JP2022069728A - Power converter - Google Patents

Abstract

To provide a power converter which can suppress recovery loss and surge voltage to occur in a rectifier circuit on a secondary side of a transformer together and whose costs can be reduced.SOLUTION: A bridge type inverter 100 having a switching element is connected with a primary winding wire 105a of a transformer 105, on the other hand, a secondary winding wire of the transformer 105 is constituted of a plurality of winding wires 105b, 105c, bridge type rectifier circuits 106, 107 having semiconductor elements 106a to 106d, 107a to 107d are individually connected with the respective secondary winding wires 105b, 105c, and the rectifier circuits 106, 107 are connected in series with each other.SELECTED DRAWING: Figure 2

Description

The present application relates to a power converter.

A power converter consisting of an isolated DC / DC converter having a transformer has a simple circuit configuration in which a bridge-type inverter is connected to the primary side of the transformer and a bridge-type rectifier circuit is connected to the secondary side of the transformer. Therefore, the number of components is small, and it has become the mainstream as a circuit system for an in-vehicle charger mounted on an electric vehicle such as an electric vehicle (EV) and a plug-in hybrid electric vehicle (PHEV).

Here, the in-vehicle charger is generally composed of an AC / DC converter and an isolated DC / DC converter, and plays a role of performing power conversion with respect to the electric power input from the system and charging the battery of the vehicle. There is. Electric vehicles have traditionally been required to have an increased cruising range, and the power and voltage of batteries are increasing. While the size of the battery is increasing, there is a strong demand for securing a living space and reducing the cost due to the widespread use of electric vehicles, and as an in-vehicle charger, there is a demand for a smaller size, lower cost, and higher withstand voltage. In order to reduce the size and cost of in-vehicle chargers, it is essential to reduce the size of magnetic parts such as transformers and reactors, and for that purpose, it is desirable to increase the drive frequency (driving at tens to hundreds of kHz). ..

However, with high frequency drive, the increase in diode recovery loss becomes a problem. Further, since the in-vehicle charger is connected to the battery whose voltage is increasing, the problem of increasing the surge voltage also arises. Therefore, it is necessary to take measures to increase the withstand voltage against the recovery loss and surge voltage generated in the rectifier circuit on the secondary side of the isolated DC / DC converter.

Therefore, in the prior art, a technique of arranging an RCD snubber circuit in parallel with a rectifier circuit on the secondary side of a transformer has been proposed in order to suppress the surge voltage. In this method, the surge voltage generated in the rectifier circuit is absorbed by the snubber capacitor via the snubber diode, and this charge is discharged via the snubber resistor.

However, this conventional one requires the addition of a diode, a capacitor, and a resistor as a snubber circuit, which increases the cost. When the frequency is increased, the absorbed surge energy is consumed by the snubber resistance, so that the snubber resistance loss increases. Further, although the surge voltage can be suppressed by the snubber circuit, the recovery loss associated with the high frequency drive is not suppressed, so that the recovery loss of the rectifier circuit increases. To deal with this, it is necessary to improve the cooling, which increases the cost of the cooler.

Further, in other conventional techniques, in order to increase the withstand voltage against surge voltage, a technique has been proposed in which a plurality of semiconductor elements are arranged in series and a capacitor is arranged in parallel with each semiconductor element to divide the applied voltage. ing. In this method, a capacitor having a considerably large capacity with respect to the capacity of each semiconductor element is arranged in parallel with each semiconductor element to divide the pressure according to the capacity.

However, this conventional one is not sufficient to reduce the recovery loss that occurs in the rectifier circuit. Moreover, in order to secure the withstand voltage, the semiconductor elements are connected in series, and the capacitors are arranged in parallel with each semiconductor element, which increases the cost. Ideally, a capacitor is connected in parallel to each semiconductor element, and the voltage is divided by the capacitance of the capacitor, so that the required element withstand voltage is halved. However, the capacitance of a capacitor generally varies greatly due to initial variation, temperature characteristics, aging deterioration, etc., and based on these, it is difficult to divide the voltage evenly, and semiconductor devices are required to have a withstand voltage more than half of the original. As a result, only the number of elements increases, resulting in a significant cost increase.

