KR20170079788A

KR20170079788A - Apparatus for compensating offset of grid-connected inverter, and grid-connected power conditioning system including the same

Info

Publication number: KR20170079788A
Application number: KR1020150190749A
Authority: KR
Inventors: 김태형; 이종학; 박기원
Original assignee: 주식회사 포스코아이씨티
Priority date: 2015-12-31
Filing date: 2015-12-31
Publication date: 2017-07-10
Also published as: KR101761033B1

Abstract

The grid-connected power management apparatus according to the present invention, which is capable of compensating for the offset of the grid-connected inverter, is connected to a battery unit including a battery rack composed of one or more batteries. The DC voltage supplied by discharging the battery unit is converted into an AC voltage And controls the power conversion unit to charge or discharge the battery unit in accordance with the charge / discharge command value and the power conversion unit that converts the system voltage of AC supplied from the system into a DC voltage to charge the battery unit Wherein the controller comprises: a signal converter for converting a system voltage supplied from the system or an output current outputted from the inverter to the system into a digital signal; an offset detector for detecting an offset of the digital signal; , And a controller Includes a compensation for compensating for the call, wherein the offset detection unit detects the offset by integrating the digital signal at a predetermined sampling number.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an offset compensating apparatus for a grid-connected inverter, and a grid-connected power management apparatus including the offset compensating apparatus.

And more particularly, to a technique for compensating an offset of a grid-connected inverter.

The battery energy storage system (BESS), which uses a secondary battery, is used not only for stabilizing the voltage and frequency of the system but also in connection with the renewable energy generation system, such as wind power or solar power, It stores energy, discharges energy stored in the battery when a peak load or a system fault occurs, supplies energy to the load, and attenuates the transient state during system recovery.

A typical battery energy storage system includes a power management device and a battery management device.

The power management system (PCS) supplies power to the system using a battery unit including a plurality of battery racks included in the battery management apparatus, and charges the battery unit using power supplied from the system.

To this end, the power management apparatus includes an inverter that converts DC power provided from the battery management device into AC power and supplies the AC power to the system, converts the AC power supplied from the system into DC power, and supplies the DC power to the battery management device.

Such a grid-connected inverter adjusts the output voltage of the inverter based on the result of sensing the grid voltage, and generates a desired output current through this operation. In order to control the inverter, the inverter controller receives the system voltage, the output current, and the DC voltage, and transmits the target voltage signal to be output to the inverter using these signals.

Conventionally, such a grid interconnected inverter and an inverter controller for controlling the same have the following problems.

1 is a graph showing a conversion result of an ADC for PWM control of an inverter.

2 is a graph showing a relationship between an analog signal and a digital signal that are ideally converted by the ADC.

The inverter controller senses the internal system voltage or output current, converts the voltage / current signal into a signal that can be input to the DSP (Digital Signal Processor) through the sensing board, and outputs this signal to the ADC (Analog to Digital Converter ).

As a result, the inverter controller obtains the result of converting the system voltage or the output current of the analog signal as shown in Fig. 1 (a) into a digital signal as shown in Fig. 1 (b).

In the ideal case, a digital signal corresponding to the analog signal of the system voltage or the output current should be outputted in the corresponding form shown in FIG. 2. However, in the conversion process, noise due to the peripheral circuit, distortion due to the input side impedance, quantization error, An offset error occurs in the converted digital signal.

In particular, in order to control the grid-connected inverter, the offset of the DC component generated in the process of sensing the grid voltage or the output current and converting it into the digital signal is superimposed on the sinusoidal wave having a predetermined period, ; RMS).

In addition, when the inverter is controlled using a synchronous coordinate system that converts an AC signal having a constant frequency to a DC signal, the offset appears as a component having a fundamental frequency on a synchronous coordinate system, which not only degrades the control performance but also causes undesired harmonic current And a direct current.

Therefore, when the target voltage signal for the inverter is generated based on the signal including the offset, the inverter output must be distorted. If the offset is not removed, the increase of the harmonic of the output current, There has been a problem that the temperature of the filter reactor, the grid-connected reactor, or the transformer due to the increase of the temperature is increased.

BACKGROUND ART [0002] Techniques that serve as a background of the present invention are disclosed in Korean Patent Laid-Open Publication No. 10-2014-0062325 entitled " Current Ripple Compensation Apparatus and Method of an Inverter, "

SUMMARY OF THE INVENTION It is an object of the present invention to improve an inverter control performance by eliminating an offset generated in sensing a system voltage and an output current for inverter control.

