Transformerless Inverter DC/DC Converter Resonant Circuit
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Solution Overview
Problem
Transformerless inverters struggle when feeding electric energy from DC current sources with high DC voltages into AC power grids, as they often exceed the peak voltage of the AC grid, leading to inefficiencies and unwanted compensation currents.
Innovation Solution
The design incorporates a DC/DC converter with a resonant circuit featuring a resonance inductance and capacitance, connected via pulsed switches to the input lines or an intermediate potential, and provides galvanic separation between the input and inverter bridge lines, along with an AC current backflow path to manage and compensate currents, allowing for flexible operation and reduced ground currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a basic DC voltage conversion with multiple partial resonance capacitances is used, then the intermediate link voltage can be scaled down (1:n conversion), but the device complexity increases and efficiency decreases when input DC voltage is already high
Solution Approach 1:
The patent divides the single resonant circuit into multiple parallel resonant circuits, each with its own resonance capacitance. This segmentation allows the system to handle high input voltages by distributing the voltage conversion task across multiple simpler circuit branches, reducing the complexity of any single branch while maintaining overall functionality.
Solution Approach 2:
Each parallel resonant circuit branch serves multiple functions: voltage conversion, current compensation, and adaptive impedance matching. The system can operate with different numbers of active branches depending on the input voltage level, providing universal adaptability across different operating conditions without requiring complete circuit reconfiguration.
2Reliability
If galvanic separation is provided between input lines and inverter bridge lines, then safety is improved, but unwanted compensation currents may flow via ground
Solution Approach 1:
The patent implements active current compensation where the control system continuously monitors the currents flowing through the resonant circuits and actively adjusts the switching of pulsed switches to balance and compensate these currents. This feedback mechanism ensures that compensation currents are minimized while maintaining galvanic separation for safety.
Solution Approach 2:
The pulsed switches act as intermediaries between the resonant circuits and the input lines, allowing controlled current flow paths that prevent unwanted ground currents while maintaining galvanic separation. These switches mediate the current distribution to eliminate harmful compensation currents.
3Power
If photovoltaic panels provide high DC voltages, then energy generation capability is improved, but the voltage exceeds the peak voltage of the AC power grid
Solution Approach 1:
The patent employs dynamic voltage conversion where the resonant circuits and pulsed switches actively adjust the conversion ratio in real-time based on the input DC voltage level. This dynamic adaptation allows the system to handle varying photovoltaic panel voltages and always output a voltage suitable for the AC grid, maintaining compatibility across different operating conditions.
Solution Approach 2:
The system changes operating parameters (switching frequencies, duty cycles, number of active resonant circuit branches) to adapt the voltage conversion ratio. By dynamically adjusting these parameters, the system can convert high DC voltages from photovoltaic panels down to the appropriate level for AC grid injection, maintaining versatility across different power levels.
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
This configuration effectively handles high DC voltages, minimizes ground currents, and provides adaptable options for intermediate link voltage control, enhancing the efficiency and reliability of energy transfer into AC power grids.
Implementation Method 1
The DC/DC converter comprises at least one resonant circuit that comprises a resonance inductance and a resonance capacitance
Data Source
AI summary
A transformerless inverter that serves to feed electricity from a DC current source into an AC power grid, has an inverter bridge and a DC/DC converter connected upstream of the inverter bridge. The DC/DC converter converts an input DC voltage that is present between two input lines of the inverter into a DC link voltage present between two input lines of the inverter bridge. The inverter bridge converts the DC link voltage present at the input lines thereof into an output AC voltage. The DC/DC converter includes at least one resonant circuit that has a resonance inductance and a resonance capacitance and is connected on its input side via at least two clocked switches to one of the two input lines of the inverter or an intermediate potential line carrying a potential in between. The input lines of the inverter and the input lines of the inverter bridge are galvanically isolated from one another by a capacitive method. The resonant circuit may be undivided and is connected alternately to the two input lines of the inverter bridge.