Variable DC Bus Voltage Control for Inverter Thermal Stress
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Solution Overview
Problem
In vehicle systems, a fixed DC bus voltage can lead to increased thermal stress on capacitors and switches in inverters, reducing their longevity, necessitating a system and method for variable DC bus voltage to mitigate this issue.
Innovation Solution
A system and method that involves a voltage command estimator determining the minimum required DC bus voltage based on direct-axis and quadrature-axis current/voltage commands for electric machines, which is then regulated by a voltage regulator to adjust the DC bus voltage, thereby reducing thermal stress and extending the lifespan of inverter components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the DC bus voltage level is designed at a higher level than required, then the available AC output of the inverter is improved, but the capacitor and switches experience increased thermal stress reducing longevity
Solution Approach 1:
The patent implements a dynamic DC bus voltage control system that adjusts the voltage level in real-time based on actual load requirements. The voltage regulator receives feedback about the required voltage and dynamically modulates the DC bus voltage, transitioning from a static fixed-voltage design to a dynamic adaptive system. This resolves the contradiction by providing high voltage only when needed for high power output, while reducing voltage during low-load conditions to minimize thermal stress on capacitors and switches.
Solution Approach 2:
The system changes the voltage parameter of the DC bus from a fixed constant value to a variable value that adapts to operational conditions. By using a voltage regulator to continuously adjust the DC bus voltage level based on load demands, the system optimizes the balance between power capability and component stress, resolving the contradiction between having sufficient voltage for AC output and minimizing thermal stress on components.
2Adaptability or versatility
If the DC bus voltage is fixed at a higher level, then the inverter can provide sufficient AC output for variable loads, but thermal stress on capacitors and switches increases
Solution Approach 1:
The patent transforms the static fixed-voltage system into a dynamic variable-voltage system that adapts to different load conditions. The voltage regulator continuously adjusts the DC bus voltage based on feedback about actual load requirements, ensuring the system has sufficient voltage headroom for variable loads while avoiding excessive voltage during light-load conditions that would cause unnecessary thermal stress.
Solution Approach 2:
The system implements a feedback control mechanism where the voltage regulator monitors the actual voltage requirements of the inverter and adjusts the DC bus voltage accordingly. This closed-loop feedback system ensures the DC bus voltage is maintained at the minimum necessary level to support the current load, preventing both insufficient voltage for load handling and excessive voltage causing thermal stress.
Data Source
AI summary
A voltage command estimator is configured to estimate a minimum required variable DC bus voltage based on the first direct-axis current/voltage command, the first quadrature-axis current/voltage command, the second direct-axis current/voltage command, and the second quadrature-axis current/voltage command for a respective time interval. The voltage command estimator is configured to provide the estimated minimum required variable DC bus voltage to a voltage regulator to adjust the observed voltage level of the variable DC voltage bus to the estimated minimum required variable DC bus voltage to maintain the operation, as commanded by the voltage/current commands, of the first electric machine under the first variable load and the second electric machine under the second variable load at the time interval.