Adaptive controller design based on input-output signal selection for voltage source converter high voltage direct current systems to improve power system stability

An input-output signal selection based on Phillips-Heffron model of a parallel high voltage alternative current/high voltage direct current(HVAC/HVDC) power system is presented to study power system stability. It is well known that appropriate coupling of inputs-outputs signals in the multivariable HVDC-HVAC system can improve the performance of designed supplemetary controller. In this work, different analysis techniques are used to measure controllability and observability of electromechanical oscillation mode. Also inputs–outputs interactions are considered and suggestions are drawn to select the best signal pair through the system inputs-outputs. In addition, a supplementary online adaptive controller for nonlinear HVDC to damp low frequency oscillations in a weakly connected system is proposed. The results obtained using MATLAB software show that the best output-input for damping controller design is rotor speed deviation as out put and phase angle of rectifier as in put. Also response of system equipped with adaptive damping controller based on HVDC system has appropriate performance when it is faced with faults and disturbance.

Is transcranial direct current stimulation a potential method for improving response inhibition?

Inhibitory control of movement in motor learning requires the ability to suppress an inappropriate action, a skill needed to stop a planned or ongoing motor response in response to changes in a variety of environments. This study used a stop-signal task to determine whether transcranial direct-current stimulation over the pre-supplementary motor area alters the reaction time in motor inhibition. Forty healthy subjects were recruited for this study and were randomly assigned to either the transcranial direct-current stimulation condition or a sham-transcranial direct-current stimulation condition. All subjects consecutively performed the stop-signal task before, during, and after the delivery of anodal transcranial direct-current stimulation over the pre-supplementary motor area （pre-transcranial direct-current stimulation phase, transcranial direct-current stimulation phase, and post-transcranial direct-current stimulation phase）. Compared to the sham condition, there were significant reductions in the stop-signal processing times during and after transcranial direct-current stimulation, and change times were significantly greater in the transcranial direct-current stimulation condition. There was no significant change in go processing-times during or after transcranial direct-current stimulation in either condition. Anodal transcranial direct-current stimulation was feasibly coupled to an interactive improvement in inhibitory control. This coupling led to a decrease in the stop-signal process time required for the appropriate responses between motor execution and inhibition. However, there was no transcranial direct-current stimulation effect on the no-signal reaction time during the stop-signal task. Transcranial direct-current stimulation can adjust certain behaviors, and it could be a useful clinical intervention for patients who have difficulties with response inhibition.

Novel torque ripple minimization algorithm for direct torque control of induction motor drive

To elucidate the principles of notable torque and flux ripple during the steady state of the conventional direct torque control （DTC） of induction machines, the factors of influence torque variation are examined. A new torque ripple minimization algorithm is proposed. The novel method eradicated the torque ripple by imposing the required stator voltage vector in each control cycle. The M and T axial components of the stator voltage are accomplished by measuring the stator flux error and the expected incremental value of the torque at every sampling time. The maximum angle rotation allowed is obtained. Experimental results showed that the proposed method combined with the space vector pulse width modulation （SVPWM） could be implemented in most existing digital drive controllers, offering high performance in both steady and transient states of the induction drives at full speed range. The result of the present work implies that torque fluctuation could be eliminated by imposing proper stator voltage, and the proposed scheme could not only maintain constant switching frequency for the inverter, but also solve the heating problem and current harmonics in traditional induction motor drives.

Hybrid Multi-Infeed Interaction Factor Calculation Method Considering Voltage Regulation Control Characteristics of Voltage Source Converter

Voltage source converter based high voltage direct current(VSC-HVDC)can participate in voltage regulation by flexible control to help maintain the voltage stability of the power grid.In order to quantitatively evaluate its influence on the voltage interaction between VSC-HVDC and line commutated converter based high voltage direct current(LCC-HVDC),this paper proposes a hybrid multi-infeed interaction factor(HMIIF)calculation method considering the voltage regulation control characteristics of VSC-HVDC.Firstly,for a hybrid multi-infeed high voltage direct current system,an additional equivalent operating admittance matrix is constructed to characterize HVDC equipment characteristics under small disturbance.Secondly,based on the characteristic curve between the reactive power and the voltage of a certain VSC-HVDC project,the additional equivalent operating admittance of VSC-HVDC is derived.The additional equivalent operating admittance matrix calculation method is proposed.Thirdly,the equivalent bus impedance matrix is obtained by modifying the alternating current(AC)system admittance matrix with the additional equivalent operating admittance matrix.On this basis,the HMIIF calculation method based on the equivalent bus impedance ratio is proposed.Finally,the effectiveness of the proposed method is verified in a hybrid dual-infeed high voltage direct current system constructed in Power Systems Computer Aided Design(PSCAD),and the influence of voltage regulation control on HMIIF is analyzed.

