KR20210004589A - Multi-level converter - Google Patents

Abstract

Disclosed is a multi-level converter which offsets ripples. The multi-level converter comprises: a multi-module in which a plurality of sub-modules formed of a two-way bridge power conversion circuit, wherein a primary side and a secondary side are insulated by a transformer, are provided, and each secondary side of the plurality of sub-modules is connected in series; and a control module controlling each of switching elements included in the multi-module.

Description

Multi-level converter {MULTI-LEVEL CONVERTER}

The present invention relates to a multi-level converter, and more particularly, to a multi-level converter for performing power conversion including a plurality of sub-modules.

Modular multi-level converters are widely used as grid-connected power regulators such as grid-connected renewable energy generators and high voltage direct current transmission (HVDC) devices.

The conventional modular multi-level converter includes a plurality of sub-modules each performing power conversion, and each sub-module requires a transformer for insulation.

For example, the conventional sub-module may adopt a two-stage power conversion structure in which a DC-DC isolation converter and a DC-AC inverter are cascaded. This is accompanied by problems of increasing price and size, reducing efficiency, and reducing reliability, and it is difficult to control precise power transfer between each sub-module because it is PWM control with variable duty ratio rather than phase shift control with fixed duty ratio.

An aspect of the present invention provides a multi-level converter that includes a plurality of sub-modules as a bidirectional DC-AC converter of a single power conversion structure including a high-frequency transformer, and outputs a multi-level PWM voltage by connecting the output terminals in series. .

Another aspect of the present invention provides a multi-level converter that connects each string composed of a plurality of sub-modules to a three-phase system or a three-phase motor, and cancels ripple by connecting input terminals of strings each connected to three phases.

The technical problem of the present invention is not limited to the technical problem mentioned above, and other technical problems that are not mentioned will be clearly understood by those skilled in the art from the following description.

In the multi-level converter of the present invention for solving the above problems, a plurality of sub-modules comprising a bidirectional bridge power conversion circuit including active switch elements are provided on the primary side and the secondary side insulated by a transformer, and a plurality of sub-modules And a multi-module including a positive leg and a negative leg connected in series to each of the secondary sides, and a control module respectively controlling switch elements included in the multi-module.

Meanwhile, the multi-module converts the DC voltage input to the primary side from the plurality of sub-modules into a voltage in the form of a square wave and outputs the converted voltage to the secondary side, and has a phase difference between the outputs of the secondary side of the plurality of sub-modules. , Each secondary side of the plurality of sub-modules is connected in series to output a multi-level PWM voltage.

In addition, the control module may control an operation phase of a switch element included in the plurality of sub-modules so as to control a power transfer amount of the multi-module by adjusting a phase difference between the outputs of each secondary side of the plurality of sub-modules. I can.

In addition, in the multi-module, a plurality of switch elements are provided on each bridge of the primary side and the secondary side, and the plurality of switch elements are phase-shifted with a fixed duty by the control module, so that power is transmitted in both directions around the transformer. A plurality of sub-modules to be transmitted may be provided.

Meanwhile, in the multi-level converter of the present invention, a plurality of sub-modules including an active switch element and a bidirectional bridge power conversion circuit are provided on the primary side and the secondary side insulated by the transformer, and each secondary side of the plurality of sub-modules Control modules each controlling a first string to a third string including a positive leg and a negative leg connected in series, and a switch element included in the first string to the third string. And the first string to the third string are connected to each phase of the three-phase system.

Meanwhile, in the first string to the third string, input terminals of a plurality of sub-modules respectively included in the first string to the third string may be connected to each other.

Further, the first string to the third string may cancel a ripple voltage of each phase of a three-phase system connected to the first string to the third string, respectively.

In addition, the first to third strings convert a DC voltage input from the plurality of sub-modules to a primary side, respectively, into a voltage in the form of a square wave, and output the converted voltage to a secondary side, and each secondary side of the plurality of sub-modules It has a phase difference between the outputs, and each secondary side of the plurality of sub-modules is connected in series to output a multi-level PWM voltage.

In addition, the control module is a switch included in the plurality of sub-modules to control the amount of power delivered to each of the first string to the third string by adjusting a phase difference between the outputs of the secondary side of the plurality of sub-modules. The operating phase of the device can be controlled.

In addition, in the first string to the third string, a plurality of switch elements are provided on each bridge of the primary side and the secondary side, and the plurality of switch elements are phase shifted to a fixed duty by the control module to control the transformer. It can transmit power in both directions to the center.

