【作者】 刘志刚；

【导师】 王宁会；

【作者基本信息】 大连理工大学 ， 电机与电器， 2013， 博士

【摘要】 随着我国高压及超高压输电事业的快速发展,与高压电力电缆相关的产业及研究工作也得以快速的展开。目前,高压电缆绝缘水平的常规检测方法主要有两种：高压电缆预防性试验及高压电缆故障定位。虽然已有相关的高压发生器可以满足这两种常规检测的需求,但其体积与重量较大,无法满足便携性的要求。为了满足测试设备的便携性,本文采用高频逆变技术及数字化控制方法研制了两台便携式高压发生器——超低频正弦波高压发生器及冲击直流高压发生器。前者用于高压电缆的预防性试验,后者用于高压电缆的故障定位。本文主要研究与高压发生器便携性密切相关的电路拓扑、变压器结构、控制策略以及控制策略所采用的数据处理方法。在超低频高压发生器的拓扑上,提出采用双高频高压变压器产生正负直流高压对电缆进行充放电,确保电缆所加电压为相对于大地电势的正弦波。并采用单变压器多驱动的模式减小超低频形成单元中高压桥臂的体积,将100kV/250mA的高压桥臂体积控制在260cm3。在冲击直流高压发生器的拓扑上,通过对比传统的冲击直流高压发生器与采用高频逆变技术的冲击直流高压发生器放电时电流回路的不同,提出了双气隙隔离加隔断开关管的抗干扰策略,减小了电晕及火花放电时产生的电磁波对低压控制单元及其它电子元器件的干扰与损坏。在放电装置距离低压控制单元及开关管小于10cm的情况下,IGBT两端干扰电压由1200V降至200V,低压控制部分干扰电压由15V降至3V,并且消除了放电时所产生的高频干扰振荡,提高了系统工作的稳定性。在控制策略上,首先采用适合于高频高压变压器的串并联(LCC)谐振技术,充分利用高频高压变压器的漏感与分布电容,通过电感电容的谐振使开关管处于软开关状态,同时使高频高压变压器次级层间电容的充放电时间展宽至半个周期,避免了次级高频振荡而引起的变压器损耗过大,提高了高压发生器的效率,减小了变压器的体积与重量。空载时直流高压发生器的效率为80%,60%-70%负载时直流高压发生器的效率最高可达到94%,单独的高频高压变压器效率在全负载范围内均大于98%。其次,为了满足两种高压发生器负载变动范围大的特点,文中对LCC谐振变换器的静态与动态进行了理论分析与建模。在此理论分析的基础上,根据不同的负载采用调频控制调整到不同的静态工作点,在这一静态工作点附近采用调整占空比的控制策略,以满足两种高压发生器负载范围变化大的特点,提高系统的响应速度及稳定性。为了使控制策略能够应用于低成本的单片机进而舍弃体积较大的计算设备,满足理论分析中小信号假设的条件。本文首次提出了分段化数据处理方法,将负载的变化范围进行分段化处理,每一段均包含符合该负载的一个稳态工作点及与该工作点相关的参数,使系统在全负载范围内均处于理论分析的有效范围内,以提高系统的控制精度及响应速度。以此数据处理方法为基础,对所研制的42kV直流高压发生器进行了阶跃响应实验,其阶跃响应时间小于120μs,并且在响应过程中,电压波形未见任何振荡及过冲。针对高频高压变压器,为了满足便携性的要求,本文对影响高频高压变压器损耗的几个因素进行了实验。通过实验与理论相结合的方式,指出影响高频高压变压器损耗的主要因素不是交流电阻而是分布电容。再通过对分布电容大小的理论分析,指出增加层数,增加分段数,增加层间距可以减小高频高压变压器次级线包的分布电容。在此理论分析的基础上,研制了3500W大功率密度高频高压变压器,其功率密度达到4.3W/cm3,重量只有2.5kg,而同样参数的工频高压变压器的重量为30Kg。最终,本文分别研制了电缆常规检测用的两种高压发生器的样机用以验证本文所提出的拓扑及控制理论的正确性,并在电气特性等效于XLPE高压电缆(8.7/10kV/300mm2/5km)的高压电容(1.5μF)上进行了试验。首先对所设计的参数为35kV/0.1Hz超低频正弦波高压发生器进行了试验,其输出电压精度优于99%,(满足《35KV及以下交联聚乙烯绝缘电力电缆超低频(O.1HZ)耐压试验方法》的行业标准),总谐波失真(THD)小于1%,完全满足IEEE400.2对THD小于5%的要求。其次将所研制的35kV冲击直流高压发生器通过2μF的高压电容直接对地放电,连续工作4小时,低压控制电路及开关管均未因电磁干扰而误动作或损坏。所研制的两台样机的体积不超过0.05m3,重量不超过12Kg,满足便携性的要求。更多还原

