Power Control Mode Research Articles

A primer on design aspects, recent advances, and challenges in cellular device-to-device communication

Device-to-Device (D2D) communication is one of the technologies on the spotlight for enhancing the cellular network performance towards the fifth generation wireless systems. It has diverse potentials to cater for both critical and non-critical applications. For example, timely information dissemination can be achieved during disasters using D2D communication. Also, content sharing and real-time applications can be effectively facilitated. Recently, new applications and technologies are beginning to embrace D2D to further improve their performance in terms of spectral efficiency, latency, and energy efficiency. However, this is not bereft of technical challenges due to the peculiar limitations of traditional D2D communication such as interference. In this paper, we focus on techniques for managing these challenges with regards to mode selection, power control, and resource allocation. As compared with other contemporary works on this subject, we discuss these issues in line with some of the most recent research trends. In addition, we compile pertinent design considerations of D2D discussed in literature while extracting new patterns to familiarize readers with applications, models, methods and metrics studied lately. Furthermore, we highlight and classify some of the key challenges of D2D communication with respect to current and future generation cellular technologies, giving a comprehensive outlook of new research problems recently identified in this area.

Operation of Parallel Inverters in Microgrid Using New Adaptive PI Controllers Based on Least Mean Fourth Technique

This paper shows the operation of the microgrid using a new adaptive PI controller based operational (control) scheme. The core of the proposed control scheme is the suggested adaptive PI controller. The parameters of the PI controller are adaptively tuned using a variable step-size least mean fourth algorithm with no need for any system model to operate this adaptive controller. The main merit of the proposed scheme is that it stabilizes the magnitude and frequency of the voltage at any loading condition such as variable balanced loads, variable unbalanced loads, and nonlinear loads. The proposed scheme has a simple structure and accurate performance. In addition, the structure of proposed scheme provides a seamless transition toward any loss or reconnection of any inverter in the microgrid. Furthermore, the suggested operational scheme is flexible enough to enable the microgrid to be operative in a grid-connected mode and to transfer from the voltage control mode to power control mode with a smooth transitional procedure. To validate the meritorious performance of the suggested scheme, its performance is compared to similar schemes based on a linear controller (regular PI controller), single-neuron PI controller (adaptive PI controller), recursive least square-support vector machine based PI controller (another adaptive PI controller), and nonlinear controller (sliding mode controller) for different operations of the microgrid.

Advanced Type-2 fuzzy logic–based pitch-angle control strategy for wind energy system

In general, pitch-angle controller regulates the generator output power when the wind speed exceeds the rated wind turbine speed. Besides this, it can also be employed to stabilize the wind energy system rotor speed during the transient disturbances. In this article, therefore, a logical pitch-angle controller strategy (in power and speed control modes) has been developed and an interval Type-2 fuzzy logic technique is proposed to design the controller. To evaluate the effectiveness of the Type-2 fuzzy logic–based pitch-angle controller, the simulations have been carried out for severe network faults and fluctuating wind conditions, and the results are compared with conventional proportional–integral and fuzzy logic controller (called as Type-1 fuzzy logic controller). Moreover, some key factors that affect the transient stability of wind generator have also been investigated. The electrical torque and mechanical torque versus rotor speed results are obtained under different pitch-angle conditions, and the concept of stable and unstable electrical–mechanical equilibrium points is established.

An adaptive time-graded control method for VSC-MTDC networks

Power flow and voltage control, beside other challenges such as DC faults, are the main concerns in the operation of multi-terminal HVDC (MTDC) networks. This paper proposes a novel DC voltage control method, which is inspired from the principles of power system protection, for VSC-based MTDC networks. This time-graded control method periodically ranks all converters; the highest priority one is dedicated to regulate the network voltage while the others operate in the power control mode. In abnormal conditions in which the grid-forming converter cannot solely control the network voltage, a sufficient number of converters are sequentially turned to the voltage control mode according to their priority. Upon recovering from the abnormal condition, the proposed controller with its conditional reclosing ability returns these mode-changed converters to the power control mode. Since the proposed method regulates the voltage of MTDC network by the minimum number of converters, the maximum ones can be employed in power flow control. Proposing an adaptive procedure to calculate appropriate mode change delays is another contribution of this communication-less control method. Simulation of a test network in MATLAB/Simulink under various conditions with both proposed and conventional droop controllers verifies the outstanding abilities of the proposed method.

