KR101334318B1 - Power converting device - Google Patents

Abstract

Embodiments relate to a power converter. The power converter according to the embodiment is connected to a generator, a generator-side converter including a multi-level converter and a generator-side converter, a DC link stage including an upper capacitor and a lower capacitor, one end is connected to the grid, The other end is connected to the DC link stage and includes a grid-side converter including two two-level converters, the two-level converters are connected in series, and the nodes of the two two-level converters in series are connected to the upper capacitor and the lower capacitor. Is connected with the neutral point.

Description

Power converting device

The present invention relates to a power converter, and more particularly, to a power converter connected to the neutral point by connecting a two-level converter in series on the grid side.

Renewable energy is an energy used by converting existing fossil fuels or converting renewable energy including sunlight, water, geothermal energy, and biological organisms, and is emerging as a future energy source for a sustainable energy supply system. I am getting it.

In particular, renewable energy has become more important due to the instability of oil prices and the regulatory response of the Climate Change Convention. Renewable energy types include wind power, wave power, tidal power, solar energy, waste energy, and renewable energy fields, such as intelligence, fuel cells, and hydrogen energy.

An essential element in the renewable energy generation system is a power converter, which is a low voltage primary energy having a variable voltage and a variable frequency characteristic due to a variable wind speed or flow rate. It is a device for purifying high quality secondary energy with constant voltage and constant frequency so that it can be linked.

In particular, the generators that are widely applied in the renewable energy generation system market include the Double-Fed Indection Generator (DFIG) and the Synchronous Generator (SG).

1 is a circuit diagram schematically showing a power conversion apparatus according to a comparative example of the present invention.

1 illustrates an example of a power conversion system that can be applied to a general three-phase generator, and illustrates a power conversion apparatus having a back-to-back three-level converter.

Referring to FIG. 1, a power converter applied to a three-phase synchronous generator 1 includes an AC / DC converter (generator side converter) 3 and a DC / AC converter (system side converter) 5 ). Each converter 3, 5 has an AC-DC-AC conversion function that converts an AC power source into a DC power source and converts it back into an AC power source.

Specifically, the output of the synchronous generator 1 is a single three-phase, DC link stage (between the generator side converter 3 connected to the synchronous generator 1 and the grid side converter 5 connected to the power grid side ( 7), converters 3 and 5 on both sides share the DC link stage 7.

At this time, the generator-side converter 3 and the grid-side converter 5 are constituted by two-level converters having twelve switching elements 11 and 12, as shown.

The voltage applied to the DC link stage 7 is controlled to always be kept constant so that energy generated through the rotor windings of the generator 1 can be delivered to the system.

However, in the case of installing a large-capacity wind generator, for example, a high voltage wind generator is installed in order to prevent waste of energy. Accordingly, the power converter must also use a high voltage power converter to control the high voltage generator.

The converters 3 and 5 include switching elements, and in the case of mainly used insulated gate bipolar transistors (IGBTs), they have a voltage level limit, and therefore, three-level diode clamped converters are used.

However, since the three-level diode clamped converter has more switching elements and clamping diodes than the two-level converter, the entire circuit is complicated and has the disadvantage of controlling the neutral point potential of the DC link stage 7.

Korean Patent Laid-Open Publication No. 2009-0056110 clamps neutral points with a switch without using a clamping diode, thereby increasing the level of the output voltage, thereby reducing the harmonics of the output voltage and the ripple of the load current, and extending to multi-levels. Disclosed is a switch clamped multi-level inverter that can be easily modularized. However, there is a difference from the configuration of controlling the neutral point by using a two-level converter connected in series with the system-side converter disclosed in the present invention.

Patent Document 1: Korean Patent Publication No. 2009-0056110 (published on June 6, 2009)

Embodiments of the present invention is to provide a power conversion device configured to have a three-level generator side converter, there is no need to control the imbalance of the neutral point voltage using a two-level converter connected in series with the grid side converter.

