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With the significant trend towards variable frequency in heating ventilating and air-conditioner (HVAC) loads, the inverter-based air conditioner load (IACL) clusters are poised to become the mainstay in participating in demand response (DR). During the process of DR, once the indoor temperature exceeds the comfort constraint, HVAC load must be forced to exit DR, which brings correlation to the behaviour of the preceding and following periods, making cluster optimization modelling and solution difficult. In order to solve the problems, this paper proposes an analogue ON/OFF state-switching (AOSS) control method suitable for IACL cluster participating in DR. Firstly, the critical working point corresponding to the comfort constraint is analysed for eliminating the temporal coupling for IACL. Then, an AOSS control method is proposed based on the critical point analysis. The feasibility of the proposed AOSS control is validated by the experimental results, with the Hisense KFR-75W/T08SBp-A2 inverter-based air conditioning DR experimental platform. Furthermore, by using the proposed AOSS control, a day-ahead scheduling model is constructed, and, the traditional state-queuing (SQ) model is transplanted to the IACL cluster for short-term power control. And the case studies verified the effectiveness and applicability of the day-ahead scheduling model and the transplanted SQ model. • Analysing the critical working point corresponding to the comfort constraint. • AOSS control is proposed to eliminate the temporal coupling for IACL. • Aggregation and optimal dispatching for IACL cluster in day-ahead time scale. • Ultra-short time scale IACL cluster power control. [ABSTRACT FROM AUTHOR]

Abstract—This article presents an enhanced control strategy for a direct-driven permanent synchronous generator based wind-power generation system with a flywheel energy storage unit. The behaviors of the direct-driven permanent magnet synchronous generator system with a flywheel energy storage unit under unbalanced grid fault conditions are investigated. Three control targets for the grid-side converter during network unbalance conditions are identified, including eliminating the oscillations in the total active power or reactive power or no negative-sequence current injecting into the grid. Meanwhile, the DC-link voltage oscillations can be effectively suppressed during the unbalanced grid fault by controlling the flywheel energy storage unit. Furthermore, a proportional–integral-resonant controller is designed for the flywheel motor to eliminate the oscillations in the DC-link voltage. Finally, the proposed coordinated control strategy for the direct-driven permanent magnet synchronous generator system with a flywheel energy storage unit has been validated by the simulation results of a 1-MW direct-driven permanent magnet synchronous generator wind power generation system with a flywheel energy storage unit under unbalanced grid fault. [ABSTRACT FROM AUTHOR]

Objective. Curcumin, an active ingredient of turmeric, is proved to be a potential candidate of controlling inflammation and bone resorption, but few reports are on the periodontitis. The purpose of this study was to evaluate whether the intra-gastric administration of curcumin could inhibit the inflammation and alveolar bone resorption in rats following ligature-induced experimental periodontitis. Materials and method. Male Wistar rats were randomly divided into three groups: no ligature placement and administration of vehicle, ligature placement and administration of vehicle, ligature placement and administration of curcumin. After the animals were sacrificed, their mandibles were collected for morphological, histological and immunohistochemical analysis; their gingival tissues were collected for cytokine measurements. Results. Bone resorption was significantly higher in the experimental periodontitis animals treated with vehicle compared with the curcumin-treated group or the control group. Furthermore, receptor activator of nuclear factor- κB ligand (RANKL), receptor activator of nuclear factor- κB (RANK), osteoprotegerin (OPG), tumor necrosis factor- α (TNF- α) and interleukin-6 (IL-6) expression levels were higher in the experimental periodontitis animals treated with vehicle compared with the curcumin treated group or the control group. Conclusions. Curcumin may decrease alveolar bone loss in the experimental periodontitis rats via suppressing the expression of RANKL/RANK/OPG and its anti-inflammatory properties. [ABSTRACT FROM AUTHOR]

Affected by extreme hot and dry weather events, the power supplied by hydropower is seriously insufficient in Sichuan province during the summer of 2022, causing severe power shortage and incalculable economic losses for the society. Therefore, a novel multi-objective scheduling model based on grid-connected hydro-wind-solar-battery energy resources combining flexible reserves is proposed to collaboratively guarantee the power supply reliability of both the contracted long-distance power transmission and the local electricity demand under extreme hot and dry weather. The intermittent nature of water inflow, wind speed, solar irradiance, and load is considered, and the multi-scenarios are produced using Latin Hypercube Sampling method. In this work, thermal plants are regarded as flexible reserves for easing the load shedding level of local load. The McCormick's Envelope method is implemented to linearize the power production model of the hydropower station. A multi-objective model, including minimum penalty cost of load shedding and carbon dioxide emission, is proposed to achieve the economic-environmental equilibrium of the power system. The proposed multi-objective optimal hybrid energy complementary strategy is transformed into a single objective model via ε -constraint method, and the fuzzy satisfying method is introduced to select the best compromise solution in the Pareto Front. The meteorological information of the summer of 2022 is collected to verify the effectiveness of this proposed mixed-integer-linear-programming energy complementary model based on a hydropower station on the Jinsha River in Sichuan province, China. Numerical experiments demonstrate that the proposed model is efficient and can enhance the reliability of real-world power systems under extreme hot and dry weather. A set of policy suggestions have been provided for Sichuan province to develop the power grid to face the extreme weather effect. [ABSTRACT FROM AUTHOR]

