JP2021168534A - Power conversion device - Google Patents

Abstract

To solve the problem that adjustment of on/off timing of a switching element is difficult, a pulse transformer is required in driving of each switching element and miniaturization is difficult in a power conversion device of a phase shift-system full-bridge type.SOLUTION: A power conversion device comprises: a bridge circuit in which a plurality of switching elements becoming a pair are arranged; a driving circuit for driving the switching elements; a control part for PWM-controlling the driving circuit; an inverter part for generating AC via the bridge circuit from a DC power supply by opening/closing the switching elements by the driving circuit; and a converter part for converting AC output of the inverter part into DC. In the driving circuit, a pulse transformer and a gate driver IC are arranged in common in the switching elements to be paired.SELECTED DRAWING: Figure 2

Description

The present application relates to a power converter.

As a method for controlling and controlling a power circuit, a phase shift type power conversion device is the mainstream. Even in-vehicle DC / DC converters that employ a phase shift method have generally been used. In such a phase shift method, in order to improve the switching efficiency, it is necessary to individually provide a drive circuit for independently driving the switching element for each element. On the other hand, in-vehicle power conversion devices are required to have smaller circuits and lower costs.

For example, there is Patent Document 1 as a power conversion device using a phase shift method. It is a phase shift type full bridge type power supply circuit, and realizes a DC / DC converter that suppresses the voltage due to the leakage inductance of the transformer.

Japanese Unexamined Patent Publication No. 2017-127051

In the phase shift method, the on / off timing of the switching element is shifted for each element to realize desired efficiency and power transmission. In order to realize high efficiency, technologies such as ZVS (Zero Voltage Switching) and ZCS (Zero Current Switching) are required. As the switching frequency becomes faster, the on / off timing adjustment accuracy of the switching element is required. Therefore, if a wide-gap semiconductor such as GaN (gallium nitride) or SiC (silicon carbide) is used to increase the switching frequency, there is a problem that it is difficult to adjust the on / off timing of the switching element.

Further, as an in-vehicle device, there is a problem that cannot be solved simply by using a phase shift method having high switching efficiency. A pulse transformer is used to insulate the power circuit and the control circuit. In the phase shift method, since the drive is controlled individually for each switching element, it is necessary to provide one pulse transformer and one gate driver IC for each switching element. Therefore, it has been a hindrance to the miniaturization of the drive circuit. Further, each pulse transformer is a cube having a size of about 10 mm square, and a structure for increasing the mounting strength is required as a measure against vibration of the vehicle.

In order to solve the above problems, it is an object of the present application to obtain a power conversion device that does not require adjustment of the drive timing of the switching element and can reduce the size and cost of the circuit.

The power conversion device according to the present application includes a bridge circuit in which a plurality of pairs of switching elements are arranged, a drive circuit for driving the switching elements, a control unit for PWM control of the drive circuit, and the switching element by the drive circuit. The switching unit is provided with an inverter unit that creates alternating current from a DC power supply via the bridge circuit by opening and closing, and a converter unit that converts the alternating current output of the inverter unit into direct current, and the drive circuit is paired with the switching unit. A pulse transformer and a gate driver IC are provided in common to the elements.

The power conversion device of the present application is composed of an inverter unit that obtains an AC output from a DC power supply by PWM controlling the switching element of the bridge circuit, and a converter unit that obtains a DC output from the AC output. There is no need for complicated timing adjustment such as the shift method.

Further, since the drive circuit is provided with the pulse transformer and the gate driver IC in common to the paired switching elements, the number of parts of the pulse transformer and the gate driver IC can be reduced, and the size of the entire device and the cost of the parts can be reduced. be.

It is a circuit diagram which shows the inverter part of the power conversion apparatus which concerns on Embodiment 1. FIG. It is a circuit diagram which shows the whole power conversion apparatus which concerns on Embodiment 1. FIG. FIG. 5 is a timing chart showing a drive signal output by a control unit of the power conversion device according to the first embodiment. It is a timing chart which shows the drive signal of the switching element of the power conversion apparatus which concerns on Embodiment 1. FIG. It is a circuit diagram which shows the whole of the power conversion apparatus which concerns on Embodiment 2. FIG.

Embodiment 1.
FIG. 1 is a circuit diagram showing an inverter portion of the power conversion device according to the first embodiment of the present application. The inverter unit 10 is a DC / AC power conversion unit that obtains an AC output from a DC input, and has a full bridge circuit 20 composed of four switching elements Qa, Qb, Qc, and Qd. Switching elements Qa to Qd have paired switching elements Qa and Qb called arms and switching elements Qc and Qd on the high-voltage side and low-voltage side of the DC input voltage, respectively, and each of the elements has a direction opposite to the voltage. A diode with continuity is provided in parallel. The AC output is taken out from the midpoints of the switching elements Qa and Qb and the switching elements Qc and Qd of each pair.

