Flexible Power Regulation and Limitation of Voltage Source Inverters under Unbalanced Grid Faults

This paper develops a flexible power regulation and limitation strategy of voltage source inverters(VSIs)under unbalanced grid faults.When the classical power theory is used under unbalanced grid faults,the power oscillations and current distortions are inevitable.In the proposed strategy,the extended power theory is introduced to compute the power feedbacks together with the classical power theory.Based on the combination of the classical and extended power theory,the proposed strategy can achieve the sinusoidal current provision and the flexible regulation between three common targets,i.e.,constant active power,balanced current,and constant reactive power.Meanwhile,the proposed strategy is associated with a power limiter,which is capable to keep the currents under the pre-defined threshold and to compute the maximum apparent power for better utilization of the inverter capacity.With this power limiter,the rated inverter capacity is fully used for both the active and reactive power provisions under unbalanced grid faults.Using the proposed power regulation and limitation,the VSI can avoid overcurrent tripping and flexibly regulate its power under unbalanced grid faults.All the conclusions are verified by the real-time hardware-in-loop tests.

Superconducting Magnetic Energy Storage Integrated Current-source DC/DC Converter for Voltage Stabilization and Power Regulation in DFIG-based DC Power Systems

Unpredictable power fluctuation and fault ridethrough capability attract increased attention as two uncertain major factors in doubly-fed induction generators(DFIGs)integrated DC power system.Present solutions usually require complicated cooperation comprising multiple modules of energy storage,current control,and voltage stabilizer.To overcome the drawbacks of existing solutions,this paper proposes a superconducting magnetic energy storage(SMES)integrated currentsource DC/DC converter(CSDC).It is mainly composed of a current-source back-to-back converter,and the SMES is tactfully embedded in series with the intermediate DC link.The proposed SMES-CSDC is installed in front of the DC-DFIG to carry out its dual abilities of load voltage stabilization under multifarious transient disturbances and power regulation under wind speed variations.Compared with the existing DC protection devices,the SMES-CSDC is designed on the basis of unique current-type energy storage.It has the advantages of fast response,extensive compensation range,concise hardware structure,and straightforward control strategy.The feasibility of the SMESCSDC is implemented via a scaled-down experiment,and its effectiveness for DC-DFIG protection is verified by a large-scale DC power system simulation.

A Two-stage Single-phase Grid-connected Solar-PV System with Simplified Power Regulation

This study focuses on the design and development of a simplified active power regulation scheme for a two-stage single-phase grid-connected solar-PV(SPV)system with maximum power point(MPP)estimation.It aims to formulate and test an improvised new control scheme to estimate the real-time MPP of the PV panel and operate only at either the MPP or on the right-hand side(RHS)of the PV characteristics of the panel.A simple active power regulatory control scheme was formulated to provide frequency control services to a single-phase grid without using an energy storage device.The plant operator provides the reserve fraction as the input for the active power regulation controller.At any time,the reserve fraction is used to determine the magnitude of the reference power to be extracted from the PV panel for injection into the grid.A simple PI controller was used to track the calculated reference power.The different modes of operation of the regulatory scheme are presented in detail.All the above control schemes are integrated and implemented through appropriate switching of the DC-DC converter alone.The DC-AC converter maintains the DC link voltage and unity power factor at the single-phase grid terminals.The proposed control schemes were tested on a 250 Wp solar panel feeding power to a 230 V,50 Hz single-phase grid through a two-stage converter.The entire scheme was modeled using the Matlab/Simulink platform,and the same was validated by hardware experimentation using Chroma Solar Simulator and NI myRIO controller under varied irradiation,temperature,and reserve fractions.The simulation and hardware results are compared and reported.

How to Optimize the Management of Science and Technology Funds in Colleges and Universities Based on the Policy of Streamlining Administration,Delegating Powers,Improving Regulation,and Strengthening Services

To advance the field of science and technology,we need to revitalize the development of science and technology through innovation.The development of science and technology has many beneficial implications on the revitalization of the country.For this reason,universities in China should give full attention to their role as the main propeller of science and technology.“Streamlining administration,delegating powers,improving regulation,and strengthening services”is a policy issued by the Chinese government for the management of science and technology funds in colleges and universities.Based on the policy of“streamlining administration,delegating powers,improving regulation,and strengthening services,”colleges and universities must optimize the management of science and technology funds for their efficient use.In this paper,we analyzed the importance of the policy and put forward an effective management strategy,aiming to improve the management of science and technology funds in colleges and universities.

