KR101516089B1 - Controlling system for multilevel inverter and controlling method for the same - Google Patents

Abstract

The multilevel inverter controlling system of the present invention, which can control the DC voltage of multi-cell inverters, includes: a multilevel inverter connected to the multi-cell inverters in series; a compensation voltage size calculation part calculating cell compensation voltage size to compare the average value of DC voltage of the multi-cell inverters as well as the DC voltage of individual cell inverter and to compensate the difference; and a compensation part compensating the size of multi-cell compensation voltage by calculating the compensation ratio, based on the threshold value and the exceeding cell compensation size when at least one of the cell compensation voltage size corresponding to the above cell inverter exceeds the threshold value.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a multi-level inverter control system,

The present invention relates to a multilevel inverter control system, and more particularly, to a multilevel inverter control system and a control method thereof that can compensate for voltage imbalance between cell inverters.

A multi-level inverter is a high-voltage, large-capacity inverter that connects a plurality of single-phase inverters (hereinafter referred to as "cell inverters") for each phase in series and uses a low-voltage power semiconductor in each cell inverter to obtain a high voltage .

A load such as an electric furnace in which reactive power fluctuates abruptly causes a severe current imbalance in the power system. The electric furnace load, which is operated by the generation of an arc, has inherently irregularity and nonlinearity, and the power factor is significantly lower than a normal load.

In order to alleviate the problem of the power quality of the system by the electric furnace, it has recently been required to apply STATCOM (STATCOM) to compensate reactive power to realize system stabilization. The above-described multi-level inverter is applied to such a compensator.

1 is a diagram showing a conventional multi-level inverter control system.

Referring to FIG. 1, a conventional multi-level inverter control system 100 is connected to a system 150 to compensate for reactive power of the system 150, and includes a multi-level inverter 120, A transformer 130 connected to one end of the transformer 120, and a switching gear 140 connected to one end of the transformer 130.

The multi-level inverter 120 is connected in parallel to the system 150 to improve the power factor of the system 150 by compensating for the reactive power of the system 150.

The multi-level inverter 120 is composed of an A phase 120a, a B phase 120b, and a C phase 120c, as shown in Fig. The A phase 120a, the B phase 120b, and the C phase 120c each include a plurality of cell inverters 122 connected in series to each other. Each of the cell inverters 122 may be an H-Bridge type inverter, and the capacitors 125 are connected in parallel.

Since the capacitor 125 is independently connected to each of the plurality of cell inverters 122, the multi-level inverter 120 generates the DC voltage imbalance between the cell inverters 122 in the same phase as well as the voltage imbalance between the phases .

DC voltage imbalance between the cell inverters 122 is a major cause of the parameter error of the capacitor 125, the loss error of the gating device, the error of the internal impedance of the system itself, and the error due to the switching technique.

The conventional multilevel inverter control system 100 finally adds the cell reference voltage value to compensate for the DC voltage error of each cell inverter 122 to the voltage reference value to eliminate the DC voltage imbalance between the cell inverters 122 . At this time, the cell compensation voltage reference value is calculated by dividing the cell compensation power reference value by the current sensed by the current sensor.

When the cell inverter 122 is controlled to have a low current, the conventional multi-level inverter control system 100 has a problem that the cell compensation voltage reference value is calculated to be higher than the rated voltage, and thus the operation becomes unstable.

In order to solve the above problem, if the reference value of the cell compensation voltage is limited to an arbitrary value, the total sum of the cell compensation voltage reference value does not become zero. Accordingly, the conventional multi-level inverter control system 100 has another problem in that stable control is difficult because the phase compensation voltage reference value of the phase compensation controller for controlling the voltage unbalance between the phases is influenced by other compensation controllers, for example.

SUMMARY OF THE INVENTION It is a general object of the present invention to provide a multilevel inverter control system and method capable of stably controlling DC voltage imbalance between cell inverters even at low currents.

It is another object of the present invention to provide a multi-level inverter control system and method in which a cell compensation voltage reference value does not affect a phase compensation controller.