In order to achieve the above object, a grid-connected power management apparatus according to the present invention is connected to a battery unit constituting a battery rack composed of one or more batteries, converts a DC voltage supplied by discharging the battery unit into an AC voltage, A power converter for converting a system voltage of an AC provided from the system into a DC voltage to charge the battery; And a control unit for controlling the power conversion unit to charge or discharge the battery unit according to a charge / discharge command value, wherein the control unit converts a system voltage supplied from the system or an output current output from the inverter to the system into a digital signal A signal converter for converting the signal into a signal; An offset detector for detecting an offset of the digital signal; And a compensator for compensating the digital signal by reflecting the detected offset, wherein the offset detector detects the offset by integrating the digital signal with a predetermined sampling number.

An apparatus for compensating an offset of a grid-connected inverter according to the present invention includes: a sensing unit for sensing a system voltage of a system connected to an inverter or an output current of the inverter; A signal converter for converting a system voltage or an output current sensed through the sensing unit into a digital signal; An offset detector for detecting an offset of the digital signal; And a compensator for compensating the digital signal by reflecting the detected offset, wherein the offset detector detects the offset by integrating the digital signal with a predetermined sampling number.

The offset compensation method of the grid-connected inverter according to the present invention comprises the steps of sensing a system voltage of a system connected to an inverter or an output current of the inverter; Converting the sensed system voltage or output current into a digital signal; Detecting an offset of the digital signal by integrating the digital signal with a predetermined sampling number; And compensating the digital signal by reflecting the detected offset.

According to the present invention as described above, the following effects can be obtained.

According to the present invention, it is possible to reduce the loss occurring in the reactor associated with the inverter of the power management apparatus and to reduce the distortion of the output current by removing the DC component on the AC side generated by the offset.

In addition, according to the present invention, since the offset is removed from the input side of the sensed signal, it is possible to avoid the complexity of designing the controller so as to compensate at the output side and minimize the processing time for performing the algorithm.

In addition, according to the present invention, whether or not the offset is substantially changed and whether or not the compensation using the offset is determined, the compensation is performed only when the predetermined condition is satisfied, thereby preventing unnecessary offset compensation or offset compensation in an unstable state, The processing time can be reduced and the system can be stably maintained.

1 is a graph showing a conversion result of an ADC for PWM control of an inverter.
2 is a graph showing a relationship between an analog signal and a digital signal that are ideally converted by the ADC.
3 is a diagram illustrating an offset compensation apparatus for a grid-connected inverter according to the present invention.
4 is a diagram illustrating a grid-connected power management apparatus including an offset compensation apparatus for a grid-connected inverter according to the present invention.
5 is a diagram illustrating a specific procedure of the offset compensation method of the grid-connected inverter according to the present invention.
6 is a diagram illustrating a concrete procedure for determining whether or not an offset is changed and whether an offset can be applied in the implementation of the offset compensation method of the grid-connected inverter according to the present invention.
FIG. 7 is a graph showing the output current of the inverter when an offset of 1% occurs in the value obtained by sensing the system voltage.
8 is a graph showing the output current of the inverter when an offset of 1% is generated in the value obtained by sensing the output current.
9 is a graph showing a result of compensating an offset of a grid link inverter according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims.

The first, second, etc. are used to describe various components, but these components are not limited by these terms. These terms are used only to distinguish one component from another. Therefore, the first component mentioned below may be the second component within the technical spirit of the present invention.

It is to be understood that each of the features of the various embodiments of the present invention may be combined or combined with each other, partially or wholly, technically various interlocking and driving, and that the embodiments may be practiced independently of each other, It is possible.

3 is a diagram illustrating an offset compensation apparatus for a grid-connected inverter according to the present invention.

3, the offset compensating apparatus 100a of the grid-connected inverter includes a sensing unit 110, a signal converting unit 120, an offset detecting unit 130, an offset buffer 140, (150).

The sensing unit 110 senses the system voltage of the system connected to the inverter or the output current of the inverter, and transmits the sensed system voltage or output current to the signal converter 120.

The signal converting unit 120 converts the system voltage or output current of the analog signal sensed through the sensing unit 110 into a digital signal. The signal converting unit 120 may be constituted by an element such as an ADC (Analog to Digital Converter).

