Model Predictive Control Method For Single Phase Three Level Traction Rectifier

China has the longest high-speed railway and the most passenger flow for one year in the world.The passenger flow has reached to 1500 million person-times in 2017.The highspeed railway system in China needs to provide high power,the high density of the locomotive and the railway station for carrying so many passengers.Thus,the traction converter in the electric multiple unit(EMU)is faced with the severe facts of the low switching frequency,the frequent fluctuation of the load,and the distortion and step-change of the grid voltage.These facts challenge the control system of the traction converter.This thesis thereby analyzes the direct power control,model predictive control for single-phase neutral-point clamped threelevel rectifier to improve the dynamic and steady state precision of the control system.The active and reactive powers need to be first estimated to achieve the direct power control(DPC)for single-phase rectifier.The active and reactive powers in single-phase system are calculated by the construction of the orthogonal component of the grid voltage and the line current,which cannot be directly achieved in the single-phase system.It restrains the application of the instantaneous power theory in the single-phase system.In order to improve the dynamic of the power calculation,the reconstruction of the orthogonal component for the line current base on the feedback of the fictitious axis is given by analyzing the power feedforward decoupled direct power control method of the grid-connected traction converter.Meanwhile,the improved second order generalized integrator(SOGI)is proposed to reconstruct the orthogonal component of the grid voltage with the distortion rejection of the grid voltage.Combining with the reconstruction of the orthogonal component for the line current and the grid voltage,the power estimator is proposed in the single-phase system and the parameter sensitivity of the proposed estimator is discussed in detail.For achieving the direct power control of the single-phase rectifier and reducing the dependence of the voltage phase detection on the control system,DPC for single-phase rectifier is proposed without the phase locked loop.In the rotational frame,the power calculation method is proposed without the reconstruction of the orthogonal component for the grid voltage and the line current.The compensation method for the frequency and the phase deviation of the grid voltage is proposed for accurately achieving the rotation frame transformation.The dynamic performance of the power feedforward decoupled direct power control with proportional integral(PI)controller depends on the controller parameter,which is difficult to tune for improving the dynamic of the rectifier.Therefore,the continuous control set(CCS)model predictive control(MPC)is proposed to improve the controller dynamic.The predefined switching sequence first is given according to the pulsewidth modulation for the single-phase NPC three-level converter.Combining with the neutral-point balancing control,the optimal duration of the voltage vector in the adopted switching sequence is calculated by online optimizing the cost function of the active and reactive powers.Meanwhile,the selection of the switching sequence is elaborated to reduce the complexity of the control method by analyzing the effect of every switching sequence on the active and reactive powers.The power fluctuation of the traction inverter-motor system and parameter deviation will cause the unbalanced equivalent load in dc-side of the rectifier.It challenges neutral-point balancing control and line current control.The effect of every switching sequence on the line current and capacitor voltage is analyzed in detail,and then the model predictive direct current control(MP-DCC)is proposed for the decoupled control of the line current and the neutralpoint control in the unbalanced load condition.Furthermore,the optimal operating range is discussed for each switching sequence.For avoiding the evaluation of the cost function,the low complexed calculation method of the optimal duration of the switching sequence is given by analyzing the relationship of between the durations for different switching sequences.The low switching frequency of the traction converter increases the predicting step of the active and reactive powers and reduces the predicting precision.A predictive method of the active and reactive powers is proposed based on the analytical solution of the mathematical model of the adopted converter.The optimal d-and q-axis components are directly calculated based on this predictive method,and then the rotation frame transformation with the voltage-second compensation is applied to obtain the optimal ?-and ?-axis components,which are fed to PWM to generate the optimal driving pulse.Moreover,the inductance parameter compensation is proposed to increase the control precision.In order verify the effectiveness and correction of the theoretical analysis,the experimental comparison is executed in the scaled-down or hardware in the loop platforms.