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 method and system that control first and second inverters coupled to a variable DC voltage bus, where a sensor measures the voltage level, and a voltage command estimator determines the minimum required DC bus voltage based on load conditions, adjusting it through a voltage regulator to maintain operation while reducing thermal stress.
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 based on real-time load conditions. The voltage regulator receives load demand signals and dynamically modifies the DC bus voltage, transitioning from a fixed high voltage design to an adaptive voltage system that maintains only the necessary voltage level for current load requirements, thereby reducing thermal stress on components while preserving adequate AC output capability.
Solution Approach 2:
The system changes the voltage parameter dynamically based on operating conditions. By monitoring load demand and adjusting the DC bus voltage accordingly, the system optimizes the voltage parameter to match actual requirements, avoiding the constant high voltage that causes excessive thermal stress while ensuring sufficient voltage for required power output.
2Reliability
If the DC bus voltage is reduced to lower thermal stress, then component longevity is improved, but the available AC output of the inverter is reduced
Solution Approach 1:
The dynamic voltage adjustment mechanism ensures that the DC bus voltage is reduced only to the extent necessary for current load conditions, while maintaining sufficient voltage levels to support the required AC output. The system continuously adapts voltage levels, preventing both excessive voltage (which causes thermal stress) and insufficient voltage (which limits power output).
Solution Approach 2:
The control system incorporates feedback mechanisms where load demand information is fed back to the voltage regulator, which then adjusts the DC bus voltage accordingly. This closed-loop control ensures that voltage levels are optimized for both component protection and adequate power delivery based on actual system requirements.
Data Source
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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.