Model Predictive Current Control Scheme For Single-Phase Cascaded H-Bridge Rectifiers

As a quick and convenient means of transportation,the high-speed railway is attracting people's increasingly concern and attention.In order to improve train speed and reduce the wear and tear of the pathway,there is a trendency to develope the traction drive system,which will achieve miniaturization,lightweight and high power density in the future.The traction drive technology based on power electronics transformer(PET)is chosen as one solution to achieve these goals.As the front-end converter in PET,the control performance of singlephase cascaded H-bridge rectifiers(CHBR)has profound impacts on the whole system.Therefore,the research on the control algorithms attains great importance to the theoretical and practiacal value.Taking the single-phase CHBR as the reaserch object,the model predictive control is regarded as the core concept to accomplish several control goals,such as: faster dynamic response,low harmonics of the line current,constant switching frequency and complexity reduction of the algorithm.And the specific content are listed as follows:Firstly,the topology and operation principle of single-phase CHBR are introduced,and its state space equation is built while the mathematical model in two-phase stationary coordinate system is established.Additionally,the definition of space voltage vectors and corresponding sector partition are described in detail.Secondly,applying the principle of model predictive control to the single-phase CHBR,the single-vector-based model predictive current control(SV-MPCC)is analyzed in detail.The implemention process of this strategy contains the deduction of line current predicve model,and the utilization of the cost function without the capitor voltage balancing term,considering the fesibility and practicability of the algorithm.Thirdly,in order to overcome disadvantage of variable switching frequency and high current harmonics in SV-MPCC scheme,a two-vector-based model predictive current control(TV-MPCC)is introduced by the effective combination of two chosen voltage vectors in each swiching horizon.Hence,the single-phase CHBR can obtain advantages of good steady-state performance and constant switching frequency.On the basis of this,a two-vector-based simplified model predictive current control(TV-SMPCC),aiming at reducing the large amount of computation and complex implemention,is proposed.The TV-SMPCC can simplify the control set selection,and the optimal sector selection is realized without the online assessment of the cost function,which leads to the computation cost reduction.And then,noting that the poor steady-state performance of the SV-MPCC and the complex realization of the voltage balancing,a multiple-vector-based model predictive current control(MV-MPCC)is proposed.The high equivalent switching frequency is realized by designing the switching sequence,which leads to a good steady-state performance.Compared with TV-SMPCC,the control set of MV-MPCC is simplified further,and free of lookuping the voltage vector table,possessing the low complexity.Finally,the hardware-in-the-loop(HIL)testing system based on RT-LAB and a singlephase CHBR experimental platform is introduced.An experimental comparison of SV-MPCC,TV-MPCC,TV-SMPCC and MV-MPCC schemes is conducted,and the experimental results have verified the feasilbity and correctness of the proposed algorithms.