Grid-Tied Power Converter Control for Negative-Sequence Voltage Reduction
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Solution Overview
Problem
Conventional grid connected power systems face challenges in accurately reducing negative-phase sequence output voltage during imbalanced short circuits, such as two-phase short-circuits or ground fault short-circuits, which increase negative-phase sequence output voltage.
Innovation Solution
A power conversion device that includes a power conversion circuit and a control circuit to calculate and generate switching control signals based on three-phase AC output voltage and current, allowing for the calculation of negative-phase sequence current command signals to reduce negative-phase sequence voltage by injecting appropriate currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional control methods are used during imbalanced short circuit, then the power conversion device can operate, but the negative-phase sequence output voltage increases and cannot be accurately reduced
Solution Approach 1:
The patent segments the control into positive-phase sequence control and negative-phase sequence control. The control circuit separately calculates positive-phase sequence current command values and negative-phase sequence current command values, then combines them to generate switching control signals. This segmentation allows independent optimization of each sequence component, enabling accurate reduction of negative-phase sequence voltage while maintaining system reliability.
Solution Approach 2:
The patent changes the control parameter from conventional single-phase or three-phase control to dual-sequence control (positive and negative phase sequences). By calculating and controlling current command values for both sequences separately, the system can precisely manipulate the negative-phase sequence voltage component, achieving accurate voltage reduction during imbalanced short circuits while maintaining overall system stability.
2Device complexity
If no negative-phase sequence control is implemented, then the control system remains simple, but the three-phase voltage imbalance cannot be mitigated
Solution Approach 1:
The control circuit segments the voltage and current analysis into positive-phase sequence and negative-phase sequence components. By separately calculating current command values for each sequence and combining them, the system achieves comprehensive control capability. This segmentation approach maintains relative control simplicity while effectively addressing three-phase voltage imbalance during imbalanced short circuits.
Data Source
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AI summary
A power conversion device includes a power conversion circuit and a power conversion control circuit. The power conversion control circuit is configured to calculate a positive-phase sequence current command signal based on a positive-phase sequence voltage of the three-phase AC output voltage and a positive-phase sequence current of the three-phase AC output current, calculate a first axis negative-phase sequence voltage value being a d-axis component of negative-phase sequence voltage, a second axis negative-phase sequence voltage value being a q-axis component of the negative-phase sequence voltage, a first axis negative-phase sequence current value being a d-axis component of negative-phase sequence current, and a second axis negative-phase sequence current value being a q-axis component of the negative-phase sequence current, by executing dq-conversion of each of a measured value of the three-phase AC output voltage and a measured value of the three-phase AC output current, calculate a first axis negative-phase sequence current command value being a d-axis component command value of the negative-phase sequence current based on the second axis negative-phase sequence voltage value, calculate a second axis negative-phase sequence current command value being a q-axis component command value of the negative-phase sequence current based on the first axis negative-phase sequence voltage value, and calculate a negative-phase sequence current command signal based on the first axis negative-phase sequence current command value, the second axis negative-phase sequence current command value, the first axis negative-phase sequence current value, and the second axis negative-phase sequence current value, and generate the switching control signal based on the positive-phase sequence current command signal and the negative-phase sequence current command signal.