According to an aspect of the present invention, there is provided a multi-level inverter control system including: a multi-level inverter having a plurality of cell inverters connected in series; A compensation voltage magnitude calculation unit for comparing a DC voltage average value of the plurality of cell inverters and a DC voltage of the individual cell inverter and calculating a cell compensation voltage magnitude for compensating the difference; And if at least one of the cell compensation voltage magnitudes for each of the plurality of cell inverters exceeds a predetermined threshold value, calculating a correction ratio based on the threshold value and the cell compensation voltage magnitude exceeding the threshold, And a correction unit for correcting the compensation voltage magnitudes.

According to another aspect of the present invention, there is provided a method for controlling a multilevel inverter, the multilevel inverter control system including a plurality of inverters connected in series. The multi-level inverter control method includes: calculating a cell compensation voltage magnitude for each inverter based on a DC voltage average value of the plurality of inverters and a DC voltage of an individual inverter; Determining whether a cell compensation voltage magnitude for each of the plurality of inverters exceeds a predetermined threshold; Limiting an excess cell compensation voltage magnitude to the threshold and correcting the remaining cell compensation voltage magnitude if the cell compensation voltage magnitude for at least one of the plurality of inverters exceeds the threshold; And calculating a cell compensation voltage reference value based on the corrected cell compensation voltage magnitude and current phase information.

According to the present invention, there is an effect that it is possible to prevent the voltage higher than the rated voltage from being outputted by limiting the cell compensation voltage reference value to not exceed the threshold value.

Also, according to the present invention, when one cell compensation voltage reference value exceeds a threshold value and the value is limited, it is possible to maintain the total sum to be 0 by correcting the size with respect to another cell compensation voltage reference value, There is another effect that the cell compensation voltage reference value can be stably controlled without affecting the phase compensation controller.

1 is a diagram showing a conventional multi-level inverter control system.
2 is a schematic diagram illustrating a multi-level inverter control system according to an embodiment of the present invention.
3 is a block diagram for explaining the cell compensation controller of FIG.
4 is a block diagram for explaining an embodiment of the correction unit shown in FIG.
5 is a block diagram for explaining another embodiment of the correction unit shown in FIG.
FIG. 6 is a block diagram for explaining another embodiment of the correction unit shown in FIG. 3. FIG.
7 is a flowchart illustrating a method of controlling a multi-level inverter according to an embodiment of the present invention.
8 is a flowchart illustrating a method of calculating a cell compensation voltage reference value according to an embodiment of the present invention.
9 is a flowchart illustrating a method of calculating a cell compensation voltage reference value according to another embodiment of the present invention.

The meaning of the terms described herein should be understood as follows.

The word " first, "" second," and the like, used to distinguish one element from another, are to be understood to include plural representations unless the context clearly dictates otherwise. The scope of the right should not be limited by these terms.

It is also to be understood that the terms "comprises" or "having" do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof .

Prior to the description of the multilevel inverter control system 200, a description will be given of a multilevel inverter.

The multi-level inverter is connected in parallel to the system to compensate the reactive power of the system. These multilevel inverters are composed of phase A, phase B and phase C, and are connected to the system through a load.

On the other hand, each of the A-phase, B-phase, and C-phase includes a plurality of series-connected cell inverters. Each cell inverter is an independent single-phase inverter structure, and a multi-level inverter can obtain a high voltage by using a low-voltage cell inverter by connecting a plurality of cell inverters in series. And, the cell inverter includes a capacitor charged or discharged according to the phase of the output voltage.

In one embodiment, the cell inverter may correspond to a single-phase H-bridge inverter configured with an IGBT (Insulated Gate Bipolar Mode Transistor).

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

2 is a schematic diagram illustrating a multi-level inverter control system according to an embodiment of the present invention.

2, a multi-level inverter control system 200 according to an exemplary embodiment of the present invention controls an amount of reactive power generated by controlling an output voltage of a multilevel inverter to be output to a system, A cell compensation control unit 220, and a voltage output unit 230. [

The voltage reference value calculation section 210 calculates a reference value (V ^* _C ) for the output voltage of the multi-level inverter.

