Power Conversion Control Device for Zero-Current Switching
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Solution Overview
Problem
The modulation factor in voltage-source inverters is reduced when zero-voltage vectors are employed for zero-current switching, particularly in current-source converters and non-linear capacitor circuits, leading to inefficiencies in power conversion.
Innovation Solution
A power conversion control device with a carrier generating unit, rectifying unit controller, and inverter controller is used to manage switching in voltage-source inverters, optimizing the timing of commutation and dead time to enhance the modulation factor by shifting the commutation timing within the isolation period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If zero voltage vector is employed in control of voltage-source inverter to realize zero-current switching in current-source converter, then switching loss is reduced, but modulation factor reduces
Solution Approach 1:
The patent dynamically adjusts the carrier wave phase angle based on the operating mode (rectification or inversion) to optimize the timing of zero-current switching. By making the carrier phase angle a variable parameter that adapts to different operational states, the system achieves zero-current switching without sacrificing modulation factor, thereby resolving the contradiction between reducing switching loss and maintaining power output capability.
Solution Approach 2:
The invention changes the parameter of carrier wave phase angle to optimize switching timing. Specifically, it sets the carrier phase angle to 30° during rectification mode and -30° during inversion mode, which aligns the zero-crossing points of the carrier wave with the optimal switching moments. This parameter adjustment enables zero-current switching while preserving the modulation factor, thus resolving the technical contradiction.
2Reliability
If zero voltage vector is employed to realize zero-current switching, then current stress on switches is reduced, but line voltage supply period to load is reduced
Solution Approach 1:
The patent employs dynamic adjustment of carrier phase angle to optimize switching timing, ensuring that zero-current switching occurs at optimal moments without excessively shortening the voltage supply period. The dynamic phase angle adjustment allows the system to maintain adequate voltage application time to the load while still achieving reduced current stress on switches through precise timing control.
Solution Approach 2:
The system performs preliminary action by pre-calculating and setting the appropriate carrier phase angle before switching operations. This preliminary configuration ensures that the switching events are timed to occur at optimal moments, reducing current stress on switches while maintaining sufficient voltage supply duration to the load.
3Loss of energy
If commutation timing is shifted to achieve zero-current switching, then switching loss is reduced, but control complexity increases
Solution Approach 1:
The invention simplifies the control complexity by reducing it to a single parameter adjustment - the carrier phase angle. Instead of implementing complex multi-parameter optimization or sophisticated control algorithms, the system achieves zero-current switching simply by adjusting the carrier phase angle to specific values (30° or -30°) depending on the operating mode. This single-parameter approach significantly reduces control complexity while still achieving the goal of reducing switching loss.
Data Source
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AI summary
A period composed of a total of three periods, namely a period when an actual voltage vector (V0) is employed and periods (Ud) before and after it can be regarded as an isolation period when an actual voltage vector (V4) is isolated in a vicinity where switching for commutation in a current-source converter (2) is generated. When the switching in the current-source converter (2) occurs at the isolation period, zero-current switching is realized. When presence of dead time (td) is thus taken into consideration, a width of the timing when the zero-current switching is realized is made to be broader than a case where the presence of the dead time (td) is not taken into consideration by the dead time (td).