3, a sensing board (not shown) may further be included between the sensing unit 110 and the signal conversion unit 120, and the sensing board may sense the analog signal sensed through the sensing unit 110 as a signal It is possible to convert the signal into a signal of a range that can be input to the conversion unit 120 and transmit the signal to the signal conversion unit 120. At this time, the range of the signals transmitted by the sensing board is different depending on the characteristics and performance of the signal converter 120.

The offset detector 130 detects an offset of the digital signal converted by the signal converter 120. In particular, in the embodiment of the present invention, the offset detector 130 detects an offset by integrating a digital signal with a predetermined sampling number.

Specifically, the system voltage or the output current is outputted as a sinusoidal wave having a drain component of a fundamental wave frequency (60 Hz) and a drain component of a switching frequency, and an offset is superimposed on a system voltage or an output current as a direct current component. The offset detector 130 detects only the offset of the DC component by integrating the digital signal and removing the system voltage or the output current component formed by the sinusoidal wave.

At this time, the fundamental wave frequency means the commercial frequency of the power component output from the system, and the switching frequency is switched between the target power for output to the system and the on / off timing of the inverter so as to follow the target power output from the system . Therefore, the switching frequency can be set to reflect the performance of the inverter, the control accuracy, and the like.

As described above, in the present invention, a predetermined sampling number is determined and integrated so that a system voltage or an output current component formed by a sinusoidal wave by integration can be removed.

Specifically, the offset detector 130 determines the sampling number Nsamp according to the following equation (1).

(Where a is a positive integer such that Nsamp is a positive integer, Te is one period of the fundamental wave period according to the fundamental wave frequency, and Tsamp means a sampling period)

The sampling period is a value indicating how often the digital signal is sampled in converting the analog signal to the digital signal.

Considering that the frequency and the cycle are inversely proportional to each other, in the embodiment of the present invention, a cycle in which a specific frequency component is repeated once is referred to as a cycle in accordance with the frequency. That is, the fundamental wave period according to the fundamental wave frequency means a period in which the fundamental wave frequency component is repeated once.

If Nsamp digital signals are integrated when a multiple Nsamp of the sampling period Tsamp coincides with one period Te of the fundamental wave period according to the fundamental wave frequency as described in Equation 1 The fundamental wave frequency included in the system voltage or the output current and the frequency components having integer multiples of the fundamental wave frequency can all be eliminated.

If a multiple of the sampling period Tsamp does not coincide with one period Te of the fundamental wave period corresponding to the fundamental wave frequency, then a multiple Nsamp of the sampling period Tsamp is multiplied by the basic Nsamp is determined in the same manner as a multiple of the wave period Te and when Nsamp digital signals are integrated, the fundamental wave frequency included in the system voltage or the output current and the frequency components having integer multiples of the fundamental wave frequency are all eliminated .

In addition, as described above, the system voltage or the output current includes a component having a multiple of the fundamental wave frequency and a component having a multiple of the switching frequency, and the switching cycle Tsw corresponding to the sampling period Tsamp and the switching frequency is "Tsamp = 2 * Tsw "or" Tsamp = Tsw ", the component having a multiple of the switching frequency can be removed together when integrated into the above-described sampling number Nsamp. Thus, it can be seen that the switching frequency component need not be considered separately.

The offset detector 130 detects an offset of the digital signal according to Equation (2) below.

In other words, since the number of samplings capable of removing the sine wave voltage or the output current is determined through Equation (1), only the offset of the DC component can be detected when integrating the digital signal through Equation (2).

In this way, in the embodiment of the present invention, the offset detector 130 determines the sampling number according to Equation 1 so that the sine wave type system voltage or output current can be eliminated through integration, Thereby detecting an offset generated as a DC component in the process of converting the system voltage or the output current into a digital signal.

The offset buffer 140 stores the offset detected through the offset detector 130.

The compensation unit 150 compensates the digital signal by reflecting the offset stored in the offset buffer 140. Specifically, the compensator 150 reduces the digital signal by the offset if the offset stored in the offset buffer 140 is a positive value, and if the offset stored in the offset buffer 140 is a negative value, However, the present invention is not limited to this, and the digital signal may be compensated by reflecting the offset in various other ways.

Also, as the number of samples determined by the offset detector 130 increases, the magnitude of the offset detected through the integration increases, so that the digital signal can be compensated regardless of the actual size of the generated offset. The unit 150 may further perform normalization on the offset magnitude in compensating the offset and may compensate the digital signal with the normalized offset.

