Apparatus and method for controlling module switching of power converting system

A technology is disclosed for controlling switching of power converters included in a power converting system. Phase angles are allocated to a plurality of sub-units corresponding to the power converters, and the respective sub-units create local switching carriers based on the allocated phase angles. The sub-units compare a reference AC voltage with the local switching carriers, and switch the power converters according to the result of the comparison.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a technology for controlling a power converting system, and more particularly, to a technology for controlling the switching of power converters included in a power converting system.

2. Description of the Prior Art

A multilevel converter may be used to convert direct current into alternating current, or alternating current into direct current. The multilevel converter in which a plurality of power converters are connected in series with each other precisely control operating time points or switching time points of the power converters to convert direct current into alternating current, or alternating current into direct current.

The switching of the serially connected power converters is controlled depending on an input waveform, and outputs of the respective power converters are summed up according to the switching time points of the power converters to configure an output waveform. Accordingly, the technology for precisely controlling the switching time points of the respective power converters is emerging as a major issue in the commercialization of the multilevel converter.

With an increase in the number of power converters included in the multilevel converter, a performance improvement such as reduction of high frequency distortion of the output waveform can be made. However, with the increase in the number of power converters, an algorithm for precisely controlling the switching time points of the respective power converters is complicated.

SUMMARY OF THE INVENTION

An aspect of the present invention is to provide an apparatus and a method for converting power which can precisely control switching time points of power converters included in a multilevel converter.

Another aspect of the present invention is to provide an apparatus and a method for converting power which can control switching time points of power converters included in a multilevel converter only with a small amount of operation.

In accordance with one aspect of the present invention, an apparatus for converting power is provided. The apparatus includes: a central controller that generates a reference AC voltage; and a plurality of sub-units, wherein the central controller allocates phase angles to the respective sub-units, and the respective sub-units individually create local switching carriers based on the allocated phase angles, and controls switching of power converters corresponding to the respective sub-units according to a result of a comparison of the individually created local switching carriers and the reference AC voltage.

The power converters may configure at least one phase leg, and, when M power converters are included in the phase leg, the central controller may allocate the phase angles such that differences between the allocated phase angles are multiples of 2π/M.

The power converters included in the phase leg may be connected in series with each other.

The phase leg may be arranged between a DC connection terminal and an AC connection terminal.

The respective sub-units may compare the local switching carriers with the reference AC voltage, and may control the switching of the power converters corresponding to the respective sub-unit according to the result of the comparison.

The power converters may include a plurality of power electronic switches connected in series with each other, and a capacitor connected in parallel with the power electronic switches.

In accordance with another aspect of the present invention, a method of converting power is provided. The method includes: allocating phase angles to a plurality of sub-units, respectively, by a central controller; individually creating local switching carriers based on the allocated phase angles, by the respective sub-units; and controlling switching of power converters corresponding to the respective sub-units according to a result of a comparison of the individually created local switching carriers and a reference AC voltage, by the respective sub-units.

The power converters may configure at least one phase leg, and, when M power converters are included in the phase leg, the central controller may allocate the phase angles such that differences between the allocated phase angles are multiples of 2π/M.

The power converters included in the phase leg may be connected in series with each other.

The phase leg may be arranged between a DC connection terminal and an AC connection terminal.

The controlling of the switching may include comparing the local switching carriers with the reference AC voltage, and controlling the switching of the power converters corresponding to the respective sub-unit according to the result of the comparison.

The power converters may include a plurality of power electronic switches connected in series with each other, and a capacitor connected in parallel with the power electronic switches.

As described above, the present invention provides an apparatus and a method for converting power which can precisely control switching time points of power converters included in a multilevel converter.

Furthermore, according to the embodiments of the present invention, switching time points of power converters included in a multilevel converter can be controlled only with a small amount of operation.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1is a view illustrating a concept of a multilevel converter for converting power by switching a plurality of power converters.

The multilevel converter converts Direct Current (DC) into Alternating Current (AC), and alternating current into direct current using the plurality of power converters. According to an aspect, the multi-level converter may include a plurality of power converters181,182,183, and184connected in series with each other as illustrated inFIG. 1.

