KR101431047B1 - Coordinated Droop Control Apparatus and the Method for Stand-alone DC Micro-grid - Google Patents

Coordinated Droop Control Apparatus and the Method for Stand-alone DC Micro-grid Download PDF

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KR101431047B1
KR101431047B1 KR1020130011073A KR20130011073A KR101431047B1 KR 101431047 B1 KR101431047 B1 KR 101431047B1 KR 1020130011073 A KR1020130011073 A KR 1020130011073A KR 20130011073 A KR20130011073 A KR 20130011073A KR 101431047 B1 KR101431047 B1 KR 101431047B1
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power
grid
energy storage
storage device
droop
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KR20140098431A (en
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한병문
이지헌
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명지대학교 산학협력단
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    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02JCIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/46Controlling of the sharing of output between the generators, converters, or transformers
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02JCIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381Dispersed generators
    • H02J3/382Dispersed generators the generators exploiting renewable energy

Abstract

The present invention relates to a cooperative control apparatus and method for a stand-alone micro-grid, and more particularly to a cooperative control apparatus and method for a stand-alone micro-grid in which an energy storage device and a distributed power source So that the power balance of the microgrid can be effectively controlled. Specifically, the energy storage device is divided into a normal mode and a low-power mode according to a charge state by using a droop control method. In the normal mode, the grid power is controlled differently according to a grid voltage, And efficiently controls. The distributed power supply assists the energy storage device to effectively control the grid power by varying the operation mode according to the grid voltage.

Description

[0001] The present invention relates to a coordinated droop control apparatus and method for a stand-alone DC micro-grid,

The present invention relates to a stand-alone micro-grid power network control apparatus and method. More particularly, the present invention relates to a control apparatus and method for effectively controlling a micro grid power grid using a coordinated control algorithm between a distributed power source such as wind power, solar power, an engine generator, and an energy storage device such as a battery.

Recently, the micro grid power grid, which is independent of the existing power grid, has been widely used in the island and remote areas of the country, along with the rise of the smart grid, by using distributed power sources such as wind power and solar power and energy storage devices. However, There is a problem that requires frequent maintenance.

The micro grid grid can be classified according to the connection method and the control method. According to the linking method, the AC microgrid connecting AC components and the DC micro grid connecting DC can be distinguished. The AC microgrid has the advantage of taking advantage of the existing distribution, but it causes synchronization, stability, and reactive power problems. DC microgrid, on the other hand, has no problems with synchronization, stability, and reactive power, and has the advantage of low system loss and cost because it does not require two-stage power conversion in linking the power produced by each power source. In particular, DC micro-grids are more efficient because the digital load, which has recently been rapidly increasing, requires a DC power source. Recently, attention has been focused on the DC micro-grid.

As a classification according to the control method, there is a method in which a central controller is first operated and the system is operated by measuring the amount of power of the components in real time. This method requires a sensor for measuring the amount of power and a communication network for transmitting the measured data to the central controller. However, in the case of using distributed power sources such as wind power generation and photovoltaic power generation, there is a problem in that the airflow can not be maintained due to the weather There is a disadvantage in that a prediction algorithm is required and the dependence on the communication is high. In addition, this method is suitable for grid-linked microgrid because operation algorithm depends on power trading and focuses on maintaining power balance of upper system.

Another control scheme is an autonomous control scheme in which each converter associated with each element of the microgrid power grid (distributed power source, energy storage device, etc.) independently controls the associated elements. This method is a method of smoothly operating the micro grid power network as a whole, while each of the connected elements controls the operation of itself independently to some extent. According to this method, it does not require expensive communication system and it can manage autonomous demand with light operation algorithm. However, since it can not transfer state between devices, energy storage device is excessively burdened, and lifespan can be drastically lowered and efficient operation of distributed power supply is difficult There is a drawback that a circulating current can flow between the respective elements. However, this autonomous control scheme is suitable for a stand-alone micro grid grid operating independently of the grid because it does not need a high-speed communication network and does not need to use a climate prediction algorithm and a complicated control algorithm. Since the stand-alone micro grid is disconnected from the existing power grid and operates independently, maintaining power balance during operation is the most important factor and the reliability determining technique.

