Mode Switching Method Research Articles

A CC/VC‐based power tracking method for photovoltaic inverter operated in voltage control mode

AbstractThe active power control of photovoltaic (PV) inverters without energy storage can flatten the fluctuating power and support the voltage amplitude and frequency of the grid. When operated in grid‐forming voltage‐control mode, because the PV power can change rapidly and widely, the PV inverter needs to track the power commands quickly and precisely. Traditionally, this goal is achieved with the estimation of PV power curve or PI‐based multiple‐loop feedback control, where flexibility, availability and accuracy are not satisfactory. Therefore, a CC/VC‐based power tracking (CVPT) method is proposed, which only uses single‐loop in control. The proposed method does not need to tune multiple loops and can respond faster, which is important for grid‐forming voltage control. Furthermore, the different operating modes due to the limitation of PV maximum power are analysed, and a mode switch method is proposed. Simulation and experimental results demonstrate that the PV inverter can cope with power disturbances from both the power and grid sides and maintain the quality of grid voltage.

Mixed Variable Parameter Energy Storage-Assisted Frequency Support Strategy

With the continuous increase in the installed capacity of new energy systems, the impact of power shocks on grid frequency is becoming more significant, seriously affecting the stability of the grid and thermal power units. For this reason, a mixed variable parameter energy storage-assisted frequency support control method is proposed. This method introduces an integral control mode based on the existing control mode and forms a co-ordinated control mode. The impact of the switching point of the mixed control mode is analyzed, and a new mode switching method is used. The model adjusts the frequency regulation parameters according to the different states of the grid frequency, making the frequency regulation more efficient. Finally, a frequency regulation model that integrates various improvement methods is built, and a 10 min continuous load disturbance is applied to compare and verify the frequency regulation performance of the model as a whole. The results indicate that the proposed control method can significantly improve the quality of grid frequency regulation, reduce the frequency deviation amplitude to 0.00096 p.u., reduce the participation time of thermal power units to 190.8393 s, and reduce the peak output to 0.1934 MW, demonstrating its engineering feasibility.

Composite control of anti-drone platform for stable tracking under disturbance.

First, focused on the complex problem that a U-shaped tracking frame is unreachable to obtain the pointing angles of an unmanned aerial vehicle target, a novel coordinate transformation method is proposed in this paper. The fixed transformation relationship between the intermediate links is deduced by establishing a unified coordinate system, simplifying the algorithm conversion process, and saving computing resources and time. Furthermore, the accuracy of the proposed method has been verified in both aspects of theory and experiment. Then, in order to achieve smooth motion performance between target pointing strategy and stable tracking strategy, a mode switching method based on hysteresis intervals is developed. Compared with the traditional single-point threshold method, the switching method overcomes the high frequency jitter problem. The experimental results validate the consistency between practical effects and theoretical expectations. Finally, to improve the disturbance rejection performance of the platform, a composite control method integrating the information from the gyroscope and circular grating is proposed. The corresponding control scheme and the compensation principle are conceived and explained. The experimental results show the anti-interference performance of the proposed composite control method is five times that of the closed-loop method based on the gyroscope speed signal and two times that of the disturbance observer control method.

Research on Human-Computer Interaction Technology of Large-Scale High-Resolution Display Wall System

As an effective solution for data visualization and analysis, the large-scale high-resolution display wall system has been widely used in various scientific research fields. On the basis of investigating existing system cases and research results, this paper introduces the SHU-VAS system (60 screens, 120 megapixels) for data visualization and analysis. In order to improve the efficiency of human-computer interaction in large-scale high-definition display wall systems, we propose an interaction framework based on gesture and double-precision pointing technology. During the interaction process, an adaptive mode switching method based on user action features is used to switch between rough and precise control modes. In the evaluation experiments, we analyzed the characteristics of different interaction methods in movement and navigation interaction tasks, and verified the effectiveness of the gesture-based interaction framework proposed in this paper.