Although not shown in FIG. 2, in one embodiment, the voltage reference value calculation unit 210 includes a DC voltage controller for constantly controlling the three-phase DC voltage average value, a phase compensation controller for controlling the voltage of each phase to have a DC voltage average value A load current detector for detecting a load current to generate a compensation reference value, and a current controller for controlling an output current.

The output values of the direct current voltage controller, the phase compensation controller, and the load current detector become the input values of the current controller, and the current controller can generate the output voltage reference value V ^* _C for outputting the desired current.

Next, the cell compensation control unit 220 controls the DC voltage (V _dc ) imbalance between the plurality of cell inverters included in the same phase. The DC voltage V _dc represents a voltage applied to a capacitor included in each cell inverter.

Hereinafter, for convenience of explanation, only the DC voltage of the cell inverter included in one cell is controlled by the cell compensation controller 220, but the present invention is not limited thereto. The cell compensation controller 220 A, B, and C, respectively.

As shown in FIG. 3, the plurality of cell inverters have a DC voltage (V _{dc (k)} ), which is obtained by a reason such as a parameter error, a loss error of a gating element, an error of internal impedance of the system itself, .

In order to uniformly control the different direct current voltage V _{dc (k)} , the cell compensation controller 220 calculates the cell compensation voltage reference value V ^* _{comp (k) for} each of the plurality of cell inverters connected in series And controls the output voltage of the cell inverter.

Hereinafter, the cell compensation control unit 220 will be described in more detail with reference to FIG.

3 is a block diagram for explaining the cell compensation controller of FIG.

3, the cell compensation control unit 220 includes a compensation power calculation unit 310, a compensation voltage magnitude calculation unit 320, a correction unit 330, and a compensation voltage reference value calculation unit 340.

First, the compensation power calculating unit 310 receives the DC voltage average value V _{dc (avg} ) of the plurality of cell inverters and the DC voltage V _{dc (k) of the} individual cell inverter, And calculates a power reference value.

The average value of the DC voltages of the plurality of cell inverters is expressed by Equation 1 below.

[Equation 1]

Wherein n represents the number of cell inverters serially connected in one phase, V _{dc (avg)} represents a DC voltage average value of n cell inverters, and V _{dc (k)} DC voltage.

The compensation power calculation unit 310 calculates the power corresponding to the difference between the DC voltage average value V _{dc (avg} ) of the plurality of cell inverters and the DC voltage V _{dc (k)} of the individual cell inverter as the compensation power reference value .

On the other hand, the compensation power calculating unit 310 is composed of a plurality of units, and calculates a compensation power reference value for each of the plurality of cell inverters. At this time, the sum of the compensation power reference values calculated by the compensation power calculating unit 310 should be zero.

Next, the compensation voltage magnitude calculation unit 320 calculates the cell compensation voltage magnitude (V _{comp (k)} ) for the individual cell inverters based on the compensation power reference value and the current effective value.

More specifically, the compensation voltage magnitude calculation unit 320 receives the compensation power reference value from the compensation power calculation unit 310. The compensation voltage magnitude calculation unit 320 receives the effective value of the current sensed by the current sensor.

Then, the compensation voltage magnitude calculating unit 320 calculates the cell compensation voltage magnitude (V _{comp (k)} ) for the individual cell inverter by dividing the compensation power reference value by the rms value of the current.

Next, the correcting unit 330 checks whether the cell compensation voltage magnitude V _{comp (k)} calculated by the compensation voltage magnitude calculating unit 320 exceeds a preset threshold value. If the cell compensation voltage magnitude V _{comp (k)} (V _{comp (k)} ).

More specifically, the corrector 330 checks whether the N cell compensation voltage magnitudes V _{comp (k)} for each of the N cell inverters exceeds a preset threshold value. Correction unit 330 then corrects all cell compensation voltage magnitude (V _{comp (k)} ) if at least one of the N cell compensation voltage magnitudes V _{comp (k)} exceeds a threshold.