This paper mainly proposes a capacity configuration strategy for a hybrid wind farm with fixed-speed induction generator (FSIG)-based and permanent magnet synchronous generator (PMSG)-based wind farms during grid faults. In this paper, FSIG-based wind farm realizes low voltage ride through (LVRT) with the associated control of nearby PMSG systems as StatComs to provide the required reactive power. By establishing the mathematical model of hybrid wind farm containing network parameters, the operation characteristics of the FSIG-based wind farm during grid faults are analyzed in detail. Based on the characteristics and the critical clearing time of FSIG-based wind farm, a novel capacity configuration method for the hybrid wind farm is proposed to calculate the required reactive power of FSIG-based wind farm for a LVRT operation. Based on the capacity configuration result, the minimum installed capacity of PMSG-based wind farm could be determined. Taking into account the impact of reactive power compensation capacity and grid transmission line parameters, the coordinated LVRT capability of the hybrid wind farm is then analyzed. Finally, simulation and experimental results demonstrate the effectiveness of the proposed capacity configuration method and the coordinated operation performance of the hybrid wind farm respectively. [ABSTRACT FROM PUBLISHER]

This paper investigates the coordinated control strategy for a hybrid wind farm with doubly fed induction generator (DFIG)-based and direct-driven permanent-magnet synchronous generator (PMSG)-based wind farms during network unbalance. The negative-sequence current output capabilities of DFIG and PMSG systems under unbalanced grid voltage condition are described. Furthermore, by considering both the negative-sequence current capabilities and requirements of different control targets for each control unit, the controllable operating regions of DFIG and PMSG systems are investigated. According to the controllable operating regions, a targets selection scheme for each control unit is proposed to improve the stability of the hybrid wind farms containing both DFIG-based and PMSG-based wind farms during network unbalance, especially to avoid DFIG-based wind farm tripping from connected power grid under severe grid voltage unbalance conditions. Finally, the proposed coordinated control strategy is validated by the simulation results of a 30-MW-DFIG-based wind farm and a 30-MW-PMSG-based wind farm under different operation conditions and experimental results on a laboratory-scale experimental rig under severe grid voltage unbalance conditions. [ABSTRACT FROM AUTHOR]

Condition monitoring is a cost-effective means to reduce the unscheduled maintenance cost of insulated gate bipolar transistor (IGBT) modules. The junction to case thermal resistance $R_{\mathrm {thjc}}$ is considered as a critical health indicator of IGBT module solder layer. However, thermal interface materials’ (TIMs) deterioration will not only reduce the heat dissipation performance but also affects the accuracy of $R_{\mathrm {thjc}}$ monitoring of IGBT modules. This article investigates the effect of thermal grease deterioration on $R_{\mathrm {thjc}}$ monitoring of IGBT module. First, it is found that the thermal grease deterioration will lead to the decrease of monitored $R_{\mathrm {thjc}}$ of IGBT module under the same health status of IGBT solder layer, despite that the thermal resistance of TIM increasing as deterioration of the TIM takes place. That is, the same monitored increment ratio of $R_{\mathrm {thjc}}$ caused by the solder fatigue may correspond to different health status of the IGBT module, which cannot accurately reflect its actual health status. Then, a compensation strategy for thermal resistance monitoring based on the TIM aging rate is proposed, which uses the established mapping relationship to decouple the negative coupling part of TIM degradation. The compensated thermal resistance can better reflect the actual health status of the IGBT module and approximately eliminate the negative impact. Finally, the feasibility of the proposed compensation strategy is verified by finite element model (FEM) analysis and experiments. [ABSTRACT FROM AUTHOR]

This paper investigates an improved control strategy for a doubly-fed induction generator (DFIG) based wind-power generation system with series grid-side converter (SGSC) under network unbalance and harmonic grid voltage distortion conditions. The integrated mathematical modeling of the DFIG system with SGSC is established by taking both the negative-sequence and harmonic components of the grid voltages into consideration with multiple synchronous rotating reference frames. Under network unbalance and harmonic distortion situations, stator voltage can be kept symmetrical and sinusoidal by the control of SGSC, which indicates that the rotor-side converter (RSC) can be still controlled with the traditional vector control strategy without modifications. Meanwhile, for the parallel grid-side converter (PGSC), three sets of selectable control targets are identified and their corresponding current references are calculated. In addition, the allocation principles for the PGSC’s current references are proposed by taking into account the PGSC’s current rating limit. The impact of PGSC’s current limit on the proposed control strategies have been investigated in detail. Furthermore, a PI regulator with a dual-frequency resonant (PI-DFR) controller in the positive synchronous reference frame for PGSC and SGSC are designed to achieve the rapid and precise regulation of the corresponding components simultaneously. Simulation studies on a DFIG system with SGSC under network unbalance and harmonic distorted voltage situation validate the proposed control strategies and allocation principles for PGSC’s current reference. [ABSTRACT FROM AUTHOR]