The reasonable allocation of battery energy storage systems (BESSs) is a long-term goal for energy storage researchers. This paper proposed an optimal allocation method for ESSs considering uncertainties of battery capacity fading and operation strategies correlation in distribution networks. Firstly, the capacity fading calculation error by semi empirical formula was modelled by distribution method and interval method according to experimental data analysis. And then, multiple operation strategies correlation of BESSs was decoupled by Cholesky factorization method for giving prominence to the flexible control strategy of BESSs. Finally, Cplex tool is used to solve the optimal allocation model of BESSs considering uncertainties of battery capacity fading with operation strategies correlation. Case studies showed that the method proposed in this paper improves the operating benefits by 18.84% and prolongs the cycle life of BESS by 8.28% compared with the single operation strategy. Also, the allocation capacity of BESSs is largely increased by about 10.1% considering the uncertainties of battery capacity fading model. Besides, the battery life decays faster under the uncertainties of battery capacity fading.

With the continuous increase of the proportion of new energy in the power system, the parallel operation of multiple virtual synchronous generators (VSGs) has become an important means to enhance the inertia and flexibility of the power grid. However, the dynamic interaction among parallel VSG units may lead to complex harmonic oscillations and sub-synchronous stability problems, and the decentralized control is difficult to coordinate the impedance characteristics of multiple VSGs. Therefore, this paper first conducts a power coupling analysis of parallel VSGs with decentralized control; secondly, it establishes the sequence impedance model of parallel VSGs with centralized control and compares it with the output impedance of decentralized control; finally, it analyzes the stability of parallel VSGs with centralized control under different grid strengths using the impedance ratio stability criterion.

Expanding deployment of grid-connected voltage source inverters elevates the critical need for impedance characteristic analysis in stability assessment. Extending beyond balanced three-phase applications, this work generalizes small-signal stability analysis methodology to unbalanced three-phase contexts. Four-leg inverter systems operating under unbalanced conditions receive specific focus through adaptation of impedance-based frequency-domain stability assessment. Characterized by interconnected positive-, negative-, and zero-sequence impedance networks, these configurations demand particular examination. Within the developed framework, dominant factors regulating zero-sequence impedance behavior are established. Unbalanced converter system modeling presents substantially greater challenges than balanced counterparts, primarily due to negative- and zero-sequence components arising from AC system asymmetries. A specialized small-signal model is constructed to determine whether voltage imbalances significantly alter inverter impedance characteristics compared to fully balanced operation. Simulation and experimental validation collectively confirm both the stability analysis methodology and small-signal model efficacy.

This paper proposed a nested bi-Level scheduling strategy for energy storage systems in hybrid microgrid considering uncertainties of battery dynamic performances. Firstly, the uncertainties in dynamic performances caused by fitting error including efficiencies, self-discharge rate, cycle life and capacity fading were modeled by interval method and probability distribution method. Simultaneously, the significant influences of battery dynamic performances on power outputs of battery were specially quantized by direct physical influence, direct electric quantity influence and indirect state influence. Then, a nested bi-level optimization model was developed for specifying the scheduling strategy of energy storage systems. Inner layer optimization was applied for realizing the operation strategy optimization of battery ESSs and outer layer optimization was applied for realizing the battery performance optimization. Case studies based on multi-scene generation mode verified the effectiveness of the proposed nested bi-level scheduling strategy. With the increase of battery dynamic performances uncertainties, more economic benefits are brought by energy storage battery, but the battery dynamic performances continuously decline. Compared with single layer optimization, nested bi-level optimization scheduling model slightly reduced the total benefits, but the battery dynamic performances f1 is significantly improved by about 20%.

Accurate estimation of battery capacity is crucial for the safe operation of energy storage power stations. This paper proposes an adaptive battery capacity estimation method based on dual-driven fusion for lithium-ion batteries in energy storage systems. Health features that are highly correlated with the capacity are extracted from historical data as the training dataset for a convolutional neural network, which constructs an online capacity estimation model. Then the discrete Arrhenius degradation model is developed for continuous estimation under time-varying conditions. Finally, a closed-loop Arrhenius model is constructed using the adaptive parameter correction method, based on the difference in capacity estimation between the two models. Experimental results show that the proposed method maintains high prediction accuracy while reducing the burden on battery monitoring equipment.

