Research on a Transformerless Hybrid Filter Capable of Direct Connection to Medium-Voltage Distribution Systems

本研究的目的是开发一种混合有源无源滤波器，能够直接连接到中压公用事业和工业电力系统，而不需要变压器。这种混合滤波器用于中压调速电机驱动的谐波电流补偿，以节省泵和鼓风机的能源。这样的电机驱动不需要再生制动，从而允许电机驱动使用三二极管整流器作为前端。本研究得出以下结论：1。研究人员对适用于三相二极管整流器电机驱动的6.6 kv无变压器混合滤波器进行了可行性研究和概念设计。该混合滤波器的特点是采用无变压器的三电平二极管箝位PWM变换器，将调谐到七次谐波频率的三相无源滤波器与三相小额定有源滤波器串联起来。研究人员对混合滤波器的谐波曲线进行了理论分析，重点研究了无源滤波器和有源滤波器所需的伏安额定值，它们的额定值在谐波电流缓解方面需要权衡。考虑到控制延迟和所谓的“死区时间”的影响，进行了计算机仿真。理论分析与计算机仿真结果进行了比较。结果证实了理论分析的有效性，同时也揭示了分析的局限性。考虑到上述理论分析和计算机仿真，研究人员设计、构建并测试了一个三相400 v 15 kw的缩小系统，其中三电平二极管箝位PWM变换器用于有源滤波器。在混合滤波器中引入三电平PWM变换器的主要问题是使两个分路直流电容的直流平均电压在稳态和瞬态状态下保持平衡。研究人员提出了一种混合滤波器的电压平衡控制方法，并通过400-V - 15kw系统的实验验证了该方法的有效性和可行性。供电侧电流THD（总谐波失真）小于5%，各谐波电流分量小于3%，其中谐波分量高达40次。THD值和谐波分量都完全符合日本谐波准则。在理论分析、计算机仿真和实验结果的基础上，对即将投入实际应用的6.6 kv无变压器混合滤波器进行了探讨。少

The aim of this research is to develop a hybrid active-passive filter capable of direct connection to medium-voltage utility and industrial power systems without transformers. This hybrid filter is intended for harmonic current compensation of a medium-voltage adjustable-speed motor drive for energy savings in pumps and blowers. Such a motor drive requires no regenerative braking, thus allowing the motor drive to use a three-diode rectifier as the front end. This research leads to the following findings:1. The investigators have done feasibility study and conceptual design of a 6.6-kV transformerless hybrid filter suitable for a motor drive with a three-phase diode rectifier. This hybrid filter is characterized by series connection of a three-phase passive filter tuned In the seventh-harmonic frequency with a three-phase small-rated active filter using a three-level diode-clamped PWM converter without transformer.2. The investigators have achieved theoretical analysis of harmonic curre … More nt mitigation by the hybrid filter, with focus on the required volt-ampere ratings of the passive filter and the active filter Their ratings have a tradeoff in terms of harmonic current mitigation. Computer simulation has been carried out, considering the effects of control delay and the so-called "dead time." The theoretical analysis has been compared with the computer simulation. As a result, the validity of the theoretical analysis has been confirmed, and a limitation of the analysis has been revealed.3. Taking into account the above-mentioned theoretical analysis and computer simulation, the investigators have deigned, constructed and tested a three-phase 400-V 15-kW downscaled system, where a three-level diode-clamped PWM converter has been used for the active filter. What is a major concern in introducing the three-level PWM converter into the hybrid filter is to keep the dc mean voltages of the two split dc capacitors balanced not only in steady states but also in transient states. The investigators have proposed a voltage-balancing control method for the hybrid filter The effectiveness and viability of the method has been verified by the experiments using the 400-V 15-kW system. The current THD (total harmonic distortion) in the supply side was less than 5%, and each harmonic current component was less than 3%, including up to 40-th harmonic components. Both the THD value and harmonic components perfectly meet the Japanese harmonic guidelines.4. Considerations on the 6.6-kV transformerless hybrid filter that will be put into practical use in the near future have been discussed on the basis of the results from the theoretical analysis, computer simulation and experiment. Less