AC System Research Articles

Achieving equitable space heating electrification: A case study of Los Angeles

A major step towards residential building decarbonization is the electrification of natural gas space heating. Current inequities such as limited access to cooling technologies and high energy burden can be addressed in transition if we take steps now to understand the economic impacts of different electric technologies. This study presents a novel high-resolution techno-economic model, the Marginal Net Present Value Upgrade Analysis model, which improves upon existing literature that examines the economics of electrifying space heating through a more detailed cost calculation and the use of a variable discount rate. Results show that 1) electrifying with heat pumps is only recommended for owners who are replacing a natural gas furnace and central AC system, 2) renters are highly vulnerable in this transition in that electric resistance technologies are the least capital intensive technology for landlords to install, with renters bearing the increased operational cost, 3) rebates from the Inflation Reduction Act of 2022 allow most qualifying landlords and owners to install even the highest efficiency heat pumps at a net savings when compared to the baseline heating and cooling system, and 4) reducing capital costs are more critical than altering utility rates to achieve high heat pump penetration. The model developed herein can support decision-making related to electrification and energy efficiency policy and rulemaking and will give insight into the impact residential building electrification can have on marginalized communities.

Assessment of the Effectiveness of Energy Transfer for Shore-to-Ship Fast Charging Systems

Charging systems from shore to ship are typically designed based on a range of operational and design parameters, encompassing onboard power and propulsion needs, available charging durations, and the capacity of local power networks. In areas with weak grid infrastructure, onshore energy storage is often employed to facilitate high-power charging for vessels requiring short charging intervals. Nevertheless, incorporating on-shore energy storage adds complexity to the system, and the selection of system configuration can profoundly affect the efficiency of energy transfer from the grid to the vessel. This study presents a comparative analysis of energy efficiency among AC, DC, and Inductive shore-to-ship charging solutions for short-distance ferries utilizing both AC and DC-based propulsion systems. Findings illustrate that an increased reliance on onshore battery power correlates with decreased overall energy efficiency during the charging process. Thus, optimizing energy efficiency necessitates careful consideration when distributing the load between the grid and onshore battery. Results indicate that DC charging offers advantages over other solutions for AC-based propulsion systems in terms of energy efficiency. However, for DC-based propulsion systems, the most efficient solution may be either DC or AC charging, contingent upon the distribution of load between the grid and onshore battery. Furthermore, it is inferred that despite adding additional conversion stages and complexity to the system, the energy efficiency of inductive charging is comparable to wired schemes. Considering the added benefits of contactless charging, such as reliability, safety, and robustness, these findings advocate for the adoption of inductive charging as a promising solution.

Global selection appraisal study for heat pump system of electric vehicle based on energetic, economic, and environmental analysis

The development of electric vehicles (EVs) exhibits rapid and remarkable progress nowadays, serving as a crucial route to accomplish the target of mitigating greenhouse gas emissions. As an integral part of the thermal management system oriented toward electric vehicles, the heat pump air conditioning system for electric vehicles is the result of a comprehensive choice that trades off the cooling and heating performance, environmental performance and economic cost. Particularly, different regions around the world suffer varying cooling and heating challenges due to the complicated climatic characteristics. Thus the most suitable refrigerant and system cycle structure may differ. This paper focuses on evaluating both the refrigerants and cycle structures to screen the most suitable choice. According to the climate conditions of different cities, the annual energy consumption, life cycle climate performance, and economic cost of the basic system (Base), two-stage compression system (TSC,IC), and vapor injection (VI) system with CO2, R134a, and R1234yf refrigerants respectively, are quantitatively analyzed and evaluated. Subsequently, through comparative analysis, a comprehensive selection map for heat pump systems in electric vehicles worldwide is developed and the most suitable heat pump air conditioning system for each cites is determined. The results can provide a selection reference and decision-making for the air conditioning system of electric vehicles from regional considerations. It was found that the CO2 HPACVI was recommended for cold regions to meet both environmental and economic requirements. In warm region, the R1234yf HPACBase system was recommended to be used. For regions transitioning from cold to warm climates, the R1234yf HPACVI system was suggested. In hot region, the R1234yf AC system was recommended.

