KR102133686B1 - Automatic Control Algorithm for Improved Stability and Charge-Discharge Efficiency - Google Patents

Abstract

Disclosed is an algorithm of an energy management system which calculates an estimated excess generation amount (Eo) and a control section margin (Cb) based on an expected generation amount (Ef) based on a generation amount (Pf) of a previous day, and controls charging by distributing an output value (Ct) which can be obtained for each control section using the control section margin (Cb) to an energy storage system (ESS) from a renewable energy certificate (REC) charge start time to an expiration time. According to the present invention, discharging immediately after full charging minimizes a pause time with high fire frequency. In addition, efficiency of power conversion system (PCS) facilities is increased when operating with a reduction between 70 to 80% than when operating at the rated (100%), and reduction operation of a PCS is possible, thereby increasing power conversion efficiency. In the case of a battery, the higher c-rate (battery charging and discharging rate) is (quick charge), the shorter the lifespan. The PCS reduction operation of the present invention can lower the battery charging rate, thereby contributing to battery life.

Description

Energy Control System with Automatic Control Algorithm for Improved Safety and Charge/Discharge Efficiency {Automatic Control Algorithm for Improved Stability and Charge-Discharge Efficiency}

The present invention relates to an energy management system to which an automatic charging and discharging control algorithm with enhanced safety and efficiency of an energy storage device (ESS) in the field of intelligent automation technology is applied.

With the recent 4th Industrial Revolution era, intelligent automation technologies and markets are growing as the core technologies of the next generation of smart new industries, ranging from smart new industries to new and renewable energy fields, according to the trend of versatility and open control and automation solutions.

In the energy-related field, the distribution of ESS (Energy Storage System, ESS), an essential system for realizing smart grids, smart cities, and smart factories is expanding with the expansion of renewable energy. In order to strengthen the system, automatic control algorithm technology based on industrial embedded PC-based control technology is required.

Meanwhile, energy storage refers to storing energy using a device or a physical medium. The device used for this is called an accumulator, and the entire system in a wider range is called an "Energy Storage System (ESS)." Even small batteries used in general household batteries or electronic products can convert and store electric energy into other forms of energy, but these small power storage devices are not referred to as ESSs, but are usually a single system that stores hundreds of kWh or more. Is called "ESS". The ESS can be installed and operated in power generation, transmission and distribution, and customers in the power system, such as frequency regulation, stabilizing the output of new and renewable generators, peak shaving, load leveling, emergency power supply, etc. Used as a function. ESS can contribute to improving energy utilization efficiency, improving utilization of new and renewable energy, and stabilizing the power supply system by storing and supplying when electric energy is used less.

The energy management system using the ESS has an operation time of charging from 10:00 to 16:00 and discharging at a time excluding the charging time. In addition, it shows the operating mode of charging from 10 o'clock to buffer as soon as possible and discharging after 1 to 2 hours of rest after 16 o'clock. Here, having a pause of 1 to 2 hours before discharge after full charge is because the battery manufacturer has requested that the warranty condition has a pause of 2 hours after full charge. In addition, when the amount of photovoltaic power was generated by 18:00 and the amount of photovoltaic power generation and ESS discharge were simultaneously performed, the discharge was conducted after 17:00 or 18:00 for reasons that could exceed the contract-linked capacity. Ignited in the air after charging was completed.

Registered Patent Publication No. 10-2039677 (announcement date 01 November 2019) Registered Patent Publication No. 10-2050803 (announcement date 04 Dec 2019)

The object of the present invention, when the weather is good, when the solar power is high, when charging the PCS at the rated value, it is fully charged at 13-14 pm. However, the PCS reduction operation is performed using the power generation prediction algorithm to be fully charged at 16:00. The aim is to provide an energy management system to which a control algorithm capable of driving adjustment is applied.

In addition, another object of the present invention is to provide an energy management system for realizing fire prevention of ESS by delaying the buffering time of the ESS by using a power generation prediction algorithm and immediately discharging without a rest time after buffering.

In addition, another object of the present invention, if the discharge starts immediately without a rest period, when the sunshine is good even at 16:00, the sum of PV power generation + ESS discharge amount may exceed the contracted capacity of KEPCO, and PV to prevent this. It is intended to provide an energy management system that improves the efficiency of ESS by transmitting power using an ESS discharge operation algorithm.

The object of the present invention as described above is to obtain the expected excess power generation (Eo) and the control interval margin (Cb) based on the expected power generation (Ef) based on the previous day power generation (Pf), each control using the control interval margin (Cb) The output value (Ct) that can be obtained for each section is achieved by an energy management system that distributes and controls charging by distributing it to the ESS from the start time to the expiration time of the REC (Renewable Energy Certificate).

