Power Conversion Device Adaptive Commutation for Regenerative Current
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Solution Overview
Problem
In direct AC power converting apparatuses, the existing technologies face challenges in handling regenerative current, especially at low load power factors, leading to overvoltage in the DC link and difficulties in maintaining operation during power factor reduction and instantaneous blackouts, due to inadequate clamp voltage and commutation mode inefficiencies.
Innovation Solution
A power converting apparatus that includes a clamp circuit with capacitors connected in series for charging and in parallel for discharging, and a shorting switch that is rendered conductive when the load power factor falls below a predetermined value, allowing for adaptive commutation modes to manage regenerative current and maintain stable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a clamp circuit is used to handle regenerative current in direct AC power converting apparatus, then the breakdown voltage requirement is reduced, but overvoltage occurs in the DC link when load power factor is low
Solution Approach 1:
The patent dynamically switches between two commutation modes (first and second modes) depending on the load power factor. When power factor is low, the system switches to the second commutation mode which prevents overvoltage in the DC link, while maintaining the benefit of reduced breakdown voltage requirements through the clamp circuit configuration.
Solution Approach 2:
The patent changes the commutation mode parameter based on load conditions. By detecting low power factor conditions and switching to an alternative commutation mode, the system adapts to prevent overvoltage while maintaining the simplified clamp circuit design with reduced breakdown voltage requirements.
2Device complexity
If commutation mode is fixed in direct AC power converting apparatus, then control is simplified, but operation becomes unstable during power factor reduction and instantaneous blackouts
Solution Approach 1:
The patent implements dynamic commutation mode switching based on detected power factor conditions. The system transitions between first and second commutation modes to maintain stable operation during power factor reduction and instantaneous blackouts, while keeping control logic relatively simple through predetermined switching criteria.
Solution Approach 2:
The patent uses feedback from power factor detection to automatically switch commutation modes. By monitoring load conditions and adjusting the commutation mode accordingly, the system maintains operational stability without requiring complex manual intervention or overly complicated control algorithms.
3Strength
If clamp circuit capacitors are connected in series for charging, then breakdown voltage requirement is reduced, but regenerative current absorption becomes insufficient at low power factors
Solution Approach 1:
The patent dynamically adjusts the commutation mode based on load power factor to compensate for the reduced regenerative current absorption capability of the series-connected clamp circuit capacitors. By switching to the second commutation mode under low power factor conditions, the system maintains reliable operation while benefiting from the reduced breakdown voltage requirements.
Solution Approach 2:
The patent changes operational parameters (commutation mode) in response to power factor conditions to ensure adequate regenerative current absorption. This parameter adjustment allows the system to maintain sufficient absorption capability despite the series connection configuration that reduces breakdown voltage requirements.
Data Source
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AI summary
Absorption of a regenerative current and direct AC power conversion are made compatible with each other in a power converting apparatus. A converter (4) and an inverter (6) are connected via a clamp circuit (5). The converter (4) performs commutation in accordance with any of a first commutation mode in which trapezoidal waves are compared with a carrier and a 120-degree conduction mode. A diode (Dc1) of the clamp circuit (5) is short-circuited by a shorting switch (Qc1). The shorting switch (Qc1) is rendered conductive when a power factor reduces or a power supply voltage reduces, and capacitors (51) and (52) of the clamp circuit (5) are connected in series between DC power supply lines (LH, LL). The converter (4) performs commutation in accordance with the 120-degree conduction mode, not in accordance with the first commutation mode, while the shorting switch (Qc1) is conductive.