Prototype of a Digital Measuring Device Based on Atmega 328P for Measuring Current, Voltage, Electrical Power, and RLC Components

Research on digital measuring device prototypes has developed over the past few years. However, there are still challenges in measuring current, voltage, electrical power, and RLC component parameters accurately. This research aims to design a digital system to measure electrical quantities such as current, voltage, resistance, inductance, and capacitance using Atmega 328P. Data retrieval is done by implementing the system as a whole, namely the AC and DC electrical measurement system and the measurement of RLC components. The results showed that the system can measure and display the result of measuring current, voltage, electric power, and RLC components correctly. The accuracy percentage for the components measuring instrument on the resistor test is 99.35%, the error is 0.65%, and the precision is 99.87%. In the inductor test measurement, the percentage value of accuracy is 94.11%, the error is 5.89%, and the precision is 96.77%. In the capacitor test measurement, the accuracy percentage is 98.03%, the error is 1.97%, and the precision is 98.65%. On the DC voltage sensor, the accuracy percentage is 97.31%, error 2.69%, and precision 99.77%.

Comparative analysis and implementation of DC microgrid systems versus AC microgrid performance

DC power systems have emerged as a cost-effective solution for electric power generation and transmission, challenging the dominance of AC distribution systems. However, a comprehensive efficiency comparison between DC and AC microgrids remains understudied. This study seeks to explore and conduct a thorough survey on development and designing of DC microgrids to address this gap. Firstly, a comprehensive literature review comparing the efficiencies of AC and DC microgrids has been presented. The analysis highlights the superior efficiency of DC distribution systems over AC systems, supported by detailed advantages. Secondly, hardware implementation has been performed to directly compare the efficiency of DC versus AC systems. Research validity and application are further improved by the hardware prototype’s scalability, which in simulation allows for a thorough assessment of system stability over a range of scenarios from four to six terminals. Test results from the built hardware prototype demonstrate an astounding 15% increase in efficiency using the DC system compared to the AC system, demonstrating its potential for improved performance in real-world scenarios. In simulation results, the designed DC microgrid demonstrates stable voltages of 500V under steady state operation and rapid recovery within 80 ms under both symmetrical and asymmetrical faults has been observed. The research being investigated utilizes hardware implementation and simulation to provide useful insights into the efficiency and stability of DC microgrids in comparison to AC systems. These results are important for developing robust power distribution networks in modern energy environments, promoting sustainability and dependability in infrastructure growth.

AC Direct Charging for Electric Vehicles via a Reconfigurable Cascaded Multilevel Converter

This paper presents a charging architecture for the Reconfigurable Cascaded Multilevel converter, which was specifically designed for electric vehicle (EV) powertrain applications. The RCMC topology is capable of executing power conversion and actively managing battery systems concurrently. The active battery management is achieved using the Reconfigurable Battery Module, which regulates the serial connection of cells via a switch pattern. In this paper, the RCMC is directly interfaced with an AC three-phase power system, facilitating the dynamic control over battery cells charging. Its inherent design allows for the implementation of various charging algorithms, customizable to specific requirements, without necessitating additional intermediary power stages. Firstly, an overview of the RCMC topology is given, and an analysis to define the optimal filter inductance is carried out. Subsequently, after the AC system characteristics are explained, two charging algorithms are presented and described: one prioritizes State of Charge (SOC) balancing among battery cells, while the other focuses on minimizing power losses. Moreover, a time estimation computation for the RCMC is carried out considering a two-level AC charging station. The result is compared with the time required for a conventional battery pack. The results show a reduction of 10 s in charging time for a mere 20% increase in SOC. Finally, the experimental setup is presented and used to validate the efficacy of the proposed algorithms.