According to one aspect of the invention, a generator-side converter connected to the generator, including a multi-level converter; A DC link stage connected to the generator-side converter and including an upper capacitor and a lower capacitor; And a grid side converter having one end connected to the grid and the other end connected to the DC link stage and including a plurality of two level converters, wherein the plurality of two level converters constituting the grid side converter are connected in series. Provided is a power converter.

In addition, a first node to which the plurality of two-level converters are connected in series is connected to a neutral point between the upper capacitor and the lower capacitor.

Also, when the two level converters are connected in series, the two level converter includes an upper two level converter connected to one end of the upper capacitor and a lower two level converter connected to one end of the lower capacitor.

In addition, the upper two-level converter and the lower two-level converter each have six switching elements, and the switching elements of the upper two-level converter are connected in series with the switching elements of the lower two-level converter.

In addition, the plurality of two-level converters do not include a clamping diode.

The generator-side converter is an NPC type three level converter or a switch clamped three level converter.

In addition, the power converter includes a control unit for controlling the operation of the generator-side converter and the grid-side converter, the control unit does not include an algorithm for controlling the neutral point imbalance.

The power converter includes a plurality of generator-side converters connected in parallel to the generator, a plurality of grid-side converters connected in parallel to the grid, and the DC link between the generator-side converter and the grid-side converter. The stages are each connected.

According to another aspect of the present invention, a generator-side converter connected to a generator and including a multi-level converter; A DC link stage connected to the generator-side converter and including an upper capacitor and a lower capacitor; And a grid side converter having one end connected to the grid and the other end connected to the DC link stage and including two two level converters, wherein the two level converters are connected in series. A node of a series connected portion may be provided with a power converter connected to a neutral point connecting the upper capacitor and the lower capacitor.

Also, the neutral point is a voltage reference point of the upper capacitor and the lower capacitor.

The two two-level converters may include an upper two level converter connected to the upper capacitor and a lower two level converter connected to the lower capacitor.

The power converter is configured to turn on / off the switching elements included in the upper 2 level converter and the lower 2 level converter to adjust the magnitude of the voltage charged in the upper capacitor and the lower capacitor based on the neutral point. It further includes a control unit for controlling the off.

Embodiments of the present invention can control the unbalance of the voltage applied to the DC link terminal appearing according to the switching state without a separate algorithm.

In addition, by changing the grid-side converter from three levels to two levels, it is possible to eliminate the clamping diode, thereby lowering the manufacturing cost of the power converter.

In addition, it is possible to operate by setting the DC link stage voltage lower than when using a conventional three-level converter to improve the durability of the system.

1 is a circuit diagram schematically showing a power conversion apparatus according to a comparative example of the present invention.
2 is a circuit diagram briefly illustrating a power conversion system including a power conversion apparatus according to an embodiment of the present invention.
3A is a graph schematically illustrating a voltage change of a DC link terminal according to a comparative example of the present invention.
Figure 3b is a graph showing a brief change in the voltage of the DC link stage according to an embodiment of the present invention.
4 is a table comparing the number of switching elements and clamping diodes included in Comparative Examples and Examples of the present invention.

It is to be understood that the specific structural or functional descriptions of embodiments of the present invention disclosed herein are only for the purpose of illustrating embodiments of the inventive concept, But may be embodied in many different forms and is not limited to the embodiments set forth herein.

Embodiments in accordance with the concepts of the present invention are capable of various modifications and may take various forms, so that the embodiments are illustrated in the drawings and described in detail herein. It should be understood, however, that it is not intended to limit the embodiments according to the concepts of the present invention to the particular forms disclosed, but includes all modifications, equivalents, or alternatives falling within the spirit and scope of the invention.

The terms first, second, etc. may be used to describe various elements, but the elements should not be limited by the terms. The terms are intended to distinguish one element from another, for example, without departing from the scope of the invention in accordance with the concepts of the present invention, the first element may be termed the second element, The second component may also be referred to as a first component.

