KR20210067102A - Operating system of solar inverters and PCS with grid compensation - Google Patents

Abstract

The present invention relates to a system for operating a solar inverter and a PCS including a grid compensation function, which can be easily connected to a grid while improving the stability and reliability of a converter-based generator by compensating for active power and reactive power in accordance with an operating algorithm function of following a solar power generation pattern which is changed every day and storing the same in an ESS, and a grid situation. The system of the present invention comprises: a solar power generation unit for producing electric energy from sunlight; a solar inverter for converting the electric energy produced by the solar power generation unit into AC power, and outputting the same; the Korea Electric Power Corporation grid for receiving the AC power converted from the solar inverter to supply the same to a load requiring power; a PCS for receiving the AC power converted from the solar inverter to convert the same into DC power, and outputting the same; an ESS for receiving the DC power converted by the PCS, and storing the same; and a PMS for determining the amount of compensation of a power grid by receiving the amount of solar power generation of the solar power generation unit and an SOC of the ESS, and receiving grid state information on the Korea Electric Power Corporation grid to check whether the capacity of a line and power sale are normal.

Description

Operating system of solar inverters and PCS with grid compensation

The present invention relates to an operating system of a solar inverter and a PCS including a system compensation function, and in particular, a solar including a system compensation function that realizes optimal operation for grid compensation and business feasibility without changing the operating algorithm or conflicting It relates to the optical inverter and PCS operating system.

The solar power business has been added to the existing system, but as the solar power business increases, the systems and lines for linking with the solar power are saturated. And the standard that requires the ability to compensate according to the state of the system is also applied to the converter based generator. It is difficult to expect great business feasibility only with the amount of solar power that varies from moment to moment depending on the season, time, temperature, and insolation.

Therefore, due to efficient storage of PV power generation, schedule mode, and compensation control that can be applied regardless of solar power generation, ESS and PCS are more often installed and operated at the site where PV inverters are installed.

Due to this, the initial installation cost is higher, but the power offered by the power provider can be sold at a higher price when needed, thereby shortening the payback time.

In general, the ESS operating system is a system that charges power to a battery and discharges it when necessary, and there are various operating methods depending on the purpose. For energy saving in buildings, it is charged during light-load hours when electricity rates are low and discharged during peak-load times when electricity rates are high, or used to control the maximum demand power.

In addition, the ESS operating system for solar power is operated to charge the ESS generated by the solar power plant during the daytime and discharge it in the evening. In the KEPCO system, it is used for frequency adjustment (FR) and is charged when the frequency is low. There are many differences in the method of charging and discharging depending on the purpose of use, such as discharging when high and high.

However, when using the ESS operating system, it must be controlled while watching the SOC, which is the state of charge or the charge rate of the battery. If the battery has a rated capacity, if the battery is operated to be fully discharged (full discharge) with an SOC of 0% or fully charged (full charge) with an SOC of 100%, the battery life will be shortened or there is a risk of fire if overcharged. SOC does not operate in the 0-100% range, but operates in a specific range.

However, the solar power/ESS promotion policy presented by KEPCO, the current power system operator, sets the time period suggested as the schedule mode, but the solar power generation pattern is different every day, and the consumption pattern varies according to the day of the week and season for each grid line. Optical/ESS operation causes an overload on the system and line.

The present invention is to solve the above problems, and by compensating for active power and reactive power according to the operating algorithm function and system conditions that follow the pattern of solar power generation that change every day and store it in the ESS, the stability of the converter-based generator and It aims to provide an operating system of a solar inverter and PCS that includes a system compensation function that improves reliability and facilitates connection to the grid.

The solar inverter and the PCS operating system including the system compensation function according to the present invention for achieving the above object includes a solar power generation unit that produces electrical energy from sunlight, and the electric energy produced from the solar power generation unit A solar inverter that converts and outputs AC power, a KEPCO system that receives AC power converted from the solar inverter and supplies it to a load that requires power, and a DC power supply by receiving the AC power converted from the solar inverter PCS that converts and outputs PCS, ESS that receives and stores the DC power converted from the PCS, receives the amount of solar power generated by the solar power generation unit and SOC of the ESS, determines the amount of compensation for the power system, and determines the amount of compensation for the KEPCO system) It is characterized in that it includes a PMS that receives the system status information of the line and checks whether there is an abnormality in the capacity of the line and the power sale.

