Building energy use is expected to grow by more than 40% in the next 20 years. Electricity remains the largest energy source consumed by buildings, and that demand is growing. To mitigate the impact of the growing demand, strategies are needed to improve buildings' energy efficiency. In residential buildings home appliances, water, and space heating are answerable for the increase of energy use, while space heating and other miscellaneous equipment are behind the increase of energy utilization in non-residential buildings. Building energy management systems support building managers and proprietors to increase energy efficiency in modern and existing buildings, non-residential and residential buildings can benefit from building energy management system to decrease energy use. Base on the type of building, different management strategies can be used to achieve energy savings. This paper presents a review of management strategies for building energy management systems for improving energy efficiency. Different management strategies are investigated in non-residential and residential buildings. Following this, the reviewed researches are discussed in terms of the type of buildings, building systems, and management strategies. Lastly, the paper discusses future challenges for the increase of energy efficiency in building energy management system.

A review of strategies for building energy management system: Model predictive control, demand side management, optimization, and fault detect & diagnosis

To protect the converters and minimize the power transmission interruption during dc line faults, it is necessary to detect the faults at ultra high speed for the modular multilevel converter (MMC)-based HVdc grids. This article reviews the state-of-the-art of dc fault protection methods of MMC-HVdc grids, and summarizes the underlying principles of each method. On this basis, the dc fault characteristics analysis in terms of modal-domain, time-domain, and frequency-domain are analyzed, which direct the protection design. Typical boundary protection and nonboundary protection schemes are reviewed. The advantages and disadvantages of existing fault protection methods are compared. A two-terminal MMC-HVdc prototype is developed to test the effectiveness of three fault protection methods. Comprehensive quantitative assessments of the protection methods discussed above are carried out in a four-terminal MMC-HVdc grid. Finally, the future trends of the protection schemes are discussed and the findings are concluded.

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DC Fault Protection Algorithms of MMC-HVDC Grids: Fault Analysis, Methodologies, Experimental Validations, and Future Trends

The design of a hybrid radio frequency (RF) and solar energy harvesting (EH) system utilizing a transparent multiport antenna for indoor applications is described. The system incorporates an eight-port transparent antenna, operating in the unlicensed 2.4-GHz band, and is constructed from transparent copper micromeshed planar conductor. The antenna is integrated on the top surface of a solar cell with rectifiers positioned underneath to form a hybrid RF-solar indoor EH system. A key advantage of this approach is that the surface area of the solar cell is reused for the antenna saving space. Another novelty is the use of a multiport antenna for increasing the RF harvested energy. It is demonstrated that with a light intensity of 360 lux, the solar cell can obtain 1.68-mW power while the rectenna can achieve an additional 4.8%–45.8% harvested power when the incident RF input power density is varied from 13.30 to 52.96 mW/m2. The transparent antenna achieves 72.4% efficiency and is one of the highest reported results. In addition, the rectifiers obtain 53.2% RF-to-dc conversion efficiency for an RF input power of −10 dBm. These results demonstrate that the proposed RF-solar energy harvester can increase harvested energy and provide energy diversity.

Hybrid RF-Solar Energy Harvesting Systems Utilizing Transparent Multiport Micromeshed Antennas

Today, 44% of global energy has been derived from fossil fuel, which currently poses a threat to inhabitants and well-being of the environment. In a recent investigation of the global demand for energy consumption across various energy consumption sectors, the building sector has been shown to be one of the primary energy consumers, with a high percentage of energy consumption deemed as unnecessary. This as a result of poor management practice and implementation of strategies to avoid excess energy consumption. Over the years, researchers in both academia and industries have focused on various techniques to deal with unnecessary energy consumption and ensuring a healthy living environment for green smart cities. Among these techniques is Smart Home Energy Management Systems (SHEMs), which transform electric home appliances, sensor nodes, into autonomous devices in order to manage energy consumption effectively. This study presents an analysis of smart home energy management system with the goal to identify current trends and challenges for future improvement. The result reveals lack of quality attributes such as security, privacy, scalability, interoperability, and difficulty in managing and adapt to the thermal comfort satisfaction of residents, exposing them to health risks. Lastly, the study described opportunities for future research that ensure energy-efficient smart homes free of unnecessary energy consumption, health challenges, and cyber security attacks.

Smart Home Energy Management Systems in Internet of Things networks for green cities demands and services

The benefits of distributed generation (DG) based on renewable energy sources leads to its high integration in the distribution network (DN). Despite its well-known benefits, mainly in improving the distribution system reliability and security, there are challenges encountered from a protection system perspective. Traditionally, the design and operation of the protection system are based on a unidirectional power flow in the distribution network. However, the integration of distributed generation causes multidirectional power flows in the system. Therefore, the existing protection systems require some improvement or modification to address this new feature. Various protection strategies for distribution system have been proposed so that the benefits of distributed generation can be fully utilized. This paper reviews the current progress in protection strategies to mitigate the impact of distributed generation in the distribution network. In general, the reviewed strategies in this paper are divided into: (1) conventional protection systems and (2) modifications of the protection systems. A comparative study is presented in terms of the respective benefits, shortcomings and implementation cost. Future directions for research in this area are also presented.

