Rotary Power Transformer LLC Soft-Start for Startup Current Spikes
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Solution Overview
Problem
LLC resonant power converters experience large current spikes during startup, which can cause circuit components to trip, when initiating operation at a target frequency.
Innovation Solution
Implement a frequency change on the gate drive signal to soft-start the LLC resonant power converter by operating it at a higher frequency during startup, reducing the gain and thus minimizing current spikes, and transitioning to a lower frequency once the output capacitor is sufficiently charged.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the LLC resonant power converter is initiated at the target frequency, then the converter operates efficiently at the desired frequency, but large current spikes occur during startup causing circuit components to trip
Solution Approach 1:
The patent applies preliminary action by initiating the LLC resonant power converter at a higher frequency than the target frequency before transitioning to the desired operating frequency. This preliminary high-frequency operation allows the output capacitor to charge gradually, preventing large current spikes that would otherwise occur during direct startup at target frequency, thereby improving reliability without complicating the manufacturing process
Solution Approach 2:
The patent employs parameter changes by dynamically adjusting the operating frequency of the LLC resonant power converter during startup. The frequency is initially set higher than the target frequency to limit inrush current, then gradually reduced to the target frequency once the output capacitor is sufficiently charged. This parameter transition resolves the contradiction between reliable startup and efficient operation
2Reliability
If the gate drive signal frequency is increased during startup, then current spikes are reduced, but the LLC gain decreases requiring frequency transition later
Solution Approach 1:
The patent applies dynamics by making the gate drive signal frequency variable rather than fixed. During startup, the frequency is dynamically adjusted from a higher initial value to the target operating frequency based on the charging state of the output capacitor. This dynamic frequency adjustment reduces current spikes while maintaining eventual operational efficiency, and the control complexity is managed through straightforward frequency transition logic
Solution Approach 2:
The patent employs periodic action through the oscillating nature of the gate drive signal at different frequencies. The switching network operates periodically at the elevated frequency during startup to charge the output capacitor, then transitions to periodic operation at the target frequency for normal operation. This periodic action at variable frequencies achieves both current spike reduction and proper operational gain
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
Reduces current spikes during startup, preventing circuit component tripping and ensuring smooth operation by gradually increasing the gain to the target level.
Implementation Method 1
The LLC resonant power converter is configured to transmit the wireless power signal across a gap separating the first platform and a second platform
Implementation Method 2
The LLC resonant power converter is also configured to receive the wireless power signal at a secondary winding of the rotary power transformer
Data Source
AI summary
A system includes a control circuit and a LLC resonant power converter. The control circuit is configured to generate a first gate drive signal to initiate operation of the LLC resonant power converter at a first frequency. The LLC resonant power converter is configured to drive a wireless power signal at a primary winding of a rotary power transformer disposed on a first platform and transmit the wireless power signal across a gap separating the first platform and a second platform that rotates relative to the first platform. The LLC resonant power converter is configured to operate, in an open loop mode without feedback control, a device mounted on the second platform. In response to satisfaction of a condition, the control circuit is configured to generate a second gate drive signal to operate the LLC resonant power converter at a second frequency that is lower than the first frequency.