【Abstract】 With the rapid development of high-voltage and extra high voltage transmission, the power cable industry and research are quickly expanded. Currently, the conventional detection methods of high voltage cable insulation level mainly include two types: high-voltage power cables preventive tests and high voltage power cable fault location. Although related products already exist to meet both routine testing, their size and weight are unable to meet the requirements of portability. In view of this situation and combination of the special electrical characteristics of the high-voltage power cables, this paper introduces two highly portable high-voltage generators which adopt high-frequency inverter technology and digitization method. One is very-low frequency sinusoidal high voltage generator, the other one is high-voltage DC pulse generator. The former is mainly used for the Cross-linked polyethylene (XLPE) cable preventive experimental, the latter not only can be used for high voltage cable fault location but also can be used for routine testing of high pressure oilpaper cable. This paper studies the concepts that related to meet the portability.On the topology of VLF high voltage generator, according to the experimental results and theoretical analysis, a novel topology of very-low frequency sinusoidal high voltage generator is designed in this paper which adopts two high frequency high voltage transformers to reduce the volume of the step-up transformer, generating positive and negative alternating high voltage sine wave. Moreover, multi-drive mode using single transformer is introduced in this paper to reduce the volume of the high voltage bridge obviously, the volume of the100kV/250mA high voltage bridge is only260cm3. On the topology of high-voltage DC pulse generator, by comparing the difference of discharge current loops of the traditional pulsed DC high voltage generator and the high frequency pulse DC high voltage generator, the topology is improved. Double air-gap isolation and cutting off switch tubes strategies which greatly reduce the interference of electromagnetic when sparking, improving the robust of the system work, at the case of the distance between control unit to discharge tube less than10cm, the interference voltage is reduced from1200V to200V. The interference voltage of control unit is reduced from15V to3V.On the Control strategy, this paper adopts series-parallel (LCC) resonant technique to achieve the soft switching of the switch tube, taking full advantage of the high frequency high voltage (HFHV) transformer distributed parameters, reducing the HFHV transformer losses, greatly improving the efficiency of the high-voltage generator. The high voltage generator no-load efficiency is80%, when the load is60%-70%the efficiency reaches94%, the efficiency of the single HFHV transformer is above98%under whole load, greatly reducing the size and weight of the HFHV transformer. In order to cope with the large ranges of output, the operating principle of LCC resonant converter is analyzed in the paper, the static and dynamic analysis is carried on also. Both the converter switching frequency and the duty cycle are utilized as actuating variables to cope with the large ranges of output, improving the response time and robust of the high voltage generator effectively. Step response experiment has been taken on42kV high voltage generator, Step change response time is less than120μs when the output changes from no-load to full-load without any overshoot and ring which verify the accuracy and feasibility of the control theory.On data processing, in order to reduce the calculation complexity significantly, shorting response time, precision control and complying with the wide range of the load, a method named segmental data processing is introduced in the paper for the first time. Each segment contains the control parameters and the error status which can be achieved by looking up the table. By increasing the number of segments, shorter response time and more accurate control can be achieved. The paper describes the principle of segmental data processing method. At the same time, program control flow of the system software and segmental data processing are given.In order to meet the requirements of portability, the volume and the size of the HFHV transformer which is the important part of both of the high voltage generator should been decreased. In this paper, several experiments have been taken on the factors that affect the loss of high frequency high voltage transformer. Through the analysis of the experimental results, this paper points out that the main factors that affect the loss of HFHV transformer is not AC resistance but distributed capacitance. By theoretical analysis of layer-to-layer capacitance of HFHV transformer, a3500W high density HFHV transformer has been successfully designed in laboratory which power density is4.3W/cm3and the weight is only2.5kg, comparing to35kg weight of traditional power frequency transform.Both of high voltage generators are developed for power cable routine test. The test of the35kV/0.1Hz VLF high voltage power supply is taken on a capacitor (1.5μF equal to XLPE cable8.7/10kV/300mm2/5km) which is equivalent to the Cross-linked polyethylene cable in the electrical characteristics. The accuracy of the sinusoidal VLF high voltage is99%and the total harmonic distortion (THD) is less than1%which meets IEEE400.2standard well. Meanwhile,35kV pulse DC high voltage generator is tested by the condition of discharging to ground directly with2μF high voltage capacitor, there is no any abnormal by continue working4hours. The above experimental results verify the feasibility and correctness of the topology and control strategy. The volume of two prototypes is less than0.05m3, and the weight is less than12kg, which can meet the requirement of portability.更多还原