Further, the apparatus for compensating an offset of the grid-connected inverter according to an embodiment of the present invention may further include an offset change determiner 160 and an offset application determiner 170.

The offset change determination unit 160 determines whether the offset amount detected by the offset detection unit 130 has been changed to an extent that requires compensation. That is, when the offset is changed only to an extent that compensation is not substantially required, the offset change determination unit 160 determines whether the size of the offset has been changed to omit the unnecessary compensation process.

Specifically, the offset change determination unit 160 determines that the offset is changed when the magnitude of the offset detected through the offset detection unit 130 exceeds the resolution of the signal conversion unit 120, and determines whether the offset is changed The flag is set to 1 and stored in the offset buffer 140.

The resolution is a measure of the ability to distinguish the value of a variable from the surrounding values. When an offset is detected below the resolution of the signal conversion unit 120, the output is not affected by the offset, The determination unit 160 determines that the offset is changed when the magnitude of the offset exceeds the resolution of the signal conversion unit 120. [

The offset application determination unit 170 determines whether compensation based on the detected offset is possible. In other words, if the offset is compensated in the transient state, the system can be made unstable. Therefore, the offset application determining unit 170 determines whether the present inverter is in a state in which compensation is possible by applying an offset do.

Specifically, the offset application determination unit 170 determines whether or not the inverter operates in a steady-state after a predetermined time has elapsed after the command of the upper control unit (not shown) of the inverter is not changed or the command of the upper control unit is changed It is determined that the compensation is possible, and the stabilization flag indicating whether or not compensation is made is set to 1 and stored in the offset buffer 140.

In this case, although not shown, the upper control unit may have a configuration such as a PMS (Power Management System) for calculating a power command value for controlling the charge / discharge operation of the battery so as to maintain the power of the system uniformly and delivering it to the power management apparatus .

As described above, in the embodiment of the present invention, the offset change determination unit 160 determines whether or not the offset is substantially changed. Only when the offset is changed, the change flag corresponding to the value is set to 1 and stored in the offset buffer 140 The offset application determining unit 170 determines whether the offset can be applied and stores the offset in the offset buffer 140 when the offset can be applied or when the stabilization flag corresponding to the offset is set to '1'.

Therefore, the compensation unit 150 compensates the digital signal only when the change flag and the stabilization flag are 1 by checking the offset buffer 140, thereby preventing unnecessary offset compensation or offset compensation in an unstable state, You can save time and keep your system stable.

Hereinafter, the configuration of the grid-connected power management apparatus including the offset compensation apparatus of the grid-connected inverter as described above with reference to FIG. 4 will be described.

4 is a diagram illustrating a grid-connected power management apparatus including an offset compensation apparatus for a grid-connected inverter according to the present invention.

4, the grid-connected power management apparatus 20 includes a power management system (PCS) controller 100 and a power conversion unit 200. [

The PCS controller 100 senses the system voltage v _s of the system 10 connected to the power conversion unit 200 and adjusts the output voltage v _c of the inverter 250 based on the system voltage v _s , , And controls such that the desired output current (i _o ) is generated through the inverter (250) through this operation. More specifically, the PCS controller 100 controls the power conversion unit 200 to charge or discharge the battery 38 of the battery management system (BCS) 30 according to the charge / discharge command value.

In particular, the PCS controller 100 according to the embodiment of the present invention detects the offset of the system voltage v _s or the output current I _o converted into the digital signal as described above, and compensates by reflecting the offset And a control device 100b for providing a target signal to be output through the inverter based on the compensated digital signal to the power converter 200. The offset compensator 100a of the system- The configuration of the offset compensating apparatus 100a of the grid-connected inverter included in the PCS controller 100 has been described in detail with reference to FIG. 3, and a detailed description thereof will be omitted.

The power conversion unit 200 plays a role of linking the system 10 and the battery management device 30. [ More specifically, the power conversion unit 200 is connected to the battery rack 34 composed of one or more batteries 38 based on the control of the PCS controller 100 to discharge the battery rack 34 and to discharge the battery from the battery rack 34 The DC voltage supplied is converted into an AC voltage and supplied to the system 10, and the system voltage of the AC provided from the system 10 is converted into a DC voltage to charge the battery rack 34.

The power conversion unit 200 includes a switch gear 210, a transformer 220, a breaker 230, a filter 240, an inverter 250, and a smoothing capacitor 270.