Damping controller design based on FO-PID-EMA in VSC HVDC system to improve stability of hybrid power system

Wind energy sources have different structures and functions from conventional power plants in the power system.These resources can affect the exchange of active and reactive power of the network.Therefore,power system stability will be affected by the performance of wind power plants,especially in the event of a fault.In this paper,the improvement of the dynamic stability in power system equipped by wind farm is examined through the supplementary controller design in the high voltage direct current(HVDC)based on voltage source converter(VSC)transmission system.In this regard,impacts of the VSC HVDC system and wind farm on the improvement of system stability are considered.Also,an algorithm based on controllability(observability)concept is proposed to select most appropriate and effective coupling between inputs-outputs(IO)signals of system in different work conditions.The selected coupling is used to apply damping controller signal.Finally,a fractional order PID controller(FO-PID)based on exchange market algorithm(EMA)is designed as damping controller.The analysis of the results shows that the wind farm does not directly contribute to the improvement of the dynamic stability of power system.However,it can increase the controllability of the oscillatory mode and improve the performance of the supplementary controller.

DSP ＆ FPGA-based control architecture for a highly integrated robot hand with enhanced impedance performance

A novel control system is developed to improve the capabilities of robet hand performing tasks in a variety of environments. A joint impedance control strategy has been successfully implemented in the low level control of a highly integrated robot hand. At flint, a real time controller with DSP＆FPGA-based multilevel control architecture is built. Then a current sensor of the single direct current （DC） link is used to measure and reconstruct the three phase currents, and a stable current signal is measured by optimizing sample instant. The experimental results of the joint impedance control show that the proposed method not only improves the effectiveness of contact environment performance, but also provides compliant interaction of robot hand with a person, which is very important for the development of friendly human robot of the next generation.

Design and implementation of a position sensorless control method for brushless DC motors

Because brushless direct current(BLDC) motors have the advantages of a compact size, high power density, high efficiency, and long operating life time, they are widely used in many industrial products and electric traction systems. It is known that the BLDC motors have no brushes for commutation. They are commutated with electronically commutation. So, the rotor position information of the BLDC motors must be known to understand which winding will be energized according to the energizing sequence. In most of the existing BLDC motor drivers, rotor position information is detected by Hall effect sensors. This kind of mechanical position sensors will bring additional connections and costs, reliability decrease and noise increase. In order to improve the control performance and extend the range of speed regulation for BLDC motors, a position sensorless control method is proposed in this paper. In the proposed control method, rotor position information of the BLDC motors is detected from the back electromagnetic forces(back-EMFs) which are estimated by an unknown-input observer with line to line currents and line to line voltages. For the purpose of verifying the effectiveness of the proposed control method, a model is built and simulated on the Matlab/Simulink platform. The simulation results show that the speed regulation performance of BLDC motors is improved compared with using Hall effect sensors. At the same time, the reliability of the BLDC motors is improved and the costs of them are reduced because the position sensor is eliminated.

Frequency Control of Power System with Renewable Power Sources by HVDC Interconnection Line and Battery Considering Energy Balancing

Recently, introduction of renewable energy sources like wind power generation and photovoltaic power generation has been increasing from the viewpoint of environmental problems. However, renewable energy power supplies have unstable output due to the influence of weather conditions such as wind speed variations, which may cause fluctuations of voltage and frequency in the power system. This paper proposes fuzzy PD based virtual inertia control system to decrease frequency fluctuations in power system caused by fluctuating output of renewable energy sources. The proposed new method is based on the coordinated control of HVDC interconnection line and battery, and energy balancing control is also incorporated in it. Finally, it is concluded that the proposed system is very effective for suppressing the frequency fluctuations of the power system due to the large-scale wind power generation and solar power generation and also for keeping the energy balancing in the HVDC transmission line.

Frequency Control of Power System with Solar and Wind Power Stations by Using Frequency Band Control and Deadband Control of HVDC Interconnection Line

In recent years, environmental problems are becoming serious and renewable energy has attracted attention as their solutions. However, the electricity generation using the renewable energy has a demerit that the output becomes unstable because of intermittent characteristics, such as variations of wind speed or solar radiation intensity. Frequency fluctuations due to the installation of large scale wind farm (WF) and photovoltaics (PV) into the power system is a major concern. In order to solve the problem, this paper proposes two control methods using High Voltage Direct Current (HVDC) interconnection line to suppress the frequency fluctuations due to large scale of WF and PV. Comparative analysis between these two control methods is presented in this paper. One proposed method is a frequency control using a notch filter, and the other is using a deadband. Validity of the proposed methods is verified through simulation analyses, which is performed on a multi-machine power system model.

