JP4701771B2 - DC / DC converter - Google Patents

Description

  The present invention relates to a DC / DC (direct current / direct current) converter whose input and output are insulated by a transformer, and more particularly, to a DC / DC converter starting method using a clamp snubber in a rectifier circuit on the secondary side of the transformer.

FIG. 4 shows an example of a DC / DC converter disclosed in Patent Document 1, for example.
In FIG. 4, reference numeral 2 denotes a DC / AC converter (DC / AC converter), and a DC power source 1 is connected to its input, and a primary winding 6 of a transformer 5 is connected to its output. The DC / AC converter 2 is an inverter composed of a U-phase leg (arm) 3 and a V-phase leg 4. The U-phase leg 3 is a semiconductor switch 3a, 3b, and the V-phase leg 4 is a semiconductor switch 4a, 4b. Consists of These semiconductor switches 3a, 3b, 4a, 4b are turned on and off based on the gate signal output from the control device 26, respectively. By this switching operation, DC power is converted to AC power, and an AC voltage is applied to the primary winding 6.

Full-wave rectifier circuits 11 and 12 are connected to the secondary windings 7 and 8 of the transformer 5, respectively, to convert the AC power converted by the DC / AC converter 2 into DC power. A smoothing inductance 13 connected between the full-wave rectifier circuits 11 and 12 and a smoothing capacitor connected between the positive side of the first full-wave rectifier circuit 11 and the negative side of the second full-wave rectifier circuit 12. The power ripple is removed by 22 and DC power is supplied to the DC load 23. Further, the load voltage V ₀ is detected by the voltage detector 24, and the DC voltage control unit 27 in the control device 26 outputs a gate signal for making the load voltage V ₀ a specified voltage.

  Reference numerals 14 and 18 denote a first snubber circuit and a second snubber circuit. The snubber circuit absorbs the energy stored in the leakage inductances 9 and 10 of the transformer 5 when the diodes composing the full-wave rectifier circuits 11 and 12 are commutated, and the snubber capacitors 15 and 19 and the snubber circuits, respectively. It consists of resistors 16 and 20 and snubber diodes 17 and 21.

The first snubber circuit 14 connects a series circuit of a first snubber capacitor 15 and a first snubber diode 17 between the positive electrode and the negative electrode of the first full-wave rectifier circuit 11, and the first snubber capacitor 15 and the first snubber diode. 17 is connected to the negative side of the smoothing capacitor 22 by the first snubber resistor 16, whereby the voltage of the first snubber capacitor 15 is clamped to the voltage of the smoothing capacitor 22. Such an action is the same for the second snubber circuit 18, and the voltage of the second snubber capacitor 19 is clamped to the voltage of the smoothing capacitor 22.
Thus, by clamping the snubber capacitor voltage to the smoothing capacitor voltage, charging / discharging of the snubber capacitor is suppressed and the loss of the snubber circuit is reduced.

JP 09-294373 A (3rd page, FIG. 1)

  By the way, in the conventional method as described above, it is necessary to make the clamp voltage of the snubber capacitor, that is, the smoothing capacitor voltage Vo higher than the output voltages Vsc1 and Vsc2 of the full-wave rectifier circuit. That is, when the smoothing capacitor voltage Vo is lower than the DC voltage of the output voltages Vsc1 and Vsc2 of the full-wave rectifier circuit at the time of starting up, an excessive current flows through the first and second snubber capacitors and the smoothing capacitor due to the potential difference. However, this inrush current cannot be suppressed by the leakage inductance of the transformer, and in the worst case, the device may be destroyed by this current.

Thus, there is a soft start as a method of suppressing overcurrent at the initial startup. This is a method of gradually increasing the ON period of the semiconductor element of the DC / AC converter to the rated value. However, depending on the speed at which the output is increased, the inrush current to the snubber capacitor cannot be suppressed and the device may be destroyed. There is.
There is a problem.
Accordingly, an object of the present invention is to suppress the inrush current as described above and prevent the destruction of the device.

In order to solve such a problem, according to the first aspect of the present invention, at the initial start-up, the semiconductor switch constituting the DC / AC converter on the primary side of the transformer is supplied with the input voltage Vi and the maximum current value Imax of the semiconductor switch. By providing a gate signal with a determined ON period, the current at startup is limited.
Further, in the invention of claim 2, initial startup, DC / AC converter to the semiconductor switches constituting the, to provide a gate signal of the input voltage Vi and output voltage Vo and a maximum current value on period determined by such Imax semiconductor switch To limit the current at startup.

According to the present invention, even when using the clamp snubber circuit the transformer secondary side DC / DC converter, on initial startup, at the input voltage Vi and the maximum current value on period determined by such Imax semiconductor switch either by, or that is the maximum current value on period determined by such Imax between the input voltage Vi output voltage Vo and the semiconductor switches, it is possible to suppress the inrush current to the snubber capacitor and the smoothing capacitor of the transformer secondary side, the device It can be started without being destroyed, and reliability can be improved.

