Power Converter Discharge Circuit Reliability
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Solution Overview
Problem
Existing discharge control systems in power conversion systems for electric vehicles face reliability issues due to heat generation and efficiency deterioration in capacitor discharge methods, particularly when the contactor or microcomputer fails, leading to potential burnout of discharge resistors.
Innovation Solution
A power conversion system incorporating a discharge circuit with a switching element connected in series to a discharge resistor, controlled by a first and second discharge control circuit, including microcomputers and pulse generation circuits, which ensures reliable discharging even in the event of failures, using insulated transmission elements and a one-shot circuit for pulse width control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a discharge resistor is connected across the capacitor to discharge stored charges, then the capacitor can be discharged, but heat generation occurs and conversion efficiency deteriorates
Solution Approach 1:
The patent implements periodic discharge control by using a one-shot circuit to generate pulse signals with predetermined widths. The switching element connected in series with the discharge resistor is activated only during specific time periods when discharge is actually needed, rather than remaining continuously conductive. This periodic activation eliminates continuous heat generation while ensuring the capacitor is discharged when required, thereby resolving the contradiction between reliable discharge control and energy efficiency.
2Loss of energy
If a switching element is connected in series with the discharge resistor to enable controlled discharging, then heat generation is reduced, but reliability of discharge control deteriorates due to potential failure modes
Solution Approach 1:
The patent applies beforehand cushioning by implementing multiple protective mechanisms before failures can occur. The one-shot circuit is designed with built-in timeout functionality that automatically interrupts the discharge path if the switching element fails to turn off. Additionally, the circuit includes protection against contactor failure modes, ensuring that even if the main contactor fails, the discharge resistor cannot burn out due to the predetermined pulse width limitation. These preventive measures cushion against potential failures before they cause damage.
Solution Approach 2:
The one-shot circuit serves as an intermediary between the control system and the discharge switching element. It mediates the control signal by generating precisely timed pulse signals with predetermined widths, ensuring that the switching element is activated only for the necessary duration. This intermediary layer provides an additional level of control and protection, preventing direct connection issues between the contactor and discharge resistor from causing resistor burnout.
3Ease of operation
If a differentiation circuit is used to detect voltage changes for discharge control, then discharge timing can be determined, but reliability of discharge control is insufficient
Solution Approach 1:
The patent replaces the mechanical/electronic differentiation circuit approach with a digital timing-based control system. Instead of using analog voltage differentiation to detect discharge conditions, the system uses a microcomputer to monitor capacitor voltage and a one-shot circuit to generate precisely timed discharge pulses. This substitution of analog detection with digital timing control provides more reliable and programmable discharge control, eliminating the reliability issues associated with analog differentiation circuits while maintaining ease of operation.
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 system improves the reliability of discharge control by preventing resistor burnout and maintaining efficient discharging operations even when the contactor or microcomputer fails, enhancing overall system reliability and reducing heat generation.
Implementation Method 1
a discharge resistor for discharging a charge stored in the capacitor
Data Source
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AI summary
A power conversion system according to the present invention includes: an inverter circuit unit that converts a direct current power supplied from a direct current source into an alternating current power, the direct current power being supplied to the inverter circuit through a contactor that conducts and interrupts the direct current; a capacitor that smoothes the direct current power; a discharge circuit unit that is connected to the capacitor in parallel, and that includes a discharge resistor for discharging a charge stored in the capacitor and a switching element for the discharge resistor, being connected in series to the discharge resistor; a voltage detection circuit unit that detects voltage between both terminals of the capacitor; a first discharge control circuit that includes a first microcomputer, and that outputs a control signal to control switching of the switching element for discharging; and a second discharge control circuit that outputs an interruption signal to interrupt the switching element for the discharge resistor.