Three-Phase Inverter Control for Independent Asymmetric Grid Infeed
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Solution Overview
Problem
Existing methods for asymmetric infeed of electrical power into a three-phase AC grid require either multiple single-phase inverters or complex regulation structures, limiting independent control of currents or powers on individual phases.
Innovation Solution
A method using a three-phase current-impressing inverter with a regulation circuit comprising a regulator and multiplier circuit to generate phase-specific sinusoidal voltage reference values and target current values, allowing independent control of currents on each phase by multiplying predetermined target current amplitudes with voltage reference values and normalizing them to grid voltages, enabling straightforward mapping of target current values for driving power switches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If three single-phase inverters are used for asymmetric infeed, then independent control of each phase is achieved, but device complexity increases
Solution Approach 1:
The patent combines three single-phase inverters into one three-phase inverter device, integrating multiple independent phase control capabilities into a single unified device. This merging approach achieves independent control of each phase (improving adaptability) while reducing the number of separate devices needed (reducing device complexity).
2Adaptability or versatility
If voltage-impressing operation is used for asymmetric infeed, then grid-forming capability is achieved, but control of infeed powers becomes dependent on AC grid behavior rather than being independently controllable
Solution Approach 1:
The patent implements dynamic switching capability that allows the inverter to operate in different modes (voltage-impressing for grid-forming, current-impressing for independent power control). This dynamic operation enables the system to adapt its control strategy based on operational requirements, achieving both grid-forming capability and independent power control at different times.
3Ease of operation
If current-impressing operation is used, then independent control of exchanged power is achieved, but grid-forming capability is lost
Solution Approach 1:
The patent designs the three-phase inverter with multi-functional capability, enabling it to perform both current-impressing operation (for independent power control) and voltage-impressing operation (for grid-forming capability). This universal design allows a single device to fulfill multiple operational roles that were previously requiring different specialized devices.
Data Source
AI summary
A method for three-phase infeed of electrical power from a DC source into a three-phase AC grid by means of an inverter includes measuring phase-specific grid voltages of the three-phase AC grid, and determining a grid frequency from the measured phase-specific grid voltages. The method also includes generating phase-specific voltage reference values from the phase-specifically measured grid voltages and the determined grid frequency, and generating phase-specific target current values using phase-specific predetermined target current amplitude values, the phase-specific voltage reference values and respective grid voltage amplitudes.