JP2018046600A - Modulation method and circuit using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for modulating a cascade multiple cell type DC/DC converter capable of performing zero voltage switching even with no load.SOLUTION: A modulation degree 1 is a state where two transformer driving means output 50% of a positive voltage and 50% of a negative voltage and being a same phase. As first procedure for decreasing the modulation degree, a duty of the positive voltage and the negative voltage output by the first transformer driving means is decreased up to any set value. As second procedure for decreasing the modulation degree, a phase of the first transformer driving means is made to advance up to a set value. As third procedure for decreasing the modulation degree, the duty of the positive voltage and the negative voltage output by the second transformer driving means is decreased up to another set value. Thus, problems are resolved.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a modulation method used in a multilevel converter having a configuration in which secondary windings of a plurality of transformers are connected in series and a rectifying / smoothing circuit is connected to the series circuit, and a circuit using the modulation method.

  A multilevel DC / DC converter used as a load of a cascade multicell type power factor correction converter is disclosed in Patent Document 1. FIG. 4 shows a circuit diagram of this system. Reference numeral 10 denotes a cascade multicell power factor correction converter, in which inputs of two circuit blocks 13 are connected in series, and a series circuit of an AC power supply 11 and a choke 12 is connected to the series circuit. In the circuit block 13, a diode 21, a diode 22, a MOSFET 31, and a MOSFET 32 are bridge-connected, and a capacitor 41 is connected to the DC output of this bridge.

  A multi-level DC / DC converter other than the cascade multi-cell power factor correction converter 10 of FIG. 4 is a multi-level DC / DC converter. The MOSFET 33, MOSFET 34, MOSFET 35, and MOSFET 36 are bridge-connected to constitute the transformer driving means 14. The DC inputs of the two transformer driving means 14 are respectively connected to the outputs of the cascade multicell power factor correction converter 10, and the primary windings of the transformer 15 and the transformer 16 are connected to the AC outputs. The secondary winding of the transformer 15 and the secondary winding of the transformer 16 are connected in series, and this series circuit is connected to a rectifier circuit composed of a diode 23, a diode 24, a diode 25, and a diode 26, and choke the output of this rectifier circuit. 17, a smoothing circuit comprising a capacitor 42 is connected. A load 18 is connected to the output of the smoothing circuit.

In this multi-level DC / DC converter, a pulse voltage is applied to the primary windings of the transformers 15 and 16 by the transformer driving means 14, and the voltage is converted by the turns ratio and then added by the series circuit of the secondary windings. Enables multi-level conversion.
Because of this principle of operation, there are several possible variations for this converter. In FIG. 4, two input power sources having different potentials are connected to each transformer driving means, but they may be connected to a common DC power source 19 as shown in FIG. Further, as shown in FIG. 6, capacitors 43 and 44 may be connected to the inputs of the two transformer driving means 14, connected in series, and the series circuit may be connected to the DC power supply 19.

  Further, the number of transformer driving means is not limited to two, but any number of two or more can be used.

  In the above description, an example in which a MOSFET is used as a switching element has been described. However, using a parallel circuit of an IGBT and an antiparallel diode has exactly the same effect.

  However, Patent Document 1 describes that the voltage appearing in the series circuit of the secondary winding can be multilevel, but does not describe a specific modulation method. Therefore, there is a problem that it is not known how to modulate the voltage output from each transformer driving means.

International Publication No. 2016/031061

  The present invention discloses a specific modulation method in a multilevel converter of the type in which the secondary windings of a transformer are connected in series.

  The multi-level converter of the type in which the secondary windings of the transformer disclosed in Patent Document 1 are connected in series can make the voltage appearing in the series circuit of the secondary windings multi-level. There is no description of the method.

The first modulation method of the present invention is applied when the number of transformer driving means is an even number,
An even number of transformers,
Transformer driving means for applying a positive voltage, a negative voltage, and a zero voltage to each primary winding of the transformer;
All secondary windings of the transformer are connected in series, and a rectifying and smoothing circuit connected to the series circuit;
A circuit modulation method comprising:
All the transformer drive means output the maximum positive voltage duty and the maximum negative voltage duty, and the state that is in phase is the state where the modulation degree is the largest,
Reducing the duty of the positive voltage and negative voltage of the transformer driving means to a first set value is a first procedure for reducing the modulation degree,
Advancing the phase of the transformer driving means whose duty is reduced in the first procedure to the first set value is a second procedure for reducing the modulation degree,
Reducing the duty of the positive voltage and negative voltage output by the transformer driving means to a second set value is a third procedure for reducing the modulation degree,
The first procedure to the third procedure are sequentially applied to the transformer driving means.