The operating system of the solar inverter and the PCS including the system compensation function according to the embodiment of the present invention has the following effects.

In other words, it improves the stability and reliability of the converter-based generator by compensating for active and reactive power according to the operating algorithm function that tracks the solar power generation pattern that changes every day and stores it in the ESS and the situation of the system. can be done easily

1 is a configuration diagram schematically showing an operating system of a PV inverter and PCS for ESS according to the present invention;
Figure 2 is a circuit diagram schematically showing the solar inverter of Figure 1
3 is a configuration diagram schematically showing the PMS of FIG. 1

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, detailed descriptions of well-known functions or configurations that may obscure the gist of the present invention in the following description and accompanying drawings will be omitted. Also, it should be noted that throughout the drawings, the same components are denoted by the same reference numerals as much as possible.

The terms or words used in the present specification and claims described below should not be construed as being limited to their ordinary or dictionary meanings, and the inventors have appropriate concepts of terms in order to best describe their inventions. It should be interpreted as meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined in Therefore, the embodiments described in this specification and the configurations shown in the drawings are only the most preferred embodiment of the present invention, and do not represent all of the technical spirit of the present invention, so at the time of the present application, various It should be understood that there may be equivalents and variations.

1 is a configuration diagram schematically showing an operating system of a solar inverter and PCS including a system compensation function according to the present invention, FIG. 2 is a circuit diagram schematically showing the solar inverter of FIG. 1, and FIG. It is a schematic diagram showing the PMS.

As shown in FIG. 1, the solar inverter and the PCS operating system including the system compensation function according to the present invention includes a photovoltaic power generation unit 110 that produces electric energy from sunlight, and the solar power generation unit 110 ), a solar inverter 120 that converts the electrical energy produced to AC power and outputs it, and the KEPCO system 130 that receives the AC power converted from the solar inverter 120 and supplies it to a load requiring power; and , a PCS 140 that receives the AC power converted from the solar inverter 120 and converts it into DC power and outputs it, and an ESS 150 that receives and stores the DC power converted from the PCS 140 ; The amount of solar power generation of the solar power generation unit 110 and the SOC of the ESS 150 are received to determine the amount of compensation for the power system, and the system state information of the KEPCO system 130 is transmitted to the capacity and power sales of the line. It is made including the PMS 160 for checking whether there is an abnormality.

Here, the solar power generation unit 110 generates DC power by converting solar energy into electrical energy in a state of being composed of a plurality of solar cells.

The solar cell is for generating electricity by condensing sunlight incident from the outside, and generally silicon and a composite material are mainly used. Specifically, the solar cell is used by bonding a P-type semiconductor and an N-type semiconductor, and uses the photoelectric effect to generate electricity by receiving sunlight. Most solar cells are made of a large-area P-N junction diode, and the electromotive force generated at the anode end of the P-N junction diode is connected to an external circuit to be used.

The minimum unit of the solar cell is called a cell, and in practice, the solar cell is rarely used as it is. This is because the voltage required for actual use is from several V to tens or hundreds of V or more, but the voltage from one cell is about 0.5 V, which is very small. For this reason, a number of unit solar arrays are connected in series or parallel with the required unit capacity. are using

In addition, when the solar cell is used outdoors, since it is subjected to various harsh environments, a plurality of cells connected to the required unit capacity are configured and used in a package to protect the plurality of cells from the harsh environment.

A junction box is provided at the rear end of the solar cell to collect voltages of the same polarity output from the solar cell into one connection point.

As shown in FIG. 2 , the solar inverter 120 includes a plurality of switching elements 121 and a grid-connected filter 122 .

The plurality of switching elements 121 are input from the DC voltage through switching of an on or off state based on a PWM (Pulse Width Modulation) signal for controlling the solar inverter 120 . The DC voltage is converted into an AC voltage.

