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In the microgrid, virtual synchronous generator technology can significantly enhance the anti-interference characteristics of the system frequency and bus voltage, as well as solve the problems of insufficient damping and low inertia. However, the system frequency and active power oscillation caused by power fluctuations and grid faults threaten the stable operation of the grid seriously. Therefore, for an alternating current (AC) microgrid multi-virtual synchronous generator (VSG) parallel system, an improved virtual synchronous generator control algorithm based on a fuzzy inference system is proposed, which adjusts the values of virtual inertia and damping coefficient dynamically through fuzzy logic rules to realize the coordinated control of the two. The enhanced VSG algorithm described in this research has a substantial influence on power-frequency oscillation suppression, decreases active power and frequency overshoot, shortens the adjustment time, and improves system frequency stability active power, according to simulation and experimental findings. Published version This research was supported in part by the International Science and Technology Cooperation Project of Jilin Province Science and Technology Department, grant number 20210402080GH, the author hereby expresses his gratitude to the abovementioned institution for their support.

New energy vehicles have become a global transportation development trend in order to achieve considerable fuel consumption and carbon emission reductions. However, as the number of new energy cars grows, new energy vehicle safety concerns are becoming more evident, posing a major threat to drivers' lives and property and limiting the industry's growth. This paper develops a charging safety early warning model for electric vehicles (EV) based on the Improved Grey Wolf Optimization (IGWO) algorithm in order to improve the timeliness and accuracy of charging safety early warning. The greatest voltage of a single battery was chosen as the study goal based on the polarization characteristics of lithium-ion batteries and the equalization features of a vehicle lithium-ion battery pack. The IGWO-BP algorithm is then used to fit the entire EV charging process and anticipate the vehicle's charging condition. At the same time, set the warning threshold and the warning error code. In real time, comparing the EV charging data with the fitted data, computing the residual, and building the EV charging safety warning model based on the residual change. Finally, case analysis is performed using daily charging data from both rapid and slow charging. The findings reveal that the proposed early warning model based on the IGWO-BP algorithm can reliably recognize the abnormal state of EV charging voltage and issue timely warnings. This research was supported in part by the International Science and Technology Cooperation Project of Jilin Province Science and Technology Department, grant number 20210402080GH, the author hereby expresses his gratitude to the above-mentioned institution for their support.

A novel control scheme to improve the performance of LLC resonant mode controller under light load operation and wide input-output voltage variations is presented in this paper. Poor light load voltage regulation in the LLC resonant converter necessitates the use of burst control mode, which results in performance degradation under light loading conditions. The proposed control scheme uses an adaptive deadband technique that avoids the burst control mode even at extremely light loads resulting in continuous operation and thereby lower output voltage and current ripple, lower noise and higher efficiency. Furthermore, a neural-network-based compensator is proposed in this paper for improving the dynamic performance of the converter under varied operating conditions. Theoretical and simulation results are provided to show the advantages of the proposed control algorithms. A 200W-LLC resonant converter is used for experimental verification of the proposed control scheme.

DC network is a desired solution to cater for the increasing penetration of DC-compatible energy sources, storages and loads. This paper proposes a novel topology of DC network in reference to the conventional AC transmission/distribution network, where there are multiple DC subgrids with same or different nominal voltages interconnected to the common bus by DC Transformer (DCT). Different voltage levels have been set in the DC network with considerations of compatibility, power loss, voltage drop, distribution distance, etc. DCT is proposed to substitute the conventional power converter for bus voltage regulation and galvanic isolation. Compared with various topologies and CLLC-type has been recommended due to its capabilities of bidirectional power flow, seamless transition and low switching loss. Different operation scenarios for the DCT of the DC network has been analyzed. DCT is designed in order to maximize the conversion efficiency and minimize output voltage variations in different conditions. The models of DCT and its implementation in the proposed DC network have been developed in Matlab/Simulink. The performances of system under different operation conditions have been confirmed.

Multiple ESs with different characteristics help to constitute hybrid energy storage systems (HESSs) which should bear desirable power/energy density and dynamic performances. For this purpose, an advanced power allocation strategy combining traditional voltage-power (V-P) droops and integral droops (IDs), could be utilized. With the harmonized integration of V-P and ID, ESs with high energy density but restrained dynamics naturally respond to low frequency components of load power, while ESs with adequate power density but limited stored energy compensate the fast changes of power demand autonomously. Regardless of the merits of presented strategy, comprehensive stability analyses for a HESS with such power management scheme have not been studied. In this paper, the HESS is fully modeled in the small signal sense, with no dynamic state being neglected. The entire system stability is analyzed through comprehensive eigenvalue loci investigations. Tome domain simulations perfectly verify the effectiveness and accuracy of the eigenvalue analyzing results.

