Abstract
Considering the advantages that dynamic reactive power (var) equipment (such as synchronous condensers (SCs), which can control var independently and improve voltage stability), SCs are widely used in AC/DC hybrid power grid to provide emergency var and voltage support. In order to evaluate the dynamic var reserve capacity of SCs and analyze the influence of SCs on the operation characteristics of power system, a model with double-infeed line-commutated converter-based high-voltage direct currents (LCC-HVDCs) and SCs is established. Through theoretical derivation and PSCAD/EMTDC simulation, the effects of SCs on the operation characteristics of double-infeed LCC-HVDCs networks are studied. Then, the non-smooth voltage waveform of electromagnetic transient simulation is approximately transformed into smooth waveform by data fitting method. Finally, the processed voltage waveform is searched step by step to explore the boundary of voltage safety region to determine the dynamic var reserve capacity of SCs. The numerical results show that SCs can enlarge the voltage security region of the direct current (DC) subsystem, thus effectively improving the steady-state and transient security level of the double-infeed LCC-HVDCs networks.
Highlights
In China, the renewable energy represented by wind energy and photovoltaic is mainly distributed in the western region of China, while the load is mainly distributed in the southeast region
1: Carry out the simulation in PSCAD/EMTDC, and simulation step size is set to 500 microseconds; 2: Collect the simulation information; 3: Increase the var output of the SCs and calculate the sensitivity coefficient K; 4: With the help of data fitting method based on improved Powell algorithm, an approximate smooth voltage curve is used to replace the original electromagnetic transient simulation curve; 5: Combined with sensitivity K, step search algorithm is carried out to obtain the dynamic var reserve capacity satisfying the voltage critical range (21); 6: The results are compared with those of transient stability-constrained optimal power flow (TSCOPF); end
In order to overcome the shortcomings of high computational complexity and low solution accuracy of traditional dynamic var reserve evaluation methods, in this paper, a novel method to obtain dynamic var reserve capacity of SCs in multi-infeed LCC-HVDCs is proposed
Summary
In China, the renewable energy represented by wind energy and photovoltaic is mainly distributed in the western region of China, while the load is mainly distributed in the southeast region. In order to effectively improve the safe operation level, the power grid topology was improved to carry out the commutation failure predictive control [3]; a new topology based on fixed capacitor and controllable capacitor commutation converter is proposed in [4]; another widely used measure is adding dynamic var compensation equipment such as static var compensator (SVC), static var generator (SVG), and synchronous condensers at the receiving end [5,6], which can meet the var demand of converter station and improve the voltage recovery speed; some valuable studies calculate the voltage security region to guarantee the voltage stability margin under N-1 faults [7,8,9] proposes a novel method to discriminate the critical commutation failure region of multi-infeed HVDCs system and the critical failure impedance boundaries on topology diagram can be delimited by examining each bus in the AC system; some other valuable works in the literature [10,11].
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