According to the present invention, since a plurality of sub-modules have a single power conversion structure, and a transformer included in each sub-module is composed of a high-frequency transformer, effects such as overall size reduction and cost reduction can be expected.

In addition, since the phase shift control of each sub-module with a fixed duty enables precise power transfer control between each sub-module, high reliability of power transfer can be ensured.

In addition, it can be applied in multiple modes, such as single input, single output or multiple inputs, and single output, and can deliver unidirectional or bidirectional power.

1 is a schematic diagram of a multi-level converter according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating the sub-module shown in FIG. 1 in detail.
3 is a diagram illustrating a multi-level converter according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION The detailed description of the present invention to be described later refers to the accompanying drawings, which illustrate specific embodiments in which the present invention may be practiced. These embodiments are described in detail sufficient to enable a person skilled in the art to practice the present invention. It is to be understood that the various embodiments of the present invention are different from each other, but need not be mutually exclusive. For example, certain shapes, structures, and characteristics described herein may be implemented in other embodiments without departing from the spirit and scope of the present invention in relation to one embodiment. In addition, it is to be understood that the location or arrangement of individual components within each disclosed embodiment may be changed without departing from the spirit and scope of the present invention. Accordingly, the detailed description to be described below is not intended to be taken in a limiting sense, and the scope of the present invention, if properly described, is limited only by the appended claims, along with all scopes equivalent to those claimed by the claims. In the drawings, like reference numerals refer to the same or similar functions over several aspects.

Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the drawings.

1 is a schematic diagram of a multi-level converter according to an embodiment of the present invention.

Referring to FIG. 1, the multi-level converter 1000 according to an embodiment of the present invention may convert an independent DC voltage into a multi-level PWM voltage and output it to a system or an AC load.

Alternatively, the multi-level converter 1000 according to an embodiment of the present invention is a converter capable of bidirectional power transfer, and may be applied to, for example, charging a battery.

The multi-level converter 1000 according to an embodiment of the present invention may convert an independent DC voltage into a multi-level PWM voltage and output it.

To this end, the multi-level converter 1000 according to an embodiment of the present invention may include a multi-module composed of a plurality of sub-modules 100.

The sub-module 100 may be configured as a two-way bridge power conversion circuit in which the primary side and the secondary side are insulated by a transformer. A detailed description of the circuit configuration of the sub-module 100 will be described later with reference to FIG. 2.

The sub-module 100 enables power conversion from the primary side to the secondary side by controlling the phase shift of a plurality of switch elements provided in the bridges of the primary side and the secondary side. The plurality of switch elements provided in the sub-module 100 may be provided with an active switch element, such as an active transistor, not a diode, and may include a transistor driving circuit. Accordingly, the sub-module 100 is capable of converting power from the secondary side to the primary side with a converter capable of bidirectional power transfer, such as a bidirectional half bridge, a bidirectional full bridge, or a bidirectional flying capacitor multilevel converter. Hereinafter, a representative example of the submodule 100 performing power conversion from the primary side to the secondary side will be described.

The primary side of the sub-module 100 may be connected to a DC power supply, and the secondary side chopping a voltage in the form of a square wave, specifically, a DC voltage by the operation of a plurality of switches provided on the bridges of the primary and secondary sides. ) One type of PWM voltage can be output.

The multi-module includes a plurality of such sub-modules 100, and each primary side of the plurality of sub-modules 100 is independently separated, and each secondary side of the plurality of sub-modules 100 is connected in series. have.

For example, the output voltage line of the first sub-module SM-P1 may be connected to the ground line of the second sub-module SM-P2, and the output voltage line of the n-th sub-module SM-Pn is a grid or AC By being connected to the load, the outputs of the n sub-modules 100 may be connected in series.

Accordingly, the multi-module outputs a DC voltage independently input to each sub-module 100 as a voltage in the form of a square wave, but the outputs of the plurality of sub-modules 100 are added to output a multi-level PWM voltage. At this time, each primary side of the plurality of sub-modules 100 may receive a DC voltage having the same magnitude, and may have a phase difference between outputs of the secondary side of the plurality of sub-modules 100.

For example, the multi-module may build a positive leg and a negative leg connected to the neutral point (a). A plurality of sub-modules 100 may be provided in each of the positive voltage leg and the negative voltage leg, and outputs between the plurality of sub-modules 100 may be connected in series. The positive voltage leg and the negative voltage leg may be configured in a vertically symmetrical shape. For example, when n sub-modules 100 are provided in the positive voltage leg, the negative voltage leg may also be provided with n sub-modules 100 to generate an AC voltage.

