DC Circuit Zero-Crossing via Transformer and Capacitor
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Solution Overview
Problem
Direct current (DC) power systems face challenges in interrupting currents due to the lack of natural zero-crossing, making existing technologies inefficient for circuit switching and fault current interruption.
Innovation Solution
The use of an isolating transformer with a primary winding and mechanical switch in series with the DC load, combined with a pre-charged capacitor, artificially generates a zero-crossing point by causing a reverse current in the primary winding, allowing the mechanical switch to interrupt the main current at zero, minimizing losses and enabling effective DC current interruption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If DC current is used in power systems, then power transmission and distribution efficiency is improved, but current interruption becomes difficult due to lack of natural zero-crossing
Solution Approach 1:
The system pre-charges a capacitor through a high-impedance power supply before interruption is needed. When interruption is required, the pre-charged capacitor is discharged through the secondary winding to generate the reverse current that forces the primary current to zero, enabling successful interruption of DC current without natural zero-crossing
Solution Approach 2:
The patent introduces a transformer with primary and secondary windings as an intermediary device. The secondary winding, when energized by the capacitor, generates a reverse current that mediates the interruption process by forcing the primary DC current to zero, allowing the mechanical switch to open without arc formation
2Ease of operation
If a mechanical switch is used to interrupt DC current, then simple switching is achieved, but high energy losses occur due to arc formation
Solution Approach 1:
The transformer acts as an intermediary that converts the simple mechanical switching action into a controlled current interruption process. By generating reverse current through the secondary winding, the system ensures the primary current reaches zero before the mechanical switch opens, eliminating arc formation and associated energy losses while maintaining switching simplicity
3Reliability
If capacitor size is increased to ensure sufficient reverse current, then zero-crossing reliability is improved, but device complexity and cost increase
Solution Approach 1:
The system incorporates a control circuit that monitors the primary current and detects when it reaches zero. This feedback mechanism allows the system to dynamically adjust the timing of capacitor discharge, ensuring reliable zero-crossing generation without requiring overly conservative (and complex) capacitor sizing. The feedback ensures the capacitor is discharged at the optimal moment to force current to zero
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution allows for efficient interruption of DC currents with minimal losses, applicable across various voltage levels and systems, including low voltage PV generation, energy storage, and high voltage T&D applications, while also improving AC circuit breaker clearing times.
Implementation Method 1
The secondary winding of the isolating transformer is connected through a switch, either solid state or mechanical, to a pre-charged capacitor. The secondary winding is electrically connected so that current through the winding opposes the current through the primary winding.
Implementation Method 2
The secondary winding of the isolating transformer is connected through a switch, either solid state or mechanical, to a pre-charged capacitor. With proper selection of capacitor size the current is sufficient to cause the primary current in the transformer to fall to below zero as the beginning part of a ringing transient.
Data Source
AI summary
Disclosed herein are methods and systems for causing a zero-current crossing in an electrical circuit. The circuit can be a DC circuit in which case a switch is caused to open at or nearly at the zero crossing. Alternatively, the circuit can be an AC circuit.