Bidirectional Chopper Control for Capacitor Overheat Protection
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Solution Overview
Problem
In power conversion devices, capacitors experience thermal runaway and breakage due to temperature increases during chopper operation, leading to the need for large-capacitance capacitors that increase device size and cost.
Innovation Solution
A power conversion device with a current detector and control circuit that estimates the temperature increase of the capacitor and stops the chopper operation when the estimated temperature exceeds a predetermined upper limit, allowing the use of smaller-capacitance capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large-capacitance capacitor is used to prevent temperature increase saturation from exceeding the upper limit value, then the reliability of the capacitor is improved, but the device size and cost increase
Solution Approach 1:
The control circuit performs preliminary estimation of the capacitor's temperature increase value before thermal runaway occurs. By continuously monitoring output current and calculating temperature increase based on the relationship between current and temperature rise, the system takes preventive action before the capacitor reaches dangerous temperature levels, eliminating the need for oversized capacitors.
Solution Approach 2:
The control circuit establishes a feedback mechanism that continuously monitors the output current of the DC power supply and uses this information to estimate the capacitor's temperature increase. The control circuit adjusts the chopper operation based on this feedback, stopping operation when the estimated temperature increase would exceed the upper limit, thereby protecting the capacitor without requiring large capacitance.
2Reliability
If a large-capacitance capacitor is used to prevent temperature increase saturation from exceeding the upper limit value, then the reliability of the capacitor is improved, but the manufacturing cost increases
Solution Approach 1:
The control circuit performs preliminary estimation of the capacitor's temperature increase value before thermal runaway occurs. By continuously monitoring output current and calculating temperature increase based on the relationship between current and temperature rise, the system takes preventive action before the capacitor reaches dangerous temperature levels, eliminating the need for oversized capacitors.
Solution Approach 2:
The control circuit establishes a feedback mechanism that continuously monitors the output current of the DC power supply and uses this information to estimate the capacitor's temperature increase. The control circuit adjusts the chopper operation based on this feedback, stopping operation when the estimated temperature increase would exceed the upper limit, thereby protecting the capacitor without requiring large capacitance.
3Reliability
If the chopper operation is continuously monitored and stopped when temperature increase exceeds the upper limit, then the capacitor reliability is improved, but the device complexity increases
Solution Approach 1:
The control circuit uses the existing output current detection capability of the power conversion device to estimate capacitor temperature increase. By utilizing already-available current information and a simple calculation based on the known relationship between current and temperature rise in capacitors, the system achieves temperature monitoring without requiring separate temperature sensors or complex measurement circuits.
Solution Approach 2:
The invention replaces physical temperature measurement (which would require temperature sensors, thermal couples, or other sensing hardware) with an electrical calculation method. The control circuit estimates temperature increase through mathematical computation based on current data, substituting a simple computational approach for what would otherwise require additional sensing hardware and processing.
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 approach enables the use of smaller-capacitance capacitors, reducing the device's size and cost while preventing capacitor breakage, thereby maintaining stability and efficiency.
Implementation Method 1
a capacitor that stabilizes the second DC voltage
Implementation Method 2
when an operation of the chopper is started, a temperature of the capacitor increases gradually
Data Source
AI summary
An uninterruptible power supply device includes a bidirectional chopper that converts a first DC voltage supplied from a battery into a second DC voltage and supplies the second DC voltage to an inverter when a power failure of a commercial AC power supply occurs. The bidirectional chopper includes a capacitor that stabilizes the second DC voltage. The uninterruptible power supply device further includes: a current detector that detects an output current of the battery; and a control circuit that, based on a detection result by the current detector, calculates an estimated temperature increase value of the capacitor every time a predetermined time period elapses, and stops an operation of the bidirectional chopper when the calculated estimated temperature increase value is higher than an upper limit value.