Traditionally, a grid-interactive inverter providing ancillary services is called a smart inverter. However, broader features will be required for the next generation of inverters that can be categorized as self-governing, self-adapting, self-security, and self-healing. For grid-interactive inverters, the self-governing feature can be identified as the capability of inverters to operate in grid-following and grid-forming control modes, where the self-adapting is referred to as more flexibility realized by adaptive controllers for stable dynamics of inverters under various grid conditions. Moreover, for supervisory control and economic dispatch in a grid with high-penetration of inverter-based power generators, a minimum communication might be necessary, but it can place grid-interactive inverters in danger of being hacked when self-security becomes essential to identify malicious setpoints. Furthermore, the self-healing is defined as fault-tolerance and stress reduction under abnormal conditions. It suggests that after realizing these features, an inverter is called a smart inverter. In this paper, the advancements toward achieving these features for grid-interactive inverters are reviewed.

In this paper, a feedforward virtual inductance control strategy is developed for the stability of voltage source inverters in weak grids. A weak grid is characterized by a low short-circuit ratio (SCR) and a low inertia constant, in which, voltage source inverters (VSIs) become susceptible to voltage distortions and instability. The proposed feedforward virtual inductance term is integrated to the current control loops of grid-tied VSIs. In this paper, the effectiveness of the virtual inductance control strategy in weak grids is first proved through closed-loop transfer function analysis, and then, the system's root locus analysis to determine the stability region of the system versus the grid impedance. The developed virtual inductance controller is also verified through laboratory experiments for different weak grid scenarios.

Mobile platforms cover a broad range of applications from small portable electric devices, drones, and robots to electric transportation, which influence the quality of modern life. The end-to-end energy systems of these platforms are moving toward more electrification. Despite their wide range of power ratings and diverse applications, the electrification of these systems shares several technical requirements. Electrified mobile energy systems have minimal or no access to the power grid, and thus, to achieve long operating time, ultrafast charging or charging during motion as well as advanced battery technologies are needed. Mobile platforms are space-, shape-, and weight-constrained, and therefore, their onboard energy technologies such as the power electronic converters and magnetic components must be compact and lightweight. These systems should also demonstrate improved efficiency and cost-effectiveness compared to traditional designs. This paper discusses some technical challenges that the industry currently faces moving toward more electrification of energy conversion systems in mobile platforms, herein referred to as E-Mobility, and reviews the recent advancements reported in literature.

An adaptive virtual-inductance feedforward scheme is presented in this paper to enhance the stable operation of smart inverters in weak grids. In the developed scheme, the virtual-inductance is updated in real-time according to an adaptation law to ensure that the response of the grid-tied inverter follows the dynamic response of a robust reference model, thereby ensuring stability without the need for any grid impedance estimation. In this paper, the developed scheme is validated with experimental results obtained from testing a small-scale 2-level, 208V, 2kW inverter.

Grid-interactive inverters allow distributed generation (DG) units to provide various ancillary services in microgrids. As the linear operation of inverters is restricted by the dc-bus voltage upper limit, providing ancillary services may drive the fundamental positive-sequence inverter voltage to the overmodulation region. Therefore, to operate in the linear modulation region the maximum active- and reactive-power of the inverter may have to be reduced unless pulse width modulation (PWM) references are adjusted. In this paper, an atypical PWM method is proposed for maximizing dc-bus utilization of grid-interactive two-level voltage source inverters (2L-VSI) providing ancillary services. Two important ancillary services, i.e. negative-sequence compensation and harmonic compensation are considered in this work. The proposed method increases the maximum active- and reactive-power that a 2L-VSI can deliver when providing ancillary services by injecting a common-mode component in the references computed based on instantaneous reference magnitudes. The validity of the proposed technique is verified through simulation, as well as experimental data obtained using a 208V three phase grid-connected 2L-VSI.