Flying Capacitor Balancing in Multi-Level MPPT Converters
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Solution Overview
Problem
Multi-level converters, such as 3-level buck or boost converters, face challenges with flying capacitor voltage deviation, leading to potential damage and increased device stress, especially in high power renewable and solar MPPT inverter applications, and existing balancing methods are limited to two-switch designs, incompatible with four-switch systems.
Innovation Solution
A secondary converter, configured as an isolated, multi-output, forward-derived converter operating in an open loop, balances flying capacitors to a target voltage and switches between active and inactive states based on voltage thresholds, with or without MCU intervention, using a transformer for isolation and PWM control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If multi-level converters use flying capacitors to provide intermediate operating voltage, then device stress is constrained to less than source voltage, but flying capacitor voltage deviation can occur leading to potential damage
Solution Approach 1:
An isolated secondary converter circuit is introduced as an intermediary component to actively regulate and maintain the flying capacitor voltage at the target level (half the source voltage). This mediator circuit includes a transformer for galvanic isolation and control circuitry that monitors and adjusts the flying capacitor voltage, preventing deviation while preserving the device stress constraints provided by the flying capacitor topology.
2Reliability
If existing balancing methods are used for two-switch designs, then flying capacitor voltage can be balanced, but these methods are incompatible with four-switch multi-level converter systems
Solution Approach 1:
The isolated secondary converter circuit is designed with universal applicability to work with both two-switch and four-switch multi-level converter topologies. The circuit uses a transformer-based isolated architecture with configurable switching arrangements that can adapt to different converter configurations, making the voltage balancing solution universally applicable across various multi-level converter designs without requiring topology-specific modifications.
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 effectively balances flying capacitors, enhancing reliability and reducing startup stress, suitable for advanced digital power conversion applications, including SiC multi-level converters, by maintaining voltage stability and preventing damage.
Implementation Method 1
using a transformer for isolation and PWM control
Data Source
AI summary
Apparatuses, systems, and methods to balance flying capacitors in high power multi-level buck or boost converters for renewable and solar maximum power point tracking (MPPT) inverter applications are provided. An exemplary method includes initializing at least a multi-level converter circuitry and an isolated secondary converter circuitry, wherein the multi-level converter circuitry includes at least a flying capacitor, and wherein the isolated secondary converter circuitry is configured to charge the flying capacitor in accordance with a default operation state in response to initialization; determining that a voltage across the flying capacitor satisfies a threshold; and causing the isolated secondary converter circuitry to switch from the default operation state to an inactive state based at least in part on the voltage satisfying the threshold.