The detection of composite insulator defects in substations still relies on manual inspection. In this paper, we propose a detection method for insulator crack shape features by improving the RCNN convolution kernel. The method can meet the premise of insufficient training sample data, but also can get better CNN training effect, and finally achieve accurate crack recognition. In the training phase, the RGB three-channel decomposition method is used to expand the training data set; the median filtering method is used to remove the noise; the improved convolutional kernel is used to train the CNN; in the test phase, the images are decomposed by RGB three-channel decomposition and input to CNN to get the exact crack center coordinates and length; the NMS algorithm is used to de-weight the images to get the final crack recognition results. The example analysis shows that the method in this paper can still achieve good recognition accuracy and accurately identify the specific location of cracks under the premise of insufficient training samples.
Electrically assisted manufacturing (EAM) is a promising and rapidly developing metal processing method. The power supply is a key sub-system for EAM, which needs to be designed properly. This paper proposes the model-based design of a low-voltage high-current pulse power supply used for EAM based on converter-level electro-thermal modeling. The thermal stress of key components is obtained by converter-level finite element simulations. A simplified thermal modeling method is proposed to reduce the computation burden of the FEM simulation to obtain the dynamic thermal profile under pulse current operation. The impact of the duration of the current pulse on the maximum temperature and temperature variations of MOSFETs is investigated based on the thermal model. A case study of a 10V/500A pulse power supply is presented to demonstrate the theoretical analyses and verification. The outcomes contribute to the design optimization and virtual prototyping of pulse power supplies for EAM applications.
When the permanent magnet assisted synchronous reluctance motor(PMaSynRM)runs at high-speed with flux-weakening control,the DC bus voltage utilization is not high,and the efficiency and torque output capacity of the motor are low. Therefore,a flux-weakening control strategy of permanent magnet assisted synchronous reluctance motor based on hexagonal trajectory was proposed. Firstly,based on the d-q axis equivalent circuit of the permanent magnet assisted synchronous reluctance motor,the voltage and current constraints of the flux-weakening process were derived,and the root cause of the flux-weakening control to improve the speed regulation ability of the motor was proved. Secondly,in order to give full play to the advantages of high-power density under high-speed operation of permanent magnet assisted synchronous reluctance motor,the over-modulation algorithm was derived. It was applied to the flux-weakening operation of permanent magnet assisted synchronous reluctance motor to achieve higher DC bus voltage utilization. Finally,the effectiveness of the proposed method was verified by simulation.
Aiming at the problem of imbalance load of feeder lines and reverse photovoltaic power flow in distribution network, the flexible interconnection scheme based on full-power converter is the key to realize intelligent control of distribution network. In this paper, a power control strategy for flexible interconnection system is proposed, which including heavy-load limiting control for the rational power distribution when some feeder lines are heavy-loaded, and power balance control for that all feeders are heavy-loaded to relieve the power supply pressure of flexible interconnection devices (FIDs). Case study based on real load data verifies that the proposed strategy can cope with different seasonal distribution network scenarios with different load characteristics and different degrees of reverse photovoltaic power flow. The proposed can suppress forward and reverse heavy load flow, and improve the power supply safety and efficiency of the distribution network.
In order to improve the sensorless control performance of permanent magnet synchronous linear motor, a sensorless control method based upon disturbance compensated flux observer was studied. The rotor flux observer studied in this paper combines the disturbance observer and the feedback compensation, which can suppress the initialization errors of dc bias and integration, and the parameter debugging is simple. In addition, the studied observer will not bring errors in the amplitude and phase of the flux linkage. The position and speed are estimated by a phase-locked loop to ensure the observation accuracy of the observer. Finally, the simulation verifies the correctness and effectiveness of this method.
The doubly-fed induction generator(DFIG)is the mainstream model in the wind power market.Since there are multiple time-scale control objectives in the wind turbine,it is difficult for conventional linear control methods to optimize the multi-objective.Model predictive control(MPC)is an effective method for wind turbine control due to the high dynamic response performance and multi-objective optimization capacity.However,model predictive control achieves multi-objective optimization through a single cost function,which leads to the coupling of the control objectives,making it difficult to design the weight factors and determine the control priority.Therefore,a dynamic sequential model predictive control(DSMPC)strategy was proposed,which a single cost function was replaced by an optimization structure composed of multiple cascade cost functions.The control objectives were ranked according to the average value of all cost functions of each control objective,and the priority was dynamically adjusted.In addition,the control threshold was used to adjust the number of candidate switch vectors from the control pre-stage to the control post-stage.This method realized the overall optimal control of multiple objectives without using weight factors.The effectiveness of the proposed method was proved by the hardware-in-the-loop results.