Regulations and Practice on Flue Gas Denitrification for Coal-Fired Power Plants in China

In China, according to the relative up-to-date regulations and standards, the maincontrol measure for NOX emission of coal-fired power plants is, in principle, low NOXcombustion. However, in recent years, more and more newlyapproved coal-fired plantswere required to install flue gas denitrification equipment. This article expounds if fluegas denitrification is necessary from several aspects, including constitution of NOX, itsimpact to environment, operation ofdeNOXequipment in USA, as wellas the differencein ambient air quality standard between China and World Health Organization. It setsforth themes in urgent need of study and areas where deNOX equipment is necessaryfor new projects, besides a recommendation that the emission standards for thermalpowerplants should be revised as soon as possible in China.

Steady-state voltage-control method considering large-scale wind-power transmission using half-wavelength transmission lines

Half-wavelength transmission can transmit large-scale renewable energy over very long distances.This paper proposes an improved steady-state voltage-control method for half-wavelength transmission systems considering largescale wind-power transmission.First,the unique voltage characteristics of half-wavelength lines are deduced based on the distributed parameter model.In the secondary voltage-control level,reactive power-transmission limits of half-wavelength lines are introduced as another control objective except for tracing the pilot bus voltage reference.Considering the uncertainty and fluctuation of wind power,the overvoltage risk-assessment method of half-wavelength lines is presented to determine specific voltage-control strategies.Simulation results demonstrate that the proposed voltage-control method delivers superior tracking performance according to a voltage reference value and prevents the overvoltage risk of halfwavelength lines effectively in different wind-power penetrations.

Hierarchical Task Planning for Power Line Flow Regulation

The complexity and uncertainty in power systems cause great challenges to controlling power grids.As a popular data-driven technique,deep reinforcement learning(DRL)attracts attention in the control of power grids.However,DRL has some inherent drawbacks in terms of data efficiency and explainability.This paper presents a novel hierarchical task planning(HTP)approach,bridging planning and DRL,to the task of power line flow regulation.First,we introduce a threelevel task hierarchy to model the task and model the sequence of task units on each level as a task planning-Markov decision processes(TP-MDPs).Second,we model the task as a sequential decision-making problem and introduce a higher planner and a lower planner in HTP to handle different levels of task units.In addition,we introduce a two-layer knowledge graph that can update dynamically during the planning procedure to assist HTP.Experimental results conducted on the IEEE 118-bus and IEEE 300-bus systems demonstrate our HTP approach outperforms proximal policy optimization,a state-of-the-art deep reinforcement learning(DRL)approach,improving efficiency by 26.16%and 6.86%on both systems.

Evaluation of intermittent-distributed-generation hosting capability of a distribution system with integrated energy-storage systems

The penetration rate of distributed generation is gradually increasing in the distribution system concerned.This is creating new problems and challenges in the planning and operation of the system.The intermittency and variability of power outputs from numerous distributed renewable generators could significantly jeopardize the secure operation of the distribution system.Therefore,it is necessary to assess the hosting capability for intermittent distributed generation by a distribution system considering operational constraints.This is the subject of this study.An assessment model considering the uncertainty of generation outputs from distributed generators is presented for this purpose.It involves different types of regulation or control functions using on-load tap-changers(OLTCs),reactive power compensation devices,energy storage systems,and the reactive power support of the distributed generators employed.A robust optimization model is then attained It is solved by Bertsimas robust counterpart through GUROBI solver.Finally,the feasibility and efficiency of the proposed method are demonstrated by a modified IEEE 33-bus distribution system.In addition,the effects of the aforementioned regulation or control functions on the enhancement of the hosting capability for intermittent distributed generation are examined.

大规模风电接入吉林电网风电消纳能力分析

针对风电大规模并入电网后,消纳风电能力受制约问题,基于吉林电网的电源负荷特性及峰谷差情况分析,在充分考虑尖峰电源备用、低谷火电机组深度调峰的情况下,提出了考虑电力平衡的最大风电消纳能力的计算方法,计算得出了2014年、2016年吉林电网最大风电可接纳容量,并分析了制约风电消纳能力的主要因素,最后提出了加快风电外送通道和加强抽水蓄能电站建设、推广电能替代工作、提高风电储能技术的实用化水平以及健全火电调峰补偿机制具体建议。

我国网络舆论监督权力的法律规制历程

我国网络舆论监督权力的法律规制是个渐进的过程,它与舆论所依赖的网络平台的发展状况以及人们对网络法律规制的认知有着紧密的关系,与我国总体的法治状况直接相关。网络舆论监督权力的法律规制历程迄今为止大致可分为3个主要阶段:即网络舆论监督权力的法律规制初建阶段、逐步完善阶段和深入推进阶段。在规制理念上分别体现为网络自由主义、网络管制主义和中国特色社会主义法治理念。网络舆论监督权力的法律规制总体呈现出不断进步的同时,也暴露了一些普遍存在的影响法律规制效果的问题,这些问题的存在及网络舆论监督法治实践的不断变化决定了网络舆论监督法律规制任重道远。

