Work Vehicle Torque Control for DC Bus Voltage Drop
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Solution Overview
Problem
In electric drive systems for work vehicles, sudden increases in load on the traveling electric motor can cause the DC bus voltage to drop below the operating voltage of the inverters, leading to system failure and cessation of operation, especially when no battery is connected to the DC bus.
Innovation Solution
A work vehicle is equipped with a controller that decreases the output torque of the traveling electric motor when the DC bus voltage drops below a threshold, preventing the voltage from falling to a level that would cause the inverters to stop functioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a battery is not connected to the DC bus in the electric drive system, then the device complexity is reduced and energy saving is improved, but the DC bus voltage may drop below the operating voltage of the inverters when load increases suddenly, causing the inverters to stop working
Solution Approach 1:
The controller performs preliminary detection of DC bus voltage and proactively reduces output torque of the traveling electric motor when voltage drops below a threshold, preventing the voltage from falling to a level that would cause inverter shutdown. This advance action maintains system reliability without requiring a battery connection.
2Productivity
If the output torque of the traveling electric motor is maintained at high levels, then the productivity is improved, but the DC bus voltage drops when load increases suddenly, causing the inverter to stop working
Solution Approach 1:
The controller continuously monitors DC bus voltage and implements feedback control by adjusting the output torque of the traveling electric motor based on voltage levels. When voltage drops below a threshold, the controller reduces torque to maintain voltage within the inverter's operating range, ensuring continuous operation and reliability while maximizing productivity under normal conditions.
Data Source
AI summary
In an electric drive system in which a battery is not connected to a DC bus, even when a load on a traveling electric motor increases suddenly, it is made possible to avoid such a situation that the DC bus voltage drops to a level equal to or lower than an operating voltage of an inverter and the inverter stops working. To this end, a DC bus voltage drop prevention device controls such that, when the voltage of the DC bus drops below a first threshold value, the output torque of the traveling electric motor is decreased according to an amount of decrease in the voltage of the DC bus, and when the voltage of the DC bus drops below a second threshold voltage lower than the first threshold voltage, the output torque of the traveling electric motor is decreased to zero or a value within a range of magnitude with which a work vehicle stays stationary on a level ground.