KR20210133647A - System-linked energy storage system and power control apparatus - Google Patents

Abstract

A power control device of the present invention is connected to a power grid to supply active power and reactive power to a grid. The power control device comprises: a bidirectional insulated DC/DC converter that converts DC power of a DC input terminal capacitor into DC power of a DC link capacitor in an isolated state; a bridge-type DC/AC inverter that converts the DC power of the DC link capacitor into AC power to supply active power and reactive power to the grid; a DC/DC controller for controlling an operation of the DC/DC converter with a voltage value of the DC link capacitor; and a DC/AC controller for controlling an operation of the DC/AC inverter with a voltage value of a DC input terminal.

Description

SYSTEM-LINKED ENERGY STORAGE SYSTEM AND POWER CONTROL APPARATUS

The present invention relates to a grid-connected energy storage system and a power control device for controlling a power conversion operation to compensate for reactive power of a grid using the same.

The energy storage system linked to the grid consists of a battery and a charge/discharge power converter, and stores surplus power and supplies insufficient power to the grid. It alleviates the imbalance of power supply and demand caused by the

1 is a circuit diagram illustrating an ESS system using a bidirectional buck-boost converter according to the prior art.

The grid-connected energy storage system of the prior art generally has a two-stage form as a charge/discharge power converter.

A basic two-stage grid-connected system uses a non-isolated bidirectional buck-boost converter as shown in FIG. 1 . Step-up and step-down operations are possible through a bidirectional buck-boost converter, and current control and voltage control of the ESS are possible. However, since only one step of step-up or step-down is possible, there is a limit to the voltage that can be controlled. In addition, since the system and the ESS stage are not insulated as a circuit without a transformer, safety problems such as leakage current occur.

Due to these shortcomings, a topology with an isolation function is recently used for the DC stage. In this case, a transformer is used to provide an insulating function, that is, a function to suppress leakage current, and the output range of voltage is widened. The inverter controls the grid current according to the DC-link voltage and grid needs, and controls the output of the ESS through a DC-DC converter with an insulation function.

This control method has disadvantages in terms of price, reliability, and size because the high energy that the DC-link capacitor can handle requires an electrolytic capacitor with a large capacity.

Republic of Korea Publication No. 10-2015-0008767

An object of the present invention is to provide a grid-connected energy storage system and a power control device having excellent reactive power compensation efficiency while reducing the capacity of a DC link capacitor.

An object of the present invention is to provide a grid-connected energy storage system and a power control device that secure an insulation function at a relatively low cost.

A power control device according to an aspect of the present invention is a power control device that is connected to a power system and supplies active power and reactive power to the grid, and converts DC power of a DC input terminal capacitor into DC power of a DC link capacitor in an insulated state. bidirectional isolated DC/DC converter that converts; a bridge-type DC/AC inverter converting the DC power of the DC link capacitor into AC power and supplying active power and reactive power to the grid; a DC/DC controller for controlling an operation of the DC/DC converter with the voltage value of the DC link capacitor; and a DC/AC controller for controlling the operation of the DC/AC inverter with the voltage value of the DC input terminal.

Here, the DC/DC converter may be a dual-active-bridge (DAB) converter including an isolation transformer and having a half-bridge structure.

Here, the DC/AC inverter may be an H-bridge inverter having four switch elements.

Here, the DC/AC controller may include: a comparator for comparing a difference between a voltage value of a battery connected to the DC input terminal and a reference voltage value; a voltage controller outputting a reference effective current value as a result of comparison of the comparator; a current controller for outputting an output voltage ratio as the reference effective current value and the reference reactive current value; and a PWM generator for generating a PWM signal for a switch element of the DC/AC inverter according to the output voltage ratio.

Here, the DC/DC controller may include: a comparator for comparing a difference between a voltage value of the DC link capacitor and a reference voltage value; a voltage controller outputting a phase value as a result of the comparison of the comparator; and a PWM generator for generating a PWM signal for a switch element of the DC/DC converter according to the phase value.

Here, the DC/DC converter may have a transfer equation according to the following equation.

: 출력 전력,

: 입, 출력 전압, N : 변압기 권선비, L : 인덕턴스,f: 스위칭 주파수,

: 제어 위상임)(here,

: output power,

: input and output voltage, N : transformer turns ratio, L : inductance, f: switching frequency,

: control phase)

A grid-connected energy storage system according to another aspect of the present invention includes: an energy storage device for storing energy for reactive power compensation for a grid; a grid output stage for supplying AC power for reactive power compensation to the grid; a DC link end between the energy storage device and the grid output end; a DC/DC converting block converting the DC power output from the energy storage device according to the voltage value of the DC link terminal and supplying it to the DC link terminal; and a DC/AC converting block that converts the DC power supplied to the DC link terminal into AC according to the voltage value of the energy storage device and provides the converted DC power to the grid output terminal.