When a component is referred to as being "connected" or "connected" to another component, it may be directly connected to or connected to that other component, but it may be understood that other components may be present in between. Should be. On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between. Other expressions that describe the relationship between components, such as "between" and "between" or "neighboring to" and "directly adjacent to" should be interpreted as well.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, the terms "comprises ", or" having ", or the like, specify that there is a stated feature, number, step, operation, , Steps, operations, components, parts, or combinations thereof, as a matter of principle.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the meaning of the context in the relevant art and, unless explicitly defined herein, are to be interpreted as ideal or overly formal Do not.

2 is a circuit diagram illustrating a portion of a converter system 100 according to an embodiment of the present invention.

Referring to FIG. 2, the power converter 10 may include a generator side converter 20, a DC link 30, and a grid side converter 40, 40 ′. The power conversion system 1 may include a power converter 10, a generator 100, and a system 200.

The generator 100 may generate three phase AC power of variable frequency from the rotation of the turbine. Alternatively, a small capacity generator can generate DC power. The generated power may be AC-DC converted through the power converter 10, or may be DC-DC converted.

The grid 200 is also referred to as a grid, and is an AC power system provided by a power company or a power generation company. For example, the system 200 is an electrical linkage formed in a large area including a power plant, a substation, and a transmission line.

The power converter 10 may include a generator side converter 20, a DC link stage 30, a grid side converter 40, and a controller 50.

The structure of the power converter 10 includes an AC / DC converter (generator side converter) 20 and a DC / AC converter (system side converter) 40 and 40 ', and supplies AC power. After converting to DC power, it converts to AC power again.

For example, the output of the generator 100 is a single three-phase, DC-link stage 30 between the generator 160 side converter 20 and the grid side converters 40 and 40 'connected to the generator 100. Can share.

The generator side converter 20 is connected to the generator 100 and may include a multilevel converter. As an example, the generator-side converter 20 may be a three-phase NPC type three level converter or a switch clamped three level converter.

The DC link stage 30 is connected to the generator side converter 20 and may include an upper capacitor 32 and a lower capacitor 34.

The grid-side converters 40 and 40 'may include a plurality of three-phase two-level converters, one end of which is connected to the system 200 and the other end of which is connected to the DC link terminal 30.

The switching elements 22 and 42 constituting the generator-side converter 20 and the grid-side converters 40 and 40 'may be a plurality of semiconductor switching elements. Switching devices include gate turn-off thyristors (GTO), Insulated Gate Bipolar Transistors (IGBTs), Integrated Gate Commutated Thyristors (IGCTs), Bipolar Junction Transistors (BJTs), and Metal Oxide Semiconductor Field Effect Transistors (MOSFETs). It may be made of. The IGBT is a junction transistor in which a metal oxide semiconductor field effect transistor (MOSFET) is placed in a gate portion. Since the voltage between the gate and the emitter is driven to generate on / off by the input signal, it is a semiconductor switching device capable of fast switching of large power. The IGBT has a characteristic of being turned on and off at a high speed of 1 kHz when a DC voltage or an alternating voltage is supplied, thereby enabling high-speed switching.

The generator side converter 20 includes four switching elements 22, four antiparallel diodes, and two clamping diodes in each phase. A three-level output voltage can be obtained by using a clamping diode without each independent DC power supply.

Specifically, each of the equivalent switching states of the three-phase NPC type three-level converter has three phase voltage states according to the conduction state of the switching element, and always paired with any phase so that the two switching elements are turned on ( keep on.

In the case of the NPC type 3 level converter, a voltage imbalance problem occurs in the DC link stage 30, which reconstructs a sequence pattern of a rectangular wave vector pulse-width modulation (R-SVPWM) control method and applies a switching vector. This can be solved through an algorithm that adjusts time. However, for this purpose, the corresponding algorithm must be implemented in the controller 50 of the power converter 10.

In addition, there is a problem that there is a region that can not control the voltage imbalance even through such an algorithm.

