JP2018078757A - Modulation method, and circuit using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a modulation method of a cascade multicell type DC/DC converter, by which input currents of respective cells can be balanced.SOLUTION: The problem is solved by a modulation method of a circuit having a pair of transformer driving means. The method comprises first and second procedures for lowering the degree of modulation, on the supposition that the degree of modulation is one(1) when the pair of transformer driving means output a positive voltage of 50% and a negative voltage of 50%, and they are in the same phase. The first procedure includes the step of decreasing the duty of a positive voltage that the first transformer driving means outputs to zero and in parallel, and decreasing the duty of a negative voltage that the second transformer driving means outputs to zero, and the second procedure includes the step of changing the phases of the first and second transformer driving means from the state of being identical with each other to the state of being opposite to each other.SELECTED DRAWING: Figure 2

Description

  The present invention includes a plurality of transformers, a modulation method used in a multi-level converter having a configuration in which secondary windings of these transformers are connected in series, and a rectifying / smoothing circuit is connected to the series circuit. It relates to the circuit used.

  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. 3 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. 3 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 type power factor correction converter 10, and the AC output includes a primary winding of the transformer 15 and a series circuit of the capacitor 43 and a primary winding of the transformer 16. And a series circuit of a capacitor 44 are connected. 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.

  Although the capacitor 43 and the capacitor 44 are not shown in Patent Document 1, when the pulse voltage output from the transformer driving means 14 includes a DC component, the capacitor 43 and the capacitor 44 have a role of removing the DC component.

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.
Therefore, the number of transformer driving means is not limited to two, but can be any number of two or more. Moreover, although the example which uses MOSFET as a switching element was given in the above description, even if it uses the parallel circuit of IGBT and an antiparallel diode, there exists the completely same effect.

The inventor of the present invention invented the modulation method of this multi-level DC / DC converter and applied for a patent (Japanese Patent Application No. 2006-177585). FIG. 4 shows a modulation method when the number of transformers is an even number, and the modulation method shown in FIG. 4 is sequentially applied to a pair of two transformers.
The upper left of FIG. 4 shows a state of modulation degree 1, and the degree of modulation decreases as the output voltage waveform of the transformer driving means is changed along the arrow, and the degree of modulation becomes 0 at the lower right. By doing so, the degree of modulation can be changed without making the exciting current of each transformer zero, and there is an advantage that zero voltage switching can be realized by discharging the output capacitance of the MOSFET using this exciting current.

  The circuit to which the modulation method described in the prior patent application is applied is not limited to FIG. 3, but may be applied to the circuit of FIG. In FIG. 3, if the voltages of the capacitors 43 and 44 are sufficiently small, it may be considered that the sum of the voltages obtained by converting the output voltage of each transformer driving means to the turns ratio appears in the secondary winding series circuit. On the other hand, in FIG. 5, 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 described in the prior patent application can be applied to the circuit of FIG.

However, the modulation method described in the prior patent application has a problem that the input currents of the transformer driving means are not balanced. The reason why the balance is not achieved is that the opportunities for the input current to flow through the respective transformer driving means are not evenly given. The input current flows through the transformer driving means when the output voltage of the transformer driving means is not zero. However, since the time is not uniform in the modulation method of Patent Document 2, the input current becomes a different value. End up.
As a specific example, FIG. 6 shows the input current waveform of each transformer driving means when the modulation method described in the prior patent application is applied to the circuit of FIG. In this example, the average value of the input current waveform is 2.21 A and 26.9 A, which is a difference of 10 times or more. If such an extreme difference occurs, the adjustment capacity on the cascade multicell type power factor correction converter side is exceeded, and there is a problem that the input voltages of the respective transformer driving means cannot be balanced.

International Publication No. 2016/031061

  The present invention discloses a specific modulation method for balancing the input current of each transformer driving means in a multilevel converter of the type in which the secondary windings of the transformer are connected in series.