At this time, the corrector 330 corrects the cell compensation voltage magnitude (V _{comp (k)} ) for each of the plurality of cell inverters so as to satisfy the following equations (2) and (3).

&Quot; (2) "

&Quot; (3) "

Where n denotes the number of cell inverters connected in series in one phase and V ^' _{comp (k)} denotes the corrected cell compensation voltage magnitude for the kth cell inverter.

Hereinafter, embodiments of the corrector 330 will be described in more detail with reference to FIGS. 4 and 5. FIG.

First Embodiment

4 is a block diagram for explaining an embodiment of the correction unit shown in FIG.

Referring to FIG. 4, the correction unit 330 includes a size limiter 410, a ratio calculator 420, a correction ratio determiner 430, and a compensation voltage magnitude corrector 440.

First, the size limit portion 410 cells compensation voltage magnitude (V _{comp (for} when ensure that cells compensation voltage magnitude (V _{comp (k))} exceeds the threshold value, and exceeds, the cell inverter for individual cell drive _k) to the threshold value.

The size limiter 410 may be composed of a plurality of cells, and may limit the cell compensation voltage magnitude (V _{comp (k)} ) for each of the plurality of cell inverters to the threshold value.

For example, the size limiter 410 may include a first size limiter 410a and a second size limiter 410b. The first size limiter 410a may limit the first cell compensation voltage magnitude V _{comp (1)} to the first cell compensation voltage magnitude V _{comp (1)} if the first cell compensation voltage magnitude V _comp And may be limited to the threshold value.

If the second cell compensation voltage magnitude (V _{comp (2)} ) for the second cell inverter connected in series with the first cell inverter exceeds the threshold value, the second size limiter 410b may limit the second cell size The compensation voltage magnitude (V _{comp (2)} ) may be limited to the threshold value.

Next, the ratio calculating unit 420 calculates the ratio limited by the size limiting unit 410 when the size of the cell compensation voltage V _{comp (k} ) is limited by the size restricting unit 410. The ratio calculating unit 420 calculates the ratio using the following equation (4).

&Quot; (4) "

The ratio calculator 420 may include a plurality of ratio calculators 420, and each of the plurality of ratio calculators 420 may be operatively connected to each of the plurality of size limiters 410 one-to-one.

For example, the ratio calculator 420 may include a first ratio calculator 420a connected to the first size limiter 410a and a second ratio calculator 420b connected to the second size limiter 410a .

When it is determined that the first cell compensation voltage magnitude (V _{comp (1)} ) exceeds the threshold value by the first size limiter 410a, the first ratio calculator 420a calculates the first cell compensation voltage It is possible to calculate the first ratio for the size (V _{comp (1)} ).

If it is determined that the second cell compensation voltage magnitude (V _{comp (2)} ) exceeds the threshold value by the second size limiter 410b, the second rate calculator 420b may calculate the second cell size A second ratio to the compensation voltage magnitude (V _{comp (2)} ) can be calculated.

Next, the correction ratio determining unit 430 determines the smallest value among the ratios calculated by the plurality of ratio calculating units 420 as the correction ratio.

Next, the compensation voltage magnitude correcting unit 440 corrects the cell compensation voltage magnitude (V _{comp (k)} ) for each of the plurality of cell inverters based on the correction ratio determined by the correction ratio determining unit 430. [

More specifically, the compensation voltage magnitude correction unit 440 multiplies the cell compensation voltage magnitude V _{comp (k)} calculated by the compensation voltage magnitude calculation unit 320 by the correction ratio to calculate a final cell compensation voltage magnitude V ^' _{comp (k)} .

Second Embodiment

FIG. 5 is a block diagram for explaining another embodiment of the correction unit shown in FIG. 2. FIG.

5, the corrector 330 includes a size limiter 510, a maximum compensation voltage determiner 520, a correction ratio calculator 530, and a compensation voltage magnitude corrector 540.

First, the size limit unit 510 cells compensation voltage magnitude (V _{comp (for} when ensure that cells compensation voltage magnitude (V _{comp (k))} exceeds the threshold value, and exceeds, the cell inverter for individual cell drive _k) to the threshold value.