The multi-module may expand the sub-module 100 according to the required power capacity.

The multi-level converter 1000 according to an embodiment of the present invention may further include a control module for controlling each of the switch elements included in the multi-module.

The control module may control a switching operation of switch elements included in each of the plurality of sub-modules 100.

For example, the control module may control a duty and a phase of each switch element by controlling a gating signal of a switch element included in each of the plurality of sub-modules 100.

The control module may include a central controller and a plurality of sub-controllers.

For example, the central controller may control a plurality of sub-controllers, and each of the plurality of sub-controllers may control one sub-module 100 in charge of itself.

In this embodiment, the control module may control switch elements included in each of the plurality of sub-modules 100 to perform power conversion in a phase shift method. In this case, the control module may control the switch elements included in each of the plurality of sub-modules 100 to have a fixed duty (eg, 50%). Accordingly, the multi-level converter 1000 according to an embodiment of the present invention can transmit active power as well as reactive power.

In addition, in this embodiment, the control module controls the operation phase of the switch elements provided on each secondary side of the plurality of sub-modules 100 to be maintained differently for each sub-module 100, thereby outputting multi-level PWM voltages in the multi-modules. Makes this possible.

In addition, in the present embodiment, the control module may control the operation phase of each switch element included in the plurality of sub-modules 100 based on the amount of power transmission required by the control module in the present embodiment. In this case, the phase difference between the secondary outputs of the plurality of sub-modules 100 is adjusted to control the amount of power transmitted by the multi-modules.

FIG. 2 is a diagram illustrating the sub-module shown in FIG. 1 in detail.

Referring to FIG. 2, the sub-module 100 may adopt a two-way bridge power conversion circuit topology composed of an input terminal 101, a primary side 110, a transformer 150, and a secondary side 120.

The sub-module 100 is a single DC-AC power conversion circuit, and FIG. 2 illustrates that the primary side 110 and the secondary side 120 are configured as a half-bridge circuit, but is not limited thereto, and a full bridge circuit, It may be composed of a single DC-AC power conversion circuit of various types capable of converting a voltage in the form of a square wave from a DC voltage, such as a flying cap circuit. Hereinafter, an example in which the primary side 110 and the secondary side 120 are configured with a half bridge circuit will be described.

The input terminal 101 is a DC voltage source, and may correspond to, for example, a renewable power source or a battery.

The primary side 110 and the secondary side 120 are half-bridge circuits in which a plurality of switch elements are provided, are insulated by the transformer 150, and bidirectional power can be transmitted by controlling the phase shift of the plurality of switch elements.

The primary side 110 is connected to the input terminal 101, and switch elements may be provided on the upper side and the lower side of the leg constituting the half bridge, respectively. The primary side 110 may be connected to the input terminal 101 in a state in which a half bridge provided with a switch element and a leg provided with a capacitor at the upper and lower sides are connected in parallel. Here, the capacitor serves to maintain the DC component.

The secondary side 120 is insulated from the primary side 110 by the transformer 150, and switch elements may be provided on the upper and lower sides of the legs constituting the half bridge, respectively. The secondary side 120 may be connected to the secondary end of the transformer 150 in a state in which a half bridge provided with a switch element and a leg provided with a capacitor at the upper and lower sides are connected in parallel. Here, the capacitor serves to maintain the DC component.

The plurality of switch elements provided on the primary side 110 and the secondary side 120 may be an active switch, for example, a MOSFET or an IGBT element. Accordingly, the submodule 100 can transmit power in both directions.

The transformer 150 may be connected to the primary side 110 and the secondary side 120 respectively to insulate the primary side 110 and the secondary side 120. In this embodiment, the transformer 150 is applied with a transformer operating at a high frequency (eg, 60 Hz or higher), so that the size of the sub-module 100 can be reduced.

The output voltage line 102 connected to the transformer 150 and the secondary side 120 may be connected to another sub-module 100. For example, the output voltage line 102 may be connected to the ground line of the adjacent sub-module SM-P2, and similarly, the output voltage line of the adjacent sub-module SM-P2 is the ground line of another sub-module SM-P3. Can be connected to.

The sub-module 100 can transmit power in both directions by controlling a phase shift of a plurality of switch elements provided on the primary side 110 and the secondary side 120. In particular, when power conversion is performed from the primary side 110 to the secondary side 120, the DC voltage may be converted into a chopped PWM type voltage.

