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Research On Several Key Technologies Of Cascaded H-bridge STATCOM

Posted on:2014-11-29Degree:MasterType:Thesis
Country:ChinaCandidate:H ChenFull Text:PDF
GTID:2252330422450765Subject:Electrical engineering
Abstract/Summary:PDF Full Text Request
With extensive use of power electronic devices, various kinds of relevantissues have been brought to the grid, which the typically ones include low powerfactor, harmonic pollution and voltage fluctuations and imbalances problems. Theappearance of Static Synchronous Compensator (STATCOM) provides a powerfultool for power quality improvement. Furthermore, it has features of goodcompensation capacity, diverse and flexible control, and impressive dynamicperformance, which make it become an important research direction for reactivepower compensation as a modern technique.Among the different types of topology, the configuration of cascaded H-bridgecircuit is chosen as the research object. Low-voltage and small-capacitycomponents can be used in the structure to achieve a high capacity output. Both thehardware and the software design adopt the modularize method in each unit, so thedevice is easy to control. The device topology has excellent performance ofharmonic suppression and capacity upgrading in medium-voltage and high-powerapplications, so it enjoys a broad prospect in smart gird.Firstly, the PI regulator delay problem in traditional STATCOM current loop ofthe cascade structure inverters is introduced, making the output current difficult totrack the reference value, which would seriously affect compensation accuracy. Toimprove the system dynamic response speed, the theory and characteristics ofmodel-based predictive control are studied at length; and the predictive model ofSTATCOM, along with the control structures, optimal control laws are designed toreduce error according to the model, achieving the deadbeat control thereby.Secondly, the overview of cascaded H-bridge multi-level inverter individualDC voltage imbalance problem and the corresponding solutions are presented. Onthis basis, the charging process of the cells is studied to clarify how the unitinstantaneous power flow affects the capacitor voltage on DC-side. Through theabove research, the duty cycle adjustment method to regulate DC voltages issummarized; and then a novel carrier offset technique in modulation link isproposed to achieve a satisfactory individual DC voltage balance effect.Thirdly, according to the power exchange between STATCOM and system, thedirect voltage compensation strategy based on the instantaneous power balance isdiscussed targeting the anomalous behaviors of the grid voltage. Based on thistheory, an output voltage regulating method is presented, whose inputs include PCCvoltage and DC-voltage of the device, for the aim of stabilizing system voltage. Inaddition, to compensate the grid voltage imbalance, dual sequences control is analyzed, and the voltage compensation strategy based on sequence decompositionis illuminated comprehensively.The proposed solutions for the key issues above have been verified in Matlabsimulations. Eventually, a medium-voltage cascaded STATCOM platform has beenestablished under the relevant theoretical and technical guidance, and severalexperiments have been carried out to test the reliability of the device and theeffectiveness of the proposed methods.
Keywords/Search Tags:Static synchronous compensator, Cascade H-bridge, Predictive control, DC capacitor voltage balance, Voltage compensation
PDF Full Text Request
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