According to an aspect, the multilevel converter may include a plurality of phase legs, and each of the phase legs may include the plurality of power converters181to184. The phase leg may be arranged between a DC terminal160and an AC terminal170to convert direct current into alternating current, or alternating current into direct current. In this case, an output of the phase leg may be the sum of outputs of the respective power converters181to184.

According to an aspect, each of the power converters181to184may simply produce direct current. However, the output of the phase leg, which is the sum of the outputs of the respective power converters181to184, may have the form of alternating current through precisely controlling the switching time points of the respective power converters181to184.

A waveform110of alternating current illustrated inFIG. 1may be obtained by approximating the output of the phase leg. The output110of the phase leg is configured by the sum of an output150of a first power converter, an output140of a second power converter, an output130of a third power converter, and an output120of a fourth power converter.

When the power converters181to184are switched from a deactivated state to an activated state, the respective power converters181to184produce the outputs. Accordingly, in order to configure the waveform110of alternating current by synthesizing the outputs of the respective power converters181to184, the switching time points of the respective power converters181to184have to be precisely controlled.

FIG. 2is a circuit diagram illustrating a structure of a power converting apparatus according to an exemplary embodiment of the present invention.

The power converting apparatus includes a plurality of phase legs, each of which includes a plurality of power converters. Furthermore, in order to control switching time points of the power converters211to214and231to234, the power converting apparatus further includes a central controller260and sub-units261to268corresponding to the respective power converters211to214and231to234.

According to an aspect, the central controller260generates a reference AC voltage. The central controller260transmits the generated reference AC voltage to the sub-units261to268. Furthermore, the central controller260may allocate phase angles to the respective sub-units261to268. The central controller260transmits the allocated phase angles to the respective sub-units261to268.

The sub-units261to268may individually create local switching carriers based on the received phase angles. According to an aspect, the respective sub-units261to268may create the local switching carriers having the same frequency. That is, the local switching carriers created by the respective sub-units261to268are sinusoidal waves having the same frequency and the phase angles determined under the control of the central controller260.

The respective sub-units261to268may control the power converters211to214and231to234such that the power converters211to214and231to234corresponding to the respective sub-units261to268are switched at intersection time points of the created local switching carriers and the reference AC voltage.

Although the respective local switching carriers have the same frequency, the phase angles thereof may be different from each other. Accordingly, the intersection time points of the respective local switching carriers and the reference AC voltage may be different from each other depending on the respective sub-units261to268. Thus, switching time points of the power converters211to214and231to234corresponding to the respective sub-units261to268are determined to be different from each other.

According to an aspect, the switching time points of the respective power converters211to214and231to234may be determined such that the sum of outputs of the power converters211to214and231to234approximates to the AC waveform as illustrated inFIG. 1.

As illustrated inFIG. 2, each of the power converters211to214and231to234may include a plurality of power electronic switches270connected in series with each other. In this case, the respective power converters211to214and231to234may include capacitors221to224and241to244connected in parallel with the power electronic switches270which are connected in series with each other.

According to the embodiment illustrated inFIG. 2, the central controller260allocates the phase angles to the respective sub-units261to268and generates the reference AC voltage, and the local switching carriers are created by the individual sub-units261to268having received the phase angles.

That is, the creation of the local switching carriers and the comparison of the local switching carriers and the reference AC voltage for the individual sub-units261to268are carried out by the respective sub-units261to268, thereby reducing a burden of an operation for the central controller. Accordingly, precise control can be made using only the simple control algorithm.

FIG. 3is a block diagram illustrating a structure of a power converting apparatus according to an exemplary embodiment of the present invention.

The power converting apparatus300may include a central controller310, sub-units321to323, and power converters331to333.

The central controller310generates a reference AC voltage. The central controller310transmits the generated reference AC voltage to the sub-units321to323. That is, the reference AC voltage is common in the sub-units321to323. According to an aspect, the reference AC voltage may be a sinusoidal wave.

