Three-Level EV Drive Neutral-Point Balancing via Dual DC-DC
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Solution Overview
Problem
Conventional three-level electric drive systems for electric vehicles require additional hardware for neutral point balancing, increasing volume and cost due to the need for high-voltage withstand power devices and complex control systems.
Innovation Solution
The system incorporates a DC-DC conversion circuit with two parallel-connected conversion circuits and a controller that balances the neutral point potential by adjusting the operating statuses of these circuits, reducing the need for hardware balancing and lowering voltage withstand requirements for power devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a hardware balanced circuit is added to balance the bus neutral point potential, then the three-level electric drive system performance is improved, but the volume and costs of the system are increased
Solution Approach 1:
The patent combines the neutral point potential balancing function with the existing DC-DC conversion circuit. The DC-DC circuit's input terminal is connected in parallel to the bus capacitor, and through coordinated control of the full bridge LLC resonant conversion circuits, it simultaneously performs power conversion and neutral point balancing, eliminating the need for separate hardware balancing circuits and reducing system volume.
Solution Approach 2:
The DC-DC conversion circuit is designed to perform multiple functions: it converts DC voltage from the bus capacitor to power the low-voltage system, while also serving as the neutral point potential balancing circuit. This multi-functional design eliminates redundant components and reduces overall system volume and cost.
2Reliability
If a hardware balanced circuit is added to balance the bus neutral point potential, then the three-level electric drive system performance is improved, but the costs of the system are increased
Solution Approach 1:
The patent merges the neutral point balancing function into the existing DC-DC conversion circuit, eliminating the need for separate hardware balancing components. This integration reduces component count, material costs, and manufacturing complexity, thereby lowering overall system cost.
Solution Approach 2:
The DC-DC conversion circuit performs dual functions as both a power conversion device and a neutral point balancing circuit. This multi-functionality eliminates redundant hardware, reducing bill of materials costs and manufacturing expenses while maintaining system reliability.
3Duration of action of moving object
If high-voltage power batteries are used to improve endurance mileage, then the vehicle range is extended, but the voltage withstand requirements for power devices increase
Solution Approach 1:
The patent introduces the DC-DC conversion circuit as an intermediary between the high-voltage power battery and the low-voltage system. The circuit steps down the high voltage from the power battery to a lower voltage level, allowing the use of high-voltage batteries for extended range while protecting downstream components from excessive voltage stress through the transformer and rectifier stages.
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 the volume and cost of the electric drive system while facilitating the use of high-voltage power batteries for improved endurance mileage, with lower switching losses and easier product selection.
Implementation Method 1
The first full bridge LLC resonant conversion circuit and the second full bridge LLC resonant conversion circuit have same dotted terminals of primary-side windings and same quantities of turns of coils and share a magnetic core of a transformer
Implementation Method 2
The first full bridge LLC resonant conversion circuit and the second full bridge LLC resonant conversion circuit have same resonance frequencies
Data Source
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AI summary
This application provides an electric drive system, a powertrain, and an electric vehicle, and relates to the field of power electronic technologies. The electric drive system is connected to power batteries and includes: a bus, a three-level inverter circuit, a DC-DC conversion circuit, and a controller. The bus includes a positive bus and a negative bus. The three-level inverter circuit includes a first bus capacitor and a second bus capacitor. The first bus capacitor is connected between the positive bus and a bus neutral point, and the second bus capacitor is connected between the negative bus and the bus neutral point. The DC-DC conversion circuit includes a first conversion circuit and a second conversion circuit, an input terminal of the first conversion circuit is connected in parallel to the first bus capacitor, and an input terminal of the second conversion circuit is connected in parallel to the second bus capacitor. An output terminal of the DC-DC conversion circuit is connected to a low-voltage system and/or a battery of the electric vehicle. The controller is configured to control the first conversion circuit and the second conversion circuit. A volume and costs of the electric drive system are reduced.