An Improved Suppression Method of AC Transient Overvoltage for Line Commuted Converter Based High Voltage Direct Current Considering AC-DC System Coupling

Commutation failures in line commuted converter-based high voltage direct current (LCC-HVDC) transmission systems leads to an increase in the converter bus voltage of the rectifier station, thus resulting in AC transient overvoltage in the sending-end grid. The transient overvoltage could lead to the disconnection of renewable energy generation and threaten the stable operation of the sending-end grid. However, the influences of the coupling between AC and DC systems caused by the interaction between the active and reactive power of the sending-end grid, the AC bus voltage of the rectifier station, and the DC current are ignored. The AC transient overvoltage cannot be accurately suppressed. Therefore, in this study, the transient voltage characteristics of the rectifier station under a commutation failure of the inverter station are analyzed. The influence of LCC-HVDC control on the AC bus voltage of a rectifier station through the active and reactive power of the rectifier station is analyzed. A dynamic model of the AC bus voltage of a rectifier station under an AC-DC system coupling is established. The calculation method of the command value of the DC current of the rectifier station is proposed by a predictive control model, and an improved suppression method for AC transient overvoltage is proposed. The case studies show that the accuracy and effectiveness of the suppression of AC transient overvoltage are improved by considering the coupling between AC and DC systems.

Analyzing Energy Consumption in Universities: A Literature Review

This study investigates energy consumption in general and in universities in particular. A literature review was used as the methodology of the study to show the energy consumption purposes, major findings, research gaps, limitations, and future research about how to analyze energy consumption levels. The number of references examined was 60, with 29 references about universities and some of them are concentrating on the buildings’ consumption in the GCC area. Most of the references concentrated on investigating case studies in different countries. Analysis of the findings showed that tools such as big data analytics, machine learning, simulations, and predictive models were used. However, big data analytics was the most important one. It was found that AC systems are the most important component of energy consumption, especially in hot weather countries. The studies also showed that monitoring the consumption rates will reduce the total consumption of energy. In universities, the type of the building and the day index were found the most important factors affecting energy consumption. Factors such as number of smart devices, location, and floor space were found to have different positive and negative impacts on energy consumption from one study to another. Recommendations for future research were also presented.

Detection and identification of bad data in AC/DC hybrid systems with LCC and MMC

Based on the CIM/XML and CIM/E documents exported from the regional dispatching system, this paper focuses on data generation and starts by converting the exported documents into raw input data for state estimation. Considering the interactions between the AC system, LCC, MMC, and LCC-MMC interfaces, a unified iterative method is proposed to model the state estimation of the 500 kV subnetwork. Subsequently, Gaussian noise is added to the original measurement data, and the maximum residual test method is employed for detecting and identifying bad data. Finally, the effectiveness of the proposed models for AC/DC state estimation and the detection and identification of bad data are validated through simulation data.

Pulse Density Modulated Three-Phase Single-Stage AC–AC System for Series Resonant Load With Low Grid Current Harmonics

Pulse Density Modulated Three-Phase Single-Stage AC–AC System for Series Resonant Load With Low Grid Current Harmonics

Coupling characteristics between MMC-HVDC and AC transmission lines on the same tower and their impact on protective relaying

Significant coupling exists between DC and AC lines erected on the same tower or sharing transmission corridors. Electromagnetic and electrostatic coupling between DC and AC lines are investigated based on ± 500 kV MMC-HVDC and 500 kV double-circuit AC lines on the same tower. The interactive coupling characteristics and their impacts on protective relaying are analyzed during normal operation and after DC or AC faults. Voltage coupling ratio and current coupling ratio are defined. The 50 Hz components in MMC-HVDC line may be higher than ripple criterion under the coupling of AC line and can be even more significant when a fault occurs on adjacent AC line. The DC reactor with larger inductance can reduce its impact on MMC-HVDC system. Zero-sequence overcurrent relaying and zero-sequence directional relaying for AC lines may mal-operate when a fault occurs on adjacent MMC-HVDC line. And there is also an interruption risk for AC systems. Improvement schemes are proposed to avoid the mal-operation of protective relaying. Simulation case studies verify the correctness of coupling characteristic analysis and the effectiveness of proposed improvement scheme.

