UPS Control Circuit Prevents Circulating Current
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Solution Overview
Problem
Conventional uninterruptible power supply apparatuses experience circulating current issues when both neutral points of commercial and bypass AC power supplies are grounded, leading to overcurrent detection and potential shutdowns.
Innovation Solution
The apparatus incorporates a forward converter, reverse converter, bidirectional chopper, and control units to manage switches and voltages, ensuring electrical isolation between AC power supplies during switching periods, preventing circulating current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If both neutral points of commercial and bypass AC power supplies are grounded, then the system can operate in lap power feed mode with both power supplies connected to the load, but circulating current flows between the two power supplies through the capacitor
Solution Approach 1:
The patent introduces a control unit as an intermediary that manages the switching between power feed modes. The control unit detects the presence of circulating current by monitoring capacitor voltage and switch currents, and automatically transitions from lap power feed mode to inverter power feed mode when circulating current is detected, thereby eliminating the harmful effect while maintaining continuous power supply capability
Solution Approach 2:
The patent implements feedback control by continuously monitoring the voltage across the capacitor and the current through switches during lap power feed mode. When the monitored parameters indicate circulating current (capacitor voltage deviation or excessive switch current), the control unit receives feedback and automatically switches to inverter power feed mode, preventing the circulating current from causing overcurrent or overvoltage shutdowns
2Reliability
If circulating current is detected through overcurrent or overvoltage detection, then the system can protect itself from damage, but the operation of the uninterruptible power supply apparatus and load is stopped
Solution Approach 1:
The patent applies preliminary action by proactively switching from lap power feed mode to inverter power feed mode when circulating current is detected through monitoring capacitor voltage and switch currents. This preventive switching occurs before overcurrent or overvoltage conditions develop that would trigger shutdown protection, thereby maintaining continuous operation while still protecting the system from damage
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively prevents circulating current even when both neutral points are grounded, ensuring continuous operation and reducing power consumption by setting reference voltages for capacitors and batteries.
Implementation Method 1
a forward converter, configured to convert three phase AC voltage to DC voltage
Implementation Method 2
a capacitor, configured to smooth DC output voltage of the forward converter
Implementation Method 3
a reverse converter, configured to convert terminal-to-terminal voltage of the capacitor to three phase AC voltage
Data Source
AI summary
A control device of an uninterruptible power supply apparatus turns on a first switch and a second switch and turns off a third switch in an inverter power feed mode, turns on the first and third switches and turns off the second switch in a bypass power feed mode, and executes a lap power feed mode of turning off the first switch and turning on the second and third switches in a switching period in which one mode of the inverter power feed mode and the bypass power feed mode is switched to the other mode.