【作者】 侯睿；

【导师】 徐殿国；

【作者基本信息】 哈尔滨工业大学 ， 电力电子与电力传动， 2014， 博士

【摘要】 随着大量电力电子设备的应用，电能质量受到了较为严重的污染。并联有源滤波器(APF)是一种新型的电能质量综合补偿装置，与传统的无源补偿器相比，具有动态响应速度快、稳态补偿精度高、补偿方式灵活、不易与电网阻抗发生谐振等优势，能够综合治理谐波、无功、不平衡等电能质量问题，对改善电网品质、维持电力系统的稳定性具有重要的意义。APF在数字化实现及实际应用中仍然存在着一些问题，诸如常用的傅里叶数学工具的分析精度对电网频率敏感；控制策略在保证良好的控制效果同时很难兼顾快速性和鲁棒稳定性；开关噪声滤波器设计缺乏系统的理论；当电网中存在容性负荷时系统易发生振荡等。这些问题都需要进一步的研究加以解决。本文针对上述问题，研究了APF在同步锁相、谐波检测、控制策略、开关噪声滤波器设计、阻尼控制等方面的关键技术，以保证APF具有优异的补偿性能和鲁棒稳定性。具体的研究内容包括以下几个方面：APF实现网侧单位功率因数控制的关键是准确获取电网的同步相量。而硬件锁相环技术易受高频噪声干扰，产生虚假的过零信号。采用基于递归离散傅里叶(RDFT)算法的同步锁相技术，具有检测精度高、占用资源少的优点。针对电网频率发生偏移时RDFT的幅度和相位检测出现较大误差的问题，提出了一种直接修正RDFT算法。通过最近两周波的相角差逐点计算获得电网的真实频率信息，再利用当前时刻的频率偏移量及递推指针的数值对普通RDFT算法获得的检测结果进行修正，即可获得精确的电网相位与幅值信息。该算法计算量小，即便电网频率动态波动时仍然具有很高的精度。提出一种基于修正RDFT算法的单相谐波检测方法，能够大幅度减小频率偏移对谐波测量造成的误差。传统的基于瞬时无功功率算法的全补偿技术应用中存在着无法精确限幅及补偿带宽过宽等问题，为此给出了一种选择性谐波补偿策略，提高了APF补偿的灵活性，便于实际应用；同时提出了一种基于同步旋转坐标变换的三相选择性谐波检测算法，数据窗长度为1/6工频周期的滑窗平均值滤波器的应用使得APF对于典型的整流桥负载仅需3.3ms即可完成负载谐波的动态跟踪。电流瞬时值比较技术具有电流环自稳定特性，分析了反馈电流检测位置及系统延迟对APF控制效果的影响。针对传统的单采样率瞬时值比较技术控制效果受制于参考值计算速度的问题，提出了一种多采样率瞬时值比较技术，能够有效提高系统的开关频率和控制效果。针对电流瞬时值比较技术存在爬坡效应及开关纹波较大等问题，给出了一种多采样率空间矢量瞬时比较算法，去除了系统的三相耦合，提高了输出波形的质量。连接电抗值对APF的性能具有较大影响，本文给出了一种系统而又简便的连接电抗值设计方法。根据APF补偿容量和负荷预估，设计满足系统跟踪性的最优连接电抗值。为减小对电网的高频污染，APF需要加装开关噪声滤波器。本文分析了接入点不同负载类型时LCL滤波系统的特性，并根据阻抗分析的方法提出一套LCL滤波器的科学设计方法，使系统兼顾优异的开关噪声滤除性能和较高的阻尼比。针对LCL滤波器对APF输出电流幅度放大，相位产生滞后的问题，给出了一套前馈补偿算法，减小了LCL滤波器的负面作用。针对LCL滤波器无源阻尼电阻发热较大的问题，并根据电流瞬时值比较控制的特点，提出了LCL并联虚拟阻尼策略。该策略不需要复杂的微分运算，实现简单。分析了系统的离散域稳定性，给出了采样频率及虚拟阻尼系数的稳定域。当APF将开关噪声滤波器包含在负载电流中时系统将不稳定，而并联虚拟阻尼控制可以抑制系统的振荡，具有统一阻尼作用。更一般的，当APF负荷中包含容性负载时前馈控制策略存在稳定性问题。本文给出了APF系统自激振荡产生的机理及抑制方法，采取同时检测负载电流和电网电流的复合控制策略，能有效抑制系统的振荡，提高补偿精度。将APF与TSC组成混合补偿系统有利于结合二者的优势，分析了当TSC作为APF负载时混合补偿系统的稳定性。实验证明了系统能够有效消除TSC的分组级差，具有较快的响应速度和很高的稳态精度。更多还原

