JP2760590B2 - Drive circuit for voltage-driven elements - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to an IGBT (Insulated Gate Bipolar Transistor).
The present invention relates to a circuit for controlling a surge voltage at the time of recovery of an anti-parallel diode when used in a voltage-source inverter bridge, particularly for a drive circuit of a voltage-driven element such as r).

(Prior Art) FIG. 6 shows a general configuration of an inverter using a voltage-driven element.

In FIG. 6, a DC power supply 1 includes a smoothing capacitor 2.
Are supplied in parallel to the inverter bridge 3, and the inverter output converted into AC supplies power to the load.

Generally, a load is composed of an inductance 4 and a load resistance 5, and allows a load current _IL to flow. The inverter bridge 3 is
It comprises IGBTs 31 to 34 and high-speed diodes 35 to 38 connected in anti-parallel to the respective IGBTs.

The operation when the load current I _L was off the IGBT31 while flowing in the direction of the arrow shown in Figure 7.

In FIG. 7, the stray inductance 6 is the wiring inductance L, and when the IGBT 31 is turned off, the load current I _L
Is commutated from the IGBT 31 to the high-speed diode 36 and flows in the circuit shown by the arrow in the figure. Then, when the IGBT 31 is turned on again, the carrier of the diode 36 is released and the DC power supply 1
An instantaneous short circuit occurs through the circuit of 1, the stray inductance 6, and the diode 36. Actually, other wiring portions also have inductance, but are omitted for the sake of simplicity.

Thereafter, a reverse recovery current flows in the diode 36 in the reverse direction, and the diode recovers the reverse characteristic. However, when the reverse recovery current attenuates rapidly, a surge voltage due to the inductance 6 is applied to the diode 36 and the IGBT 32.

The reverse recovery current can be discerned by observing a current i, at time t ₁ IGBT 31 is turned on when the current i becomes zero and decreases the size of -I _L, rapidly after subsequent reverse recovery current flows becomes zero, a large surge voltage V _D to the diode 36 by the stray inductance 6 at this time is applied to.

Since the surge voltage V _D is determined by -L di / dt, or reduce the size of L, it is possible to reduce the surge voltage by either reducing the di / dt, decreases the stray inductance L Since there is a limit in terms of wiring, a method of reducing di / dt is generally effective.

One of the ways to reduce di / dt is to design the recovery time of a high-speed diode to be short. For example, a diode with a withstand voltage of several tens of volts is 30 to 50 ns, and a diode with a withstand voltage of 500 V is 10 ns.
Diodes with a voltage of 0 to 200 ns and a withstand voltage of 1000 V have been developed for 300 to 800 ns. Further, a soft recovery diode in which the recovery current is gradually attenuated has been developed, but there is a limit. As another method, a method of turning on the IGBT 31 slowly to reduce the short-circuit current i has been considered.

Waveform a in FIG. 7 shows a case where the IGBT 31 is rapidly turned on, and the rise with the current at that time is fast and the surge voltage V _D
Is also a large value. On the other hand, waveform b shows the case where gentle on the IGBT 31, the value of the reverse current i is small the value of di / dt, hence also low surge voltage V _D.

(Problem to be Solved by the Invention) FIG. 8 shows a conventional method for making the rise of the gate voltage gentle. FIG. 8 (A) is a circuit diagram thereof, and FIG. 8 (B).
Is an operation waveform diagram.

In Figure 8, the gate signal V _G through a resistor 10 IGBT
Is input to the 31 gates of the gate, between the cathode via a temporary delay circuit by rising the resistor 10 and the capacitor 12 of the gate voltage V _GE by adding a capacitor 12 are gradual. Since there is a capacitor 13 corresponding to the stray capacitance due to the structure of the IGBT, the capacitor 12 may be omitted.
Diode 11 is provided in order to reduce turn-off losses by fast fall of the gate voltage V _GE.

Slowly raised by positively stand raising the gate voltage V _GE of the IGBT primary delay the gate signal V _G from the negative to the time t _1,
At time t ₂ IGBT 31 starts on, but the gate voltage V _GE performs IGBT imperfect switching operations due to insufficient.

Thus the collector-emitter voltage V _CE of the IGBT31 remains in the intermediate voltage, current i Figure 8 becomes gentle inclination of positively increasing from the negative, yet the peak value of the current i is limited, the time t ₃ ~ surge voltage is reduced di / dt between t ₄ is reduced.

