Isolated DC/DC Converter Startup Frequency Control for Inrush Suppression
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Solution Overview
Problem
Inrush currents occur during the transition period when AC power is supplied to a charging system, leading to unstable DC power conversion.
Innovation Solution
The charging system employs an AC/DC converter and a DC/DC converter with a control circuit that initiates operation at a higher frequency for the switching elements during activation, transitioning to a lower frequency for steady operation, using pulse width modulation (PWM) and pulse frequency modulation (PFM) controls to manage the duty ratio and frequency of the switching elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the AC/DC converter and DC/DC converter are activated and convert AC power to DC power, then power conversion function is achieved, but inrush current is generated due to unstable DC power in transition period
Solution Approach 1:
The control circuit dynamically adjusts the switching frequency of the switching elements in the DC/DC converter based on the operational state. During startup transition period, the switching frequency is set to a first frequency, and during steady operation, it is set to a second frequency. This dynamic adjustment allows the system to adapt to changing conditions and suppress inrush current while maintaining effective power conversion.
Solution Approach 2:
The invention changes the operational parameter (switching frequency) of the switching elements to control the output voltage of the isolation transformer. By adjusting the switching frequency, the control circuit regulates the transformation ratio of the isolation transformer, thereby controlling the output voltage to prevent inrush current during startup while ensuring proper power conversion functionality.
2Object-generated harmful factors
If the switching elements operate at high frequency during activation, then the output voltage of the isolation transformer is controlled to suppress inrush current, but the operation frequency needs to be changed during steady operation
Solution Approach 1:
The control circuit monitors the operational state of the AC/DC converter and DC/DC converter and adjusts the switching frequency accordingly. During activation, when the DC/DC converter output voltage is unstable, the control circuit maintains a first switching frequency to control the isolation transformer output voltage and suppress inrush current. During steady operation, when voltage stability is achieved, the control circuit switches to a second frequency for optimal performance.
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 effectively suppresses inrush currents by gradually adjusting the operation frequency and duty ratio, ensuring stable power conversion and appropriate gate signal adjustment, thereby preventing excessive current surges.
Implementation Method 1
The DC/DC converter includes an isolation transformer, a primary circuit, and a secondary circuit. The primary circuit is disposed on a primary side of the isolation transformer. The secondary circuit is disposed on a secondary side of the isolation transformer.
Implementation Method 2
The primary circuit includes switching elements. The control circuit is configured to cause the switching elements to start operation at a first frequency when the AC/DC converter and the DC/DC converter are activated. The control circuit is configured to cause the switching elements to operate at a second frequency when the AC/DC converter and the DC/DC converter are in steady operation.
Data Source
AI summary
A charging system includes an AC/DC converter a DC/DC converter, and a control circuit. The AC/DC converter is connected between first/second input nodes and first/second intermediate nodes and is connected to an AC power supply via the first/second input nodes. The DC/DC converter is connected between the first/second intermediate nodes and first/second output nodes and is connectable to a battery via the first/second output nodes. The DC/DC converter includes an isolation transformer, a primary circuit, and a secondary circuit. The primary circuit includes switching elements. The control circuit causes the switching elements to start operation at a first frequency when the AC/DC converter and the DC/DC converter are activated, and causes the switching elements to operate at a second frequency when the AC/DC converter and the DC/DC converter are in steady operation. The first frequency is higher than the second frequency.