The grid-connected filter 122 includes a power conversion device, grid-side inductors (Li, Lg), and a filter capacitor (Cf). That is, the system-linked filter 122 may be implemented as an LCL filter. Alternatively, the systematically linked filter 122 may be implemented as an LC filter.

Here, the LCL filter may be represented by a power converter and system-side inductors (Li, Lg) and a filter capacitor (Cf). When the LCL filter is used, a resonance phenomenon occurs by L and C, and a resonance band is formed around a resonant frequency.

The PCS 140 converts the DC power produced by the solar power generation unit 110 into AC power through the solar inverter 120 , converts it back into DC power, and stores it in the ESS 150 . In addition, the PCS 140 may convert the DC power stored in the ESS 150 into AC power and supply it to the load.

The storage information of the ESS 150 is information on the type and charging time of a battery whose capacity efficiency varies according to the size of power during charging/discharging. More specifically, the storage information of the ESS 140 represents the load capacity, and is information on how much rectification is stored or the current amount of charge.

Meanwhile, the solar power generation unit 110 generates a difference between the actual power generation amount and the reference power generation amount according to changes in the location, season, and climate of the installed region as well as temperature and weather. That is, since the actual power generation pattern of the solar power generation unit 110 is different every day, the present invention receives the solar power generation amount and the SOC of the ESS 150 from the PMS 160 and calculates and compensates the power system compensation amount.

To this end, the PMS 160 is configured as shown in FIG. 3 , and is composed of a power system compensation unit 161 and an optimal operation unit 162 to determine the amount of charge of the ESS based on the power generation state of the solar power generation unit 110 . and determine the amount to be sold to the KEPCO system 130 based on the ESS status and business feasibility. A control command for compensating according to the system state of the KEPCO system 130 is executed.

_{Therefore, the present invention determines the charging pattern (P exp} ) to be charged in the ESS 150 during one day in consideration of the weather conditions, system conditions, days and seasons of the solar power generation unit 110 .

_{For example, if the charging pattern (P exp} ) is determined early in the case of charging in the early, middle, and late stages of solar power generation due to weather or system conditions, not only can the capacity waste of the ESS 150 be reduced, but also You can flexibly respond accordingly. This not only provides efficient charging, but also compensates for system stability and achieves optimal operation at the same time.

First, the power system compensation unit 161 receives the solar power generation amount P _pv of the photovoltaic power generation unit 110 and the SOC of the ESS 150, which vary from moment to moment, and determines the power system compensation amount.

And check the maintenance state of the KEPCO system 130 to check whether there is any abnormality in the line capacity and power sales. Alternatively, the amount of active and reactive power to be compensated for by the request of the KEPCO system 130 is checked.

In general, since the KEPCO system 130 is stabilized, there is no amount to be compensated, and most of the amount of solar power generation (P _pv ) is charged in the ESS 150 or sold directly to the KEPCO system 130 .

To determine this, the optimal operation unit 162 determines the amount of power (Pess) to be charged in the ESS 150 .

At this time, in order to prevent the collision of the optimal operation unit 162 and the power system compensation unit 161 of the PMS 160, the operating variable D is placed and D = 0 is a common case, so the profit business of solar and ESS is carried out. do.

However, when compensation is required in the KEPCO system 130, the power system compensation unit 161 may increase the amount of power to be compensated by increasing the operating variable D to a positive value other than 0.

When the amount of power system compensation requested by the KEPCO system 130 is less than the amount that can be provided by the power system compensation unit 161, the operating variable D has a value between 0 and 1, and power system compensation It is determined through the RMS magnitude of the frequency and voltage observed by the unit 161 .

When the amount of power required for compensation is greater than the amount that can be compensated by the KEPCO system 130, the operating variable D becomes 1 to stop energy charging, and both the solar inverter 120 and the PCS 140 participate in compensation. .

When D=1, stability and compensation functions are performed, when 0 < D < 1, compensation-predicted behavior within the variation range according to SOC is performed, and when D=0, it operates in the basic schedule mode.

