Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By amplitude
Reexamination Certificate
1999-08-10
2001-06-26
Wells, Kenneth B. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By amplitude
C327S093000
Reexamination Certificate
active
06252436
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for determining state information of a power semiconductor, the power semiconductor comprising a collector, an emitter and a gate, and a gate driver comprising auxiliary voltage input is connected to the gate of the power semiconductor.
High-speed semiconductors are applied in modern power electronic devices, such as frequency converters used for controlling the rotation speed of short-circuit motors, for instance. Typically, the semiconductors are IGB transistors, which generally tolerate a short-circuit for 10 microseconds at the most. Hence it is important that information on an overcurrent stressing the device is received as soon as possible, in order that power semiconductors can be switched to a non-conducting state before they are damaged as a result of overheating.
Saturation voltage of an IGB transistor, i.e. voltage across the collector and emitter of said component while the collector current flows, depends on the magnitude of the current passing through the semiconductor and its value on a normal operating range is 2 to 4 volts. Saturation voltage rises quickly, when the collector current exceeds the nominal current and so this fact is commonly used for detecting overcurrent. For instance in frequency converters, the maximum value of saturation voltage in direct short-circuit can be close to the voltage of the frequency converter's intermediate circuit. In general, the maximum value of saturation voltage depends on the short-circuit impedance. Commonly the detection limit is the voltage of 10 to 20 volts and the detection must continue for at least two microseconds without a break, in order that the situation would be regarded as an overcurrent that calls for action.
It is previously known to measure the saturation voltage of the power semiconductor in frequency converters by using, for instance, phase-specific and intermediate-circuit-specific voltage dividers with matched speed and amplitude against the negative bar of the frequency converter, and by comparing the value obtained by subtraction with the known reference value. The obtained digital data is in the negative bar potential, but it can be separated galvanically by using optoisolators, for instance.
BRIEF DESCRIPTION OF THE INVENTION
The object of the present invention is to provide a method which eliminates the above-described drawbacks and a plurality of components, and the tuning thereof, required by the above-described method, and makes it possible to provide information on saturation voltage of a power semiconductor and thereby to provide information on a phase state, referenced to desired potential, in a simpler, more reliable and more cost-effective manner. This is achieved with a method of the invention, which is characterized by comprising the steps of
using an auxiliary voltage of a gate driver as a reference voltage,
comparing a saturation voltage of a power semiconductor with the reference voltage using an optoisolator, and
generating a detection signal of state information depending on the magnitudes of the saturation voltage and the reference voltage.
The method of the invention is based on the fact that the existing input voltage of the gate driver is used as such as reference voltage, and the existing optoisolator, needed for galvanic separation, is used as a comparator comparing the saturation voltage of the power semiconductor and the reference voltage. The only additional component required is a separating diode of the optoisolator, which should tolerate in the reverse direction the same voltage as the power semiconductor does. However, this diode is very economical, since only a current of a few milliamperes, in the forward direction of the optoisolator photodiode, passes therethrough. By comparing the saturation voltage information obtained at the optoisolator output and the gate control information of the power semiconductor to be monitored, it can be logically deduced, whether a dangerous overcurrent situation or a common 'switch open situation is concerned.
The invention also relates to an arrangement for determining state information of a power semiconductor, the power semiconductor comprising a collector, an emitter and a gate, and a gate driver comprising auxiliary voltage input is connected to the gate of the power semiconductor, whereby the arrangement is characterized by comprising a reference voltage referenced to the emitter potential of the power semiconductor, and a separation diode and a power semiconductor state detector in series, a first end of the series connection being connected to the reference voltage and a second end to the collector of the power semiconductor. By means of this arrangement the advantages provided by the method of the invention can be achieved with a simple and reliable structure.
REFERENCES:
patent: 4591734 (1986-05-01), Laughton
patent: 5383082 (1995-01-01), Nishizawa
patent: 5635823 (1997-06-01), Murakami et al.
patent: 6094087 (2000-07-01), He et al.
patent: 44 28 675 (1996-02-01), None
patent: 44 39 967 (1996-05-01), None
patent: 431 215 A1 (1991-06-01), None
patent: 0 743 751 (1996-11-01), None
ABB Industry OY
Dykema Gossett PLLC
Nguyen Hiep
Wells Kenneth B.
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