Cascaded Chopper Cell Power Converter Circulating Current Control
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Solution Overview
Problem
Existing power conversion devices face challenges in reliably controlling AC and DC electric quantities and circulating currents due to limitations in voltage command values and harmonic suppression, particularly with circulating currents containing DC and fundamental components.
Innovation Solution
The power conversion device selectively configures at least one chopper cell in each leg circuit to control circulating currents, AC electric quantities, and DC electric quantities, using a control device that generates and adjusts voltage command values to manage these components independently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If all converter cells are used for both AC-DC conversion and circulating current control, then capacity utilization is maximized, but control reliability deteriorates due to voltage command value restrictions
Solution Approach 1:
The patent applies local quality by assigning different control functions to different converter cells within the same system. Some converter cells are dedicated to AC-DC conversion control, while others are dedicated to circulating current control. This local differentiation allows each cell to optimize its specific function without compromising overall system reliability, even though not all cells are used for both purposes simultaneously.
2Object-generated harmful factors
If voltage command value for circulating current control is combined with AC and DC terminal control voltages, then circulating current suppression is achieved, but the voltage command value for AC-DC conversion is restricted
Solution Approach 1:
The patent extracts the circulating current suppression function from the combined voltage command value and handles it through a separate control path. By taking out the circulating current control component and managing it independently, the system achieves effective circulating current suppression without restricting the voltage command values needed for ideal AC-DC conversion performance.
Solution Approach 2:
The patent introduces an intermediary control mechanism that separately generates voltage command values for circulating current suppression and for AC-DC conversion. This intermediary approach allows both control objectives to be achieved without direct interference, as each has its own dedicated control path that can operate independently.
Data Source
Figure 1
Figure 2(a)~2(c)
Figure 3
AI summary
A power conversion device includes a plurality of leg circuits (8a, 8b, 8c) and a control device (5). The plurality of leg circuits (8a, 8b, 8c) correspond to respective phases of an AC circuit (2) and connected in parallel between common first and second DC terminals (Np, Nn). Each leg circuit includes a plurality of chopper cells (1) each including an energy storage and cascaded to one another and at least one inductance (7a, 7b) connected in series to the plurality of chopper cells (1). The control device (5) controls an operation of only at least one chopper cell (6c, 6d) included in each leg circuit (8) based on a circulating current which circulates through the leg circuits (8).