Therefore, for example, Patent Document 1 below proposes a technique of arranging a SiC (Silicon Carbide) diode for reflux in parallel with a rectifier circuit in order to suppress both recovery loss and surge voltage. This is to suppress the occurrence of recovery loss and the occurrence of surge voltage due to recovery by bypassing the recovery current of the rectifier circuit with a SiC diode for reflux.

Japanese Patent No. 5642245

The above-mentioned one described in Patent Document 1 has a very small recovery loss and a high withstand voltage due to the characteristics of the SiC diode as a freewheeling diode, and both the recovery loss and the surge voltage can be suppressed. However, the cost of the SiC diode is very high, about 5 to 10 times that of the conventional mainstream Si (Silicon) diode, and the cost increases significantly.

The present application discloses a technique for solving the above-mentioned problems, and relates to a power converter composed of an isolated DC / DC converter having a transformer, a recovery loss and a surge generated in a rectifier circuit on the secondary side. It is an object of the present invention to provide a low-cost power converter capable of increasing the frequency and applying an element having a low withstand voltage by suppressing both voltages.

The power converter disclosed in the present application includes a transformer, and a bridge type inverter having a switching element is connected to the primary winding of the transformer, while the secondary winding of the transformer has a plurality of windings. A bridge-type rectifier circuit having a semiconductor element is connected to each of the plurality of windings that are configured and constitutes the secondary winding, and the rectifier circuits are connected in series with each other.

According to the power converter disclosed in the present application, since the voltage applied to the semiconductor element constituting each rectifier circuit is divided, the semiconductor element having a lower withstand voltage than the conventional one can be applied, and the power converter is low. Cost reduction is possible.

It is a circuit block diagram of the power converter as a comparative example of this application. It is a circuit block diagram of the power converter according to Embodiment 1 of this application. It is a circuit block diagram of the power converter according to Embodiment 2 of this application.

Embodiment 1.
FIG. 1 is a circuit configuration diagram of a power converter as a comparative example of the present application, which is shown to clarify the features of the present application.
The power converter shown in FIG. 1 is an isolated full-bridge DC / DC converter, includes a transformer 113, and a single-phase inverter 100 is connected to the primary winding 113a of the transformer 113. On the other hand, the secondary side of the transformer 113 is provided with only one secondary winding 113b corresponding to the primary winding 113a without being divided. A rectifier circuit 114 is connected to the secondary winding 113b.

Here, the above-mentioned single-phase inverter 100 has switching elements 101 to 104 connected in a bridge type (full bridge), and converts the DC voltage Vin of the DC power supply 111 into an AC voltage. Further, the rectifier circuit 114 is configured by connecting diodes 114a to 114d as its rectifier element in a bridge type (full bridge). An output smoothing reactor 108 and an output capacitor 109 are connected to the output side of the rectifier circuit 114, and a DC voltage Vout is output to the load 110.

Further, a control unit 112 is arranged outside the main circuit. The control unit 112 monitors the DC voltage Vin input from the DC power supply 111 and the DC voltage Vout output to the load 110 so that the DC voltage Vout output to the load 110 becomes a target value depending on the situation. By outputting the gate signals 101a to 104a to the switching elements 101 to 104, the on-duty (on period) of the switching elements 101 to 104 is controlled, and PMW (Pulse Width Modulation) control is performed.

In the circuit configuration shown in FIG. 1, SiC diodes are used as the diodes 114a to 114d constituting the rectifier circuit 114. That is, in the circuit shown in FIG. 1, as a rectifying element for constituting the rectifying circuit 114, the recovery loss is small and the output is output to the load 110 because the heat is generated by driving at a high frequency of several tens to several hundreds of kHz. High withstand voltage is required in consideration of the surge voltage generated by increasing the DC voltage Vout. Therefore, a SiC diode is applied as a semiconductor element having characteristics that meet the requirements of both.

However, as described above, the cost of the SiC diode is very high, about 5 to 10 times that of the conventional mainstream Si diode, and the cost of the power converter increases significantly.

FIG. 2 is a circuit configuration diagram of the power converter according to the first embodiment of the present application. In addition, the same sign is attached to the component corresponding to FIG.

The power converter of the first embodiment is an isolated full-bridge DC / DC converter and includes a transformer 105. A single-phase inverter 100 is connected to the primary winding 105a of the transformer 105.

