Power Converter Control Unit for Dynamic Current Limits
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Solution Overview
Problem
Existing power conversion apparatuses require significant time to set output conditions due to the difficulty in determining the maximum allowable current without actual current application, especially when operating at lower frequencies or intermittent outputs, leading to inefficient use of the switching device.
Innovation Solution
A power conversion apparatus that includes a rectifier converting AC power to constant-current DC power, a resonant inverter with a switching device, and a control unit that sets and operates based on input current values, current-supplying time, operation rate, and resonance frequency, using pre-associated data to determine operability within the switching device's temperature limits, thereby optimizing output conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the maximum rated value of the inverter is determined and fixed based on the maximum frequency of an operation range with an assumption of continuous output, then the inverter can operate reliably at maximum frequency, but operation with lower output frequency and/or short-time output becomes uneconomical due to the limitation posed by the maximum rated value
Solution Approach 1:
The maximum rated value of the inverter is made dynamically adjustable based on operating conditions such as output frequency and current-supplying time. The control unit changes the maximum rated value within a temperature range in which the switching device can be used, allowing the inverter to operate at higher power levels when frequency is reduced or when operation time is limited, thereby resolving the contradiction between reliability at maximum frequency and productivity at lower frequencies.
2Stability of the object's composition
If voltage-constant control is performed by converting AC power into constant-voltage DC power, then voltage stability is maintained, but it becomes difficult to know how much current will pass through the switching device without actually applying electric current
Solution Approach 1:
The control unit determines the maximum allowable current before actual current application by using pre-stored data associated with output frequency, current-supplying time, and operation rate. This preliminary determination of current limits allows for faster setting of output conditions while maintaining voltage-constant control, resolving the contradiction between voltage stability and time efficiency.
3Reliability
If the control unit detects output current based on current feedback signal and stops or lowers output when current exceeds maximum allowable current, then switching device protection is ensured, but the condition setting must be repeated which takes time
Solution Approach 1:
The control unit performs preliminary calculation of the maximum allowable current based on stored data before actual operation begins. By determining current limits in advance using the association between output frequency, current-supplying time, and operation rate, the system avoids repeated condition setting and trial-and-error adjustments, thereby reducing time loss while maintaining switching device protection.
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 solution reduces the time required for setting output conditions by determining operability without actual current application, allowing efficient utilization of the switching device's capacity and reducing temperature-related losses.
Implementation Method 1
a rectifier configured to convert AC power into DC power
Implementation Method 2
an inverter configured to convert the DC power smoothed by the smoothing filter into high-frequency AC power through on and off of a switching device
Implementation Method 3
When the output frequency of 100 kHz is compared with the output frequency of 10 kHz, a switching loss of the power semiconductor device is ten times larger, and a temperature rise of the power semiconductor device is also significantly different
Data Source
AI summary
A power conversion apparatus includes a rectifier to convert AC power into constant-current DC power, a resonant inverter to convert the DC power into AC power to be output to a load, and a control unit to receive settings of an output current value of the inverter, a current-supplying time of the inverter, an operation rate defined by dividing the current-supplying time by a sum of the current-supplying time and a non-current-supplying time, and a resonance frequency of the load. The control unit operates the rectifier and the inverter only when it determines that it is operable to perform an output in accordance with the set conditions, based on data in which the output frequency, the current-supplying time and the operation rate are associated with an allowable output current value of the inverter at a temperature equal to or lower than a maximum operable temperature of a switching device.