基于对称基准旋转相量的谐波电流检测方法

提出一种适用于有源电力滤波器补偿电流检测新方法。利用对称基准旋转相量求解基波正序有功电流的幅值,并分别计算电压、电流与基准旋转相量相位差的正余弦值,从而求出基波功率角,消除基准旋转相量与电网电压的相位偏差。仿真结果表明:该方法在电网电压不对称且畸变的条件下能准确提取基波正序有功电流,适用于有源电力滤波系统中谐波、无功及负序电流的综合补偿。     

一种改进的ip-iq检测法的研究

提出了一种关于静止无功补偿器的无功电流检测的改进方法。该无功电流方法首先将电网三相电压进行分解,分离出其实时的正序分量,将其转到同步参考坐标中计算出同步的旋转向量,再通过一系列数学运算,得出精确的无功电流值。从而解决了传统方法在不对称三相电压情况下检测无功电流产生较大误差的问题。通过理论分析和MATLAB软件仿真,验证该算法的可行性。     

一种基于park变换的新型UPQC检测方法

介绍UPQC的结构和工作原理,并提出利用瞬时无功功率理论中的park变换和park反变换,提取出三相不对称畸变电压系统的基波正序电压,再利用能量平衡原理计算出电源参考电流的检测方法.该方法与现有的UPQC检测方法相比,简单易行,实时性好.仿真结果验证了该方法的正确性和有效性.     

基于形态学及dq变换的电能质量检测新方法

现代化电力系统要求实现电力系统和电气设备的数字化检测、控制与保护,而这些都是基于对电气参数的及时、准确和可靠检测基础上的。先用dq变换将电压信号分解成直流量和倍频分量,再采用形态学滤波算法提取出电压的基频分量。仿真与实际应用表明,该方法实时性好、测量精度高、易于硬件开发。     

基于电压dq变换的电压暂降特征量检测法

供电系统电压暂降已逐步成为严重的电能质量问题之一。电压暂降的实时检测是电压暂降补偿控制的基础和依据。本文介绍了运用瞬时电压dq变换原理对电压暂降特征量所进行的实时测量方法,阐述了瞬时电压dq变换低通滤波法的检测算法与补偿控制原理,并通过仿真性分析验证该方法的实用性。     

采用FFT的11相无刷励磁机正常运行时的谐波分析

采用快速傅立叶变换(FFT)分析了11相无刷励磁机正常稳态运行的谐波问题,给出了输出负载电压的直流分量、基波和25次以下的谐波计算结果,为该电机的应用、检测诊断提供谐波分析方面的依据。     

三相逆变器控制策略的研究与仿真分

为实现电动汽车能量稳定高效地回馈给智能电网,三相逆变器控制策略的研究仍是当前研究的热点。提出改进的基于dq坐标系下的前馈解耦双闭环控制策略,使系统在单位功率因数下工作,减小并网过程中电流的冲击和谐波,改善控制效果。基于三相静止坐标系和两相旋转坐标系,分别建立三相逆变器的数学模型,在电压、电流双闭环控制的基础上,在电流环中引入电流前馈解耦。建立Simulink仿真模型,分析逆变过程开关器件的脉冲信号、直流侧电压、交流侧电压与电流、谐波等,验证了所提控制策略的可行性和有效性。     

p-q和ip-iq两种谐波检测方法的仿真对比

针对基于瞬时无功功率理论的p-q和ip-iq两种谐波检测方法建立了仿真模型,并在电网电压有无畸变时进行了仿真和对比。结果表明,ip-iq法在电网电压有无畸变时均能从负载电流中准确地将谐波检测出来,而p-q法只在电网电压无畸变时,才能将负载电流中的基波分量和谐波分量有效地分离开。本研究为在谐波抑制中合理选取谐波检测方法提供了理论依据。     

前馈解耦控制380V电网不平衡补偿的优化方法

为解决城市供电无功功率消耗和三相电网不平衡运行等问题,以380V供电电网为例,通过融合静止同步补偿器的方式对电网无功功率消耗进行补偿,运用信号延时法分离正负序分量,以前馈解耦控制优化补偿性能,构建仿真实验对补偿方法进行检验。实验结果表明：改进补偿方法能够有效解决城市380V电网供电不平衡问题,降低无功功率消耗,实现精确补偿的目的,具有较强的实用性和可行性。     

基于MRA的三相不对称系统谐波监测的研究

首先论述了基于小波变换的谐波检测的原理,根据目前小波变换在三相不对称系统谐波检测中存在的无法分离基波信号之不足,介绍了一种用于三相不对称系统的基于周期交错的测量方法。针对MRA算法既不能直接可靠地估算三相交流信号的基波成分(50 Hz),也不能精确地提取信号的谐波分量的缺点,探讨了将快速傅立叶变换和小波变换相结合的方法,利用小波变换的奇异信号检测能力和较好的时域分辨率,结合傅立叶变换准确的频域分辨能力对电网谐波信号模型进行了分析。文中归纳出基于小波变换的谐波监测方法。该方法的技术优势是可以实时跟踪谐波信号的变化。仿真实验结果表明了该方案能够满足电力系统中谐波检测的实时性要求。     

