Cascaded Inverters for Grid-Connected Photovoltaic Systems

With the extraordinary market growth in grid-connected PV systems, there is increasing interests in grid-connected PV inverters. Focus has been placed on cheap, high-efficiency, and innovative inverter solutions, leading to a high diversity within the inverters and new system configurations. This dissertation chooses cascaded multilevel inverter topologies for grid-connected PV systems to reduce the cost and improve the efficiency. First, a single-phase cascaded H-bridge multilevel PV inverter is discussed. To maximize the solar energy extraction of each PV string, an individual maximum power point tracking (MPPT) control scheme is applied, which allows independent control of each dc-link voltage. A generalized nonactive power theory is applied to generate the reactive current reference. Within the inverter’s capability, the local consumption of reactive power is provided to realize power factor correction. Then, the modular cascaded H-bridge multilevel inverter is connected to a three-phase utility system and nine PV panels. Individual MPPT control is also applied to realize better utilization of PV modules. Also, mismatches between PV panels may introduce unbalanced power supplied to the three-phase grid-connected system. Thus, a modulation compensation scheme is applied to balance the three-phase grid current by injecting a zero sequence voltage. A modular cascaded multilevel inverter prototype has been built and tested in both the single-phase and three-phase PV system. Simulation and experimental results are presented to validate the proposed control schemes. The three-phase cascaded voltage source inverter (VSI), as another cascaded inverter topology, is also proposed for grid-connected PV applications. The equivalent model and average model of the three-phase cascaded VSI are established to realize the central control. In addition, the control scheme applied in the traditional three-phase two-level VSI is modified for this application. Simulation and experimental results are presented as well. The targets of reducing the cost and improving the overall efficiency of the PV inverters can be achieved by applying the cascaded PV inverters and the proposed control schemes

A New Distributed Optimization for Community Microgrids Scheduling

This paper proposes a distributed optimization model for community microgrids considering the building thermal dynamics and customer comfort preference. The microgrid central controller (MCC) minimizes the total cost of operating the community microgrid, including fuel cost, purchasing cost, battery degradation cost and voluntary load shedding cost based on the customers’ consumption, while the building energy management systems (BEMS) minimize their electricity bills as well as the cost associated with customer discomfort due to room temperature deviation from the set point. The BEMSs and the MCC exchange information on energy consumption and prices. When the optimization converges, the distributed generation scheduling, energy storage charging/discharging \ and customers’ consumption as well as the energy prices are determined. In particular, we integrate the detailed thermal dynamic characteristics of buildings into the proposed model. The heating, ventilation and air-conditioning (HVAC) systems can be scheduled intelligently to reduce the electricity cost while maintaining the indoor temperature in the comfort range set by customers. Numerical simulation results show the effectiveness of proposed model

Community Microgrid Scheduling Considering Network Operational Constraints and Building Thermal Dynamics

This paper proposes a Mixed Integer Conic Programming (MICP) model for community microgrids considering the network operational constraints and building thermal dynamics. The proposed multi-objective optimization model optimizes not only the operating cost, including fuel cost, electricity purchasing/selling, storage degradation, voluntary load shedding and the cost associated with customer discomfort as a result of the room temperature deviation from the customer setting point, but also several performance indices, including voltage deviation, network power loss and power factor at the Point of Common Coupling (PCC). In particular, we integrate the detailed thermal dynamic model of buildings into the distribution optimal power flow (D-OPF) model for the optimal operation. Thus, the proposed model can directly schedule the heating, ventilation and air-conditioning (HVAC) systems of buildings intelligently so as to to reduce the electricity cost without compromising the comfort of customers. Results of numerical simulation validate the effectiveness of the proposed model and significant savings in electricity cost with network operational constraints satisfied

Genome-wide identification of micro-ribonucleic acids associated with human endometrial receptivity in natural and stimulated cycles by deep sequencing

Objective: To identify microRNAs (miRNAs) associated with endometrial receptivity. Design: Observational study. Setting: Medical center. Patient(s): Healthy, regularly cycling women undergoing IVF treatment. Intervention(s): Gonadotropin stimulation and endometrial biopsy. Main Outcome Measure(s): Quantification of miRNA expression profiles by deep sequencing. Result(s): The miRNA expression profiles in human endometrium on days LH+2 and LH+7 (LH = 0 is the day of the LH surge) in natural cycles as well as on days hCG+4 and hCG+7 (hCG = 0 is the day of hCG injection) in stimulated cycles were determined by deep sequencing. In natural cycles, there were 20 significantly changed miRNAs in human endometrium on LH+7 compared with LH+2. These miRNAs were predicted to target a large set of genes with different functions, including cell cycle, transport, cell adhesion, cell death, and metabolism. In stimulated cycles, 22 miRNAs were significantly dysregulated on hCG+7 in comparison with LH+7, 11 of which exhibited putative estrogen response elements or P response elements in the promoters. Additionally, unsupervised hierarchical clustering analysis demonstrated that the miRNA expression profile on hCG+4 was similar to that on LH+7, suggesting that ovarian stimulation may alter the window of endometrial receptivity. Conclusion(s): MiRNAs may be novel biomarkers for human endometrial receptivity and may help optimize the protocol for IVF treatment. (Fertil Steril (R) 2011;96:150-5. (C)2011 by American Society for Reproductive Medicine.)Department of Joint Logistics, Nanjing Military Region, China[08ma068]; National Key Basic Research Program of China[2011CB944402]; National Natural Science Foundation of China[30930013