In order to solve the voltage imbalance problem of the neutral point 35, the grid-side converter 30 includes a three-phase two-level converter connected in series. The two level converter does not have a clamping diode. For example, when two two-level converters are connected in series, the first node 45 connected in series may be connected to a neutral point 35 connecting between the upper capacitor 32 and the lower capacitor 34.

The upper two-level converter 40 of the two two-level converters may adjust the voltage of the upper capacitor 32, and the lower two-level converter 40 ′ may adjust the voltage of the lower capacitor 34. The neutral point 35 serves as a reference point for measuring the voltage of the upper capacitor 32 and the voltage of the lower capacitor 34.

The upper two level converter 40 and the lower two level converter 40 'each include six switching elements 42 and 42', and the upper two level converter 40 and the lower two level converter 40 'are connected in series. The connection is the same as that in which the switching element 42 of the upper two-level converter 40 and the switching element 42 'of the lower two-level converter 40' are connected in series.

Each of the two-level converters 40 and 40 ′ may adjust the voltage values of the upper capacitor 32 and the lower capacitor 34 to solve the voltage unbalance problem of the neutral point 35 of the three-level converter as a whole. Accordingly, the controller 50 does not include an algorithm for controlling the neutral 35 voltage imbalance. As a result, the execution burden of the controller 50 may be reduced.

In addition, as the region where the neutral point 35 voltage imbalance cannot be controlled, capacitors 32 and 34 may be designed to have a voltage lower than that of the DC link terminal 7, thereby enhancing system durability.

In addition, the number of switching elements 42 and 42 'constituting two three-phase two-level converters connected in series is identical to the number of switching elements 12 constituting the conventional power converter shown in FIG. According to the embodiment of the present invention, unlike a conventional power converter, a clamping diode is unnecessary. Therefore, the hardware cost can be reduced by the number of clamping diodes.

The controller 50 may control the power of the generator 100 by controlling the on / off of the switching element 22 constituting the generator-side converter 20, the voltage of the generator 100 side Power factor control of over current can be performed. In addition, the controller 50 controls the voltage of the DC link stage 30 by controlling the on / off of the switching elements 42 and 42 'constituting the grid-side converters 40 and 40'. The power factor control of the voltage and current of the system 200 may be performed.

Further, when the grid side converter 40 is three series connected two level converters, the generator side converter 20 may be a four level NPC type converter, and the grid side converter 40 is four series connected two level converters. In this case, the generator-side converter 20 may be a five-level NPC type converter.

In addition, a plurality of such power converter 10 may be provided in parallel, respectively, to constitute a power conversion system (1). That is, the plurality of generator-side converters 20 are connected in parallel to the generator 100, the plurality of grid-side converters 40 are connected in parallel to the system 200, and the plurality of generator-side converters 20 and the plurality of generator-side converters 20 are connected in parallel. DC link stages may be connected between the grid-side converter 40 of each.

 3A is a graph schematically illustrating a voltage change of a DC link terminal according to a comparative example of the present invention.

Figure 3b is a graph showing a brief change in the voltage of the DC link stage according to an embodiment of the present invention.

2, 3A, and 3B, the voltage charged to the upper capacitor 32 is Vdc_H, and the voltage charged to the lower capacitor 34 is Vdc_L. This size is determined based on the neutral point 35. 3A is a voltage change curve of a capacitor constituting the DC link stage 7 according to the comparative example of the present invention. As time passes, the magnitude of the voltage Vdc_H charged in the upper capacitor 32 increases, and the magnitude of the voltage Vdc_L charged in the lower capacitor 34 decreases.

Therefore, it can be seen that the voltage variation of the capacitors accumulates, resulting in an unbalanced DC power supply voltage in which the voltage difference between the capacitors increases. When the voltages between the capacitors are inconsistent, the hexagons formed by the space voltage vectors are asymmetrically distorted, thereby distorting the voltage output. In addition, the magnitude of the voltage across one switching element may exceed the rated voltage of the element, which may destroy the switching element.

