Non-sinusoidal Power Transmission System for Urban Grid Capacity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Urban power grids face challenges with insufficient transmission capacity, high short-circuit currents, and difficulty in reactive power voltage regulation due to increased load and interwoven grid structures, which are exacerbated by the limitations of existing alternating current transmission systems, particularly in cable lines where insulation and capacitance issues restrict power transmission.
Innovation Solution
A power transmission system utilizing non-sinusoidal alternating current transmission with bidirectional current conductivity through voltage source current converters and switch handover devices, which converts sine waves to alternating square waves and back, maximizing transmission capacity without increasing short-circuit currents and maintaining insulating properties, while providing dynamic reactive power compensation and harmonic suppression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If alternating current transmission capacity is increased by adding FACTS devices or building new lines, then transmission capacity is improved, but device complexity and land requisition resistance increase
Solution Approach 1:
The invention changes the waveform parameter of the transmitted current from sinusoidal to square wave. This parameter change allows the system to utilize the full insulation strength of the line, increasing transmission capacity by up to 60% without requiring additional FACTS devices or new infrastructure, thereby avoiding increased device complexity
Solution Approach 2:
The invention employs periodic switching of the third polar lead connection between the first and second polar leads using switch handover devices. This periodic action enables bidirectional current conductivity and allows uniform distribution of line loss among the three leads, improving transmission capacity while maintaining system reliability
2Power
If new alternating current lines are built to solve insufficient power supply, then transmission capacity is improved, but short-circuit current increases
Solution Approach 1:
The invention introduces dynamic control through switch handover devices that periodically connect and disconnect the third polar lead between different polar leads. This dynamic switching enables the system to adapt current flow paths in real-time, increasing transmission capacity while controlling short-circuit current levels through intelligent path management rather than simply adding more lines
3Adaptability or versatility
If alternating current cable lines are used for power transmission, then transmission flexibility is improved, but capacitance current restricts transmission length
Solution Approach 1:
The invention changes the current waveform parameter from sinusoidal to square wave, which fundamentally alters the capacitance current characteristics. In square wave transmission, steady-state capacitance current is reduced to only the ripple voltage component, extending the practical transmission length of cable lines from limited distances to much longer distances while maintaining the flexibility advantages of cable line deployment
4Power
If alternating current cable lines are converted to direct current operation to extend transmission length, then transmission length is improved, but space charge accumulation causes insulator breakdown
Solution Approach 1:
Instead of converting to direct current as conventionally done, the invention inverts the approach by using alternating current with a square wave waveform. This inverted approach maintains the benefits of extended transmission length while avoiding space charge accumulation because the alternating polarity continuously clears accumulated charges, preventing insulator breakdown and maintaining reliability
Solution Approach 2:
The invention changes the waveform parameter from sinusoidal to square wave, which creates periods of zero voltage stress on insulators. During these zero-voltage periods, space charges are cleared from the insulator surfaces, preventing the accumulation that leads to breakdown. This parameter change enables long-distance cable transmission without the reliability issues of direct current operation
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
Provided is a power transmission system for improving the transmission capacity of an urban power grid through non-sine alternating current power transmission. The system comprises a first waveform conversion system and a third waveform conversion system both for converting a sine wave into an alternating square wave, and a second waveform conversion system and a fourth waveform conversion system both for converting the alternating square wave into the sine wave; the first waveform conversion system is connected with the second waveform conversion system through a first polar wire and a second polar wire, and the first polar wire is arranged parallelly to the second polar wire; the third waveform conversion system is connected with the fourth waveform conversion system through a third polar wire. Through the use of the capability of bidirectional current conduction of voltage source converters and with the help of switching devices, the power transmission system provided in the present invention well solves the problem as to capacity expansion of alternating current transmission lines without increasing the short-circuit current level of the power grid, and moreover, the power transmission system has transient functions, such as dynamic reactive power compensation, and consequently is of great importance to addressing the contradiction between the increasingly growing loads in large cities and the gradually rising difficulty in building new transmission lines.