【作者】 唐诗颖；

【导师】 康勇； 彭力；

【作者基本信息】 华中科技大学 ， 电气工程， 2011， 博士

【摘要】 随着工业现代化进程的发展,电力系统中非线性负载不断增加,电网谐波污染日益严重,谐波成为影响电能质量的主要因素之一。并联有源滤波器(SAPF)作为治理电流源型谐波污染的有效手段,成为研究的热点。早期的SAPF一般采用电感作为输出滤波器。L型滤波器结构简单、可靠性高、易于控制,但是对开关纹波的衰减能力不足,将向电网注入较大的纹波电流。而三阶LCL滤波器可以以较小的电感量获得更好的开关纹波衰减能力,逐渐成为SAPF输出滤波器的发展趋势。本文以基于LCL滤波器的单相SAPF为研究对象,主要针对LCL滤波器的参数设计、滤波器有源阻尼技术以及如何提高谐振电流控制器的响应速度进行了深入的研究。LCL滤波器的参数设计是在滤波器各项性能指标间折衷的过程,工程上通常采用step-by-step的凑试设计方法。虽然凑试方法过程简单直接,但是设计过程需要进行反复的凑试,并且在凑试过程中由于不能明确性能指标之间的相互影响,设计结果往往顾此失彼,对滤波器的优化帮助不大。针对上述问题,本文提出了一种滤波器参数的图解设计方法。利用图解方法的直观性可以根据性能指标的限制条件直接获得满足设计要求的滤波器参数。而在近一步优化滤波器性能的过程中,也可以明确性能指标之间的相互影响,为优化滤波器性能提供了较为直观的参考。SAPF要跟踪大量的谐波电流,电流控制器设计难度较大。谐振控制由于良好得稳态跟踪精度和分频控制的灵活性,在SAPF中得到广泛的应用。对于谐波补偿次数较高的场合,应用谐振控制时需要进行相位补偿。本文详细比较了不同形式的谐振控制器及其相位不惭对控制性能的影响。分析表明：PR控制不能应用于谐波补偿次数较高的场合,并且闭环系统对频率略大于谐振频率的指令分量有很大的放大作用；采用相位补偿的方法,PR控制可以用于补偿高次谐波电流,指令放大现象也可以得到有效的抑制,但是,控制系统闭环频率特性不如VPI控制和P+VPI控制平滑,对电网频率变化较为敏感。采用谐振控制时通常利用比例环节来提高系统动态响应速度,但是比例系数受稳定裕度的限制取值有限,对提高较高次谐波电流的跟踪速度并没有太大帮助。只有合理的设计谐振控制器参数才能有效提高SAPF电流控制的动态响应速度。本文针对上述问题,以提高电流控制跟踪速度为目标,提出了采用迭代算法配置系统主导极点实部的控制器参数设计方法。对于VPI控制,系统主导极点配置到离虚轴的可能的最远距离时,系统相角裕度只有轻微的减小。因此,以此最远距离设计谐振控制器参数可以获得最快的电流跟踪速度。对于P+VPI控制,受比例环节影响,系统主导极点不能远离虚轴太远,否则系统相角裕度会迅速减小。设计控制器参数时应该首先确定系统相角裕度,然后折衷考虑对低频电流指令的跟踪速度和总体的响应时间分别确定谐振控制器比例系数和广义积分系数采用LCL滤波器作为输出滤波器时必须阻尼滤波器谐振。对于单状态反馈的有源阻尼方法,在理想情况下只有电容电流比例反馈可以有效阻尼滤波器谐振,因此现有研究大多采用电容电流比例反馈或等效的电容电压微分反馈的阻尼方法。但是实际系统中,受数字控制的一拍滞后和零阶保持效应的影响,上述方法的阻尼特性将发生变化。针对上述问题,本文在考虑一拍控制滞后和零阶保持效应的基础上详细分析了电容电流、电容电压和输出电流比例反馈阻尼滤波器谐振极点的能力。根据滤波器谐振频率与控制频率比值γ的不同,确定了上述三种有源阻尼方法的适用范围。电容电流反馈法的适用范围为0.05<γ<0.1和0.35<γ<0.4；电容电压反馈法的适用范围为0.1<γ<0.225；而输出电流反馈法的适用范围为0.225<γ<0.35。由于在SAPF中γ取值通常在0.225-0.35的区间内,采用输出电流反馈法不仅阻尼效果最好、而且不需要额外的状态变量采样,可以降低系统硬件成本,因此本文选择输出电流反馈法阻尼滤波器谐振。样机实验证明了该方法的有效性。输出电流反馈法在有效阻尼滤波器谐振的同时,可以降低电网电压扰动传递函数的低频增益,有利于抑制电网谐波对输出电流的影响。而电网谐波电压是影响并网逆变器输出电流波形质量的重要因素之一,因此将输出电流反馈法推广到并网逆变器中将具有特别的意义。本文采用滞后控制+输出电流反馈的方式,可以将输出电流反馈法用于γ大于0.14的并网变换器。样机实验证明了上述方法的有效性。对于γ更小的情况,增加的一拍控制滞后不能有效的阻尼滤波器谐振,而增加滞后拍数将进一步减小电流控制带宽。因此,该方法不适合用于γ很小的情况。更多还原