The size limiter 510 may be formed of a plurality of cells to limit the cell compensation voltage magnitude V _{comp (k)} for each of the plurality of cell inverters to the threshold value.

Next, the maximum compensation voltage determination unit 520 determines the maximum cell compensation voltage magnitude having the largest value among the cell compensation voltage magnitudes that are determined to exceed the threshold value by the size limiter 510. [

Next, the correction ratio calculating unit 530 calculates the correction ratio based on the maximum cell compensation voltage magnitude and the threshold value. More specifically, the correction ratio calculating section 530 calculates the ratio of the threshold value to the maximum cell compensation voltage magnitude, and determines the calculated value as the correction ratio.

Next, the compensation voltage magnitude correction unit 540 corrects the cell compensation voltage magnitude (V _{comp (k)} ) for each of the plurality of cell inverters based on the correction ratio determined by the correction ratio calculation unit 530. [

More specifically, the compensation voltage magnitude correcting unit 540 multiplies the cell compensation voltage magnitude V _{comp (k)} calculated by the compensation voltage magnitude calculating unit 320 by the correction ratio to calculate a final cell compensation voltage magnitude V ^' _{comp (k)} .

Third Embodiment

FIG. 6 is a block diagram for explaining another embodiment of the correction unit shown in FIG. 2. FIG.

6, the correction unit 330 includes a maximum compensation voltage determination unit 610, a size restriction unit 620, a correction ratio calculation unit 630, and a compensation voltage magnitude correction unit 640.

First, the maximum compensation voltage determination unit 610 determines the maximum cell compensation voltage magnitude having the largest value among the cell compensation voltage magnitudes V _{comp (k)} for the plurality of cell inverters.

Next, the size limiter 620 checks whether the maximum cell compensation voltage magnitude exceeds the threshold value, and if it exceeds, limits the maximum cell compensation voltage magnitude to the threshold value.

Next, when it is confirmed that the maximum cell compensation voltage magnitude exceeds the threshold value by the size limiter 510, the correction ratio calculating unit 630 calculates the correction ratio based on the maximum cell compensation voltage magnitude and the threshold value.

More specifically, the correction ratio calculating unit 630 calculates the ratio of the threshold value to the maximum cell compensation voltage magnitude, and determines the calculated value as the correction ratio.

Next, the compensation voltage magnitude correcting unit 640 corrects the cell compensation voltage magnitude (V _{comp (k)} ) for each of the plurality of cell inverters based on the correction ratio determined by the correction ratio calculating unit 630. [

More specifically, the compensation voltage magnitude correction unit 640 multiplies the cell compensation voltage magnitude V _{comp (k)} calculated by the compensation voltage magnitude calculation unit 320 by the correction ratio to calculate a final cell compensation voltage magnitude V ^' _{comp (k)} .

3, the compensation voltage reference value calculation unit 340 calculates the cell compensation voltage reference value V ^* _{comp (k)} based on the final cell compensation voltage magnitude V ^' _{comp (k} ) and the current phase information do.

More specifically, the compensation voltage reference value calculation unit 340 is configured of a plurality of compensation voltage reference values, and calculates a cell compensation voltage reference value for each of the plurality of cell inverters.

The compensation voltage reference value calculation unit 340 receives the final cell compensation voltage magnitude V ^' _{comp (k)} for the corresponding cell inverter from the correction unit 330. The compensation voltage reference value calculation unit 340 receives the phase information of the current sensed by the current sensor.

The compensation voltage reference value calculation unit 340 compares the DC voltage V _{dc (k)} of the corresponding cell inverter with the DC voltage average value V _{dc (avg)} of the plurality of cell inverters. If the DC voltage V _{dc (k)} of the corresponding cell inverter is smaller than the average value V _{dc (avg)} , the compensation voltage reference value calculation unit 340 calculates the compensation voltage reference value V _{c (k)} And outputs a cell compensation voltage reference value V ^* _{comp (k) that} is in phase with the phase.