Here, the DC/DC converting block may include a DC/DC converter that converts DC power output from the energy storage device into DC power of a DC link terminal in an insulated state; and a DC/DC controller for controlling the operation of the DC/DC converter with the voltage value of the DC link terminal.

Here, the DC/DC converter may be a dual-active-bridge (DAB) converter including an isolation transformer and having a half-bridge structure.

Here, the DC/AC converting block includes: a DC/AC inverter that converts the DC power of the DC link stage into AC power and supplies the active power and reactive power to the grid; and a DC/AC controller for controlling the operation of the DC/AC inverter with the battery voltage value of the energy storage device.

Here, it may further include an input terminal capacitor.

Here, a DC link capacitor may be further included.

If the grid-connected energy storage system and/or power control device according to the spirit of the present invention having the above configuration is implemented, there is an advantage in that it is possible to achieve excellent reactive power compensation efficiency while reducing the capacity of the DC link capacitor.

The grid-connected energy storage system and/or power control device of the present invention has an advantage in that the non-isolated DC-DC converter can be replaced with an isolated type.

The grid-connected energy storage system and/or power control device of the present invention has an advantage in that reliability can be secured even when the number of elements is reduced.

The grid-connected energy storage system and/or power control device of the present invention has an advantageous advantage when a high voltage is increased due to an increase in a battery stage capacitor.

The grid-connected energy storage system and/or power control device of the present invention requires insulation as well as most fields in which an insulated DC-DC converter is used, for example, grid-connected solar power, wind power, and fuel cell system fields. It has the advantage that it can be used for AC-DC power converters of all general home appliances.

1 is a circuit diagram illustrating an energy storage system using a bidirectional buck-boost converter according to the prior art.
2 is a circuit diagram illustrating an energy storage system having an isolated converter according to an embodiment of the present invention.
3 is a block diagram of a converter/inverter controller according to the prior art for an ESS equipped with an insulated bidirectional converter.
4 is a block diagram of a converter/inverter controller according to the idea of the present invention for an ESS equipped with an insulated bidirectional converter.
5 is a waveform diagram illustrating a waveform for supplying active power to a system with a battery of a control method proposed by the present invention.
6 is a waveform diagram illustrating a battery CV charging waveform of the control method proposed by the present invention.
7 is a waveform diagram illustrating a battery CC charging waveform of the control method proposed by the present invention.
8 is a waveform diagram illustrating an operation waveform in which battery power is supplied to the system through the conventional control method.
9 is a waveform diagram illustrating an operation waveform of the conventional method in which a DC-link capacitor is added.
10 is a waveform diagram illustrating a reactive power supply waveform using the method proposed in the present invention.
11 is a waveform diagram illustrating a reactive power absorption waveform using the method proposed in the present invention.

In describing the present invention, terms such as first, second, etc. may be used to describe various components, but the components may not be limited by the terms. The terms are only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, a first component may be referred to as a second component, and similarly, a second component may also be referred to as a first component.

When a component is referred to as being connected or connected to another component, it may be directly connected or connected to the other component, but it can be understood that other components may exist in between. .

The terms used herein are used only to describe specific embodiments, and are not intended to limit the present invention. The singular expression may include the plural expression unless the context clearly dictates otherwise.

In this specification, the terms include or include are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, and includes one or more other features or numbers, It may be understood that the existence or addition of steps, operations, components, parts or combinations thereof is not precluded in advance.

In addition, shapes and sizes of elements in the drawings may be exaggerated for clearer description.

2 is a circuit diagram illustrating a grid-connected energy storage system having an insulated converter according to an embodiment of the present invention.

The illustrated grid-connected energy storage system includes an energy storage device 100 for storing energy for reactive power compensation for the grid; a grid output stage 700 for supplying AC power for reactive power compensation to the system; a DC link end between the energy storage device 100 and the grid output end 700; DC/DC converting blocks 200 and 20 for converting the DC power output from the energy storage device 100 according to the voltage value of the DC link terminal and supplying the converted DC power to the DC link terminal; and DC/AC converting blocks 500 and 50 that convert the DC power supplied to the DC link terminal into AC according to the voltage value of the energy storage device 100 and provide the converted DC power to the grid output terminal 700 . have.