FIG. 1 is a circuit configuration diagram showing the principle of the present invention. The difference from the conventional example of FIG. 4 is that a control device 28 is used instead of the control device 26. Hereinafter, the difference will be mainly described.
In FIG. 1, the control device 28 includes a DC voltage control unit 27 and a changeover switch 30. The changeover switch 30 determines the output based on the output voltage detection value Vo and the reference voltage as follows.

That is, the output voltage detection value Vo is compared with the reference voltage at the time of start-up, and if Vo <reference voltage, the minimum pulse command less than the rise time required for switching is used as the gate signal of the semiconductor element of the DC / AC converter 2. The value t1 is selected, and initial charging of the transformer secondary side snubber capacitor and smoothing capacitor is performed.
When Vo reaches the reference voltage and startup is completed, the gate signal determined by the DC voltage control unit 27 is selected.

Figure 2 is a circuit diagram showing an essential portion of a form of implementation of the present invention.
The difference from the above is that a control device 40 including a comparator 25, a DC voltage control unit 27, a changeover switch 30, a start pulse width calculation unit 32, and the like is used. Hereinafter, the difference will be mainly described.
The output voltage detection value Vo and the reference voltage are compared by the comparator 25 at the time of start-up. When Vo <reference voltage, the start pulse width calculation unit 32 determines the gate signal of the semiconductor element of the DC / AC converter 2. The gate signal t2 is selected.

The gate signal t2 is determined by the following equation (1), for example, assuming that the inductance of the transformer and wiring is L, the maximum current of the semiconductor element is Imax, and the input voltage detection value is Vi.
t2 = L · Imax / Vi (1)
Then, the initial charging of the snubber capacitor and the smoothing capacitor on the secondary side of the transformer is performed by the gate signal having the starting pulse width t2. Thereafter, when Vo reaches the reference voltage and the start-up is completed, a gate signal determined by the DC voltage control unit 27 is selected.

FIG. 3 is a main circuit diagram showing another embodiment of the present invention.
The difference from the conventional one is that a control device 50 including a comparator 25, a DC voltage control unit 27, a changeover switch 30, a start pulse width calculation unit 33, and the like is used. Hereinafter, the difference will be mainly described.
The output voltage detection value Vo and the reference voltage are compared by the comparator 25 at the time of start-up. When Vo <reference voltage, the start pulse width calculation unit 33 determines the gate signal of the semiconductor element of the DC / AC converter 2. The gate signal t3 is selected.

The gate signal t3 is, for example, a transformer, the inductance of the wiring is L, the maximum current of the semiconductor element is Imax, the input voltage detection value is Vi, and n is the transformation ratio (primary winding number / secondary winding number of the transformer 5). The output voltage detection value is set as Vo and is determined as in the following equation (2).
t3 = L · Imax / (Vi−nVo) (2)
In this way, since the starting pulse width t3 can be increased in accordance with the increase in the output voltage Vo, the charging time for the snubber capacitor and the smoothing capacitor on the secondary side of the transformer can be shortened. Thereafter, when Vo reaches the reference voltage and the start-up is completed, a gate signal determined by the DC voltage control unit 27 is selected.

Circuit diagram showing the principle of the present invention Essential-portion circuit diagram showing a form of implementation of the invention The principal part circuit diagram which shows another embodiment of this invention Circuit diagram showing a conventional example

  DESCRIPTION OF SYMBOLS 1 ... DC power supply, 2 ... DC / AC (DC / AC) converter, 5 ... Transformer, 6 ... Primary winding, 7, 8 ... Secondary winding, 9, 10 ... Leakage inductance, 11, 12 ... Full wave rectifier circuit, 13 ... smoothing reactor, 14, 18 ... snubber circuit, 22 ... smoothing capacitor, 23 ... DC load, 24 ... voltage detector, 25 ... comparator, 27 ... DC voltage controller, 28, 40, 50 ... Control device, 30 ... Changeover switch, 31 ... Input voltage detector, 32, 33 ... Starting pulse width calculator.

Claims (2)

A DC / AC converter mainly composed of a semiconductor switch and having an input connected to a DC power supply is connected to the primary side of the transformer, and at least a rectifier circuit including a clamp snubber circuit is provided on the secondary side of the transformer. In a DC / DC converter having
At the time of initial start-up, the current at start-up is limited by giving a gate signal of an ON period determined by at least the input voltage and the maximum current of the semiconductor switch to the semiconductor switch constituting the DC / AC converter. DC / DC converter. A DC / AC converter mainly composed of a semiconductor switch and having an input connected to a DC power supply is connected to the primary side of the transformer. In a DC / DC converter having
At the time of initial startup, the current at startup is limited by giving a gate signal of an on period determined by at least the input voltage, the output voltage, and the maximum current of the semiconductor switch to the semiconductor switch constituting the DC / AC converter. DC / DC converter characterized by the above.

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