A three-phase unbalanced system will reduce mechanical and electrical energy interaction and thus, to some extent, inhibit subsynchronous resonance (SSR). Based on this principle, a compensation method using a single-...
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A three-phase unbalanced system will reduce mechanical and electrical energy interaction and thus, to some extent, inhibit subsynchronous resonance (SSR). Based on this principle, a compensation method using a single-phase static synchronous series compensator (SSSC) is proposed. In this method, only one phase employs an SSSC to replace part of the fixed series capacitor, while the other two phases have fixed series compensation (FSC). By controlling the SSSC, the three-phase reactance at power frequency is balanced, while at sub-synchronous frequencies, the system is unbalanced and thus inhibits SSO. A single-phase SSSC model based on a cascaded H bridge topology is built for time-domain simulations. The damping effect and the minimum degree of compensation required from the SSSC are analyzed by transient simulations. Simulation results show the method can effectively restrain SSO and has little effect on the three-phase voltage unbalance factor. Compared with employing SSSC in all three phases, this method is more economical.
In this paper, powersystem electromagnetic and electromechanical transient hybrid real-time simulation technology is expounded in details, which has advantages of the electromagnetic transient simulation program and ...
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In this paper, powersystem electromagnetic and electromechanical transient hybrid real-time simulation technology is expounded in details, which has advantages of the electromagnetic transient simulation program and electromechanical one. The more details needed to analyze the dynamic characteristics of powersystems are provided by this hybrid simulation technology, and the scale of powersystem simulated is not limited in the hybrid simulation program. The hybrid simulation program is applied to analyze the powersystem subsynchronous oscillation problem occurred in a power plant with 4 turbine generators located in the northwestern China. According to the simulation results, it is clear that the stability of generators is threatened by the subsynchronous oscillations caused by capacitor series compensation in the transmission line connecting the power plant and the load center system. In meantime, the effectiveness of the countermeasure is validated simultaneously by the hybrid simulation results.
Wind power penetration to powersystems is increasing rapidly in the recent years due to its environmental benefit, while wind power fluctuation also brings some problems to powersystem operation which impacts the tr...
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ISBN:
(纸本)9781424480807
Wind power penetration to powersystems is increasing rapidly in the recent years due to its environmental benefit, while wind power fluctuation also brings some problems to powersystem operation which impacts the transmission company's willingness to accept wind power. The most serious conflict influencing wind power development is that the currently adopted price of wind power on-grid does not take this fluctuation or the impact on the system operation into account. Currently, quotas and enforcing access is broadly used in wind power regulation. It is now required that all wind power output should be accepted by the grid, and is rewarded with a guided rate. But with the increase of wind power penetration to power grid, a more effective price regulation to wind power should be set up with wind output uncertainty into account. This paper takes wind farms in different areas in China as the research objects and uses accounting cost analysis approach to calculate wind power costs, which enables the wind farms in different areas to get the same rate of return on investment as that of thermal power plants. These tariffs will be derived as a basic price for the reference by the power grid then. The basic wind power prices are multiplied by a penalty factor which is an innovative as the final prices paid to the wind farms. The penalty factor is related to the accuracy of wind power output. If the accuracy of the wind farm output is higher than that of the regional average one, the penalty factor will be greater than one, so that the really paid wind power price is higher than the base value and the income of the wind farm will be increased, otherwise the earnings will be reduced. To illustrate the problem, an example is given. The use of this penalty factor will eventually help stimulate wind farms to improve the accuracy of wind power output, and improve the stable operation of the systems with large wind power penetration, and promote the sustainable development of wind
A new principle of single-ended fault location is presented. It is proposed to carry out the correct fault distance by comparing the reverse traveling waves break time at the fault point, after transition resistance i...
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A new principle of single-ended fault location is presented. It is proposed to carry out the correct fault distance by comparing the reverse traveling waves break time at the fault point, after transition resistance is calculated approximately. Distortionless model is employed to deduce the single-ended electric quantities to the verification point. The judging criterion for fault point verification and algorithm for the transition resistance calculation are introduced in detail, after reviewing the relationship between fault branch currents and fault current traveling waves. In this paper, the traveling wave propagation velocity and load current affect the calculation accuracy, will not affect the result of fault location. The simulation and calculation results by ATP and MATLAB confirm sensitivity and reliability of the principle.
Wind energy has drawn worldwide attention. Because of simple structure, high efficiency, stable operation and other inherent advantages, variable speed constant frequency (VSCF) direct-drive wind power generation syst...
