【作者】 荣飞；

【导师】 罗安；

【作者基本信息】 湖南大学 ， 电气工程， 2008， 博士

【摘要】 配电网静止同步补偿器(D-STATCOM)能稳定接入点电压、补偿负载所缺无功,受到越来越广泛的重视,但存在很多技术问题有待解决。为此,论文从D-STATCOM电压控制技术,D-STATCOM电流控制技术,正序电压和无功电流实时检测方法,输出滤波器结构设计及参数优化等方面进行了深入研究,提出了一些可行的解决办法。论文在传统双环控制(电压外环和电流内环控制)的基础上,利用能量守恒原理,在dq坐标系中,推导了逆变器输出电压和输出电流之间的代数关系,从而取代了双环控制中的电流内环,减少了PI调节器,提高了响应速度。当三相负荷不平衡时,往往会引起接入点电压的不平衡,为了解决这一问题,论文引入负序电压前馈环节以维持接入点电压保持三相平衡,并推导了负序电压情况下逆变器输出电压和输出电流之间的代数关系。同时,论文还提出采用模糊神经网络算法在线调节PI参数,将PI参数分解为两部分之积:ωi(k)和Ki (k),在误差较大时,采用模糊推理算法快速调节PI参数的Ki (k)部分,在误差较小时,采用单神经元算法在线修正PI参数的ωi(k)部分,有效提高了系统的动态特性和鲁棒性。为了有效补偿无功,论文还提出采用变结构空间矢量的D-STATCOM直接电流控制方法。论文以无功电流I Sq=0构造切换曲面,推导了使系统保持稳定的滑模控制率,但是该控制率只有在电流跟踪误差不为0的情况下才有控制量产生,在误差为0的情况下没有控制量产生。为此,当系统处于暂态时,论文直接选择滑模控制率使暂态分量迅速减小,当系统处于稳态时,引入基于电压空间矢量的直接电流控制方法,使误差电流趋于0缓慢变化,在有效补偿系统无功的同时,提高了系统的动态特性,并大大降低了系统振荡的可能性。同时由于电压空间矢量控制方法的引入,还能有效降低逆变器开关频率,减少损耗,稳定直流电压。为了提高D-STATCOM装置的工作性能,对正序电压和无功电流的快速准确检测显得至关重要。论文仔细分析了传统同步坐标变换法,指出如果将该方法直接应用于三相不平衡系统,将会出现很大的检测误差,这是由于在三相不平衡情况下无法准确获得与电网基波同步的相位角而引起的。为此,论文将单相电压通过一个微分器得到与该相电压正交的微分量,然后利用二者的正交关系直接通过数学关系求解出同步旋转角,成功解决了锁相环带来的影响。在这种求解过程中,微分器的性能决定了检测的精度,为此,论文还着重分析了数字微分器的实际微分效果,结果表明利用差分方式设计的数字微分器性能优良,能准确地获得同步旋转角。在此基础上,论文利用所检测得到的基波正序电压代替D-STATCOM接入点电压进行Ip-Iq变换,克服了接入点电压不平衡对Ip-Iq变换法的影响,实现了参考信号的快速、准确检测。为了有效滤除逆变器产生的高频谐波,论文首先分析了各种形式滤波器的滤波性能,指出对LCL型输出滤波器的滤波电容串联一个阻值不大的电阻能有效抑制与电网发生的谐振,然后从无功补偿能力和瞬态电流跟踪能力两方面分析了输出滤波器对D-STATCOM装置的影响,并以此为基础提出运用改进遗传算法进行输出滤波器参数的优化设计,将各优化目标对装置的影响程度考虑到适应度函数中。实例设计表明该方法能够确保输出滤波器更好地满足D-STATCOM的要求。在上述理论研究基础上,论文最后提出了容量为50kvar的D-STATCOM实验样机的研制方案,并详细给出了样机的设计技术和实验结果。实验结果表明,采用所提出的技术后,D-STATCOM的工作性能具有满意的效果。更多还原

【Abstract】 D-STATCOM has been paid more and more attention since it can stabilize the voltage of the common coupling point and compensate the reactive power. But there are still many problems to be resolved. Therefore, a deep research has been done for the voltage control technology and the current control technology of D-STATCOM, the positive sequence voltage and reactive current detection method, as well as the structure design of output filter and its parameter optimization. At the same time, the possible solutions are presented in this dissertation.In order to stabilize the common coupling point voltage, basis of the traditional double loop control method (voltage outer loop and current inner loop), the algebraic relations between the VSI(voltage source inverter) output voltage and the VSI output current in dq coordinate are deduced by using the energy conservation principle, and replace the current inner loop of the double loop control method, and so reduce the PI adjusters. When the load is unbalanced, it will cause voltage imbalance on the common coupling point. In order to solve this problem, the negative sequence feed forward control module is imported, and the new algebraic relations under negative sequence voltage conditions are deduced too. At the same time, to improve the systems’s robustness and dynamic characteristics, the fuzzy-neural-network algorithm is adopted to adjust the PI parameters on line which divides the PI parameters into two parts, theωi(k) and the Ki (k). When the tracking error is great, the fuzzy algorithm is chose to adjust Ki (k) quickly, and when the tracking error is small, the neutral-network is chose to adjustωi(k).To compensate reactive power effectively, the direct current control method based on variable structure space vector method is adopted in this dissertation. The sliding mode control rule which can maintain the system stability is deduced when choose I Sq=0 to construct switching surface. However, the sliding mode control rule has control quantity only when the tracking error is not in zero. So, When the power system is in transient, the sliding mode control rule is chose directly to make transient component decrease quickly, and when the power system is in stability, the direct current control method based on voltage space vector method is imported to make the error current reduce to zero by inches and avoid surge. Furthermore, the control method can reduce the switch frequency, decrease the switch loss, and stabilize the direct voltage. The rapid and accurate detection of positive sequence voltage and reactive current is crucial for improving the performance of D-STATCOM. The traditional synchronization coordinate transformation method is analyzed in detail in this dissertation. And it is pointed out that if use this method in unbalanced system, it will bring great examination error. The reason is that it can’t obtain synchronous rotate angle under unbalanced system. To solve this problem, a new way has been proposed, in which a single phase voltage’s differential is obtained at first, and then the synchronous rotation angle is calculated by the orthogonal relations of the single phase voltage and its differential directly. Because the examination precision is decided by the differentiator performance, the differentiator’s actual differential effect is analyzed emphatically in this dissertation, and the results indicate that the digital differentiator designed by difference equation has fine performance. On the basis of discussion above, a new Ip-Iq transformation method by using positive sequence voltage component instead of common coupling point voltage is proposed to ensure that the reactive current can be detected accurately under unbalanced voltage system.In order to filter out the harmonics voltage output by inverter, the performance of existing filters are analyzed. Then the new LCL type filter which connected a small resistance to the capacity is pointed out can suppress the resonance effectively. Furthermore, the output filter’s influence to the D-STATCOM is discussed from the ability of reactive power compensation and transient current tracking. According to this, the optimization method of parameters for output filter is proposed by using the advanced genetic algorithm that considering the influence degree of each optimized goal to the D-STATCOM into the fitness function. The simulation results show that the optimization method can meet the requirement of the reactive power compensation better than the ones designed just by experience.Based on theoretical study, The research plan of 50kvar D-STATCOM experimental prototype is proposed at the end of this dissertation. The design technology and experimental results is presented in detail. The experimental results show that the D-STATCOM can attain a satisfactory performance by adopting the proposed techniques.更多还原