Inverter Phase Current Control via Zero Sequence Switching
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Solution Overview
Problem
Three-phase inverters face challenges in controlling phase currents, particularly in reducing zero sequence currents that can lead to circulating currents and undesirable system oscillations, especially in parallel-connected configurations, which reduce total output power.
Innovation Solution
The method employs direct hysteresis current control combined with switching a selected phase of the inverter based on the zero sequence current, using a predefined hysteresis window to limit zero sequence currents and minimize switching losses, and incorporates SDHC current control to enhance dynamics and robustness, while maintaining a flat-top characteristic.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If direct hysteresis current control is used for phase current control, then dynamics and robustness are improved, but zero sequence currents occur causing circulating currents and system oscillations
Solution Approach 1:
The patent detects zero sequence currents and converts this harmful effect into a useful control signal. By using the zero sequence current as a switching criterion for the selected phase, the system transforms the harmful circulating current into a beneficial control mechanism that actively suppresses zero sequence current generation while maintaining the dynamics of direct hysteresis control
Solution Approach 2:
The patent introduces an intermediary control mechanism that mediates between the direct hysteresis current control and the zero sequence current suppression. A selected phase is controlled as an intermediary element, switching based on zero sequence current levels to suppress circulating currents while allowing the main direct hysteresis control to maintain system dynamics
2Object-generated harmful factors
If additional switching of a selected phase is implemented to reduce zero sequence current, then zero sequence current is reduced, but switching losses increase
Solution Approach 1:
Instead of controlling all three phases to reduce zero sequence current, the patent applies partial action by selecting only one phase for additional switching control. This selective approach achieves zero sequence current suppression with minimal additional switching operations, thereby reducing switching losses compared to controlling all phases
Solution Approach 2:
The selected phase automatically adjusts its switching behavior based on the zero sequence current level without requiring external intervention. The phase serves itself by detecting when zero sequence current exceeds thresholds and switching accordingly, minimizing unnecessary switching operations and associated losses
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 approach effectively reduces zero sequence currents and circulating currents between parallel-connected inverters, improving output power and reducing switching losses, thereby enhancing the overall system's modularity, cost-effectiveness, and robustness.
Implementation Method 1
a first hysteresis window is predefined for the zero sequence current and the selected phase is switched when the zero sequence current leaves the first hysteresis window
Data Source
AI summary
The invention relates to a method for controlling phase currents (iU_WR1, iv_WR1, iw_WR1) of a three-phase inverter (WR1), the phase currents (iU_WR1, iv_WR1, iw_WR1) of the inverter (WR1) being controlled by way of a direct hysteresis current control and a selected phase of the inverter (WR1) being additionally switched depending on a zero system current (i0_WR1) of the inverter (WR1).