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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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 paper presents the dynamic model and control schemes of a variable speed pitch wind turbine with permanent magnet synchronous generator (PMSG). The model includes a PMSG model, a pitch-angled controlled wind turbi...
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The paper presents the dynamic model and control schemes of a variable speed pitch wind turbine with permanent magnet synchronous generator (PMSG). The model includes a PMSG model, a pitch-angled controlled wind turbine model and a drive train model. The drive train model uses one-mass model to represent the mechanical characteristics of the generator set. The generator model is established in the dq-synchronous rotating reference frame. The wind turbine model details the mechanism of variable speed operation of the turbine by a pitch control. The control schemes in the paper include a pitch angle control for the wind turbine and a speed control for the generator. The pitch angle control uses wind speeds and electric power output as the input signals to ensure normal operation in high wind speed. The speed control is realized through field orientation where the d-axis current is set to zero and the q-axis current is used to control the rotational speed of the generator according to the variation of wind speed. In order to verify the presented model and the control strategy, simulations with MATLAB/Simulink software have been conducted. Simulation results prove the validity of the model and the control schemes.
Three design schemes of compensation currents for D-STATCOM in delta connection used for unbalanced load compensation are introduced. They are the schemes based on compensation principle of admittance, no zero sequenc...
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Three design schemes of compensation currents for D-STATCOM in delta connection used for unbalanced load compensation are introduced. They are the schemes based on compensation principle of admittance, no zero sequence component design and an optional design method of maximum minimizing phase current. Comparisons are made considering technical indexes and engineering significance among the proposed three schemes. In serious unbalanced operating conditions, the obvious difference in amplitude among the compensation currents in three phases may lead to one or two phase overloading and the compensation capability is restricted. The optional design makes the compensation currents in three phases to be equal or close to each other as possible as it can, which is helpful to ensure the D-STATCOM having high-usage and desirable compensation effect. Similar performance can be obtained to some extent with the simpler scheme of no zero sequence component design.
In the paper multiterminal voltage source converter based HVDC (VSC-HVDC) is proposed to interconnect wind farms to AC grids. The method highlights the control at the level of wind generator cluster that comprises sev...
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In the paper multiterminal voltage source converter based HVDC (VSC-HVDC) is proposed to interconnect wind farms to AC grids. The method highlights the control at the level of wind generator cluster that comprises several permanent magnet synchronous generators without the primary converters on themselves. For the cluster control, active and reactive power decoupling scheme is applied to adjust the rotational speed of the cluster according to wind speed. The paper studies the schemes to control grid side converter based on the philosophy of linear decoupling control, which aims to control the DC voltage as well as the reactive power of VSC-HVDC. In the proposed control scheme, the two goals are achieved by controlling the q- and rf-axis components of the grid's fundamental current. Simulation has been performed using engineering software Matlab/Simulink to verify the interconnection method and validate the control scheme as well.
More and more IEDs have been commissioned in powersystems, such as digital relays, PMUs, metering and control devices, fault recorders and so on. Once there is a disturbance (for example, fault, low-frequency oscilla...
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More and more IEDs have been commissioned in powersystems, such as digital relays, PMUs, metering and control devices, fault recorders and so on. Once there is a disturbance (for example, fault, low-frequency oscillation, etc.), large amount of information will pour into the control center. Therefore, how to identify the disturbance and then take corresponding countermeasures is crucial for powersystemsecurity and reliability. A multi-layer disturbance processing system based on multiple information sources is proposed in this paper. Firstly, the characteristics of different kinds of information sources, including PMUs, RTUs, digital relays and fault recorders, are analyzed. Secondly, according to the arrival times of the information, the framework and functions of multi-layer fault diagnosis system is presented in detail. After a disturbance occurs, the suggested system could realize disturbance identification, fault element diagnosis and detailed post-fault analysis in succession at different time frames with the information coming, which fits the needs of operators well.
In the neutral ungrounded system, potential transformer (PT) ferro-magnetic resonance is a kind of interior overvoltage which is frequently appears and creates most of the accidents. Whether the elimination measures a...
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In the neutral ungrounded system, potential transformer (PT) ferro-magnetic resonance is a kind of interior overvoltage which is frequently appears and creates most of the accidents. Whether the elimination measures are reasonable and effective or not affects the security and stability of the powersystem directly. Fundamental research has been done on the resonance region changeable situation and the characteristics of each resonance region under different system parameter and PT saturation characteristics. According to the occurring principle of PT ferromagnetic resonance and the characteristics, a novel effective controllable damping device is designed, which will change the correlative parameter that lead to resonance to make the circuit parameter of the system get out of the resonance area to eliminate the resonance. The accuracy of the fundamental analysis and the effectiveness of the elimination measure have been verified by the digital simulation based on EMTDC/PSCAD and by the high voltage propotype experiment.
With rising electricity loading in developing country, measuring capacity of pumped-storage station (P-S station) is becoming more critical. This paper tries to establish mathematic model on obtaining capacity of P-S ...
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With rising electricity loading in developing country, measuring capacity of pumped-storage station (P-S station) is becoming more critical. This paper tries to establish mathematic model on obtaining capacity of P-S station for maximum cost sayings. The paper first deducts the relationship between capacity of P-S station, peak load and the vale load by simulating cost curve of thermoelectric unit, and then deducts the formula for calculating optimal capacity of P-S station. Based upon these findings and the load curve, the paper then develops the curve to describe the relationship between volume of generated electricity and capacity of the P-S station and provides the solution for obtaining optimal capacity of the P-S station. Finally, the paper discusses the impact of selecting initial solution or certain iterative solution on iterative speed and suggests the direction for further research.
In this paper, a new method of hybrid non-linear state estimation with PMU is proposed. Firstly, the voltage phasor measurements are transformed into indirect equivalent branch current measurements, with which the con...
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In this paper, a new method of hybrid non-linear state estimation with PMU is proposed. Firstly, the voltage phasor measurements are transformed into indirect equivalent branch current measurements, with which the conventional state estimator takes the impact of PMU into consideration. Secondly, the indirect measurement errors caused by the measurement transforming are analyzed and calculated in detail. Thirdly, the accuracy of hybrid estimator is analyzed in the paper. The simulation results show that the proposed method improves the accuracy of estimator and the convergence speed also.
Aimed at the necessary on the automatic detection level in unattended substation, a new method which monitoring and diagnosis the high-voltage (HV) power equipment running state based on image processing is put forwar...
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