KR101696510B1 - Inverter controlling system for compensating distortion of output voltage - Google Patents

Abstract

An inverter control system according to an aspect of the present invention for preventing distortion of an output voltage and generation of a third harmonic current includes a plurality of cell inverters including a DC voltage source for each phase; A main controller for determining a reference voltage with respect to an output voltage of the cell inverter as a value compensated by a time series; And a cell controller for estimating a voltage of the DC voltage source based on the compensated reference voltage, generating a PWM signal according to the estimated DC voltage source voltage and the reference voltage, and outputting the PWM signal to the cell inverter.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an inverter control system for compensating an output voltage distortion,

The present invention relates to an inverter control system, and more particularly, to an inverter control system capable of compensating for output voltage distortion and a control method thereof.

Three-phase voltage source inverters are widely used in variable-speed drives of AC motors, uninterruptible power supplies and stationary reactive power compensation devices. Such a three-phase voltage source inverter may be configured as a three-phase half-bridge inverter sharing a voltage of a DC voltage source, and the voltage of each phase DC voltage source may be independently configured as a multi-stage multi-level inverter . As described above, in a configuration in which the voltage of the DC voltage source is not shared, the pulsation component corresponding to twice the power frequency appears.

1 shows an example in which a multi-stage multi-level inverter is applied to a stationary reactive power compensation device.

1, the conventional stationary reactive power compensating apparatus 100 is connected to the power system 150 to compensate for the reactive power of the power system 150. The stationary reactive power compensating apparatus 100 includes a multi-stage multi-level inverter 120, A reactor 160, a transformer 130, and a switching gear 140.

The multistage 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.

The plurality of cell inverters 122 constitute unit cells, and are connected in series with each other. The plurality of cell inverters 122 are connected to the transformer 130 through the reactor 160 provided for each phase and the transformer 130 is connected to the power system 150 through the switching gear 140. [ .

Each of the cell inverters 122 may be an H-bridge type inverter, and the capacitors 125 may be connected in parallel to the DC voltage source.

In this multi-level multi-level inverter 120, each cell inverter 122 generates a voltage and supplies a desired reactive power to the power system 150 according to the PWM signal.

The capacitor voltage of the cell inverter 122 includes a pulsating voltage component other than the DC voltage component. The PWM signal takes into consideration the magnitude of the reference voltage and the capacitor voltage for supplying the desired power to the power system 150, .

If the value of the compensated pulsation component for PWM signal generation is not correct or is delayed at the time of compensation, the output voltage of the cell inverter 122 is significantly distorted.

Due to such distortion of the output voltage, the conventional multi-level multi-level inverter control system 100 has a problem that system performance is degraded and an undesired third harmonic current is generated.

In addition, the conventional multistage multi-level inverter control system 100 has another problem that the third harmonic current flows into the cell inverter 122, thereby lowering the current utilization and efficiency of the system.

An object of the present invention is to provide an inverter control system and method capable of accurately estimating a voltage of a DC voltage source including a ripple voltage component.

According to an aspect of the present invention, there is provided an inverter control system including: a plurality of cell inverters including a DC voltage source for each phase; A main controller for determining a reference voltage with respect to an output voltage of the cell inverter as a value compensated by a time series; And a cell controller for estimating a voltage of the DC voltage source based on the compensated reference voltage, generating a PWM signal according to the estimated DC voltage source voltage and the reference voltage, and outputting the PWM signal to the cell inverter.

According to the present invention, it is possible to prevent an error between the reference voltage and the output voltage of the cell inverter from being generated by accurately estimating the voltage of the DC voltage source based on the reference voltage and the current information, .

Further, according to the present invention, generation of the third harmonic current can be prevented because distortion of the output voltage does not occur, and thus the current utilization efficiency and efficiency can be improved.

Further, according to the present invention, it is possible to more accurately estimate the voltage of the DC voltage source by estimating the rms value and the phase / ground information of the current using the normal current, the reverse phase current and the image minute current converted into the synchronous coordinate axes There is another effect.

1 is a diagram showing an example in which a multi-stage multi-level inverter is applied to a stationary reactive power compensation device.
2 is a view for explaining pulsation of a capacitor voltage.
3 is a diagram showing an error of an output voltage according to a delay time.
4 is a schematic view illustrating an inverter control system according to an embodiment of the present invention.
5 is a block diagram for explaining the current information estimating unit of FIG.
6 is a block diagram illustrating the cell controller of FIG.
7 is a graph showing a capacitor voltage sensed at the time of calculating the PWM signal when the conventional inverter control system is used and a capacitor voltage at the time when the actual PWM signal is outputted.
8 is a graph showing a capacitor voltage estimated at the time of calculating the PWM signal and a capacitor voltage at the time of outputting the actual PWM signal according to the inverter control system according to an embodiment of the present invention.

