DC Flexible Loop Closing Circuit for Low-Cost Power Mutual Aid
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Solution Overview
Problem
Existing flexible interconnection devices for distribution networks face challenges such as large equipment capacity and size, high operation and maintenance costs, and low equipment utilization rates, which limit their application and effectiveness in ensuring reliable and flexible power supply.
Innovation Solution
A grid direct-current flexible loop closing control device and method that employs a series-parallel configuration with two alternating-current ports and a direct-current port, including a three-port series coupling unit, a two-port parallel coupling unit, a bypass switch, and a direct-current loop closing main controller, to realize flexible loop closing and power mutual aid in distribution networks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If back-to-back bidirectional converters are used for alternating-current loop closing, then flexible power flow control capacity is achieved, but equipment capacity and size become excessively large and cost increases
Solution Approach 1:
The patent divides the loop closing device into two independent units: a series unit with a converter for voltage control and a parallel unit with a converter for current control. This segmentation allows each converter to be smaller and more specialized, reducing overall equipment capacity and size while maintaining flexible power flow control capability through coordinated operation of both units.
Solution Approach 2:
The series and parallel units work together to provide multiple functions: voltage regulation, current control, power flow management, and loop closing operations. This multi-functionality eliminates the need for large-capacity equipment, as each unit performs specific tasks efficiently, reducing overall equipment size and cost while achieving flexible adaptability.
2Adaptability or versatility
If back-to-back bidirectional converters are used for alternating-current loop closing, then flexible interconnection of transregional distribution networks is achieved, but operation and maintenance cost becomes excessively high
Solution Approach 1:
By segmenting the system into series and parallel units with specialized converters, each unit can be manufactured more efficiently with lower cost components. The simplified structure of each unit reduces manufacturing complexity and ongoing maintenance requirements, lowering overall operation and maintenance costs while preserving flexible interconnection capability.
Solution Approach 2:
The patent employs converters with reduced capacity and simpler designs that are more cost-effective to manufacture and maintain. While individual converters may need replacement sooner due to reduced redundancy, the overall system cost is reduced, making the device more economically viable for widespread deployment.
3Shape
If traditional sectionalizing switches and tie switches are used for loop closing, then network structure optimization is achieved, but flexible power mutual aid cannot be realized and large impact current occurs
Solution Approach 1:
The patent replaces traditional mechanical switches with power electronic converters in the series and parallel units. These converters provide controlled switching capability, enabling flexible power mutual aid and gradual power transfer that eliminates large impact currents while optimizing network structure through intelligent control.
4Adaptability or versatility
If alternating-current loop closing devices are used, then flexible interconnection is achieved, but phase-angle loop closing condition must be taken into account and operation becomes time-consuming
Solution Approach 1:
The patent changes the operating parameters from alternating-current with phase-angle considerations to direct-current operation. This parameter change eliminates the need for phase-angle detection and synchronization, significantly reducing operation time while maintaining flexible interconnection capability through voltage and current control of the converters.
Data Source
AI summary
A grid direct-current flexible loop closing control device is a series-parallel device and includes a series coupling unit, a parallel coupling unit, a bypass switch circuit, and a loop closing main controller. The series-parallel devices is connected in series between each distribution line and a load, and after a loop closing instruction is received, the loop closing control devices are set to work in a voltage control mode; after direct-current bus voltages of two loop closing control devices are identical, a system enters a loop closing state. Before exiting loop closing, the loop closing control devices are set to be in a PQ control mode, access switches are sequentially turned off after P and Q are gradually decreased to zero, and a loop closing process is ended. The device is simple in structure, low in cost and high in efficiency, and has fewer loop-closing monitoring quantities.