This autonomous control scheme is applied to a stand-alone micro grid, which is advantageous in that it does not require a high-speed communication network, a climate prediction algorithm and a complicated central control algorithm. However, problems such as generation of circulating current and excessive use of energy storage devices cause problems Therefore, when controlling a stand-alone DC micro-grid power grid based on the autonomous control method, a control method for improving the reliability by power balance of the micro grid power grid, suppressing the circulating current between the power elements, and improving the life of the energy storage device Is required.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and it is an object of the present invention to provide a method and apparatus for controlling a stand-alone microgrid by an autonomous control system while suppressing a circulating current, improving the life of the energy storage device, The present invention provides a control system and method for a stand-alone micro grid power grid.

A cooperative droop control device for a stand-alone micro-grid including at least one distributed power source and an energy storage device according to the present invention is characterized in that the voltage reference value (Vdroop) A droop controller of an energy storage device controlled by a droop control method set by Equation (1) to allow the energy storage device to supply power to the microgrid or adjust power balance of the microgrid by receiving electric power; Wherein the distributed power source supplies power to the microgrid and controls power supplied from the distributed power source to the microgrid according to the grid voltage so that the energy storage device cooperatively operates to control the power balance of the microgrid A power cooperating controller; And a control unit.

[Equation 1]

Figure 112013009418314-pat00001

Where V DROOP is the voltage control reference value, V Rate is the rated voltage, Rv is the equivalent resistance, and I ES is the output current of the energy storage device.

A cooperative droop control method for a stand-alone micro-grid including at least one distributed power source and an energy storage device according to the present invention is characterized in that the energy storage device has a voltage reference value (Vdroop) Controlled by a droop control scheme set by Equation (1) such that the energy storage device is controlled to supply power to the microgrid or receive power to regulate the power balance of the microgrid; Wherein the distributed power source supplies power to the microgrid and controls power supplied from the distributed power source to the microgrid according to the grid voltage so that the energy storage device cooperatively operates to control the power balance of the microgrid Controlled; .

[Equation 1]

Figure 112013009418314-pat00002

Here, V DROOP V Rate is the rated voltage, Rv is the equivalent resistance, and I ES is the output current of the energy storage device.

According to the cooperative drop control method for a stand-alone micro grid according to the present invention, circulation current between the elements constituting the power grid is suppressed, the excessive use of the energy storage device is restricted to improve the lifespan and reliability of the overall operation of the micro grid power grid There is an advantage to increase.

1 is a conceptual diagram of a stand-alone micro-grid power network according to an embodiment of the present invention.
Figure 2 is a block diagram of a droop controller of an energy storage device.
FIG. 3 is a graph showing a droop curve graph for illustrating the droplet control method of the energy storage device
4 is a conceptual view of a cooperative control between an energy storage device and distributed power sources
FIG. 5 is a flowchart showing the operation of the battery according to the charging state and the grid voltage.

The present invention can be achieved by the following description. It is to be understood that the following description is of a preferred embodiment of the present invention, and the present invention is not limited thereto.

1 is a conceptual diagram of a stand-alone micro-grid power network according to an embodiment of the present invention. The independent microgrid power grid according to the present invention includes an energy storage unit (ES) 110, a load unit 210, a wind generator (WG) 310, a photovoltaic array 410, and an engine generator (EG) 510, as needed. The power elements include respective power conversion converters 120, 220, 320, 420, 520 to perform the required power conversion between each power element and the DC grid.

The droop controller 130 of the energy storage device controls the power flow between the energy storage device 110 and the DC grid using a droop control technique to control the overall power balance of the DC grid. A distributed source (DS) of a wind power generator, a solar array, an engine generator, etc., is provided with respective coordination controllers 330, 430, and 530 to assist the energy storage device, Perform cooperative control to effectively balance balance. Each of the coordinator controllers 330, 430, and 530 and the droop controller 130 perform cooperative control for overall power balance of the microgrid according to the present invention, but also play a role of controlling the normal operation of each power converter .

The wind generator (WG) 310 of FIG. 1 generates power using wind power and supplies the generated power to the DC micro grid. A conventional wind turbine generator is a rotary generator based power generator, and since the output is AC, the power converter 320 connected to the wind turbine generator 310 converts the alternating current into direct current and supplies it to the DC grid. Wind turbines have variable output power depending on wind speed, typically using a maximum output point tracking method to obtain maximum output in a given weather situation.

To this end, the power conversion converter 320 connected to the wind power generator 310 performs maximum power point tracking (MPPT) control in order to maximize the output of the wind power generator which varies according to the wind speed, Can be converted and supplied to the DC grid. As a wind turbine generator, it is preferable to use a PMSG (permanent magnet synchronous generator) which is easy to connect to a DC grid and has a wide range of availability. When the current control is performed so that the angular velocity of the wind turbine is constant, the output coefficient of the blade becomes the maximum, so that the mechanical output can be maximized. The WG coordinator controller 330, which is a controller of the wind turbine generator, always measures the DC grid voltage Vdc and selects the operation mode according to the DC grid voltage to control the wind turbine generator to perform the cooperative control according to the present invention. .

