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Research on the Control Strategy for Cascade Multilevel STATCOM under Unbalanced Condition

Author: HeShuang
Tutor: ZuoChunYan
School: Huazhong University of Science and Technology
Course: High Voltage and Insulation Technology
Keywords: CASCADE STATCOM Grid voltage unbalance Split-phase instantaneous current tracking control Single-phase SVPWM Redundant state vector
CLC: TM761.1
Type: Master's thesis
Year: 2011
Downloads: 119
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Abstract


The paper chain static synchronous compensator (STATCOM) as the object of study, first introduced the works of STATCOM and STATCOM main circuit of of ± 2.8kVar three-phase delta connection chain modeling and parameter design, and focusing on DC capacitor voltage balance control, the control strategies of the grid voltage unbalance conditions, transient current track and the single-phase space vector modulation (SVPWM) and other key technologies. DC side capacitor voltage problem has been one of the technical problems of Cascaded STATCOM. DC capacitor voltage imbalance mechanism from the perspective of energy conservation analysis that at all levels of the associated H-bridge unit absorption and energy consumption inconsistencies led to the DC side capacitor voltage imbalance. And change the energy absorbed by the H-bridge unit and analysis unit of the H-bridge output voltage, current, and DC side capacitor charge / discharge status of the relationship, and a based on meritorious vector superimposed control strategy, the active component real-time charge / discharge states of the capacitors and the capacitor voltage error joint decision. Matlab simulation to prove the correctness and validity of the control strategy. CASCADE STATCOM control grid voltage unbalance conditions other technical problems. This study, pointed out that the STATCOM not only unbalanced outputs positive and negative sequence voltage, but also the third harmonic generation, come to the the imbalance conditions CASCADE STATCOM correct equivalent sequence network, and the introduction of a sub- phase instantaneous current tracking control strategy. The paper gives a fast and accurate access to the unbalanced grid voltage amplitude and phase information, and, respectively, of the three operating modes of the chain STATCOM: reactive power control mode, voltage control mode, unbalanced load current compensation mode. Articles proportion of repetitive control composite controller instantaneous current no static error tracking, and detailed design method is given. The simulation results show that the split-phase current instantaneous control strategy can guarantee CASCADE STATCOM unbalanced condition normal work effectively. Composite controller and PI controller comparative study showed that the composite controller can better track the instantaneous current and harmonic suppression. CASCADE STATCOM topology characteristics, the paper proposed a novel single-phase SVPWM algorithm. The algorithm is not only simple in form, suitable for any level cascade inverter, directly applicable to the three-phase unbalanced output. More importantly, its redundancy vector assignment capability provides the possibility to control the optimization of the performance. This article is based on reducing the switching losses, the equalizer switch load balanced DC bus voltage for two purposes, two redundant vector selection principle. Matlab simulation proved the correctness and validity of the algorithm and redundancy of the modulation vector selection principle.

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CLC: > Industrial Technology > Electrotechnical > Transmission and distribution engineering, power network and power system > Power system automation > Automatically adjusts > Automatic adjustment of voltage and reactive power
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