Voltage Control and Power-Shortage Mode Switch of PV Inverter in the Islanded Microgrid Without Other Energy Sources

The growing installation capacity of distributed photovoltaic inverter needs change of the operation method in the modern power grid. Recently, to better integrate into the grid, the active power control is investigated in photovoltaic inverter. Meanwhile, without energy storage, the photovoltaic inverter can use voltage control method to further support the grid voltage and frequency. Due to the stochastic photovoltaic power, the mode switch is needed when the maximum power still cannot meet the grid demands. The operation of PV inverter in this power shortage mode has not been sufficiently studied. Therefore, this paper investigates the mode switch method for voltage-controlled two-stage photovoltaic inverter. The power conversion principle of synchronous generator is realized in the inverter and the dc/dc converter maintains the dc-side voltage. The mode switch method between normal operation and power-shortage state is proposed. With this method, the PV inverter can real-time adjust the output power of photovoltaic battery and match the load demand without support from other energy source even under PV output power's intense change.

A Blockchain Enhanced Coexistence of Heterogeneous Networks on Unlicensed Spectrum

Due to the forecasted fast increasing cellular traffic and the already highly congested licensed spectrum, it is critical to exploit and utilize the unlicensed spectrum resources for the fifth-generation (5G) and beyond networks. A challenging problem is the coexistence of 5G and other networks with fair, reliable, and efficient sharing of the unlicensed spectrum. In this paper, we propose a blockchain-enhanced distributed spectrum sharing scheme for coexisting multiple operators and multiple WiFi APs. We design a novel lightweight and efficient consensus mechanism, named Proof of Strategy (PoG). In this consensus mechanism, the problem of spectrum sharing is used as a consensus puzzle, and the part of the unlicensed spectrum is used as the ‘fee’ of miners. With such a design, the computing overhead of the consensus process is expected to be reduced significantly. We develop a non-cooperative game to analyze the behavior of the miners and obtain a symmetric Bayesian Nash equilibrium under the uniform distribution of mining cost estimation. It can be found mathematically and experimentally that the strategy of the winner tends to maximize the system revenue by sharing the unlicensed spectrum resource. Furthermore, to reduce the impact of heavy interactions on system throughput, the operation of WiFi APs in the proposed scheme can be adaptively switched between ‘contention mode’ and ‘blockchain mode’ according to the network traffic load. The dynamic behavior is constructed as an evolutionary game, and the existence and uniqueness of equilibrium points are proved by theoretical analysis. Simulations demonstrated the fairness and effectiveness of the proposed blockchain-based scheme and the mode switching method for distributed spectrum sharing by heterogeneous wireless networks.

Synergistic balancing control for low-inertia power systems with high PV penetration: Tibet as a case study

This paper proposes a novel synergistic balancing control scheme for low-inertia power systems with high photovoltaic (PV) penetration in Tibet power grid (TPG). The mechanism and dispatching principle of choosing the suitable area control error (ACE) control mode for TPG are analyzed., An adaptive control mode switching method is proposed to meet the different control demands for the dynamically changing topologies. Then, we propose a new coordinated control scheme to dispatch hydropower generators and PV power stations. A set of optimum control objectives considering balancing control performance, regulation mileage of conventional generators, and power curtailment of PV are first presented. The control objectives are decomposed and simplified by step-by-step approximation and linearization, which are easily extended to be applied to real-world automatic generation control (AGC) systems. The simulation results show the effectiveness of the proposed solutions for synergistic balancing control by using the equivalent TPG test system. The equivalent system includes 63 generators with total power equal to 1618.5 MW and 51 PV power stations over 1100 MW. In addition, the actual operation cases present that the coordinated control between conventional and renewable generation dispatched by AGC has the basic conditions in the actual operation of the power grids, which will play a more significant role with the rapid increase of renewable generation sources in the future.