A photovoltaic array (PV) array 410 of FIG. 1 may use a conventional solar array that produces electrical energy from solar light. The power conversion converter 420 connected to the solar array serves to convert the output of the solar array and supply it to the DC grid. In order to always obtain the maximum output from the solar cell whose output varies depending on the solar radiation amount and the temperature, Power Point Tracking) control. In general, since the voltage level of the open state of the solar array is lower than the grid voltage, the solar power conversion converter 420 preferably uses a DC-DC converter having a boost function capable of raising the voltage. As an example of the step-up DC-DC converter, a boost converter can be used. When using the MPPT control method, it may be desirable to use a three-phase interleaved Boost DC-DC converter to reduce this current ripple because the output contains a ripple of a certain frequency . In addition, among the MPPT control techniques, the Perturbation & Observation technique is advantageous in that it can be implemented easily and stably. In the solar cooperative controller 430, as in the cooperative controller 330 of the wind power generator, the cooperative control is performed by determining the operation mode of the converter by always measuring the DC grid voltage, which will be described later.

An engine generator (EG) 510 of FIG. 1 receives a power command according to a DC grid voltage from an associated coordinator controller 530 and supplies appropriate power to the DC grid. The power conversion converter 520 of the engine generator converts the alternating-current engine generator output to direct current and supplies it to the grid. As the method of controlling the output of the engine generator, it is preferable to use the angular speed control method. The EG coordinator controller 530 of the engine generator controls the output of the engine generator to balance the power of the grid power grid according to the cooperative control algorithm of the present invention, which will be described later.

The load (load) 210 shown in FIG. 1 is a power element consuming power and consuming power from the micro grid. The power conversion converter 220 provided between the load and the grid converts the direct current grid voltage into a proper type of power required by the load to supply power to the load. Generally, there may be an AC load and a DC load in the load. In order to supply power to an AC load, a DC / AC inverter that converts the DC grid voltage to AC is converted into a desired AC load and supplied. For example, in the case of a household load, the load power conversion converter 220 can be converted into a single-phase 220V AC used in a household and supplied. In the case of a DC load such as a digital load, the DC voltage level can be converted and supplied to the DC grid through the DC-DC converter. In this way, the stand-alone DC micro-grid can be converted to a digital load that requires DC power without AC conversion process, so that it is possible to supply only the voltage level, thereby reducing loss, cost, and size.

Next, an energy storage device (ES) 110 of FIG. 1 and its related configuration will be described. As described above, the wind power generator, the solar array, and the engine generator are distributed power sources for supplying electric power and the load is a configuration for consuming electric power. If the balance between the power generated by these distributed power sources and the power consumed by the load is not balanced, the energy storage device 110 will balance power in the microgrid power grid while receiving or supplying power. Typical examples of energy storage devices include batteries, fuel cells, and the like.

The power conversion converter 120 connected to the energy storage device 110 controls power of the grid while performing bidirectional power conversion and power transfer functions between the microgrid and the energy storage device. Since the energy storage device must supply power from the grid and store or supply the stored power to the grid, the power conversion converter 120 uses a bidirectional DC-DC converter capable of transmitting power in both directions between the grid and the energy storage device . In particular, batteries used mainly in energy storage devices require low harmonic content in the incoming current, and current ripple during charging and discharging affects the life of the battery. Therefore, a bidirectional three-phase interleaved DC-DC converter Bidirectional 3-phase interleaved DC-DC converter).

The droop control technique according to the present invention is used for the power conversion converter 120 of the energy storage device to adjust the power balance of the grid while suppressing the circulation current.

Next, a cooperative droop control method for the independent microgrid according to the present invention will be described.

Since the stand-alone micro grid is disconnected from the existing grid, maintaining power balance during operation is the most important factor and determines the reliability. In the cooperative droop control method according to the present invention, the distributed power sources and the energy storage devices (hereinafter referred to as "batteries" because a battery is typically used, but other storage devices other than the battery may be used) While maintaining the overall power balance by operating cooperatively according to the grid voltage.

To this end, the battery uses a droop control method to control the grid voltage while suppressing the circulating current, and also considers battery protection by setting the operation region according to the state of charge (SOC: stae of charge) of the battery. The distributed power sources set the cooperative operation area according to the grid voltage so that the operation mode is selected according to the grid voltage so that the battery operates cooperatively to control the power. This cooperative control method can improve the operational reliability and stability of the whole micro grid.