On the other hand, the DC voltage of the corresponding cell, the inverter (V _{dc (k))} a mean value (V _{dc (avg))} is greater than the compensation voltage reference value calculating unit 340 is the final cell compensation voltage magnitude (V _{'comp (k))} And outputs a cell compensation voltage reference value (V ^* _{comp (k)} ) that is opposite in phase to the current phase.

Referring again to FIG. 2, the voltage output unit 230 adds the cell compensation voltage reference value V ^* _{comp (k)} to the voltage reference value V ^* _{C (k) for} each of the plurality of cell inverters, (V ' ^* _{C (k)} ). The voltage output unit 230 outputs a voltage V _{C (k)} corresponding to the calculated final voltage reference value V ' ^* _{C (k)} .

The relationship between the voltage reference value V ^* _{C (k)} , the final voltage reference value V ' ^* _{C (k} ) and the voltage V _{C (k)} output by the voltage output unit 230 is expressed by the following equation 5.

&Quot; (5) "

7 is a flowchart illustrating a method of controlling a multi-level inverter according to an embodiment of the present invention.

Hereinafter, for the sake of convenience, the multi-level inverter control system 200 according to the embodiment of the present invention controls only a plurality of cell inverters connected in series on one phase. However, But also the cell inverter included in each of the A-phase, B-phase and C-phase can be controlled.

Referring to FIG. 7, first, the multi-level inverter control system 200 calculates a voltage reference value V ^* _C (S701).

Next, the multi-level inverter control system 200 calculates a cell compensation voltage reference value V ^* _{comp (k) for} each of a plurality of cell inverters connected in series (S702).

Hereinafter, a method of calculating the cell compensation voltage reference value V ^* _{comp (k)} will be described in more detail with reference to FIGS. 8 and 9. FIG.

8 is a flowchart illustrating a method of calculating a cell compensation voltage reference value according to an embodiment of the present invention.

8, the multi-level inverter control system 200 senses the DC voltage V _{dc (k)} of each of the plurality of cell inverters and detects the average value (V _{dc (k)} ) of the sensed DC voltages V _dc V _{dc (avg)} ) (S801).

Next, the multilevel inverter control system 200 calculates a compensation power reference value for the individual-cell inverter based on the average value Vdc _(avg) and the DC voltage Vdc _(k) of the individual-cell inverter (S802) .

The multilevel inverter control system 200 calculates the power corresponding to the difference between the DC voltage average value V _{dc (avg} ) of the plurality of cell inverters and the DC voltage V _{dc (k)} of the individual cell inverter as the compensation power reference value can do.

Next, the multi-level inverter control system 200 calculates the cell compensation voltage magnitude (V _{comp (k)} ) for the individual cell inverter based on the compensation power reference value and the current effective value (S803). At this time, the current rms value corresponds to the rms value of the current sensed by the current sensor installed to detect the current of each phase.

The multi-level inverter control system 200 calculates the cell compensation voltage magnitude (V _{comp (k)} ) for the individual cell inverter by dividing the compensation power reference value by the rms value of the current.

Next, the multi-level inverter control system 200 determines whether the cell compensation voltage magnitude (V _{comp (k)} ) for the cell inverter exceeds a predetermined threshold value, and if it exceeds, the corresponding cell compensation voltage magnitude (S805 and S806).

The multi-level inverter control system 200 repeatedly performs S805 and S806 for all of the plurality of cell inverters.

The multilevel inverter control system 200 determines whether or not the cell compensation voltage magnitude (V _{comp (k)} ) exceeds a threshold value for all the cell inverters, and determines the correction ratio based on the calculated ratio when the ratio calculation is completed (S808 and S809).

More specifically, the multi-level inverter control system 200 selects the smallest one of the at least one ratio and determines it as a correction ratio if at least one of the cell compensation voltage magnitudes V _{comp (k)} exceeds the threshold value do.

On the other hand, the multi-level inverter control system 200 determines the correction ratio to be 1 if there is no value exceeding the threshold value among the cell compensation voltage magnitudes V _{comp (k)} .

