Fuel Cell DC Bus Voltage Control for Motor Efficiency Mapping
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Solution Overview
Problem
In fuel cell vehicles, the DC bus voltage is not independently controllable, and the operational efficiency of electric machines is dependent on torque and voltage, which limits the vehicle's efficiency and hydrogen consumption.
Innovation Solution
A controller is programmed to dynamically control the DC bus voltage using DC/DC converters based on the efficiency relationship stored in a lookup table, considering electric machine torque, rotational speed, and temperature, to maximize electric machine efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If DC bus voltage is directly connected to battery pack without control, then system complexity is reduced, but electric machine efficiency cannot be optimized
Solution Approach 1:
The patent implements dynamic DC bus voltage control where the voltage setpoint is adjusted in real-time based on electric machine operating conditions (torque, speed, temperature). The controller continuously updates the target DC bus voltage to match optimal efficiency points, transforming a static system into a dynamic one that adapts to changing operational requirements.
Solution Approach 2:
The system changes the DC bus voltage parameter dynamically based on electric machine efficiency maps. By retrieving optimal voltage values from pre-stored efficiency data and applying them in real-time, the system optimizes electric machine performance without requiring complete redesign of the powertrain architecture.
2Use of energy by moving object
If DC bus voltage is made controllable to optimize electric machine efficiency, then energy usage is improved, but device complexity increases
Solution Approach 1:
The patent pre-calculates and stores optimal DC bus voltage values in lookup tables based on electric machine efficiency maps covering various torque, speed, and temperature conditions. This preliminary preparation allows the controller to simply retrieve and apply pre-determined optimal values during operation, avoiding complex real-time optimization calculations.
Solution Approach 2:
The controller acts as an intermediary between the battery pack and DC bus, introducing a voltage regulation layer that decouples the direct connection. This intermediary component manages the complexity by implementing a straightforward control strategy: retrieve target voltage from lookup table, compare with actual voltage, and adjust DC/DC converter duty cycle accordingly.
3Loss of energy
If DC bus voltage is dynamically adjusted based on electric machine conditions, then hydrogen consumption is reduced, but control system complexity increases
Solution Approach 1:
The system implements feedback control by continuously monitoring actual DC bus voltage and comparing it with the target voltage retrieved from lookup tables. The controller adjusts the DC/DC converter duty cycle based on the voltage error signal, ensuring the system maintains optimal operating conditions despite disturbances or parameter variations.
Solution Approach 2:
The control system serves itself by using pre-stored efficiency data to automatically determine optimal operating parameters. The controller retrieves target voltages from pre-computed lookup tables based on current operating conditions, eliminating the need for complex external optimization algorithms or manual tuning during operation.
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 allows the electric machines to operate near peak efficiency under various conditions, improving overall vehicle efficiency and reducing hydrogen consumption.
Implementation Method 1
A DC/DC converter may be used to increase or decrease the voltage provided from the fuel cell or provided to/from the traction battery to a level suitable for use in powering the electric machines
Implementation Method 2
Fuel cell vehicles harness a chemical reaction between hydrogen and oxygen to generate DC power
Implementation Method 3
converted to AC to power one or more electric machines to propel the vehicle
Data Source
AI summary
A vehicle includes a fuel cell stack, a traction battery, at least one DC/DC converter electrically coupling the fuel cell stack and the traction battery to a DC bus, an electric machine coupled to the DC bus via an inverter, and a controller programmed to control the at least one DC/DC converter to provide a DC bus voltage to maximize efficiency of the electric machine based on torque, rotational speed, and temperature of the electric machine.