【Abstract】 As the development of modern industry, more and more non-linear loads are used in power system, resulting in increasingly severe harmonic pollution. Shunt active power filter (SAPF), as the most effective method to eliminate harmonic, has been paid more and more attention recently. Traditional SAPFs usually adopt simple L filters to filter out the switch ripples. It is simple, reliable and easy to be controlled, but lack of high frequency attenuation capability. While the third order LCL filter could obtain better high frequency attenuation capability with small inductance, it gradually becomes the mainstream of output filter of SAPFs. This paper chose the single-phase SAPF with LCL filter as the research object. Works have been focused on the parameters design of LCL filter, active damping strategy and rapid output current control.In the LCL filter parameter design process, tradeoff between various performance indicators needed to be made. The step by step design method usually been adopted in this process. Although step by step design method is simple and direct, the influence of performance indicators is not clear in the design process, which usually causes some performance indicators unoptimum. This design method is helpless for parameter optimization. To overcome the defect of step by step design method, this paper proposed a graphic design method. Although the graphic design method still need to try-in in design process, however, with the help of the graphic, the tradeoff between various performance indicators can be easy to maded.Designing the current control for SAPF is a hard work for the ability to traking for harmonic current. Due to the perfect control precision and the flexible of resonant control, it is widely used in SAPFs. To apply the resonant control for high order harmonics, phase-lag compensation must be included in the current controller. The performance of different resonant control and their phase-lag compensation methods was discussed in this paper. The PR control cannot be used for high order harmonic compensation, and closed-loop system would amplify the current command which frequency is slightly bigger than the resonance frequency. With delay compensation, the PR control can be used for high order harmonic compensation, and the amplify phenomenon can be also mitigated. However, the frequency characteristics of closed-loop system are not as smooth as that of the VPI or P+VPI control, which sensitivity to grid frequency variation.In the resonant control, proportional controller is usually used to improve the responding speed. However, to achieve an adequate phase magin, the value of proportional parameter is usually low. Proportional control is insufficient for tracking high order harmonics. Excellent responding speed can only be achieved by carefully design the resanont controller parameters. In this paper, a novel parameter design method to achieve rapid current tracking is proposed. The design method is besed on an iterative algorithm to arrange the real part of dominant poles of closed-loop system. For the VPI control, system phase margin only slightly minish when dominant poles reach the possible furthest distance away from imaginery axis. So that position should be used to tune controller parameters, to ensure fastest responding speed. For the P+VPI control, the dominant poles cannot far away from the imaginary axis, otherwise system phase margin would reduce rapidly. To design the controller parameters, phase margin must be ensured. Then, the proportion and generalized integral coefficients can be obtained by tradoff the tracking speed of low and high frequency current command.To using the LCL filter, filter resonance must be damped. Current researchs of active damping method are focused on the capacitor current, since in the ideal condition only the proportional feedback of capacitor current can damping LCL resonance. However, in the practical system, the performance of this method would be changed. In this paper, the analysis of active damping effects of the capacitor current, capacitor voltage and grid-side current feedback method was discussed, by considering the one-step delay and the affect of zero-order holder. According to the ratio beteen resonant frequency of LCL filter and control frequency, the suitable range for the three active damping methods is discused. Capacitor current feedback method is suitable for 0.05<γ<0.1 and 0.35<γ< 0.4. Capacitor voltage feedback method is suitable for 0.1<γ< 0.225. Grid-side current feedback method is suitable for 0.225<γ<0.35. Since the grid-side current feedback method is especially suitable to SAPF, there is no need of extra sensors for additional states measurements and grid voltage disturbance rejection could be enhanced while offer a good resonance damping, the grid-side current feedback method is applied in a sigle-phase SAPF. The experimental results demonstrate the effect this damping method.Since the influence of grid harmonic on grid-side current is one of the main problems for grid-connected inverter, extending the grid-side current feedback method into the application of grid-connected inverter would be rewarding. This paper combined the lag control and grid-side current feedback to make it possible to be used in converters which yis, greater than 0.14. Experimental results on a single-phase grid-connected inverter prove the effectiveness of the proposed methods. For the y smaller than 0.14, additional one-step delay cannot damp LCL resonace effectively, and increase the delay time would further reduce the current control bandwidth. Therefore, this method is not suitable for the condition whereγis too small.更多还原