In order to describe the cooperative drop control method according to the present invention in detail, a droop control method for a battery droop controller 130 for controlling power of a grid will be described with reference to FIGS. 2 and 3, Referring to FIG. 5, how each power element operates cooperatively for power balance of the grid according to the present invention will be described.

For convenience of explanation, in FIGS. 2 to 5 and related descriptions, values of ± 5%, ± 3%, ± 1%, etc. are used for the grid voltage value for determining the operation mode of each element, , 55% to 85% of the grid voltage, 400V for the rated value of the grid voltage, and 100%, 70%, and 10% for the charge / discharge power of the battery. And is a value that can maximize the effects of the invention. However, other values may be used depending on the design conditions.

It should also be noted that the description of 5% of the grid voltage in Figures 2 to 5 and related description is a 5% increase in the grid rated voltage (i.e., 105% of the rated voltage) % Reduction value (i.e., 95% of the rated voltage). ± 3%, ± 1%, etc. can be understood in the same manner.

In the stand-alone microgrid of the present invention, an autonomous control scheme that does not transmit and receive information between the devices is used. When the autonomous control system is used, each of the two or more power converters is set to control the voltage (Vdc) of the DC grid. When a plurality of components control the voltage of the same node, a circulation current is inevitably generated if a difference occurs in the output voltage due to the error of the sensor, the error of the controller, and the line impedance. The circulating current is similar to the AC reactive power and is directly related to the loss of the entire system. Therefore, a control method for suppressing the circulating current is necessary because it can adversely affect the equipment to be connected.

Since the circulating current is caused by the difference in the output voltage of each distributed power source operating as a voltage source, a method of easily reducing the circulating current is to insert an actual resistance between the output terminal of each distributed power source and the DC grid. However, this method is impractical in terms of loss, cost, and size.

2, a feedback loop for changing the voltage reference value V DROOP is added to the voltage controller 131 that controls the output voltage of the droop controller 130 by feeding back the output current I ES Control). That is, the output DC current I ES is detected and multiplied by the gain Rv 132, and the result is subtracted from the output voltage target value V rate to generate the corrected voltage target value V DROOP . The current reference value I ES_REF is generated through a compensator 133 such as a PI or the like and the difference between the corrected target value V DROOP and the actual grid voltage Vdc is generated. So that the grid voltage Vdc follows the corrected voltage reference value V DROOP .

Since the grid voltage Vdc, which is the output voltage, will follow V DROOP by the function of the controller as described above, the grid voltage can be expressed by the following equation (1).

[Equation 1]

Figure 112013009418314-pat00003

Here, Rv serves as an equivalent resistance such that a resistor exists at the output terminal. That is, as the output current I ES increases, the output voltage Vdc is reduced by a voltage corresponding to the voltage drop Rv I ES of the resistor Rv. In this way, since the output voltage is formed as if there is a resistor even if there is no resistor, it can be seen that the circulating current generated by the difference of the output voltage with other converters can be suppressed by the equivalent resistor Rv.

From the magnitude of the voltage change (△ V dc) of the output current, the maximum value of the battery energy storage system (I MAX) can be obtained an equivalent resistance (Rv) as shown in Equation (2), the operating power of the battery (P Batt) The equivalent resistance can be obtained by using Equation 3 as a variable. That is, by setting the operating power value of the battery and the voltage variation value at that time, an equivalent resistance can be obtained.

&Quot; (2) "

Figure 112013009418314-pat00004

&Quot; (3) "

Figure 112013009418314-pat00005

Here, Rv is the equivalent resistance, △ V dc is an output voltage fluctuation due to the equivalent resistance, and the output current I ES, V dcmin is the minimum value of the output voltage, P Batt is an operational power of the battery.

3 shows a Droop curve showing the DC grid voltage variation according to the current I ES and a conceptual diagram for the cooperative control of the battery energy storage device and the distributed power sources. Droop curves are classified into three areas according to the voltage of the DC grid and the state of charge of the battery (SOC) as shown in FIG.

The area A is the area that controls the grid power using the battery as maximum power (100% in the example) when the DC grid voltage is within a certain range (for example, -5% -3% and -3% -5% , And the equivalent resistance (R V - 100 % ) at this time can be calculated in the same manner as in Equation (4). In the region above + 3% of the rated voltage, surplus power is increased, so the output of the distributed power source is reduced. Less than -3% of the rated voltage is the region where the power is insufficient in the DC grid. Keep balance.