Simulation Study of the Control Strategy of a DC Inverter Heat Pump Using a DC Distribution Network

Photovoltaics,energy storage,direct current and flexibility(PEDF)are important pillars of achievement on the path to manufacturing nearly zero energy buildings(NZEBs).HVAC systems,which are an important part of public buildings,play a key role in adapting to PDEF systems.This research studied the basic principles and operational control strategies of a DC inverter heat pump using a DC distribution network with the aim of contributing to the development and application of small DC distribution systems.Along with the characteristics of a DC distribution network and different operating conditions,a DC inverter heat pump has the ability to adapt to changes in the DC bus voltage and adds flexibility to the system.Theoretical models of the DC inverter heat pump integrated with an ice storage unit were developed.The control strategies of the DC inverter heat pump system considered the influence of both room temperature and varied bus voltage.A simulation study was conducted using MATLAB&Simulink software with simulation results validated by experimental data.The results showed that:(1)The bus fluctuation under the rated working voltage had little effect on the operation of the unit;(2)When the bus voltage was fluctuating from 80%-90%or 105%-107%,the heat pump could still operate normally by reducing the frequency;(3)When the bus voltage was less than 80%or more than 107%,the unit needed to be shut down for the sake of equipment safety,so that the energy storage device could adjust to the sharp decrease or rise of voltage.

基于钳位型断路器的柔直系统控保协同技术

柔性直流系统以其在输电领域的巨大优势而获得广泛应用.但在直流系统中,短路故障的强冲击性与电力电子器件的脆弱性之间的矛盾异常尖锐,现有保护策略难以同时满足高速动性与高可靠性的要求.本文从控保协同思想出发,基于一种电压钳位原理的直流断路器,提出一种新的故障处理模式,初步探究在柔直系统中控制与保护深度融合的可能性.当发生短路故障时,投入断路器和换流器相配合的限流功能,一方面限制电力电子器件的过流,解决其脆弱性问题;另一方面为保护提供边界,辅助实现故障的快速定位.在甄别出故障线路后,利用断路器的故障切除功能将故障隔离.此方案同时实现了故障限流、保护边界和故障切除3项功能,可有效缓减由于模块化多电平换流器(modular multilevel converter,MMC)器件脆弱性所带来的一系列保护问题.在PSCAD/EMTDC中搭建四端双极柔性直流电网模型,仿真结果表明,本控保协同方案能在5 ms内准确识别并隔离故障线路,而且具有较强的耐受过渡电阻能力.

海洋电磁发射机可控源整流电路动态性能优化

海洋电磁发射机在非理想状况工作时母线会产生冲击电压,严重时损坏开关管和滤波电容,为此提出一种混合控制策略。首先,基于dq坐标系的前馈解耦控制策略分析海洋电磁发射机可控源整流电路的动态性能,其次,通过理论证明负载扰动和无功电流iq≠0影响控制系统的动态性能,然后提出在dq电流解耦控制中引入瞬态直接电流思想的改进q轴混合控制方法,在dq电流解耦控制中引入负载电流前馈和无功电流iq≠0环节,改善了d轴电流id的响应速度,提高了控制系统的动态性能。最后,实验结果对比表明,混合控制方法在负载突变、直流侧电压给定值突变和船上柴油发电机电压跌落3种情况下,直流侧电压超调差最小,与最长调整时间相比减少了65%左右。

断路器选相投切系统在换流站中的应用研究

在换流站滤波器组及换流变压器配置断路器选相投切系统,可改善断路器开合暂态过程,在取消合闸电阻工况下仍可避免对电力设备及系统造成冲击。基于多个换流站选相投切工程实施及调试经验,进行了换流站选相投切系统应用的调查。介绍了选相投切系统构成、选相投切要求、断路器配套及预测试方法等。重点针对滤波器组、换流变压器的选相投切应用,总结了控制策略、选相投切系统带电冲击试验,及工程使用中需重点关注的问题、设备运维要求等,为相关技术人员提供参考。试点工程在特高压断路器中创新性地采用取消合闸电阻、增设选相合闸的专项改造方案。断路器选相投切系统总体运行效果良好,为技术的推广积累了工程运行经验。

