Dynamic DC Bus Voltage Control for Hybrid Vehicle Power Conversion
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Solution Overview
Problem
In hybrid vehicles, high DC bus voltage during deceleration regeneration leads to increased generation loss in step-down DC/DC converters and inverters, and the cell balance function of high voltage batteries cannot be realized in real time, resulting in larger and more costly components and slower cell voltage balance.
Innovation Solution
A power conversion device with a dual half-bridge DC/DC converter system that selectively switches between multiple electric storage devices to control the DC bus voltage, reducing losses and downsizing inverters and DC/DC converters by maintaining the DC bus voltage at a lower level when not necessary, and enabling real-time cell voltage balance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the DC bus voltage is maintained at a high value during deceleration regeneration to increase energy regeneration amount, then the energy regeneration amount is increased, but the generation loss in the step-down DC/DC converter increases and the converter size increases
Solution Approach 1:
The patent applies dynamics by making the DC bus voltage adjustable rather than fixed. The voltage is dynamically changed between a first voltage (higher) during deceleration regeneration to maximize energy recovery, and a second voltage (lower) during normal operation to minimize generation loss in the DC/DC converter. This temporal variation in voltage levels resolves the contradiction between maximizing energy regeneration and minimizing converter losses.
Solution Approach 2:
The patent changes the voltage parameter of the DC bus based on operational conditions. By switching between two distinct voltage levels (first voltage during regeneration, second voltage during normal operation), the system optimizes both energy recovery efficiency and converter efficiency, preventing the converter from operating continuously at high voltage where generation losses occur.
2Power
If the DC bus voltage remains at a high voltage during heavy load state to supply power to 14V electrical components, then the power supply capability is maintained, but the generation loss in the step-down DC/DC converter increases
Solution Approach 1:
The system dynamically adjusts the DC bus voltage based on the operational state. During heavy load conditions, the voltage is set to the second (lower) voltage level, which reduces generation loss in the DC/DC converter while still providing adequate power to 14V electrical components through the converter's power conversion function.
3Power
If the DC bus voltage is kept high during M/G start to enable engine restart, then the starting capability is achieved, but the generation loss in the inverter increases and cooling performance must be improved
Solution Approach 1:
The patent implements dynamic voltage control where the DC bus voltage is set to the second (lower) voltage level during M/G start operations. This reduces the generation loss in the inverter while maintaining the motor generator's ability to restart the engine, thereby reducing the required cooling performance and system complexity.
4Device complexity
If a single high voltage battery is used for energy storage, then the system structure is simple, but the cell balance function cannot be realized in real time
Solution Approach 1:
The patent segments the single high voltage battery into multiple battery packs, each with its own voltage. By connecting these packs in series/parallel configurations and using DC/DC converters between them, the system enables independent charge control of each pack, achieving real-time cell balance functionality while maintaining a relatively simple overall structure.
Solution Approach 2:
The patent introduces DC/DC converters as intermediary devices between multiple battery packs. These converters enable independent power flow control between packs, allowing the system to balance charge states across different packs in real time while maintaining system simplicity through modular architecture.
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
The solution reduces generation losses in inverters and DC/DC converters, downsizes these components, and allows for real-time cell voltage balance, improving fuel efficiency and reducing component size and cost.
Implementation Method 1
the first half bridge includes a first switching element and a second switching element connected in series to each other and is connected between terminals of one of the plurality of second electric storage devices
Data Source
AI summary
A power convertor including an inverter driving a motor generator, a first DC/DC converter connected to a DC bus of the inverter, a second DC/DC converter varying voltage of the DC bus, and a control device controlling the inverter, the first DC/DC converter, and the second DC/DC converter. The power converter is a power conversion device setting voltage of the DC bus in a second control state higher than a voltage of the DC bus in a first control state by controlling the second DC/DC converter according to the control device. By setting the voltage of the DC bus of the inverter to a low voltage when it is not necessary, it is possible to reduce loss in the inverter and the step-down DC/DC converter, and to downsize the inverter and the step-down DC/DC converter.