基于dq0变换的电压暂降检测方法研究

提出了一种基于dqO变换的可用于三相不平衡电压暂降检测的方法。介绍了电压暂降及dqO变换的概念,分析了利用dqO变换后得到的ua,uq,u0分量特征值来辨识不同情况下的电压暂降信号,最后给出控制检测的算法和原理框图。     

基于电压闭环控制的矩阵变换器仿真研究

针对矩阵变换器开环控制碰到扰动输出电压波形不能自动调节的问题,采取电压闭环的控制方式,通过坐标系变换将输出电压采样变换得到空间矢量,与目标电压矢量进行比较得到偏差量,以此来进行反馈控制,并运用MATLAB软件进行器件建模及控制策略、电压闭环控制方法的仿真。通过对两种典型干扰仿真研究,表明电压闭环控制方法对于输入干扰抑制的有效性。     

Diagnosis of stator faults in induction motor based on zero sequence voltage after switch-off

To improve the accuracy of the stator winding fault diagnosis in induction motor, a new diagnostic method based on the Hilbert-Huang transform （HHT） was proposed. The ratio of fundamental zero sequence voltage to positive sequence voltage after switch-off was selected as the stator fault characteristic, which could effectively avoid the influence of the supply unbalance and the load fluctuation, and directly represent the asymmetry in the stator. Using the empirical mode decomposition （EMD） based on HHT, the zero sequence voltage after switch-off was decomposed and the fundamental component was extracted. Then, the fault characteristic can be acquired. Experimental results on a 4-kW induction motor demonstrate the feasibility and effectiveness of this method.     

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 imphes 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.     

Dynamic modeling and direct power control of wind turbine driven DFIG under unbalanced network voltage conditions

This paper proposes an analysis and a direct power control （DPC） design of a wind turbine driven doubly-fed induction generator （DFIG） under unbalanced network voltage conditions. A DFIG model described in the positive and negative synchronous reference frames is presented. Variations of the stator output active and reactive powers are fully deduced in the presence of negative sequence supply voltage and rotor flux. An enhanced DPC scheme is proposed to eliminate stator active power oscillation during network unbalance. The proposed control scheme removes rotor current regulators and the decomposition processing of positive and negative sequence rotor currents. Simulation results using PSCAD/EMTDC are presented on a 2-MW DFIG wind power generation system to validate the feasibility of the proposed control scheme under balanced and unbalanced network conditions.     

二阶广义积分器在三相 PWM 整流器中的应用

针对电网电压出现频率偏移时,传统锁相环精度差、响应速度慢等问题,提出一种基于双二阶广义积分器正交信号发生器的新型锁相环,分析了新型锁相环工作原理,并建立基于新型锁相环的三相三电平电压型SVPWM整流器模型.通过MATLAB/Simulink对模型进行分析验证,结果表明：该新型锁相环能够在频率突变情况下实现频率跟踪,实现有功、无功分量独立控制以及较高功率因数运行.     

中央空调一机多水泵运行能效分析

针对中央空调系统运行管理中实际存在的启动时段内运行一台冷水机组、二台冷冻水泵和二台冷却水泵的现象（称为“一机多水泵运行”）,根据现场测试获得的中央空调系统运行数据,从冷冻水流量、冷水机组能效、冷冻泵效率、冷冻水侧能效和冷冻站能效等多个角度对该运行管理方式进行了分析和评价,指出应改变现有的运行管理方式,使空调系统保持良好的运行性能模式.     

A novel control strategy for load converter of DC isolated distribution system under unbalanced loading conditions

A novel control strategy for the load converter supplying the unbalanced AC load in a DC isolated distribution system is presented. The control algorithm results in balanced and sinusoidal load voltages under unbalanced AC loading. The unbalanced load is characterized in the d-q-0 rotating coordinate based on symmetrical sequence components. Also, the mathematical model of the load converter in both a-b-c and d-q-0 coordinates is derived by using the average large signal model. Then, two control strategies for the load converter are presented. The first one uses the conventional d-q-0 controller to ensure the voltage and current regulation. The second one is a newly proposed control strategy based on the decomposition of the voltage and current into in- stantaneous positive, negative, and zero sequences. These three sequences are controlled independently in their own reference frames as DC signals. The performance of the load converter using these two control strategies is compared. Simulation results show the validity and capability of the newly proposed control strategy.     

Analysis and management strategies for the low voltage problems of rural power grid based on the distribution network flow calculation method

For a long time, because of the lack of investment capital and enough attentions, the overall constructions of rural power grid were far behind than the urban power grid in Chongqing Jiangbei Power Company. The low voltage problems were highlighted in the rural power grid due to the characteristics of rural power grid. Using the distribution network flow calculation method, we evaluated the low voltage problems of the rural power grid which belongs to Chongqing Jiangbei Power Company. In addition, we collected the data of distribution transformers in electricity consumption peak period. Some practical management strategies were proposed by the analysis and evaluation of potential and appeared low voltage problems.