The area B is a region where the DC grid voltage is within the range of -3% to 3% of the rated voltage and the battery controls the grid power with normal power (for example, 70%) and is a normal operating region. In order to increase the life of the battery, the battery is managed such that the battery charge / discharge power is normally used only at the normal power (70%, for example) instead of the maximum power. The equivalent resistance (R V - 70% Can be obtained.

C area is a protection area for overcharge and over-discharge of the battery. When the state of charge (SOC) exceeds the predetermined operating range, the amount of electric power for charging / discharging the battery is rapidly reduced to protect the battery. The operating power at this time is the minimum power (for example, 10% power) and an example of the calculated equivalent resistance (R V - 10%) is shown in Equation (6).

As shown in FIG. 3, the gradient of the droop curve changes in each region because the equivalent resistance Rv forming the droop curve changes as the power of the battery changes.

&Quot; (4) "

Figure 112013009418314-pat00006

&Quot; (5) "

Figure 112013009418314-pat00007

&Quot; (6) "

Figure 112013009418314-pat00008

The values used in the equations (4) to (6) are calculated values, for example, regarding the grid voltage, the variation of the grid voltage, the capacity of the battery, etc., Of course.

Thus, by dividing the operating power of the battery into three levels according to the state of charge (SOC) of the battery and the grid voltage, the equivalent resistance Rv of the droop controller 130 is changed, Power balance control function.

Fig. 4 shows a cooperative control algorithm of the wind power generator (WG), the photovoltaic generator (PV), the engine generator (EG) and the energy storage device (ES), which constitute the power elements constituting the independent microgrid.

First, the wind generator (WG) and the photovoltaic generator (PV) have two operation modes according to the grid voltage (Vdc). When the grid voltage is within a certain range (for example, within the range of -5% to 5% of the rated voltage in FIG. 4), the wind power generator and the solar generator operate so as to obtain the maximum power by the MPPT control method mode). If the grid voltage rises to more than 5% of the rated voltage, the grid will be supplied with energy that exceeds the capacity of the battery, so wind power generators and solar generators will stop generating electricity and operate in standby mode. If the grid voltage drops below a certain value (for example -3%) of the rated voltage during operation in the standby mode, the power supplied to the grid is insufficient. Therefore, the wind power generator and the solar power generator are operated again, do. In this way, the wind generator (WG) and the photovoltaic generator (PV) operate in the maximum power mode when the grid voltage is within a certain range and operate in the standby mode when the grid voltage is higher than a certain value.

The engine generator (EG) is a distributed power supply that can regulate the output and performs coordinated control in three states (3-states) according to the voltage of the DC grid. Specifically, when the voltage of the DC grid is in a certain range (for example, -3% to 3%), it operates in a normal mode and is controlled to supply power required by the load. The engine generator may be controlled to supply a predetermined constant power in the normal mode and may be controlled to vary the supply power in accordance with the power demand of the load. In the case of supplying a constant power, the engine generator can operate under the condition of producing the electric power with the highest efficiency. Therefore, there is an advantage that the fuel efficiency can be increased. In the case of varying the supply electric power according to the load power demand, The balance control function is shared, and the power balance of the grid can be controlled more efficiently.

If the grid voltage is higher than 3% of the rated voltage (103% of the rated voltage) while the engine generator is operating in normal mode, the power supply is sufficient. Therefore, the engine generator operates by switching to the minimum power mode, And also reduces fuel consumption. In the minimum power mode, when the grid voltage falls below 1% of the rated voltage (that is, 101% of the rated voltage), it switches back to the normal mode. If the grid voltage drops below -3% of the rated voltage (97% of the rated voltage) while operating in the normal mode, the power supplied to the grid is insufficient. Therefore, the engine generator operates in the maximum power mode, Increase supply. If the grid voltage is higher than -1% of the rated voltage (ie, 99% of the rated voltage) during operation in the maximum power mode, the power supplied to the grid is large. In this way, the engine generator operates in one of three states according to the grid voltage, so that the battery operates in a coordinated manner to regulate the power balance while reducing the fuel consumption by minimizing the output when there is room in the power of the grid.

Next, the control of the battery, which is an energy storage device, will be described. Excessive charging or discharging of the battery adversely affects the battery life. Therefore, in the case of the battery, not only the grid voltage but also the state of charge (SOC: stae of charge) of the battery is taken into account.