The second modulation method of the present invention is applied when the number of transformer driving means is an odd number,
An odd number of transformers,
Transformer driving means for applying a positive voltage, a negative voltage, and a zero voltage to each primary winding of the transformer;
All secondary windings of the transformer are connected in series, and a rectifying and smoothing circuit connected to the series circuit;
A circuit modulation method comprising:
All the transformer drive means output the maximum positive voltage duty and the maximum negative voltage duty, and the state that is in phase is the state where the modulation degree is the largest,
Reducing the duty of the positive voltage and negative voltage of the transformer driving means to a first set value is a first procedure for reducing the modulation degree,
Advancing the phase of the transformer driving means whose duty is reduced in the first procedure to the first set value is a second procedure for reducing the modulation degree,
Reducing the duty of the positive voltage and negative voltage output by the transformer driving means to a second set value is a third procedure for reducing the modulation degree,
Reducing the duty of the positive voltage and negative voltage output by the transformer driving means to a third set value is a fourth procedure for reducing the modulation degree,
Increasing the duty of positive voltage and negative voltage output by the transformer driving means to the maximum duty is a fifth procedure for reducing the modulation degree,
The transformer driving means is divided into three and the remaining even number,
When the remaining even number of the transformer driving means are present, the third procedure from the first procedure is sequentially applied to the remaining even number of the transformer driving means,
Applying the first procedure and the second procedure to any one of the three transformer driving means,
Applying the third procedure to any one of the remaining two of the three transformer driving means;
Applying the fourth procedure to the remaining one of the three transformer driving means;
The fifth procedure is applied to the transformer driving unit to which the first procedure and the second procedure are applied among the three transformer driving units.

  The modulation method of the present invention has the following effects.

  By the modulation method of the present invention, the voltage appearing in the series circuit of the secondary winding can be made multilevel. In addition, even if the modulation factor becomes zero, the effective voltage of each transformer primary winding does not become zero, so an exciting current can be secured even without a load, and the MOSFET can be switched to zero voltage using this exciting current. .

FIG. 1 shows a first embodiment of the modulation method of the present invention. FIG. 2 is a diagram for explaining how the waveform of each transformer driving means is changed as the modulation degree is lowered when the number of transformer driving means is two. FIG. 3 is a diagram for explaining how the waveform of each transformer driving means is changed as the modulation degree is lowered when the number of transformer driving means is three. FIG. 4 is a circuit diagram of the cascade multicell type power factor correction converter disclosed in Patent Document 1 and a multilevel DC / DC converter as its load. FIG. 5 is another embodiment of the multilevel DC / DC converter of FIG. FIG. 6 is another embodiment of the multilevel DC / DC converter of FIG. FIG. 7 shows an example of a modulation method in which the transformer excitation current cannot be secured. FIG. 8 shows another embodiment of the multilevel DC / DC converter of FIG.

  The mode for carrying out the present invention will be apparent from the following description of the preferred embodiments when read with reference to the accompanying drawings. However, the drawings are for explanation only and do not limit the technical scope of the present invention.

  A state in which the effective voltage of the transformer secondary winding series circuit is maximized is defined as a modulation degree 1, and a state in which the effective value voltage is minimized is defined as a modulation degree 0. Modulation degree 1 is a state in which all transformer drive means output positive voltage 50% and negative voltage 50% and are in phase, and modulation degree 0 is a state in which the voltage of the transformer secondary winding series circuit becomes zero. is there.

  The simplest modulation method is to sequentially decrease the duty of the positive voltage and the negative voltage of each transformer driving means from 50% to 0%. As an example, FIG. 7 shows the transformer drive means output voltage and the secondary winding series circuit voltage when there are two transformers. Here, the duty of the first transformer driving means 7-1 is lowered from 50% to 25% and 0%, and then the duty of the second transformer driving means 7-2 is lowered from 50% to 25% and 0%. Yes.

  The problem with this method is that the excitation current of the transformer becomes zero when the duty is 0%. The exciting current has the effect of discharging the output capacitance of the MOSFET during the dead time period to perform zero voltage switching, thereby reducing switching loss and switching noise. Therefore, when the exciting current becomes zero, there is a problem that these effects are lost. Embodiments 1 and 2 solve this problem.