Analysis of Rail Potential and Stray Current with an Unified Chain Model of Dual Traction Power Supply System

In dual traction power supply systems, the overhead catenary system operates in different power supply modes. It passes across the AC section, DC section, and a neutral part, which influences the features and properties of the feedback current and aggregates its effects on stray current and rail potential. This research paper presents an integrated model of an AC and DC traction power system (TPS), along with a unified chain equivalent circuit model, the ground wire through the AC section, and the insulation joints fixed in the AC–DC neutral section under different operating positions. To make a unified impedance and admittance matrix for traction network, a virtual conductor wire has been added in the DC section to make the balance order of the TPS. The influence of reflex system configuration on rail potential, stray current, and distribution of rail potential at AC and DC stations has also been calculated. The simulation results demonstrate that establishing the insulation joints in the AC–DC section and using ground wires in the AC part can significantly decrease the stray current and rail potential.

Compressor speed control for optimizing energy matching of PV-driven AC systems during the cooling season

Photovoltaic-driven air conditioning (PVAC) systems innovatively utilize PV power for building cooling, reducing PV power fluctuation impact on the utility grid. This study introduced a novel PVAC system that optimizes the energy matching between PV generation and air conditioning electricity demand through directly controlling of the compressor speed in accordance with the real-time PV power generation. A PID control method was employed to regulate the compressor speed of PVAC, and three control strategies were proposed and successfully implemented during the experiments. The system's efficiency was evaluated using metrics such as the self-consumption rate (SCR), self-sufficiency rate (SSR), real-time zero energy proportion (RZEP), and the mean absolute error (MAE) of indoor temperature. The results of this study confirm that the proposed control method significantly enhances the power matching between the PV power generation and the air conditioning electricity demand. Implementing the recommended strategy, SCR increased from 0.53 to 0.625 and SSR from 0.716 to 0.808, all while maintaining indoor thermal comfort. Moreover, the proposed approach mitigates the impact of distributed PV generation on the utility grid and potentially diminishes energy storage needs, which can contribute to a lower system investment requirements and operating costs.

Transient characteristics and protection coordination strategy of hybrid AC / DC system based on modular multilevel converters under AC/DC transmission lines touching fault

Rapid development of hybrid AC/DC transmission systems has increased the probability of the touching faults between AC and DC overhead lines. The mechanism of coupling interaction is so complex that the adaptability of the existing hybrid system protection is affected. Previous studies mainly focus on the line-commutated converter based high-voltage direct current (LCC-HVDC) system and AC system, this paper concentrates on the fault coupling characteristics analysis and coordination protection of modular multilevel converter based on high voltage direct current(MMC-HVDC) and AC transmission systems. The analytical expressions of fault current are deduced under the different operating states of the converters and the valve-side AC circuit breaker. Subsequently, the fault current coupling characteristics and generation mechanism are revealed. On this basis, the adaptability of existing hybrid system protection is assessed. Further, by comparing and analyzing the influence and risk of mal-operation of AC transmission line protection, the coordination reclosing protection strategies for hybrid system is proposed. Finally, the simulation tests were carried out based on PSCAD/EMTDC. The simulation results show that the proposed coordination of AC and MMC-HVDC system reclosing strategy is effective for improving the reliability of hybrid system.

