基于LCL的中压级联STATCOM控制策略的研究

发布时间：2018-05-22 20:03

本文选题：静止同步补偿器 + LCL滤波器　；参考：《中国矿业大学》2017年硕士论文

【摘要】：近年来,随着工业的发展,各种非线性、冲击性及不平衡负荷迅速增多,由此导致低功率因数,谐波污染,三相不平衡等一系列影响电网电能质量的问题。静止同步补偿器(Static Synchronous Compensator,简称STATCOM)因具备同时解决上述问题的能力备受关注,在配电网络中具有广阔的应用前景。本文以LCL型级联STATCOM为研究对象,对一些关键问题进行研究。首先,建立LCL型STATCOM在abc静止坐标系和dq旋转坐标系下的数学模型,为控制系统的设计打下基础。针对LCL滤波器参数设计的问题,本文在分析滤波原理的基础上,研究滤波器性能与各参数之间的关系,并给出滤波器设计的约束条件和设计步骤,仿真结果验证了参数设计的有效性。其次,研究LCL滤波器阻尼策略和电流跟踪策略。针对数字控制系统延迟对有源阻尼策略的影响,给出了电容电流即时反馈的有源阻尼方法,通过将电容电流反馈延时降低至0.5拍,提高了系统的稳定性。为提高装置的谐波抑制能力,本文引入PI加重复控制的复合控制策略。针对复合控制在负荷波动时补偿电流畸变的问题,提出一种改进控制策略,通过对比当前电流跟踪误差和1/6周期前电流跟踪误差,调节重复控制器输入,负荷波动剧烈时PI控制器单独工作,负荷平稳时重复控制器投入运行。仿真结果验证了所提控制策略的有效性,且重复控制器延迟时间降低至基波周期的1/6,动态响应速度得到提升。再次,给出平衡工况下直流侧电压的分层控制策略。通过总体电压控制,相间电压控制,相内电压控制实现电容电压的均衡。本文采用零序电压注入法实现相间电压的均衡控制;针对相内电容电压不均衡的问题,采用同向载波层叠调制,根据电容电压的高低和当前充放电状态实时调整各模块的调制波,维持相内电压的稳定。仿真结果验证了控制策略的有效性。最后,给出负载不平衡工况下STATCOM的控制策略。针对正序无功和负序电流综合补偿的控制目标,采用对称分量法建立装置的正负序数学模型,通过正负序双环控制实现电流跟踪;由于STATCOM补偿负序电流,三相直流侧电压无法均衡,针对此问题采取零序电压注入法,并推导出所注入零序电压与补偿电流中无功和负序电流的比例相关;针对STATCOM输出电压有限,零序电压过大时输出电压过调制的问题,本文在得到负序电流补偿极限的基础上,给出了限制负序指令电流的控制策略,仿真结果表明,所提控制策略在负载不平衡度较大时能够保证装置稳定,有效补偿负序电流。
[Abstract]:In recent years, with the development of industry, all kinds of nonlinear, impact and unbalanced load increase rapidly, which leads to a series of problems affecting power quality, such as low power factor, harmonic pollution, three-phase imbalance and so on. Static Synchronous compensator (Statcom) has attracted much attention for its ability to solve the above problems at the same time, so it has a broad application prospect in distribution networks. In this paper, some key problems of LCL cascaded STATCOM are studied. Firstly, the mathematical models of LCL type STATCOM in the abc stationary coordinate system and the dq rotation coordinate system are established, which lay the foundation for the design of the control system. Aiming at the problem of parameter design of LCL filter, based on the analysis of filter principle, the relationship between filter performance and parameters is studied, and the constraint conditions and design steps of filter design are given. Simulation results verify the effectiveness of the parameter design. Secondly, damping strategy and current tracking strategy of LCL filter are studied. Aiming at the effect of delay in digital control system on active damping strategy, the active damping method of capacitive current instant feedback is presented. By reducing the delay of capacitance current feedback to 0.5 beats, the stability of the system is improved. In order to improve the harmonic suppression ability of the device, a compound control strategy of Pi plus repetitive control is introduced in this paper. An improved control strategy is proposed to compensate for current distortion during load fluctuation. By comparing current tracking error with current tracking error before 1 / 6 cycle, the repetitive controller input is adjusted. Pi controller works alone when load fluctuates intensely, and repetitive controller is put into operation when load is stable. The simulation results show that the proposed control strategy is effective, and the delay time of the repetitive controller is reduced to 1 / 6 of the fundamental period, and the dynamic response speed is improved. Thirdly, the layered control strategy of DC side voltage under balanced condition is given. The capacitor voltage can be equalized by total voltage control, interphase voltage control and intra-phase voltage control. In this paper, the zero-sequence voltage injection method is used to realize the equalization control of the interphase voltage, and the codirectional carrier stacked modulation is used to solve the problem of the unbalance of the capacitance voltage in the phase. The modulating wave of each module is adjusted in real time according to the capacitance voltage and the current charge and discharge state to maintain the stability of the voltage in the phase. Simulation results verify the effectiveness of the control strategy. Finally, the control strategy of STATCOM under unbalanced load condition is given. Aiming at the control target of integrated compensation of positive and negative sequence reactive power and negative sequence current, the mathematical model of positive and negative sequence of the device is established by symmetrical component method, and the current tracking is realized by positive and negative sequence double loop control, because STATCOM compensates negative sequence current, The three-phase DC side voltage can not be equalized. The zero-sequence voltage injection method is adopted to solve this problem, and the proportion of the injected zero-sequence voltage and the reactive and negative sequence current in the compensation current is deduced, and the output voltage of STATCOM is limited. When the zero sequence voltage is too large, the output voltage is overmodulated. On the basis of obtaining the compensation limit of negative sequence current, a control strategy to limit the negative sequence instruction current is given. The simulation results show that, The proposed control strategy can ensure the stability of the device and compensate the negative sequence current effectively when the load unbalance is large.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM761.12

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