频率动态过程中基于FFT的电力谐波测量研究

发布时间：2019-04-20 09:53

【摘要】：随着非线性设备的广泛应用,尤其是近年来新能源并网工程的大量投用,电力系统中的谐波污染日趋严重。对电力谐波参数进行准确、实时的测量是治理谐波污染的前提和重要技术手段。基于快速傅里叶变换(FFT)的谐波测量方法由于计算速度快、易于工程实现等优势,在电力谐波在线监测中得到了广泛的应用。然而,风电、光伏等新能源发电的有功输出功率具有不确定性,可能造成发电与负荷不平衡,从而导致电网频率偏移,甚至发生频率宽范围波动和频率崩溃等现象。在频率动态过程中,由于非同步采样造成的频谱泄漏等问题的存在,基于FFT的电力谐波测量方法存在较大的误差,甚至可能测量失败。非同步采样下的改进测量方法,从采样方式上分为两类:定速率采样与自适应采样。定速率采样方法的采样频率恒定,通过时域或频域上的插值等算法来减小非同步采样的影响。自适应采样方法通过实时跟踪电网频率,自适应调整采样频率,使实际采样序列接近理想同步采样序列,包括硬件同步和软件准同步。考虑频率动态过程,分别对定速率采样方法与自适应采样方法进行改进。对于定速率采样方法,考虑了频率动态过程中的频率变化率,以相位差校正法为例,推导了基于频率变化率修正的归一化频率校正量公式,提高了频率动态过程中的谐波参数连续测量精度;对于自适应采样方法,在连续测量中根据前次测得的基波频率与前次计算所得的频率变化率来预测电网的实时基波频率,从而实时调整采样频率以跟踪变化的电网频率,减小了频率动态过程产生的频谱泄漏。对采用不同频率变化模型的电网信号进行仿真分析,并考虑互感器精度对测量系统的总误差进行评价。结果表明,本文所提出的改进方法较原方法具有更高的测量精度与实时性,更适用于频率动态过程中的谐波测量,实用性较高。
[Abstract]:With the wide application of non-linear equipment, especially in recent years, a large number of new energy grid-connected projects, harmonic pollution in the power system is becoming more and more serious. Accurate and real-time measurement of power harmonic parameters is the premise and important technical means to control harmonic pollution. The harmonic measurement method based on Fast Fourier transform (FFT) has been widely used in power harmonic on-line monitoring due to its advantages of fast computing speed and easy engineering realization. However, the active output power of new energy such as wind power, photovoltaic and so on is uncertain, which may cause the imbalance between power generation and load, thus lead to the frequency offset of the power grid, and even occur the phenomenon of wide range of frequency fluctuation and frequency collapse. In the frequency dynamic process, due to the existence of spectrum leakage caused by asynchronous sampling, the measurement method of power harmonic based on FFT has a large error and may even fail to measure. The improved measurement method based on asynchronous sampling can be divided into two types: constant rate sampling and adaptive sampling. The sampling frequency of the constant-rate sampling method is constant, and the influence of non-synchronous sampling is reduced by interpolation in time-domain or frequency-domain. The adaptive sampling method tracks the power network frequency in real time and adaptively adjusts the sampling frequency to make the actual sampling sequence close to the ideal synchronous sampling sequence including hardware synchronization and software quasi-synchronization. Considering the frequency dynamic process, the constant rate sampling method and the adaptive sampling method are improved respectively. For the constant rate sampling method, the frequency change rate in the frequency dynamic process is considered. Taking the phase difference correction method as an example, the normalized frequency correction quantity formula based on the frequency change rate correction is derived. The continuous measurement accuracy of harmonic parameters in frequency dynamic process is improved. For the adaptive sampling method, the real-time fundamental frequency of the power network is predicted according to the fundamental frequency measured earlier and the frequency change rate obtained from the previous calculation in continuous measurement, so that the sampling frequency can be adjusted in real time to track the changing power network frequency. The frequency spectrum leakage caused by frequency dynamic process is reduced. The power system signals with different frequency variation models are simulated and analyzed, and the total error of the measurement system is evaluated considering the accuracy of the transformer. The results show that the improved method is more accurate and real-time than the original method, and is more suitable for harmonic measurement in frequency dynamic process.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM935

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