A pulse transformer 5 common to each pair is provided in the drive circuit 1 that drives the gates of the switching elements Qa and Qb and the switching elements Qc and Qd, which are a pair of these elements, to control PWM control. It is activated by the drive output of one gate driver IC 6 having two outputs by the signal from the unit 30. A gate resistor 7a and a DC cut capacitor 8 are provided between the gate driver IC 6 and the pulse transformer 5. Further, the output of the pulse transformer 5 is input to each gate of the switching elements Qa to Qd via the gate resistor 7b.

The switching elements Qa to Qd provided in the full bridge circuit 20 are MOSFETs (Metal-Oxide-Semiconductor Field Effect Transistors). Although it is possible to use a semiconductor such as an IGBT (Insulated Gate Bipolar Transistor) or a next-generation wide bandgap semiconductor such as GaN and SiC, it will be described as a MOSFET in this embodiment. Since MOSFETs are voltage-driven, drive loss is small, and they are also suitable for high-frequency operation.

The control unit 30 has output terminals Ga and Gb, compares a carrier wave (for example, a triangular wave) with a carrier wave (for example, a triangular wave) based on a reference sine wave signal, and outputs a square wave on / off signal having a pulse width as a result. Output to Ga and Gb. The outputs of the output terminals Ga and Gb are signals that are out of phase with each other and are not turned on at the same time. The switching element Qa and the switching element Qd, and the switching element Qb and the switching element Qc, which are diagonally arranged in the full bridge circuit 20 with the output signal matched to the sinusoidal signal, are turned on / off as a set. AC output can be output with. Such a control form is called PWM control.

The pulse transformer 5 is a 1-input 2-output type transformer, and is driven by a combination of switching elements Qa and Qb of the MOSFET and switching elements Qc and Qd, one arm at a time. Further, by applying the pulse transformer, the high voltage power circuit side and the low voltage control circuit side can be insulated, and it is not necessary to add a new power supply circuit to drive the MOSFET. Therefore, the number of power supply circuits can be minimized.

In the present embodiment, when the switching element Qa and the switching element Qd are turned on, the polarities on the output side of the pulse transformer 5 are connected to each other so as to turn off the switching element Qb and the switching element Qc. By doing so, it is possible to prevent an arm short circuit in which the switching element Qa and the switching element Qb, and the switching element Qc and the switching element Qd are turned on at the same time. Further, it is possible to reduce the on / off timing delay of Qd from the switching element Qa located diagonally of the full bridge circuit.

The gate driver IC 6 drives MOSFETs via these pulse transformers 5. In the present embodiment, one gate driver IC6 having two outputs is used, but two one-output type gate driver ICs 6 may be used or a discrete circuit may be used.

The capacitor 8 is provided to cut the DC component to the input of the pulse transformer 5. As a result, the loss of the pulse transformer 5 is reduced and the magnetic saturation of the pulse transformer 5 is suppressed.

FIG. 2 is a circuit diagram showing the entire power conversion device. In FIG. 2, in addition to FIG. 1, a converter unit 40 that converts the AC output of the inverter unit 10 and outputs a direct current is additionally shown. It is composed of a transformer 41 that converts the AC output shown in FIG. 1 into a voltage, a diode 42 that rectifies the voltage-converted AC, a reactance 43 that smoothes the converted rectified voltage, and a capacitor 44.

Further, FIG. 2 shows an example in which a phase shift type controller IC is used for the control unit 30. As shown in the timing chart of FIG. 3, the control unit outputs drive signals from the switching elements Qa to Qd from the output terminals OutA to OutD. These timings drive the on / off of the switching elements Qa and Qb at a duty ratio of 50%, and shift the phases of the switching elements Qc and Qd to realize desired efficiency and power transmission. Here, in order to realize high efficiency, it is necessary to realize ZVS and ZCS, and it is necessary to adjust the dead time (td) for that.

In the first embodiment, Qd is driven from the switching element Qa by providing the AND circuit 31 provided in the control unit 30. The switching element Qa and the switching element Qd arranged diagonally of the full bridge circuit 20 and the switching element Qb and the switching element Qc are set and turned on / off at the same time by PWM control to operate the switching element Qa to Qd. Therefore, it is not necessary to adjust the dead time (td).

Here, in the phase shift method, the output of the control unit 30 from the switching element Qa to the Qd is the switching element Qa and the output terminal OutA, the switching element Qb and the output terminal OutB, the switching element Qc and the output terminal OutC, and the switching element Qd and the output terminal OutD. However, an AND circuit 31 is provided between the gate driver IC 6 and the control unit 30, and the gate signals of the output terminals OutA and OutD and the output terminals OutB and OutC of the control unit 30 are ANDed. It is possible to form a switching control signal such as.

As described above, the paired switching element Qa and switching element Qb, and the pulse transformer 5 and gate driver IC 6 for driving the elements in each of the switching element Qc and the switching element Qd can be shared. The points will be reduced, and the cost can be reduced. Further, since the number of pulse transformers 5 is changed from four to two, the structure for increasing the mounting strength for vibration resistance can be simplified.