Before describing the inverter control system 400, the distortion of the output voltage due to pulsation and pulsation of the DC voltage will be described in more detail below.

2 is a view for explaining pulsation of a capacitor voltage.

As shown in FIG. 2, since the cell inverters of each phase use an independent DC power source, the capacitor voltage of the cell inverter has a direct current component and a pulsating component corresponding to twice the angular frequency due to the instantaneous power input and output.

These relations are expressed by the following equations.

)에 의하여 커패시터의 직류 전압에도 맥동이 나타나게 된다. The pulsating power (

The pulse voltage is also induced in the DC voltage of the capacitor.

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A multistage multilevel inverter configured by connecting a plurality of cell inverters in series is designed to transmit and receive data between the main controller and the cell controllers in order to secure sufficient insulation between the individual controllers. Due to such a configuration, the control system that controls the multi-level multi-level inverter generates a signal due to the conditions such as the communication speed and the number of communication data. Therefore, An error occurs in the pulsation component.

)는 지연시간(Td)이 0이 되지 아니하는 한 0보다 큰 값을 가지게 된다. 이러한 출력전압의 오차(

)를 지연시간에 따라 나타내면 도 3과 같다.When there is a delay time between the time at which the PWM signal is calculated and the time at which the PWM signal is output, the error of the output voltage from the actual cell inverter

Has a value larger than 0 as long as the delay time Td does not become zero. The error of this output voltage

) Is shown in FIG. 3 according to the delay time.

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)를 나타내고, 도3b는 지연시간(Td)이 2msec일 때 출력전압의 오차(

)를 나타내며, 도3c는 지연시간(Td)이 3msec일 때 출력전압의 오차(

)를 나타낸다. 이때, 커패시터 전압의 맥동성분의 크기는 정격전류에서 커패시터 전압 평균값의 약 5% 이내가 되도록 셀 인버터의 직류측 커패시턴스 값을 선정하는 것으로 가정한다.FIG. 3A shows an error of the output voltage when the delay time Td is 1 msec

FIG. 3B shows the error of the output voltage when the delay time Td is 2 msec

3C shows the error of the output voltage when the delay time Td is 3 msec.

). At this time, it is assumed that the magnitude of the ripple component of the capacitor voltage is selected so that the DC side capacitance value of the cell inverter is within 5% of the average value of the capacitor voltage at the rated current.

)는 지연시간(Td)이 커질수록 그 값이 커지는 것을 알 수 있다.Referring to FIGS. 3A to 3C, the error of the output voltage

) Becomes larger as the delay time Td becomes larger.

)로부터 발생하는 전류의 오차(

)는 기본주파수 전류성분과 3차 고조파 전류성분이 포함된다. 출력전압과 계통전압 사이의 리액터를 0.1pu로 설계하고 지연시간(Td)이 2msec일 때, 출력전압의 오차(

)는 0,034pu이며, 이로부터 발생하는 전류의 오차(

)는 기본주파수 전류성분이 0.34pu이다. 그리고, 전류의 오차(

)는 3차 고조파 전류성분이 0.11pu으로 무시할 없는 크기를 가진다.Output voltage error (

The error of the current generated from the

) Includes the fundamental frequency current component and the third harmonic current component. When the reactor between the output voltage and the grid voltage is designed as 0.1pu and the delay time (Td) is 2msec, the error of the output voltage

) Is 0.034pu, and the error of the current resulting therefrom

) Has a basic frequency current component of 0.34 pu. Then, the error of the current

) Has a harmonic current component of 0.11 pu which is negligible.

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As a result, when a delay time occurs between the time at which the PWM signal is calculated and the time at which the PWM signal is output, an error occurs not only between the reference voltage and the output voltage of the cell inverter but also an undesired third harmonic current .

Therefore, the inverter control system not only degrades the performance of various controllers designed based on the assumption that the actual output voltage follows the reference voltage of the main controller, but also unnecessary third harmonic current flows into the cell inverter, It lowers current utilization and efficiency.