However the time t ₁ until the ON actually IGBT from varied from OFF to ON gate signal V _G in this way
~t ₂ becomes longer, during which time or not can be switched by the short pulse wasted time, dead time for simultaneously not to turn on the upper and lower elements of the bridge circuit is increased, the inverter output by uncontrolled therebetween There is a problem that the distortion of the waveform becomes large and causes an unstable phenomenon when used for driving the electric motor.

The present invention provides a rational voltage-drive element drive circuit that can reduce the IGBT operation delay with respect to the gate signal and reduce the surge voltage by softening the recovery current of the diode against the above problems. It is intended to provide.

[Configuration of the invention]

(Means and Actions for Solving the Problems) In order to solve the above-mentioned problems, the present invention relates to a voltage-driven element of a bridge circuit in which a plurality of voltage-driven elements in which high-speed diodes are connected in anti-parallel are bridge-connected. In a drive circuit of a voltage-driven element that outputs a gate drive voltage for performing a switching operation, a switch element that is turned on and off based on a gate control signal that instructs the switching operation; A gate control signal circuit is provided for applying a voltage equal to or less than a predetermined voltage for a timer time determined by the resistance and outputting a gate control signal for applying the predetermined voltage after the timer time has elapsed.

That is, the gate voltage at the time of turning on the IGBT is limited by raising the gate voltage at a voltage at which the IGBT operates in an analog manner, thereby limiting the recovery current of the diode, thereby reducing the rate of change of the recovery current and reducing the surge voltage. Things.

Further, the configuration is simple because it is only necessary to provide a gate control signal circuit for applying a predetermined voltage or less for a timer time determined by the capacitor and the resistance and outputting a gate control signal for applying the predetermined voltage after the timer time has elapsed. Has features.

(Embodiment) An embodiment of the present invention is shown in FIG. FIG. 1 shows only the gate drive circuit for the IGBT 31 in the inverter circuit shown in FIG. 6 and corresponds to FIG. 8 in the prior art. Therefore, the same parts as those in FIG. The description is omitted.

In FIG. 1, DC power supplies 14 and 15 are gate drive power supplies, and a transistor 17 is connected to a DC power supply 1 using a resistor 17 as a load.
Connect to both ends of 4, 15 and drive transistor by drive signal Vs
Turn 16 on and off.

The collector of the transistor 16 is connected to the base of the transistor 18 and 19, the transistor 18 and 19 the emitters are commonly connected, and outputs a gate signal V _G relative IGBT 31. The collector of the transistor 18 is connected to the positive electrode of the DC power supply 14, and the collector of the transistor 19 is connected to the negative electrode of the DC power supply 15.

On the other hand, from the collector of the transistor 16 to the capacitor 20,
The base of the transistor 23 is driven through a differentiating circuit in which resistors 21 and 22 are connected in series, and the collector of the transistor 23 is connected to the bases of the transistors 18 and 19 and the zener diode 24.
To change the voltage applied to the bases of the transistors 18 and 19. Diode 25 is capacitor 20
Is provided in order to accelerate the discharge of the battery.

Next, the circuit operation of FIG. 1 will be described with reference to FIG. 2 and FIG.

When the drive signal V _S becomes zero at time t ₁ in FIG. 2, the transistor 16 changes from ON to OFF, the collector potential of the transistor 16 rises, and a current flows through the capacitor 20 and the resistor 21 to the base of the transistor 23. flow, while the transistor 23 at the time t ₁ and t ₃ is turned on.

The collector potential of the transistor 16 is a Zener diode 24
If the gain (input impedance) of the transistors 18 and 19 is sufficiently high, the gate signal V _G
Is the voltage difference between the collector of transistor 16 and the midpoint between DC power supplies 14 and 15.

Gate voltage V _GE of IGBT 31 becomes delayed waveform by a resistor 10 and a capacitor 13, IGBT 31 at time t ₂ begins flowing collector current. Time t ₂ ~t ₃ between the lower gate voltage V _GE, IGBT has an analog operation.

Transistor 23 is turned off at time t _3, the gate drive voltage V _G
Is the highest, and the IGBT 31 is in a complete switching state.

The waveform shown by the solid line a of the current i and the diode voltage across V _D in FIG. 3 is a case of applying the gate voltage of the IGBT full voltage stepwise, the same waveform as a in Figure 7.

Contrast is applied separately gate signal V _G of the IGBT in two stages even if the gate voltage V _GE becomes two stages as shown in the figure, time t ₂
During the ~t ₃ current i is the peak current is limited so that the broken line c.

This is because, as seen from the characteristics of the IGBT shown in FIG. 9, if for example V _GE = 8V, the collector current I _C is because the analog operations as limited to about 13A.

