Hybrid Work Machine DC Bus Voltage Control
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Solution Overview
Problem
In hybrid work machines, the DC bus voltage needed by the electric motor depends on both rotation speed and load magnitude, leading to inefficient output and increased heat generation in the power converter when controlled at a fixed value, limiting the electric motor's output.
Innovation Solution
A controller temporarily raises the DC bus voltage when the required torque exceeds the outputtable torque at the existing voltage, allowing for increased electric motor output without reducing rotation speed and minimizing heat generation in the power converter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the DC bus voltage is controlled at a fixed value all the time, then the heat generation due to switching loss is reduced, but the electric motor output is limited because the DC bus voltage is low
Solution Approach 1:
The patent applies dynamics by transitioning from fixed DC bus voltage control to dynamic voltage adjustment. The control unit temporarily raises the DC bus voltage when the electric motor requires maximum torque (during large load conditions), and maintains normal voltage during other operations. This dynamic adjustment allows the system to optimize both heat generation and motor output according to actual operational needs.
2Power
If the DC bus voltage is held high all the time to enable maximum torque output, then the electric motor can develop maximum torque according to rotation speed, but heat generation due to switching loss increases adversely affecting the power converter
Solution Approach 1:
The patent applies parameter changes by adjusting the DC bus voltage level based on operational requirements. During normal operations, the voltage is maintained at a standard level to minimize heat generation. When maximum torque is required, the control unit temporarily increases the DC bus voltage, enabling the electric motor to deliver maximum torque without continuously operating at high voltage and generating excessive heat.
3Productivity
If the DC bus voltage is variably controlled according to rotation speed of the electric motor, then efficient driving is achieved for turning operations, but the electric motor may fail to develop necessary output when subjected to large load for short time irrespective of rotation speed
Solution Approach 1:
The patent enhances the dynamic control capability by adding load condition detection to the existing rotation-speed-based voltage control. The control unit monitors both rotation speed and load magnitude, and temporarily raises the DC bus voltage when large load is detected, regardless of rotation speed. This ensures the electric motor can deliver maximum torque during brief high-load events (such as wheel loader travel) while maintaining efficient variable voltage control during normal turning operations.
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 enhances the electric motor's output torque temporarily, improving working efficiency while reducing heat generation in the power converter, enabling the hybrid work machine to operate effectively under varying loads without speed reduction.
Implementation Method 1
a buck-boost converter disposed between the DC buses and the electricity storage device, and configured to perform power transfer between the DC buses and the electricity storage device by raising and lowering a voltage of the DC buses
Implementation Method 2
a controller configured to temporarily raise the voltage of the DC buses when a torque required for the electric motor exceeds a torque outputtable at the voltage of the DC buses connected to the power converter
Implementation Method 3
the buck-boost converter boosts a voltage supplied by the electricity storage device to a DC input voltage to the power converter and the power converter converts DC to AC so as to drive the motor generator
Implementation Method 4
an engine-assist motor generator attached to the engine; an electricity storage device configured to store generated power of the motor generator
Implementation Method 5
an electric motor for use in a part of a driving system of the work machine
Data Source
AI summary
A hybrid work machine includes: an engine configured to drive a hydraulic pump as a hydraulic source of a hydraulic actuator; an engine-assist motor generator attached to the engine; an electric motor for use in a part of a driving system of the work machine; an electricity storage device configured to store generated power of the motor generator; a power converter disposed between the electric motor and DC buses; and a buck-boost converter disposed between the DC buses and the electricity storage device, and configured to perform power transfer between the DC buses and the electricity storage device by raising and lowering a voltage of the DC buses, the hybrid work machine, further comprises: a controller configured to temporarily raise the voltage of the DC buses when a torque required for the electric motor exceeds a torque outputtable at the voltage of the DC buses connected to the power converter.