H∞position transfer and regulation for floating offshore wind turbines

This paper proposes H∞controller design for platform position transfer and regulation of floating offshore wind turbines.The platform movability of floating wind turbines can be utilized in mitigating the wake effect in the wind farm,thereby maximizing the wind farm's total power capture and efficiency.The controller is designed so that aerodynamic force is adjusted to meet the three objectives simultaneously,that is,1)to generate the desired electrical power level,2)to achieve the desired platform position,and 3)to suppress the platform oscillation.To acquire sufficient aerodynamic force to move the heavy platform,the pitch-to-stall blade pitching strategy is taken instead of the commonly-used pitch-to-feather strategy.The desired power level is attained by the standard constant-power strategy for the generator torque,while Hstate-feedback control of blade pitch and nacelle yaw angles is adopted for the position regulation and platform oscillation suppression.Weighting constants for the H∞controller design are adjusted to take the trade-off between the position regulation accuracy and the platform motion reduction.To demonstrate the efficiency of the proposed controler,a virtual 5-MW semi-submersible wind turbine is considered.Simulation results show that the designed H∞controller successfully accomplishes the platform position transfer and regulation as well as the platform oscillation reduction against wind and wave disturbances,and that it outperforms a previously-proposed linear quadratic controller with an integrator.

Design and analysis of control system using neural network for regulated DC power supply

Conventional control systems used for regulated power supplies,including the proportional integral and derivation(PID)controller,have some serious disadvantages.The PID controller has a delayed feedback associated with the control action and requires a lot of mathematical derivations.This paper presents a novel controlling system based on the artificial neural network(ANN),which can be used to regulate the output voltage of the DC power supply.Using MATLABTM,the designed control system was tested and analyzed with two types of back-propagation algorithms.This paper presents the results of the simulation that includes sum-squared error(SSE)and mean-squared error(MSE),and gives a detailed comparison of these values for the two algorithms.Hardware verification of the new system,using RS232 interface and Microsoft Visual Basic 6.0,was implemented,showing very good consistency with the simulation results.The proposed control system,compared to PID and other conventional controllers,requires less mathematical derivation in design and it is easier to implement.

Coordination control method to block cascading failure of a renewable generation power system under line dynamic security

The large application of renewable energy generation(REG)has increased the risk of cascading failures in the power system.At the same time REG also provides the possibility of new approaches for the suppression of such failures.However,the capacity and position of the synchronous generator(SG)involved in regulation limit the power regu-lation speed(PRS)of REG to the overload line which is the main cause of cascading failures,while the PRS of SG is related to the position and shedding power.REG and SGs have difficulty in achieving effective cooperation under constraints of system power balance.Particularly,the dynamic variation of line flow during power regulation causes new problems for the accurate evaluation of line thermal safety under overload.Therefore,a new strategy for quan-titatively coordinating shedding power and power regulation to block cascading failures in the dynamic security domain is proposed in this paper.The control capability and dynamic security domain of the overload line are mod-eled,and the coordination control method based on power regulation is then proposed to minimize shedding power.The algorithm for the optimal control scheme considers the constraints of load capacity,power source capacity and bus PRS.The correctness of the proposed method is verified using case studies.

Non-isolated stacked bidirectional soft-switching DC-DC converter with PWM plus phase-shift control scheme

In this paper, a non-isolated stacked bidirectional DC-DC converter with zero-voltage-switching(ZVS) is introduced for the high step-up/step-down conversion systems. The extremely narrow turn-on and/or turn-off duty cycle existing in the conventional bidirectional buck-boost converters can be extended due to the stacked module configuration for large voltage conversion ratio applications. Furthermore, the switch voltage stress is halved because of the series connection of half bridge modules. The PWM plus phase-shift control strategy is employed, where the duty cycle is adopted to regulate the voltages between the input and output sides and the phaseshift angle is applied to achieve the power flow regulation.This decoupled control scheme can not only realize seamless bidirectional transition operation, but also achieve adaptive voltage balance for the power switches. In addition, ZVS soft-switching operation for all active switches is realized to minimize the switching losses. Finally, a prototype of 1 kW operating at 100 kHz is built and tested to demonstrate the effectiveness of the proposed converter and the control strategy.