Inverter Switching Element Speed Limiting for Voltage Protection
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Solution Overview
Problem
Existing electric motor control systems in hybrid and electric vehicles fail to effectively manage voltage applied to semiconductor switching elements in inverters, leading to potential damage due to abnormal voltages generated during malfunctions, particularly at varying temperatures.
Innovation Solution
An electric motor control system that includes an inverter with a temperature observation unit, a rotational speed upper limit setting unit, and a limiting unit, which sets and enforces a rotational speed limit based on the temperature of the switching elements to ensure the voltage applied remains within the elements' withstand voltage, and similarly for regenerative operations, to prevent excessive voltage during power generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the rotational speed of the electric motor is increased to improve power output, then the power generation capability is improved, but the voltage applied to the switching elements may exceed their withstand voltage
Solution Approach 1:
The patent implements dynamic adjustment of the rotational speed upper limit based on real-time temperature monitoring of the switching elements. The control unit varies the rotational speed limit according to temperature changes, allowing higher speeds when temperatures are low (withstand voltage is high) and reducing speeds when temperatures rise (withstand voltage decreases), thus dynamically optimizing power output while ensuring protection against voltage breakdown.
Solution Approach 2:
The patent changes the operational parameters (rotational speed limit) based on temperature conditions. By establishing a relationship between temperature and withstand voltage, and consequently between temperature and rotational speed upper limit, the system adjusts key parameters to maintain safe operation across varying thermal conditions while maximizing power generation capability.
2Reliability
If the rotational speed upper limit is reduced to protect switching elements from excessive voltage, then the reliability is improved, but the power generation capability is reduced
Solution Approach 1:
The system dynamically adjusts the rotational speed upper limit based on real-time temperature monitoring. When switching element temperatures are low, the withstand voltage is high, allowing the system to permit higher rotational speeds and maximize power generation. When temperatures increase and withstand voltage decreases, the system reduces the rotational speed limit to prevent breakdown. This dynamic approach ensures protection while minimizing impact on power generation capability.
Solution Approach 2:
The patent implements a feedback mechanism where the control unit continuously monitors the temperature of the switching elements and adjusts the rotational speed upper limit accordingly. The temperature detection unit provides real-time feedback to the control unit, which then modifies the operational parameters to maintain safe voltage levels while optimizing power output based on current thermal conditions.
3Reliability
If temperature-based rotational speed limiting is implemented to prevent voltage breakdown, then the protection function is improved, but the device complexity increases
Solution Approach 1:
The system employs self-service principles by using the existing temperature detection unit (already present in the inverter for thermal management) to also determine the rotational speed upper limit for protection purposes. The control unit, which already exists for motor control, is enhanced to incorporate the protection logic based on temperature readings. This approach leverages existing system components to provide additional protection functionality without requiring entirely new hardware, thus limiting the increase in device complexity.
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 system effectively limits rotational speed and power generation output to prevent voltage exceeding the switching elements' withstand voltage, minimizing performance limitations and energy loss, while allowing operation at high speeds and outputs within safe temperature ranges.
Implementation Method 1
a predetermined relationship between the withstand voltage and a temperature of the switching elements, indicating that the withstand voltage increases with increasing temperature of the switching elements
Data Source
AI summary
An electric motor control system includes an inverter, an element temperature observation data acquiring device, a rotational speed upper limit setting device, and a rotational speed limiter. The inverter includes switching elements. The element temperature observation data acquiring device is configured to acquire element temperature observation data indicating an observation value of a temperature of the switching elements of the inverter. The rotational speed upper limit setting device is configured to set a rotational speed upper limit of an electric motor in accordance with the observation value of the temperature of the switching elements so as to satisfy a first condition that a voltage applicable to the switching elements in a case where the electric motor is operated at the rotational speed upper limit is lower than or equal to a withstand voltage of the switching elements.