Hybrid AC/DC microgrid (MG) is a promising electrical power system architecture that enables to harmonize AC and DC energy conversions. Due to the complicated configuration, comprehensive stability analyses for a complete hybrid MG still stand as an unsurmountable challenge. To address this issue, this paper decomposes the MG system into several electrical modules, i.e., an AC source, a DC source, multi-paralleled interlinking converters (ICs) and line impedances. These modules are first individually modeled in the small signal sense. They are then combined to establish a full autonomous mathematical expression for characterizing dynamics of the hybrid MG. To investigate MG system stability, the influences of diversified operating points, line impedances and the selected key control parameters are examined by evaluating eigenvalue loci of the derived mathematical model. Time-domain simulations reveal the perfect matching between the results given by Matlab/Simulink and eigenvalue loci plots.

This paper presents an integrated series-parallel microgrid(MG), where a few distributed generation(DG) units in series type are used to form a DG string, then DG strings supply power to the common load in parallel type. With this structure, low-voltage devices could be integrated into MG without DC-DC boost converters. It provides a more flexible and efficient way to form higher voltage level MG. But it is difficult to find a decentralized control method to achieve power balance for this integrated system because of the difference between power transmission characteristics of parallel and series converter system. For this proposed MG in island mode, a unified distributed control strategy is proposed. With low bandwidth communication, accurate power sharing can be realized by exchanging information between the first converters connected to the bus of adjacent DG strings and between adjacent converters inside each DG string. Because the central controller is not used, the communication pressure of the system is reduced and the reliability is guaranteed. Simulation test has verified the feasibility and validity of the proposed control strategy.

Hybrid AC/DC microgrids (MG) offer a promising way to incorporate heterogeneous energy sources into AC or DC subgrids while minimizing energy conversions stages. For a MG working in long term, the capacities of both AC and DC subgrids would inevitably increase, which may result in more power interactions between the two subgrids. In this context, a single bidirectional interlinking converter (BIC) which bridges AC and DC subgrids may suffer from overstress. Hence, multi-paralleled BICs configuration should be adopted and well managed. This paper proposes a dynamic consensus approach for proportional power allocation among multiple BICs, thereby avoiding the overcurrent of a particular BIC and enhancing the flexibility of system communication. The effectiveness of the proposed power management strategy has been verified by simulation results.

Solar PV is renowned all around the world, but its prevalence varies with a country’s solar profile. Singapore is an island country which has limited potential towards various renewable options. On the UN’s request to submit the Intended Nationally Determined Contribution (INDC) against carbon emissions, Singapore, as a promoter of efficient energy, has come up with an elaborate Climate Action Plan towards carbon emission reduction. Solar PV is the most promising renewable energy option for the country. An aspiring leap towards 350MWp PV capacity by 2020 is on trial, which would involve numerous PV installation projects. The project on installing PV with Energy Storage System (ESS) in Jurong Port (JP) distribution grid is one of them. This paper proposes a 3.3MWp PV installation in the low voltage side of the JP distribution grid by providing comprehensive steady-state analyses in different loading scenarios. Comparison among different configurations of PV and ESS is done and it is found that the PV could reduce line congestions and circumvent substantial transmission losses. Also, during light loading, it sends surplus power back to the grid.

To enhance the interaction between the thermal and electrical, a hybrid AC/DC microgrid (MG) embedded energy hub (EH) is proposed. In EH, electrical, thermal, i.e. heat and cooling are supplied and managed to increase the operational efficiency while meeting the energy demand. It formulates a two-stage stochastic optimization problem. In the first stage, i.e. day-ahead operation, the hourly generation, conversion, and storage are optimized to minimize the fuel cost. In the second stage, considering the stochastic nature of photovoltaic and demand, the heat and cooling supply are adjusted to realize the power balancing in the electrical system, while meeting the thermal energy demand. The two-stage optimization problem is reformulated to a deterministic optimization problem, using sample average approximation. Simulations have been carried out on the test system. Results have verified the effectiveness of the proposed method, collecting the flexibility of the thermal system to the electrical networks via EH.

Hybrid AC/DC microgrid exhibits better compatibility with renewable energy sources, energy storages and various loads. The conventional smart grid system are building based and require customized system design, which is costly and time-consuming. In this paper, smart energy hub, which is the modularized microgrid system design, is proposed to simplify system deployment. In order to realize the three-level hierarchical control to ensure both speed of response and system control accuracy, different sub-systems have been designed and developed. Multi-mode operation of the power electronic converters is enabled to cater for system operation in different scenarios. Resource manager serves as a super smart meter + relay controller to simplify the SCADA system design and enhance the speed of response. Microgrid operating system is designed to coordinate all the function blocks to realize hierarchical control in robust manner. Prototype of the proposed energy hub has been designed and developed to integrate all the sub-systems (both hardware and software).

As the penetration of renewable energy increasing in power systems, the contribution of VSC-HVDC for system stability is highly expected. Due to the decoupling modulating of active and reactive power output, the influence of HVDC on the inter-area oscillation is widely studied. This paper proposes a new ANN (Artificial Neural Network) based control design scheme for VSC-HVDC systems to damp inter-area oscillations of power systems. The controller is integrated to the conventional vector control to enhance the damping of the inter-area oscillations. Simulation test in a two-area-four-machine interconnection power system is studied. The test result showed that the VSC-HVDC with proposed damping controller can enhance the system damping under various disturbances.