A simplified control parameter optimisation method of the hybrid modular multilevel converter in the medium‐voltage DC distribution network for improved stability under a weak AC system

AbstractTo improve the stability of the hybrid modular multilevel converter (MMC), a simplified dominant mode‐based control parameter optimisation method of the hybrid MMC system is proposed. Firstly, in the medium‐voltage DC distribution network, the small‐signal model of the hybrid MMC is established. Secondly, the influence of a weak AC system on stability is analysed through eigenvalue analysis. Finally, a simplified objective function is designed for eigenvalues of the dominant mode by considering only real parts, and improved small‐signal stability can be achieved by control parameters optimisation. The proposed method optimises all control parameters at the same time, which further reduces the number of algorithm iterations. Simulation results show that by the proposed control parameter optimisation method, the hybrid MMC has better transient performance and reduced disturbance under SCR variation, indicating a significantly improved system stability, and the dynamic response time can be reduced.

Research on optimal power flow of AC/DC hybrid system for civil more electric aircraft

Modern civil more electric aircraft often use AC/DC systems instead of AC systems to reduce the weight of the power system. Compared with the AC/DC system of the land power grid, the aircraft power system needs to pursue economic operation mode under more complex security constraints. This paper establishes the optimal power flow model of the AC/DC hybrid system of more electric aircraft, which takes minimizing the active power loss of the line as the optimization objective, including the steady-state operation constraints and security constraints of the AC/DC system. The interior point method and prediction correction interior point method are used to solve the model. Then, based on the simplified steady-state model of the B787 power system, the model and algorithm are verified by experiments. The experimental results show that by optimizing the power flow distribution of the power system, the power utilization efficiency of the system has been significantly improved, and its stability and reliability can also be better guaranteed.

Experimental investigation of a photovoltaic solar air conditioning system and comparison with conventional unit in the context of the state of Piaui, Brazil

Globally the building sector is responsible for a big share of electric energy consumption and emissions. To alleviate these impacts it is necessary to improve the energy efficiency besides implementing renewable energy sources for building sector sustainability. PV panels for generating electric energy are most preferred by the sector. In the present study, two similar rooms were prepared one with a conventional air conditioner of the window type powered from the grid and the other is powered from PV panels. The heat load was calculated and used to define the conventional air conditioner and also to define the area of photovoltaic solar panels and the associated equipments to install a PV circuit for supplying electric energy to the PV air conditioner. Both rooms were equipped with calibrated instrumentation including thermocouples to measure the temperature distribution in rooms as well as electric energy consumption during the experiments. Ambient temperature, wind speed, temperature in the vicinity of the photovoltaic panels, humidity, solar radiation, voltage, current, flow of energy consumed by the systems were measured and registered by data acquisition system. Experiments were carried out with the systems working simultaneously at pre-defined times. The solar PV-based air conditioner consumed approximately 342 kWh during 30 days of experiments, while the air conditioner connected to the grid, consumed about 330 kWh, which is 5 % less than the solar PV air conditioner confirming that solar PV air conditioner is viable. The COP for the solar-based air conditioner is about 2.6 and the COP for conventional air conditioner is 2.9. The incident solar radiation is high and stable in Teresina, Piauí, Brazil which ensures viability of the solar PV air conditioner. The power supply from CC showed better quality and costs an AC system, and that PV System can save about $700.00 in energy consumption and the payback occurs in 3.7 years.

Enhanced energy balancing and optimal load curtailment strategy for DC microgrid integration in hybrid AC/DC distribution networks

