Miscellaneous active electrical nonlinear devices – circuits – and – Gating – Signal transmission integrity or spurious noise override
Reexamination Certificate
1999-12-03
2001-08-07
Cunningham, Terry D. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Gating
Signal transmission integrity or spurious noise override
C327S381000, C327S387000, C327S434000, C327S170000
Reexamination Certificate
active
06271709
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a gate drive circuit for a voltage drive switching element, such as an FET or IGBT.
FIG. 9
shows an example of the general circuit composition of a voltage invertor using an IGBT (insulated gate bipolar transistor). By turning an IGBT constituting three vertical series arms on or off alternately, AC power can be supplied from a DC power source E to a motor which operates as a load. In the drawing, Ls indicates a stray inductance of the main circuit cable. Progress has been made recently in the invertor mounting art such that the value of Ls, which is conventionally close to 1 &mgr;H, can be reduced to a value less than 150 nH. As a result, the energy accumulated in the stray inductance Ls is smaller, so that a snubber circuit (for example, as seen in
FIG. 10
) for controlling a spike voltage at the switching time is not necessary, and simplification of the main circuit can be realized.
However, the stray inductance Ls of the main circuit cable plays a role in the determination of di/dt at the time of power ON, and the snubber circuit (for example, as seen in
FIG. 10
) plays a role in controlling dv/dt at the time of power OFF, so that a new problem arises in that a high di/dt and a high dv/dt are generated at the time of switching of the IGBT due to the simplification of the main circuit.
The generation of a high di/dt and high dv/dt during the switching operation of the invertor circuit not only causes malfunctions of the peripheral equipment, but also adversely affects the motor which operates as a load. For example, in an invertor for a car, a motor which operates as a load is often installed at a location distant from the invertor. In the motor cable, the stray capacity Cs′, indicated by dashed lines in
FIG. 9
, is included in addition to the inductance Ls′. Therefore, as dv/dt of the invertor increases, the impedance of the motor appears to be large, so that a resonance produced by Ls′ and Cs′ is generated. As a result, a voltage close to two times the output voltage of the invertor is applied to the motor, and this may cause a failure, such as dielectric breakdown of the motor. In view of this problem, it is important to control di/dt and dv/dt at the time of switching of the IGBT.
It is known that the switching speed for turning the IGBT, which is a voltage drive switching element, on or off can be controlled by the gate drive method, for example, by increasing the gate resistance and prolonging the charging time constant of the gate capacity of the IGBT. However, by using this method, the switching time is made longer and the loss by the IGBT is excessively large. Accordingly, an improvement wherein the gate resistance of the gate drive circuit is switched according to the switching timing of the IGBT has been proposed (Japanese Patent Application Laid-Open 1-183214, Japanese Patent Application Laid-Open 3-93457, Japanese Patent Application Laid-Open 6-291631, Japanese Patent Application Laid-Open 8-322240, Japanese Patent Application Laid-Open 10-150764, U.S. Pat. No. 5,936,387, U.S. Pat. No. 5,808,504 etc.).
Furthermore, in the Institute of Electrical Engineers of Japan, EDD-94-44, SPC-97-71, pages 13 to 18 and Japanese Patent Application Laid-Open 8-186976, it is suggested that di/dt can be suppressed by detecting di/dt and switching the gate resistance of the gate drive circuit.
However, when it is attempted to widen the variable range of di/dt and dv/dt by switching the gate resistance, many resistors and switches for changing over the range are required, and the control becomes complicated.
SUMMARY OF THE INVENTION
The object of the present invention is to control di/dt and dv/dt at the time of switching by controlling an increase in the switching time or a loss of a voltage drive switching element, such as an IGBT.
According to the present invention, when turning a voltage drive switching element on, a drive means for amplifying a signal for controlling the switching operation of the voltage drive switching element, a means for detecting the operation status (main voltage, or main current, or gate voltage) of the voltage drive switching element, a power decrease means for slowly decreasing the output power when turning the drive means on in the course of time, and a power increase means for slowly increasing the output power are provided, and by switching from the power decrease means to the power increase means according to a detected value of the operation status of the voltage drive switching element, the di/dt control amount can be changed when turning the voltage drive switching element on.
Further, according to the present invention, when turning a voltage drive switching element off, a drive means for amplifying a signal for controlling the switching operation of the voltage drive switching element, a means for detecting the operation status (main voltage, or main current, or gate voltage) of the voltage drive switching element, a power decrease means for continuously decreasing the output power when turning the drive means on in the course of time, and a power increase means for continuously increasing the output power are provided, and by switching from the power decrease means to the power increase means according to a detected value of the operation status of the voltage drive switching element, the di/dt control amount can be changed when turning the voltage drive switching element off.
Further, according to the present invention, a drive means for amplifying a signal for controlling the switching operation of a voltage drive switching element, a means for detecting the operation status (main voltage, or main current, or gate voltage) of the voltage drive switching element, a means for continuously decreasing or increasing the output power when turning the drive means on or off in the course of time, a detection means for detecting the temperature of the voltage drive switching element, and a means for converting the temperature detection amount to a voltage are provided, and by changing the switching timing from the power decrease means of the drive means to the power increase means or from the power increase means to the power decrease means according to a detected value of the operation status (main voltage, or main current, or gate voltage) of the voltage drive switching element and the temperature detection amount of the voltage drive switching element, and by making the power increase period shorter than the power decrease period, the di/dt control amount can be changed when turning the voltage drive switching element on or off.
Furthermore, according to the present invention, the power increase means and power decrease means are realized by a simple circuit, such as a parallel or serial arrangement of a resistor, capacitor, and switching element.
REFERENCES:
patent: 4779013 (1988-10-01), Tanaka
patent: 4814638 (1989-03-01), Weick
patent: 4985644 (1991-01-01), Okihara et al.
patent: 5099138 (1992-03-01), Fukunaga
patent: 5767728 (1998-06-01), Michail et al.
patent: 5808504 (1998-09-01), Chikai et al.
patent: 5936387 (1999-08-01), Tabata et al.
patent: 1-183214 (1989-07-01), None
patent: 3-93457 (1991-04-01), None
patent: 6-291631 (1994-10-01), None
patent: 8-186976 (1996-07-01), None
patent: 8-322240 (1996-12-01), None
patent: 100150764 (1998-06-01), None
Inarida Satoru
Kimura Shin
Miyazaki Hideki
Nagasu Masahiro
Suzuki Katsunori
Antonelli Terry Stout & Kraus LLP
Cunningham Terry D.
Hitachi Ltd
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