Shorting Period Control in Inductive Power Transfer Resonant Converters
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Solution Overview
Problem
Existing inductive power transfer (IPT) systems require additional components and complex feedback loops for primary-side power flow control and zero-voltage switching (ZVS), leading to increased size, cost, and complexity, and often necessitate bi-directional communication, which adds to the system's complexity and power requirements.
Innovation Solution
A current-fed push-pull resonant converter with a parallel-tuned resonant tank and a controller that selectively controls the shorting period of the resonant converter using slow feedback, allowing for primary-side power flow control or ZVS operation without the need for fast detection circuits or additional hardware, and utilizes inductive coupling for communication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If additional components (switched capacitors, multiple switching devices) are added for primary-side power flow control, then power flow regulation capability is improved, but device complexity and size increase
Solution Approach 1:
The patent extracts the power flow control function from complex additional components and implements it through control of the existing resonant tank's shorting period. By controlling when the resonant tank is shorted (via switches Q1-Q4), the system achieves power regulation without needing multiple switched capacitors or additional switching devices, thus maintaining adaptability while reducing device complexity
Solution Approach 2:
The resonant tank serves multiple functions: it provides the resonant circuit for power transfer and simultaneously acts as the control element for power flow regulation. By controlling the shorting period of this universal component, the system achieves both power transfer and power regulation functions without requiring separate dedicated control components, thereby reducing overall system complexity
2Loss of energy
If fast detection circuits are added for ZVS control, then switching efficiency is improved, but device complexity and cost increase
Solution Approach 1:
The patent employs feedback control where the controller monitors the resonant tank's state and adjusts the switching signals accordingly. The feedback mechanism detects when the resonant tank voltage approaches zero and triggers the appropriate switching action, achieving ZVS without requiring complex high-speed detection circuits. This feedback-based approach reduces switching losses while keeping the detection circuitry simple
Solution Approach 2:
The resonant tank itself provides the detection function needed for ZVS control. The natural oscillation and voltage characteristics of the resonant tank contain the information needed to determine when switching should occur. By utilizing the resonant tank's own characteristics for detection rather than adding external high-speed detection circuits, the system achieves low switching losses with minimal additional complexity
3Reliability
If bi-directional communication circuits are added for coordination, then power transfer reliability is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent merges the communication function with the existing power transfer magnetic field. By modulating the load on the secondary side, information is transmitted back to the primary side through the same inductive coupling used for power transfer. This eliminates the need for separate bi-directional communication circuits, maintaining power transfer reliability through load modulation while significantly reducing device complexity and power consumption
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 solution enables efficient power flow regulation and zero-voltage switching with reduced component count and complexity, avoiding capacitor shorting and maintaining operation across varying coupling and load conditions, while allowing for low-bandwidth communication using frequency modulation.
Implementation Method 1
The high-frequency alternating current produces a changing magnetic field about the primary conductor, which induces a voltage at the secondary pick-up coil to power the load
Implementation Method 2
a parallel-tuned resonant tank
Data Source
AI summary
The present invention provides a power supply for an inductive power transfer (IPT) system, comprising a current-fed push-pull resonant converter comprising a parallel-tuned resonant tank and a pair of switches enabling selective shorting of the resonant tank; and a controller adapted to control a shorting period of the resonant converter by selectively operating the switches. Methods for controlling an IPT power supply are also disclosed. The power supply may be controlled to regulate the output of an IPT pick-up inductively coupled with the power supply in use, or to operate at a zero voltage switching (ZVS) frequency.