Research Of Cascaded H-bridge Active Power Filter

As a new type of power electronic device, active power filter(APF) is receiving moreand more attention because of the ability for suppressing and compensating harmonicdynamically. However, in the high voltage and high-volume work environment, the activepower filter with conventional topology is limited by pressure level and working frequencyof power electronic switching devices that cannot meet the operating requirements. In viewof the practical problems, this paper mainly studied the H-bridge cascaded shunt APF, thistopology can be used in high-voltage and high-power occasions, and easy to modularizeddesign and packaging, which has a good application prospect in power quality control fieldof high-power.First of all, this paper put forward cascaded H-bridge multilevel converter with Carrierphase-shifted SPWM (CPS-SPWM), CPS-SPWM combines the advantages ofmulti-modular technique and SPWM technique, the high equivalent switching frequencycan be obtained with low switching frequency devices, and have a good harmonicperformance through low harmonics mutually offsetting. The structure of cascadedH-bridge is built by a number of same converter units (single phase full bridgecircuit),which increase the capacity of the converter and decrease the voltage on the powerelectronic switching devices.Secondly, ip-iqalgorithm was used to detect the harmonic and reactive current forreal-time based on the instantaneous reactive power theory. Because the DC side capacitorsof the H-bridge converter are independent from each other, yet, a constant value of the DCbus voltage is the premise of the main circuit tracking the command signal accurately. Thispaper used the strategy of voltage loop control to guarantee the stability and balancing ofthe capacitance voltage. The precision of current loop control determines the compensationperformance of APF, however PI control cannot track the periodic command signal withoutsteady error, in this paper a composite control strategy which combined PI control andrepetitive control was used to the command signal tracking, additional, the stability of thewhole closed loop control system was analyzed. In order to guarantee tracking performance,the parameters of repetitive controller was determined by the two aspects of amplitude andphase.Moreover, a large number of low voltage simulation experiment were carried out based on MATLAB simulation platform, then comparing the results under differentconditions, so the feasibility and the effectiveness of the control strategy described in thispaper was verified through the analysis of voltage and current waveforms and the THDvalue. The last of all, three-phase five voltage level of cascaded H-bridge shunt APFexperiment platform was built. The hardware design and software design of theexperimental prototype was discussed in detail, and verifying the correctness of theoreticalanalysis further by means of a series of experimental studies.