Unified Control Scheme of Grid-Connected Inverters for Autonomous and Smooth Transfer to Stand-Alone Mode

As one of the approaches for a grid-sustaining inverter, the inverter should cover not only grid-connected (GC) mode but also stand-alone (SA) mode for power supply to local loads; therefore, there are separate control loops for each mode. In order for an uninterruptible power supply to the local load, it should be seamless to change from GC mode to SA mode. This carries two types of issues. One is a transient state caused by switching the control loops. The other is an uncontrolled state during the time interval between a grid failure and its detection, called clearing time. These can lead to unstable voltage for the local load. Hence, a smooth and autonomous mode switching method is required even if the fault detection is late. Existing mode transfer methods considering both the issues have been accompanied by a slow dynamic response, additional sensors, restriction of adopting filter, or controller complexity due to third-order plant. To overcome them, in this article, a control scheme realized by a unified control loop is proposed for smooth and autonomous mode switching with a novel antiderailing control. Furthermore, the proposed control scheme can achieve a high bandwidth for the output power control in GC mode because it is based on controlling the current flowing the inverter-side inductor, and both filter types, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> , can be adopted. To validate the proposed concept, simulations and experiments were conducted. The results show that the proposed control scheme can be used to achieve autonomous and smooth mode transition even under reactive power reference and reactive load conditions.

Seamless mode‐switching control for electric spring with capacitor DC bank

Electric spring (ES) has been proposed to suppress the fluctuations of critical load voltage under the condition of the increasing proportion of renewable energy in the power grid, but existing popular control methods have not fully released its application potential. Therefore, a novel control strategy that enables it to operate in the entire scope is proposed in this study, which differs from the conventional methods since the fully known of all system parameters is not indispensable. Furthermore, a seamless operating mode switching method is discussed, which is important for practical application. In the end, the simulation results in PSCAD/EMTDC verify that the ES can operate stably in various regions, and can seamlessly switch between capacitive and inductive modes.

Bypassing-contravariant mode switching method for UPS in economic mode based on DSP program

Uninterrupted power supply has the highest efficiency and reliability under economic mode. When the grid power quality is qualified, the economic model UPS uses the grid power supply to supply the load directly, which achieves the highest system efficiency. However, when the voltage is too high, too low or the frequency is not normal, the large circulation will cause device damage or UPS failure, which cannot meet the requirements of load on power quality. To solve this problem, this paper proposes a switching control method of UPS system from bypass power supply state to inverter power supply state in economic mode based on DSP program. The method analyses the theoretical basis and switching time sequence of over-high detection of mains power in detail, and proves the effectiveness of the proposed method through experiments.

A Novel DC Fault Ride-Through Method for Wind Farms Connected to the Grid Through Bipolar MMC-HVDC Transmission

Modular multilevel converter based high voltage direct current (MMC-HVDC) transmission is the prospective technology for large-scale wind farms integration. In this paper, a comprehensive coordinated control strategy for DC fault ride-through (FRT) of wind farms connected to the grid through bipolar MMC-HVDC transmission is proposed. To reduce the requirement of breaking speed and capacity of DC breakers, an active current-limiting control method is proposed to limit the rise rate of DC fault current, and the principle of parameter selection is designed. After DC breakers isolate fault, the control mode switching methods of bipolar MMC are designed to make the fault pole MMC operate as a STATCOM to support the AC grid and improve the active power transmission capability of the healthy pole MMC, which can reduce the impact range of unbalanced power between wind farms and converter station. In addition, a coordinated control strategy for wind farms load-shedding considering speed constraints is designed to realize the optimal distribution of load-shedding power among wind turbines, which can regulate unbalanced power together with the healthy pole MMC to realize DC FRT. Finally, the effectiveness and feasibility of the proposed control methods are verified by simulation results.

