DC Link Capacitor Discharge Timing for Quiet Resonant Converter Startup
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Solution Overview
Problem
Existing resonant power conversion apparatuses face challenges in improving the power factor and reducing repulsive forces without discharging the voltage of a DC link capacitor, leading to potential damage and noise during operation initiation.
Innovation Solution
A method and apparatus that include a discharge circuit with a resistor and a switch controlled by a switch control circuit, which determines a discharge time point and period based on zero-voltage cross and voltage comparator signals to gradually discharge the capacitor before initiating operation, preventing instantaneous current flow and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the DC link capacitor voltage is not discharged before initiating operation, then the power conversion apparatus can start operation immediately, but drastic current changes and noise occur during startup
Solution Approach 1:
The patent applies preliminary action by discharging the DC link capacitor before initiating the switching operation of the power conversion apparatus. The control unit detects whether the capacitor voltage is above a reference voltage, and if so, activates a discharge path to reduce the voltage to below the reference voltage before allowing the switching element to operate. This preliminary discharge prevents drastic current changes and noise during startup while maintaining relatively quick startup time.
2Object-affected harmful factors
If a discharge circuit is added to discharge the DC link capacitor, then current surge and noise are reduced, but the device complexity increases
Solution Approach 1:
The patent applies multi-functionality by designing the discharge circuit such that the same switching element and control unit that manage the main power conversion also control the capacitor discharge. The discharge path utilizes existing circuit components (switching element, capacitor, and control unit) rather than requiring completely separate dedicated discharge components. This approach reduces current surge and noise while minimizing the increase in device complexity.
Solution Approach 2:
The control unit performs self-service by autonomously detecting the capacitor voltage level and automatically activating the discharge path when needed. The control unit monitors the voltage across the DC link capacitor and, upon detecting that it exceeds the reference voltage, automatically controls the switching element to create a discharge path, eliminating the need for external manual intervention or complex additional control circuits.
3Object-affected harmful factors
If the capacitor is discharged using a resistor, then the capacitor voltage is reduced, but power loss occurs during discharge
Solution Approach 1:
The patent applies periodic action by controlling the discharge of the DC link capacitor in a time-limited manner. The control unit activates the discharge path only for a specific discharge period when the capacitor voltage exceeds the reference voltage, then deactivates it once the voltage is reduced below the reference level. This periodic, controlled discharge reduces the capacitor voltage effectively while minimizing power loss compared to continuous discharge, as the discharge occurs only when necessary and for limited durations.
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 stabilizes the operation by preventing drastic current changes and reducing noise during startup, thereby protecting components and ensuring efficient power conversion.
Implementation Method 1
a capacitor configured to be charged with the rectified AC power
Implementation Method 2
a discharge circuit configured to discharge the capacitor before the AC power source is supplied to the load
Data Source
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AI summary
A method is provided for operating a resonant power conversion apparatus. The method may include charging a capacitor connected to a power source in parallel, and determining a discharge time point and a discharge period of a discharge circuit, where the discharge circuit includes a resistor and a switch connected in series and is connected to the capacitor in parallel. The method may also include outputting, by a switch control circuit, a switch control signal by determining the switch control signal based on the discharge time point and the discharge period, and discharging the charged capacitor through the resistor based on the switch control signal applied to the switch. A resonant power conversion apparatus for performing the above-described method is provided.