Therefore to thereby flow out the same carrier a charge amount of the high-speed diode whereas the recovery diodes at t ₄ in the case of a, since the recovery time t ₅ the delayed For c according to the invention, equivalently the for the Figure 7 b and becomes similar to soft recovery, the surge voltage V _D of the diode dashed c
Are limited to the low values shown in

The interval of time t ₁ and t ₃ in FIG. 2, may be set to correspond to the time the diode to recover 1~2μ
s.

Slowing the rate of change of the recovery current of the diode in this way makes it possible to reduce the surge voltage at both ends of the diode. Improvement of device reliability by voltage drop and EM
A reduction in I noise can be expected.

FIG. 4 shows another embodiment of the present invention. FIG. 4A is a circuit diagram thereof, and FIG. 4B is an operation waveform diagram thereof.

In FIG. 4, a series circuit of a resistor 26 and a capacitor 27 is connected in parallel between the collector and the emitter of the transistor 16, and a diode 25 is connected in order to accelerate the discharge of the capacitor 27.

In the circuit of FIG. 4, when the transistor 16 is turned off, the IG
The gate signal V _G to BT31 to a value which is divided by resistors 17 and 26 minutes to rise rapidly, slowly increases with a time constant determined by the subsequent resistor 17, 26 and a capacitor 27.

For this reason, the delay time from the drive signal Vs to the turning on of the IGBT 31 is short, and the gate voltage of the IGBT is low for a while after the turning on, so that the IGBT operates analogously and limits the recovery current of the diode, and the gate voltage rises As IGBT
Since V _CE is reduced, the loss is low.

 FIG. 5 shows still another embodiment of the present invention.

In FIG. 5, the emitter of the transistor 23 is connected to the midpoint between the DC power supplies 14 and 15, and the voltage divided by the resistor 28 is used instead of the Zener diode. In this case, the on-voltage is not affected by the power supply 15, and is effective when there is a voltage fluctuation. The diode 29 is for preventing the back pressure of the base and the emitter of the transistor 23.

In the case of a small-capacity inverter, only the DC power supply 14 may be used and the gate voltage may be changed only to zero and positive.

In the above, the case where the IGBT is used as the power element has been described. However, the present invention can be commonly applied to a voltage-driven element in which the ON speed changes and the ON characteristics change depending on the gate voltage.

〔The invention's effect〕

As described above, according to the present invention, at the moment when the IGBT is turned on, the IGBT is operated in analog by applying a low gate voltage,
This limits the recovery current of the diode to reduce the di / dt during recovery, suppresses the surge voltage across the diode, and increases the gate voltage of the IGBT after diode recovery to lower the saturation voltage, Since the steady loss is reduced, a highly reliable and highly efficient drive circuit for a voltage-driven element having a good waveform ratio and low EMI noise can be obtained.

Further, the gate control signal circuit may be a simple circuit since it is only necessary to provide a timer circuit determined by a capacitor and a resistor and a circuit for applying a predetermined voltage to the gate after the timer time has elapsed.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, FIGS. 2 and 3 are waveform diagrams for explaining the operation of the present invention, and FIGS. 4 and 5 are other embodiments of the present invention, respectively. FIG. 6 is a circuit diagram showing an example, FIG. 6 is a general main circuit diagram of an inverter using a voltage-driven element, FIGS. 7 and 8 are explanatory diagrams of the operation of a conventional driving circuit, and FIG. 9 is a general diagram of an IGBT. FIG. 1. DC power supply for main circuit 2. Capacitor for main circuit 3. Inverter 4, Load inductance 5. Load resistance, 31-34 IGBT 35-38 High-speed diode, 6. Floating Inductance 10,17,21,22,28… Resistance, 11,25,29… Diode 12,20… Capacitor, 13… Floating capacitor 14,15… DC power supply for gate circuit 16,18,19, 23: Transistor, 24: Zener diode

Claims (1)

(57) [Claims] 1. A drive circuit for a voltage-driven element for outputting a gate drive voltage for performing a switching operation of each voltage-driven element of a bridge circuit in which a plurality of voltage-driven elements in which high-speed diodes are connected in anti-parallel are bridge-connected.
A switch element that is turned on and off based on a gate control signal for instructing the switching operation and a gate voltage of the voltage-driven element are applied for a timer time determined by a capacitor and a resistor at a predetermined voltage or less, and after the timer time elapses, A driving circuit for a voltage-driven element, comprising a gate control signal circuit for outputting a gate control signal for applying a predetermined voltage.