The virtual synchronous generator (VSG) control has been extensively applied for realizing grid-friendly interconnections of power converters. Nevertheless, due to the direct shaft dynamics emulation, low-frequency power oscillations may be introduced in the case of limited damping effects. To solve this issue, power control law modifications have been proposed based on the feedback control theory. Although power oscillations can be suppressed to an acceptable level, the original inertial response of the VSG will be significantly degraded. This letter proposes a new damping method based on the reference feedforward control. The proposed method is able to effectively attenuate poorly damped power oscillations in VSG-controlled converters without affecting the original inertial response. Theoretical analysis and effectiveness of the proposed damping method have been validated by both electromagnetic transient simulations and experiments.

To eliminate low-frequency oscillations, this article proposes an active-damping method for multiple grid-tied virtual synchronous generators (VSGs) in a power plant. First, using Lyapunov’s indirect method, the damping ratio of multiple VSGs in parallel is analyzed. The average damping ratio reveals that this multi-VSG power plant can be poorly damped in a wide range of inertia and damping settings. Then, self- and mutual-damping controllers are developed to suppress self- and mutually induced low-frequency power oscillations, respectively. For practical implementation, an adaptive tuning algorithm that enables automatic realization is proposed. Through a reassessment, a remarkable damping-ratio improvement is validated. Moreover, the inertial response improvement is validated by the frequency response analysis. Finally, simulations in Digsilent/PowerFactory and experiments are performed to demonstrate the accuracy of the analyses and the effectiveness of the proposed method.

Fault-tolerant control is normally required to achieve continuous operation under post-fault modes in some critical fields. Regarding remedial strategies for open-end-winding permanent magnet synchronous machines (OW-PMSMs) in the case of open-phase fault, the typical way is to reconfigure the controller after the fault is detected. Different from those mainstream control strategies which account for the post-fault situations by reconfiguring controllers or modulators, the fault-tolerant predictive control strategy proposed in this paper handles the asymmetry in a different manner. By combining the predictive control strategy with an embedded vector-resonant control scheme, the proposed strategy can achieve effective regulation of OW-PMSMs in both pre- and post-fault operations. Controller reconfiguration and switching between pre- and post-fault control modes based on fault detections are thus avoided. Besides, with the rotor flux harmonics taken into account and benefiting from the proposed zero-sequence controller, the triple-frequency component in the zero-sequence current is successfully suppressed to reduce torque ripples while the fundamental-frequency component is properly retained under post-fault operations, which is required in order to obtain an uninterrupted rotating magnetic field after one phase is open circuited. Experimental validations are conducted to verify the effectiveness of the proposed strategy and its superiority over conventional voltage compensation methods.

Open-end winding permanent magnet synchronous machines (OW-PMSMs) supplied by dual inverters have gained increasing research focus due to its advantages in multilevel modulation, flexible control capability, and enhanced fault-tolerant performance. Zero-sequence current is one of the most concerned issues when the common DC bus configuration is adopted. Feedback control of zero-sequence current has been previously proved to be an effective solution to suppress zero-sequence current. However, due to the existence of current measurement errors, DC disturbance and periodic disturbances will inevitably occur in zero-sequence current, which may result in obvious deteriorations of the suppression performance of zero-sequence current. Zero-sequence current circulates in the OW-PMSM, which will lead to unexpected power losses and reduced efficiency. In addition, current measurement errors also cause increased periodic disturbances in the torque and the rotor speed, resulting in torque ripples and speed fluctuations. To address these problems, the exact closed-form hold-equivalent model of OW-PMSMs is derived, and the specific periodic disturbances introduced by current measurement errors are analyzed. Subsequently, zero-sequence current controller and speed controller are designed with enhanced mitigation capability of periodic disturbances resulting from current measurement errors. Its effectiveness under different operation conditions is confirmed experimentally on a 2.3-kW OW-PMSM setup.

Seaports are well known as the medium that has evolved into the central link between sea and land for complex marine activities. The growth in maritime logistics particularly necessitates a large volume of energy supply in order to maintain the operation of sea trade, resulting in an imbalance between generation and demand sides. Future projections for three major concerns show an increase in load demand, cost of operation, and environmental issues. In order to overcome these problems, integrating microgrids as an innovative technology in the seaport power system appears to be a vital strategy. It is believed that microgrids enhance seaport operation by providing sustainable, environmentally friendly, and cost-effective energy. Although microgrids are well established and widely used in a variety of operations on land, their incorporation into the seaport is still limited. The involvement of a variety of heavy loads such as all-electric ships, cranes, cold ironing, and buildings infrastructure renders it a complicated arrangement task in several aspects, which necessitates further research and leaves space for improvement. In this paper, an overview of the seaport microgrids in terms of their concepts and operation management is presented. It provides the perspectives for integrating the microgrid concept into a seaport from both shore side and seaside as a smart initiative for the green port’s vision. Future research directions are discussed towards the development of a more efficient marine power system.

In this letter, a novel control scheme is proposed by combining the fractional-order control and the virtual synchronous generator, whereby more degrees of freedom are involved in the controller design. A well-damped power control without oscillations is achieved. At the same time, a significant improvement in the inertial effect is attained. Both theoretical and experimental results have validated the feasibility.