On the other hand, on the secondary side of the transformer 105, the secondary winding is evenly divided into two. That is, it is composed of secondary windings 105b and 105c that are evenly divided into two. Therefore, the number of turns of each of the secondary windings 105b and 105c is equal to each other. The rectifier circuits 106 and 107 are individually connected to the secondary windings 105b and 105c, and the two rectifier circuits 106 and 107 are connected in series with each other.

Here, the above-mentioned single-phase inverter 100 has switching elements 101 to 104 connected in a bridge type (full bridge), and converts the DC voltage Vin of the DC power supply 111 into an AC voltage. Further, one rectifier circuit 106 is configured by connecting diodes 106a to 106d as its rectifier element in a bridge type (full bridge). Similarly, the other rectifier circuit 107 is configured by connecting diodes 107a to 107d as its rectifier element in a bridge type (full bridge). In this case, the diodes 106a to 106d and 107a to 107d are not SiC diodes as shown in FIG. 1, but Si diodes as semiconductor elements, which have been the mainstream in the past, are all applied.

An output smoothing reactor 108 and an output capacitor 109 are connected to the output of the configuration in which the rectifier circuit 106 and the rectifier circuit 107 are connected in series, and the DC voltage Vout is output to the load 110.

Although each of the switching elements 101 to 104 constituting the single-phase inverter 100 is applied with a self-extinguishing semiconductor switching element such as Si (Silicon)-MOSFET (Metal Oxide Semiconductor Field Effect Transistor). However, the present invention may be limited to, for example, a wideband gap semiconductor such as SiC (Silicon Carbide) or GaN (Gallium Nitride), or a semiconductor switching element using a diamond system.

As described above, in the power converter of the first embodiment shown in FIG. 2, the transformer 105 includes two evenly divided secondary windings 105b and 105c.
Here, for example, assuming that the number of turns of the primary winding 105a of the transformer 105 is N1, the total number of turns of the two secondary windings 105b and 105c is N2, and the required number of turns ratio is 1.5 (= N2 / N1), the primary winding is primary. When the number of turns N1 = 8 turns of the winding 105a, the total number of turns N2 = 12 turns of the entire secondary winding is required. Therefore, the number of turns N2b = 6 turns of one of the equally divided secondary windings 105b and the other The number of turns N2c of the secondary winding 105c is 6 turns.

By providing the two evenly divided secondary windings 105b and 105c in this way, the voltage generated on the secondary side can be evenly divided. Therefore, the element withstand voltage of the diodes 106a to 106d and 107a to 107d, which are the rectifying elements constituting the rectifying circuits 106 and 107, is half the withstand voltage of the SiC diodes 114a to 114d constituting the rectifying circuit 114 shown in FIG. To establish.

Further, in the power converter of the first embodiment shown in FIG. 2, the Vf (forward voltage) characteristic and the recovery characteristic are generally improved as the withstand voltage of the element is lowered. Therefore, by halving the withstand voltage of the element, the loss per diode is greatly reduced, and the heat generation can be increased. Therefore, it is possible to apply the conventional mainstream Si diode instead of the SiC diode. ..

With this configuration change, the number of diodes used is double that of the configuration shown in FIG. 1, but the unit price of the diodes 106a to 106d and 107a to 107d is 1/5 to 1/10 of that of the SiC diode. Therefore, the unit price of the element can be significantly reduced, and the cost of the entire device can be reduced.

The secondary side of the transformer 105 is composed of two evenly divided secondary windings 105b and 105c, but the total number of turns N2 required for the secondary winding as a whole is not changed. That is, in the above example, N2b (6 turns) + N2c (6 turns) = N2 (12 turns). The number of turns N1 of the primary winding 105a of the transformer 105 has the following relationship (Equation 1), where the magnetic flux density is ΔB, the applied voltage is Vtr, the applied time is ton, and the core cross-sectional area of the transformer 105 is Ae.

ΔB = (Vtr · ton) / (Nl · Ae) (Equation 1)

Here, since Vtr and ton are determined by the drive frequency or operating conditions, in order to suppress the magnetic saturation of the core of the transformer 105, the number of turns N1 and the number of turns N1 of the primary winding 105a so that the magnetic flux density ΔB does not exceed the magnetic flux saturation density. It is necessary to set the core cross-sectional area Ae of the transformer 105. Further, the core loss of the transformer 105 is generally proportional to the square of the magnetic flux density ΔB. Therefore, it is preferable that N1 × Ae is larger because the smaller ΔB is less likely to be magnetically saturated and the core loss is smaller.