Research on the mode switching control of vehicle electromagnetic suspension employing linear motor

An electromagnetic suspension employing linear motor is able to harvest the energy otherwise wasted in the suspension vibration while the vehicle is running on rough road. A switch method of operation modes is put forward to coordinate the contradiction between energy regeneration and vibration isolation. A dynamic model is created to analyse the general properties of energy regeneration suspension under different working modes. Both simulation and experiments are conducted to verify the modelling and advantages. In energy regenerative mode, the dynamic properties of electromagnetic suspension are basically coincident with those of passive suspension, and more than 14 W of electricity is harvested while driving at 20 m s−1 on level C road. In active control mode, the RMS of vehicle body vertical acceleration and tyre dynamic load are decreased by 21.35% and 4.24% respectively, much better than passive suspension, which proves that the mode switching method is simple and effective.

Research on the mode switching control of vehicle electromagnetic suspension employing linear motor

An electromagnetic suspension employing linear motor is able to harvest the energy otherwise wasted in the suspension vibration while the vehicle is running on rough road. A switch method of operation modes is put forward to coordinate the contradiction between energy regeneration and vibration isolation. A dynamic model is created to analyse the general properties of energy regeneration suspension under different working modes. Both simulation and experiments are conducted to verify the modelling and advantages. In energy regenerative mode, the dynamic properties of electromagnetic suspension are basically coincident with those of passive suspension, and more than 14 W of electricity is harvested while driving at 20 m s−1 on level C road. In active control mode, the RMS of vehicle body vertical acceleration and tyre dynamic load are decreased by 21.35% and 4.24% respectively, much better than passive suspension, which proves that the mode switching method is simple and effective.

Coordinated Control Strategy for Operation Mode Switching of DC Distribution Networks

Due to the advantages such as low line cost, low transmission loss, and high power supply reliability, DC distribution networks have become the main development trend for future distribution networks. In this paper, a typical DC distribution network with multiple voltage levels is considered as a research object. It is proposed that the interface converters between DC buses with different voltage levels be implemented through the series-parallel combination of full-bridge LLC resonant converters. To realize the decentralized self-discipline control of DC voltage under various working conditions, different slack buses are prepared according to the voltage ranges of the DC buses, and the voltage regulation modes of the DC distribution network are divided into main voltage regulation mode, backup voltage regulation mode, and off-grid voltage droop regulation mode. By introducing a voltage coefficient related to DC voltage deviation as a basis for mode switching, the voltage fluctuations caused by slow switching between control modes in the method of traditional voltage margin control is reduced, facilitating fast and smooth switching between different voltage regulation modes. Finally, a simulation model for DC distribution networks is constructed utilizing MATLAB/Simulink. Simulation results verify the effectiveness and feasibility of the proposed voltage regulation modes and switching methods for DC distribution networks. Finally, an experimental platform is also constructed to verify the feasibility of the mode switching method proposed in this paper.

A Simple Flexible and Robust Control Strategy for Wind Energy Conversion Systems Connected to a Utility Grid

This paper presents a simple and robust control strategy for a variable speed wind turbine conversion system using a squirrel-cage induction generator and a three-phase voltage source (AC/DC/AC) Pulse Width Modulation (PWM) converter connected to the utility grid through an LCL filter. The control strategy integrates for the generator side an adaptive radial basis function (RBF) neurosliding mode controller associated with the rotor flux oriented vector control which is used to regulate the turbine rotation speed, rotor flux, and the DC bus voltage. For the grid side, the inverter current and voltage regulation as well as the current injected into the grid are regulated by PI controllers for two modes of operation, namely, the stand-alone mode and grid connected mode. The main contribution of this article is the introduction of a new and simple control algorithm allowing automatic mode switching method based on wind speed. The proposed scheme is very efficient and can be easily implemented in practice. Simulation results illustrate the effectiveness and feasibility of the proposed algorithm.

All-fiberized transverse mode-switching method based on temperature control.

