Inverter Controller Dynamic Overcurrent Protection
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Solution Overview
Problem
Existing power conversion apparatuses for hybrid and electric automobiles face issues with overcurrent protection, as the fixed overcurrent detection level leads to excessive regenerative energy during high-speed motor operation, potentially damaging the DC-side capacitor due to overvoltage, and current limiting methods are wasteful by allowing unnecessary output currents during restarts.
Innovation Solution
A power conversion apparatus with a controller that dynamically adjusts the overcurrent and current limit levels based on motor rotation speed, using a current detecting unit, overcurrent level determining unit, and current limit level determining unit to generate signals for turning off semiconductor switching devices or limiting output current, ensuring lower values as rotation speed increases, thereby reducing regenerative energy and preventing capacitor breakdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed overcurrent detection level is used in the inverter, then the inverter can be protected from overcurrent under normal operating conditions, but during high-speed rotation the regenerative energy becomes excessively large causing capacitor breakdown due to overvoltage
Solution Approach 1:
The patent applies dynamics by making the overcurrent detection level variable rather than fixed. The control device dynamically adjusts the overcurrent detection level based on the motor's rotation speed - using a higher level at low speeds and a lower level at high speeds. This dynamic adjustment prevents capacitor breakdown during high-speed operation while maintaining adequate protection during normal operation.
Solution Approach 2:
The patent changes the parameter of overcurrent detection level according to rotation speed. Specifically, the overcurrent detection level is set to a first level when rotation speed is below a threshold, and to a second level (lower than the first) when rotation speed exceeds the threshold. This parameter change approach directly addresses the contradiction by adapting the protection level to operating conditions.
2Reliability
If all gates of the inverter are shut off to stop the inverter in an emergency during high-speed rotation, then overcurrent protection is achieved, but large regenerative energy is generated causing overvoltage on the capacitor
Solution Approach 1:
The patent applies dynamics by adjusting the overcurrent detection level dynamically based on rotation speed. During high-speed operation, the lower detection level triggers protection earlier, preventing the accumulation of excessive regenerative energy that would occur with a fixed high-level threshold.
Solution Approach 2:
The patent applies preliminary anti-action by setting a lower overcurrent detection level before high-speed operation begins. This preliminary setting prevents the condition where large regenerative energy would be generated, rather than reacting after the problem occurs. The control device proactively adjusts parameters to prevent harmful effects.
3Ease of operation
If a fixed current limit level is used during restart, then the inverter can be restarted after emergency stop, but unnecessary output current flows causing increased losses
Solution Approach 1:
The patent applies dynamics by making the current limit level variable based on rotation speed. During restart after emergency stop, the current limit level is dynamically adjusted to a lower value when the motor is rotating at high speed, rather than maintaining a fixed high level. This reduces unnecessary current flow and energy losses while still enabling successful restart.
Solution Approach 2:
The patent changes the current limit level parameter according to rotation speed conditions. When the motor rotates at high speed during restart, the current limit level is set to a lower value to reduce losses, while still maintaining sufficient current for successful motor restart. This parameter adaptation resolves the contradiction between restart capability and energy efficiency.
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 effectively reduces overcurrent and current limit levels with increasing motor speed, minimizing voltage on the DC-side capacitor and reducing losses during emergency stops and restarts, enhancing efficiency and preventing capacitor damage.
Implementation Method 1
when the inverter is stopped in an emergency during high-speed rotation of the motor, large energy is regenerated to a DC-side capacitor of the inverter
Data Source
AI summary
A controller for switching an inverter includes a current detecting unit, an overcurrent level determining unit which determines an overcurrent level for stopping the inverter in accordance with a value corresponding to the number of revolutions of a motor, a current comparing unit which compares a detected output current value of the inverter with the overcurrent level, and a gate signal generating unit which generates a signal for turning off all semiconductor switching devices of the inverter when the current comparing unit makes a determination that the detected output current value has reached the overcurrent level. The overcurrent level is lowered as the number of revolutions of the motor increases.