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The estimated power generation (Ef) is

ts: REC charging start time (10 o'clock)

te: REC charging expiration time (16:00)

The expected excess power generation (Eo) is

Ke: ESS installation capacity

Ks: REC 충전 허용 시간 동안의 제어구간마진을 결정지을 시간The control section margin (Cb) is

Ks: Time to determine control section margin during REC charging allowable time

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The output value (Ct) that can be obtained for each control section is:

Pr: PV output value

Here, the output value (Ct) that can be obtained for each control section may be applied to the adjusted control interval margin (Cu) obtained in proportion to the size of the expected excess power generation (Eo).

The adjusted control interval margin (Cu) is

The output value (Ct) that can be obtained for each control section is:

Pr: PV output value

In addition, the output value (Ct) that can be obtained for each control section is an additional correction value to the adjusted control section margin (Cu) based on a softplus relationship function between the elapsed charging time and the ratio of the actual power generation to the expected power generation. The final correction control interval margin (Cv) obtained by applying may be applied.

The final correction control interval margin (Cv) is

On the other hand, the object of the present invention is also distributed by the energy management system for discharging and charging in the ESS from the start time of the REC charge to the expiration time according to the output value (Ct) that can be obtained for each control section, and discharge control according to the equation Can be achieved.

The discharge value (Cd) is,

Kg: maximum output of solar power contract

Pfs: Early short-term predicted power generation (or actual power generation at the time of control)

Km: discharge control margin

According to the present invention, the efficiency of the PCS facility is higher when it is reduced between 70 and 80% than when it is operated at the rated (100%), and the present invention can reduce the operation of the PCS, thereby improving power conversion efficiency.

In addition, it is possible to minimize downtime with high fire frequency by performing discharge immediately after buffering.

In addition, in the case of a battery, the higher the c-rate (battery charge/discharge rate) (quick charge), the shorter the life, but the PCS reduction operation of the present invention can lower the battery charging speed, which also helps with battery life.

The advantages and effects that can be obtained in the present invention are not limited to the advantages and effects mentioned above, and other advantages and effects that are not mentioned are from those described below to those skilled in the art to which the present invention pertains. It will be clearly understood.

1 is an exemplary view showing a solar power generation amount and a predicted value on a clear day,
Figure 2 is an exemplary diagram showing the amount of solar power generation and forecasts on a cloudy day,
Figure 3 is an exemplary view showing the expected amount of power generation (Ef) based on the previous day power generation (Pf) according to the present invention,
4 is a view showing a state of charge of the ESS according to the control of the present invention,
5 and 6 is a view showing the occurrence of loss of the ESS charge according to the application of the control section margin when the weather is clear,
7 is a view showing a state in which the loss of the ESS charge amount is reduced according to the adjusted control interval margin of the present invention,
8 is a view showing that the expected power generation shows a considerable level of deviation from the actual power generation,
9 is a view showing functions (blue lines) when the constants Ktm and Kln are 750 and 20, respectively;
10 is a view showing a control result to which the final correction control interval margin (Cv) is applied,
11 is a diagram showing that efficient charging was possible without affecting the control section margin adjustment when the amount of power generation on a cloudy day was small.

The present invention can be applied to various transformations and can have various embodiments, and specific embodiments will be illustrated in the drawings and described in detail in the detailed description. Effects and features of the present invention and methods for achieving them will be clarified with reference to embodiments described below in detail together with the drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various forms.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, and the same or corresponding components will be given the same reference numerals when describing with reference to the drawings, and redundant description thereof will be omitted. .

The present invention was devised as a problem of the highest fire frequency during the rest period after the completion of charging the ESS (Energy Storage System).

On a clear day, when the solar power generation is high, charging the PCS (Power Conversion System) at full charge will be fully charged at 13-14 PM. At 16:00, the PCS reduction operation will be performed using an energy management system that includes a power generation prediction algorithm. It is characterized by driving to be fully buffered.

In addition, it is characterized in that the discharge is performed immediately after 16:00 after discharge after 18:00 for 1 to 2 hours after the buffering until 16:00, and the discharge is performed without a rest time after buffering. At this time, if the discharge starts at 16:00, when the sunshine is good even at 16:00, there is a problem that the combined amount of PV power generation + ESS discharge can exceed the contracted capacity of KEPCO. Therefore, it is characterized by transmitting by using an energy management system that includes a PV generation amount + ESS discharge operation algorithm so as not to exceed the contracted connection capacity.