The switchgear 210 blocks an accidental current from entering the system 150 or from entering the power conditioning system 130 in the event of an accident.

The transformer 220 reduces the system voltage of the AC supplied from the system 10 to a predetermined value and supplies it to the inverter 250 or boosts the AC voltage output from the inverter 250 to a predetermined value, .

The breaker 230 is connected to the transformer 220 and receives the AC voltage. The breaker 230 blocks the fault current from flowing into the system 10 when an accident occurs.

The filter 240 serves to reduce the harmonics of the AC voltage output from the inverter 250.

Although FIG. 4 illustrates that the filter 240 is configured as an LCL type, the present invention is not limited to this, and thus it is possible to configure the filter 240 in various forms including other elements.

The inverter 250 converts the AC voltage output from the filter 240 into a DC voltage or converts a DC voltage supplied from the battery management device 30 into an AC voltage.

The smoothing capacitor 270 performs a role of smoothing the DC voltage input from the battery management device 30 to the inverter 250 or the DC voltage output from the inverter 250. It is possible to prevent an inrush current from occurring when the battery management apparatus 30 is connected to the power conversion unit 200 before the voltage of the smoothing capacitor 270 is pre-charged.

If the smoothing capacitor 270 is not charged when the battery management device 30 is connected to the power conversion unit 200, an inrush current may be generated and the device may be damaged or a fire may occur.

In order to prevent this, the power converter 200 according to the present invention further includes an initial charge module (not shown), thereby preventing an inrush current from being generated when the smoothing capacitor 270 is charged.

The battery management device 30 connected to the power conversion device 20 stores the power supplied from the renewable energy source or the system 10 and supplies the stored power to the system 10 when a peak load or a system fault occurs do.

In the embodiment of the present invention, the battery management device 30 may be configured as any one of the battery rack group 32, the battery rack 34 and the battery module 36. [ The battery module 36 means a unit composed of a plurality of batteries 38 and the battery rack 34 means a unit composed of a plurality of battery modules 36. The battery rack group 32 includes a plurality Means a unit composed of battery racks 34.

For example, the battery module 36 may be configured by connecting a plurality of batteries 38 in series or in parallel, and the battery rack 34 may be configured by connecting a plurality of battery modules 36 in series, The battery rack group 32 may be configured by connecting a plurality of battery racks 34 in parallel.

Also, in the embodiment of the present invention, the batteries 38, which is the minimum unit constituting the battery management device 30, may be a secondary battery.

As described above, by applying the PCS controller 100 including the offset compensating apparatus 100a of the grid-connected inverter according to the present invention to the power converting unit 200, It is possible to reduce errors due to noise, CT (Current Transformer) saturation, quantization error, and the like, and accurately sense the grid voltage and output current to the inverter 250 of the power conversion unit 200. Therefore, the inverter 250 can be controlled with a more accurate target signal.

5 is a diagram illustrating a specific procedure of the offset compensation method of the grid-connected inverter according to the present invention.

6 is a diagram illustrating a concrete procedure for determining whether or not an offset is changed and whether an offset can be applied in the implementation of the offset compensation method of the grid-connected inverter according to the present invention.

5 and 6, the sensing unit 110 senses the system voltage of the system connected to the inverter or the output current of the inverter (S100), and the signal converter 120 converts the system voltage of the sensed analog signal Or converts the output current into a digital signal (S200).

Next, the offset detector 130 determines the sampling number to detect the offset of the digital signal converted through the signal converter 120 (S300), integrates the system voltage and the output current of the digital signal with the determined sampling number, (S400).

Since a specific equation for determining a predetermined sampling number and integrating the digital signal by the number of sampling is described with reference to Equations (1) and (2), repetitive description will be omitted.

Next, the compensation unit 150 compensates the system voltage or the output current of the digital signal by reflecting the offset detected through the above-described step S400 (S500).

In FIG. 5, it is described that the offset is detected and the detected offset is directly reflected to compensate the digital signal. However, the present invention is not limited to this.

Specifically, after the above-described step S400 in the embodiment of the present invention, the offset change determination unit 160 determines whether or not to change the offset based on whether the magnitude of the detected offset exceeds a predetermined size S420). If it is determined that the offset is changed, the change flag indicating whether the offset is changed is set to 1 and the offset is updated (S440).

