【摘要】：針對(duì)當(dāng)前含分布式電源(DER)的有源配電網(wǎng)的結(jié)構(gòu)特點(diǎn)與發(fā)展需求,DER并網(wǎng)運(yùn)行在提高電力系統(tǒng)的穩(wěn)定性與靈活性,改善電能質(zhì)量的同時(shí),也給電網(wǎng)帶來(lái)諸如電壓暫降、繼電保護(hù)誤動(dòng)等新的問(wèn)題,尤其是電力系統(tǒng)的非計(jì)劃孤島運(yùn)行,有可能嚴(yán)重影響電力系統(tǒng)運(yùn)行的穩(wěn)定性,威脅電力設(shè)備安全甚至人身安全。因此,對(duì)于無(wú)法維持自身穩(wěn)定的非計(jì)劃孤島狀態(tài),必須進(jìn)行有效的孤島保護(hù),將DER切離配電網(wǎng),盡可能縮短孤島運(yùn)行時(shí)間,避免引起一系列的安全隱患。而有效的孤島保護(hù)依賴于快速可靠的孤島檢測(cè),就目前常見的孤島檢測(cè)方法,均存在一定的缺陷與局限性,其中基于通信的遠(yuǎn)程檢測(cè)法成本較高,經(jīng)濟(jì)性差,基于本地電氣突變量的被動(dòng)檢測(cè)法在孤島系統(tǒng)內(nèi)功率匹配程度較高時(shí)存在檢測(cè)盲區(qū),基于向電網(wǎng)注入擾動(dòng)信號(hào)的主動(dòng)檢測(cè)法對(duì)電能質(zhì)量有一定的影響。 本文基于對(duì)并網(wǎng)逆變器PQ恒功率輸出控制模式的研究分析,建立額定頻率下的并聯(lián)RLC恒功率負(fù)荷模型,理論推導(dǎo)了DER并網(wǎng)與孤島運(yùn)行時(shí)的系統(tǒng)電壓、頻率變化特征及其受不平衡功率的影響,結(jié)果發(fā)現(xiàn)孤島系統(tǒng)內(nèi)的電壓、頻率變化與本地的負(fù)荷特性主要相關(guān),這與具有恒定外特性的系統(tǒng)電網(wǎng)迥然不同。孤島后的電壓幅值變化主要由不平衡有功(ΔP)決定,ΔP越大,則電壓幅值變化越大。孤島后的頻率變化受ΔP的影響較小,主要由不平衡無(wú)功(ΔQ)決定。對(duì)于有功匹配程度較高(ΔP較小)的情形,電壓幅值變化較小,難以體現(xiàn)孤島特征,而此時(shí)的ΔQ對(duì)孤島系統(tǒng)頻率的決定性影響依然顯著。同時(shí)頻率變化所帶來(lái)的電壓相位變化較之本身卻更為突出,因此提出了基于廣域相位比較的孤島檢測(cè)方法,由配電網(wǎng)母線側(cè)與DER并網(wǎng)側(cè)之間的電壓相位差構(gòu)成孤島檢測(cè)判據(jù),兩側(cè)電壓相位的同步測(cè)量與計(jì)算由饋線自動(dòng)化終端(FTU)完成,并經(jīng)快速通信系統(tǒng)實(shí)現(xiàn)信息交換。 通過(guò)配置于配電網(wǎng)母線側(cè)與DER并網(wǎng)側(cè)的FTU,實(shí)現(xiàn)同步相量測(cè)量,實(shí)時(shí)測(cè)量計(jì)算兩側(cè)電壓相位θs(t)與θDER(t),配電網(wǎng)側(cè)FTU將帶時(shí)標(biāo)的θs(t)經(jīng)快速通信系統(tǒng)傳輸至DER并網(wǎng)側(cè)FTU,由此FTU進(jìn)行兩側(cè)帶同一時(shí)標(biāo)的電壓相位作差比較,并考慮一定的測(cè)量計(jì)算與通信誤差,與設(shè)定的孤島判定閾值θz比較,完成孤島檢測(cè)。DER并網(wǎng)側(cè)FTU根據(jù)檢測(cè)結(jié)果啟動(dòng)孤島保護(hù),斷開DER并網(wǎng)開關(guān),使其停止對(duì)外輸出功率。建立基于Matlab的有源配電網(wǎng)孤島檢測(cè)仿真模型,仿真分析了DER并網(wǎng)與孤島運(yùn)行時(shí)的系統(tǒng)電壓、頻率及相位變化特征,排除了本地負(fù)荷突變與配網(wǎng)線路故障對(duì)孤島檢測(cè)的影響,同時(shí)基于本地負(fù)荷特性,充分考慮了不平衡功率差異對(duì)孤島檢測(cè)的影響。實(shí)驗(yàn)結(jié)果與理論分析相符,驗(yàn)證了本方法的正確性與適用性。
[Abstract]:In view of the structural characteristics and development requirements of active distribution network with distributed power supply (DER), Der is used to improve the stability and flexibility of power system and improve the power quality, at the same time, it also brings voltage sag to the power network. Some new problems, such as maloperation of relay protection, especially the unplanned island operation of power system, may seriously affect the stability of power system operation and threaten the safety of power equipment and even personal safety. Therefore, for the unplanned island state which can not maintain its own stability, it is necessary to carry out effective islanding protection, cut DER off the distribution network, shorten the island operation time as far as possible, and avoid a series of security risks. The effective islanding protection depends on the fast and reliable islanding detection. There are some defects and limitations in the current common islanding detection methods, among which the remote detection method based on communication is of high cost and poor economy. The passive detection method based on the local electric abrupt change quantity has the blind spot when the power matching degree in the isolated island system is high. The active detection method based on injecting disturbance signal into the power network has certain influence