Next, the multi-level inverter control system 200 calculates the final cell compensation voltage magnitude V ^' _{comp (k)} by correcting the cell compensation voltage magnitude V _{comp (k)} based on the correction ratio (S810).

More specifically, the multi-level inverter control system 200 calculates the final cell compensation voltage magnitude V ^' _{comp (k)} by multiplying the cell compensation voltage magnitude (V _{comp (k)} ) for each of the plurality of cell inverters, .

Next, the multilevel inverter control system 200 calculates and outputs the cell compensation voltage reference value V ^* _{comp (k)} based on the final cell compensation voltage magnitude (V ^' _{comp (k)} ) and current phase information (S811 ). At this time, the current phase information corresponds to the phase of the current sensed by the current sensor installed to detect the current of each phase.

The multi-level inverter control system 200 compares the DC voltage V _{dc (k)} of the corresponding cell inverter with the DC voltage average value V _{dc (avg)} of the plurality of cell inverters. If the DC voltage of the corresponding cell, the inverter (V _{dc (k))} is less than the average value (V _{dc (avg)),} multi-level inverter control system 200 includes a current to the final cell, the compensation voltage magnitude (V _{^'comp (k))} And outputs a cell compensation voltage reference value V ^* _{comp (k) that} is in phase with the phase.

On the other hand, the DC voltage of the corresponding cell, the inverter (V _{dc (k))} a mean value (V _{dc (avg))} is greater than, the multilevel inverter control system 200 is the final cell compensation voltage magnitude (V _{^'comp (k))} And outputs a cell compensation voltage reference value (V ^* _{comp (k)} ) that is opposite in phase to the current phase.

9 is a flowchart illustrating a method of calculating a cell compensation voltage reference value according to another embodiment of the present invention.

9, the multi-level inverter control system 200 senses the DC voltage V _{dc (k)} of each of the plurality of cell inverters and detects the average value (V _{dc (k)} ) of the sensed DC voltages V _dc V _{dc (avg)} ) is calculated (S901).

Next, the multilevel inverter control system 200 calculates a compensation power reference value for the individual-cell inverter based on the average value Vdc _(avg) and the DC voltage Vdc _(k) of the individual-cell inverter (S902) .

Next, the multi-level inverter control system 200 calculates the cell compensation voltage magnitude V _{comp (k)} for the individual cell inverter based on the compensation power reference value and the current effective value (S903).

Next, the multi-level inverter control system 200 determines the maximum cell compensation voltage having the largest cell compensation voltage magnitude (V _{comp (k)} ) for each of the plurality of cell inverters (S904).

Next, the multi-level inverter control system 200 determines whether the maximum cell compensation voltage magnitude exceeds the threshold value, and if so, calculates a correction ratio based on the threshold value and the maximum cell compensation voltage magnitude (S905 and S906) .

Next, the multi-level inverter control system 200 calculates the final cell compensation voltage magnitude V ^' _{comp (k)} by correcting the cell compensation voltage magnitude V _{comp (k)} based on the correction ratio (S907).

More specifically, the multi-level inverter control system 200 calculates the final cell compensation voltage magnitude V ^' _{comp (k)} by multiplying the cell compensation voltage magnitude (V _{comp (k)} ) for each of the plurality of cell inverters, .

Meanwhile, the multi-level inverter control system 200 sets the cell compensation voltage magnitude V _{comp (k} ) to the final cell compensation voltage magnitude (V ^' _{comp (k)} ) if the maximum cell compensation voltage magnitude does not exceed the threshold value .

Next, the multi-level inverter control system 200 calculates and outputs the cell compensation voltage reference value V ^* _{comp (k)} based on the final cell compensation voltage magnitude V ^' _{comp (k} ) and current phase information (S908 ).

Referring again to FIG. 7, the multi-level inverter control system 200 calculates the final voltage reference value V ' ^* _{C (k)} for each of the plurality of cell inverters (S703).

