IGBT Current Estimation via Sense Transistor and Temperature
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Solution Overview
Problem
Existing electric power conversion devices using IGBTs face challenges in accurately measuring principal currents due to non-linear voltage-current characteristics and the high cost and temperature limitations of current sensors.
Innovation Solution
An electric power conversion device with principal current estimation means that utilizes a sense current and temperature measurement on the same semiconductor substrate, allowing for accurate current measurement without a current sensor, by using a differential amplifier and microcomputer to estimate the principal current based on the ratio of currents through the principal and sense IGBTs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current sensor is used to measure the principal current, then the current measurement can be obtained, but the cost increases and the device cannot operate at high temperature
Solution Approach 1:
The patent creates a sense IGBT that copies the structure and characteristics of the principal IGBT, but with a smaller size. The sense IGBT replicates the voltage-current characteristics and temperature dependencies, allowing current measurement through voltage comparison rather than direct current sensing. This copying approach eliminates the need for external current sensors that have temperature limitations.
Solution Approach 2:
The patent replaces the mechanical/current-based sensing system with an electrical voltage comparison system. Instead of using a physical current sensor with magnetic cores and hall elements, the invention uses voltage measurements across the sense and principal IGBTs, processed through operational amplifiers and microcomputers, to determine the principal current. This substitution enables high-temperature operation.
2Measurement precision
If a current sensor is used to measure the principal current, then the current measurement can be obtained, but the device cost increases
Solution Approach 1:
The patent creates a sense IGBT that copies the structure and characteristics of the principal IGBT, but with a smaller size. The sense IGBT replicates the voltage-current characteristics and temperature dependencies, allowing current measurement through voltage comparison rather than direct current sensing. This copying approach eliminates the need for external current sensors that have temperature limitations.
Solution Approach 2:
The patent replaces expensive current sensors with a cost-effective integrated solution using standard semiconductor components. The sense IGBT is fabricated using the same semiconductor process as the principal IGBT, and the measurement system uses operational amplifiers and microcomputers that are inexpensive and widely available, significantly reducing overall device cost.
3Ease of operation
If the sense current ratio method is used to measure principal current, then current measurement is achieved, but the non-linear voltage-current characteristics of IGBT reduce measurement accuracy
Solution Approach 1:
The patent changes the measurement parameter from direct current ratio comparison to voltage comparison. By measuring the voltages across the sense and principal IGBTs and using the relationship V1/I1 = V2/I2, the system transforms the non-linear current-voltage problem into a voltage measurement problem that can be accurately processed through operational amplifiers and microcomputers, compensating for non-linearities.
Data Source
AI summary
An object of the present invention is to provide an electric power converter including means for accurately detecting a principal current of IGBT. An electric power conversion device according to the present invention includes principal current estimation means for estimating a principal current by using: an output of temperature measuring means whose diode is disposed in the same semiconductor substrate as an IGBT including an emitter having flowing therethrough the principal current and a sense emitter having flowing therethrough a sense current proportional to the principal current; the sense current; and the information, preliminarily stored in memory means, on the relationship among the semiconductor substrate temperature, the principal current and the sense currant.