In the context of smart cities, sustainability is an essential dimension. One of the ways to achieve sustainability and reduce the emission of greenhouse gases in smart cities is through the promotion of sustainable energy. The demand for affordable and reliable electrical energy requires different energy sources, where the cost of production often outweighs the environmental factor. This paper aims to investigate the ways smart cities promote sustainability in the electricity sector. For this, a systematic literature review using the PRISMA protocol was employed as the methodological approach. In this review, 154 journal articles were thoroughly analyzed. The results were grouped according to the themes and categorized into energy efficiency, renewable energies, and energy and urban planning. The study findings revealed the following: (a) global academic publication landscape for smart city and energy sustainability research; (b) unbalanced publications when critically evaluating geographical continents’ energy use intensity vs. smart cities’ energy sustainability research outcomes; (c) there is a heavy concentration on the technology dimension of energy sustainability and efficiency, and renewables topics in the literature, but much less attention is paid to the energy and urban planning issues. The insights generated inform urban and energy authorities and provide scholars with directions for prospective research.

An event-triggered output feedback control approach is proposed via a disturbance observer and adaptive dynamic programming (ADP). The solution starts from constructing a nonlinear disturbance observer which only depends on the measurement of system output. A state observer is then developed based on approximation information of system dynamics via neural networks. In order to avoid continuous transmission and reduce communication burden in the closed-loop system, an event-triggered mechanism is introduced such that the control signal is updated only at specific instant that a triggered condition is violated. By virtue of the disturbance observer and state observer, an output-feedback ADP control approach then is developed, where only a critic network is employed to estimate the value function. Based on Lyapunov stability theory, stability of the closed-loop system is rigorously analyzed, and the effectiveness of the proposed control approach is verified by two simulation examples.

Aiming at the problem of interpolar voltage unbalance in bipolar low voltage dc (BLVDC) microgrid, a family of bipolar dc–dc converters with interpolar voltage self-balancing is proposed in this article. The proposed converters are composed of a full bridge inverter and four types of bipolar voltage multiplier (BVM) circuits. Benefiting from the characteristics of the proposed topology, its output power can automatically flow to the output side with lower voltage and has the ability to maintain the voltage balance between BLVDC buses. In addition, the proposed converters have ZVZCS soft-switching characteristics, and the control and driving circuits are consistent with the traditional full bridge inverter. The topology derivation, working principle, soft-switching and voltage self-balancing performances of the proposed converter are analyzed, and a 1 kW experimental prototype with its control system is designed. The experimental results verify the accuracy of the theory and analysis.

The bipolar dc power architecture provides a new high-efficiency and high-reliability solution. Maintaining interpolar voltage balance is crucial in bipolar structures to ensure the reliable and stable operation of the system. This article proposes a family of bipolar dc-dc converters based on bipolar voltage multipliers (BVMs). Notably, the proposed BVM structure has the capacity to autonomously achieve interpolar voltage balance without external balance control strategy. This inherent feature significantly alleviates control circuit complexity. Meanwhile, the BVM structure possesses rectification functionality, facilitating its connection to various front-stage structures with ac output. This article provides a detailed exposition of the operational principles and performance analysis of the proposed voltage balancers (VBs) and discusses a 1-kW prototype experiment. The experimental results validate the accuracy of the theoretical analysis.