Conservation voltage reduction of networked microgrids

This study proposes a strategy for coordinated operation of networked microgrids (MGs), distributed energy resources (DERs), and volt-VAR control devices in the implementation of volt-VAR optimisation (VVO). The authors’ formulation is focused on implementing conservation voltage reduction, although it can be extended for any other VVO problems. They consider the voltage–power control modes of DERs contemplated in IEEE Std. 1547, namely, constant power factor, voltage–reactive power, active–reactive power, and constant reactive power. DERs are considered at the distribution network (DN) and within the MGs. The problem is formulated as a bi-level optimisation problem where the DN operator (DNO) is in the upper-level and each MG in the lower-level. The DNO and each MG are assumed to be players with their individual objective functions. Finally, they validate their formulation in two test systems: a 9-node system and a modified IEEE 33-node system. On average the proposed method can improve the efficiency of the grid by 4% compared to the economic operation scenario. The results of the study show that the different control modes of the DERs can have better performance depending on the objective of the VVO formulation. The findings of this study are compelling for the implementation of VVO in active distribution systems with networked MGs.

Distributed Strategy for Optimal Dispatch of Unbalanced Three-Phase Islanded Microgrids

This paper presents a distributed strategy for the optimal dispatch of islanded microgrids, modeled as unbalanced three-phase electrical distribution systems. To set the dispatch of the distributed generation (DG) units, an optimal generation problem is stated and solved distributively based on primal–dual constrained decomposition and a first-order consensus protocol, where units can communicate only with their neighbors. Thus, convergence is guaranteed under the common convexity assumptions. The islanded microgrid operates with the standard hierarchical control scheme, where two control modes are considered for the DG units: a voltage control mode, with an active droop control loop, and a power control mode, which allows setting the output power in advance. To assess the effectiveness and flexibility of the proposed approach, simulations were performed in a 25-bus unbalanced three-phase microgrid. According to the obtained results, the proposed strategy achieves a lower cost solution when compared with a centralized approach based on a static droop framework, with a considerable reduction on the communication system complexity. Additionally, it corrects the mismatch between generation and consumption even during the execution of the optimization process, responding to changes in the load consumption, renewable generation, and unexpected faults in units.

Transient Modeling and Analysis of VSC Based DC Microgrid During Short Circuit Fault

The application of distributed renewable energy (DER) drives the development of DC microgrid based on voltage source converter (VSC). And short circuit fault protection is a significant challenge for the development of VSC based DC microgrid. This paper proposes a transient modeling method for VSC based DC microgrid. Firstly, the transient characteristics of VSC under DC bus voltage control mode and active power control mode are analyzed. And then the faulty DC microgrid model, which consists of VSC model and DC line model, is modeled. And the calculation expressions of state variables in DC microgrid are presented. Next, the correctness of proposed modeling approach is verified by comparing with the electromagnetic transient (EMT) simulation by Matlab/Simulink. Moreover, the case study on the parameters configuration of DC microgrid protection devices shows that the transient modeling method can be effectively used in faulty DC microgrid analysis. The method proposed in this paper can not only ensure the calculation efficiency, but also improve the accuracy of DC microgrid analysis on fault.

