Research On Inverse System Sliding Mode Control Method Of Cascaded STATCOM

With the development of power electronics technology,the function of static synchronous generator(STATCOM)is also more powerful,in which a representative cascaded STATCOM for easy to expand capacity,less harmonic output,achieving boost and other advantages in power quality comprehensive management of power system has played an important role.With the expansion of the size of the grid,in order to better improve the power quality,the performance of cascaded STATCOM also need to continuously improve,but because of the controller design of cascaded STATCOM is exceedingly complex,so the AC-side control,DC capacitor voltage control,imbalance condition control and signal detection control still has many problems to be solved.In this paper,firstly,the basic principles and design methods of inverse system and sliding mode control is introduced,on this basis,the principle of combination of inverse system and sliding mode variable structure is described,and the proof of sliding mode control improving system robustness is given,thus,which proved the sliding mode control can provide a guarantee for the inverse system to achieve linear decoupling,so as to lay the foundation for the study of the control method of cascaded STATCOM.Then the modulation method of H-bridge module,and the working principle of cascaded STATCOM is analyzed,and the dynamic working mathematical model of balance condition and unbalance condition is established.On this basis,the control method of cascade STATCOM is extensively studied,the inverse system model is established,and the sliding mode control of positive and negative sequence current is designed.Then,the reason of causing the DC capacitor voltage unbalance is analyzed,the three capacitor voltage balancing method is proposed,the inter-phase balance control and inner-phase balance control is emphatically studied,by changing the negative sequence current of device output to achieve a inter-phase capacitor voltage balance,and by translating modulation wave method,changing the conduction time of switching device,to achieve inner-phase capacitor voltage balance.Finally,the signal detection method is discussed,the effect of the impact synchronous rotation angle detection accuracy of the signal and the second harmonic component of the filtering effect,the influence of synchronous rotation angle for signal detection accuracy and second harmonic component for filtering effect is analyzed,and the positive and negative sequence current detection method of improved filtering method filtering based on correcting synchronous rotation angle is proposed.Finally,building simulation models in MATLAB,to verify the control method ofcascaded STATCOM.In the case of disturbance,the proposed inverse system and sliding mode control method in this paper can achieve decoupling of active and reactive of positive and negative sequence current,and improve system robustness and anti-interference ability.In balanced conditions as well as unbalanced conditions,three balance control method can achieve the capacitor voltage maintaining in a stable range with small fluctuations.The improved positive and negative sequence current detection method can achieve to track the grid frequency accurately,and improve the response speed as well as accuracy of the signal detection.The simulation structure also verify the correctness and validity of cascaded STATCOM control method.