That is, when the offset is changed only to the extent that compensation is not required, the offset change determining unit 160 determines that the offset has changed only when the size of the offset exceeds a predetermined size to omit an unnecessary compensation process .

At this time, the predetermined size may be set based on the resolution of the signal conversion unit 120 that converts the system voltage or the output current into a digital signal in the above-described step S200.

The resolution is a measure of the ability to distinguish the value of a variable from the surrounding values. When an offset is detected below the resolution of the signal conversion unit 120, the output does not affect the output even though the offset is reflected. It can be determined that the offset is changed only when the size exceeds the resolution of the signal converting unit 120. [

The offset application determining unit 170 determines whether the inverter operates in a normal state (S460), considering that the offset can be made unstable when the inverter compensates for the offset in the transient state (S460) It is determined that compensation is possible and the stabilization flag indicating whether or not compensation is performed is set to 1 (S480).

That is, when the command of the upper control section for the inverter is not changed or the inverter operates in a normal state after a predetermined time has elapsed after the command of the upper control section is changed, the system is not unstable even if the offset is compensated. ) Judges that compensation is possible when the inverter operates in the normal state.

In step S500, the compensator 150 confirms the change flag and the stabilization flag by checking the offset buffer 140, compensates the digital signal when the change flag and the stabilization flag are 1, By preventing offset compensation in an unstable state, the algorithm execution processing time of the system can be reduced and the system can be stably maintained.

6, the step of determining whether the offset has been substantially changed is performed first, and the step of determining whether offset compensation is possible is performed later. However, since the present invention is not limited to this, May be performed first and the step of determining whether the offset has substantially changed may be performed later, and each step may be performed at the same time.

FIG. 7 is a graph showing the output current of the inverter when an offset of 1% occurs in the value obtained by sensing the system voltage.

8 is a graph showing the output current of the inverter when an offset of 1% is generated in the value obtained by sensing the output current.

9 is a graph showing a result of compensating an offset of a grid link inverter according to the present invention.

As shown in FIG. 7, when an offset of 1% occurs in the value obtained by sensing the grid voltage, the inverter is controlled based on the offset, thereby confirming that an offset of about 7% occurs in the output current of the inverter . That is, as the offset occurs in the sensed value, an offset of about 7% occurs in the A-phase current, and an offset of about -7% occurs in the C-phase current.

As shown in FIG. 8, when an offset of 1% occurs in the value obtained by sensing the output current, the inverter is controlled based on the offset, and an offset of about 1% occurs in the output current of the inverter can confirm.

On the other hand, as shown in FIG. 9, it can be confirmed that there is no imbalance in the output current of each phase when the offset of the grid-connected inverter is compensated according to the present invention.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, have. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. Therefore, it should be understood that the above-described embodiments are illustrative in all aspects and not restrictive. The scope of protection of the present invention should be construed according to the claims, and all technical ideas within the scope of equivalents should be interpreted as being included in the scope of the present invention.

20: power management device 100: PCS controller
100a: Offset compensation device of grid-connected inverter 100b: Control device
110: sensing unit 120: signal conversion unit
130: Offset detector 140: Offset buffer
150: compensation unit 160: offset change judgment unit
170: Offset application determination unit 200:
210: Switchgear 220: Transformer
230: breaker 240: filter
250: inverter 270: smoothing capacitor

Claims

The battery system includes a battery pack including at least one battery. The battery pack includes at least one battery pack. The at least one battery pack is connected to the at least one battery pack. The at least one battery pack is connected to the at least one battery pack. A power converter for charging the battery unit; And
And a controller for controlling the power conversion unit to charge or discharge the battery unit according to a charge / discharge command value,
The controller comprising:
A signal converter for converting a system voltage supplied from the system or an output current outputted from the inverter to the system into a digital signal;
An offset detector for detecting an offset of the digital signal; And
And a compensator for compensating the digital signal by reflecting the detected offset,
Wherein the offset detecting unit detects the offset by integrating the digital signal with a predetermined sampling number.

The method according to claim 1,
Wherein the offset detector is configured to determine the predetermined sampling number such that a multiple of the sampling period for the digital signal coincides with a multiple of the fundamental period of the fundamental wave frequency included in the system voltage or the output current, And the offset is detected by using the offset.

