Method and system for fast search of cascading failures in hybrid ac/dc power systems

Patent metadata

Field	Value
Publication number	US-2020348353-A1
Application number	US-201816640786-A
Country	US
Kind code	A1
Filing date	Oct 23, 2018
Priority date	Aug 30, 2018
Publication date	Nov 5, 2020
Grant date	—

Abstract

A fast search method and system for cascading failures in hybrid AC/DC power systems. The fast search method for cascading failures in hybrid AC/DC power systems includes: Determining the initial failures and forming a failure set of the first-stage failure, setting the DC blocking or the failure level reaching the threshold as the search stop condition; Judge the cascading failures in the failure set of the current stage can trigger DC blocking, if a cascading failure can trigger DC blocking, store the DC blocking failure as the next-stage failure. Otherwise, cascading failures are searched on the AC side and the failure set of the next stage is determined based on the pruning search method and the outage risk value; If the search stop condition is satisfied, stop the search, otherwise, the number of failure stages is increased by one and return to judge the cascading failures to continue the search.

First claim

1 . A fast search method for cascading failures in hybrid AC/DC power systems, the method comprising:
step 1: determining an initial failure and forming a failure set of the first-stage failures; setting a DC blocking or the number of failure levels reaching a threshold as a search stop condition; step 2: judging whether cascading failures in the current stage failure set can trigger a DC blocking; if the cascading failure causes a DC blocking, the DC blocking failure is stored in a next stage of the cascading failure; otherwise, cascading failures are searched on an AC side and the failure set of the next stage is determined based on a pruning search method and an outage risk value; step 3: if the search stop condition is satisfied, stop the search; otherwise, the number of failure stages is increased by one and return to Step 2 to continue the search.

2 . The method according to claim 1 , wherein, in the Step 1, according to an actual situation of the system, AC lines near a vicinity of a DC terminal location are selected as the initial failures in the cascading failure search, and the initial failures are simulated in time-domain to check whether it will trigger a DC blocking.

3 . The method according to claim 1 , wherein, in the Step 2, when judging whether cascading failures of the current-stage failure set can trigger a DC blocking, extreme failures are identified by comparing a multi-infeed short circuit ratio (MISCR) with the preset threshold of MISCR; then, these extreme failures are judged whether causing a DC blocking by time-domain simulations.

4 . The method according to claim 1 , wherein, in the Step 2, when judging whether cascading failures of the current-stage failure set can trigger a DC blocking, the non-extreme failures are fast judged whether can trigger a DC blocking by the LMNN.

5 . The method according to claim 4 , wherein, for non-extreme failures, the specific process of using the LMNN to fast judge whether the current-stage failures can trigger a DC blocking is:
partition the AC/DC power system to be analyzed; a partition principle is that each DC system terminal location is as one area, cascading failure chains of different stages are randomly selected near the vicinity of the DC terminal location and as a training sample set; for the training sample set, extreme cascading failure chains are removed, and the remaining non-extreme cascading failure chains are used for training of LMNN; the trained LMNN is utilized to quickly estimate a voltage dip degree of a commutation bus after failures and measure the severity of AC failures; for cascading failures whose severity exceeds the preset threshold, time-domain simulation is used to verify whether they can cause a DC blocking.

6 . The method according to claim 5 , wherein, in the process of using the LMNN to quickly estimate whether the current-stage non-extreme failures can trigger DC blocking, failure chains are sorted according to the severity of each AC failure, and the most serious failure is simulated by the time-domain simulation; if the failure will trigger a DC blocking, next failure is simulated continually; otherwise, there is no need to simulate the remaining failures.

7 . The method according to claim 1 , wherein, in the Step 2 , the pruning search method is used, and a pruning condition is based on the outage risk value; the process of searching the next-stage failures on the AC side is:
calculate the remaining line outage risk for each failure chain in turn; take the line outage risk value as the pruning condition, the corresponding failure chains are sorted according to the outage risk value; the preset number of failure chains are stored and complete the pruning process, then the next-stage failures are searched on the AC side.

8 . The method according to claim 7 , wherein, in the process of calculating the remaining line outage risk for each failure chain, the calculation is based on two aspects: a line outage probability and a line outage consequence;
or in the process of calculating the remaining line outage risk for each failure chain, the calculation is based on a single aspect: a line outage probability or a line outage consequence.

9 . The method according to claim 8 , wherein the line outage probability considers an influence of line load rate and hidden failures of protection systems on a line outage; the higher the line load rate is, the greater the probability of outage is; the fluctuation of line power flow and heavy load of AC lines will trigger hidden failures of protection systems; the more severe the fluctuation of line power flow is and the higher the load rate is, the greater the possibilities of hidden failures of protection systems are;
the load rate and distribution of the remaining lines after a line outage are defined as the consequences of the line outage; the LODF method is used to calculate the power flow after line outages.

10 . A system for fast search of cascading failure in hybrid AC/DC power systems, the system comprising a memory and a processor;
the processor is configured to perform the following steps: determine initial failures and form the failure set of the first stage; set a DC blocking or the number of failure stages reaching the threshold as the search stop condition; estimate whether there are cascading failures in the current stage can trigger a DC blocking; if a failure chain will trigger a DC blocking, store the DC blocking as the next stage failure of; otherwise, use the pruning search method and the outage risk value as the pruning condition to search for failures on the AC side and determine the failure set of the next stage; judge whether the search stop condition is satisfied, and if the condition is satisfied, the search is stopped; otherwise, the number of failure stages is increased by one and return to the previous step to continue the search.

Assignees

• Univ Shandong

Inventors

• Liu Yutian
• Zhu Yuanzhen
• Li Wenbo

Classifications

• H02J13/12

  Monitoring network conditions, e.g. electrical magnitudes or operational status · CPC title

• Y04S10/52

  Outage or fault management, e.g. fault detection or location · CPC title

• H02H7/28

  for meshed systems · CPC title

• H02J3/001 Primary

  Arrangements for handling faults or abnormalities, e.g. emergencies or contingencies · CPC title

• G01R31/086 Primary

  in power transmission or distribution networks, i.e. with interconnected conductors · CPC title