城市轨道交通供电系统谐波分布研究

针对城市轨道交通供电系统,对系统产生的谐波类型进行了分析,指出了谐波的危害性,分析了其特征,并详细分析了不同情况下注入系统节点的谐波大小的计算方法,特别是计算了35kV 系统和 110kV 系统在不同负荷状态下的特征次谐波的大小,并进行了实际的测量,建立系统谐波计算的分布图.对 110kV 侧的谐波电流进行了收集整理和研究,提出了降低谐波的方法和必要性.在此基础上,明确指出轨道交通供电系统应安装滤波装置或者有源滤波装置(APF),这不但可以大大地减小对电网的影响,也可以提高自身系统的运行质量和可靠性.     

谐波电流对低压配电网的影响分析

在理论上分析了谐波电流对中性线和变压器的影响.利用数字式示波表FlukeView190C对低压民用负荷和办公楼配电系统的谐波状况进行了实测,实测数据基本代表了非线性负荷和低压电网的谐波现状.根据实测数据,对谐波电流引起的各种问题及其对配电网的影响进行分析研究,发现三相四线制建筑配网普遍存在三相不平衡,谐波电流放大,中性线电流过大,网损增加,变压器出力下降等问题.最后简单的提出了一些解决上述问题的对策.     

谐波电流对低压配电网的影响分析

在理论上分析了谐波电流对中性线和变压器的影响。利用数字式示波表FlukeView190C对低压民用负荷和办公楼配电系统的谐波状况进行了实测,实测数据基本代表了非线性负荷和低压电网的谐波现状。根据实测数据,对谐波电流引起的各种问题及其对配电网的影响进行分析研究,发现三相四线制建筑配网普遍存在三相不平衡,谐波电流放大,中性线电流过大、网损增加,变压器出力下降等问题。最后简单的提出了一些解决上述问题的对策。     

基于巨磁阻的电力系统三相电流测量及其应用

在叙述了巨磁阻基本原理的基础上,提出了用巨磁阻传感器测量电力系统三相电流的原理和方法,解决了三相电流磁场相互干扰情况下三相电流的测量问题。     

基于电力电子开关的三相整流电路谐波注入滤波方法

对基于电力电子开关的三次谐波注入滤波方法的原理进行了详细的理论分析，它的基本原理是三相整流固有的三次谐波注入到交流输入端，抵消电流中所含有的大部分谐波分量，推导出三次谐波注入法的最佳注入条件，给出滤波电路的结构。通过模拟试验证明，三相整流电路交流侧电流中的谐波含量由原来的30％左右下降到10％左右，滤波效果明显。     

有源电力滤波器在电铁谐波抑制中的应用与仿真

对应用于补偿电铁谐波的有源电力滤波器的性能进行了分析,并讨论了其工作原理。采用基于鉴相原理的检测法检测出待补偿电流的指令值,并利用单周控制的双向互补控制策略,使逆变器产生出补偿电流,来抵消电铁谐波源对电力系统带来的不利影响。同时在MATLAB/SIMULINK的仿真软件下,建立了电铁牵引供电系统,利用有源电力滤波器进行谐波抑制的仿真,仿真结果验证了该方案的正确性和可行性。     

Operations of the dominant harmonic active filter (DHAF) underrealistic utility conditions

This paper presents laboratory test results of the dominant harmonic active filter (DHAF) prototype. The DHAF system achieves harmonic isolation at the dominant harmonics using square-wave active filter inverters. The key advantages of the DHAF system are the low rating and low bandwidth requirements of the active filter inverter. Such characteristics allow cost-effective and viable applications of the DHAF system to mitigate harmonic problems for high-power nonlinear loads (10-100 MW and above). Several practical situations, including source-sink resonance, ambient harmonic interferences, and unbalanced grid voltages are applied to the DHAF prototype to validate its performance. The operation principles of the DHAF system and the synchronous-reference-frame-based controller are discussed to explain how harmonic isolation at the dominant harmonics is accomplished. A design example of the DHAF system for a 20 MVA rectifier load at an industrial site is also given to illustrate its application     

A DSP based power factor correction converter to reduce total harmonic distortion of input current for improvement of power quality