The inverter control system according to an embodiment of the present invention can eliminate the error between the reference voltage and the output voltage and the generation of the third harmonic current by accurately estimating the voltage of the DC voltage source including the pulsating component.

4 is a schematic view illustrating an inverter control system according to an embodiment of the present invention.

Referring to FIG. 4, an inverter control system 400 according to an embodiment of the present invention includes a main controller 410, a cell controller 430, and a plurality of cell inverters 440. In FIG. 4, a plurality of cell inverters 440 are shown, but in another embodiment, the cell inverters 440 may be formed as one unit. In other words, although FIG. 4 illustrates control of a plurality of cell inverters as one embodiment for convenience of explanation, control of one cell inverter is not excluded.

First, each of the plurality of cell inverters 440 is composed of a power conversion unit (not shown) and a DC voltage source (not shown). The power conversion section includes a plurality of switching elements, and converts the direct current power into the alternating current power by the switching operation of the plurality of switching elements.

In one embodiment, the switching device may be an IGBT (Insulated Gate Bipolar mode Transistor), but the present invention is not limited thereto. Also, in one embodiment, the plurality of switching elements may be arranged in the form of an H-bridge or a full-bridge inverter.

The DC voltage source is connected to the power conversion unit in parallel, and in one embodiment, the DC voltage source may include a capacitor connected in parallel. The capacitor can be charged with power proportional to the capacitance. At this time, the voltage measured across the capacitor is referred to as a capacitor voltage.

Hereinafter, the voltage of the DC voltage source and the capacitor voltage are used in combination, but the capacitor voltage is a voltage measured at both ends of the capacitor when a capacitor is used as an example of the DC voltage source, meaning that the voltage is included in the voltage of the DC voltage source.

Next, the main controller 410 calculates the reference voltage V ^* of each phase of the cell inverters 440. In one embodiment, the main controller 410 includes a DC voltage controller for constantly controlling the average value of the three-phase capacitor voltage, a phase compensation controller for controlling the voltage of each phase to have a capacitor voltage average value, And a current controller for controlling the 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 reference voltage V ^* for outputting the desired current.

Meanwhile, the main controller 410 transmits the reference voltage V ^* to the cell controller 430, at which time a communication delay occurs between the main controller 410 and the cell controller 430. If the communication delay is not compensated for by the reference voltage V ^* , the cell controller 430 is less accurate in controlling the cell interferer 440. Thus, the main controller 410 calculates the compensated reference voltage V ^* to guarantee the accuracy of the control on the cell inverter 440.

The main controller 410 also transmits the current information of the cell inverters 440 required to estimate the capacitor voltage of the cell inverter 440 to the cell controller 430 in the cell controller 430. The output current information includes the rms value and the phase information of the current.

In one embodiment, the main controller 410 senses the current of the cell inverters 440 and can obtain the rms value and phase information of the current using the sensed signal. The main controller 410 can obtain the rms value and phase information of the current through the sensed signal and the virtual signal obtained by phase delaying the sensed signal.

,

), 역동기좌표축으로 변환된 역상분 전류(

,

), 및 동기좌표축으로 변환된 영상분 전류(

,

)를 기초로 셀 인버터(440)의 전류의 실효값 및 위상 정보를 추정할 수 있다. 이때, 주 제어기(410)는 전류의 위상 정보로서, 전류의 진상/지상 정보를 추정할 수 있다.In another embodiment, the main controller 410 receives the normalized minute current (< RTI ID = 0.0 >

,

), A reverse phase current transformed to an inverse synchronous coordinate axis (

,

), And the image minute current (

,

) Of the cell inverter (440) based on the output of the inverter (440). At this time, the main controller 410 can estimate the current / ground information as the phase information of the current.

,

), 역동기좌표축으로 변환된 역상분 전류(

,

), 및 동기좌표축으로 변환된 영상분 전류(

,

)를 기초로 각 상에 대한 전류 실효값을 추정할 수 있다.More specifically, the main controller 410 receives the normalized minute current (

,

), A reverse phase current transformed to an inverse synchronous coordinate axis (

,

), And the image minute current (

,

The current rms value for each phase can be estimated.

)는 동기좌표축으로 변환한 정상분 전류(

,

)와 아래 수학식 9와 같은 관계를 가진다.Peak current (current)

) Is the normalized minute current (

,

) And the following equation (9).