Referring to FIG. 4, use of the maximum value (MAX) and the minimum value (MIN) in the SOC region of the battery may adversely affect the service life. For example, charge mode is 55% ~ 85%). In this normal mode, 70% or 100% power control is performed depending on the DC grid voltage. When the state of charge (SOC) of the battery exceeds the predetermined HIGH or falls below LOW, it operates in a low power mode in which the equivalent resistance of the battery drop control unit is adjusted to convert the battery charge capacity to 10%. In the low power mode, when the battery charging state returns to the normal region again, the normal mode is operated again. In FIG. 4, a 5% decrease value of High (95% of High value) and a 5% rise value of Low (105% of Low value) are used as a reference value for entering the normal mode in the low power mode, Hysteresis function is provided to prevent frequent switching between mode and low power mode.

5 is a view for explaining the operation of the battery in consideration of not only the state of charge (SOC) of the battery but also the grid voltage. In the present invention, in order to protect the battery, the case where the charged state of the battery is within a predetermined range is set as a normal region (for example, 55% to 85% . When the state of charge of the battery is in a normal range, the grid voltage is set to a power of 70% within a certain range of the rated value (for example, -3% to +3%) according to the grid voltage, It is controlled at a power of 100%. That is, even when the charged state of the battery is in the normal range, 100% of the power capability is not used at normal times (when the grid voltage is within the proper range), and when the grid voltage is out of the proper range, So that the battery life is prolonged.

If the battery charge state exceeds the upper limit value (for example, 85%), the battery is overcharged. In this case, in consideration of the grid voltage, the grid voltage is controlled to a low power (for example, 10% power) when the battery is continuously charged because the grid voltage is higher than the rated value. If the grid voltage is lower than the rated value, Management.

If the battery charge falls below the lower limit (for example, 55%), it is overdischarged. In this case, considering the grid voltage, if the grid voltage is lower than the rated value, the battery is in a state of continuously discharging. Therefore, when the battery is charged because the grid voltage is higher than the rated power (for example, 10% .

As described above, by controlling the battery in consideration of both the state of charge (SOC) of the battery and the grid voltage, it is possible to balance the power of the grid while reducing the burden on the battery. Here, controlling the charge power of the battery to 100%, 70%, 10%, etc. is performed by changing the equivalent resistance Rv of the output terminal of the battery droop controller 130 as described above. Although the values exemplified by the reference value of the state of charge of the battery, the reference value of the grid voltage, and the power of the battery are selected as the values at which the effects of the battery protection and the grid power control according to the present invention can be maximized, It is needless to say that other values may be used depending on the characteristics of the optical disk.

The operation of distributed power sources (wind power generator, solar array and / or engine generator) and batteries has been described separately, and in the following, with reference to FIGS. 4 and 5 in terms of coordinated operation for control of grid power Explain.

In the case where the state of charge of the battery is normal and the grid voltage is within a certain range (± 3% in the example of FIGS. 4 and 5), the battery uses the power reserve capacity of 70% And serves as the primary controller for regulating the power balance of the microgrid while supplying or accepting power.

When the grid voltage becomes higher than a certain range, the power supplied to the grid is greater than the power received by the battery. Therefore, the battery converts to 100% power-saving capability to accommodate the grid power while the engine generator is switched to the minimum output, Cooperate to control balance. If the grid voltage continues to rise and rises above 5% of the rated value, the wind power generator or solar array will also switch to standby mode, stopping the power supply and cooperating with the power control function of the battery. The reason for converting the engine generator to the minimum output before the wind generator or solar array is to reduce the fuel consumption since the engine generator consumes the fuel to generate electric power. When the grid voltage returns to normal, the battery regulates power with 70% power reserve capacity and converts distributed power sources into normal operation. 4 shows an example in which the distributed power sources are switched to the normal operation mode (the grid voltage is reduced to -3% or less of the rated voltage for the wind power generator and the solar array, and the engine generator is 1% ) Other conditions may apply.

If the grid voltage drops below -3% of the rated voltage when the battery is in a normal charging state, the grid is powered down, so the battery switches to a 100% power reserve capacity to supply power to the grid, To assist the power balance function of the battery. In this case, since the power is insufficient, the wind power generator and the solar array keep the maximum power mode continuously. When the grid voltage rises to the normal range, the battery and the engine generator will switch back to normal operating mode.

