimentally on actual platform. The reliability and effectiveness of the proposed control method have also been compared with the traditional VSG control.

This paper presents a small signal stability analysis to assess the stability issues facing PV (photovoltaic) inverters connected to a weak grid. It is revealed that the cause of the transient instabilities, either high-frequency or low-frequency oscillations, is dominated by the outer control loops and the grid strength. However, most challenging oscillations are low-frequency oscillations induced by coupling interaction between the outer loop controller and PLL (Phase-Locked Loop) when the inverter is connected to a weak grid. Therefore, the paper proposes a low-frequency damping methodology in order to enhance the high system integration, while maintaining the stability of the system. The control method uses a DC link voltage error to modulate the reference reactive current. The proposed control reduces the low-frequency coupling between the DVC (DC link voltage controller), AVC (AC voltage controller) and PLL (Phase-locked loop). According to this study’s results, the performance capability of the grid-connected PV inverter is improved and flexibility in the outer loop controller design is enhanced. The control strategy proposed in this paper is tested using the PLECS simulation software (Plexim GmbH, Zurich Switzerland) and the results are compared with the conventional method.

Based on inherent dynamics similarity between synchronous generator (SG) and DC capacitor power port, this study proposes an improved synchronisation control method of grid‐connected PV inverter based on DC capacitor voltage control where a DC‐link capacitor voltage is regulated to provide the synchronisation angle. The proposed control method uses the estimated grid angle feedforward to improve the damping performance of the system under disturbances. To assess the robustness of the proposed control method, a two‐step procedure is followed. Firstly, a reduced‐order model of the system was derived. Secondly, the performance and stability of the proposed control method were fully investigated through the eigenvalue analysis. The offline simulations and real‐time simulations are carried in PLECS software and PLECS RT Box, respectively in order to validate and demonstrate the effectiveness of the proposed control method. It has been found that the proposed control method yields a large band controller parameter setting while maintaining system stability. The results showed that the proposed method improved the operating capability and enhanced the performance of the system under disturbances and weak grid operation.

This paper investigates the control performance of a physical configuration of a microgrid (MG), integrated with photovoltaic (PV) arrays, battery energy storage systems (BESSs), and variable loads. The main purpose is to achieve cooperative optimal control under both grid-connected and islanded modes for the MG. For the grid-connected mode, a voltage source inverter (VSI) based on swoop control is used to control the MG connection to the grid even if PV arrays are under partially shading conditions (PSC). Then, for the islanded mode, the paper analyzes the model of the PV unit and BESS unit detailed from the small signal point of view and designs the suitable control strategy for them. Finally, the whole MG system combines the droop control and the main/slave control to stabilize the DC bus line voltage and frequency. Both simulation and experimental results confirm that the proposed method can achieve cooperative control of the MG system in both grid-connected and islanded mode.

High‐voltage direct current (HVDC) techniques play an important role in the power transmission, especially for the distance district. For the HVDC, control system is necessary to the operation of flexible transmission system, so it is significant to research its control strategy. Normally, the traditional control method is proportional integral (PI) control under the dq frame system, but if the grid voltage is unbalanced, the traditional control method cannot reach the required aim. So the article proposed the full‐order terminal sliding mode (TSM) control under the frame system. In the proposed control strategy, the cross‐coupled term of current in two‐phase stationary reference frame is avoided; thus, the feed‐forward decoupling is not needed and the whole control system becomes simple. At last, the proposed control strategy is simulated in PSCAD/EMEDC, and simulation results show that the proposed control strategy is correct and effective.