Variable Voltage Traction Motor Drive for Hybrid Vehicles
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Solution Overview
Problem
Inverter-driven traction motors in electrified vehicles experience high switching losses due to constant DC-link voltage, which is not optimized for low-speed operations, leading to inefficient energy use and reduced fuel economy.
Innovation Solution
A method to control the traction motor by varying the input voltage to the inverter, tracking the transition point between constant-torque and field-weakening regions, thereby reducing switching and harmonic losses by decoupling the main DC link voltage from the traction inverter and using a separate DC-to-DC converter to provide a variable DC link voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a substantially fixed DC link voltage is used to ensure sufficient voltage for high speed/torque operating points, then the motor can achieve the upper end of speed and torque ranges, but switching losses in the IGBTs and reverse recovery losses in the anti-parallel diodes increase during low speed operations
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed DC link voltage to a variable DC link voltage that adapts to different operating conditions. The voltage is dynamically adjusted based on the motor's speed and torque requirements, being higher for high-speed operations and lower for low-speed operations, thereby optimizing performance across the entire operating range while minimizing energy losses.
Solution Approach 2:
The patent changes the voltage parameter from constant to variable. By modulating the DC link voltage according to the operating point, the system achieves better efficiency at low speeds while maintaining sufficient voltage for high-speed operations. This parameter change directly addresses the contradiction between power capability and energy loss.
2Device complexity
If a substantially fixed DC link voltage is used to maintain consistent operating conditions for the generator and battery, then system simplicity is maintained, but harmonic losses in the traction motor increase during low speed operations
Solution Approach 1:
The system dynamically adjusts the DC link voltage to match the motor's instantaneous requirements. During low-speed operations, the reduced voltage minimizes harmonic content and associated losses. The dynamic control ensures that voltage is only increased when actually needed for high-speed or high-torque operations, balancing efficiency with performance.
3Loss of energy
If the DC link voltage is reduced during low speed operations to reduce switching losses, then energy efficiency improves, but the voltage may be insufficient for achieving the required speed and torque ranges
Solution Approach 1:
The system employs dynamic voltage adjustment where the DC link voltage is reduced during low-speed operations to minimize switching losses, and increased during high-speed or high-torque operations to maintain power capability. This dynamic adaptation resolves the contradiction by matching voltage levels to actual operational requirements in real-time.
Solution Approach 2:
The voltage parameter is changed from a fixed value to a variable value that responds to operating conditions. The control system monitors speed and torque demands and adjusts the DC link voltage accordingly, ensuring sufficient voltage for power requirements while minimizing voltage-related losses during low-demand 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 reduces switching and harmonic losses, improving overall energy efficiency and fuel economy by optimizing voltage usage across different operating points, especially during low-speed vehicle operations.
Implementation Method 1
A first DC-to-AC inverter is connected between the main bus and a traction motor to propel the vehicle
Implementation Method 2
The inverter pulse-width modulates the DC link voltage to deliver an approximation of a sinusoidal current output
Implementation Method 3
The IGBTs and their reverse-recovery diodes have associated switching losses
Implementation Method 4
inverter-driven electric machines to provide traction torque and regenerative braking torque
Implementation Method 5
A second DC-to-AC inverter is connected between the main bus and a generator to convert mechanical power from an internal combustion engine into electricity
Implementation Method 6
variable voltage converter (VVC) to regulate a main bus voltage across a main DC linking capacitor
Data Source
AI summary
A method is provided for controlling a traction motor for an electrified vehicle, wherein the motor is driven by a pulse-width modulated inverter. A drive command from a driver of the vehicle is converted into a demanded torque. A substantially fixed DC link voltage is maintained from a DC power source. An input voltage for supplying to the inverter is calculated that causes the motor to deliver the demanded torque at a transition point between a constant-torque region and a field-weakening region of torque production. The voltage from the DC link is converted to the determined input voltage at an input to the inverter. By lowering the voltage applied to the inverter, switching losses and harmonic losses are reduced.