Integrated Precharge Discharge Circuit for EV Drive Capacitors
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Solution Overview
Problem
Existing electric drive systems for electric vehicles require complex and costly circuitry for precharging and discharging capacitors, leading to increased size and component count in the Inverter System Controller (ISC) module, which is undesirable.
Innovation Solution
An integrated precharging and discharging circuit using a common resistance element that connects to the capacitors via a precharge contactor during activation and a discharge switch during deactivation, reducing the number of components and simplifying the module.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate precharging and discharging circuits are used, then the capacitors can be safely precharged and discharged, but the device complexity and component count increase
Solution Approach 1:
The patent combines separate precharging and discharging circuits into a single integrated circuit. The precharge contactor and discharge switch work together with a common resistance element to provide both precharging and discharging functions through unified circuit topology, reducing overall system complexity while maintaining safety.
Solution Approach 2:
The resistance element serves dual purposes: it limits inrush current during precharging and provides a discharge path during deactivation. This multi-functional component eliminates the need for separate dedicated components for each function, reducing component count while ensuring reliable operation.
2Object-affected harmful factors
If a current-limiting resistor is used during precharging, then inrush current is limited, but voltage drop and power consumption occur during normal operation
Solution Approach 1:
The circuit dynamically switches the resistance element into and out of the circuit based on operational state. During precharging, the resistance element is connected to limit inrush current. During normal operation, the precharge contactor opens to disconnect the resistance element, eliminating voltage drop and power consumption. During deactivation, the discharge switch connects the resistance element to dissipate capacitor charge.
Solution Approach 2:
The precharging circuit is activated before main contactors close to preemptively charge capacitors to safe voltage levels. This preliminary action prevents harmful inrush current before it can occur, and the resistance element is subsequently disconnected to avoid ongoing energy losses during normal operation.
3Device complexity
If passive discharge resistor is used, then the circuit is simple, but discharge time is too long (one to two minutes)
Solution Approach 1:
The discharge switch dynamically changes the resistance value in the discharge path. When activated, it connects a smaller resistance value in parallel with or instead of the passive discharge resistor, significantly reducing discharge time from one-two minutes to a few seconds while maintaining circuit simplicity through controlled switching.
4Loss of time
If active discharge circuit with smaller resistance is used, then discharge time is reduced, but component count and ISC module size increase
Solution Approach 1:
The discharge switch and resistance element are integrated into the existing precharging circuit infrastructure. The same resistance element used for precharging also serves as the low-value discharge resistor when activated by the discharge switch. This eliminates the need for separate dedicated discharge components, reducing component count while achieving rapid discharge.
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 allows for efficient precharging and discharging with fewer components, reducing the size and cost of the ISC module while ensuring safe and rapid discharge of capacitors during shutdown.
Implementation Method 1
The simplest conventional methods for discharging the link capacitor use a resistance placed across the capacitor to dissipate the charge
Data Source
AI summary
A shared resistor performs precharging and discharging functions of capacitors in an electric vehicle drive system. In a precharge state, the shared resistor is connected between the capacitors and a DC source via a precharge relay. In a discharge state, the resistor is connected across the capacitors via a discharge transistor. Otherwise, the resistor is disconnected. A bypass switch is connected between the resistor and an input capacitor. The bypass switch is rendered conductive during the precharge state and during the discharge state. The discharge transistor is activated only during the discharge state. As a result, the invention uses less components by virtue of eliminating separate resistance elements for pre-charging and discharging and by eliminating discharge switches dedicated to separate resistances. The circuit integration and the placement of components outside the inverter module improves overall system cost and packaging size.