In this paper, an all-fiberized transverse mode-switching method was proposed based on temperature control of few-mode (FM) fiber Bragg gratings (FBGs). Two types of fibers were selected to fabricate the FBG pair in order to match the reflection peaks of the desired mode. The temperature-dependence property of the FM FBGs has been utilized to tune the reflection spectra. Through temperature control, 20 W level output power was obtained when the output laser was switched between the LP11 mode and the LP01 mode in both an all-fiberized ytterbium-doped laser and a Raman laser, which is increased by ∼2 orders of magnitude compared with previous demonstrations (almost less than 100 mW).

An Energy Conservation Strategy Based on Drive Mode Switching for Multi-Axle In-wheel Motor Driven Vehicle

A multi-axle in-wheel motor driven vehicle requires a reasonable drive mode switching method to achieve energy conservation control, which is not sufficiently investigated in the past. To fill the blank, an energy conservation strategy based on drive mode switching is studied in this paper to reduce the energy consumption of multi-axle in-wheel motor driven vehicles. The strategy is developed on the basis of a four-axle in-wheel motor driven vehicle, and a drive mode switching subsystem is established in a hierarchical vehicle dynamics integrated control system. The proposed strategy will determine the number and position of the wheels that involved in driving in real time according to the characteristics of the in-wheel motor and the road conditions, and improve the efficiency of driving system by making the involved wheels work in high efficiency zone as much as possible. Results of the comparison simulation which conducted in Matlab/Simulink environment shows that the presented strategy based on drive mode switching could markedly reduce the energy consumption of four-axle in-wheel motor driven vehicle. The basic idea of this driving mode switching method is also applicable to other multi-axle in-wheel motor driven vehicles.

Switching Characteristics Optimization of Two-Phase Interleaved Bidirectional DC/DC for Electric Vehicles

In electric vehicles (EVs), bidirectional DC/DC(Bi-DC/DC) is installed between the battery pack and the DC bus to step up the voltage. In the process of mode switching under step signal, the Bi-DC/DC will be affected by a large current inrush which threatens the safety of the circuit. In this paper, a Bi-DC/DC mode switching method based on the optimized Bézier curve is proposed. The Boost and Buck modes can be switched based on the proposed method with fast and non-overshoot switching performance. The experimental results show that the mode switching can be finished in 4 ms without overshoot based on the optimal switching curve.

Integrated control strategy for articulated heavy vehicles based on a linear model with real-time parameters

A control strategy for lateral performance improvement of articulated heavy vehicles (AHVs) by integrating active trailer steering and differential braking is presented. A linear model with real-time parameters is adopted in the strategy to achieve precise control for AHVs under the real-time vehicle states and conditions. The strategy is divided into a path following control mode and rollover control mode. A mode switching method is employed by the strategy to achieve good path following and yaw stability under normal working conditions and to avoid vehicle rollover under the limit conditions. Moreover, in order to obtain the optimal control effects for different control objectives and achieve fusion and coordination of multiple subsystems, the genetic particle swarm optimisation algorithm is used to obtain the optimal weight coefficients of the strategy. Experimental verification results indicate that the presented strategy achieves good control for AHVs across a wide range of different operating conditions.

Integrated control strategy for articulated heavy vehicles based on a linear model with real-time parameters

A control strategy for lateral performance improvement of articulated heavy vehicles (AHVs) by integrating active trailer steering and differential braking is presented. A linear model with real-time parameters is adopted in the strategy to achieve precise control for AHVs under the real-time vehicle states and conditions. The strategy is divided into a path following control mode and rollover control mode. A mode switching method is employed by the strategy to achieve good path following and yaw stability under normal working conditions and to avoid vehicle rollover under the limit conditions. Moreover, in order to obtain the optimal control effects for different control objectives and achieve fusion and coordination of multiple subsystems, the genetic particle swarm optimisation algorithm is used to obtain the optimal weight coefficients of the strategy. Experimental verification results indicate that the presented strategy achieves good control for AHVs across a wide range of different operating conditions.