Due to the lack of a common DC bus in cascade H-bridge energy storage converters, the DC-side currents to battery modules contain significant second-order harmonic components. These harmonics can cause battery heating and accelerate aging. Effective measures are needed to suppress these harmonic currents. This study introduces the cascade H-bridge energy storage system's topology and control strategy, analyzes the generation mechanism of second-order harmonic currents using power conservation principles, and examines their impact under traditional intra-phase SOC balancing control. It proposes a modified intra-phase SOC balancing control strategy that injects a third-order harmonic voltage. This method adds a third-order harmonic voltage to the modulation voltages of each submodule, converting second-order harmonic currents into fourth-order harmonics that are easier to filter out, thereby reducing ripple current in the battery modules. Additionally, this approach ensures that second-order ripple currents across battery modules in phase are consistent in amplitude and phase, aiding in centralized filtering. Simulation results validate the effectiveness of intra-phase SOC balancing control strategy with THVI(Third Harmonic Voltage Injection).

A cascaded H-bridge(CHB) grid-forming energy storage control strategy considering the state of charge (SOC) balance in unbalanced grid is presented. Utilizing voltage-type virtual synchronous generator (VSG) control enables grid-forming energy storage to address issues arising from the characteristics of renewable energy sources, such as low inertia and underdamping, which result in insufficient voltage support and lower power supply reliability. Establishing a mathematical model of the VSG, the synthesized three-phase voltage serves as the positive-sequence voltage command signal for the voltage-current loop. Addressing SOC issues present in VSG based on CHB in unbalanced grids, a SOC-balancing control method based on negative-sequence voltage closed-loop is proposed, with the injected negative-sequence voltage serving as the instruction signal. The stability of the VSG is assessed through root locus analysis, followed by the design of critical parameters. Finally, simulation analysis is conducted to validate the effectiveness of the proposed CHB grid.forming energy storage control strategy considering SOC-balancing in unbalanced grid.

In response to the issue of battery energy storage systems' response to dynamic real-time electricity prices in the electricity market environment, this paper proposes a nested bi-level method for battery energy storage system optimized operation in active distribution networks considering differences of dynamic electricity prices. Firstly, the influence factors of real-time electricity prices with multi -dimensional randomness are considered, and an autoregressive average time series approach and the least squares method are used to establish dynamic real-time electricity price models with multiple scenarios. Then, by modeling and analyzing the participation of loads in demand response, a nested bi-level optimization operational model that considers differences of dynamic electricity prices is established. The inner layer manages the peak shaving and valley filling rate of the active distribution network, while the outer layer manages the operational benefits of the active distribution network while satisfying the optimization of the inner layer. The bi-level optimization result is obtained through nested iterative calculation. Finally, the proposed method was validated on an active distribution network system comprising IEEE14 nodes. The results indicate that energy storage has the strongest response capability when subjected to dynamic real-time electricity prices based on error perturbation. The active distribution network achieved its peak operating benefits and peak shaving and valley filling rate, which respectively increased to $185.92 and 0.912, representing enhancements of 37.78 % and 59.72 %.

Molecular dynamics simulation (MDS) is adopted to analyze how the nanoparticles morphology affects the fluid phase transition of nanofluid. In this simulation system, the nanochannel surfaces and nanopar-ticles are composed of solid copper and the base fluid is argon fluid. In addition, physical quantities such as total energy, average temperature, density, gas atomic number and thermal conductivity of these atomic structures are calculated. Through the addition of nanoparticles containing circle-, cubic-, and cylinder-shaped base fluid, it is observed that the time of phase transition onset is reduced and the rate of temperature increase increases with the decrease of specific surface area of nanoparticles, and among the nanoparticles with the same specific surface area, the cube nanoparticles have the greatest effect on the time of phase transition onset with 22.2 % reduction. The number of atoms in the gas phase after 17 ns decreases when nanoparticles are added to the Ar fluid. Conversely, increasing the specific surface area of nanoparticles reduces the temperature rise rate and prolongs the time of atomic phase transition. The nanofluid thermal conductivity is increased to 18 % in comparison with the base fluid. Increasing the specific surface area of nanoparticles enhances the perturbation of the particles. Finally, the most signif-icant increase in thermal conductivity is observed for the cubic shape nanoparticles in comparison to the different shapes of nanoparticles. The thermal conductivity of nanofluid containing spherical, cubic, and cylindrical nanoparticles increase by 5 %, 18 %, and 16 %, respectively, by comparison with the thermal conductivity of Ar fluids. The obtained results can explain more clearly how the shape and specific surface area of nanoparticles affect the boiling phase transition of nanofluids, not only Cu-Ar nanofluids, but also other types of nanofluids.(c) 2022 Elsevier B.V. All rights reserved.