Furthermore, the central controller310allocates phase angles to the respective sub-units321to323. According to an aspect, the central controller310may allocate the phase angles to the sub-unit321to323such that the sum of outputs created by the respective power converters331to333to be switched by controlling the sub-units321to323has the AC waveform.

The sub-units321to323receive the reference AC voltage and the phase angles. The respective sub-units321to323create local switching carriers using the received phase angles. According to an aspect, the local switching carriers may be the same frequency of sinusoidal waves having different phases depending on the phase angles allocated by the central controller310.

The respective sub-units321to323compare the reference AC voltage with the created local switching carriers, and control switching of the power converters331to333corresponding to the respective sub-units321to323according to the result of the comparison.

According to an aspect, every time the local switching carriers intersect with the reference AC voltage, the respective sub-units321to323may control the power converters331to333to be switched.

According to an aspect, the plurality of power converters331to333may configure one phase leg340. The power converters331to333included in the phase leg340may be connected in series with each other. The phase leg340is arranged between a DC connection terminal and an AC connection terminal of the power converting apparatus.

According to an aspect, the phase leg340may include M power converters. In this case, the central controller310may allocate the phase angles to the sub-units321to323such that differences between the phase angles allocated to the respective sub-units321to323are multiples of 2π/M.

According to an aspect, each of the power converters331to333may include a plurality of power electronic switches. Each of the power electronic switches may be an element in which a transistor and a diode are connected in parallel with each other. Furthermore, the power electronic switches included in each of the power converters331to333may be connected in series with each other. Moreover, each of the power converters331to333may include a capacitor connected in parallel with the power electronic switches which are connected in series with each other.

FIG. 4is a flowchart illustrating a power converting method according to an exemplary embodiment of the present invention.

In step410, a central controller generates a reference AC voltage. The central controller transmits the generated reference AC voltage to sub-units. That is, the reference AC voltage is common in the sub-units. According to an aspect, the reference AC voltage may be a sinusoidal wave.

In step410, the central controller allocates phase angles to the respective sub-units. According to an aspect, the central controller may allocate the phase angles to the respective sub-units such that the sum of outputs created by the respective power converters to be switched by controlling the sub-units has the AC waveform.

In step420, the respective sub-units receive the reference AC voltage and the phase angles. The respective sub-units create local switching carriers using the received phase angles. According to an aspect, the local switching carriers may be the same frequency of sinusoidal waves having different phases depending on the phase angles allocated by the central controller.

In step430, the respective sub-units compare the reference AC voltage with the created local switching carriers, and controls switching of the power converters corresponding to the respective sub-units according to the result of the comparison.

According to an aspect, every time the local switching carriers intersect with the reference AC voltage, the respective sub-units may control the power converters331to333to be switched.

According to an aspect, the plurality of power converters may configure one phase leg. The power converters included in the phase leg may be connected in series with each other. The phase leg is arranged between a DC connection terminal and an AC connection terminal of the power converting apparatus.

According to an aspect, the phase leg may include M power converters. In this case, the central controller may allocate the phase angles to the sub-units such that differences between the phase angles allocated to the respective sub-units are multiples of 2π/M.

According to an aspect, each of the power converters may include a plurality of power electronic switches. Each of the power electronic switches may be an element in which a transistor and a diode are connected in parallel with each other. Furthermore, the power electronic switches included in each of the power converters may be connected in series with each other. Moreover, each of the power converters may include a capacitor connected in parallel with the power electronic switches which are connected in series with each other.

The methods according to the embodiments of the present invention may be implemented in the form of a program command which may be executed through various computer means, and may be recorded in a computer readable medium. The computer readable medium may include a program command, a data file, a data structure, and the like independently or in combination. The program command recorded in the medium may be things specially designed and configured for the present invention, or things that are well known to and can be used by those skilled in the computer software related art.

Although the present invention has been described by the restricted embodiments and the drawings as described above, the present invention is not limited to the aforementioned embodiments, and various modifications and alterations can be made from the descriptions by those skilled in the art to which the present invention pertains.

Accordingly, the scope of the present invention should not be determined by the above-described embodiments, and should be determined by not only the following claims but also their equivalents.