不平衡电网下三相PWM整流器的自适应滑模控制

发布时间：2018-08-15 13:00

【摘要】：三相PWM整流器作为新一代“绿色”变流装置，因其高功率因数、正弦波电流控制和AC/DC变换可控等优点受到了广泛的关注与发展，，在现代电能转换装置中得到广泛的应用。然而，在实际的电网当中，由于大量非线性负载以及各相间负载不平衡等原因，导致三相电网电压不平衡现象普遍存在。电网三相电压的不平衡将会给三相PWM整流器的性能带来较为严重的负面影响，因此，电网不平衡条件下，如何改进三相PWM整流器的控制方法以消除不平衡带来的负面影响成为一个亟待解决的问题。首先，本文基于基尔霍夫电压电流定律以及瞬时功率理论推导出三相PWM整流器在电网不平衡时的瞬时功率模型，以此为基础，分析了电网不平衡时系统二次功率脉动的成因，并对所能达到的最佳控制效果进行了讨论。其次，在存在谐波的情况下，传统正负序分离方法将不再有效，本文提出了一种基于改进最小二乘法的正负序分离方法。通过分离计算过程中的时变部分与常数部分以及分解矩阵求逆运算等方法，降低了算法的实时计算量以及对舍入误差的敏感程度。在此基础上，结合对称分量法，推导出正负序分量的分离算法。该方法在保证实时提取速度基础上，增强了对谐波干扰的抑制能力。然后，在直接功率控制基础上，为了提高系统鲁棒性，提出了改进的电网不平衡时三相PWM整流器的不平衡控制策略。该策略考虑有功和无功二次脉动对系统带来的影响，并通过引入功率给定修正环节对其进行了消除。结构上，采用基础控制器加抗扰控制器的结构，基础控制器以保证控制系统基本性能为目的，通过逆系统方法对原系统解耦与线性化之后建立；抗扰控制器以增强系统鲁棒性为目的，采用自适应滑模控制算法。该控制策略可以有效的解决由于电网电压不平衡对三相PWM整流器的控制带来的电流畸变，功率脉动以及功率因数降低等问题。通过Simulink仿真以及基于dSPACE的半实物验证实验证明，本文所提出的电网不平衡时三相PWM整流器的控制策略可以有效的解决电网不平衡对系统带来的各种负面影响，可以较为精确地达到所设计的控制目标。具有动态响应快，鲁棒性好等优点。
[Abstract]:As a new generation of "green" converter, three-phase PWM rectifier has been widely concerned and developed for its advantages of high power factor, sinusoidal current control and AC/DC conversion controllability, and has been widely used in modern power conversion devices. However, because of a large number of nonlinear loads and load imbalance between phases, the voltage imbalance of three-phase power network is widespread in the actual power network. The unbalance of three-phase voltage will bring serious negative effects to the performance of three-phase PWM rectifier. How to improve the control method of three-phase PWM rectifier to eliminate the negative effects caused by imbalance has become an urgent problem. Firstly, based on Kirchhoff's law of voltage and current and instantaneous power theory, the instantaneous power model of three-phase PWM rectifier in unbalanced power network is derived. Based on this model, the cause of secondary power pulsation is analyzed. The optimal control effect is discussed. Secondly, in the presence of harmonics, the traditional positive and negative sequence separation method will no longer be effective. In this paper, an improved least square method for positive and negative sequence separation is proposed. By separating the time-varying part from the constant part and the factorization matrix inversion, the real-time computation and the sensitivity to rounding error of the algorithm are reduced. On this basis, combined with the symmetric component method, the separation algorithm of positive and negative ordered components is derived. This method enhances the ability to suppress harmonic interference on the basis of guaranteeing real-time extraction speed. Then, on the basis of direct power control, in order to improve system robustness, an improved unbalanced control strategy for three-phase PWM rectifier is proposed. The effect of active and reactive power secondary pulsation on the system is considered in this strategy, and it is eliminated by introducing a given power correction link. In structure, the structure of the basic controller plus disturbance rejection controller is adopted. The basic controller is established after decoupling and linearizing the original system by inverse system method to ensure the basic performance of the control system. In order to enhance the robustness of the system, the disturbance rejection controller adopts an adaptive sliding mode control algorithm. This control strategy can effectively solve the problems of current distortion, power pulsation and power factor reduction caused by the control of three-phase PWM rectifier due to the unbalanced voltage of the power network. Through the Simulink simulation and the hardware-in-the-loop verification experiment based on dSPACE, it is proved that the control strategy of the three-phase PWM rectifier proposed in this paper can effectively solve the negative effects of the unbalanced power grid on the system. The designed control objectives can be achieved more accurately. It has the advantages of fast dynamic response and good robustness.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM461

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