低开关频率有源中点钳位三电平整流器控制策略研究

发布时间：2018-07-12 12:34

本文选题：有源中点钳位 + 复矢量　；参考：《中国矿业大学》2017年硕士论文

【摘要】：多电平拓扑以其较小的电流畸变率、能量双向流动等优点被广泛应用在中高压大功率场合。在中高压大功率系统中,功率器件的损耗较大,可通过降低功率器件开关频率的方法来降低损耗。但随着开关频率的降低会导致多电平系统的控制性能下降。本文基于有源中点钳位(ANPC)三电平整流器,研究了整流器的SPWM调制算法,并在开关频率降低时对控制系统进行数学建模以及设计了两种电流内环控制器。首先,基于三电平ANPC整流器拓扑结构,建立控制系统的数学模型以及功率器件损耗模型。并对三电平ANPC、NPC整流器不同换流方式进行分析,可知三电平ANPC整流器在零电平状态拥有更多的换流方式,通过在零电平切换过程选择不同的零开关状态可以解决NPC整流器器件损耗不平衡问题。研究三电平ANPC整流器的三种传统SPWM调制算法。其次,利用复矢量分析法分析低开关频率下控制系统性能的变化情况,建立相应的复矢量数学模型。在低开关频率下,采用常规PI电流调节器以及带前馈解耦的PI电流调节器控制时系统内部仍存在耦合,不能实现控制系统完全解耦。通过传递函数分析可知,复矢量控制器可以完全抵消系统耦合项,利用bode图、单位阶跃响应证明了复矢量调节器在降低开关频率时仍具有较好的动静态特性。再次,为使在低开关频率下控制系统仍具有较好的动稳态性能,基于模型预测控制进行研究。根据三电平ANPC整流器的控制目标:较好的电流跟随性、中点电位平衡控制,对27种电压矢量进行滚动优化得到控制系统的最优电压矢量;由于存在冗余零开关状态,为将零电压矢量转换为唯一输出开关状态,基于损耗预测模型,对损耗进行滚动优化从而实现电压矢量状态向开关状态的转换。为使损耗、系统控制性能以及开关频率同时达到最优状态,改进控制算法。此外,为获得较小的电流畸变率,在模型预测控制的基础上,利用滑动傅里叶变换提取的基波及各次谐波量,通过滚动优化后实现较小电流谐波的的控制性能,通过仿真验证控制算法的有效性。最后,基于三电平ANPC整流器实验平台。完成了三电平ANPC整流器SPWM调制算法、复矢量控制、模型预测控制方法的实验,验证了低开关频率下两种控制方法的可行性。
[Abstract]:Multilevel topology is widely used in high power applications due to its low current distortion rate and bidirectional energy flow. In medium and high voltage power systems, the loss of power devices is large, which can be reduced by reducing the switching frequency of power devices. However, with the decrease of switching frequency, the control performance of multilevel system will decline. In this paper, based on the active neutral point clamping (ANPC) three-level rectifier, the SPWM modulation algorithm of the rectifier is studied, and the mathematical model of the control system and two current inner loop controllers are designed when the switching frequency is reduced. Firstly, based on the topology of the three-level ANPC rectifier, the mathematical model of the control system and the loss model of the power device are established. The different commutation modes of the three-level ANPC-NPC rectifier are analyzed. It is known that the three-level ANPC rectifier has more converters in the zero-level state. The loss imbalance of NPC rectifier devices can be solved by selecting different zero-switching states in the zero-level switching process. Three traditional SPWM modulation algorithms for three-level ANPC rectifier are studied. Secondly, the complex vector analysis method is used to analyze the change of control system performance at low switching frequency, and the corresponding mathematical model of complex vector is established. At low switching frequency, the conventional Pi current regulator and the Pi current regulator with feedforward decoupling still have coupling in the control system, which can not realize the complete decoupling of the control system. According to the analysis of transfer function, the complex vector controller can completely cancel the coupling term of the system. Using the bode diagram and the unit step response, it is proved that the complex vector controller still has better dynamic and static characteristics when the switching frequency is reduced. Thirdly, in order to make the control system still have better dynamic and steady performance at low switching frequency, the model predictive control is studied. According to the control objectives of the three-level ANPC rectifier: better current following and neutral point potential balance control, the optimal voltage vector of the control system is obtained by rolling optimization of 27 voltage vectors. In order to convert the zero-voltage vector to the unique output switching state, based on the loss prediction model, the loss is optimized by rolling to realize the switching from the voltage vector state to the switching state. In order to achieve the optimal state of loss, system control performance and switching frequency simultaneously, the control algorithm is improved. In addition, in order to obtain lower current distortion rate, based on model predictive control, the control performance of small current harmonics is realized by rolling optimization by using the fundamental wave and harmonic quantity extracted by sliding Fourier transform. The effectiveness of the control algorithm is verified by simulation. Finally, based on the three-level ANPC rectifier experimental platform. The experiments of SPWM modulation algorithm, complex vector control and model predictive control for three-level ANPC rectifier are carried out, and the feasibility of the two control methods at low switching frequency is verified.
【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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