This paper proposes a controlled approach to be used in power factor correction (PFC) circuits to decrease total harmonic distortion (THD) of input current by eliminating the input current harmonics. This method removes the problems of the conventional PFC converters. Since in conventional PFC circuits the input current is controlled to follow the ac input voltage, it will have the same harmonics of the input voltage. This is an important disadvantage of the conventional method especially when the input voltage is distorted. In this approach, a sinusoidal signal is generated by the DSP microprocessor and is used as reference in controlling the converter switch to obtain a sinusoidal input current based on zero crossing points of distorted input voltage. Due to the reflection of input voltage distortions to the output voltage, an adaptive digital FIR filter is designed and embedded into the voltage control loop. The feed forward is also used into the control algorithm. The implementation of feed forward and adaptive digital FIR filter improves the converter performance to obtain a near unity power factor correction with lower input current THD. Average current control mode is implemented and operated in continuous conduction mode. The experiments performed in the laboratory for different cases of operation verify the theoretical and simulation studies performed in MATLAB/Simulink. The control approach is programmed by the TMS320F2812 DSP microprocessor. The experimental results are good in accordance with IEC 61000-3-2 Current Harmonic Standard.     

Realization of active power filter based on indirect current control algorithm using Xilinx system generator for harmonic elimination

Realization of active power filter with Model Based Design approach is presented in this paper. The approach adopts different modeling platforms as well as selection of proper hardware for step wise verification and testing. The active power filter model is developed using the Matlab/Simulink platform for single phase. The efficiency of the control algorithms such as synchronous detection method and indirect current control for active power filter is analyzed. Efficient control algorithm is developed by Xilinx system generator which is incorporated into Simulink as Xilinx tool box. Xilinx system generator provides a virtual platform for easy and effective design of the required system models in FPGA (field programmable gate array) design environments. Optimized automatic VHDL code is generated for the control algorithm which is simulated using ISE 13.2 for the generation of switching signals for the control of IGBTs of the active power filter. Suitable compensation signal is generated from the active power filter for the better elimination harmonics to improve the power quality. THD is reduced to a considered value which is able to satisfy the limits of the IEEE standard.     

Investigation of harmonic currents and power factor on power rectifier circuits with nonequi-PWM and equi-PWM control (inductive load)

Lately, on the power rectifier circuit with semiconductor switching device, PWM control is generally employed for the purposes of reducing the harmonic currents on the dc side and improving the power factor of fundamental wave. In this case, the analysis of the current waveform becomes fairly complex. However, we express the PWM controlled voltage waveform by the step function, and can easily analyze the current waveform. We reported formerly some results of analysis about the waveform and harmonics of the current. In this paper, on the power rectifier circuit to which the nonequi-PWM and equi-PWM control are applied, we exactly calculate the harmonic currents on the dc and ac side, and the power factor by the use of the above analytical results. The characteristics of both control methods are compared on condition that each controlled factor of the load voltage is equal. These results are shown in the calculated charts. The following items can be seen from these charts on the power rectifier circuit: (1) The nonequi-PWM control can let the harmonic currents on the dc side decrease more than the equi-PWM control. But on the contrary, the harmonic currents on the ac side increase. Consequently, when the nonequi-PWM control is applied, the total power factor decreases by the increase of distortion factor of the current on the ac side. (2) The difference between the harmonic currents on the dc and ac side to both of the nonequi-PWM and equi-PWM control increases with the increase of controlled factor of the load voltage. © 1999 Scripta Technica, Electr Eng Jpn, 129(4): 117–125, 1999     

方波型逆变器总谐波失真度(THD)与其负载Q值的关系

对于方波型逆变器，总谐波失真度（THD）不仅仅随占空比变化，而且受负载类型的影响。本文在定义了一个反映负载特性的参数Q之后，报告了对THD与Q的变化关系的分析结果。     

极坐标系下主动配电网三相线性潮流计算方法

线性潮流计算方法可以提高主动配电网集中优化控制的鲁棒性和快速性。随着分布式电源在主动配电网中的广泛接入,配电网中的电压控制节点逐步增多,以保持正常的电压水平。现有直角坐标系下三相线性潮流无法处理本地压控节点,现有极坐标下的线性潮流模型未能详尽考虑分布式电源控制特性、网损分摊特性与配电网三相特点。因此提出三相极坐标系下的线性潮流计算方法来解决这个问题。所提方法考虑了Y或Delta型连接ZIP负荷、单相或三相分布式电源(Distributed Generators, DGs)等类型。同时考虑了DGs的详细控制模型和分布式松弛母线模型。最后通过三相不平衡的IEEE 13,34,37和123节点系统验证所提方法的精度和对各种节点类型的适应性。     