Operation of Stand-Alone Microgrids Considering the Load Following of Biomass Power Plants and the Power Curtailment Control Optimization of Wind Turbines

Various stand-alone hybrid power systems are widely used to fulfil the electric loads for remote, rural villages. Although there are many investigations based on various aspects of renewable hybrids energy microgrids, the discussions about the application of biomass combustion power plants are rare. Also, detailed investigations of the system steady and transient stability analysis, and the power curtailment control optimization of wind turbines in these stand-alone hybrid systems are seldom found. This paper focuses on wind/biomass/diesel/battery stand-alone microgrids and discusses the system operation, energy management and dispatch issues detailed. The renewable and controllable biomass power is localized to follow the load fluctuations over a long timescale to decrease the power production from diesel and the peak-load shifting demands of the battery banks. An optimization strategy of the wind power curtailment control is also proposed to effectively decrease the frequency and amplitude of the pitch actor and, to some extent, improve the power generation through the combination of the active turbine speed control and pitch regulation. Then a parallel double-mode optimal operation strategy with a “fault detector” is presented to realize economic optimization dispatch under the normal mode and emergency power control for large disturbance scenarios. Finally, case studies of a microgrid on a remote Canadian aboriginal community are conducted to demonstrate the performance of the proposed methods.

Joint channel and Power Allocation for Device-to-Device Communication on Licensed and Unlicensed Band

Device-to-Device communications (D2D) are being used to improve the spectral efficiency and to reduce the load of the base station (BS) by reutilizing the licensed spectrum. However, the primary cellular users may face high interference from D2D users. There is also a scarcity of licensed spectrum due to the dense deployment of smart devices. To alleviate this problem, in this paper, we are extending the D2D users to the unlicensed band. In this scenario, the D2D users are allowed to reuse the licensed spectrum or share the unlicensed spectrum with the incumbent WiFi users. However, cellular and WiFi users experience high interference if an efficient interference management scheme is not used. In this paper, we propose a joint mode selection, channel allocation, and power control algorithm using particle swarm optimization to manage the interference and improve the overall throughput of cellular and D2D users such that the minimum data rate requirement of WiFi users is guaranteed. Through numerical simulations, we show that the proposed algorithm can significantly mitigate the interference and improve the throughput of the system.

Coordination control strategy for LLCL‐filter based grid‐tied inverter with indirect sliding mode power control and virtual impedance

Coordination control strategy for LLCL‐filter based grid‐tied inverter with indirect sliding mode power control and virtual impedance

Frequency-Selectable RF Ablation Treatment System

In order to support study of new radiofrequency ablation treatments and finally realize of precise conformal ablation of targeted tissue, this paper proposed a system which is able to generate radio frequency currents at different frequencies. The designed system bases on the basic principle of Class E power amplifier and uses MSP430 microcontroller as a controller and uses a touch screen as human-machine interface to design a frequency-selectable radiofrequency ablation treatment system,. The RF signals at frequencies of 230 kHz, 460 kHz, 920 kHz, and 2 000 kHz were tested to verify the feasibility of the system, and by using a tissue phantom, tested the heating ability of the RF signals at frequencies of 460 kHz, 920 kHz, and 2 000 kHz. The results show the device could well heat the tissue at the three frequencies. The study has also found that both the highest temperature and the ablation area decreases with RF frequency, when using the constant power control mode.

Research on Control Strategy of Integrated Gasification Humid Air Turbine Cycle

Integrated gasification humid air turbine (IGHAT) cycle is an advanced power generation system, combining gasification technology and humid air turbine (HAT) cycle. It draws great attention in the energy field considering its high specific power, high efficiency, and low emission. There are only a few HAT cycle plants and IGHAT cycle is still on the theory research stage. Therefore, the study on control strategies of IGHAT cycle has great significance in the future development of this system. A design method of control strategy is proposed for the unknown gas turbine systems. The control strategy design is summarized after IGHAT control strategy and logic is designed based on the dynamic simulation results and the operation experience of gas turbine power station preliminarily. Then, control logic is configured and a virtual control system of IGHAT cycle is established on the Ovation distribution control platform. The model-in-loop control platform is eventually set up based on the interaction between the simulation model and the control system. A case study is implemented on this model-in-loop control platform to demonstrate its feasibility in the practical industry control system. The simulation of the fuel switching control mode and the power control mode is analyzed. The power in IGHAT cycle is increased by 24.12% and 32.47%, respectively, compared to the ones in the simple cycle and the regenerative cycle. And the efficiency of IGHAT cycle is 1.699% higher than that of the regenerative cycle. Low component efficiency caused by off-design performance and low humidity caused by high pressure are the main limits for system performance. The results of case study show the feasibility of the control strategy design method proposed in this paper.

