Research And Application On Three-phase-four-wire Dstatcom With Split Capacitor Type Structure

With the rapid development of the power system expansion and themodern power electronics technology, Static Synchronous Compensator(STATCOM) has become a hot topic in the field of power system energysaving and power quality control research. STATCOM, as a dynamic fastcontrollable reactive power compensation device, can improve efficiencyof reactive power compensation, resist voltage fluctuation and eliminatethe three-phase unbalance, so as to raise power quality of power system.This thesis focuses on the related technology of DSTATCOM, mainlyincluding the control strategy and grid-connected current optimizationmethod based on full harmonic elimination of DSTATCOM with splitcapacitor type structure in three-phase-four-wire power system.Firstly, in order to compensate any unbalanced reactive load with athree-phase-four-wire DSTATCOM, this thesis does some researches onthe control strategy under abc coordinate frame. Meanwhile, to solve theproblem that traditional PI controller tracks with the periodic signalpoorly, a double-loop-controller-based control strategy is proposed. Inthis method, the PI controller with a quick response to instruction iscombined with repetitive controller which has a high accuracy controlperformance of periodic signal to constitute a double-loop controller, thenapply both to the inner link of current tracking of the three-phase four-wire DSATACOM with split capacitor type structure. Its design isanalyzed in detail and verified by the simulation using Matlab/Simulink.Results indicate that with the proposed method, DSTATCOM canguarantee the response speed, has a higher accuracy of current trackingand a lower aberration rate of DSTATCOM output current and a bettercompensation effect compared with the traditional PI control method.Secondly, in order to solve the influence caused by dead zone ofpower electronic switching devices, the DC capacitor voltage fluctuations,system voltage harmonics and other factors on tracking accuracy in thepractical application of DSTATCOM, a current tracking optimizationmethod based on full harmonic elimination is proposed to eliminate theharmonics of the grid-connected current and improve operational stabilityof reactive power compensation device. In the implementation of theprocedure, a feed-forward adjustment link is combined with double-loopmethod based on the full harmonic elimination on the use of a slidingwindow iterative DFT algorithm. After that, it rebuilds the PWMmodulation wave through the method of harmonic opposite infusion, soas to rectify the current waveform distortion and optimize the trackingperformance of grid-connected current. Simulation results inMatlab/Simulink show the feasibility of the related control strategy.Finally, on account of all of the research mentioned above, theproject to the floating-type DSP controller program is completed in thesystem of DSP+FPGA hardware platform. Through massive experimentson DSTATCOM device, it is verified that the developedthree-phase-four-wire DSTATCOM with split capacitor type structure hasa high-performance in tracing dynamic reactive load. And the proposedcontrol strategy based on double-loop control algorithm has a greatimprovement of the current tracking performance than the traditional PIcontrol method. Concurrently，effective control of distortion rate of the DSTATCOM output current can be realized because of the full harmonicelimination current tracing optimization based on sliding windowiterative algorithm DFT harmonic detection, so as to improve thecompensation effect of DSTATCOM.