More specifically, the multilevel inverter control system 200 adds the cell compensation voltage reference value V ^* _{comp (k} ) to the voltage reference value V ^* _{C (k} ) of each cell inverter to obtain the final voltage reference value V ' ^* _{C (k)} ).

Next, the multilevel inverter control system 200 controls each cell inverter to output a voltage corresponding to the final voltage reference value V ' ^* _{C (k)} (S704).

It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the present invention as set forth in the following claims It can be understood that

Claims (10)

A multi-level inverter in which a plurality of cell inverters are connected in series;
A compensation voltage magnitude calculation unit for comparing a DC voltage average value of the plurality of cell inverters and a DC voltage of the individual cell inverter and calculating a cell compensation voltage magnitude for compensating the difference; And
Calculating a correction ratio based on the threshold value and the cell compensation voltage magnitude exceeding a predetermined threshold value when at least one of the cell compensation voltage magnitudes for each of the plurality of cell inverters exceeds a predetermined threshold value, And a correction unit for correcting the voltage magnitudes,
Wherein,
The cell compensation voltage magnitude for the plurality of cell inverters is

,

Is corrected to satisfy the condition

Is a corrected cell compensation voltage magnitude for a Kth cell inverter. delete The apparatus according to claim 1,

To calculate a ratio of the cell compensation voltage magnitude exceeding the threshold value to the cell compensation voltage magnitude,

A ratio calculating unit for calculating a cell compensation voltage magnitude for a Kth cell inverter; And
And a correction ratio determining unit for determining a smaller value among the calculated ratios as the correction ratio. The apparatus according to claim 1,
And correcting the plurality of cell compensation voltage magnitudes by multiplying each of the plurality of cell compensation voltage magnitudes by the correction ratio. The apparatus according to claim 1,
A maximum compensation voltage determination unit for determining a maximum cell compensation voltage magnitude among the plurality of cell compensation voltage magnitudes; And
And a correction ratio calculating unit for calculating a ratio of the threshold value to the maximum cell compensation voltage magnitude and determining the calculated ratio as a correction ratio. 2. The multi-level inverter control system according to claim 1,
Wherein when the DC voltage of the individual cell inverter is greater than the DC voltage average value, the cell compensation voltage reference value is in phase with the current phase in the corrected cell compensation voltage magnitude, if the DC voltage of the individual cell inverter is smaller than the DC voltage average value, Further comprising a compensating voltage reference value calculating unit for calculating a cell compensating voltage reference value that is opposite in phase to the current phase to the corrected cell compensation voltage magnitude. Calculating a cell compensation voltage magnitude for the individual cell inverter based on the DC voltage average value of the plurality of cell inverters connected in series and the DC voltage of the individual cell inverter;
Determining whether cell compensation voltage magnitudes for each of the plurality of cell inverters exceeds a predetermined threshold;
Limiting an excess cell compensation voltage magnitude to the threshold and correcting the remaining cell compensation voltage magnitude when the cell compensation voltage magnitude for at least one of the plurality of cell inverters exceeds the threshold; And
Calculating a cell compensation voltage reference value based on the corrected cell compensation voltage magnitude and the phase information of the current sensed by the current sensor,
Wherein the correcting comprises:
Wherein the cell compensation voltage magnitude for the plurality of inverters is

,

Is corrected to satisfy the condition

Is a corrected cell compensation voltage magnitude for a Kth cell inverter. delete 8. The method of claim 7,
The ratio of each of the cell compensation voltage magnitudes exceeding the threshold value to

; And
Detecting a smallest value among the ratios to determine a correction ratio, and multiplying the determined correction ratio by a cell compensation voltage magnitude for each of the plurality of cell inverters. 8. The method of claim 7,
A maximum cell compensation voltage magnitude having a largest value among the cell compensation voltage magnitudes for each of the plurality of cell inverters is determined; and when the maximum cell compensation voltage magnitude exceeds the threshold value, Calculating the ratio of And
Determining the calculated ratio as a correction ratio, and multiplying the determined correction ratio by the cell compensation voltage magnitude for each of the plurality of inverters.

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