Three-phase four-wire cascaded multilevel inverter can be utilized in lithium battery cascade utilization and other fields. However, the conditions of power balance control may conflict with the voltage support conditions, which may cause the failure of the control strategy. To solve the problems existed in the three-phase three-wire system, a split-capacitor three-phase four-wire system is adopted in this paper with the dc side midpoint connected to the neutral line which can provide access to zero-sequence components. Thus the new constraint equations are formed from the power generated by zero sequence components to achieve power balance and voltage support simultaneously. A new control strategy with peak current limitation for three-phase four-wire cascaded multilevel inverter under asymmetrical grid fault is proposed in this paper. The control strategy proposed in this paper ensures that the inverter operates safely during voltage sags, limiting the injected current to the maximum allowed by the inverter. Simulation and experiment results verified the effectiveness of the strategy.

In this paper, the influence of surface roughness inside the nanochannel on nanofluid flowing properties was studied by using molecular dynamics simulation (MDS). In our simulations, water molecules were employed as the base fluid, and copper atoms were adopted to model the nanochannel walls and nanoparticles. In order to investigate the effect of surface roughness including rectangular, triangular, and hemispherical roughness on the flow properties of nanofluid, parameters such as temperature, total potential energy, velocity, and density profiles of H2O/Cu nanofluid were calculated. From the above simulation results, we find that increasing the roughness height increases the temperature and velocity of nanofluid. In addition, the surface roughness increases the velocity and temperature in the nanochannel by shrinking the cross-section with constant roughness height. And the surface roughness also reduces the range of fluctuations of the density near the walls in the nanochannel, which is because fewer fluid particles reside near the rough nanochannel walls compared to the ideal nanochannel. The other result is that the triangular roughness has the greatest effect on the flow properties of nanofluid, the effect of surface roughness on the flow property of nanofluid cannot be ignored. (C) 2021 Published by Elsevier B.V.

The fuel cell/battery durability and hybrid system stability are major considerations for the power management of fuel cell hybrid electric bus (FCHEB) operating on complicated driving conditions. In this paper, a real time nonlinear adaptive control (NAC) with stability analyze is formulated for power management of FCHEB. Firstly, the mathematical model of hybrid power system is analyzed, which is established for control-oriented design. Furthermore, the NAC-based strategy with quadratic Lyapunov function is set up to guarantee the stability of closed-loop power system, and the power split between fuel cell and battery is controlled with the durability consideration. Finally, two real-time power management strategies, state machine control (SMC) and fuzzy logic control (FLC), are implemented to evaluate the performance of NAC-based strategy, and the simulation results suggest that the guaranteed stability of NAC-based strategy can efficiently prolong fuel cell/battery lifespan and provide better fuel consumption economy for FCHEB. (c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

The battery thermal management system plays a crucial role for lithium-ion battery in electric vehicles because of its susceptible performance during fast discharging. In this study, the Newman, Tiedemann, Gu, and Kim (NTGK) electrochemical model is applied to investigate the numerical simulation on the temperature distribution within battery when discharging at various rates, which is comprehensively validated with experimental data. Following the verification, a threedimensional heat pipe integrated system (HPIS) is designed with a novel thermal resistance model on the basis of equivalent thermal circuit method. The combination of thermal resistance between pipes and fins at the condenser section greatly predicts the temperature distribution of the system. Then the simulation model is employed to obtain the cooling efficiency of heat pipe (HP) under transient conditions. The temperature difference and maximum temperature of the battery pack under natural and forced air convection are compared. Implementation of insulating board overcomes the thermal runaway and propagation to protect the lithium-ion battery during a rapid discharging rate of adjacent cell. Simulation results reveal that the HPIS-based battery pack not only improves the heat dissipation capability, but also provides the thermal runaway protection to ensure the battery cell safety.

