Power Conversion Device Autonomous Operation Current Control
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Solution Overview
Problem
Conventional power conversion devices face challenges in maintaining operation continuity and preventing over-discharge when connected to loads beyond their rated output, particularly with solar battery power sources, and may cause motor stalls due to inrush currents, leading to potential damage.
Innovation Solution
A power conversion device with a power conversion circuit and control section that includes an AC current suppression section and DC voltage shortage suppression section, which dynamically adjusts current limits to prevent over-discharge and limit inrush currents, enabling autonomous operation and high resistance to disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the current suppression value is set to a high value, then the operation continuation ability is improved, but over-discharge occurs and the device cannot operate continuously
Solution Approach 1:
The patent implements dynamic adjustment of the current suppression value based on the DC link voltage status. When voltage sags occur, the control section automatically adjusts the current limit, transforming the static current suppression mechanism into a dynamic one that adapts to real-time voltage conditions, thereby preventing over-discharge while maintaining operation continuity
Solution Approach 2:
The control section monitors the DC link voltage and uses this feedback to adjust the current suppression value. When voltage sags are detected, the system responds by modifying the current limit, creating a closed-loop control mechanism that prevents over-discharge while ensuring continuous operation
2Loss of energy
If the current suppression value is set to a low value, then over-discharge is prevented, but power output is excessively limited and motor stalled state occurs
Solution Approach 1:
The system dynamically adjusts the current suppression value based on voltage conditions rather than using a fixed low value. This allows the system to maintain low current limits during normal operation to prevent over-discharge, while temporarily increasing the limit when voltage sags occur, thereby preventing motor stalled states
Solution Approach 2:
The patent changes the current suppression parameter dynamically based on voltage sag detection. By adjusting this parameter according to real-time voltage conditions, the system prevents over-discharge during normal operation while allowing sufficient power output during voltage disturbances to avoid motor stalled states
3Reliability
If autonomous operation is implemented without grid power, then power supply continuity is improved, but current detection accuracy deteriorates due to voltage sags
Solution Approach 1:
The control section detects voltage sags in advance and preemptively adjusts the current suppression value before accurate current measurement can be obtained. This preliminary action compensates for the measurement inaccuracies that would otherwise occur during voltage sags in autonomous operation mode
Solution Approach 2:
The system takes preliminary action by detecting voltage sags and adjusting current limits before the current detection accuracy deteriorates. This proactive adjustment ensures that current suppression remains effective even when voltage sags affect measurement precision during autonomous operation
Data Source
AI summary
A power conversion circuit for converting DC power supplied from a DC power supply to AC power; and a power conversion control section for controlling operation of the power conversion circuit so as to generate autonomous operation power as an AC voltage source in a parallel-off state from a power grid. The power conversion control section includes: an AC voltage control section for controlling AC voltage; an AC current suppression section for limiting AC current to a predetermined current limit value or smaller; and a DC voltage shortage suppression section for, when DC voltage of the power conversion circuit reduces, in response thereto, reducing the current limit value to be given to the AC current suppression section.