Here, the DC/DC converting blocks 200 and 20 include a DC/DC converter 200 that converts DC power output from the energy storage device into DC power of the DC link terminal in an insulated state; and a DC/DC controller 20 for controlling the operation of the DC/DC converter with the voltage value of the DC link terminal.

Similarly, the DC/AC converting block (500, 50), a DC/AC inverter (500) for converting the DC power of the DC link stage into AC power and supplying the active power and reactive power to the grid; and a DC/AC controller 50 for controlling the operation of the DC/AC inverter with the battery voltage value of the energy storage device.

The DC link terminal may be implemented as a DC link capacitor 301 as shown. That is, the DC/DC converter 200 and the DC/AC inverter 500 are connected via the DC link capacitor 301 .

Meanwhile, the energy storage device 100 and the DC/DC converter 200 may also be connected via an input terminal capacitor 199 .

Meanwhile, an inductor 601 may be interposed between the grid output terminal 700 and the DC/AC inverter 500 .

Considering that the ESS and the charging/discharging power converter can be installed separately at the site, the DC/DC converting blocks 200 and 20 and the DC/AC converting blocks 500 and 50 among the configurations of FIG. 2 are charged and discharged. It can be classified as a separate power control device for power conversion.

The power control device according to the spirit of the present invention divided from the above point of view is a power control device that is connected to a power system and supplies active power and reactive power to the system, in which the DC power of the DC input terminal capacitor 199 is insulated. a bidirectional isolated DC/DC converter 200 that converts the DC power of the DC link capacitor 301 into DC power; a bridge-type DC/AC inverter 500 for converting the DC power of the DC link capacitor 301 into AC power and supplying active power and reactive power to the grid; a DC/DC controller 20 for controlling the operation of the DC/DC converter 200 with the voltage value of the DC link capacitor 301; and a DC/AC controller 50 for controlling the operation of the DC/AC inverter 500 with the voltage value of the DC input terminal.

Specifically, the illustrated DC/DC converter 200 is a DAB (dual-active-bridge) converter including an isolation transformer and having a half-bridge structure. That is, the illustrated DC/DC converter 200 includes an isolation transformer 220 in the center, and two switch elements 215 and 216 and two switch element replacement capacitors on the primary side of the isolation transformer 220 . (201, 202) is provided, and the secondary side of the isolation transformer 220 is provided with two switch elements (217, 218) and two switch element replacement capacitors (241, 242). A resistor 231 and an inductor 232 may be provided on the primary side and/or the secondary side of the isolation transformer 220 . The illustrated detailed circuit configuration is merely an example, and is not limited thereto. For example, it may be replaced with a DAB (Dual-active-bridge) converter having a full bridge structure, and it is natural that this also falls within the scope of the present invention.

Specifically, the DC/AC inverter 500 has an H-bridge inverter configuration including four full-bridge switch elements 501 to 504 . The illustrated detailed circuit configuration is merely an example, and is not limited thereto.

The power control device shown in FIG. 2 applies a dual half bridge (DHB) converter that uses a minimum element among DC-DC switching converters with an insulation function to the DC stage, and uses a phase-shift method to control the power That is, the illustrated power control device uses an H-bridge inverter as a DC-AC inverter as a two-stage grid-connected system, and uses a DHB converter as an insulated DC-DC converter.

By controlling the voltage current of the ESS rather than the DC link voltage through the control of the DC/AC inverter 500 , the capacity of the DC link capacitor 301 may be reduced by reducing the energy that the DC link can handle.

Existing circuits using the same structure control the DC-link voltage through the inverter and control the voltage at the ESS stage through the DHB converter.

In the present invention, it is assumed that the energy storage device is a battery, and CC-CV mode operation is possible by controlling the voltage and current of the ESS unit battery through an inverter. The DHB DC/DC converter 200 controls the voltage of the DC-link. Since the ripple energy by the system is transferred to the ESS stage, it is possible to reduce the capacity of the DC-link capacitor 301 .

The DHB DC/DC converter 200 uses the smallest element among other bidirectional converters having an insulating function, and generates a voltage difference between both ends of the transformer inductor using a phase shift to control the flowing current of the inductor. The transmission formula is the same as Equation 1d below, and since the input voltage and the power to be delivered are determined by the inverter, the output voltage can be controlled by adjusting the phase.

: 출력 전력,

: 입, 출력 전압, N : 변압기 권선비, L : 인덕턴스,f: 스위칭 주파수,

: 제어 위상이다.In Equation 1 above,

: output power,

: input and output voltage, N : transformer turns ratio, L : inductance, f: switching frequency,

: Control phase.