The multilevel 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 about a specific modulation method.
A specific modulation method is described in the prior patent application (Japanese Patent Application No. 2006-177585). However, in this modulation method, the input current of each transformer driving means may be a completely different value. There was a problem that exceeded the adjustment capacity of the rate improvement converter.

The modulation method of the present invention is applied when the number of transformer driving means is plural,
A plurality of transformers,
Transformer driving means for applying a positive voltage, a negative voltage, and a zero voltage to each primary winding of the transformer;
A rectifying and smoothing circuit connected to a series circuit in which all the secondary windings of the transformer are connected in series;
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,
As a pair of the transformer driving means,
In order to reduce the modulation factor, the duty of one positive voltage of the set of the transformer driving means is reduced to zero and at the same time the duty of the other negative voltage of the set of the transformer driving means is reduced to zero. As the first step of
Shifting one phase of the set of transformer driving means and the other phase of the set of transformer driving means from the same phase to the opposite phase is a second procedure for reducing the modulation degree,
In the first procedure, the amount to reduce the duty of the positive voltage is equal to the amount to reduce the duty of the negative voltage,
In order to lower the modulation degree, the first procedure and the second procedure are sequentially applied to all the transformer driving means.

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 to this, even if the modulation degree 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. .

  Furthermore, the input current of each transformer driving means can be made equal. For this reason, even when a multilevel DC / DC converter is connected as a load of the cascade multicell type power factor correction converter, there is an advantage that the input voltage of each transformer driving means can be balanced.

FIG. 1 shows an 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 in the modulation method of the present invention. FIG. 3 is a circuit diagram of a cascaded multi-cell type power factor correction converter and a multi-level DC / DC converter as a load thereof. FIG. 4 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 in the conventional modulation method. FIG. 5 is another embodiment of the multilevel DC / DC converter of FIG. FIG. 6 shows waveforms of output voltage and input current of each transformer driving means in the conventional modulation method. FIG. 7 shows waveforms of output voltage and input current of each transformer driving means in the modulation method of the present invention.

  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.

(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.

  3 is a part of the transformer driving means 7 in FIG. 1, and the transformer driving means 7 in FIG. 1 includes a MOSFET driving circuit and a driving signal generating 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 in FIG. 2 is the modulation degree 1, the modulation degree is lowered along the arrow, and the lower left is the modulation degree 0.

  When the modulation degree is decreased from 1, first, the positive voltage duty of the first transformer driving means 7-1 is first lowered from 50% to 0%, and at the same time, the negative voltage duty of the second transformer driving means 7-2 is decreased. Decrease from 50% to 0%. The upper right of FIG. 2 shows a state where the positive voltage duty and the negative voltage duty are reduced to 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 positive voltage duty of the first transformer driving means 7-1 and the negative voltage duty of the second transformer driving means 7-2 reach 0%, the middle stage right in FIG. At this time, the voltage of the transformer secondary winding series circuit is all ½ duty.

  In order to further reduce the modulation degree from here, the phases of the first transformer driving means 7-1 and the second transformer driving means 7-2 are shifted from the same phase to the opposite phase. The middle left of FIG. 2 represents the middle of shifting the phase. As a result of this modulation, the voltage of the transformer secondary winding series circuit is set such that the maximum voltage is 1, the duty of 1/2 is decreased, the duty of 0/2 is increased, and the effective value voltage is decreased.

  The lower left of FIG. 2 represents a state in which the phase is completely reversed. At this time, all voltages of the transformer secondary winding series circuit have a duty of 0/2, and the modulation degree becomes 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. The case of an odd number of transformers is not described, but it can be assumed that it can be handled.

(Effect of Example 1)
Next, the merit of this modulation method will be described. The first merit is that the MOSFET can be zero-voltage switched.
Since the voltage time product of the first transformer driving means 7-1 and the second transformer driving means 7-2 never becomes zero in all states from the modulation degree 1 to the modulation degree 0, the excitation current of the transformer is It will never be zero. Therefore, the MOSFET can be zero-voltage switched using this exciting current regardless of the modulation factor.