Further, the gate resistors 7a and 7b can adjust the waveform applied to the drive unit of the MOSFET, and can suppress the surge voltage during the switching operation of the main circuit. As a result, noise generation due to switching of the main circuit can be suppressed.

Further, since the DC component to the pulse transformer input is cut by the capacitor 8, the loss of the pulse transformer can be reduced and the magnetic saturation of the pulse transformer can be suppressed. As a result, the capacity of the pulse transformer can be reduced, leading to miniaturization.

Further, it has a simple structure in which AC output is output from the inverter unit 10 by PWM control, and the AC output is converted to DC by the converter unit 40. Unlike the phase shift method, it is a simple method in which the diagonal arms are turned on / off alternately, so that it is no longer necessary to adjust the on / off timing of the switching element for ZVS and ZCS. Increasing the switching frequency eliminates the need for what was considered difficult to adjust, enabling high-speed switching drive to increase conversion efficiency.

Further, since the high-speed switching drive becomes easy, the next-generation semiconductor device suitable for the high-speed switching drive can be used in the power conversion device.

Although the DC / DC converter has been described above as an example, it can be similarly applied to a power conversion device such as an in-vehicle charger, an AC / DC converter, and an inverter. If the main circuit is provided with a bridge circuit as in the above example, the technique of the present application can be applied, and the same effect can be expected.

Embodiment 2.
FIG. 5 is a circuit diagram showing the entire power conversion device according to the second embodiment. Instead of the configuration in which two pulse transformers 5 of the first embodiment are used, in the second embodiment, one 1-input 4-output type pulse transformer 51 is used as shown in FIG.

By doing so, since it can be driven by one pulse transformer, further miniaturization and cost reduction can be realized.

Although the present application describes various exemplary embodiments and examples, the various features, embodiments, and functions described in one or more embodiments are applications of a particular embodiment. It is not limited to, but can be applied to embodiments alone or in various combinations. Therefore, innumerable variations not illustrated are envisioned within the scope of the techniques disclosed herein. For example, it is assumed that at least one component is modified, added or omitted, and further, at least one component is extracted and combined with the components of other embodiments.

Qa, Qb, Qc, Qd switching element, Ga, Gb output terminal, OutA, OutB, OutC, OutD output terminal, 1 drive circuit, 5 pulse transformer, 6 gate driver IC, 7a, 7b gate resistor, 8 capacitors, 10 inverters Part, 20 full bridge circuit, 30 control part, 31 AND circuit, 40 converter part, 41 transformer, 42 diode, 43 reactors, 44 capacitor, 51 pulse transformer.

The power conversion device according to the present application includes a full bridge circuit in which switching elements are arranged at each apex of a square, a drive circuit for driving the switching element, a control unit for PWM control of the drive circuit, and the drive circuit. The control unit includes an inverter unit that creates alternating current from a DC power supply via the full bridge circuit by opening and closing the switching element, and a converter unit that converts the alternating current output of the inverter unit into DC. Of the signals from the controller IC, two driving signals of the switching elements arranged diagonally are combined by an AND circuit and input to the gate driver IC of the driving circuit. The output signal of the gate driver IC is input to the pulse transformer, and the output signal of the pulse transformer drives the switching elements arranged diagonally .

Claims (10)

A bridge circuit in which multiple pairs of switching elements are lined up,
The drive circuit that drives the switching element and
A control unit that PWM-controls the drive circuit and
By opening and closing the switching element by the drive circuit,
An inverter unit that creates alternating current from a DC power supply via the bridge circuit,
A converter unit that converts the AC output of the inverter unit into direct current,
With
A power conversion device characterized in that a pulse transformer and a gate driver IC are provided in common to the switching elements to be paired in the drive circuit. The power conversion device according to claim 1, wherein four switching elements are provided and arranged in a full bridge type. The power conversion device according to claim 1 or 2, wherein the switching element is a MOSFET. The power conversion device according to any one of claims 1 to 3, wherein the pulse transformer is a pulse transformer having one input and two outputs. The power conversion device according to any one of claims 1 to 4, wherein gate resistors are provided on each of the input side and the output side of the pulse transformer. The power conversion device according to any one of claims 1 to 5, wherein a capacitor is provided on the input side of the pulse transformer. The control unit is a phase shift type controller IC, and of the four switching elements arranged in the full bridge type, two driving signals of the switching elements arranged diagonally are combined by an AND circuit. The power conversion device according to claim 2, wherein the drive circuit is driven. The power conversion device according to any one of claims 2 to 7, wherein the pulse transformer is a pulse transformer having one input and four outputs. The power conversion device according to claim 1 or 2, wherein the switching element is an IGBT. The power conversion device according to claim 1 or 2, wherein the switching element is a wide bandgap semiconductor.

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