Inverter Thermal Management for Electric Vehicle Startability
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Solution Overview
Problem
Electrical machines in hybrid or electric vehicles experience high thermal loading during low rotational speeds, leading to non-uniform power component loading and temperature swings, which can reduce the lifetime of semiconductor components in inverters, necessitating torque or power reduction to prevent damage.
Innovation Solution
A method and control device that determine phase currents, voltages, and temperatures for each half-bridge branch of an inverter, calculate power losses, and simulate temperature swings using transfer functions to adjust torque or power without impairing component lifetime, allowing for sustained starting torque at low rotational speeds without exceeding maximum temperature limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the electrical machine operates at low rotational speeds with high currents, then the starting torque is sufficient, but the power components experience high thermal loading and temperature swings that reduce their lifetime
Solution Approach 1:
The inverter is divided into multiple half-bridge branches, each with its own temperature monitoring and independent power loss calculation. This segmentation allows selective control of individual branches to manage thermal loading while maintaining overall torque output.
Solution Approach 2:
The control system dynamically adjusts the operating point of the electrical machine based on real-time temperature measurements and power loss calculations. At low rotational speeds, the system actively manages current distribution to prevent excessive temperature swings, while at higher speeds where thermal time constants dominate, normal operation continues.
2Reliability
If the current for generating the torque-generating field is reduced to limit temperature swing, then the power components are protected, but the torque or power of the electrical machine is limited
Solution Approach 1:
The system implements closed-loop feedback by continuously measuring temperatures at power components, calculating power losses, determining temperature swings, and using this information to adjust the operating point. This feedback mechanism allows the system to maintain maximum power output while staying within safe temperature swing limits.
Solution Approach 2:
The control system changes operating parameters (current, voltage, switching frequency) based on the determined temperature swings and baseplate temperature. By dynamically adjusting these parameters, the system optimizes the balance between power output and thermal management.
3Reliability
If torque reduction is applied to prevent excessive temperature swings, then the power components are protected, but the startability of the vehicle is impaired
Solution Approach 1:
The system performs preliminary temperature assessment and power loss calculation before torque limitation is applied. By determining the actual temperature swings and baseplate temperature in advance, the system can make informed decisions about whether torque reduction is necessary, avoiding unnecessary power limitations.
Solution Approach 2:
The control system autonomously manages the balance between torque output and thermal protection without external intervention. It self-adjusts the operating point based on real-time temperature and power loss data, ensuring both vehicle startability and component protection.
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 improved startability of electric vehicles by maintaining torque at low rotational speeds while preventing excessive temperature swings, thus extending the lifespan of power components and reducing the need for precautionary power reductions.
Implementation Method 1
From the current respectively flowing at a power component and from the voltage respectively present, a power loss is calculated for each of the power components
Implementation Method 2
From the power losses a respective temperature swing is then determined for each of the power components and for temperature sensors serving to determine the temperatures on the semiconductor modules
Data Source
AI summary
The invention relates to a method for operating an electrical machine (1) controlled by an inverter (2), wherein the inverter (2) comprises half-bridge branches (10-U, 10-V, 10-W) having power components in the form of controllable power switching elements (3) and power diodes (4) respectively connected in parallel therewith, wherein each of the half-bridge branches (10-U; 10-V; 10-W) is arranged on a separate semiconductor module (11-U; 11-V; 11-W), which are arranged jointly on a baseplate (12), wherein the phase currents (1_U, 1_V, 1_W) flowing through the half-bridge branches (10-U, 10-V, 10-W), the voltages present at the power components and temperatures (t_Sens_U, t_Sens_V, t_Sens_W) on the semiconductor modules (11-U, 11-V, 11-W) are determined, from the current (1_U; 1_V; 1_W) respectively flowing at a power component and from the voltage respectively present a power loss (P) is calculated for each of the power components, from the power losses (P) a relevant temperature swing (Δt; Δt_Sens) is determined for each of the power components and for temperature sensors (13-U, 13-V, 13-W) serving to determine the temperatures on the semiconductor modules, a temperature (TempCooler) of the baseplate (12) is determined from the determined temperatures (t_Sens_U, t_Sens_V, t_Sens_W) on the semiconductor modules (11-u, 11-V, 11-W) and the determined temperature swings (Δt_Sens) at the temperature sensors (13-U, 13-V, 13-W), and a torque or a power of the electrical machine (1) is determined in a manner dependent on the determined temperature swings (Δt) and the determined temperature (TempCooler) of the baseplate (12).