Vehicle Inverter Overvoltage Protection via Zero Vector Control
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Solution Overview
Problem
In electric vehicles, the inverter system faces damage due to overvoltage issues when the front wheel motor diverges, causing excessive electric energy to flow into a capacitor, leading to rapid increases in DC link voltage across the inverter system.
Innovation Solution
A system comprising two inverters and capacitors connected in parallel, with a controller that monitors voltage levels and operates switching elements to apply zero vectors and zero torque commands, thereby managing voltage across capacitors and preventing overvoltage damage by disconnecting relays and controlling current flows.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the front wheel motor diverges excessively during regenerative braking, then electric energy flows toward the capacitor causing rapid voltage increase, but this leads to overvoltage damage to the inverter
Solution Approach 1:
The controller pre-stores current commands (first current commands causing zero vector application and second current commands causing zero torque generation) to be executed when overvoltage is detected. This preliminary preparation enables immediate protective action without delay, preventing the inverter from damage while managing the capacitor voltage safely
Solution Approach 2:
The controller acts as an intermediary between the capacitor and the inverter, detecting voltage levels and intervening by turning off the relay and executing specific current commands. This intermediary control prevents direct harmful interaction between the overvoltage capacitor and the inverter, resolving the contradiction between energy storage and protection
2Reliability
If the relay connecting the energy storage device and motor is turned off to prevent overvoltage, then inverter damage is prevented, but the motor cannot receive power normally
Solution Approach 1:
The system dynamically adjusts the relay state based on real-time voltage conditions. The relay is turned off only when capacitor voltage reaches dangerous levels during regenerative braking, and can be reopened when voltage is managed safely. This dynamic control maintains inverter protection while restoring normal motor operation when safe
Solution Approach 2:
The controller changes the operating parameters of the inverter by executing specific current commands (zero vector and zero torque commands) after turning off the relay. These parameter changes allow the inverter to operate in a protective mode that prevents damage while maintaining system functionality, bridging the gap between protection and 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
Effectively prevents inverter damage from overvoltage and maintains a stable DC link terminal voltage, extending the driving time of electrical components by managing voltage within a predetermined range.
Implementation Method 1
a first capacitor connected in parallel between the first inverter and the energy storage device and configured to store electric energy of the first motor during regenerative braking
Implementation Method 2
a first inverter having a plurality of switching elements and configured to convert energy provided from an energy storage device into alternating current (AC) power
Data Source
AI summary
A system for protecting a vehicle inverter from overvoltage includes a first inverter having switching elements and converting energy from an energy storage device into AC power. A first motor is driven by receiving the converted AC power. A second inverter is connected in parallel with the first inverter, includes a switching elements, and converts energy from the energy storage device into AC power. A second motor is driven by receiving the converted AC power. A first capacitor is connected in parallel between the first inverter and the energy storage device and stores electric energy of the first motor during regenerative braking. A controller turns off a relay connecting the energy storage device and the motor when a voltage of the first capacitor is equal to or greater than a predetermined voltage and operates the switching elements in the inverters in response to first and second current commands.