AbstractUnleashing the potential of distributed renewable energy sources (RESs), intelligent and autonomous microgrids are becoming pivotal in attaining net‐zero carbon emission goals. Hybrid AC/DC microgrids rise as cutting‐edge microgrid topologies, capitalising on the best of both AC and DC systems. However, the integration of intermittent renewables and uncertainties in loading poses stability challenges. Advanced bidirectional converter controls provide efficient power exchange, but in extreme contingencies, a resilient supervisory control framework (load management/load curtailment approach) is inevitable to withstand/avoid unplanned renewable disruptions/blackouts. Moreover, the operational paradigm shift towards achieving net‐zero emissions, isolated operation of RESs, and conventional load shedding methods are anticipated to encounter substantial challenges, necessitating the development of alternative strategies. In order to improve the stability of hybrid microgrid systems in islanding scenarios, this research presents an energy balancing and load curtailment strategy. The proposed method aims at optimising resource utilisation, prioritising essential loads, and executing an optimal load curtailment strategy (if required), thereby augmenting the stability of systems. Unlike a meta‐heuristic or exhaustive search, which depends on 2n − 1 possible combinations and become unworkable as load numbers increase, the suggested methodology is based on a mathematically modelled load restriction method. By including load criticality, this strategy effectively prevents blackouts even with an increasing number of loads, providing a significantly more useful and practical solution. Additionally, the proposed charging algorithm ensures that the energy storage system imports energy from the grid during off‐peak hours and maximises power generation from the DC subgrid. The efficacy of the proposed strategy is validated using a modified IEEE‐33 bus system as a test case for a hybrid AC/DC microgrid. Simulation results demonstrate the effectiveness of the MILP‐based load curtailment approach in maintaining system stability and preventing blackouts during unforeseen events.

Numerical modeling and dynamic response analysis of an integrated semi-submersible floating wind and aquaculture system

Floating wind turbines (FWT) are facing the challenges of high cost of energy. Integrating floating wind with offshore aquaculture cages presents a mutually beneficial approach to address cost concerns and maximize overall benefits. This study introduces and numerically models an integrated system, encompassing a self-designed semi-submersible FWT coupled and an aquaculture cage (FWT + AC). Comprehensive, fully coupled aero-hydro-servo-elastic-mooring models for this integrated system are established. Subsequently, the numerical model of the FWT is validated against wave basin model tests. The research further discusses the coupled dynamic response characteristics of the integrated system for both the FWT with and without the aquaculture cage. The results highlight that integrating aquaculture cages leads to an increase in the mean surge response by up to 12.6%, while significantly reducing pitch motion by as much as 7.69% under combined wind, wave, and current conditions. Moreover, the mean mooring loads, particularly for line 4 which faces the direction of wind, wave, and current, do not exhibit an increase of more than 15%. This integration not only enhances the stability of wind power generation under different wind degree, but also minimally impacts the average power generation efficiency, showing a variation of only about 2% under rated wind speed. The findings provide beneficial theoretical support for the design of the integrated FWT + AC system, demonstrating the potential of such integrated systems in promoting offshore sustainable development and enhancing wind energy utilization efficiency.

Energy Consumption Behavior Analysis in the UAE Educational Buildings for Sustainable Economy: A Case Study of Ras Al Khaimah Schools

Energy-saving in educational building has a significant contribution and a vital role in the economic and social development of nations. In this paper, the energy consumption of some educational buildings in the United Arab Emirates (UAE) are collected and analyzed. Four schools within the region of Ras Al Khaimah were selected to study their buildings’ energy consumption behavior. Key energy, economic and environmental parameters were calculated and investigated such as the total annual energy consumption, energy consumption per person, energy consumption per area, energy consumption by category (AC, lighting, other devices, etc.), energy cost, and the amount of greenhouse gas (GHG) emissions. A detailed energy audit was applied to one of the selected schools in order to identify the major areas of energy usage within the school, and to suggest the appropriate measures for potential energy and cost savings. Results revealed that total annual energy consumption of the investigated schools is very high with a range of 3700 - 3900 MWh. Significantly, in these hot climatic regions, AC systems alone accounts for over 80% of the overall annual energy consumption, standing out as the predominant energy consumers particularly during the summer months. The annual energy consumption per unit area was also excessive with values ranging from 200 to 500 kWh per m2. Total annual cost of energy was relatively substantial for all schools with values in the order of 1.2 - 1.5 million AED ($330,000 - $400,000). The negative effects of the CO2 emissions were estimated to be around 500 - 600 ton of CO2/year per a single school.