The method according to claim 1,
Wherein the offset detector is configured to determine the predetermined number of samples based on one periodic component of the fundamental wave frequency of the system voltage or the output current and a sampling period of the digital signal and to detect the offset using the determined sampling number Wherein said power management device comprises:

The method according to claim 1,
The offset detector
Equation

(Where Nsamp is a sampling number,? Is a positive integer such that Nsamp is a positive integer, Te is one period of a fundamental wave frequency, and Tsamp is a sampling period)
(Nsamp) is determined based on the sampling number
Equation

And integrates the digital signal based on the digital signal.

The method according to claim 1,
Further comprising an offset change determiner for determining whether the offset is changed based on whether the magnitude of the detected offset exceeds a resolution of the signal converter,
Wherein the offset change determination unit determines that the offset is changed when the size of the offset exceeds the resolution and the compensation unit compensates the digital signal if the offset is determined to be changed through the offset change determination unit Grid - connected power management device.

The method according to claim 1,
Further comprising an offset application determination unit for determining whether compensation for the digital signal is possible,
The offset application determining unit may determine that the compensation is not performed when the command of the upper control unit for the inverter is not changed or when the inverter operates in a steady-state after a predetermined time has elapsed after the command of the upper control unit is changed Wherein the compensating unit compensates the digital signal if it is determined that the digital signal can be compensated through the offset application determining unit.

The method according to claim 1,
Wherein the change flag is set to 1 when the size of the offset exceeds the resolution of the signal conversion unit,
Wherein the compensation unit checks the offset buffer and compensates the digital signal by reflecting the offset if the change flag is 1. The system of claim 1,

The method according to claim 1,
Further comprising an offset buffer in which a stabilization flag indicating whether or not the compensation is to be stored is set, the stabilization flag is set to 1 when the inverter operates in a normal state,
Wherein the compensation unit checks the offset buffer and compensates the digital signal by reflecting the offset if the stabilization flag is 1. The system of claim 1,

A sensing unit for sensing the system voltage of the system connected to the inverter or the output current of the inverter;
A signal converter for converting a system voltage or an output current sensed through the sensing unit into a digital signal;
An offset detector for detecting an offset of the digital signal; And
And a compensator for compensating the digital signal by reflecting the detected offset,
Wherein the offset detector detects the offset by integrating the digital signal with a predetermined number of samples.

10. The method of claim 9,
Wherein the offset detecting unit determines the predetermined sampling number so that a multiple of the sampling period for the digital signal coincides with a multiple of the fundamental period of the fundamental wave frequency included in the system voltage or the output current. Offset compensation device of inverter.

10. The method of claim 9,
Wherein the offset detector is configured to determine the predetermined number of samples based on one periodic component of the fundamental wave frequency of the system voltage or the output current and a sampling period of the digital signal and to detect the offset using the determined sampling number Wherein said power management device comprises:

10. The method of claim 9,
The offset detector
Equation

(Where Nsamp is a sampling number,? Is a positive integer such that Nsamp is a positive integer, T _e is one period of a fundamental wave period according to a fundamental wave frequency, and Tsamp means a sampling period)
(Nsamp) is determined based on the sampling number
Equation

And integrates the digital signal based on the digital signal.

10. The method of claim 9,
Further comprising an offset change determiner for determining whether the offset is changed based on whether the magnitude of the detected offset exceeds a resolution of the signal converter,
Wherein the offset change determination unit determines that the offset is changed when the size of the offset exceeds the resolution and the compensation unit compensates the digital signal if the offset is determined to be changed through the offset change determination unit Offset Compensator for Grid - Linked Inverters.

10. The method of claim 9,
Further comprising an offset application determination unit for determining whether compensation for the digital signal is possible,
The offset application determining unit may determine that the compensation is not performed when the command of the upper control unit for the inverter is not changed or when the inverter operates in a steady-state after a predetermined time has elapsed after the command of the upper control unit is changed And the compensation unit compensates the digital signal if it is determined that the digital signal can be compensated through the offset application determination unit.

10. The method of claim 9,
Wherein the change flag is set to 1 when the size of the offset exceeds the resolution of the signal conversion unit,
Wherein the compensation unit checks the offset buffer and compensates the digital signal by reflecting the offset when the change flag is 1. The offset compensator of claim 1,

10. The method of claim 9,
Further comprising an offset buffer in which a stabilization flag indicating whether or not the compensation is to be stored is set, the stabilization flag is set to 1 when the inverter operates in a normal state,
Wherein the compensation unit checks the offset buffer and compensates the digital signal by reflecting the offset when the stabilization flag is 1. The offset compensator of claim 1,