Continuously increasing demand of microgrids with high penetration of distributed energy generators, mainly renewable energy sources, is modifying the traditional structure of the electric distribution grid. Major power consumer countries are looking for alternative energy sources to avoid the impact of higher fossil fuel consumption. Thus, different policies have been promulgated to promote renewable energy technologies (RETs) and distributed energy resource (DER) deployment and are encouraging technological innovation. These policies aim to reduce greenhouse gas (GHG) emissions and achieve energy security and independence to meet an ever-increasing electricity demand. Many studies have been performed on the successful integration of RET and DER operation and control, protection and stability issues, all simultaneously and satisfactorily implemented during feasible microgrid operation. However, apart from the technical challenges, few microgrid studies exist on effective policies and incentives for microgrid promotion and deployment. This survey investigates the policy, regulatory and financial (economical and commercial) barriers, which hinder the deployment of microgrids in the European Union (EU), United States (USA) and China. In this paper, a clear view on microgrid policy instruments and challenges are investigated to aid future developments.

The transport sector generates a considerable amount of greenhouse gas (GHG) emissions worldwide, especially road transport, which accounts for 95% of the total GHGs. It is commonly known that Electric vehicles (EVs) can significantly reduce GHG emissions. However, with a fossil-fuel-based power generation system, EVs can produce more GHGs and therefore cannot be regarded as purely environmentally friendly. As a result, renewable energy sources (RES) such as photovoltaic (PV) can be integrated into the EV charging infrastructure to improve the sustainability of the transportation system. This paper reviews the state-of-the-art literature on power electronics converter systems, which interface with the utility grid, PV systems, and EVs. Comparisons are made in terms of their topologies, isolation, power and voltage ranges, efficiency, and bi-directional power capability for V2G operation. Specific attention is devoted to bidirectional isolated and non-isolated EV-interfaced converters in non-integrated architectures. A brief description of EV charger types, their power levels, and standards is provided. It is anticipated that the studies and comparisons in this paper would be advantageous as an all-in-one source of information for researchers seeking information related to EV charging infrastructures.

In order to overcome the limitations of the existing classical and solid-state Marx Pulse Generators, this paper proposes a new modular multilevel voltage-Boosting Marx Pulse Generator (BMPG). The proposed BMPG has hardware features that allow modularity, redundancy and scalability as well as operational features that alleviate the need of series connected switches and allows generation of a wide range of pulse waveforms. In the BMPG, a controllable low-voltage input boost converter supplies, via Directing/Blocking (D/B) diodes, two arms of a series modular multilevel converter Half-Bridge Sub-Modules (HB-SMs). At start up, all the arm's SM capacitors are resonantly charged in parallel from 0V, simultaneously via directing diodes, to a voltage in excess of the source voltage. After first pulse delivery, the energy of the SM capacitors decreases due to the generated pulse. Then, for continuous operation without fully discharging the SM capacitors or having a large voltage droop as in the available Marx generators, the SM-capacitors are continuously re-charged in parallel, to the desired boosted voltage level. Because all SMs are parallel connected, the boost converter duty ratio is controlled by a single voltage measurement at the output terminals of the boost converter. Due to the proposed SMs structure and the utilization of D/B diodes, each SM capacitor is effectively controlled individually without requiring a voltage sensor across each SM capacitor. Generation of the commonly used pulse waveforms in electroporation applications is possible, whilst assuring balanced capacitors, hence SM voltages. The proposed BMPG has several topological variations, such as utilizing a buck-boost converter at the input stage and replacing the HB-SM with full-bridge SMs. The proposed BMPG topology is assessed by simulation and scaled-down proof-of-concept experimentation to explore its viability for electroporation applications.

This paper presents a dual Modular Multilevel Converter (MMC) topology that utilizes energy exchange between adjacent arm Sub-Modules (SM), operating with out-of-phase modulation. The proposed configuration is applicable to medium-voltage, high-power variable-speed drives incorporating open-end stator winding machines. A novel concept of power redistribution between adjacent SMs in the dual MMC topology is realized through high-frequency transformer-based dc-dc converter modules. This concept offers a significant reduction in the sizing requirement of the SM capacitance and the stored energy in the MMC system, while avoiding the problem of wide voltage fluctuations of SM capacitors, especially at low operating frequencies. The proposed configuration can produce dc voltage, therefore, a machine speed-range from zero speed to the rated speed is possible under the rated torque operating condition. The operating principles of the proposed dual MMC configuration are elaborated and necessary mathematical analysis is derived. Simulation and experimental results verify the concept of the proposed drive configuration.

This paper presents a drive system based on a modular multilevel converter (MMC) with high-frequency magnetic channels between adjacent-arm submodules (SMs), suitable for medium-voltage, high-power three-phase variable-speed machines. The configuration employs chains of dual half-bridge (DHB) modules linking adjacent SMs of three-phase symmetrical arms. The DHB modules are operating as power channels enabling energy exchange to restore the power imbalance among the SM capacitors. This allows arms' ripple-powers to be entirely decoupled through bidirectional power transfer between adjacent-arm SMs, resulting in a near ripple-free SM capacitor voltage profile. Therefore, the MMC common problem of wide voltage fluctuation across SM capacitors is comprehensively solved, independent of the operating frequency. Additionally, a significant reduction in the sizing requirement of SM capacitance is achieved. The configuration is able to drive multi-megawatt machines from standstill to the rated speed at the rated torque operating condition. The operating principle of the proposed MMC configuration is explained and necessary mathematical analysis is derived. Features and viability of the proposed drive system are verified through simulation and experimentation.

This paper proposes a new asymmetric neutral point diode clamped multi-level (NPC) converter for a four-phase switched reluctance motor drive. The inbuilt NPC clamping capacitors are used for both voltage level clamping and also as dc rail voltage-boosting capacitors to increase the output power of the motor, particularly for high speed electric vehicle applications. The new converter allows regenerative energy to be recovered back to the dc supply for rapid machine braking, thus increasing overall drive efficiency. Analysis of the different modes of converter operation, along with design equations for sizing the voltage-boosting capacitors, are detailed. The effect of capacitance on boost voltage and increased motor base speed is presented. Simulation and experimental results confirm the effectiveness of the proposed converter.