基于广域相位比较的孤岛检测与孤岛保护研究
发布时间：2018-08-03 09:19
【摘要】：针对当前含分布式电源(DER)的有源配电网的结构特点与发展需求,DER并网运行在提高电力系统的稳定性与灵活性,改善电能质量的同时,也给电网带来诸如电压暂降、继电保护误动等新的问题,尤其是电力系统的非计划孤岛运行,有可能严重影响电力系统运行的稳定性,威胁电力设备安全甚至人身安全。因此,对于无法维持自身稳定的非计划孤岛状态,必须进行有效的孤岛保护,将DER切离配电网,尽可能缩短孤岛运行时间,避免引起一系列的安全隐患。而有效的孤岛保护依赖于快速可靠的孤岛检测,就目前常见的孤岛检测方法,均存在一定的缺陷与局限性,其中基于通信的远程检测法成本较高,经济性差,基于本地电气突变量的被动检测法在孤岛系统内功率匹配程度较高时存在检测盲区,基于向电网注入扰动信号的主动检测法对电能质量有一定的影响。 本文基于对并网逆变器PQ恒功率输出控制模式的研究分析,建立额定频率下的并联RLC恒功率负荷模型,理论推导了DER并网与孤岛运行时的系统电压、频率变化特征及其受不平衡功率的影响,结果发现孤岛系统内的电压、频率变化与本地的负荷特性主要相关,这与具有恒定外特性的系统电网迥然不同。孤岛后的电压幅值变化主要由不平衡有功(ΔP)决定,ΔP越大,则电压幅值变化越大。孤岛后的频率变化受ΔP的影响较小,主要由不平衡无功(ΔQ)决定。对于有功匹配程度较高(ΔP较小)的情形,电压幅值变化较小,难以体现孤岛特征,而此时的ΔQ对孤岛系统频率的决定性影响依然显著。同时频率变化所带来的电压相位变化较之本身却更为突出,因此提出了基于广域相位比较的孤岛检测方法,由配电网母线侧与DER并网侧之间的电压相位差构成孤岛检测判据,两侧电压相位的同步测量与计算由馈线自动化终端(FTU)完成,并经快速通信系统实现信息交换。 通过配置于配电网母线侧与DER并网侧的FTU,实现同步相量测量,实时测量计算两侧电压相位θs(t)与θDER(t),配电网侧FTU将带时标的θs(t)经快速通信系统传输至DER并网侧FTU,由此FTU进行两侧带同一时标的电压相位作差比较,并考虑一定的测量计算与通信误差,与设定的孤岛判定阈值θz比较,完成孤岛检测。DER并网侧FTU根据检测结果启动孤岛保护,断开DER并网开关,使其停止对外输出功率。建立基于Matlab的有源配电网孤岛检测仿真模型,仿真分析了DER并网与孤岛运行时的系统电压、频率及相位变化特征,排除了本地负荷突变与配网线路故障对孤岛检测的影响,同时基于本地负荷特性,充分考虑了不平衡功率差异对孤岛检测的影响。实验结果与理论分析相符,验证了本方法的正确性与适用性。
[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.
【学位授予单位】：昆明理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM732
本文编号：2161294
[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.
【学位授予单位】：昆明理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM732
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