However, if the core cross-sectional area Ae is increased, the impact on the size of the transformer is large. Therefore, it is common to increase N1 to suppress magnetic saturation and secure core heat formation. Therefore, in the first embodiment, N1 = 8 turns and N2 = 12 turns are set as described above instead of N1 = 2 turns and N2 = 3 turns for the required turns ratio of 1.5. .. Therefore, the secondary winding can be divided into two without changing the total number of turns N2 required for the secondary winding as a whole. Since the total number of turns N2 of the two secondary windings 105b and 105c is the same as that in FIG. 1, there is almost no cost increase due to the division of the secondary windings into two.

As described above, according to the first embodiment, the secondary winding of the transformer 105 is evenly divided into two, that is, the two evenly divided secondary windings 105b and 105c are provided to provide two rectifications. The voltage applied to the circuits 106 and 107 can be divided into two equal parts. This makes it possible to halve the element withstand voltage for the diodes 106a to 106d and 107a to 107 constituting the respective rectifier circuits 106 and 107 as compared with the circuit configuration of FIG. Loss can be reduced by improving the directional voltage) and recovery characteristics.

As a result, the Si diode, which has been the mainstream in the past, can be applied, so that the cost can be significantly reduced. Further, since the total number of turns N2 of the entire secondary windings 105b and 105c has not been changed and the cost does not increase due to the division into two, the cost of the power converter can be reduced. Further, since the two rectifier circuits 106 and 107 are connected in series with each other, the DC voltage Vout similar to the configuration of FIG. 1 can be supplied to the load 110.

Embodiment 2.
FIG. 3 is a circuit configuration diagram of the power converter according to the second embodiment of the present application. The components corresponding to the first embodiment shown in FIG. 2 are designated by the same reference numerals.

In the power converter of the second embodiment, the point that the secondary winding of the transformer 105 is divided into two is the same as that of the first embodiment, but as in the first embodiment, the second of the transformer 105 Instead of evenly dividing the next winding into two, the number of turns N2b of one secondary winding 105b and the number of turns N2c of the other secondary winding 105c are different (N2b ≠ N2c).

For example, assuming that the number of turns of the primary winding 105a of the transformer 105 is N1, the number of turns of the divided secondary windings 105b and 105c is N2, and the required number of turns ratio is 1.5 (= N2 / N1), the primary winding 105a When the number of turns N1 = 6 turns, the total number of turns N2 = 9 turns of the entire secondary winding is required. Therefore, the number of turns N2b = 4 turns of one of the divided secondary windings 105b and the other secondary winding 105c. The number of turns N2c = 5 turns.

As described above, since the number of turns N2b of one secondary winding 105b and the number of turns N2c of the other secondary winding 105c are different, the rectifier circuits 106 and 107 individually connected to the respective secondary windings 105b and 105c. The withstand voltage of the diodes 106a to 106d and 107a to 107d are not the same, and the withstand voltage of each of the rectifier circuits 106 and 107b is different.
Since other configurations are the same as those of the first embodiment shown in FIG. 2, detailed description thereof will be omitted here.

As described above, in the second embodiment, the voltage generated on the secondary side is made uneven by making the number of turns N2b of one secondary winding 105b different from the number of turns N2c of the other secondary winding 105c. Can be split. In that case, since N2b = 4 turns and N2c = 5 turns, the voltage division ratio is 4: 5.

Therefore, compared with the withstand voltage of the SiC diodes 114a to 114d selected in the circuit configuration (comparative example) of FIG. 1, the element withstand voltage of the diodes 106a to 106d constituting one rectifier circuit 106 is 4/9 times, and the withstand voltage of the other is rectified. The element withstand voltage of the diodes 107a to 107d constituting the circuit 107 is 5/9 times, the element withstand voltage in each of the rectifier circuits 106 and 107 can be reduced, and the element unit price can be significantly reduced. The improvement of the characteristics for lowering the withstand voltage of the element and the influence of the cost on the division of the secondary winding are as described in the first embodiment, and the cost of the power converter can be reduced.