(Configuration of Example 1)
In the first embodiment of the modulation method of the present invention, the output of the target voltage generating means 1 and the output of the output voltage detecting means 2 are connected to the input of the compensator 3 as shown in FIG. The output of the compensator 3 is connected, and the inputs of the duty setting means 5-1 to 5-n and the inputs of the phase shift amount setting means 6-1 to 6-n are connected to the output of the modulation means 4 by the number of transformers, The outputs of the duty setting means 5-1 to 5-n and the outputs of the phase shift amount setting means 6-1 to 6-n are connected to the inputs of the transformer driving means 7-1 to 7-n to drive each transformer. The outputs of the means 7-1 to 7-n are connected to the transformers 8-1 to 8-n.
In the first embodiment, it is assumed that the number of transformer driving means is an even number.

  4 is a part of the transformer drive means 7 in FIG. 1, and the transformer drive means 7 in FIG. 1 includes a MOSFET drive circuit and drive signal generation means in addition to this.

(Operation of Example 1)
In the modulation method of the first embodiment configured as described above, the compensator 3 is a means for phase compensation, and an integrator, a PI compensator, a PID compensator, or the like is used. In the case of an analog circuit, an error amplifier circuit composed of an operational amplifier, a resistor, and a capacitor is used. Therefore, the output of the compensator 3 is a signal representing the modulation degree.

  Next, the operation of the modulation means 4 when there are two transformers will be described with reference to FIG. This figure shows how the output of the first transformer driving means 7-1 and the output of the second transformer driving means 7-2 are changed when the modulation degree is lowered from 1. The upper left of FIG. 2 is the modulation degree 1, the modulation degree is lowered along the arrow, and the lower right is the modulation degree 0.

  When the modulation degree is lowered from 1, first, the duty of the first transformer driving means 7-1 is lowered from 50% to a predetermined duty. This predetermined duty is called a remaining duty. FIG. 2 shows a case where the remaining duty is 31.25%. As a result of this modulation, the voltage of the transformer secondary winding series circuit assumes that the maximum voltage is 1, the duty of 1 decreases, the duty of 1/2 increases, and the effective voltage decreases.

  When the duty of the first transformer driving means 7-1 is lowered to the remaining duty, the phase of the first transformer driving means 7-1 is then advanced. Only the remaining duty is advanced. Due to this modulation, the voltage of the transformer secondary winding series circuit decreases the duty of 1 and increases the duty of 0, and the effective value voltage decreases.

  After the phase of the first transformer driving means 7-1 is advanced to the remaining duty, the duty of the second transformer driving means 7-2 is then lowered. Only the remaining duty is reduced. Due to this modulation, the voltage of the transformer secondary winding series circuit decreases by ½ duty, increases by 0 duty, and decreases the effective value voltage.

  When the duty of the second transformer driving means 7-2 reaches the remaining duty, the output of the first transformer driving means 7-1 and the output of the second transformer driving means 7-2 are in opposite phases, and the transformer 2 The voltage of the next winding series circuit becomes zero. This is a state where the modulation degree is zero.

The above description is for the case where there are two transformers. For example, when there are four transformers, the same modulation method is applied to the third transformer driving means 7-3 and the fourth transformer driving means 7-4. Finally, the output of the third transformer driving means 7-3 and the output of the fourth transformer driving means 7-4 are out of phase, and the voltage of the transformer secondary winding series circuit becomes zero. Become.
When the above idea is expanded, it can be seen that if the modulation method described in FIG. 2 is sequentially applied to a pair of two transformers, it is possible to cope with all cases where there is an even number of transformers.

(Effect of Example 1)
With the above operation, the first embodiment of the modulation method according to the present invention is such that the voltage of the transformer secondary winding series circuit is zero from the modulation degree 1 state where the voltage of the transformer secondary winding series circuit is maximum. Can be modulated up to a modulation degree of 0. In addition, since the minimum value of the duty of each transformer is the remaining duty, the excitation current of the transformer can be secured above a certain value in all modulation states, and the MOSFET can be switched to zero voltage.

(Configuration of Example 2)
The configuration of the second embodiment of the modulation method of the present invention is represented in FIG. 1 as in the first embodiment.
However, in the second embodiment, it is assumed that the number of transformer driving means 7 is an odd number.

