Motor-Inverter Voltage Step-Down for EV Accessory Loads
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Solution Overview
Problem
Existing vehicle electrical systems for battery electric vehicles require separate DC/DC converters to step down battery voltage for accessory loads, increasing cost, mass, and volume.
Innovation Solution
A vehicle electrical system with a power inverter and electric motor that cycles between operational states to step down the rechargeable energy storage system's voltage for accessory loads, using semiconductor switches and inductors to convert DC to AC and mitigate current ripple, allowing the accessory load to be connected directly to the neutral terminal for voltage reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separate DC/DC converter is used to step down battery voltage for accessory loads, then the voltage conversion function is achieved, but the cost, mass, and volume of the vehicle electrical system increase
Solution Approach 1:
The patent combines the DC/DC converter functionality with the existing power inverter by sharing semiconductor switches and control circuitry. The power inverter's switches are utilized to perform both AC conversion for the motor and DC/DC conversion for accessory loads, eliminating the need for a separate DC/DC converter and reducing system mass
Solution Approach 2:
The power inverter is designed to perform multiple functions: converting DC battery voltage to AC for the electric motor, and simultaneously stepping down DC voltage for accessory loads. This multi-functionality approach allows one component to replace what would traditionally require separate dedicated components
2Reliability
If a separate DC/DC converter is used to step down battery voltage for accessory loads, then the voltage conversion function is achieved, but the cost, mass, and volume of the vehicle electrical system increase
Solution Approach 1:
The patent combines the DC/DC converter functionality with the existing power inverter by sharing semiconductor switches and control circuitry. The power inverter's switches are utilized to perform both AC conversion for the motor and DC/DC conversion for accessory loads, eliminating the need for a separate DC/DC converter and reducing system mass
Solution Approach 2:
The power inverter is designed to perform multiple functions: converting DC battery voltage to AC for the electric motor, and simultaneously stepping down DC voltage for accessory loads. This multi-functionality approach allows one component to replace what would traditionally require separate dedicated components
3Reliability
If a separate DC/DC converter is used to step down battery voltage for accessory loads, then the voltage conversion function is achieved, but the cost, mass, and volume of the vehicle electrical system increase
Solution Approach 1:
The patent combines the DC/DC converter functionality with the existing power inverter by sharing semiconductor switches and control circuitry. The power inverter's switches are utilized to perform both AC conversion for the motor and DC/DC conversion for accessory loads, eliminating the need for a separate DC/DC converter and reducing system mass
Solution Approach 2:
The power inverter is designed to perform multiple functions: converting DC battery voltage to AC for the electric motor, and simultaneously stepping down DC voltage for accessory loads. This multi-functionality approach allows one component to replace what would traditionally require separate dedicated components
4Reliability
If the power inverter cycles between connecting and disconnecting the RESS to machine windings, then the voltage is stepped down for accessory loads, but the system complexity increases
Solution Approach 1:
The power inverter is designed to perform multiple functions: converting DC battery voltage to AC for the electric motor, and simultaneously stepping down DC voltage for accessory loads. This multi-functionality approach allows one component to replace what would traditionally require separate dedicated components
Solution Approach 2:
The system dynamically switches between different operational modes: motor drive mode where the power inverter converts DC to AC for the motor, and DC/DC conversion mode where the same power inverter steps down voltage for accessory loads. The semiconductor switches are controlled to transition between these states, enabling flexible voltage management
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 solution reduces the need for additional DC/DC converters, minimizing system weight, cost, and volume while efficiently providing the required voltage to accessory loads, enhancing system efficiency and performance.
Implementation Method 1
The machine windings are a plurality of inductors
Implementation Method 2
The power inverter includes a set of semiconductor inverter switches that are configured to convert direct current (DC) power to alternating current (AC) power
Data Source
AI summary
An example of a vehicle electrical system includes a rechargeable energy storage system (RESS) having a first voltage and a power inverter electrically connected to the RESS. The system further includes an electric motor having a plurality of machine windings with each of the machine windings including a polyphase terminal electrically connected to the power inverter. The electric motor further includes a neutral terminal separate from the polyphase terminals. The system further includes an accessory load electrically connected to the power inverter and the neutral terminal of the electric motor, with the accessory load requiring a second voltage that is below the first voltage. A current flows through the machine windings to step down the first voltage to the second voltage. The power inverter is configured to cycle between first and second operational states, such that the power inverter steps down the first voltage to the second voltage.