In other words, the illustrated DC/DC converter 200 is controlled by the DC link terminal voltage (V _dc-link ) to reduce the ripple input to the DC link capacitor 301 , and the illustrated DC/AC inverter 500 is controlled by the battery voltage (V _batt ), and the ripple is reduced by mutual adjustment of the demand amount of the grid (system load) and the supply amount of the ESS 100, compared to the prior art, the DC link capacitor 301 generated Ripple can be greatly reduced. This prevents the DC link capacitor 301 from having an unnecessary margin capacity, thereby achieving capacity reduction of the DC link capacitor 301 .

3 is a block diagram of a converter/inverter controller according to the prior art for an ESS equipped with an insulated bidirectional converter.

4 is a block diagram of a converter/inverter controller according to an idea of the present invention for an ESS equipped with an insulated bidirectional converter.

The converter and inverter controller shown in FIG. 3 follow a general converter/inverter control method, and accordingly, the DC/DC converter connected to the battery side _{is controlled by the battery voltage (V batt} ), and the DC/AC inverter connected to the grid (grid) side. is controlled by the DC link voltage (V _{dc-link ).}

On the other hand, by the converter controller and the inverter controller shown in FIG. 4 according to the spirit of the present invention, the DC/DC converter 200 of FIG. 2 is controlled by the DC link terminal voltage (V _dc-link ), and the DC of FIG. /AC inverter 500 is controlled by the _{battery voltage (V batt ).}

In the case of the conventional method of FIG. 3 , the voltage of the DC link terminal is controlled by an inverter, and _{the power component that C dc} is responsible for is determined by the inverter, and as the power increases, a large-capacity capacitor is required for ripple attenuation. The battery voltage is controlled by the DHB converter.

In the case of the method proposed by the present invention of FIG. 4 , the battery voltage (V _batt ) is controlled through the DC/AC inverter ( 500 ), and the DHB controls the DC link terminal voltage (V _dc-link ). As a result, the bandwidth of the voltage controller can be increased, so that fast control is possible, and the capacity of the DC-link capacitor 301 can be reduced by reducing the ripple component.

The DC/AC controller 50 according to the configuration of FIG. 4 includes a comparator for comparing a difference between _{a voltage value (V batt} ) of a battery connected to the DC input terminal and a reference voltage value (V _{batt *);} a voltage controller outputting a _{reference effective current value (I d} *) as a comparison result of the comparator; a current controller for outputting an output voltage ratio (m) to the reference active current value (I _d *) and the reference reactive current value (I _{q *);} and a PWM generator for generating a PWM signal for a switch element of the DC/AC inverter according to the output voltage ratio (m). Here, the output voltage ratio (m) is _{for configuring the formula Vo} (output voltage) = mV _i (input voltage).

Similarly, the DC/DC controller 20 according to the configuration of FIG. 4 includes a comparator for comparing a difference between _{a voltage value (V dc-link} ) of the DC link capacitor and a reference voltage value (V _{dc-link *);} a voltage controller outputting a phase value ? as a result of comparison of the comparator; and a PWM generator for generating a PWM signal for a switch element of the DC/DC converter according to the phase value. Here, a predetermined fixed weight D may be applied.

Next, we will look at the control method proposed by the simulation waveform and the operation example of the existing method, and also confirm the operation of the CC-CV mode for charging the battery.

5 exemplifies a waveform for supplying active power to a system using the battery of the control method proposed in the present invention.

5 is a waveform when the battery supplies power to the system in the proposed control method, and it can be seen that the power of the battery is well transmitted to the system. The battery voltage has a ripple of less than 5% and a ripple value of 10% without a separate DC-link capacitor.

6 illustrates a battery CV charging waveform of the control method proposed by the present invention.

7 illustrates a battery CC charging waveform of the control method proposed by the present invention.

6 and 7 show waveforms of the CC-CV mode charging operation according to the proposed control method. Power from the grid is stored in the battery.

8 illustrates an operation waveform in which battery power is supplied to the system in an existing control manner.

8 is an example of an operation using an existing control method. As in the case of FIG. 5 , the battery supplies power to the system. In both the example of FIG. 5 and the example of FIG. 8, the same capacitor is used for the battery terminal and the DC-link terminal. The voltage ripple of the DC-link stage is maintained at around 10% in a general power control device. However, in the case of the proposed method with the same capacitor capacity (FIG. 5), the DC-link voltage maintains a voltage ripple within 10%, whereas the ripple of the conventional method has a ripple value of 50% or more. It can be seen that the inverter output power is also affected by this.

9 illustrates an operation waveform of a conventional method in which a DC-link capacitor is added.