(Operation of Example 2)
In the first embodiment, the number of the transformer driving means 7 is an even number, and it is shown that the whole can be modulated by sequentially applying the modulation method for the two transformer driving means 7.
Also in the second embodiment, the transformer driving means 7 is paired by two, and the modulation method of the first embodiment is applied. Therefore, if the three remaining transformer driving means can be modulated from a modulation degree of 1 to 0 while securing an exciting current, the whole can be modulated.
Therefore, a modulation method for the three transformer driving means will be described next.

  FIG. 3 shows that when there are three transformer driving means, the first transformer driving means 7-1, the second transformer driving means 7-2, and the third transformer driving means 7-3 when the modulation degree is lowered from 1. It shows how to change the output of. In FIG. 3, the upper left is the modulation degree 1, the modulation degree is lowered along the arrow, and the lower right is the modulation degree 0.

  When the modulation degree is lowered from 1, first, the duty of the first transformer driving means 7-1 is lowered to the remaining duty. As a result of this modulation, the voltage of the transformer secondary winding series circuit is set so that the maximum voltage is 1, the duty of 1 is decreased, the duty of 2/3 is increased, and the effective voltage is decreased.

  When the duty of the first transformer driving means 7-1 is lowered to the remaining duty, the phase of the first transformer driving means 7-1 is then advanced. Only the remaining duty is advanced. Due to this modulation, the voltage of the transformer secondary winding series circuit decreases by 1 duty, increases by 1/3 duty, and decreases effective voltage.

  After the phase of the first transformer driving means 7-1 is advanced to the remaining duty, the duty of the second transformer driving means 7-2 is then lowered. Due to this modulation, the voltage of the transformer secondary winding series circuit decreases by 2/3, increases by 1/3, and decreases the effective voltage.

  When the duty of the second transformer driving means 7-2 reaches the remaining duty, the output of the first transformer driving means 7-1 and the output of the second transformer driving means 7-2 are in opposite phases, The sum voltage becomes zero. Up to this point, the modulation method is the same as in the first embodiment.

  Next, the duty of the third transformer driving means 7-3 is reduced. With this modulation, the voltage of the transformer secondary winding series circuit decreases by 1/3, increases by 0, and decreases the effective value voltage.

  As the duty of the third transformer driving means 7-3 is reduced, the sum of the waveforms of the second transformer driving means 7-2 and the third transformer driving means 7-3 eventually becomes the same as the waveform of 50% duty. Become. Therefore, the duty of the first transformer driving means 7-1 having a phase opposite to the sum voltage waveform is increased. With this modulation, the voltage of the transformer secondary winding series circuit decreases by 1/3, increases by 0, and decreases the effective value voltage.

  When the duty of the first transformer driving means 7-1 reaches the maximum value, the voltage of the transformer secondary winding series circuit becomes zero and the modulation degree becomes zero. The duty of the first transformer driving means 7-1 to the third transformer driving means 7-3 does not become zero in the range of the modulation degree 1 to 0, and the exciting current does not become zero.

(Effect of Example 2)
As a result of the above operation, the second embodiment of the modulation method of the present invention is such that the voltage of the transformer secondary winding series circuit is zero from the modulation degree 1 state where the voltage of the transformer secondary winding series circuit becomes maximum. Can be modulated up to a modulation degree of 0. Moreover, since the duty of each transformer does not become zero, the transformer excitation current can be secured at a certain value or more in all modulation states, and the MOSFET can be switched to zero voltage.

Although FIGS. 4, 5, and 6 are given as the circuits to which the modulation method of the present invention is applied, other circuits can be applied to the circuit of FIG. 4, 5, and 6, the transformer driving means and the transformer primary winding are directly connected, and the sum of voltages obtained by converting the output voltage of each transformer driving means to the turns ratio appears in the secondary winding series circuit.
In FIG. 8, since the resonance circuit 20 is inserted between the transformer driving means and the transformer primary winding, this relationship does not hold. However, if the output voltage of the transformer driving means 14 increases, the voltage applied to the resonance circuit 20 increases and more power passes through the resonance circuit. Therefore, the relationship that the output power increases as the degree of modulation increases does not change. Therefore, the modulation method of the present invention can be applied to the circuit of FIG. Although the resonance circuit is inserted on the primary side in FIG. 8, the same effect can be obtained even if it is inserted on the secondary side, for example, between the series circuit of the secondary winding and the rectifying / smoothing circuit.
In order to widen the load range in which zero voltage switching can be realized, a circuit in which a choke is inserted between the transformer driving means 14 and the transformer primary winding in the circuit of FIG. 4 is also generally known. However, the modulation method of the present invention can be applied.