Stretchable Thermoelectric Fibers with Three-Dimensional Interconnected Porous Network for Low-Grade Body Heat Energy Harvesting

Electricity generation from body heat has garnered significant interest as a sustainable power source for wearable bioelectronics. In this work, we report stretchable n-type thermoelectric fibers based on the hybrid of Ti3C2Tx MXene nanoflakes and polyurethane (MP) through a wet-spinning process. The proposed fibers are designed with a 3D interconnected porous network to achieve satisfactory electrical conductivity (σ), thermal conductivity (κ), and stretchability simultaneously. We systematically optimize the thermoelectric and mechanical traits of the MP fibers and the MP-60 (with 60 wt % MXene content) exhibits a high σ of 1.25 × 103 S m–1, an n-type Seebeck coefficient of −8.3 μV K–1, and a notably low κ of 0.19 W m–1 K–1. Additionally, the MP-60 fibers possess great stretchability and mechanical strength with a tensile strain of 434% and a breaking stress of 11.8 MPa. Toward practical application, a textile thermoelectric generator is constructed based on the MP-60 fibers and achieves a voltage of 3.6 mV with a temperature gradient between the body skin and ambient environment, highlighting the enormous potential of low-grade body heat energy harvesting

Stretchable Thermoelectric Fibers with Three-Dimensional Interconnected Porous Network for Low-Grade Body Heat Energy Harvesting

Electricity generation from body heat has garnered significant interest as a sustainable power source for wearable bioelectronics. In this work, we report stretchable n-type thermoelectric fibers based on the hybrid of Ti3C2Tx MXene nanoflakes and polyurethane (MP) through a wet-spinning process. The proposed fibers are designed with a 3D interconnected porous network to achieve satisfactory electrical conductivity (σ), thermal conductivity (κ), and stretchability simultaneously. We systematically optimize the thermoelectric and mechanical traits of the MP fibers and the MP-60 (with 60 wt % MXene content) exhibits a high σ of 1.25 × 103 S m–1, an n-type Seebeck coefficient of −8.3 μV K–1, and a notably low κ of 0.19 W m–1 K–1. Additionally, the MP-60 fibers possess great stretchability and mechanical strength with a tensile strain of 434% and a breaking stress of 11.8 MPa. Toward practical application, a textile thermoelectric generator is constructed based on the MP-60 fibers and achieves a voltage of 3.6 mV with a temperature gradient between the body skin and ambient environment, highlighting the enormous potential of low-grade body heat energy harvesting

Stretchable Thermoelectric Fibers with Three-Dimensional Interconnected Porous Network for Low-Grade Body Heat Energy Harvesting

Electricity generation from body heat has garnered significant interest as a sustainable power source for wearable bioelectronics. In this work, we report stretchable n-type thermoelectric fibers based on the hybrid of Ti3C2Tx MXene nanoflakes and polyurethane (MP) through a wet-spinning process. The proposed fibers are designed with a 3D interconnected porous network to achieve satisfactory electrical conductivity (σ), thermal conductivity (κ), and stretchability simultaneously. We systematically optimize the thermoelectric and mechanical traits of the MP fibers and the MP-60 (with 60 wt % MXene content) exhibits a high σ of 1.25 × 103 S m–1, an n-type Seebeck coefficient of −8.3 μV K–1, and a notably low κ of 0.19 W m–1 K–1. Additionally, the MP-60 fibers possess great stretchability and mechanical strength with a tensile strain of 434% and a breaking stress of 11.8 MPa. Toward practical application, a textile thermoelectric generator is constructed based on the MP-60 fibers and achieves a voltage of 3.6 mV with a temperature gradient between the body skin and ambient environment, highlighting the enormous potential of low-grade body heat energy harvesting

Stretchable Thermoelectric Fibers with Three-Dimensional Interconnected Porous Network for Low-Grade Body Heat Energy Harvesting

Electricity generation from body heat has garnered significant interest as a sustainable power source for wearable bioelectronics. In this work, we report stretchable n-type thermoelectric fibers based on the hybrid of Ti3C2Tx MXene nanoflakes and polyurethane (MP) through a wet-spinning process. The proposed fibers are designed with a 3D interconnected porous network to achieve satisfactory electrical conductivity (σ), thermal conductivity (κ), and stretchability simultaneously. We systematically optimize the thermoelectric and mechanical traits of the MP fibers and the MP-60 (with 60 wt % MXene content) exhibits a high σ of 1.25 × 103 S m–1, an n-type Seebeck coefficient of −8.3 μV K–1, and a notably low κ of 0.19 W m–1 K–1. Additionally, the MP-60 fibers possess great stretchability and mechanical strength with a tensile strain of 434% and a breaking stress of 11.8 MPa. Toward practical application, a textile thermoelectric generator is constructed based on the MP-60 fibers and achieves a voltage of 3.6 mV with a temperature gradient between the body skin and ambient environment, highlighting the enormous potential of low-grade body heat energy harvesting