Traction Inverter Active DC Bus Discharge Without Bleeder Resistors
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Solution Overview
Problem
Existing traction inverter systems for electric vehicles face inefficiencies in safely and effectively discharging capacitor banks, particularly due to the sporadic use of bleeder resistors which result in inefficiencies during regenerative braking events.
Innovation Solution
A system utilizing a plurality of power transistors and gate drivers to actively control the discharge of the DC bus capacitor bank by applying a voltage across the power transistors, allowing for controlled current conduction and safe dissipation of energy, operating within specific voltage thresholds and regions to manage the discharge process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dedicated power transistor and high-voltage resistor are used for capacitor bank discharge, then discharge safety and control are improved, but device complexity and cost increase
Solution Approach 1:
The patent makes the power transistors perform a dual function: motor drive operation and capacitor bank discharge. By controlling the gate drivers to apply voltage across selected power transistors, the same transistors used for motor control are utilized to actively discharge the DC bus capacitor bank, eliminating the need for separate discharge transistors and resistors.
Solution Approach 2:
The invention merges the motor drive circuit and capacitor discharge circuit into a single integrated system. The power transistors, gate drivers, and control logic that originally served only motor control now also handle capacitor discharge, combining previously separate functions into one unified circuit architecture.
2Loss of energy
If a dedicated high-voltage resistor is used for capacitor discharge, then energy dissipation is improved, but footprint and space requirements increase
Solution Approach 1:
The patent extracts the dedicated discharge resistor component from the system entirely. Instead of using a physical high-voltage resistor to dissipate energy, the system uses the inherent resistance of the power transistors when operated in their linear region, removing the need for separate discharge resistance hardware.
Solution Approach 2:
The power transistors serve dual purposes: motor drive switching and energy dissipation during discharge. By operating transistors in their linear (ohmic) region rather than saturation mode, they function as controllable variable resistors that dissipate capacitor energy without requiring dedicated discharge components.
3Reliability
If bleeder resistors are used for capacitor discharge, then discharge function is provided, but efficiency is reduced due to sporadic use during regenerative braking
Solution Approach 1:
The patent transforms the static, passive bleeder resistor into a dynamic, active discharge system. The gate drivers dynamically control the power transistors to operate in their linear region, enabling variable resistance that adapts to discharge requirements. This active control allows efficient energy dissipation only when needed, rather than continuous energy loss through a fixed resistive path.
Solution Approach 2:
The invention changes the operating parameters of the power transistors from binary switching modes (on/off) to linear region operation during discharge. By adjusting gate voltage to maintain transistors in their ohmic region, the system creates a variable resistance that can be precisely controlled to match discharge requirements, improving efficiency over fixed resistive 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 approach enables controlled and efficient discharge of the capacitor bank, reducing inefficiencies and overhead costs associated with traditional bleeder resistors, while ensuring safe energy dissipation and compliance with safety regulations.
Implementation Method 1
causing the plurality of power transistors to conduct current during the controlled time
Implementation Method 2
safely dissipate the energy extracted from the capacitors
Data Source
AI summary
Systems, circuits, and methods provide controlled active DC bus discharge, such as for electric vehicles (EVs) or hybrid vehicles. Controlled active DC bus discharge can be provided using gate drivers to control operation of traction inverter switches, such as power transistors, to accomplish a charge bleeding function. Power transistors can be configured so that the gate is connected to the drain, thereby forcing the gate threshold voltage across drain and source. The gate of a power transistor can be actively driven between a threshold voltage and Miller plateau threshold voltage. As a result, several volts can be generated across the power transistor while current decays, therefore safely discharging the system DC bus.