  The present invention is a modulation method applicable to a multi-level converter having a configuration in which secondary windings of a plurality of transformers are connected in series and a rectifying / smoothing circuit is connected to the series circuit. Therefore, the zero voltage switching of the MOSFET can be realized and the switching loss and switching noise can be reduced, so that the industrial applicability is high.

DESCRIPTION OF SYMBOLS 1 Target voltage generation means 2 Output voltage detection means 3 Compensator 4 Modulation means 5 (5-1 to 5-n) Duty setting means 6 (6-1 to 6-n) Phase shift amount setting means 7 (7-1 to 1) 7-n) Transformer driving means 8 (8-1 to 8-n) Transformer 10 Cascade multi-cell type power factor correction converter 11 AC power supply 12 Choke 13 Circuit block 14 Transformer driving means 15 and 16 Transformer 17 Choke 18 Loads 21 to 26 Diodes 31-36 MOSFET
41-44 capacitors

Claims (7)

An even number of transformers,
Transformer driving means for applying a positive voltage, a negative voltage, and a zero voltage to each primary winding of the transformer;
All secondary windings of the transformer are connected in series, and a rectifying and smoothing circuit connected to the series circuit;
A circuit modulation method comprising:
All the transformer drive means output the maximum positive voltage duty and the maximum negative voltage duty, and the state that is in phase is the state where the modulation degree is the largest,
Reducing the duty of the positive voltage and negative voltage of the transformer driving means to a first set value is a first procedure for reducing the modulation degree,
Advancing the phase of the transformer driving means whose duty is reduced in the first procedure to the first set value is a second procedure for reducing the modulation degree,
Reducing the duty of the positive voltage and negative voltage output by the transformer driving means to a second set value is a third procedure for reducing the modulation degree,
A modulation method of sequentially applying the third procedure to the transformer driving unit from the first procedure. An odd number of transformers,
Transformer driving means for applying a positive voltage, a negative voltage, and a zero voltage to each primary winding of the transformer;
All secondary windings of the transformer are connected in series, and a rectifying and smoothing circuit connected to the series circuit;
A circuit modulation method comprising:
All the transformer drive means output the maximum positive voltage duty and the maximum negative voltage duty, and the state that is in phase is the state where the modulation degree is the largest,
Reducing the duty of the positive voltage and negative voltage of the transformer driving means to a first set value is a first procedure for reducing the modulation degree,
Advancing the phase of the transformer driving means whose duty is reduced in the first procedure to the first set value is a second procedure for reducing the modulation degree,
Reducing the duty of the positive voltage and negative voltage output by the transformer driving means to a second set value is a third procedure for reducing the modulation degree,
Reducing the duty of the positive voltage and negative voltage output by the transformer driving means to a third set value is a fourth procedure for reducing the modulation degree,
Increasing the duty of positive voltage and negative voltage output by the transformer driving means to the maximum duty is a fifth procedure for reducing the modulation degree,
The transformer driving means is divided into three and the remaining even number,
When the remaining even number of the transformer driving means are present, the third procedure from the first procedure is sequentially applied to the remaining even number of the transformer driving means,
Applying the first procedure and the second procedure to any one of the three transformer driving means,
Applying the third procedure to any one of the remaining two of the three transformer driving means;
Applying the fourth procedure to the remaining one of the three transformer driving means;
A modulation method in which the fifth procedure is applied to the transformer driving unit to which the first procedure and the second procedure are applied among the three transformer driving units. The modulation according to any one of claims 1 and 2, further comprising a resonance circuit between each of the transformer driving means and each of the transformers, or between a series circuit of the secondary winding and the rectifying and smoothing circuit. Method. A circuit using the modulation method according to any one of claims 1, 2, and 3. 5. The circuit according to claim 4, wherein each of the transformer driving means is connected as a load of a cascade multicell type power factor correction converter. 5. The circuit according to claim 4, wherein the circuit is a power supply device, and each of the transformer driving means is connected to a common input power supply. 5. The circuit according to claim 4, wherein the circuit is a power supply device, the transformer driving units are connected in series, and the series circuit of the transformer driving units is connected to an input power source.

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