)는 역동기좌표축으로 변환한 역상분 전류(

,

)와 아래 수학식 10과 같은 관계를 가진다.In addition, the reversed phase currents (

) Is the inverse phase current converted into the inverse synchronous coordinate axis

,

) And the following equation (10).

)는 동기좌표축으로 변환한 영상분 전류(

,

)와 아래 수학식 11과 같은 관계를 가진다.Also, the image minute current (

) Is the image minute current (

,

) And the following Equation (11).

,

,

)은 페이서로 나타낸 정상분 전류(

), 역상분 전류(

), 영상분 전류(

)와 수학식 12와 같은 관계를 가진다.On the other hand,

,

,

) Represents the normal current (

), Reverse phase current (

), Image minute current (

) And Equation (12).

,

,

)은 동기좌표축으로 변환한 정상분 전류(

,

), 역동기좌표축으로 변환한 역상분 전류(

,

), 동기좌표축으로 변환한 영상분 전류(

,

)와 수학식 13와 같은 관계를 가짐을 알 수 있다.When Equations (9) to (11) are applied to Equation (12), the phase currents

,

,

) Is the normalized minute current converted to the synchronous coordinate axis

,

), The reverse-phase current converted into the reverse synchronous coordinate axis (

,

), Image minute current converted to synchronous coordinate axis (

,

) And Equation (13).

)를 복소수로 표현하면, 실수값과 허수값은 수학식 14 및 수학식 15과 같다.According to Equation (13), the current of the phase A

) Is represented by a complex number, the real number value and the imaginary number value are expressed by the following equations (14) and (15).

)를 복소수로 표현하면, 실수값과 허수값은 수학식 16 및 수학식 17와 같다.Current on B phase (

) Is represented by a complex number, the real number value and the imaginary number value are expressed by Equations (16) and (17).

)를 복소수로 표현하면, 실수값과 허수값은 수학식 18 및 수학식 19과 같다.Current on C phase (

) Is represented by a complex number, the real and imaginary values are expressed by Equations (18) and (19).

)에 대한 실효값(

)을 추정할 수 있다.The main controller 410 calculates the A-phase current (< RTI ID = 0.0 >

) ≪ / RTI >

) Can be estimated.

)에 대한 실효값(

)을 추정할 수 있다.Further, the main controller 410 calculates the B-phase current (

) ≪ / RTI >

) Can be estimated.

)에 대한 실효값(

)을 추정한다.Also, the main controller 410 calculates the C-phase current (

) ≪ / RTI >

).

,

), 역동기좌표축으로 변환된 역상분 전류(

,

), 및 동기좌표축으로 변환된 영상분 전류(

,

)를 기초로 각 상에 대한 전류의 진상/지상 정보를 추정할 수 있다.Then, the main controller 410 outputs the normal minute current (

,

), A reverse phase current transformed to an inverse synchronous coordinate axis (

,

), And the image minute current (

,

/ RTI > can be used to estimate the current / ground information of the current for each phase.

이므로,

=0을 기준으로 진상/지상 정보를 추정할 수 있다. 이에 따라, 주 제어기(410)는

가 양의 값인 경우 A상의 전류를 진상으로 추정하고, 반면,

가 음의 값인 경우 A상의 전류를 지상으로 추정할 수 있다.The main controller 410 determines whether the phase of the A-

Because of,

= 0 can be estimated. Accordingly, the main controller 410

Is a positive value, the current of the phase A is estimated as a phase,

The current of the phase A can be estimated as the ground.

이므로,

=

을 기준으로 진상/지상 정보를 추정할 수 있다. 이에 따라, 주 제어기(410)는

가

보다 작은 경우 B상의 전류를 진상으로 추정하고, 반면,

가

보다 큰 경우 B상의 전류를 지상으로 추정할 수 있다.The main controller 410 determines whether the phase of the B-

Because of,

=

Can estimate the ground / ground information on the basis of. Accordingly, the main controller 410

end

The current of the phase B is estimated as a true phase,

end

The current of the phase B can be estimated as the ground.

이므로,

=-

을 기준으로 진상/지상 정보를 추정할 수 있다. 이에 따라, 주 제어기(410)는

가 -

보다 작은 경우 C상의 전류를 진상으로 추정하고, 반면,

가 -

보다 큰 경우 C상의 전류를 지상으로 추정할 수 있다. The main controller 410 determines whether the phase of the C-

Because of,

= -

Can estimate the ground / ground information on the basis of. Accordingly, the main controller 410

In addition,

The phase current of C phase is estimated as a phase,

In addition,

The current in C phase can be estimated as the ground.

