DC Link Circuit for Floating Source Inverter
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Solution Overview
Problem
Conventional photovoltaic power harvesting systems face safety and efficiency issues when generating high DC voltage for three-phase inverters, as they require over 600 volts, leading to increased cost, complexity, and electromagnetic interference, while also reducing overall power conversion efficiency.
Innovation Solution
A DC link circuit that converts floating DC power to dual DC output using a resonant circuit with a charge storage device, allowing for low voltage input and efficient switching through IGBTs and diodes, reducing electromagnetic interference and maintaining high DC voltage for efficient AC power generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If solar panels are connected in series to provide high DC voltage (over 600V) to the three-phase inverter, then the DC input voltage is sufficient for AC power generation, but safety compliance issues arise under regulation UL1741
Solution Approach 1:
The patent divides the single high-voltage DC input into multiple lower-voltage DC rails (positive and negative rails relative to ground) that can be independently controlled and switched. This segmentation allows the system to achieve the required voltage levels through controlled switching without continuously maintaining high voltage, thereby improving safety compliance while maintaining sufficient voltage for inversion.
Solution Approach 2:
The patent employs periodic switching of semiconductor devices (IGBTs, MOSFETs) to generate the required dual DC rails from a single DC input. By periodically switching between different circuit configurations, the system creates positive and negative voltage rails relative to ground, enabling safe operation under UL1741 while providing sufficient voltage magnitude for three-phase AC generation.
2Stress or pressure
If a boost circuit or transformer-isolated circuit is added to generate dual DC rails from low voltage input, then the required DC voltage is achieved, but device complexity and cost increase
Solution Approach 1:
The three-phase inverter circuit is designed to perform multiple functions: it not only converts DC to three-phase AC but also generates the required dual DC rails from a single DC input through its switching mechanism. The IGBTs/MOSFETs and associated diodes in the inverter circuit serve dual purposes - power conversion and voltage rail generation - eliminating the need for separate boost or transformer-isolated circuits.
Solution Approach 2:
The patent combines the voltage multiplication function with the DC-to-AC inversion function in a single integrated circuit. The switching network that generates positive and negative DC rails is merged with the three-phase inverter bridge, allowing both functions to be achieved simultaneously without adding separate circuit modules, thereby reducing overall device complexity.
3Stress or pressure
If a boost circuit or transformer-isolated circuit is added to generate dual DC rails, then the required DC voltage is achieved, but electromagnetic interference increases and overall efficiency decreases
Solution Approach 1:
The patent extracts the voltage generation function from separate dedicated circuits (boost converters, transformer-isolated circuits) and integrates it directly into the three-phase inverter switching network. By removing the need for intermediate voltage conversion stages, the system eliminates the electromagnetic interference and efficiency losses associated with those separate circuits while maintaining the required voltage levels through direct switching.
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 conversion of DC power to three-phase AC power with reduced switching losses and electromagnetic interference, while avoiding the need for additional boost or transformer-isolated circuits, thus improving overall system efficiency and safety compliance.
Implementation Method 1
A DC link circuit that converts floating DC power to dual DC output using a resonant circuit with a charge storage device, allowing for low voltage input and efficient switching through IGBTs and diodes
Data Source
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AI summary
A device for converting power from a floating source of DC power to a dual direct current (DC) output, the device includes: positive and negative input terminals connectible to the floating source of DC power; and positive and negative, and ground output terminals connectible to the dual DC output that may feed an inverter. The inverter may be either a two or three level inverter. A charge storage device may be connected in parallel to, and charged from, the positive and negative input terminals. A resonant circuit may be also connected between the charge storage device and the dual DC output. The resonant circuit may include an inductor connected in series with a capacitor. The charge storage device may discharge through the resonant circuit by switching through to either the negative output terminal or the positive output terminal.