The second merit is that the input current of each transformer driving means becomes equal. In order to explain this, first, the conditions under which the input current does not flow through the transformer driving means will be described.
The input current of the transformer driving means becomes zero when the output voltage of the transformer driving means becomes zero. This is apparent when considering that the input current does not flow to the transformer driving means when the MOSFET 33 and the MOSFET 34 are turned on, or when the MOSFET 35 and the MOSFET 36 are turned on.

  The voltage of the transformer secondary winding series circuit has three states of ± 1, ± 1/2, and 0, where the maximum voltage is 1. When ± 1, the output voltage of both transformer driving means is not zero, so that an input current flows through both transformer driving means. Since each secondary winding is connected in series and the same current flows, the input current is also the same. When the voltage of the transformer secondary winding series circuit is zero, since the output voltage of both transformer driving means is zero, the input current of each transformer driving means is equally zero.

  When the voltage of the transformer secondary winding series circuit is ± 1/2, the output voltage of one transformer driving means is zero, and the output voltage of the other transformer driving means is not zero. Therefore, at this time, the input currents of the transformer driving means are not equal.

In the modulation method of FIG. 2, the output voltage of each transformer driving means is symmetric, and when the voltage of the transformer secondary winding series circuit is ± 1/2, the chance of input current flowing through each transformer driving means is equal. Is given to.
That is, when the voltage of the transformer secondary winding series circuit is ± 1/2, the time when the output voltage of the transformer driving means 7-1 becomes zero and the time when the output voltage of the transformer driving means 7-2 becomes zero. Always equal. Therefore, the input current of each transformer driving means becomes equal.

  As a specific example to which this modulation method is applied, FIG. 9 shows output voltage waveforms and input current waveforms of each transformer driving means when applied to the circuit of FIG. It can be seen that the input current waveforms of the respective transformer driving means are equal.

The present invention is a modulation method that can be applied to a multi-level converter configured to connect a rectifying and smoothing circuit to a series circuit in which secondary windings of a plurality of transformers are connected in series.Because the excitation current of the transformer can be secured at all modulation degrees, Since the zero voltage switching of the MOSFET can be realized and the switching loss and the switching noise can be reduced, the industrial applicability is high.
In addition, since the input current of each transformer driving means can be made equal, the above multilevel converter can be used as a load of the cascade multicell type power factor correction converter.

DESCRIPTION OF SYMBOLS 1 Target voltage generation means 2 Output voltage detection means 3 Compensator 4 Modulation means 5-1 to 5-n Duty setting means 6-1 to 6-n Phase shift amount setting means 7-1 to 7-n Transformer driving means 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 drive means 15, 16 Transformer 17 Choke 18 Load 20 Resonance circuit 21 to 26 Diode 31 to 36 MOSFET
41-44 capacitors

Claims (5)

A plurality of transformers,
Transformer driving means for applying a positive voltage, a negative voltage, and a zero voltage to each primary winding of the transformer;
A rectifying and smoothing circuit connected to a series circuit in which all the secondary windings of the transformer are connected in series;
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,
As a pair of the transformer driving means,
In order to reduce the modulation factor, the duty of one positive voltage of the set of the transformer driving means is reduced to zero and at the same time the duty of the other negative voltage of the set of the transformer driving means is reduced to zero. As the first step of
Shifting one phase of the set of transformer driving means and the other phase of the set of transformer driving means from the same phase to the opposite phase is a second procedure for reducing the modulation degree,
In the first procedure, the amount to reduce the duty of the positive voltage is equal to the amount to reduce the duty of the negative voltage,
A modulation method in which the first procedure and the second procedure are sequentially applied to all the transformer driving means in order to lower the modulation degree. The modulation method according to claim 1, wherein the plurality of transformers is an even number. The modulation method according to claim 1, further comprising a resonance circuit between each of the transformer driving units and each of the transformers, or between a series circuit of the secondary winding and the rectifying and smoothing circuit. 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.

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