In FIG. 3B, by connecting two two-level converters connected in series with the neutral point 35 of the DC link terminal 30, the voltages Vdc_H and Vdc_L of the upper capacitor 32 and the lower capacitor 34 are almost the same. Can be.

4 is a table comparing the number of switching elements and clamping diodes included in Comparative Examples and Examples of the present invention.

Referring to the number of switching elements, for example, an IGBT and a clamping diode constituting the power converter shown in FIG. 1 and the power converter shown in FIG. 2 as a comparative example of the present invention, the power shown in FIG. The inverter consists of 12 IGBTs and 12 clamping diodes.

The power converter 10 shown in FIG. 2 includes the same 12 IGBTs as the power converter shown in FIG. 1, but does not include a clamping diode. That is, by configuring as a two-level converter in this way, it is possible to eliminate the clamping diode, which is an essential component of the NPC converter, thereby reducing the hardware cost.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It should be understood that various modifications may be made by those skilled in the art without departing from the spirit and scope of the present invention.

10: power converter 20: generator side converter
22: switching element 30: DC link stage
40, 40 ': grid-side converter 42, 42': switching element
50 control unit 100 generator
200: System

Claims (11)

A generator-side converter coupled to the generator and including a multi-level converter;
A DC link stage connected to the generator-side converter and including an upper capacitor and a lower capacitor;
A grid side converter having one end connected to the grid and the other end connected to the DC link stage and including a plurality of two-level converters; And
A control unit for controlling the operation of the generator-side converter and the grid-side converter,
The plurality of two-level converters constituting the grid-side converter is connected in series,
A first node to which the plurality of two-level converters are connected in series is connected to a neutral point between the upper capacitor and the lower capacitor,
The two level converter includes an upper two level converter connected to one end of the upper capacitor and a lower two level converter connected to one end of the lower capacitor,
The upper two level converter and the lower two level converter each have six switching elements,
The switching element of the upper two level converter is connected in series with the switching element of the lower two level converter,
Each switching element is
Insulated Gate Bipolar Transistors (IGBTs),
The control unit
Controlling on / off of switching elements included in the upper two-level converter and the lower two-level converter to adjust the magnitude of the voltage charged in the upper capacitor and the lower capacitor based on the neutral point;
The plurality of two-level converter,
Power converter without clamping diode. delete delete delete delete The method of claim 1, wherein the generator-side converter,
Power converter which is an NPC type 3 level converter or a switch clamped 3 level converter. The apparatus of claim 1,
The power converter does not include an algorithm for controlling the voltage of the upper capacitor and the lower capacitor. The method of claim 1, wherein the power converter,
And a plurality of generator side converters are connected in parallel to the generator, a plurality of grid side converters are connected in parallel to the grid, and the DC link stage is connected between the generator side converter and the grid side converter, respectively. In the power converter,
A generator-side converter coupled to the generator and including a multi-level converter;
A DC link stage connected to the generator-side converter and including an upper capacitor and a lower capacitor; And
One end is connected to the grid, the other end is connected to the DC link stage, and includes a grid side converter including two two level converters,
The two-level converter is connected in series, the node of the portion where the two two-level converter is connected in series is connected to the neutral point connecting the upper capacitor and the lower capacitor,
The neutral point is a voltage reference point of the upper capacitor and the lower capacitor,
The two two-level converter,
An upper two level converter connected to the upper capacitor and a lower two level converter connected to the lower capacitor,
The power converter is configured to turn on / off the switching elements included in the upper 2 level converter and the lower 2 level converter to adjust the magnitude of the voltage charged in the upper capacitor and the lower capacitor based on the neutral point. Further comprising a control unit for controlling the off,
Switching elements included in the upper two-level converter and the lower two-level converter
Insulated Gate Bipolar Transistor (IGBT)
The two two-level converter
Power converter without clamping diode. delete delete

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