When the charged state of the battery is out of the normal range, the operation is different depending on whether it is the charging mode or the discharging mode (see FIG. 5). If the charge mode of the battery is higher than the normal range, or if the charge mode (grid voltage is higher than the rated voltage) or the charge state of the battery is lower than the normal range, the battery is overcharged or overdischarged It protects the battery by reducing the charge / discharge power of the battery to 10%. In this case, since the capacity of the battery to regulate the grid power balance is reduced, the grid power is supplementarily controlled by the mode switching function according to the grid voltage of the distributed power sources as described above. On the other hand, even when the charged state of the battery is out of the normal range, unless it is continuously charged in the overcharge state or is continuously discharged in the over discharge state (that is, when the charged state is higher than the normal range, Is below the normal range but the grid voltage is higher than the rated value), the battery operates in the same manner as when the charging state is in the normal range.

When the battery is in the normal charge state, the grid power is mainly controlled. The distributed power sources detect the grid voltage and cooperatively operate the grid power control of the battery. When the battery is out of the normal charge range, And control distributed power sources to control the grid power, thereby effectively controlling the grid power with simple control method even in the absence of a central controller or mutual information transmission for controlling between the battery and distributed power sources .

As described above, in the stand-alone micro grid, the operation of the battery and the distributed power sources is controlled cooperatively based on the state of charge (SOC) of the battery and the grid voltage, thereby reducing the burden on the battery and efficiently controlling the power balance of the microgrid . In particular, the battery has an effect of reducing the excessive burden of the battery and increasing the reliability of the system by adjusting the equivalent resistance of the droop controller according to the charging state and the grid voltage by adjusting the power of the battery in three steps.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, Those skilled in the art will appreciate that many modifications and variations are possible in light of the above teachings. Accordingly, all such appropriate modifications and changes, and equivalents thereof, should be regarded as within the scope of the present invention.

110: Energy storage device (battery)
120: Power Conversion Converter for Energy Storage
130: ES droop controller
131: Voltage controller of the ES droop controller 132: Equivalent resistance
133: PI compensator of voltage controller 210: Load
220: load power conversion converter 310: wind power generator (WG)
320: a power conversion converter for a wind power generator 330: a WG cooperative controller
410: Solar Array (PV) 420: Power Converter for Solar Power Converter
430: PV co-ordination controller 510: Engine generator (EG)
520: Power converter for engine generator 530: EG cooperative controller

Claims (20)

  1. A cooperative droop control device for a stand-alone microgrid comprising at least one or more distributed power sources and an energy storage device,
    The voltage reference value (Vdroop) of the controller of the energy storage device is controlled by a droop control method set by the following equation (1) so that the energy storage device supplies power to the microgrid or receives power, A droop controller of the energy storage device for adjusting the power balance of the energy storage device; And
    Wherein the distributed power source supplies power to the microgrid and controls power supplied from the distributed power source to the microgrid according to the grid voltage so that the energy storage device cooperatively operates to control the power balance of the microgrid A power cooperating controller; , ≪ / RTI &
    The droop controller of the energy storage device operates in a normal mode when the state of charge (SOC) of the energy storage device is within a third predetermined range (high to low), and when the state of charge is out of a third predetermined range, Wherein the control unit is operable to control the droplet control unit so that the droplet is controlled to operate.
    [Equation 1]
    Figure 112014027820008-pat00009

