IGBT Turn-Off Detection Using Dynamic Reference Voltage
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Solution Overview
Problem
Current power conversion apparatuses face challenges in accurately detecting and controlling the turn-off times of power semiconductor elements, particularly IGBTs, due to variations in collector current, leading to current imbalances and potential damage from tail currents.
Innovation Solution
A control device with gate drive circuits, timing detection comparators, and sample and hold circuits that compare sense voltages to detect turn-on and turn-off times, using a divided reference voltage to accurately determine turn-off times independently of the collector current, thereby aligning the turn-on and turn-off times of parallel-connected power semiconductor elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed reference voltage is used to detect turn-off time, then the detection circuit is simple, but the turn-off time detection becomes inaccurate when collector current varies
Solution Approach 1:
The reference voltage is changed from a fixed value to a dynamic value that varies with the collector current. The sample and hold circuit captures the sense voltage at turn-on moment, and the voltage division circuit creates a reference voltage proportional to the actual collector current, enabling accurate turn-off detection across different current levels
Solution Approach 2:
The reference voltage parameter is made variable instead of fixed. By using the sense voltage (which reflects collector current) as the basis for generating the reference voltage, the system adapts the detection threshold to match the actual operating conditions, ensuring consistent turn-off detection accuracy
2Reliability
If turn-off detection is based on fixed reference voltage, then the circuit operation is simple, but current imbalance occurs due to tail current effects
Solution Approach 1:
The system uses feedback by sampling the actual sense voltage at turn-on moment and using it to generate the reference voltage for turn-off detection. This feedback mechanism ensures that the detection threshold automatically adjusts to the actual collector current level, compensating for tail current effects and improving current balance
Solution Approach 2:
The sense voltage is sampled and held at the turn-on moment before the IGBT turns off. This preliminary capture of the current state allows the system to prepare an appropriate reference voltage that accounts for the actual collector current, enabling accurate turn-off detection even when tail currents are present
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 enables precise detection and correction of turn-off times, reducing current imbalances and preventing damage from tail currents, ensuring accurate control of power semiconductor elements regardless of the collector current magnitude.
Implementation Method 1
timing detection comparators each configured to compare a sense voltage detected as a voltage proportional to a main current that flows when a corresponding one of the plurality of power semiconductor elements is turned on, with a reference voltage to detect turn-on and turn-off times
Implementation Method 2
sample and hold circuits each configured to hold the sense voltage when the power semiconductor element is turned on
Implementation Method 3
divide the sense voltage being held when the corresponding power semiconductor element is turned off, and supply a resulting divided voltage as the reference voltage
Data Source
AI summary
A sense voltage obtained by feeding a sense current of an IGBT into a sense resistor is input to a comparator, and as the reference voltage of the comparator, a sense voltage immediately before the IGBT is turned off is held by a sample and hold circuit for each switching, and is then divided by a voltage dividing circuit and the divided voltage is input to the comparator. The comparator compares the sense voltage with the voltage based on the sense voltage immediately before the IGBT is turned off, and therefore the comparator may accurately detect the falling edge time of the sense voltage and is used for the control for dissolving the imbalance in current with respect to the other IGBTs connected in parallel.