基于自抗扰控制的圆纬机恒张力输纱控制系统设计

针对当前圆纬机积极式送纱方式中存在的纱线张力及输送速度不可任意调节、纱线张力波动大等问题,提出了一种可为圆纬机输送恒定张力纱线的输纱控制系统。构建了以无刷直流电动机速度环为内环、以纱线张力为外环的纱线恒张力双闭环反馈控制系统,通过自抗扰控制技术获取纱线实时动态指标,并对无刷直流电动机目标转速进行调整,最后通过磁场定向控制技术驱动无刷直流电动机。详细阐述了纱线张力的形成机制、纱线恒张力输送控制方案、系统硬件设计及控制算法。输纱测试表明,该控制系统可实现多种类型纱线的恒定张力输送。其中,棉纱张力波动标准差为1.5 cN(300 m/min测试条件),氨纶包芯纱的张力波动标准差为0.33 cN(240 m/min测试条件)。输纱速度的调节范围为0~600 m/min,纱线张力的控制范围为2.0~50.0 cN。

一种抑制后续换相失败的电流偏差控制参数整定方法

电网换相换流器型高压直流输电(line commutated converter-based high voltage direct current,LCC-HVDC)系统若发生后续换相失败,将严重影响交直流混联电网的安全稳定运行。文中首先针对LCC-HVDC系统故障恢复过程中电流偏差控制作用阶段易再次发生换相失败的问题,对电流偏差控制参数与换相失败之间的关系进行理论分析,发现此阶段系统若不发生换相失败,逆变侧LCC直流电压和交流换相电压须满足一定的约束关系,且该约束关系受电流偏差控制参数的直接影响。然后,基于理论分析结果,提出一种电流偏差控制参数整定方法,可改善系统故障恢复过程中对直流电压恢复速度和程度的控制要求,使系统更易满足直流电压与交流换相电压稳定运行约束关系,以降低后续换相失败概率。最后,利用PSCAD/EMTDC仿真平台CIGRE标准测试模型验证了理论分析的正确性以及参数整定方法的有效性。

匹配控制构网型直驱风电场经LCC-HVDC 送出 系统的次同步振荡特性及机理分析

在“沙戈荒”地区风电经电网换相高压直流输电(line-commutated-converter based high voltage direct current,LCC-HVDC)外送系统中,采用基于匹配控制的构网型直驱风机(matching control permanent magnet synchronous generator,MC-PMSG)可以提升送端电网的稳定性。然而,当MC-PMSG位于LCC-HVDC整流站近区时,系统的次同步振荡(sub-synchronous oscillation,SSO)特性尚未明确。针对上述问题,该文采用模块化建模法建立MC-PMSG经LCC-HVDC送出系统的小信号模型,通过特征值法研究MC-PMSG与LCC-HVDC对系统各SSO模态的参与情况与系统运行方式变化对次同步振荡阻尼特性的影响,通过阻尼重构法分析LCC-HVDC并网对系统振荡风险的影响机理。研究结果表明,系统存在匹配控制型风机主导、LCC-HVDC参与的SSO模态,MC-PMSG与LCC-HVDC间的次同步交互作用为SSO提供负阻尼;当混合型风电场中的MC-PMSG占比增大、MC-PMSG风电场容量增大或短路比减小、LCC-HVDC定电流控制器的比例系数增大、风机网侧换流控制器外环积分系数减小、直流电容增大时,SSO阻尼增大。通过PSCAD/EMTDC电磁暂态仿真证明理论分析结果的有效性。

混合级联特高压直流功率损失计算方法研究

混合级联特高压直流(UHVDC)在降低直流换相失败风险的同时提升了直流输电的灵活性,但由于LCC与VSC混合拓扑导致不同阀组闭锁后健全阀组的功率传输能力存在不确定性,影响了直流功率损失准确计算。此处提出了一种适用于混合级联UHVDC的功率损失计算方法。直流控制系统以极为单位计算阀组闭锁后的直流功率并发送安控系统计算直流功率损失,设计了合理接口与数据处理方式保证阀组单次及相继故障直流功率损失计算的准确性。最后通过试验,验证了所提方法的正确性与有效性。

级联多端特高压直流控制保护系统配置及策略

该文针对金上直流工程主回路拓扑结构与运行方式的特点,设计了送端分址级联多端特高压直流控制保护系统的配置方案;提出送端分站的高、低压换流器的电压平衡控制方案,根据送端两站间通信条件,切换采用附加电压平衡控制的触发角协调控制和串联两换流器一个定电压、另一个定电流的控制策略;基于送端分站级联拓扑,研究了其直流保护功能配置方案,并提出针对送端站1内的极区/换流器区故障或者送端两站之间直流线路永久故障的快速清除方法。基于控制保护工程样机的RTDS闭环仿真结果表明,该级联多端特高压直流控制保护系统可以满足实际工程应用的要求。