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Wind energy has drawn worldwide attention. Because of simple structure, high efficiency, stable operation and other inherent advantages, variable speed constant frequency (VSCF) direct-drive wind power generation system using permanent magnetic synchronous generator(PMSG) is the development trend and one of the focuses of wind power generation system, on which this paper researches through its converter's topological. To be the interface between PMSG and the grid, typical converter topology structure of direct-driven wind powersystem with PMSG are analyzed, including the diode rectifier + DC to DC converter + inverter, and the back to back double PWM converter. The topological characteristics and applications of some high-voltage, high-power converters are introduced in detail, including Diode-clamped multi-level converter, Cascaded H-bridge multilevel converter and Flyingcapacitor multilevel converter. Their implementations, working principles, advantages and disadvantages are discussed and compared. Judging from the current situation, for the advantages of low-cost and simple control strategy, diodeclamped three-level PWM converter is the hot spot of current converting technique study for direct-driven wind powersystem.
Microgrid technologies are highly developed in low voltage networks, improving the power supply reliability and energy efficiency. Therefore, in this paper, the concept, including the configuration, principle and oper...
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Microgrid technologies are highly developed in low voltage networks, improving the power supply reliability and energy efficiency. Therefore, in this paper, the concept, including the configuration, principle and operation of microgrid, will be specified, comparing the microgrid with the prior distributed generation. Additionally, in order to justify the feasibility, the economical benefit analysis of the application will be identified via some methodological viewpoints which are advised to regulate the operation of the microgrid in an economical approach. At the end, the costs, benefit and the share of the microgrid and micro-generation are discussed by analyzing the test case.
In this paper, a static synchronous series compensator (SSSC) combined with a fixed capacitor, which is called hybrid series compensation (HSC), is proposed to avoid subsynchronous oscillation (SSO) in a series compen...
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In this paper, a static synchronous series compensator (SSSC) combined with a fixed capacitor, which is called hybrid series compensation (HSC), is proposed to avoid subsynchronous oscillation (SSO) in a series compensated transmission system and its characteristic is studied based on IEEE first benchmark model for SSO analysis. By employing the complex torque coefficient method and time-domain simulation, the performance of HSC on damping SSO is analyzed in the aspects of component proportion of HSC, installation location and control strategy mode. A supplementary sub-synchronous damping controller (SSDC) for SSSC is also designed to increase the damping performance of HSC at critical oscillation frequency.
A three-phase unbalanced system will reduce mechanical and electrical energy interaction and thus, to some extent, inhibit subsynchronous resonance (SSR). Based on this principle, a compensation method using a single-...
详细信息
A three-phase unbalanced system will reduce mechanical and electrical energy interaction and thus, to some extent, inhibit subsynchronous resonance (SSR). Based on this principle, a compensation method using a single-phase static synchronous series compensator (SSSC) is proposed. In this method, only one phase employs an SSSC to replace part of the fixed series capacitor, while the other two phases have fixed series compensation (FSC). By controlling the SSSC, the three-phase reactance at power frequency is balanced, while at sub-synchronous frequencies, the system is unbalanced and thus inhibits SSO. A single-phase SSSC model based on a cascaded H bridge topology is built for time-domain simulations. The damping effect and the minimum degree of compensation required from the SSSC are analyzed by transient simulations. Simulation results show the method can effectively restrain SSO and has little effect on the three-phase voltage unbalance factor. Compared with employing SSSC in all three phases, this method is more economical.
To avoid the mal-operation of transformer differential protection when external fault occurs with current transformer (CT) saturation, a new algorithm based on the mathematical morphology is put forward in this paper....
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To avoid the mal-operation of transformer differential protection when external fault occurs with current transformer (CT) saturation, a new algorithm based on the mathematical morphology is put forward in this paper. Unlike the conventional Time Differential Method, the new algorithm only needs detecting the instant of fault occurring, while the instant of differential current appearance is no more needed. A new current waveform is obtained by a symmetrical transformation of initial part of differential current after fault occurrence, and then its characteristic is exacted by morphological gradient. In the case of CT serious saturation, a discrimination of external fault and internal fault can be clearly made by this algorithm. In addition, analysis shows that the new algorithm based on the mathematical morphology could also be applied for the identification of transferring fault (external fault transfers to internal fault). Simulation results of MATLAB validate its feasibility and reliability.
With the expansion of the powersystems, DC power transmission has been increasingly applied in interconnection of grids. The determination of Available Transfer Capability (ATC) for the AC/DC transmission systems is ...
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With the expansion of the powersystems, DC power transmission has been increasingly applied in interconnection of grids. The determination of Available Transfer Capability (ATC) for the AC/DC transmission systems is significant to the system planning and operation. So far, most studies have been focused on ATC determination for AC transmission systems, few are on the AC/DC system ATC determination. In this paper, the ATC determination model for the AC/DC systems is proposed. Multi-terminal DC (MTDC) system is considered in ATC computation model. Conventionally, the power injection variations are determined by load variations and generation dispatch, both of them are nonlinear. To model these nonlinear variations, an alternate iterative continuation power flow (CPF) method with multiple load variations and generation economic dispatch patterns is presented to solve the proposed model. The MTDC system configurations, the converter control strategies and the transformer's tap adjustment strategies are incorporated to this modified CPF algorithm. The modified IEEE 30-bus test system is used to verify the presented approach.
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