Control Technology Research Of Cascade H-bridge Multilevel Converter Based On Natural Frame

In recent years,distributed generation has been widely studied,and energy internet has a broad development prospect.However,a large number of distributed generation equipment will introduce harmonics to the distribution network,which will affect the stability of the power system,and the requirements of voltage withstand level of grid connected converter is improved.The traditional two-level converter has low voltage withstand level and high harmonic content of output voltage.The multilevel converter has a higher voltage withstand level and a lower harmonic content of output voltage,which is an ideal alternative to the traditional two-level converter.In the topology of the multilevel converter,the cascaded H-bridge(CHB)multilevel converter has the advantages of fewer required originals and easy modular design,so it has been widely studied and applied.Firstly,according to the basic structure of the single-phase cascaded H-bridge multilevel converter,the switch function method is used to build the mathematical model,and its structural characteristics and modulation methods are analyzed.The existing dq control method and natural coordinate control method are introduced.The traditional dq control method is widely used,but its performance is affected by the phase-locked loop(PLL),and its dynamic response is relatively slow.The existing natural coordinate method does not need PLL or coordinate transformation,and has a fast dynamic response,but it will face challenges under distorted grid voltage conditions.Secondly,in order to realize the control of single-phase cascaded H-bridge multilevel converter with fast dynamic response under distorted grid voltage conditions,the equivalent model of natural frame control method is analyzed,and a new control method based on cascaded delayed signal cancellation(CDSC)and grid voltage feedforward is proposed.In addition,a stationary frame control method is proposed.The control effect of this method is equivalent to the natural frame control,but the algorithm complexity is slightly reduced.A simulation model based on MATLAB / Simulink2016 a is established to verify the effectiveness of the proposed control method under distorted grid voltage conditions.Finally,the experimental test of the proposed method are carried out through the cascade H-bridge multilevel converter experimental platform.Using TMS320F28377 D DSP as the controller,the digital control of the experimental platform is implemented.The experimental results show that the control method proposed in this paper can achieve the control of cascade H-bridge multilevel converter under distorted grid voltage,and the generated ac side current has lower harmonic distortion.Compared with the traditional dq control method,the control method presented in this paper has faster dynamic response performance.