    Where V DROOP is the voltage control reference value, V Rate is the rated voltage, Rv is the equivalent resistance, and I ES is the output current of the energy storage device.
  2. The method according to claim 1,
    Wherein the distributed power source comprises at least one of a wind power generator or a solar array,
    The wind power generator or solar array includes a respective cooperative controller,
    The cooperative controller of the wind power generator or the cooperative controller of the solar array supplies power in the maximum power mode when the grid voltage is within the first predetermined range and switches to the standby mode when the grid voltage becomes higher than the first predetermined range To control;
    A cooperative droop control device for a stand-alone micro-grid,
  3. 3. The method of claim 2,
    Wherein the first predetermined range is from 95% to 105% of the rated voltage. ≪ RTI ID = 0.0 > 11. < / RTI &
  4. The method according to claim 1,
    Wherein the distributed power source includes an engine generator and a coordination controller for an engine generator,
    The coordinator controller for the engine generator operates in a normal mode when the grid voltage is within the second predetermined range and operates in the minimum power mode when the grid voltage is higher than the second predetermined range and when the grid voltage is lower than the second predetermined range Controlling the engine generator to have three states operating in the maximum power mode
    A cooperative droop control device for a stand-alone micro-grid,
  5. 5. The method of claim 4,
    Wherein the second predetermined range is in the range of 97% to 103% of the rated voltage. A cooperative droop control device for a stand-alone micro-
  6. delete
  7. The method according to claim 1,
    Wherein the third predetermined range of the state of charge of the energy storage device is between 55% and 85%. ≪ RTI ID = 0.0 > A < / RTI &
  8. The method according to claim 1,
    The low-power mode increases the fluctuation of the voltage control reference value (V droop ) with respect to the current by decreasing the equivalent resistance value of the droop controller to a value greater than the equivalent resistance value in the normal mode, thereby reducing the power consumption of the energy storage device A cooperative droop control device for a stand-alone microgrid
  9. The method according to claim 1,
    The equivalent resistance value of the droop controller is set differently according to the grid voltage even in the normal mode in which the charging state of the energy storage device is within the third predetermined range
    A cooperative droop control device for a stand-alone micro-grid,
  10. 10. The method of claim 9,
    The equivalent resistance value of the droop controller may be set differently according to the grid voltage by setting the equivalent resistance value when the grid voltage is out of the fourth constant range to be smaller than the equivalent resistance value when the grid voltage is within the fourth constant range, And controls the power storage capacity of the energy storage device to be increased when the grid voltage is out of the fourth predetermined range
    A cooperative droop control device for a stand-alone micro-grid,
  11. A cooperative droop control method for a stand-alone microgrid comprising at least one or more distributed power sources and an energy storage device,
    Wherein the energy storage device is controlled by a droop control method in which a voltage reference value (Vdroop) is set by the following equation (1) so that the energy storage device supplies power to the microgrid or receives power, Controlled to adjust the balance,
    Wherein the distributed power source supplies power to the microgrid and controls power supplied from the distributed power source to the microgrid according to the grid voltage so that the energy storage device cooperatively operates to control the power balance of the microgrid Is controlled,
    The energy storage device operates in a normal mode when the state of charge (SOC) of the energy storage device is within a third predetermined range (high to low), and in a low power mode when the state of charge is out of a third predetermined range Wherein the coarse droplet control method is a coarse droplet control method for a stand-alone microgrid.
    [Equation 1]
    Figure 112014027820008-pat00010

    Where V DROOP is the voltage control reference value, V Rate is the rated voltage, Rv is the equivalent resistance, and I ES is the output current of the energy storage device.
  12. 12. The method of claim 11,
    Wherein the distributed power source comprises at least one of a wind power generator or a solar array,
    Wherein the wind power generator or the solar array is controlled to supply power in a maximum power mode when the grid voltage is within a first predetermined range and to switch to a standby mode when the grid voltage becomes higher than the first predetermined range;
    A cooperative droop control method for a stand-alone microgrid
  13. 13. The method of claim 12,
    Wherein the first predetermined range is 95% to 105% of the rated voltage. A cooperative droop control method for a stand-alone microgrid
  14. 12. The method of claim 11,
    Wherein the distributed power source comprises an engine generator,
    The engine generator operates in a normal mode when the grid voltage is within a second predetermined range and operates in a minimum power mode when the grid voltage is higher than the second predetermined range. When the grid voltage is lower than the second predetermined range, Lt; RTI ID = 0.0 >
    A cooperative droop control method for a stand-alone microgrid
  15. 15. The method of claim 14,
    Wherein the second predetermined range is in the range of 97% to 103%. A cooperative droop control method for a stand-alone microgrid
  16. delete
  17. 12. The method of claim 11,
    Wherein the third predetermined range of the state of charge of the energy storage device is 55% to 85%. ≪ RTI ID = 0.0 > 8. < / RTI &
  18. 12. The method of claim 11,
    The low power mode increases the fluctuation of the voltage control reference value (V droop ) with respect to the output current by increasing the equivalent resistance value of the droop controller to be greater than the equivalent resistance value in the normal mode, thereby reducing the power consumption of the energy storage device Cooperative droop control method for a stand-alone microgrid
  19. 12. The method of claim 11,
    The equivalent resistance value of the droop controller is set differently according to the grid voltage in the normal mode in which the state of charge of the energy storage device is within the third predetermined range
    A cooperative droop control method for a stand-alone microgrid
  20. 20. The method of claim 19,
    The equivalent resistance value of the droop controller may be set differently according to the grid voltage by setting the equivalent resistance value when the grid voltage is out of the fourth constant range to be smaller than the equivalent resistance value when the grid voltage is within the fourth constant range, When the grid voltage is out of the fourth certain range, the power storage capacity of the energy storage device is increased
    A cooperative droop control method for a stand-alone microgrid
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