on the power quality. Based on the research and analysis of PQ constant power output control mode of grid-connected inverter, a parallel RLC constant power load model with rated frequency is established, and the system voltage of DER grid-connected and islanding operation is derived theoretically. The characteristics of frequency variation and its influence by unbalanced power show that the variation of voltage and frequency in isolated island system is mainly related to the local load characteristics, which is very different from the power grid with constant external characteristics. The variation of voltage amplitude after isolated islands is mainly determined by unbalanced active power (螖 P). The larger 螖 P is, the greater the change of voltage amplitude is. The frequency change of isolated islands is less affected by 螖 P, which is mainly determined by unbalanced reactive power (螖 Q). In the case of higher active power matching (螖 P is smaller), the amplitude of voltage changes little and it is difficult to reflect the characteristics of isolated islands, but the decisive effect of 螖 Q on the frequency of islanding system is still significant. At the same time, the voltage phase change caused by frequency change is more prominent than that of itself. Therefore, an islanding detection method based on wide-area phase comparison is proposed, which consists of the voltage phase difference between the bus side of the distribution network and the DER grid-connected side, which constitutes the islanding detection criterion. The synchronous measurement and calculation of the voltage phase on both sides are accomplished by the feeder automation terminal (FTU), and the information exchange is realized through the fast communication system. The synchronous phasor measurement is realized by the FTU which is arranged on the bus side of distribution network and connected to the DER side. Real time measurement and calculation of voltage phase 胃 s (t) and 胃 DER (t), distribution network side FTU transmit 胃 s (t) with time scale to DER grid-connected side through the fast communication system, so that FTU makes a comparison of voltage phase difference between two sides with the same time scale. Considering the measurement calculation and communication error, compared with the determined threshold 胃 z, the islanding detection. Der grid-connected side FTU starts the islanding protection according to the detection result, disconnects the DER grid-connected switch, and makes it stop the external output power. The simulation model of islanding detection in active distribution network based on Matlab is established. The characteristics of voltage, frequency and phase change of DER and islanding operation are analyzed, and the influence of local load mutation and distribution line fault on islanding detection is eliminated. At the same time, based on the local load characteristics, the influence of unbalanced power difference on islanding detection is fully considered. The experimental results agree with the theoretical analysis and verify the correctness and applicability of the method.
【學(xué)位授予單位】：昆明理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2014
【分類號(hào)】：TM732

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