Power Conversion Device Discharge Control via Contactor Merging
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Solution Overview
Problem
Existing rapid discharge circuits for power conversion devices in electric vehicles are complex and prone to failure, requiring high-voltage transistors and detection circuits, which complicates the discharge process and reduces reliability.
Innovation Solution
A power conversion device with a rapid discharge control circuit and a discharging switching element, utilizing a low-resistance resistor and a driver circuit board to rapidly discharge the capacitor, with a self-shut-off function and temperature-dependent PWM frequency adjustment to ensure safe and reliable discharge within 30 seconds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a rapid discharge circuit with a low-resistance discharge resistor and semiconductor switch is provided, then the discharge time is reduced to 30 seconds or less, but the circuit becomes complicated with high-voltage transistors, detection circuits, and control circuits
Solution Approach 1:
The patent combines the discharge switch function with the existing contactor mechanism. The contactor, which already exists to connect/disconnect the battery from the inverter, is utilized to also perform the discharge switch function by connecting the discharge resistor to the capacitor when the contactor opens. This eliminates the need for separate high-voltage transistors and control circuits, reducing circuit complexity while maintaining rapid discharge capability.
Solution Approach 2:
The contactor is given a dual function: it serves both as the main power connection/disconnection switch and as the discharge switch for the capacitor. By making the contactor multi-functional, the patent eliminates the need for dedicated discharge circuit components, thereby simplifying the overall circuit structure while achieving rapid discharge within 30 seconds.
2Loss of time
If a discharge resistor with 20 kΩ or less resistance is used to discharge the capacitor within 30 seconds, then the discharge time is reduced, but power loss increases significantly when 400V is applied
Solution Approach 1:
The discharge resistor is not continuously connected but is activated periodically or conditionally - specifically, it is connected only when the contactor opens and discharge is needed. This intermittent activation allows the use of a low-resistance discharge resistor for rapid discharge without incurring continuous power loss during normal operation, thus resolving the contradiction between fast discharge and energy efficiency.
Solution Approach 2:
The discharge resistor is pre-positioned in the circuit through the contactor mechanism, ready to be activated when needed. When the contactor opens, the discharge resistor automatically connects to the capacitor, initiating rapid discharge before the system requires shutdown or maintenance. This preliminary preparation allows fast discharge without continuous energy loss.
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
The solution improves the reliability of the discharge function by providing a redundant discharge mechanism using the driver circuit board, ensuring safe and efficient discharge of the capacitor even if the rapid discharge control circuit fails, while minimizing heat generation and maintaining a compact device design.
Implementation Method 1
a rapid discharge circuit in which a rapid discharge resistor and a discharging switching element are connected in series to each other, and the series circuit is connected in parallel to the voltage smoothing capacitor
Data Source
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AI summary
A power conversion device (140) includes an inverter circuit (12) that includes a bridge-connected power semiconductor element and is connected to a DC power supply through an openable and closable contactor (15), a driver circuit (21) to drive the power semiconductor element, a driver circuit control part (18) that performs PWM (Pulse Width Modulation) control on the driver circuit and causes the power semiconductor element to perform a switching operation, a voltage smoothing capacitor (500) connected in parallel to an input side of the inverter circuit, a driver power supply circuit (27) that is connected in parallel to the voltage smoothing capacitor, is inputted with a voltage applied to the voltage smoothing capacitor and supplies electric power to the driver circuit, a discharge circuit that includes a resistor (25) for discharging an electric charge of the voltage smoothing capacitor and a discharging switching element (26) connected in series to the resistor, and is connected in parallel to the voltage smoothing capacitor, and a discharge control part (24) that turns on the discharging switching element when the contactor is placed in an open state and causes the discharge circuit to discharge.