Three-Level Converter Balancing for Seamless Buck Boost Switching
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Solution Overview
Problem
Charging circuits with three-level converters face challenges in seamlessly switching between buck and boost modes without disconnection of input power, particularly in complex operation conditions involving both wired and wireless charging, due to deviations in current flow times affecting flying capacitor voltage balancing.
Innovation Solution
A balancing circuit is implemented in the charging circuit, which includes a balancing control circuit and a switching control circuit to automatically adjust the control direction based on the designated mode, allowing seamless switching between buck and boost modes without sensing inductor current, ensuring the flying capacitor voltage remains at half the input voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a three-level converter is used in a charging circuit to reduce inductor capacity and improve power conversion efficiency, then power conversion efficiency is improved, but seamless switching between buck and boost modes becomes difficult due to current flow time deviations affecting flying capacitor voltage balancing
Solution Approach 1:
The patent implements dynamic switching between first and second balancing modes based on the operational state (buck or boost mode) of the three-level converter. The balancing control circuit automatically adjusts the balancing strategy by detecting the current flow directions and timing, ensuring the flying capacitor voltage remains balanced during mode transitions. This dynamic adaptation resolves the contradiction by making the balancing mechanism flexible enough to handle both efficiency benefits and switching reliability requirements.
Solution Approach 2:
The patent employs a balancing control circuit that continuously monitors the flying capacitor voltage and current flow characteristics, then provides feedback control signals to adjust the switching elements' duty cycles. This feedback mechanism detects deviations in current flow times and compensates for them by adjusting the balancing strategy, ensuring seamless mode switching while maintaining the power conversion efficiency benefits of the three-level converter architecture.
2Adaptability or versatility
If the charging circuit operates in complex conditions with both wired and wireless charging paths, then charging versatility is improved, but flying capacitor voltage balancing becomes challenging due to varying power demands and mode transitions
Solution Approach 1:
The patent designs a universal balancing control circuit that can operate in both first balancing mode (for buck operation) and second balancing mode (for boost operation) within the same three-level converter architecture. This multi-functional balancing mechanism handles varying power demands from wired and wireless charging paths by automatically adapting its balancing strategy, thus maintaining voltage balancing precision across diverse charging scenarios without requiring separate balancing circuits for each mode.
Solution Approach 2:
The balancing control circuit dynamically adjusts its operation based on the detected charging mode and power flow direction. When transitioning between wired and wireless charging paths or between buck and boost modes, the circuit automatically switches between different balancing strategies, ensuring continuous voltage balancing precision despite the varying operational conditions and power demands.
3Measurement precision
If current sensing is implemented to monitor inductor current for balancing control, then balancing precision is improved, but device complexity increases
Solution Approach 1:
The patent implements a self-service balancing mechanism where the balancing control circuit uses the existing switching signals and voltage measurements to infer current flow characteristics and determine the appropriate balancing strategy. Instead of requiring separate current sensing circuits, the system leverages the information already available from the switching elements and flying capacitor voltage measurements, thus achieving adequate balancing precision without adding the complexity of dedicated current sensors.
Solution Approach 2:
The patent uses the flying capacitor voltage as an intermediary parameter to indirectly monitor and control the balancing state. Rather than directly sensing inductor current, the balancing control circuit monitors the flying capacitor voltage and uses this information to adjust the switching elements' duty cycles, achieving effective balancing control through an intermediary measurement that simplifies the overall circuit complexity while maintaining adequate precision.
Data Source
AI summary
A charging circuit of an electronic device having a three-level converter, and a method and a device for controlling balancing in a charging circuit are provided. The electronic device includes a battery, at least one processor, and a charging circuit. The charging circuit includes, as a three-level converter, a switching circuit including multiple switching elements and a flying capacitor, and a filter circuit including an inductor and a capacitor. The charging circuit includes, as a balancing circuit, a balancing control circuit configured to, during balancing corresponding to a designated a mode, based on whether the balancing corresponds to targeted balancing, generate an output for maintaining or switching a balancing control direction configured for the designated mode, and a switching control circuit configured to perform switching for the switching elements in a balancing control direction corresponding to the designated mode, based on an output of the balancing control circuit, or perform switching for the switching elements in a direction reverse to a balancing control direction corresponding to the designated mode.