【摘要】：與單饋入直流輸電相比,多饋入直流(Multi-infeed Direct Current,MIDC)輸電系統(tǒng)具有更大的輸送容量和更靈活的運(yùn)行方式。然而由于各直流逆變站電氣距離較近,交流系統(tǒng)的一個(gè)擾動(dòng)可能誘發(fā)多回直流發(fā)生換相失敗,一旦一回或多回直流的換相失敗得不到有效控制,出現(xiàn)單極或雙極功率停運(yùn),則將導(dǎo)致直流傳輸功率大幅度下降,繼而影響電網(wǎng)的頻率穩(wěn)定,電網(wǎng)的安全穩(wěn)定運(yùn)行受到嚴(yán)重影響。因此,采用適當(dāng)?shù)目刂撇呗砸种芃IDC輸電系統(tǒng)的后續(xù)換相失敗具有重要意義。基于MIDC輸電系統(tǒng)換相失敗已有的國內(nèi)外研究內(nèi)容,本文首先對(duì)換相失敗的機(jī)理進(jìn)行了深入地研究,通過在高壓側(cè)、低壓側(cè)換流閥設(shè)置不同時(shí)刻故障來研究換相失敗的故障特性。然后對(duì)換相失敗的影響因素進(jìn)行了全面地分析,將多饋入短路比(Multi-infeed Interaction Short Circuit Ratio,MISCR)、諧波及交流系統(tǒng)故障對(duì)換相失敗的影響進(jìn)行了數(shù)學(xué)模型推導(dǎo)及Matlab驗(yàn)證。同時(shí)將換相失敗的影響分為換流母線電壓降落故障分量及換相失敗電流分量的作用,對(duì)MIDC輸電系統(tǒng)換相失敗相互影響關(guān)系進(jìn)行了詳細(xì)的數(shù)學(xué)關(guān)系推導(dǎo)。最后提出了電壓補(bǔ)償式變斜率低壓限流(Voltage Dependent Current Order Limiter,VDCOL)的抑制措施,通過PSCAD/EMTDC仿真驗(yàn)證得出增加該控制策略后MIDC輸電系統(tǒng)的暫態(tài)特性得到改善,換相失敗的概率也明顯降低。在該基礎(chǔ)上,提出了選擇性電壓補(bǔ)償式變斜率VDCOL協(xié)調(diào)控制策略,即只在嚴(yán)重故障時(shí)切入補(bǔ)償系數(shù)K值,在正常及輕微故障情況下K值為0。搭建上海電網(wǎng)4回多饋入直流輸電系統(tǒng)的PSCAD/EMTDC仿真模型并進(jìn)行仿真研究,研究表明,該控制策略在減少直流系統(tǒng)發(fā)生換相失敗概率的同時(shí)也在一定程度上提高了系統(tǒng)的恢復(fù)性能,防止發(fā)生因直流系統(tǒng)恢復(fù)速度過慢導(dǎo)致的交流系統(tǒng)功角不平衡引發(fā)后續(xù)的換相失敗。
[Abstract]:Compared with single feed DC transmission system, Multi-infeed Direct current MIDC (MIDC) transmission system has larger transmission capacity and more flexible operation mode. However, because of the close electric distance of each DC inverter station, a disturbance of AC system may induce commutation failure of multiple DC. Once the commutation failure of one or more DC can not be effectively controlled, the unipolar or bipolar power outage occurs. The DC transmission power will be greatly reduced, and the frequency stability of the power grid will be affected, and the safe and stable operation of the power grid will be seriously affected. Therefore, it is important to adopt appropriate control strategy to suppress the subsequent commutation failure of MIDC transmission system. Based on the existing research contents of commutation failure of MIDC transmission system at home and abroad, the mechanism of commutation failure is deeply studied in this paper, and the fault characteristics of commutation failure are studied by setting the commutation valve at different times on the high voltage side and the low pressure side. Then, the influencing factors of commutation failure are analyzed, and the influence of multi-infeed interaction short circuit MISCR, harmonic and AC system fault on commutation failure is deduced and verified by Matlab. At the same time, the effect of commutation failure is divided into two parts: the fault component of commutation bus voltage and the component of commutation failure current, and the mathematical relation between commutation failure and commutation failure is deduced in detail. Finally, a voltage dependent current order limiter-VDCOL (Voltage dependent current order) suppression method is proposed. The simulation results of PSCAD / EMTDC show that the transient characteristics of MIDC transmission system are improved and the probability of commutation failure is obviously reduced by increasing the control strategy. On this basis, a coordinated control strategy of variable slope VDCOL with selective voltage compensation is proposed, that is, the compensation coefficient K is only cut in serious faults, and the K value is 0 in normal and slight fault cases. The PSCAD / EMTDC simulation model of Shanghai power grid 4 times multiple feed in DC transmission system is built and simulated. The research shows that the control strategy not only reduces the probability of commutation failure in DC system, but also improves the recovery performance of the system to a certain extent. To prevent the subsequent commutation failure caused by the unbalanced power angle of AC system caused by the slow recovery speed of DC system.
【學(xué)位授予單位】：華北電力大學(xué)(北京)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TM721.1

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本文編號(hào)：2121001