Interactions between a polymer electrolyte membrane fuel cell and boost converter utilizing a multiscale model

In a fuel cell vehicle, a direct current boost converter (DCC) is required to link a polymer electrolyte membrane fuel cell system (FCS) and lithium battery packages. The DCC is installed to regulate the output power of the FCS, and can be controlled in different ways, via current, voltage, or power modes. Interactions between a DCC and FCS have attracted growing interests in recent years, because they affect dynamic and stable performances of the entire system. This paper outlines a simulation study on interactions between high-frequency switching operations of a DCC and internal states of an FCS based on a multiscale model. Results are as follows. (1) High-frequency switching operations have a major influence on the cathode overpotential, voltage ohmic loss and water transport through the membrane, whereas the influence on the partial pressures of gas species inside the stack is slight. (2) The FCS is more stable in the case of membrane dehydration than in that of water flooding. DCC's control mode has a greater influence on the FCS when water flooding occurs than membrane dehydration. The power control mode is the most unstable of the three, whereas the current control mode is the most stable.

Mode selection considering fairness in D2D‐enabled cellular networks

AbstractIn this paper, we consider the problem of mode selection, resource allocation, and power control for device‐to‐device (D2D) communications in cellular networks. We propose optimization frameworks based on max‐min fairness and proportional fairness where cellular and D2D links share the cellular resources. The optimization problem is solved in different resource sharing modes (ie, cellular, overlay, and underlay), and the mode leading to the highest optimal value is selected in the system. We further propose a two‐stage mode selection scheme based on channel quality in which the resource partitioning is expressed in closed form. We compare the performance of the proposed schemes with that of optimization framework based on sum‐rate and no‐mode selection scheme. The numerical results indicate that cellular and D2D links achieve higher rates in proportional fairness and max‐min fairness schemes compared to no‐mode selection scheme. While the rate improvement of D2D link is more significant in sum‐rate optimization, the cellular link may achieve lower rate in this scheme compared to other methods including the no‐mode selection scheme. The results also reveal that the rates of cellular and D2D links in channel quality scheme can vary within the range of rates obtained in max‐min and sum‐rate optimization frameworks.

Adaptive fractional integral terminal sliding mode power control of UPFC in DFIG wind farm penetrated multimachine power system

With an aim to improve the transient stability of a DFIG wind farm penetrated multimachine power system (MPN), an adaptive fractional integral terminal sliding mode power control (AFITSMPC) strategy has been proposed for the unified power flow controller (UPFC), which is compensating the MPN. The proposed AFITSMPC controls the dq- axis series injected voltage, which controls the admittance model (AM) of the UPFC. As a result the power output of the DFIG stabilizes which helps in maintaining the equilibrium between the electrical and mechanical power of the nearby generators. Subsequently the rotor angular deviation of the respective generators gets recovered, which significantly stabilizes the MPN. The proposed AFITSMPC for the admittance model of the UPFC has been validated in a DFIG wind farm penetrated 2 area 4 machine power system in the MATLAB environment. The robustness and efficacy of the proposed control strategy of the UPFC, in contrast to the conventional PI control is vindicated under a number of intrinsic operating conditions, and the results analyzed are satisfactory.

A Reliable Microgrid With Seamless Transition Between Grid Connected and Islanded Mode for Residential Community With Enhanced Power Quality

This paper presents a reliable microgrid for residential community with modified control techniques to achieve enhanced operation during grid connected, islanded, and resynchronization mode. The proposed microgrid is a combination of solar photovoltaic, battery storage system and locally distributed generation (DG) systems with residential local loads. A modified power control technique is developed such that local load reactive power demand, harmonic currents, and load unbalance are compensated by respective residential local DG. However, active power demand of all local residential load is shared between the microgrid and respective local DG. This control technique also achieves constant active power loading on the microgrid by supporting additional active power local load demand of respective residential DG. Hence, proposed modified power control technique achieves transient free operation of the microgrid during residential load disturbances. An additional modified control technique is also developed to achieve seamless transition of microgrid between grid-connected mode and islanded mode. The dynamic performance of this microgrid during grid-connected, islanded, and resynchronization mode under linear and nonlinear load variations is verified using real-time simulator.

