The modulation is the key technique for multilevel inverter, an improved line voltage modulation strategy is proposed, which is based on the nonorthogonal AX coordinates SVPWM and makes some further comprehensive anal...
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The modulation is the key technique for multilevel inverter, an improved line voltage modulation strategy is proposed, which is based on the nonorthogonal AX coordinates SVPWM and makes some further comprehensive analysis on the original conclusions. The advantage of the strategy is that it has clearer physical meaning and more simple form. One improved three phases balance modulation algorithm for the single phase is got by the proper arrangement of output vectors taking advantage of the basic circuit theory;and then the generalized modulation strategy is deduced, which is suitable for three phases unbalance situation by the consideration of pulse area equal principle. This proposed modulation algorithm has simple format and clear physical concept, in addition, it's easy for the digital implementation. The digital simulations and experiments are presented to verify the conclusions.
In recent years, several cases of mal-operation of transformer differential protection due to sympathetic inrush appeared, but the problem how to distinguish the sympathetic inrush has not been resolved yet. Based on ...
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In recent years, several cases of mal-operation of transformer differential protection due to sympathetic inrush appeared, but the problem how to distinguish the sympathetic inrush has not been resolved yet. Based on the synchronization measurement of the change of line current and differential current, an algorithm of distinguishing the sympathetic inrush and blocking the differential protection was put forward, which is applicable to two paralleled wye-delta connected transformers. Under the condition that the current transformer saturated, a method based on the mathematical morphology to identify the synchronization of the change of line current and differential current was proposed. Adopting the abrupt change of line current in the other side as auxiliary criterion, this algorithm could distinguish the sympathetic inrush, and internal, external fault during sympathetic inrush occurring. Simulation results validate its feasibility and reliability.
A power quality evaluation method combining extenics and AHP(Analytic Hierarchy Process) is presented. Three matter-element models are set based on power quality analysis using matter -element theory of extenics, and ...
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A power quality evaluation method combining extenics and AHP(Analytic Hierarchy Process) is presented. Three matter-element models are set based on power quality analysis using matter -element theory of extenics, and quantified to form relationship matrix using relation-function theory of extenics. The target weights are figured out using AHP. The final quantitative grade of the power quality is calculated based on relation-matrix and target weights. The power quality level of synthetic evaluation is obtained by combining the relationship matrix and the target weights. As an example, the power quality of PCC(the Point of Common Coupling) is evaluated, which shows that, the proposed method can evaluate power quality quantitatively and qualitatively and distinguishes different power quality levels effectively.
On basis of transformer loop equation, a novel principle of transformer protection using equivalent instantaneous leakage inductance is presented. The principle is independent of short-circuit reactance and leakage in...
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On basis of transformer loop equation, a novel principle of transformer protection using equivalent instantaneous leakage inductance is presented. The principle is independent of short-circuit reactance and leakage inductance of each side can be effectively monitored in real time. Therefore, sensitivity and reliability of transformer protection can both be improved by calculating equivalent instantaneous leakage inductance. The principle is also applicable for three-winding transformer. dynamic testing results verify this scheme that has been stable during inrush current and is able to reliably and quickly clear internal fault even fault is light.
Cascading trips caused by flow transferring are the crucial reason of a lot of well-known blackouts. It threatens the security and reliability of powersystems severely. A wide area measurement system (WAMS) based con...
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Cascading trips caused by flow transferring are the crucial reason of a lot of well-known blackouts. It threatens the security and reliability of powersystems severely. A wide area measurement system (WAMS) based control strategy to prevent cascading trips caused by flow transferring is presented. By analysis of the relationship of node injection current and branch current of network, the principle of control nodes selection of load shedding and generator tripping and the calculation method of control quantity are proposed. The corresponding of the control strategy is also given. The calculation method of branch current before the control action during powersystemdynamic process is given. The simulation results of 10-generator 39-bus New England system show that the control strategy can prevent cascading trips effectively.
The researches on measurement-based load modeling have been continued for more than twenty years in China. However, since lacking of system measured data of major disturbance, it is doubtful for load model generalizat...
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For accurate simulation of voltage stress on secondary circuits caused by very fast transient over-voltage in gas insulated substation (GIS), a sophisticated modeling of potential and current transformers (PT/CT) is o...
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For accurate simulation of voltage stress on secondary circuits caused by very fast transient over-voltage in gas insulated substation (GIS), a sophisticated modeling of potential and current transformers (PT/CT) is of vital importance. A new method is proposed to setup high frequency two-port circuit model of PT based on scattering parameters. First, the scattering parameters of PT are transformed in to Y-parameters and equivalent 'π' circuit model could be established. Second, vector fitting method is used to approximate admittances of equivalent 'π' circuit model by rational functions. At last, a circuit synthesis method for rational functions is applied to build circuit model. The simulation and measurement results are presented, which confirmed validity of the proposed model. The proposed method is effective and general, and overcomes the limitation of former methods. The model setup by this method can make simulation more accurate of conductive coupling through PT/CT in GIS.
Resonance mechanism is one of the theories that interpret powersystem low frequency oscillation. According to the resonance mechanism, power disturbance of prime mover can arouse powersystem forced low frequency osc...
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Resonance mechanism is one of the theories that interpret powersystem low frequency oscillation. According to the resonance mechanism, power disturbance of prime mover can arouse powersystem forced low frequency oscillations. Therefore, the causes of turbine power disturbance were analyzed. The coupling model between thermodynamicsystem of plant and powersystem was set up by MATLAB. The possibility of combustion ratio of boiler and control valve of governing system disturbance inducing the variation of turbine power was researched in detail. The simulation results indicate that powersystem low frequency oscillations of resonance mechanism might be caused by the disturbance of control valve, when it's frequency is consistent with or close to powersystem natural oscillations frequency. Because of the biggish inertia of boiler, the disturbance of combustion ratio cannot invoke powersystem low frequency oscillation of resonance mechanism.
The lack of quantitative stability analysis software for powersystem is one of the main reasons for losing good chance to implement the emergency control and even finally resulting in the large outage. Recently, the ...
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The lack of quantitative stability analysis software for powersystem is one of the main reasons for losing good chance to implement the emergency control and even finally resulting in the large outage. Recently, the rapidly developing wide area measurement system (WAMS) gives a new way for quick on-line quantitative transient stability assessment. Starting with the single machine energy function, the relationship between the variation rate of transient unbalance energy and multi-swing stability was analyzed in detail, and the corresponding characteristic of the variation rate of transient energy was proved. Then, a new multi-swing stability assessment criterion based on WAMS was proposed. Numerical simulations were conducted on 6-machine 22-bus system of China electric power research institute to demonstrate the effectiveness of this criterion.
Cascading trips caused by flow transferring are the crucial causation of a lot of well-known blackouts. It severely threatens the security and reliability of powersystems. Flow transferring relativity factor (FTRF) i...
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Cascading trips caused by flow transferring are the crucial causation of a lot of well-known blackouts. It severely threatens the security and reliability of powersystems. Flow transferring relativity factor (FTRF) is extended from single branch removal event to multi-branches removal event. According to refraction and reflection process of flow transferring, the calculation formula of FTRF for multi-branches chain removal event is deduced. Moreover, by using the relationship of node injection currents and branch currents, a method of post-fault branch current estimation and a flow transferring identification algorithm based on WAMS to distinguish flow transferring in transient period is presented. The simulation results of 10-generator 39-bus New England system show that the proposed estimation method and the identification algorithm work well.
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