9 shows a waveform obtained by attenuating the ripple of the DC-link stage by adding a capacitor to the DC-link stage. As described above, the conventional method requires a capacitor with a larger capacity in the DC-link stage than the proposed method for DC-link ripple attenuation.

10 illustrates a reactive power supply waveform using the method proposed in the present invention.

11 illustrates a reactive power absorption waveform using the method proposed in the present invention.

10 and 11 are reactive power control waveforms through the proposed control method. When the system does not require active power, the battery maintains only a constant voltage and can supply ( FIG. 10 ) or absorb ( FIG. 11 ) reactive power. That is, the energy storage device according to the control method of the present invention can be absorbed or supplied by controlling active power and reactive power as in the conventional case. In addition, while maintaining the battery voltage ripple above a certain level through the spirit of the present invention, the effect of reducing the capacity of the DC-link capacitor is achieved.

Those skilled in the art to which the present invention pertains should understand that the present invention can be embodied in other specific forms without changing the technical spirit or essential characteristics thereof, so the embodiments described above are illustrative in all respects and not restrictive. only do The scope of the present invention is indicated by the following claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be construed as being included in the scope of the present invention. .

20: DC/DC controller 50: DC/AC controller
100: energy storage device 199: input terminal capacitor
200: DC/DC converter 301: DC link capacitor
500: DC/AC inverter 601: inductor
700: grid output stage

Claims (12)

As a power control device that is connected to the power system and supplies active and reactive power to the grid,
a bidirectional insulated DC/DC converter that converts the DC power of the DC input stage capacitor into DC power of the DC link capacitor in an isolated state;
a bridge-type DC/AC inverter that converts the DC power of the DC link capacitor into AC power and supplies active power and reactive power to the grid;
a DC/DC controller for controlling an operation of the DC/DC converter with the voltage value of the DC link capacitor; and
DC/AC controller that controls the operation of the DC/AC inverter with the voltage value of the DC input terminal
A power control device comprising a.
According to claim 1,
The DC/DC converter is
A power control device that is a dual-active-bridge (DAB) converter with an isolation transformer and a half-bridge structure.
According to claim 1,
The DC/AC inverter,
A power control unit that is an H-bridge inverter with 4 switch elements.
According to claim 1,
The DC / AC controller,
a comparator for comparing a difference between a voltage value of a battery connected to the DC input terminal and a reference voltage value;
a voltage controller outputting a reference effective current value as a result of comparison of the comparator;
a current controller for outputting an output voltage ratio as the reference effective current value and the reference reactive current value; and
A PWM generator that generates a PWM signal for a switch element of the DC/AC inverter according to the output voltage ratio
A power control device comprising a.
According to claim 1,
The DC / DC controller,
a comparator for comparing a difference between a voltage value of the DC link capacitor and a reference voltage value;
a voltage controller outputting a phase value as a result of the comparison of the comparator; and
A PWM generator that generates a PWM signal for a switch element of the DC/DC converter according to the phase value
A power control device comprising a.
According to claim 1,
The DC/DC converter is
A power control device having a transmission formula according to the following equation.

(here,

: output power,

: input and output voltage, N : transformer turns ratio, L : inductance, f: switching frequency,

: control phase)
Energy storage device for storing energy for reactive power compensation for the system;
a grid output stage for supplying AC power for reactive power compensation to the grid;
a DC link end between the energy storage device and the grid output end;
a DC/DC converting block converting the DC power output from the energy storage device according to the voltage value of the DC link terminal and supplying it to the DC link terminal; and
A DC/AC converting block that converts the DC power supplied to the DC link terminal into alternating current according to the voltage value of the energy storage device and provides it to the grid output terminal
A grid-connected energy storage system comprising a.
8. The method of claim 7,
The DC/DC converting block is
a DC/DC converter that converts DC power output from the energy storage device into DC power of a DC link terminal in an isolated state; and
DC/DC controller for controlling the operation of the DC/DC converter with the voltage value of the DC link terminal
A grid-connected energy storage system comprising a.
9. The method of claim 8,
The DC/DC converter is
A grid-connected energy storage system that is a dual-active-bridge (DAB) converter with an isolation transformer and a half-bridge structure.
8. The method of claim 7,
The DC/AC converting block is
a DC/AC inverter converting the DC power of the DC link stage into AC power and supplying active power and reactive power to the grid; and
DC/AC controller for controlling the operation of the DC/AC inverter with the battery voltage value of the energy storage device
A grid-connected energy storage system comprising a.
8. The method of claim 7,
A grid-tied energy storage system further comprising an input stage capacitor.
8. The method of claim 7,
A grid-connected energy storage system further comprising a DC link capacitor.

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