Three-Level DC/DC Converter Neutral Point Potential Control
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Solution Overview
Problem
Existing DC/DC conversion devices with three-level power conversion circuits face challenges in reducing variations in potential at the neutral point, as techniques developed for AC/DC conversion are not applicable to DC/DC conversion, leading to imbalances between capacitors.
Innovation Solution
A DC/DC conversion device with three-level power conversion circuits in multiple phases, equipped with voltage detectors and a voltage control unit that performs imbalance-reduction control by dividing one of the divided voltages into half of the input DC voltage, ensuring balanced operation across phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a three-level power conversion circuit is used in DC/DC conversion, then the input voltage can be effectively utilized when the input voltage is high relative to switching element withstand voltage, but variations in potential at the neutral point occur due to capacitor voltage imbalance
Solution Approach 1:
The invention changes the control parameters of the switching elements to actively manage capacitor voltage balance. By adjusting the duty ratios and switching patterns of the upper-arm and lower-arm switching elements, the system maintains equal voltage distribution across the series-connected capacitors, thereby stabilizing the neutral point potential while utilizing high input voltages effectively.
Solution Approach 2:
The invention implements a feedback control mechanism that monitors the voltage across each capacitor and adjusts the switching element control accordingly. The voltage control unit detects voltage differences between capacitors and modifies the switching patterns to correct imbalances, ensuring the neutral point remains stable during DC/DC conversion operation.
2Stability of the object's composition
If pulse-width modulation is used to adjust DC or AC components in switching functions, then neutral point potential variations can be reduced in DC/AC conversion, but this technique is not applicable to DC/DC conversion where output terminal polarity is not varied
Solution Approach 1:
The invention inverts the approach by applying pulse-width modulation techniques traditionally used for AC output control to DC/DC conversion. Instead of varying output polarity, the system modulates the switching functions to actively balance capacitor voltages, adapting the modulation principle to the DC/DC context where polarity remains constant but voltage distribution must be controlled.
Solution Approach 2:
The invention modifies the switching function parameters specifically for DC/DC application by adjusting duty ratios and switching patterns to achieve capacitor voltage balance. The control strategy changes the temporal distribution of switching actions to ensure equal charge-discharge cycles for series-connected capacitors, making the modulation technique effective for DC/DC conversion.
Data Source
Figure 1
Figure 2~3
Figure 4(a)~4(b)
AI summary
A DC/DC conversion device that includes three-level power conversion circuits in a plurality of phases. The DC/DC conversion device includes voltage detectors 21 and 22 that detect at least two voltages (Efc and EfcL) of an input DC voltage, a first divided voltage, and a second divided voltage; and a voltage control unit 3 that controls an output voltage of three-level power conversion circuits 12a and 12b. At least one phase (the power conversion circuit 12b) of the three-level power conversion circuits 12a and 12b operates as an imbalance-reduction phase that executes imbalance-reduction control such that one (EfcL) of the first and second divided voltages is divided into half of the input DC voltage Efc.