Three-Phase Inverter DC Link Discharge via Rotating Half-Bridge Shorts
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Solution Overview
Problem
Existing methods for discharging DC link capacitors in electric vehicles are either expensive, require additional components, or fail to ensure rapid and safe discharge, potentially leading to thermal overloading or injury during crashes.
Innovation Solution
A control apparatus for a three-phase inverter that simultaneously switches on lower half-bridge switches and alternates the switch-on of upper half-bridge switches with a temporal offset to rapidly discharge the DC link capacitor without thermal overloading, using existing semiconductor components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a brake chopper with power resistor is used to discharge the DC link capacitor, then the discharge function is achieved, but additional heat sinks are required which are expensive and require structural space, thereby reducing the power density of the inverter
Solution Approach 1:
The existing IGBT half-bridge switches are made to serve dual functions: their primary function for motor control and an additional function for DC link discharge. By alternating the activation of upper and lower switches, the existing semiconductor components perform the discharge function without requiring dedicated discharge components like brake choppers or power resistors.
Solution Approach 2:
The inverter's existing components (IGBT half-bridge switches) are utilized to discharge the DC link capacitor themselves, without needing external discharge devices. The system serves its own discharge need through intelligent switching control of its inherent components, eliminating the need for separate discharge circuitry.
2Device complexity
If discharge by way of motor winding is used, then no additional components are required, but a sufficiently rapid discharge cannot be ensured in all cases and discharge current can induce unwanted motor torques
Solution Approach 1:
The switching strategy dynamically alternates between upper and lower half-bridge switches during the discharge process. This dynamic switching creates a controlled current path that rapidly discharges the capacitor while preventing unwanted motor torques through precise timing and sequence control of the switch transitions.
Solution Approach 2:
The discharge process employs periodic alternating activation of upper and lower switches in a defined sequence. This periodic switching pattern ensures rapid and controlled discharge current flow while maintaining system stability and preventing harmful motor torques through rhythmic current redirection.
3Reliability
If IGBT weak short-circuiting is used to discharge the DC link capacitor, then discharge is achieved, but different gate voltages are required which makes the solution expensive and potentially fault-susceptible
Solution Approach 1:
The solution uses uniform gate voltage control for all IGBT switches throughout the discharge process. By treating all switches symmetrically with the same control methodology and voltage levels, the system avoids the complexity and cost of differentiated gate voltage circuits while achieving effective discharge through alternating switch activation.
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
Ensures a rapid and safe discharge of the DC link capacitor within milliseconds, preventing thermal damage to components and ensuring a non-critical voltage level is reached, thus enhancing safety in vehicle crashes.
Implementation Method 1
The discharge current is converted into heat by the equivalent resistance of the motor windings
Implementation Method 2
the respectively alternating switch-on of one of the upper half-bridge switches of the inverter, in particular with a temporal offset
Data Source
AI summary
A control device for a three-phase inverter of a vehicle prime mover is configured to activate active discharge of a DC link of the inverter and at the same time to switch on the lower half-bridge switches of the inverter during the active discharge, and to switch on an upper half-bridge switch of the inverter. The three-phase inverter has three half-bridges, each having an upper half-bridge switch and a lower half-bridge switch.