Research On Protection And Control Technology For Distribution Network With The Distributed Generation

The distributed generation technology has attracted wide attention around the world in recent years, which provides new strategies for renewable energy sources utilization, energy conservation and emission reduction. However, the access of the distributed generation makes the precondition of traditional staged current protection and control unable to be satisfied and brings new challenges and problems, such as protection failure or malfunction, the non-synchronous reclosing, and the longer action time of the automatic bus transfer or even the automatic bus transfer failure. In order to solve these problems, the protection schemes and coordinated control strategy are systemically researched in this paper. The main research achievements are shown as follows:1. With the purpose of evaluating the impact of the distributed generation’s access on selectivity and sensitivity of traditional staged current protection, a method to calculate the accessing capacity of the inverter-based distributed generation is proposed considering the setting principle of traditional current protection system. Accoding to this method, the accessing capacity that meets the demands on protection selectivity and sensitivity can be obtained. Moreover, the corresponding protection configuration schemes are also given to make the distribution network adapt to the access of the inverter-based distributed generation with different capacities.2. The selectivity and sensitivity of traditional staged current protection might not be satisfied after the access of the distributed generation. In addition, the access makes the setting of staged current protection hard as well. After analyzing the relationship between the positive-sequence voltage and positive-sequence current with different fault types and fault locations, an adaptive instantaneous trip protection principle based on positive-sequence current is proposed. This protection principle can reduce or even eliminate the negative impacts on protection scope, thus improving the protection performance.3. On the other hand, a new protection scheme based on multi-point state informationis proposed as well to selectively protect the overall length of each line without additional equipment. A new criterion of the polarity information of compensation impedance, which can be obtained according to the voltage and current information at feeder head and the point of common coupling, is designed in this scheme. Corresponding to this criterion, the fault location method is proposed as well. Additional potential transformers are not necessary and any fault line in the distribution network containing the distributed generation can be isolated rapidly and accurately according to the polarity information of compensation impedance and action information of over-current protection.4. In order to solve the related problems on the automatic reclosing and automatic bus transfer, the coordinated strategies of protection and automatic control devices for the distribution feeder region and substation region are proposed separately, which are based on wide-area information. These strategies integrate the automatic reclosing and automatic bus transfer with the wide-area protection system. Therefore, the protection and automatic control devices can work coordinately by taking full advantage of wide-area information.5. As for the inverter-based distributed generation with different operation modes, two active islanding detection methods are proposed to eliminate the non-detection zone. A fast islanding detection method is presented for the inverter-based distributed generation simultaneously generating both active and reactive power. This method provides the reactive power reference for the inverter-based distributed generation to guarantee the consistency of the frequency variation trends caused by both active and reactive power mismatches, thus accelerating the islanding detection speed. As for the inverter-based distributed generation owning the islanded operation ability, a nondestructive islanding detection method is proposed. Due to the method’s non-destructive effect on the frequency, it helps to avoid the serious transient process during control strategy transformation of the inverter-based distributed generation for islanded operation.