Dual Power Switching for Inductive Loads Without Inrush Surges
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Solution Overview
Problem
Conventional power switching methods in static transfer switches (STS) for data centers lead to prolonged waiting times and low output voltage due to the need to wait for current to drop to zero before switching, risking equipment shutdown from excessive surge currents and magnetic flux saturation.
Innovation Solution
A dual power switching system using four thyristors and a controller to independently control thyristors in static transfer switches, calculating magnetic flux and determining a commutable time to switch power sources while maintaining magnetic flux within thresholds, thereby reducing inrush currents and shortening switching times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the conventional power switching method waits for current to drop to zero before switching, then inrush current is avoided, but switching time is prolonged and output voltage drops too low
Solution Approach 1:
The controller pre-charges the capacitor to the voltage of the second power source before switching. This preliminary action prepares the circuit in advance, allowing the switching to occur without waiting for current to drop to zero, thus reducing switching time while preventing inrush current
Solution Approach 2:
A capacitor is introduced as an intermediary element between the power sources and the load. The capacitor acts as a buffer that can be pre-charged and then used to maintain power supply continuity during switching, enabling faster transition without causing inrush current
2Loss of time
If the switching occurs without waiting for current to drop to zero, then switching time is reduced, but excessive surge current and magnetic flux saturation occur
Solution Approach 1:
The capacitor is pre-charged to the voltage of the second power source before the switching event. This preliminary charging action ensures that when switching occurs, there is no voltage difference to cause surge current, and the magnetic flux in the transformer remains within safe limits
Solution Approach 2:
The voltage across the capacitor is changed from zero to the voltage of the second power source before switching. By changing this parameter in advance, the system avoids the harmful effects of sudden voltage changes during switching, preventing surge current and magnetic flux saturation
3Reliability
If the waiting time is extended to ensure safe switching, then inrush current is prevented, but output voltage drops too low risking equipment shutdown
Solution Approach 1:
The capacitor is pre-charged before switching, which eliminates the need for extended waiting time. The pre-charged capacitor maintains output voltage levels during the brief switching transition, preventing equipment shutdown while still preventing inrush current
Solution Approach 2:
The pre-charged capacitor serves as an intermediary power source during the switching transition. It maintains the output voltage level while the switch transitions between power sources, ensuring continuous stable power supply to the load without voltage drops
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
The system effectively reduces inrush currents and shortens switching times, ensuring stable power supply to critical loads by avoiding improper switching and magnetic flux saturation.
Implementation Method 1
The first static transfer switch includes a first thyristor and a second thyristor connected in reverse parallel. The second static transfer switch includes a third thyristor and a fourth thyristor.
Implementation Method 2
Since the transformer is an inductive device, when the accumulated magnetic flux is too high, there will be a problem of magnetic flux saturation.
Implementation Method 3
when the accumulated magnetic flux is too high, there will be a problem of magnetic flux saturation
Implementation Method 4
The controller calculates a total magnetic flux according to a current magnetic flux of the inductive device and an expected magnetic flux of the second power source
Data Source
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AI summary
A dual power switching system (100) selects a first power source (110) or a second power source (111) to supply power to a load (121) coupled to an inductive device (120). The dual power switching system (100) includes a first thyristor (130a), a second thyristor (130b), a third thyristor (131a), a fourth thyristor (131b), and a controller (134). The controller (134) calculates a total magnetic flux (Φall) according to a current magnetic flux (ΦLoadReal) of the inductive device and an expected magnetic flux (Φfuture) of the second power source. When the power-supplying source is switched, the controller (134) turns off the first thyristor (130a) and the second thyristor (130b), and determines whether a commutable time is reached according to a power parameter of the first static transfer switch (130) and the second static transfer switch (131). When the commutable time is reached, the controller (134) correspondingly turns on at least one of the third thyristor (131a) and the fourth thyristor (131b) according to the total magnetic flux (Φall) being less than a threshold (Φthz).