Progress on Protection Strategies to Mitigate the Impact of Renewable Distributed Generation on Distribution Systems

This paper presents a novel phase change material based thermal energy storage system (PCMTESS) that is suitable for smart building energy management, together with its corresponding thermal-electric combined two-stage dispatching strategy. Benefiting from the phase change materials’ thermal characteristic of absorbing or releasing a significant amount of heat at a constant temperature, this thermal energy storage system is endowed with a high capacity and a relatively stable thermal state during its charge/discharge process. To evaluate the thermal performance of the PCMTESS, which is integrated as a part of building wallboard, a detailed analytic thermodynamic building model is proposed that considers the influence of the forced air convection and the external environments, such as solar radiation. Furthermore, a two-stage electric-thermal combined dispatching scheme is designed to minimize the electricity consumption expenditure and power fluctuation on the premise of maintaining a comfortable indoor temperature. Simulation studies on a smart building indicate that the proposed thermal energy storage system is a feasible and economical solution for solving peak load shaving and power fluctuation.

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A Novel Thermal Energy Storage System in Smart Building Based on Phase Change Material

To solve the following problem: the action speed of protection based on a phasor is restricted by the length of the filtering algorithm time window and the vulnerability to false data, a new pilot protection principle for transmission lines based on waveform similarity is proposed in this paper. By comparing the discrete point sets of current sampling values, a waveform similarity-based algorithm called the Hausdorff distance distinguishes the difference between both side currents of a protected transmission line, realizing fast identification, and removal of the fault. Based on the characteristics of the algorithm, setting methods and protection criterion are discussed. Finally, an improved Hausdorff distance algorithm is proposed to cope with false data. The effectiveness and advantages of the proposed algorithm are validated with theoretical analysis and extensive simulation test results.

Similarity Comparison Based High-Speed Pilot Protection for Transmission Line

In order to predict the changing trend of the dissolved gas in the transformer oil accurately and guide the condition-based maintenance of a power transformer, a combined forecasting model based on cross-entropy is proposed and its application is analyzed. First, a combined forecasting model is established on the basis of radical basis function neural network, back propagation neural network, least squares support vector machine with two different kernel functions, and grey model. Then, the weight coefficient of each algorithm is determined by cross-entropy theory. After that, an application method of the combined forecasting model by the pattern of a variable time window is proposed for the purpose of arranging the equipment maintenance in advance. In this way, the increased budget due to emergency maintenance can be alleviated, and potential loss due to lack of timely maintenance can be reduced. Finally, the accuracy of the combination forecasting method and the effectiveness of the application method are verified by a series of examples.

Combined Forecasting Method of Dissolved Gases Concentration and Its Application in Condition-Based Maintenance

For those protective relays highly dependent on common centralized timing synchronization, the threat of loss of data synchronism, e.g., due to cyber-attack, cannot be ignored. In this case, measurements could be falsely timestamped, leading to undesired mal-operation of protection or evident performance deterioration if countermeasures are lacking. In this paper, several different timing attack scenarios and impacts to protective relays on the transmission line are analyzed. To cope with the timing attack scene, a remedial pilot main protection scheme-based only on modulus information of measurements for a transmission line is proposed, independent of timing information. The proposed remedial scheme includes a modulus summation impedance relay, a mid-part relay, and an instantaneous over-current relay. The effectiveness of the proposed scheme has been validated by theoretical analysis and simulation tests.

Remedial Pilot Main Protection Scheme for Transmission Line Independent of Data Synchronism

Ignoring the dynamic impedance characteristics of a thyristor-controlled series-capacitor-type fault current limiter (TCSC-FCL) may lead to maloperation/fail-to-trip or slow response of distance protection. To solve the above problem, the TCSC-FCL dynamic impedance analysis model was established. Taking the special operation mode of the TCSC-FCL into account, the time-varying characteristics of the TCSC-FCL during the whole process from the series compensation mode to the current-limiting mode were analyzed. Then, this paper proposed the function expression of dynamic impedance characteristics of the TCSC-FCL and put forward the distance protection setting strategy based on a dynamic offset impedance circle in order to eliminate the influence of TCSC-FCL dynamic impedance characteristics to the distance protection operation. By establishing a typical simulation model including the TCSC-FCL, the correctness of dynamic feature's analytic expression and the distance protection setting strategy is proved with extensive simulation results.

Le Chen

Papers

A Novel Thermal Energy Storage System in Smart Building Based on Phase Change Material

Similarity Comparison Based High-Speed Pilot Protection for Transmission Line

Combined Forecasting Method of Dissolved Gases Concentration and Its Application in Condition-Based Maintenance

Remedial Pilot Main Protection Scheme for Transmission Line Independent of Data Synchronism

A New Distance Protection Method Considering TCSC-FCL Dynamic Impedance Characteristics