A comprehensively two-dimensional model is established to investigate the thermal performance of two-phase closed thermosyphon (TPCT) charged with acetone. A Volume of Fluid (VOF) method is utilized to simulate the phase change and two-phase flow behaviors. The mass and heat transfer process during the evaporation and condensation are implemented by a user-defined function (UDF) source. The application of thermosyphon can meet the requirements of space structure of battery pack and transfer massive heat from the cell to the environment by phase change mechanism. Additionally, an extended condenser surface of the thermosyphon is developed to enhance the heat transfer performance of liquid film condensation by extended surface, which is estimated by several indicators in terms of temperature distribution, vapor volume fraction, thermal resistance, wall heat transfer coefficient, and velocity. The results reveal that TPCT with extended condenser surface can maintain a great thermal homogeneity and generate well-distributed bubbles along the vertical axial without heat accumulation at the upper zone of evaporator section. Compared with normal condenser, the total thermal resistances decrease by 5%, 25.7% and 17.0% respectively, while the heating power are 5 W, 10 W and 15 W. Moreover, higher power inputs can significantly accelerate the formation of bubbles at the boiling pool, as well as the droplets and liquid film at the condenser section, which increase the thermal performance of thermosyphon.

This paper proposes a control strategy for voltage support and power balance between phases based on the cascaded system. The reference currents injected into the system are closely related to the grid-connected impedance and the grid voltage unbalance factor in the proposed strategy. Simultaneously, it focuses on the reasonable design of the negative-sequence current injection to achieve the proposed target for balancing active power among phases. In order to avoid excessive injection current, the maximum injected current is controlled within the safe and reliable operating range of the inverter. Finally, the proposed control strategy is simulated on Matlab/Simulink.

As an important part of AC-DC hybrid microgrid, battery energy storage systems (ESSs) can improve the flexibility and economy of system operation. This paper presented an optimized operation method for AC-DC hybrid microgrid considering the dynamic efficiency and maximum absorption power of vanadium redox flow battery (VRB). Firstly, the model of dynamic efficiency and maximum absorption power for VRB ESSs were respectively established. And then, the structure of AC-DC hybrid microgrid was designed and the operation optimization method of AC-DC hybrid microgrid was reasonably constructed. Finally, the proposed optimized operation method for AC-DC hybrid microgrid was solved by particle swarm optimization. Case studies showed that dynamic efficiency and maximum absorption power of VRB ESSs have a great influence on the operation of AC-DC hybrid microgrid.

In order to design a high voltage capacitor ageing tester, topology of multilevel cascaded H-bridges is used. Considering the economics of the system, the converter contains only one dc source and the rest of H-bridges are fed with capacitors. However, the challenge brought with economy is control of the capacitor voltages. Existing researches mostly based on phase-shifting modulation approach. In this paper, a voltage vector superposition based control strategy and a method to select dc voltages are proposed. This control approach has merits of simple control principle and control parameters are easy to design. In the end of this paper, the simulation results validate this control strategy.

The parallel inverter system with common AC and DC bus has the advantages of small size, low cost and high reliability. However, due to the inconsistency of switch status and main circuit parameters, zero sequence circulating current will be generated between inverters, which will cause serious distortion of grid-connected current, increase of system loss, and decrease of efficiency. This paper focuses on the research on zero-sequence circulating current suppression of parallel inverter systems with common AC and DC bus. First, the zero-sequence circulating current model of parallel inverters is analyzed, and the reasons for the generation of zero-sequence circulating current are analyzed. The circulation suppression method with zero-sequence component feedforward based on traditional PI control is proposed. Finally, the effectiveness of the proposed control method is verified by simulation and experiment.

Due to the low output distortion and switch voltage stress, Vienna rectifiers have been widely utilized in high-power applications such as communication power supplies, wind power systems and electric vehicle charging piles. However, Vienna rectifiers still have to face tough challenges under unbalanced grid considering the inherit operating range limitation caused by its structure. Consequently, a deadbeat predictive power control (DBP-PC) for the Vienna rectifier under unbalanced grid is proposed. Using the positive and negative sequence double dq decoupling current control strategy, the operating range of the Vienna rectifier under unbalanced grid is analyzed. Furthermore, an improved DBP-PC for Vienna rectifiers under unbalanced grid is proposed. By the improved DBP-PC, the stable operating range can be effectively extended. Finally, the corresponding simulations and experiments are executed to demonstrate the performance of the proposed control strategy.

The high voltage direct hanging energy storage system can effectively solve the problems of fluctuation and intermittence caused by environmental factors, and improve the ability of power system to absorb new energy. By controlling the energy storage, the new energy station has certain inertia and damping characteristics, so that the new energy power station can be connected to the grid friendlier. Starting from the time scale division method of inertial response control, this paper studies the energy demand of inertial response of large-scale new energy power station in different time scales, and gives the inertial response control strategy under different time scales. The model of high voltage direct hanging energy storage system is established, and the inertia response characteristics control technology is verified.