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Research On Parameters Optimization Of The Main Circuits And Controllers In HVDC Systems

Posted on:2008-06-15Degree:DoctorType:Dissertation
Country:ChinaCandidate:F Y YangFull Text:PDF
GTID:1102360242464335Subject:Power system and its automation
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Localization of designing techniques and equipments manufacturing for HVDC projects in China, shows great significance in enhancing our strength in HVDC technology. Relevant research is carried out on parameters optimization of the main circuits and controllers in HVDC systems. The main works are organized as follows:(1) Transient responses of typical HVDC transmission systems are studied. Functions of the main controllers for a general HVDC system, together with the cooperation among the controllers, are analyzed. With different DC tie-line types for connecting AC systems, the transient responses at different faults are simulated and compared. The three studied HVDC models are with long-distance overhead line, submarine cable, and no DC line (i.e. back-to-back HVDC systems), respectively. The initiation of the commutation failure and its recovery characteristics when AC faults occur are studied specially. Also, when a DC short occurs, the HVDC controllers' action and the DC line's overcurrent level are studied.(2) A method for PI parameters optimization of HVDC controllers is proposed based on the system stability and dynamic performance criteria. The proposed method has the merit of global optimum, and we name the method optimization method based on parameters feasible region's division. Take the constant current (CC) control for example. According to the open-loop transfer function of the control system, the feasible region for PI parameters optimization is attained satisfying the system stability. Then the obtained optimization set is divided with different steps of Kp and Ki, respectively, with different grid schemes generated. With each optimization set corresponding to a certain grid size, the optimal PI parameters are obtained corresponding to the minimum of objective function. The adopted objective function is based on ITAE (integral of time multiplied by the absolute value of the error), one of the synthetic performance indexes for evaluating the controller's performance. The controller with the PI optimum is verified robust.(3) Parameters optimization of the main circuits is investigated preliminarily. Influences of the converter transformer's short circuit impedance uk on the factors such as valve surge current, reactive power consumption of the converters, and total cost of the converter are analyzed, and the conclusion is drawn that the short circuit impedance can be optimized in terms of the thyristor valve surge current. Next, an integrated expression is deduced for selecting the reactance of the smoothing reactor, with the main restrictions on the smoothing reactance considered. The concept of current slope factor Si is introduced, and the meaning of Si is analyzed for signifying the effect that the smoothing reactor restrains the fault current's rising. Finally, the validity of the proposed method for optimizing the both main circuit parameters is verified.(4) Effects of harmonics restraint of the filtering equipments at DC side are analyzed. And then the parameters optimization of DC filters is studied. The criterion for DC harmonic level is introduced, and the influences of factors such as smoothing reactor's layout, stray capacitor, and neutral bus capacitor, on DC harmonic level are analyzed. The trend that the equivalent disturbing current Ieq varies with the neutral bus capacitance is revealed, and the principle of determining the neutral bus capacitance is proposed. Affects of DC filter's key parameters on its filtering effect are analyzed, and optimization of the DC filters is studied preliminarily.(5) The principle for commutation capacitance optimization and its realization are proposed for an HVDC system applying CCC (Capacitor Commutated Converter) technology. The peak-value expression of the valve voltage is deduced, and the influence of the commutation capacitor's size on the peak valve voltage is analyzed. From the analysis, the principle for commutation capacitance optimization is revealed, together with the principle's realization in practical projects. A method for measuring the inverter's real extinction angleγreal and apparent extinction angleγapp is suggested. Both the steady-state characteristics and the transient response characteristics of the CCC-HVDC system are studied, which are compared with those of LCC-HVDC system respectively. The economic analysis is carried out when the CCC converters are applied in HVDC projects, which reveals the main application of CCC technology.
Keywords/Search Tags:HVDC, Localization, Steady-state response, Transient response, Parameters optimization, PI parameters, HVDC controller, Stability, Main circuit parameters, DC filter, Neutral bus capacitor, Capacitor Commutated Converter, Commutation Capacitor
PDF Full Text Request
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