电网不平衡情况下PWM整流器控制策略研究

发布时间：2019-06-13 16:43

【摘要】：PWM整流器具有功率因数可控、网侧电流畸变率小和能量能够双向流动等特点,在交流电气传动、有源电力滤波及新能源并网发电等领域得到了广泛的应用。在实际应用中,由于三相负荷不对称等原因会导致电网不平衡。此时,若仍然采用电网平衡时设计的PWM整流器控制策略,将会导致网侧电流畸变和直流侧电压波动,严重时会影响电力设备的正常运行,甚至损坏设备。为此,本文对电网不平衡情况下的PWM整流器控制策略进行了深入研究。首先,根据基尔霍夫定律和瞬时功率理论分别建立了电网不平衡情况下三相PWM整流器的电压电流数学模型和瞬时功率数学模型。通过对比发现,电网不平衡情况下的PWM整流器数学模型同样适用于电网平衡情况下,在电网状态发生变化时,无需考虑系统模型变化可能造成的问题。其次,在三相PWM整流器数学模型的基础上,深入地研究了电网不平衡情况下PWM整流器双电流控制策略和电网不平衡情况下PWM整流器滑模变结构直接功率控制策略。针对以上两种控制策略存在的问题,本文提出了一种电网不平衡情况下PWM整流器无差拍预测直接功率控制策略。为提高系统动态性能,本文设计了全数字化的无差拍控制器作为功率内环控制器,实现了两相静止坐标系下瞬时功率对给定功率的快速跟踪控制;为优化无差拍控制器的性能,分析了时间延迟对控制器的影响并提出了相应的补偿方案。与此同时,通过设置三个控制目标来对系统进行控制,即抑制负序电流、抑制有功功率波动、抑制无功功率波动。为简化控制结构、减少运算量,通过采用一种新型瞬时功率分析方法,无需正负序分量提取就可针对设置的三个控制目标进行不同的功率项补偿,进而实现控制目标。仿真验证了该策略的有效性。最后,搭建了电网不平衡情况下PWM整流器实验平台,对所提控制策略进行了相关实验。通过实验结果分析,进一步验证了该策略的有效性。
[Abstract]:PWM rectifier has been widely used in AC electric drive, active power filtering and new energy grid-connected power generation because of its controllable power factor, low current distortion rate on the grid side and two-way flow of energy. In practical application, the imbalance of power grid will be caused by the asymmetry of three-phase load. At this time, if the PWM rectifier control strategy designed when the power grid is balanced, it will lead to the current distortion on the network side and the voltage fluctuation on the DC side, which will seriously affect the normal operation of the power equipment and even damage the equipment. Therefore, the control strategy of PWM rectifier under unbalanced power grid is deeply studied in this paper. Firstly, according to Kirchhoff's law and instantaneous power theory, the mathematical models of voltage and current and instantaneous power of three-phase PWM rectifier under unbalanced power grid are established respectively. Through comparison, it is found that the mathematical model of PWM rectifier under the condition of power grid imbalance is also suitable for the case of power grid balance, and the possible problems caused by the change of system model do not need to be considered when the power grid state changes. Secondly, on the basis of the mathematical model of three-phase PWM rectifier, the double current control strategy of PWM rectifier under unbalanced power grid and the direct power control strategy of sliding mode variable structure of PWM rectifier under unbalanced power grid are deeply studied. In order to solve the problems of the above two control strategies, a deadbeat predictive direct power control strategy for PWM rectifier under unbalanced power grid is proposed in this paper. In order to improve the dynamic performance of the system, a fully digital deadbeat controller is designed as the power inner loop controller to realize the fast tracking control of instantaneous power to a given power in a two-phase static coordinate system. In order to optimize the performance of the deadbeat controller, the influence of time delay on the controller is analyzed and the corresponding compensation scheme is proposed. At the same time, the system is controlled by setting three control objectives, that is, suppressing negative sequence current, suppressing active power fluctuation and suppressing reactive power fluctuation. In order to simplify the control structure and reduce the amount of computation, a new instantaneous power analysis method is adopted, which can compensate the three control targets with different power terms without the extraction of positive and negative sequence components, and then realize the control objectives. The effectiveness of the strategy is verified by simulation. Finally, the experimental platform of PWM rectifier under the condition of unbalanced power grid is built, and the related experiments of the proposed control strategy are carried out. The effectiveness of the strategy is further verified by the analysis of experimental results.
【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】：TM461

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