Supply interruption may occur during the operation of permanent magnet synchronous motor(PMSM)in some special applications and it needs to be restarted in the rotating state which is called flying start,the accurate initial position/speed observation is the foundation of flying start.Aiming at the problem that the pulse width and interval time cannot be adjusted automatically when the traditional zero-voltage vector(ZVV)pulse method is used to observe the initial position/speed,the adaptive adjustment strategy of ZVV pulse was studied.The ZVV action time was adjusted adaptively through comparing the amplitude of short circuit current vector monitored in real time with the threshold value.The ZVV interval time was adjusted adaptively according to the speed prediction results of single ZVV pulse method.The experimental results show that the designed adaptive double ZVV pulse method can adjust appropriate pulse width and interval time of ZVV pulse for different initial speed,which is conducive to improving the performance of initial position/speed observation and flying start at high speed.
Focus on the stator winding insulation of asynchronous motor, the transition process of the pulse voltage output by the frequency converter was analyzed, the voltage equivalent mathematical models and simulation model of the stator winding, reactor and cable were established. For rolling mill in metallurgical industry, the different voltage slope was verified by using real high-power asynchronous motor and frequency converter for pulse voltage test. Aiming at the voltage oscillation caused by different cables length, the second order system fitting was used to analyze the voltage spectrum characteristics, and the reactor’s suppression effect for voltage oscillation was also verified.
In the long cable driven induction motor drive systems,speed sensorless control is usually adopted due to the long distance between the controller and the motor.In addition,long cable increases the stator side impedance of the induction motor,especially the equivalent stator resistance by an order of magnitude,which increases the impact of the temperature drift of the stator resistance on the flux observation and reduces the performance of the flux observer.A magnetic flux observation method with strong stator resistance robustness was proposed for induction motor drive systems powered by long cables..This method improves the traditional hybrid model flux observer,a model reference adaptive speed observer that is completely robust to the stator resistance was used to obtain the speed,meanwhil,the current model was used to calculate the rotor flux,and this flux calculation process was used to replace the original current model.The flux calculation process is completely robust to the stator resistance,so the robustness of the observer to the stator resistance is improved.Hardware-in-the-loop(HIL)test results verify the feasibility and effectiveness of this method.
According to the 90 s regular breaking and 15 s emergency breaking requirement for 60 MW axial compressor used in some large scientific facility,a control strategy of electric hybrid breaking in the convertor was designed.The hybrid braking control strategy was analyzed and calculated,and the optimal braking control process for the compressor and the parameters of the braking resistance were determined.The control strategy and breaking time were verified by real-time digital simulator(RTDS)simulation and experiment.The simulation result and experiment result show that simulation result is closed to experiment result,and the hybrid breaking control strategy of convertor is safe and reliable.The real regular breaking time is 87.54 s and the real emergency breaking time is 14.82 s.The regular breaking time and the emergency breaking time fulfil the technical performance.
The reliability and stability of electric energy transmission in the power grid are the guarantee of driving safety,due to the impact of external interference fluctuations and current arcs on the power grid structure,its parameter acquisition and dynamic modeling become difficult.Firstly,the characteristics of grid structure distortion and model structure changes were analyzed,fuzzy control based on theory sets was used to analyze the characteristics of dynamic electric energy transmission in power systems.Secondly,data fusion was performed for multivariate models of sampled currents,combined with adaptive control strategies to online correct error overshoot and suppress fluctuations,and to seek fuzzy control constraints to maintain the stability of its local minimum error mean square value.Finally,a Simulink fuzzy simulation model was established through experimental parameters to verify that adaptive data fusion technology can effectively correct errors and fluctuations,ensure good driving power transmission.
Permanent magnet synchronous motor(PMSM)has become the development direction of the new generation of rail transit traction system due to its characteristics of high efficiency and high power density.Among them,the research on the identification method of the initial position and frequency of the motor rotor in coasting condition is an important part of the position sensorless control technology of PMSM.Therefore,the zero voltage vector single pulse method and double pulse method were firstly studied.When the PMSM was in coasting condition,one or two pulses were short-circuited by all the lower bridge arms of three-phase inverter,and the initial position and frequency of rotor were obtained according to the short-circuit response current.On this basis,a method of short circuit time selection of zero voltage vector pulse method and a zero voltage vector compound pulse method were proposed to ensure that PMSM can stably restart at different coasting frequency.Through Matlab/Simulink simulation and the test conducted in the test center of CRRC Dalian Electric Traction R&D Center Co.,Ltd.,the results show that PMSM under different frequencies can stably restart,the frequency identification error is less than 0.6 Hz,the rotor position identification error is less than 5°.
Maximum torque per ampere(MTPA)control is one of the important methods to improve the efficiency of sensorless drive system of permanent magnet synchronous motor(PMSM).In the sensorless drive system,the traditional calculation method deduces the analytical solution of the optimal current vector angle according to the formula,which ignores the characteristics of the position error changes,and the accuracy of the injection virtual signal optimization method is also reduced by the position error.In order to solve this problem,an MTPA control method considering position estimation error was proposed.By comparing the optimal current vector angle tracking result of the above two methods in the sensorless drive system,the position error was estimated.Then the estimated position error was applied to correct the motor mathematical model for the high-accuracy tracking of the optimal current vector angle.Finally,the effectiveness of the proposed method was verified on the 2.2 kW interior PMSM(IPMSM)experimental platform.