Meanwhile, the main controller 410 transmits the reference voltage V ^* and the current information to the cell controller 430 through a CAN (Controller Area Network) communication.

Next, the cell controller 430 is provided for each phase, and controls the cell inverter 440 so that the reference voltage V ^* received from the main controller 410 can be output.

The cell controller 430 generates a PWM (Pulse Width Modulation) control signal and controls the cell inverter 440 to output a voltage corresponding to the reference voltage V ^* . At this time, the PWM control signal is generated using the reference voltage V ^* and the capacitor voltage of the cell inverter 440. The capacitor voltage V _dc represents the voltage across the capacitors included in each cell inverter 440.

The cell controller 430 according to the present invention generates a PWM control signal by sensing the capacitor voltage of the cell inverter 440 and using the sensed value and the reference voltage V ^* Estimates the capacitor voltage of the cell inverter 440 using the reference voltage V ^* and the current information received from the inverter 440, and generates the PWM control signal using the estimated capacitor voltage value.

When the inverter control system 400 is applied to a stationary reactive power compensation device, the phase of the phase current always has a phase relationship of 90 degrees with the phase voltage. This is because the current flowing in each phase in a cell inverter has mostly reactive power components, except for some active power components that compensate for system losses.

,

,

)과 맥동성분(

,

,

)을 포함한다.In the inverter control system 400, the capacitor voltage of each phase is a DC component (

,

,

) And pulsating component (

,

,

).

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,

,

)을 추정하기 위하여 기준전압(V^*) 및 전류정보를 이용한다. 이에 대한 구체적인 설명은 도 5를 참조하여 후술하도록 한다.The cell controller 430 receives the ripple component of the capacitor voltage

,

,

(V ^* ) and current information in order to estimate the voltage (V ^* ). A detailed description thereof will be given later with reference to Fig.

Hereinafter, the cell controller 430 estimates the capacitor voltages of the plurality of cell inverters included in the A-cells. However, the present invention is not limited thereto, Phase, B-phase, and C-phase, respectively, to estimate the capacitor voltage for the connected phase.

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

Referring to FIG. 5, the cell controller 430 includes a phase calculator 510, a DC voltage estimator 520, and a PWM signal generator 530.

)에 대한 위상을 산출한다.First, the phase calculator 510 calculates the phase component of the a-phase capacitor voltage based on the reference voltage V ^* received from the main controller 410

). ≪ / RTI >

The reference voltage on a is shown in Equation 26 below.

When the reference voltage of the a phase is passed through the global pass filter to delay the phase, the following equation (27) is obtained.

)에 대한 위상을 산출한다. a상 커패시터 전압의 맥동성분(

)에 대한 위상(

)은 아래 수학식 28과 같다.The phase calculator 510 calculates the phase component of the a-phase capacitor voltage (i.e.,

). ≪ / RTI > the ripple component of the a-phase capacitor voltage (

) For the phase

) ≪ / RTI >

As described above, the phase calculating unit 510 calculates the phase of the pulsating component based on the reference voltage. Since the reference voltage used for calculating the phase of the pulsating component is a value that has been compensated for by the communication delay between the main controller 410 and the cell controller 430, The compensated value is calculated.

)에 대한 위상(

), a상의 기준전압의 크기(

), 전류정보를 이용하여 a상 커패시터 전압(

)을 추정한다.Next, the DC voltage estimator 520 estimates the a-phase capacitor voltage. More specifically, the DC voltage estimating unit 520 estimates the DC component of the pulsating component < RTI ID = 0.0 >

) For the phase

), the magnitude of the reference voltage on a (

), The a-phase capacitor voltage (

).

)는 아래 수학식 29을 이용하여 산출된다.The magnitude of the reference voltage on a (

) Is calculated by using the following expression (29).

Applying equations (28) and (29) to the capacitor voltage of each phase in the inverter control system leads to Equation (30) below.

)을 추정한다. 직류전압 추정부(520)는 주제어기(410)로부터 수신한 a상의 전류정보, 즉, 전류 실효값(

)과 진상/지상 정보(

), 그리고, a상의 기준전압(

,

)을 수학식 19에 대입하여 a상 커패시터 전압(

)을 산출할 수 있다.The DC voltage estimation unit 520 calculates the a-phase capacitor voltage (

). The DC voltage estimator 520 estimates current information of a phase received from the main controller 410, that is, current effective value

) And phase / ground information (

), And a reference voltage of a (

,

) Into the equation (19) to obtain the a-phase capacitor voltage

) Can be calculated.