电力电子变压器在有源配电网无功优化中的应用

尽可能地降低配电网中节点电压的偏差,是配电网运行的基本要求。为实现对节点电压的有效控制,提出利用电力电子变压器通过对其一次侧和二次侧电力电子变换器的脉宽调制控制(Pulse Width Moderation, PWM),改变其一次侧和二次侧潮流的方法加以解决。为此,构建了含分布式电源、储能元件和电力电子变压器在内的有源配电网无功优化模型,并运用粒子群优化算法进行求解。仿真结果表明,含电力电子变压器的有源配电网无功优化后的网损,低于采用有载调压变压器(On-Load Tap Changer, OLTC)对应网络无功优化后的网损;且其节点电压与额定值的相对偏差也优于后者,从而说明了在有源配电网中应用电力电子变压器,利用其灵活的无功调节功能,能提高配电网的运行水平。     

Current waveform control of a high‐power‐factor rectifier circuit for harmonic suppression of voltage and current in a distribution system

This paper presents the input current waveform control of the rectifier circuit which realizes simultaneously the high input power factor and the harmonics suppression of the receiving‐end voltage and the source current under the distorted receiving‐end voltage. The proposed input current waveform includes the harmonic components which are in phase with the receiving‐end voltage harmonics. The control parameter in the proposed waveform is designed by examining the characteristics of both the harmonic suppression effect in the distribution system and the input power factor of the rectifier circuit. The effectiveness of the proposed current waveform has been confirmed experimentally. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(4): 62–71, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10046     

New adaptive reclosing technique using second-order difference of THD in distribution system with BESS used as uninterruptible power supply

This paper proposes a new adaptive reclosing technique that considers the battery energy storage system (BESS) in a distribution system. The proposed technique focuses on operation of the BESS as an uninterruptible power supply (UPS). The algorithm detects the fault clearance using second-order differences of total harmonic distortion (THD) (SODT) of the current supplied by the BESS and allows the BESS to keep feeding to the healthy phase. A synchronism check is adopted between the utility and the BESS to minimize the transients at the moment of reclosing. To verify the proposed algorithm, the whole system and algorithm were modeled using ATP-EMTP. Various simulations are performed by varying the fault clearance time, fault types, fault resistances, and fault locations. The simulation results show that the BESS can be operated as a UPS and provide an improved reclosing scheme.     

The Electromagnetic Transients Program (EMTP) as an effective tool to evaluate active power filters for harmonic compensation

The Institute of Electrical and Electronic Engineers (IEEE) ‘Recommended Practices and Requirements for Harmonic Control in Electric Power Systems’ sets limits for the current and voltage harmonic distortions at the point of common coupling in order to maintain an acceptable quality of electric power in the presence of nonlinear loads. Both the utility and its customers share a common responsibility since enforcement of the above practice by the utility would require that the affected customer use a suitable harmonic mitigating method. To this effect, this paper demonstrates how the Electromagnetic Transients Program (EMTP) may be used to investigate two harmonic mitigating methods, namely, the use of shunt passive power filters and the combination of a series active (APF) and shunt passive (PPF) power filters. Both methods reduce the harmonic currents injected into the distribution system; however, the combination of the series APF and shunt PPFs has a better compensation characteristic with a higher capital cost than only shunt PPFs. Before a final decision is reached, the cost of the higher harmonic losses throughout the distribution system when using only shunt PPFs must be taken into account.     

An approach to harmonic current-free AC/DC power conversion forlarge industrial loads: the integration of a series active filter with adouble-series diode rectifier

This paper proposes a new harmonic current-free AC/DC power conversion system characterized by the integration of a small-rated series active filter, with a large-rated double-series diode rectifier. The DC terminals of the active filter are directly connected in parallel with those of the diode rectifier, thereby forming a common DC bus. The active filter enables the diode rectifier to draw three-phase sinusoidal currents from the utility. In addition, it can provide the supplementary value-added function of regulating the common DC-bus voltage to a limited extent of ±5%, slightly increasing the RMS voltage rating, but not increasing the peak voltage rating. Experimental results obtained from a 5 kW laboratory system verify the practical viability and cost effectiveness of the proposed system     

Using the DC-bus current to improve the power factor in low-cost electric drives

In this paper, a new approach is presented aimed at improving the power factor of pulsewidth-modulation inverters that equip low-power electric motor drives for household appliances. The key feature of the proposed approach consists of exploiting the dc-bus current as a suitable dither generator by means of a high-frequency transformer. Such a strategy is used to force the diode rectifier to draw current from the mains in those periods when, in conventional systems, the diodes are reverse biased, i.e., when the dc-bus capacitor voltage exceeds the ac input voltage. The proposed method allows for elimination of the power-factor controller (PFC) front end, traditionally used to comply with power quality requirements. In comparison with standard PFCs based on a dc/dc converter, the proposed approach represents a cheaper and more feasible solution, not using additional power devices and control circuits. Simulation and experimental results confirm the consistency of the proposed approach.