In order to ensure the efficient and stable operation of high-temperature submersible motors,and to timely avoid motor failures caused by high operating temperatures,which may affect production,it is necessary to obtain their underground temperature without temperature sensors.Based on this situation,a temperature recognition and prediction method for high-temperature submersible motors based on improved wavelet neural network(I-WNN)was proposed.Firstly,the operating data of high-temperature submersible motors were classified.Then,an improved wavelet neural network was used to train historical data,a mapping relationship between the operating data of high-temperature submersible motors and temperature was established,and the weight parameters of the wavelet neural network were optimized to obtain the most weighted values.Finally,through experimental simulation,the fitted temperature values and predicted temperature values of the high-temperature motor were obtained.
In order to solve the problems of large volume and short service life of the traditional electrolytic capacitor frequency converter,the thin film capacitor was used to replace the electrolytic capacitor to constitute the AC-DC-AC frequency converter without electrolytic capacitor.Aiming at the problem of bus voltage oscillation in the process of low frequency V/F operation of electrolytic capacitor-less inverter,firstly,the bus voltage ripple and resonance in different working modes were analyzed according to the equivalent circuit model of induction motor,and the stability condition of electrolytic capacitor-less drive system was analyzed by using Rous stability criterion.Secondly,according to the mathematical model of the drive system without electrolytic capacitor,the relationship between the bus voltage and the stator reactive current during the oscillation process was analyzed.Finally,a reactive current feedback control strategy based on stator voltage direction was proposed to suppress bus voltage oscillation and improve system stability.The simulation and experimental results show that the proposed control strategy can realize the stable operation of the induction motor in the global range and effectively improve the stability of the system.
To address the problem of the long detection time of the current detection method during the open circuit fault diagnosis of inverter insulated gate bipolar transistor(IGBT)of the permanent magnet synchronous motor(PMSM)drive system,an error current polarity method based on model predictive current control(MPCC)was investigated.By combining the variation of the cost function in MPCC with the current detection method,the fault detection time can be effectively reduced.However,the MPCC is susceptible to changes in motor parameters,the load torque and speed changes may lead to changes or mismatches in the motor parameters,which in turn affect the output of the cost function and lead to misdiagnosis.To address the issue,the fault detection indicators were normalized and a counting method was added to the MPCC-based error current polarity method to further improve the robustness of fault diagnosis.
Permanent magnet synchronous motor(PMSM)driving stable platform directly is often used in guided rockets to realize the decoupling control of stable platform.Due to the extended state observe(ESO)contained in the active disturbance rejection controller(ADRC),it can accurately estimate the speed of the rotated carrier and the uncertain disturbances accurately without requiring exact mathematic model of system.Based on active disturbance rejection control technique,an ADRC for single-axis stable platform was designed,and optimized the controller.The Matlab simulation and experimental verification show that the system has strong anti-interference ability and high control quality.
原有的电力系统调度模型是物理模型与信息模型分立的.建立信息物理融合的电力系统调度模型,可以充分分析与挖掘可调资源的调节能力,扩大电力系统可调度空间,增强电网对可再生能源的消纳能力.为此以我国现有电力系统调度框架为基础,提出了一种信息物理融合的电力系统日前-日内调度框架,在此框架下对电力系统源-网-荷建模,形成信息物理融合的电力系统日前-日内调度模型.基于所建模型,以经济调度为目标,提出了电力系统日前-日内优化调度策略.算例分析验证了所提策略的有效性,结果表明电力系统的信息物理融合建设可以降低系统的运行成本.最后指出在电力系统的信息物理融合建设过程中应以目标为导向,建设多时间尺度的分层级信息物理融合电力系统.
现有特高压直流换流站的安全监测多采用人工现场检测,存在较大的安全隐患,人工成本高.为满足输电系统的安全需要,设计了基于远距离无线电(LoRa)技术的特高压直流换流站多角度联合监控系统,监测模块对换流站的重要系统进行多角度联合监测,采用LoRa无线传输技术进行通信传输.实验结果表明,该方案监测数据准确率高,工作功耗低,传输距离远,可以有效提高换流站的无线监控管理的智能水平.
以明晰5G电磁辐射对换流站内继电保护通信控制设备的干扰影响为目标,建立了中心频率3.5 GHz的微带天线仿真模型.首先分析了微带天线的电磁辐射传播衰减规律,发现由于微带贴片的非对称性,其贴片法线方向正上方或正下方方位的增益显著高于其他方位.其次,以空气为对照组,分别分析了PVC塑料、混凝土、不锈钢板等材料的干扰抑制能力,发现不锈钢板相较于其他2种材料有更好的电磁干扰屏蔽能力.最后,为保证屏蔽盒内单极子天线的正常通信需求,对不锈钢屏蔽盒的布置方式进行优化,通过在盒体上均匀开挖5 mm通孔的方式,将外部电磁干扰由66.5 dB降至30 dB.研究结果对于明确微带天线的5G辐射的空间传播规律以及屏蔽措施的合理选择提供了有益借鉴.
