Current estimating device, electric compressor, current estimating method, and motor current effective value estimating method
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Solution Overview
Problem
In inverter integrated electric compressors for vehicle air conditioners, accurately estimating the capacitor current is challenging, which hinders effective compressor operation and failure prevention.
Innovation Solution
A current estimating device that calculates the capacitor current using a voltage utilization rate, derived from input voltage and motor rotation speed, and applies it to specific calculation expressions to determine the capacitor current, along with estimating the motor current effective value by multiplying constants with the input current of the inverter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current sensor is installed to directly measure capacitor current, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent uses an intermediary approach by measuring the motor current (which is easier to access) and using calculation based on the voltage utilization rate to derive the capacitor current. This avoids direct measurement of capacitor current while still achieving accurate estimation through a mathematical relationship: Ic = α × Im, where α is derived from the voltage utilization rate.
Solution Approach 2:
The patent replaces the physical measurement system (current sensor on capacitor) with a computational system. By substituting direct electrical measurement with mathematical calculation based on readily available motor current and voltage utilization rate data, the system achieves the same measurement objective without additional hardware complexity.
2Reliability
If additional sensors are added to measure capacitor current, then reliability is improved, but compactness and ease of manufacture deteriorate
Solution Approach 1:
The system uses existing sensors (motor current sensor and voltage sensor) to serve multiple purposes. The same sensors that monitor motor operation are also used to calculate the voltage utilization rate and subsequently estimate the capacitor current, making the existing measurement infrastructure work harder rather than adding new sensors.
Solution Approach 2:
The patent makes the existing current and voltage sensors universal by using them for both motor control functions and capacitor current estimation. The voltage utilization rate calculation repurposes existing measurements to provide additional diagnostic capability without requiring dedicated sensors for capacitor monitoring.
3Reliability
If direct capacitor current measurement is implemented, then compressor failure prevention is improved, but device complexity increases
Solution Approach 1:
The system performs preliminary calculation of the voltage utilization rate and capacitor current estimation continuously during operation, rather than waiting for failure conditions. This ongoing estimation provides early warning capability and allows preventive action before actual failures occur, maintaining reliability without complex emergency detection systems.
Data Source
AI summary
A current estimating device that estimates a capacitor current of a high-voltage circuit for driving a motor, wherein the current estimating device calculates a voltage utilization rate using the input voltage of an inverter included in the high-voltage circuit and the speed of the motor, calculates a first constant by applying the voltage utilization rate to a predetermined first arithmetic expression, and calculates the capacitor current of an electrical condenser included in the high-voltage circuit by multiplying the first constant by a motor current effective value.