This paper presents the establishment and operation control strategy of a DC microgrid incorporated with bidirectional inductive power transfer (BIPT) system for Electric Vehicles (EVs) charging applications. The primary side of IPT system is powered by a DC microgrid which is established from PV as renewable energy source and battery for energy storage. The proposed concept minimizes power electronic components requirement while maintaining high power efficiency due to the reduction of power conversion stages and the proposed control strategy. The proposed concept is applicable for low to medium power level EV charging applications.

Buildings are important places and parts in the society. The conventional power supply of a building is AC power from the utility grid. As the growing penetration of renewable energy source and DC loads, it becomes practical and common for a building supplied by the distributed generators with DC power. Considering this unprecedented transition from the conventional AC building to the hybrid AC/DC building, more and more electronic devices will be utilized as well as the nonlinear loads, which will motivate harmonics in the power network of the building. As harmonics might decrease the power quality and increase losses, the harmonic assessment in designing a new building become urgent, which lacks guidance in the literature. In this work, the basic power network of a hybrid AC/DC building is firstly introduced as well as the harmonics. Based on the harmonic analysis methods, i.e. harmonic power flow calculation and the harmonic frequency scan, it can be found that the AC/DC exchange current and the power network structure both affect the harmonics, which is helpful to the design of hybrid AC/DC building.

The second-order sliding-mode controller based on improved sub-optimal algorithm for synchronous Buck converte r is designed, and the converter can be controlled only by detecti ng the output voltage without measuring the capacitance current of the converter. By introducing hysteresis to sub-optimal algorit hm, the switching frequency of the converter is limited when the output voltage is stable. In the Simulink, the first-order sliding-mode and second-order sliding-mode controller are actualized by using the state machine, the simulation test and verify the start-up performance and steady-state behavior and the robust against the large load disturbance jump from 10A to 20A and the power disturbance jump from 5V to 10V. The simulation results show that the proposed second-order sliding-mode controller retains the robustness of sliding mode control and is superiors to first order s liding-mode control in the aspect of resisting disturbance.

This paper presents the implementation of a hardware-in-the-loop simulation (HIL) workbench for hybrid AC/DC micro grid. The hybrid AC/DC micro grid integrates both distributed sources and loads in AC/DC systems to respective links directly. For DC system, photovoltaic arrays with boost converter (PVBC), battery with bi-directional DC/DC converter and DC loads are covered. Diesel generator (DGs) and conventional AC loads are included in AC grid. Between AC and DC girds, a four-quadrant operating three phase converter is applied which can act as either an inverter or a rectifier to maintain power balance between two systems. The power units of this hybrid micro grid are simulated with Opal-RT real-time simulator while the control units are implemented on TI TMS320F28335 DSPs. This hardware-in-the-loop simulation workbench offers a good platform for system level control algorithm design and verification in micro grid. And it serves as a basis for future power-hardware-in-the-loop simulation (PHIL) with power stage involved.

This paper presents a coordination secondary control strategy for autonomous hybrid AC/DC microgrids with global power sharing operation. In the previous work, primary control with droop control method was applied to distributed generators to ensure local power sharing without communication links in either ac or dc microgrid. An extension of local power sharing for individual microgrid is the global power sharing for hybrid microgrids. With global power sharing control, all distributed generators throughout the hybrid system are capable of sharing the entire ac and dc loads without any information exchange. The coexistence of local power sharing and global power sharing in hybrid system is thereafter defined as generalized primary control, which is usually employed for fully decentralized power management throughout the whole hybrid system. To eliminate the inherent voltage/frequency deviations caused by the generalized primary control, the secondary control is usually applied to each distribution generator for voltage/frequency restoration. This however will degrade the performance of global power sharing operation because of its characteristics of voltage/frequency deviation dependence. To achieve voltage/frequency restoration while maintaining the global power sharing operation, a coordination secondary control was proposed and the effectiveness of the proposed method has been verified by the simulation results.

Since there are many convertors, invertors, bidirection convertors, sensors and meters in the AC&DC smart micro-grid system, how to collect the real-time data from these devices and send the control command to them to carry out the remote optimization control in high-efficiency is the main problem the smart micro-grid communication system need to face and solve. In this paper, a 3-layer communication architecture is designed for AC&DC smart micro-grid. In this system, we use different communication method to solve the problem that there are many different devices with different type communication protocol. Finally, we built up the demo system in our lab and realize the function that the data from different terminal device can be transform to central control system and the control command can be send to terminal devices more reliability and effectively, which can provide an useful demo for development of AC&DC hybrid smart micro-grid control and monitoring system.

This paper articulates a novel oscillator design that can provide stable frequency operation over a wide temperature range with self-calibration technique. A simple ring oscillator is implemented to sense the temperature variation, and some digital circuits tune the output frequency according to the sensing outcomes. Simulation results show that the circuit can generate a stable frequency of 13.8MHz. The power consumption of the whole system is only 52.8µW. The temperature coefficient is less than ±0.4% ranging from -55 to 125 ◦C in the worst process corner whereas the supply voltage is ultra-low at 0.6V. Accepted version