Here, ω ₁ is the objective function weight 1, ω ₂ is the objective function weight 2, ω ₃ is the objective function weight 3, respectively, c ₁ is the amount of electrical energy sold at 5 times the weight, and c ₂ is the cost of selling without weight. It represents the amount of electrical energy, Pexp is a power reference for filling the generated energy to the capacity of the battery, Pcap.loss is the power loss caused by capacity efficiency, and Psell represents the amount of power sold without weight.

The weights w1, w2, and w3 are input in order to appropriately adjust them because the grid status of the KEPCO system and the capacity of the ESS are different.

In the Pcap.loss, energy that cannot be used due to loss due to capacity efficiency is weighted 5 times according to the market price. It minimizes the monetary loss suffered by the user as much as the loss caused by putting a large amount of power without considering capacity efficiency.

The content corresponding to the Psell is to reduce the amount sold in real time without a weight without charging a part of the power generation amount in the ESS 150 . Although it is beneficial to have less power loss due to capacity efficiency due to reduced power of the battery, it is a device that can properly prepare and operate generation patterns and price information by reflecting the price information that changes every moment.

Finally, (Pexp-Pess) ² suggests that the system follows the predicted power generation pattern and charge/discharge amount due to special system conditions.

Due to this, it is possible to simultaneously implement optimal operation for system compensation and business feasibility without changing the operation algorithm or conflicting.

The existing solar/energy storage system inputs and outputs power according to the solar power generation/energy storage device generation time period suggested by the government. Due to this, side effects due to the schedule mode such as duck curve occur in systems with many solar and ESS-linked systems, and the instability of the system increases.

In addition, converter-based generators other than the existing diesel generators have been excluded from improving the stability and reliability of the system because they do not have or lack an active power/reactive power compensation function, thereby limiting the capacity connected to the system.

However, in the present invention, the system compensation capability is loaded into the operation algorithm prior to the profit business due to solar power and ESS through the operation variable D, and the two functions are substituted into one optimization problem and adjusted.

The present invention has solar power generation and ESS charging and discharging and system compensation functions for profit industry, so it is easier to connect to the grid than other general solar and ESS connected systems, and stability and reliability can be improved.

The embodiments of the present invention described above are merely exemplary, and those of ordinary skill in the art to which the present invention pertains will appreciate that various modifications and equivalent other embodiments are possible therefrom. Therefore, it will be well understood that the present invention is not limited to the forms recited in the above detailed description. Therefore, the true technical protection scope of the present invention should be determined by the technical spirit of the appended claims. Moreover, it is to be understood that the present invention covers all modifications, equivalents and substitutions falling within the spirit and scope of the invention as defined by the appended claims.

110: solar power generation unit 120: solar inverter
130: KEPCO 140: PCS
150: ESS 160: PMS

Claims (5)

A solar power generation unit that produces electrical energy from sunlight,
A solar inverter for converting the electrical energy produced by the solar power generation unit into AC power and outputting it;
A KEPCO system that receives AC power converted from the solar inverter and supplies it to a load that requires power;
a PCS that receives the AC power converted from the solar inverter and converts it into DC power and outputs;
an ESS for receiving and storing the DC power converted from the PCS;
PMS that receives the amount of photovoltaic power generation from the photovoltaic unit and the SOC of the ESS to determine the amount of compensation for the power system, and receives the system state information of the KEPCO system) to check whether there is an abnormality in the capacity of the line and the power sale. The operating system of the solar inverter and PCS including a system compensation function, characterized in that made by According to claim 1, wherein the PMS is composed of a power system compensation unit and an optimal operation unit to determine the amount of charge of the ESS based on the power generation state of the solar power generation unit, and the amount to be sold to the KEPCO system based on the ESS state and business feasibility. The operating system of the solar inverter and PCS with a grid compensation function, characterized in that it determines. The operating system of claim 1, wherein the PMS executes a control command to compensate according to the system state of the KEPCO system. According to claim 1, wherein the PMS is a solar inverter including a system compensation function, characterized in that for determining the charging pattern to be charged in the ESS for one day in consideration of the weather conditions, system conditions, days and seasons of the solar power generation unit; PCS operating system. The operating system of claim 1, wherein the PMS checks the amount of active and reactive power to be compensated according to the request of the KEPCO grid.

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