By the way, in general, the lineup of withstand voltage of semiconductor elements takes discrete discrete values. Therefore, the element withstand voltage of the diodes 106a to 106d and 107a to 107d constituting the rectifier circuits 106 and 107 may not be compatible with 4/9 times or 5/9 times as described above. In that case, if the voltage division ratio of N2b and N2c is always fixed, it is necessary to apply an element having a larger withstand voltage in order to secure the required withstand voltage, resulting in excessive design and cost increase. ..

As a countermeasure, the ratio of N2b to N2c may be changed without changing the total number of turns N2 of the secondary winding. For example, by setting N2b = 3 turns and N2c = 6 turns, the withstand voltage of the SiC diodes 114a to 114d selected in the circuit configuration (comparative example) of FIG. 1 is compared with the withstand voltage of the diodes 106a to the one constituting the rectifier circuit 106. The element withstand voltage of 106d is 3/9 times, and the element withstand voltage of the diodes 107a to 107d constituting the other rectifier circuit 107 is 6/9 times.

As described above, when there is no appropriate lineup for the withstand voltage of the semiconductor element (here, diodes 106a to 106d, 107a to 107), it is necessary to change the turns N2b and N2c of the secondary windings 105b and 105c. The withstand voltage is adjustable. Therefore, excessive design can be prevented and cost reduction can be realized.

It should be noted that the present application is not limited to the configurations shown in the above-described first and second embodiments, and the configurations may be appropriately combined or partially modified within the range not deviating from the purpose of the present application. , It is possible to omit a part of the configuration.

For example, in the above-described first and second embodiments, the case where the secondary winding is divided into two has been described, but the present invention is not limited to this, and the number of divisions of the secondary winding may be an integer of 3 or more. Further, it is also possible to apply a switching element instead of the diode constituting the rectifier circuits 106 and 107.

Also, although various exemplary embodiments have been described in the present application, the various features, embodiments, and functions described in one or more embodiments may be applied to a particular embodiment. It is not limited, and can be applied to embodiments alone or in various combinations.

Therefore, innumerable variations not exemplified are envisioned within the scope of the techniques disclosed in the present application. For example, it may include the case of transforming, adding, or omitting at least one component, and further, the case of extracting at least one component and combining it with the components of other embodiments. ..

100 single-phase inverter, 111 DC power supply, 101-104 switching element,
101a-104a gate signal, 105 transformer, 105a primary winding,
105b secondary winding, 105c secondary winding, 106 rectifier circuit,
106a-106d Diode (semiconductor element), 107 rectifier circuit,
107a-107d Diode (semiconductor device), 108 Output smoothing reactor,
109 output capacitor, 110 load, 112 control unit, 113 transformer,
113a primary winding, 113b secondary winding, 114 rectifier circuit,
114a-114d diode, Vin DC voltage (input voltage),
Vout DC voltage (output voltage), number of turns of N1 primary winding, number of turns of N2b secondary winding,
The number of turns of the N2c secondary winding.

The power converter disclosed in the present application includes a transformer, and a bridge type inverter having a switching element is connected to the primary winding of the transformer, while the secondary winding of the transformer has a plurality of windings. A bridge-type rectifying circuit having a semiconductor element is connected to each of the plurality of windings configured and constituting the secondary winding, and the rectifying circuits are connected in series with each other . The number of turns of the plurality of windings constituting the secondary winding is different from each other.

Claims (8)

A bridge type inverter having a transformer and having a switching element is connected to the primary winding of the transformer, while the secondary winding of the transformer is composed of a plurality of windings to form the secondary winding. A power converter in which a bridge-type rectifier circuit having a semiconductor element is connected to each of the plurality of windings, and the rectifier circuit is connected in series with each other. The power converter according to claim 1, wherein the plurality of windings constituting the secondary winding have the same number of turns. The power converter according to claim 1, wherein the plurality of windings constituting the secondary winding have different turns. The power converter according to claim 2, wherein all the semiconductor elements constituting the rectifier circuit have the same withstand voltage. The power converter according to claim 3, wherein the semiconductor element constituting the rectifier circuit has a withstand voltage different for each rectifier circuit. The power converter according to any one of claims 1 to 5, wherein the number of the plurality of windings of the secondary winding is two. The power converter according to any one of claims 1 to 6, wherein the semiconductor element constituting the rectifier circuit is a diode. The power converter according to any one of claims 1 to 6, wherein the semiconductor element constituting the rectifier circuit is a switching element.

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