Decoupled AC/DC Power Flow Strategy for Multiterminal HVDC Systems

AbstractThis paper proposes a decoupled AC/DC power flow approach for multi-terminal HVDC systems. The proposed method simplifies the power flow computation of multi-terminal HVDC systems while accurately reflecting the operation and control characteristics of VSC (voltage source converter) stations in a HVDC network. In the DC network, the power flow calculation is conducted based on a slack DC bus VSC station and power commends issued to other VSC stations from the power system control center. Then, in the AC power flow calculation, VSC stations are treated as special AC generators that can generate and absorb power from the AC grid in active and reactive power or active power and bus voltage control mode. For validation purpose, the conventional unified power flow method for multi-terminal HVDC systems is built. The paper compares the proposed method with the unified power flow method for an 8-bus multi-terminal HVDC system based on MATPOWER. Then, more case studies for different VSC control modes are conducted and evaluated for the 8-bus system. Afterwards, the proposed method is applied to the power flow study of a more practical and complicated multi-terminal HVDC system based on the IEEE 118-bus system.

An Emergency Control Strategy for Isolated Power System of Three-Phase Inverter and Diesel-Engine Generator Operating in Parallel

In the isolated power system of renewable energy power generation inverter and diesel-engine generator operating in parallel, the generator usually runs in the voltage and rotate speed droop control mode, and the three-phase inverter runs in the constant power-control mode. In this case, a sudden load change will be completely undertaken by the generator, which may lead to its overload or reverse power. In order to solve this problem, this paper has proposed an emergency control strategy based on the detection of the rate of system frequency change. In emergency conditions, the strategy can be used to automatically adjust the inverter output power to deal with the aforementioned overload or reverse power and prevent the system from shedding load and avoid protective actions of the generator. Thus, the power-supply capacity and continuity of the system are guaranteed, and its safety and stability are also improved. Time-domain simulations and experiments show that the proposed strategy is feasible and effective.

Hot target magnetron sputtering for ferromagnetic films deposition

This work is an investigation on the operation parameters for Ni films deposition by magnetron sputtering from target working at temperatures higher than the Curie temperature due to magnetic phase transition of the sputtered target, which is partial heat-insulated from the water-cooled magnetron body. The ferro- to paramagnetic transition of the target results in decrease of discharge voltage and rise of discharge current. Thereby, discharge power increases under voltage control mode or hot Ni target sputtering can occur at lower pressures under power control mode. Heating of the Ni target and its ferro- to paramagnetic transition leads to stabilization of the discharge parameters. The changes of the discharge current and power decreased from 10.5% to 2.5% during a single sputtering process under voltage control mode. Moreover, a slight increase of the deposition rates of 20…25% was determined, when hot target sputtering was performed. The XRD assessment showed that Ni films deposited by hot target sputtering have a textured crystal structure with larger grain sizes and lower residual stresses in comparison with cooled Ni target sputtering. When passing from cooled to hot target sputtering, the type of film growth changes from zone 1 to zone T, and surface roughness of Ni films decreased.

Ultra-Dense Heterogeneous Networks with Full-Duplex Small Cell Base Stations

The FD communication technique has been recently proposed as a new paradigm to increase the spectral efficiency of wireless systems. In this article, we investigate the application of FD communications to ultra-dense heterogeneous networks where small base stations can work in the FD mode. In such networks, it is a challenging task to coordinate various kinds of interference caused by FD communications, including self-interference, intra-cell and inter-cell uplink-todownlink interference. To deal with it, we have developed a novel ICIC scheme, which consists of four steps: base station association, user pairing and mode selection, power control, and resource block allocation. The implementation issue of the proposed scheme is also discussed. Simulation results demonstrate that our proposed ICIC scheme can effectively harvest the FD gain for ultra-dense heterogeneous networks. Finally, several important future directions and open challenges are identified in this article.