As described above, in the multi-level converter 1000 according to an embodiment of the present invention, a plurality of sub-modules 100 constituting a multi-module are configured as a single bidirectional DC-AC converter of a bridge type, and the output terminals thereof are serially connected to Level PWM voltage output is possible. At this time, since the plurality of sub-modules 100 have a single power conversion structure, and the transformer 150 included in each sub-module 100 is configured as a high-frequency transformer, effects such as overall size reduction and cost reduction can be expected.

3 is a diagram illustrating a multi-level converter according to another embodiment of the present invention.

Referring to FIG. 3, a multi-level converter 2000 according to another embodiment of the present invention may be applied to a three-phase system or a three-phase motor.

The multilevel converter 2000 according to another embodiment of the present invention may include a first string to a third string connected to each phase of a three-phase system or a three-phase motor, and each string multiplies an independent DC voltage. It can be converted into a level PWM voltage and output.

To this end, each of the first string to the third string may be configured in the same manner as the multi-module included in the multi-level converter 1000 according to the embodiment of the present invention illustrated in FIG. 1. Since the first string to the third string have the same configuration, the first string will be described as a representative example.

The first string may include a plurality of sub-modules 100.

The sub-module 100 may be configured as a two-way bridge power conversion circuit in which the primary side and the secondary side are insulated by a transformer. A detailed description of the circuit configuration of the sub-module 100 is replaced with the above.

The sub-module 100 enables power conversion from the primary side to the secondary side by controlling the phase shift of a plurality of switch elements provided in the bridges of the primary side and the secondary side. The plurality of switch elements provided in the sub-module 100 may be provided with an active switch element, such as an active transistor, not a diode, and may include a transistor driving circuit. Accordingly, the sub-module 100 is capable of converting power from the secondary side to the primary side with a converter capable of bidirectional power transfer, such as a bidirectional half bridge, a bidirectional full bridge, or a bidirectional flying capacitor multilevel converter. Hereinafter, a representative example of the submodule 100 performing power conversion from the primary side to the secondary side will be described.

The primary side of the sub-module 100 may be connected to a DC power supply, and the secondary side chopping a voltage in the form of a square wave, specifically, a DC voltage by the operation of a plurality of switches provided on the bridges of the primary and secondary sides. ) One type of PWM voltage can be output.

The first string includes a plurality of such sub-modules 100, and each primary side of the plurality of sub-modules 100 is independently separated, and each secondary side of the plurality of sub-modules 100 is connected in series. I can.

For example, the output voltage line of the first sub-module SM-P1 may be connected to the ground line of the second sub-module SM-P2, and the output voltage line of the n-th sub-module SM-Pn is a three-phase system. Alternatively, by being connected to the A phase of the three-phase motor, the outputs of the n submodules 100 may be connected in series.

Accordingly, the first string outputs a DC voltage independently input to each sub-module 100 as a voltage in the form of a square wave, but the outputs of the plurality of sub-modules 100 are added to output a multi-level PWM voltage. At this time, each primary side of the plurality of sub-modules 100 may receive a DC voltage having the same magnitude, and may have a phase difference between outputs of the secondary side of the plurality of sub-modules 100.

For example, the first string may form a positive leg and a negative leg connected to the neutral point (a). A plurality of sub-modules 100 may be provided in each of the positive voltage leg and the negative voltage leg, and outputs between the plurality of sub-modules 100 may be connected in series. The positive voltage leg and the negative voltage leg may be configured in a vertically symmetrical shape. For example, when n sub-modules 100 are provided in the positive voltage leg, the negative voltage leg may also be provided with n sub-modules 100 to generate an AC voltage.

The first string may expand the submodule 100 according to the required power capacity.

The output terminal of the first string may be connected to the A phase of the three-phase system or the three-phase motor, the output terminal of the second string may be connected to the B phase, and the output terminal of the third string may be connected to the C phase.

Input terminals of the first string to the third string may be connected to each other. Specifically, the n-th sub-module among n sub-modules included in the first string, the n-th sub-module among n sub-modules included in the second string, and the n-th sub-module among n sub-modules included in the third string The input terminals of can be connected to each other. This is to offset the ripple voltage of each phase of the three-phase system.

For example, when the multi-level converter 2000 according to another embodiment of the present invention outputs a voltage of 60 Hz, a ripple voltage of 120 Hz will occur in the A phase, B phase, and C phase. In this case, the ripple voltage of each phase may be canceled by connecting the input terminals of the first string to the third string connected to each phase.

