Research On DC Side Voltage Fluctuation Analysis And Control Strategy Of Cascaded H-Bridge STATCOM

The cascaded H-bridge STATCOM device can track the load reactive current quickly and in real time,control the output voltage of the cascaded H-bridge through the H-bridge modulation strategy to perform reactive compensation,and has strong anti-interference ability.It is obtained in the medium-high voltage system.widely used.In this paper,the current feedforward decoupling control strategy and modulation strategy of cascaded H-bridge STATCOM are analyzed.The causes of capacitor voltage imbalance and capacitor voltage double-frequency fluctuation are analyzed.Two kinds of injections of zero-sequence voltage are used to suppress it.The method of double frequency fluctuation.In this paper,the topology of STATCOM device is analyzed,and the equivalent model of STATCOM is established.The compensation principle is further analyzed in detail.The bipolar and the unipolar frequency-multiplying carrier phase-shift modulation strategy are respectively double Fourier.Analysis,comparing the advantages and disadvantages,and simulation verification.Through simulation comparison,it is concluded that the unipolar frequency doubling modulation strategy has advantages in cascading H-bridges.According to the mathematical model of STATCOM device,the feedforward decoupling control strategy is analyzed.The simulation and experimental results show that the feedforward decoupling control has good reactive power compensation performance.The variable angle carrier phase shift modulation method is introduced to reduce the fundamental frequency harmonic content.The theoretical derivation and Fourier analysis of the variable angle carrier phase shift are carried out,and the corresponding simulation model is built to verify its correctness.The simulation results show that Whether under balanced conditions or unbalanced conditions,the variable angle carrier shift has good performance relative to the reduction of the fundamental harmonic content.Through the power equation of the H-bridge module,the factors affecting the voltage balance of the capacitor are analyzed.The overall,in-phase and phase-to-phase three-layer control method is used to control the capacitor voltage module to be consistent.The capacitor voltage generation of the STATCOM device is described in detail.Based on the principle of frequency doubling fluctuation,two methods to suppress the second frequency fluctuation by injecting zero sequence voltage are studied,and the corresponding simulation model is built to verify the effectiveness of the above method.The main circuit components of the H-bridge STATCOM experimental platform and the components of the main circuit are described.The experimental verification is carried out according to the experimental platform.The unipolar CPS-PWM,capacitor voltage balance control,capacitor voltage fluctuation suppression experiment is verified.The correctness of the above strategy.