【Abstract】 With the increasing prevalence of power electronics device applications, the power quality of the grid has been severely polluted. Comparing with traditional passive compensators, shunt active power filter (APF) is a novel power quality compensation device with fast dynamic response, high precision of steady state compensation, flexible compensation manners, and less probability having resonance with the grid impedance. APF is capable of comprehensively tackling power quality problems associated with harmonics, reactive power and unbalanced grid, which is crucial for improving power quality and maintaining the stability of power system. There are still some challenges for the digital implementation and industrial application of APF. For example, the analysis precision of commonly used Fourier mathematical tools is sensitive to grid frequency; if control strategy ensures good control performance, it is difficult to give consideration to rapidity and robust stability simultaneously; design of switching noise filter lacks specific theory; system is prone to oscillate in the situation of capacitive load, and so on.In order to resolve the above problems, this paper thoroughly researches on the key technologies of synchronous phase-locked loop (PLL), harmonic detection, control strategies, switching noise filter design and damping control to ensure an excellent compensation performance and a robust stability of APF system. Specific research issues run as follows:Obtaining accurate synchronized phasor of the grid is essential for APF to achieve grid-side unit power factor control. The hardware PLL technology is susceptible to high frequency noise, resulting in a false zero-crossing signal. This paper proposes a synchronized phasor measurement method based on recursive discrete Fourier (RDFT) algorithm, possessing higher precision while taking up fewer resources. However, large errors might be expected for the amplitude and phase detection of RDFT algorithm when the grid frequency shifts, so a direct correction algorithm of RDFT is also proposed. This algorithm obtains the real grid frequency through piecewise calculation of the phase angle difference for two consecutive periods, and then employs the current phase shift and recursive pointer value to correct the detection results gathered by the traditional RDFT algorithm, which will yield the accurate amplitude and phase information of the grid. The total amount of calculation for this algorithm is rather small, while it is still able to maintain a high precision with dynamic fluctuations of grid frequency. This research also established a single-phase harmonic detection method for correcting RDFT algorithm, which could significantly reduce the harmonic measurement errors due to shifts of frequency.The traditional application of every-order compensation based on instantaneous reactive power theory is not capable of accurately limiting the amplitude or restricting compensation bandwidth, this paper introduced a selective harmonic compensation strategy to improve the flexibility of APF compensation and further facilitate its industrial application. Moreover, a three-phase selective harmonic detection method based on synchronous rotating coordinate transformation is also put forward, and a sliding window averaging filter with data window length of1/6frequency cycle enables APF to complete the dynamic tracking of load harmonics in only3.3ms for the typical rectifier bridge. Instantaneous current value comparison is able to maintain self-stability of the current loop, and the impacts on the control performance of APF as positioning of feedback current and system delay are also analyzed. In addition, a multi-sampling rate instantaneous comparison technique is adopted to effectively enhance the switching frequency and control performance of the APF system. The instantaneous current comparison technique may experience obstacles as “climbing ripple effect” and large switching ripples, so a multi-sampling rate instantaneous space vector comparison algorithm is also proposed to realize three-phase decoupling and improve output waveforms.Inserting reactance loads exerts a large influence on the performance of APF, this paper presents a systematic and simple design connection reactance loads. According to the compensation capacity and load prediction of APF, the system is designed to meet the traceability with optimal reactance value. In order to reduce the high-frequency pollution to the grid, APF need to install an additional switching noise filter. This paper analyzes the characteristics of LCL filter system with different types of load, and proposes a set of scientific LCL filter design methods based on impedance analysis to grant the system with both excellent switching noise filtering and high damping ratio. However, LCL filter may also amplify output current and give rise to extensive phase lag problems; therefore, a corresponding feed-forward compensation algorithm is presented to reduce the above negative effects of LCL filter.Overheating is a major problem for passive damping resistors of LCL filter; this research focuses on a LCL parallel virtual damping strategy in accordance with the characteristics of instantaneous current value comparison, which does not require complex differential operations and is basically simple to implement. Sampling frequency and stable domain of virtual damping ratio is also presented by analyzing the system stability in discrete domain. As the APF system would become unstable with the incorporation of switching noise filter, the implementation of parallel virtual damping control could suppress system oscillations with uniform damping effect. Generally speaking, there are always concerns for stability issues of feed-forward control strategies when the load for APF contains high frequency paths. In this paper, the mechanism of self-excited oscillation and suppression method of APF system is proposed, and meanwhile the hybrid control strategy of simultaneously detecting the load current and grid current is also put forward to inhibit system oscillation and improving compensation accuracy. The APF and TSC hybrid compensation system is in favor of combining the advantages of both, and the stability of a hybrid compensation system which TSC performs as the load of APF is also analyzed. The experimental results have demonstrated that the system could effectively eliminate the TSC grouping differential, and the system possesses fast dynamic response and high precisions in steady-state performance.更多还原