Research On The Control Stratagies Of Dual Converter Based On Open-end Winding Topology

ABSTRACT:Focusing on dual series converter with open-end winding topology, this dissertation discusses control strategies of different topologies and in different applications, including modulation strategies of dual3L-NPC converter with common DC link and isolated DC link respectively, dual converter control strategies applied in wind power generation and photovoltaic system. The main contents go as follow:Firstly, differential value of common mode voltage and neutral point voltage balance modulation strategies of dual3L-NPC converter with common DC link topology are proposed. Mathematical model of common DC link topology is established and the principle of zero sequence injection SPWM strategy is analyzed. The generation mechanism of differential value of common mode voltage is described and its elimination strategy with zero sequence voltage injection is proposed, which can suppresses the high frequency and low frequency voltage completely. Based on the analyses of redundant vectors effects on neutral point voltage, the neutral point balance control with no differential value of common mode voltage is realized.Secondly, single-phase zero sequence voltage and three-phase zero sequence voltage untied injection SPWM strategy of dual3L-NPC converter with isolated DC link topology is presented. Based on mathematical model and space vector distribution of isolated DC link, single-phase zero sequence voltage and three-phase zero sequence voltage can be used to realize the nearest three vector and optimal loss modulation strategies. Finally, neutral point balance control of dual converter with nearest three vector strategy is given, and the neutral point control ability under different modulation and power factor is also analyzed.Thirdly, dual converter control strategies applied in open-end winding motor for wind power generation are investigated. For the zero sequence voltage of emf harmonic in the open-end winding motor, the suppression of zero sequence current is presented. After a detailed analysis of field weaken control region with zero sequence emf,180°no zero sequence voltage injection strategy is beneficial to promote the voltage loop instruction of field weaken control that can make the motor work in higher speed level. Based on the analyses above, using the established converter loss model, the field weaken control of optimal converter efficiency which can obtain the field weaken current command is researched. Finally, by the discuss of the dual modulation waves working scope, the neutral point balance of common DC link based on zero sequence emf is realized andthe neutral point control ability under zero sequence emf is analyzed.Fourthly, the topologies and control strategies for photovoltaic grid connected inverter with dual series converter are presented. By proposing means of the dual series converter topology for single DC source, the differential value of common mode voltage elimination strategy with dual two-level converter is optimized, and power balance control of two converter with the differential value of common mode voltage elimination strategy is realized. Furthermore, for the LCL filter in open-end winding topology, the mathematical model and equivalent circuit of common filter capacitor and isolated filter capacitor respectively which can obtain the LCL resonance point is established, and based on the bandpass filter, the active damping control is presented. Finally, in order to improve the power generation efficiency of series photovoltaic system, the dual series converter topology for isolated DC source is proposed. Focusing on the topology, the dual voltage loop control for stabling each DC voltage and independent MPPT control for dual PV panels are accomplished,.