The multi-level converter 2000 according to another embodiment of the present invention may further include a control module for controlling each of the switch elements included in the first string to the third string.

The control module may control a switching operation of switch elements included in each of the plurality of sub-modules 100.

For example, the control module may control a duty and a phase of each switch element by controlling a gating signal of a switch element included in each of the plurality of sub-modules 100.

The control module may include a central controller and a plurality of sub-controllers.

For example, the central controller may control a plurality of sub-controllers, and each of the plurality of sub-controllers may control one sub-module 100 in charge of itself.

In this embodiment, the control module may control switch elements included in each of the plurality of sub-modules 100 to perform power conversion in a phase shift method. In this case, the control module may control the switch elements included in each of the plurality of sub-modules 100 to have a fixed duty (eg, 50%). Accordingly, the multi-level converter 2000 according to another embodiment of the present invention can transmit active power as well as reactive power.

In addition, in the present embodiment, the control module controls the operation phase of the switch elements provided on each secondary side of the plurality of sub-modules 100 to be maintained differently for each sub-module 100, thereby outputting multi-level PWM voltages in each string. Makes this possible.

In addition, in the present embodiment, the control module may control the operation phase of each switch element included in the plurality of sub-modules 100 based on the amount of power transfer of each string required by the control module in the present embodiment. In this case, the phase difference between the secondary outputs of the plurality of sub-modules 100 is adjusted to control the amount of power delivered to each string.

Although the above has been described with reference to embodiments, those skilled in the art will understand that various modifications and changes can be made to the present invention without departing from the spirit and scope of the present invention described in the following claims. I will be able to.

1000: multi-level converter
100: sub module

Claims (10)

A plurality of sub-modules consisting of a bidirectional bridge power conversion circuit including an active switch element are provided on the primary side and the secondary side insulated by the transformer, and a positive leg in which each secondary side of the plurality of sub-modules is connected in series. ) And a multi-module including a negative leg; And
A multi-level converter comprising a control module for controlling each of the switch elements included in the multi-module. The method of claim 1,
The multi-module,
The DC voltage input from each of the plurality of sub-modules to the primary side is converted into a voltage in the form of a square wave and output to the secondary side, but has a phase difference between the outputs of the secondary side of the plurality of sub-modules, A multi-level converter that outputs multi-level PWM voltage by connecting each secondary side in series. The method of claim 2,
The control module,
A multi-level converter for controlling an operation phase of a switch element included in the plurality of sub-modules so as to control a power transfer amount of the multi-module by adjusting a phase difference between the secondary outputs of the plurality of sub-modules. The method of claim 1,
The multi-module,
A plurality of switch elements are provided in each bridge of the primary and secondary sides, and the plurality of switch elements are phase shifted with a fixed duty by the control module, and a plurality of sub-modules that transmit power in both directions around a transformer are provided. A multi-level converter is provided. A plurality of sub-modules consisting of a bidirectional bridge power conversion circuit including an active switch element are provided on the primary side and the secondary side insulated by the transformer, and a positive leg in which each secondary side of the plurality of sub-modules is connected in series. ) And a first string to a third string including a negative leg; And
A control module for controlling each of the switch elements included in the first string to the third string,
The first string to the third string are each connected to each phase of a three-phase system multi-level converter. The method of claim 5,
The first string to the third string,
A multi-level converter in which input terminals of a plurality of sub-modules respectively included in the first string to the third string are connected to each other. The method of claim 6,
The first string to the third string,
A multi-level converter for canceling a ripple voltage of each phase of a three-phase system connected to the first string to the third string, respectively. The method of claim 5,
The first string to the third string,
The DC voltage input from each of the plurality of sub-modules to the primary side is converted into a voltage in the form of a square wave and output to the secondary side, but has a phase difference between the outputs of the secondary side of the plurality of sub-modules, A multi-level converter that outputs multi-level PWM voltage by connecting each secondary side in series. The method of claim 8,
The control module,
Controlling an operation phase of a switch element included in the plurality of sub-modules so as to control a power transfer amount of each of the first string to the third string by adjusting a phase difference between the secondary outputs of the plurality of sub-modules Multi-level converter. The method of claim 5,
The first string to the third string,
A plurality of switch elements are provided in each bridge of the primary and secondary sides, and the plurality of switch elements are phase shifted with a fixed duty by the control module, and a plurality of sub-modules that transmit power in both directions around a transformer are provided. A multi-level converter is provided.

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