)은 센싱한 커패시터 전압의 평균값으로 산출될 수 있다.On the other hand, the DC voltage component (

) Can be calculated as an average value of the sensed capacitor voltage.

Next, the PWM signal generating unit 530 generates the PWM control signal using the capacitor voltage estimated by the DC voltage estimating unit 520 and the reference voltage. The technique for generating the PWM control signal will be apparent to those skilled in the art, so a detailed description thereof will be omitted.

6A shows a capacitor voltage 610 sensed at the time of calculating the PWM signal when the conventional inverter control system is used and an actual capacitor voltage 620 at the time when the actual PWM signal is output. FIG. 6B shows the capacitor voltages 610 and 620, respectively.

6A and 6B, in the conventional inverter control system, an error occurs between the capacitor voltage 610 sensed at the time when the PWM signal is calculated and the actual capacitor voltage 620 at the time when the PWM signal is output.

Accordingly, the conventional inverter control system has a problem that not only the distortion of the output voltage but also an undesired third harmonic current occur in addition to the fundamental frequency current.

7A shows the capacitor voltage 710 estimated at the time of calculating the PWM signal in accordance with the inverter control system according to the embodiment of the present invention and the actual capacitor voltage 720 at the time when the actual PWM signal is outputted, 7b represent the error between the capacitor voltages 710 and 720. [

7A and 7B, the inverter control system 400 according to an embodiment of the present invention includes a capacitor voltage 710 estimated at the time of calculating the PWM signal and a real capacitor at the time of outputting the PWM signal, An error between the voltages 20 hardly occurs.

Accordingly, the inverter control system 400 according to the embodiment of the present invention does not distort the output voltage and does not generate the third harmonic current.

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 (8)

A plurality of cell inverters including a DC voltage source for each phase;
A main controller for determining a reference voltage with respect to an output voltage of the cell inverter as a value compensated by a time series; And
And a cell controller for estimating a voltage of the DC voltage source based on the compensated reference voltage, generating a PWM signal according to the voltage of the estimated DC voltage source and the reference voltage, and outputting the PWM signal to the cell inverter system. The method according to claim 1,
Wherein the voltage of the DC voltage source includes a ripple voltage component,
The cell controller includes:
Wherein the pulse voltage component is estimated using the reference voltage and a virtual voltage obtained by phase-delaying the reference voltage. 3. The method of claim 2,
The phase of the ripple voltage component is

Is calculated using the equation

Represents the reference voltage,

Is a virtual voltage obtained by delaying the reference voltage by 90 degrees. The method according to claim 1,
Wherein the main controller is configured to convert the normalized minute current

,

), A reverse phase current transformed to an inverse synchronous coordinate axis (

,

), And the image minute current (

,

The current information is estimated based on the current information,
Wherein the cell controller estimates the voltage of the DC voltage source based on the estimated reference voltage and the estimated current information. 5. The apparatus of claim 4,

and

Phase current (< RTI ID = 0.0 >

), B-phase current (

), And C-phase current (

Of the inverter control system. 5. The method of claim 4,
Wherein the current information includes an effective value of the current,
The main controller includes:

The rms value of each phase current (

Of the inverter control system. 5. The method of claim 4,
Wherein the current information includes phase / ground information for the current,
The main controller includes:

Is a positive value, the current of the phase A is estimated as a phase,

The current of the phase A is estimated as the ground,

end

The current of the phase B is estimated as a true phase,

end

Lt; RTI ID = 0.0 > B-phase < / RTI >

In addition,

The current of the phase C is estimated as a phase,

In addition,

And estimates the current of the C phase to the ground. 5. The method of claim 4,
Wherein the voltage of the DC voltage source includes a ripple voltage component,
The cell controller includes:
When the phase of the phase current has a phase relationship of 90 degrees with the phase voltage, the ripple voltage component of each phase is

Is estimated using the equation

Represents the ripple voltage,

Represents the current / ground information of the current,

Represents an effective value of the current,

Represents the reference voltage,

Represents a virtual voltage obtained by phase-delaying the reference voltage,

Represents the fundamental frequency of the voltage of the DC voltage source,

Represents the capacitance of the DC voltage source,

And wherein the inverter control system comprises a DC voltage component included in the voltage of the DC voltage source.

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