The algorithm sets the charging control section margin value based on the approximate daily power generation prediction value based on solar power generation 24 hours ago. Through this, the charge is evenly distributed from 10 to 16:00, which is the time for charging the REC (Renewable Energy Certificate). The amount of photovoltaic power generation can be predicted by various approaches, but due to inaccuracies in weather forecasts, there will be significant errors. On a clear day, there is an error, but the expected power generation and actual power generation progress similarly as shown in Fig. 1, but on a cloudy day, the error is greater as shown in Fig. 2 because it is greatly affected by clouds. Accordingly, it is also possible to compare the amount of solar power generated according to the current time and the amount of solar power generated according to the current time and the amount of solar generated according to the past time in units of hours, and determine the expected power generation amount of the next time according to whether or not they match. Here, the time can be considered in seconds, minutes, and hours.

When the power generation prediction information as shown in FIG. 3 is obtained, the estimated power generation Ef is as shown in Equation 1 below.

ts: REC charging start time (10 o'clock)

te: REC charging expiration time (16:00)

When the estimated generation amount Ef is obtained, the estimated excess generation amount Eo is obtained using Equation 2 below.

Ke: ESS installation capacity

The excess power generation prediction error correction constant (10%) was reflected. (10% can be implemented to be automatically adjusted through operation)

From the values of Equations 1 and 2, the control margin baseline Cb is obtained through Equation 3 below.

Ks: Time to determine the control interval margin during the allowable time for REC charging (control step (e.g. 6 hours * 60 minutes * 60 seconds = 21600 for seconds control, 6 hours * 60 minutes = for minutes control) 360))

The output value Ct obtained for each control section by using the control interval margin Cb obtained by Equation 3 is as shown in Equation 4 below, and performs control in the form of a graph in FIG. 4.

Pr: PV output value

In actual operation, since it is impossible to perform charging beyond the set SOC (storage capacity) buffer point, the storage value indicating the chargeable spare capacity of the ESS in the graph of FIG. 4 cannot fall below 0, and accordingly, FIG. 3 In such a clear weather, it can be expected that charging will be completed before 16: 00 minutes, which is the allowable time for REC charging.

This is the part to be supplemented through the ramp control of the REC charge/discharge section, and it will be a level capable of minimizing the overvoltage state until the start of discharge after charging is completed.

In the case of a day when a similar level of power generation compared to the ESS capacity is generated as shown in FIGS. 5 and 6, the ESS can be buffered as the power is continuously transmitted due to the control section margin (Cb) applied when the weather is clear. In spite of the high level of power generation, it is not possible to charge about 17% of the negligible generation energy.

To this end, the control section margin Cb may be corrected according to the following steps. First, as shown in Equation 5, a control section margin (Cu) adjusted in proportion to the magnitude of the expected excess power generation is obtained.

When the adjusted control interval margin Cu according to Equation 5 is applied, a somewhat improved charging control as shown in FIG. 7 is achieved. 17% REC charge loss was reduced to 12%.

Referring to FIG. 8, the expected solar power generation shows a considerable level of deviation from the actual power generation. Due to this deviation, a formula for compensating for the control section margin error is required.

Final correction control interval margin as shown in Equation 6 by applying additional correction value to the adjusted control interval margin (Cu) based on the softplus relationship function between the charging elapsed time and the ratio of actual power generation to expected power generation as follows: Find (Cv).

Here, the adjustment constants Ktm and Kln can be automatically generated based on the execution result data.

The functions (blue line) when the constants Ktm and Kln are 750 and 20, respectively, are as shown in Fig. 9 (the actual power/predicted power in orange).

The result of applying the above function to apply the final correction control interval margin (Cv) is the same as in Fig. 10, and the result of reducing the charging loss from 12% to 10% was obtained. This is the result of gradually reducing the control section margin to compensate for the actual decrease in power generation as the charging time elapses.

When the amount of power generation was low due to cloudy weather, it was confirmed that efficient charging is possible without affecting the adjustment of the control section margin as in the case of clear weather (see FIG. 11).

In the case of weather conditions that are difficult to control, i.e., when the power generation is close to the ESS installation capacity and approximate level, there may be an uncharged amount corresponding to 10% of the ESS installation capacity, which may result in loss of REC sales, but this is quite rare (specific sites) We found only one case in the data for the month of March in March, which, arithmetically, is a record drop in REC sales by around 0.3%).

On the other hand, it is expected that more effect can be obtained by minimizing the duration of the high voltage state of the ESS, as well as suppressing the possibility of fire occurrence and reducing the deterioration due to the maximum charge/discharge due to the decrease in the ESS charge and discharge output value.

On the other hand, the discharge value Cd can be obtained simply as in Equation 7.

Kg: maximum output of solar power contract

Pfs: Early short-term predicted power generation (or actual power generation at the time of control)

Km: discharge control margin

However, since the change in the amount of power generation continues to occur even between control cycles, in order to correct the discharge control value obtained by Equation 7, an ultra-short-term analysis algorithm capable of determining the change in the amount of power generation in real time is required.

Since the discharge time in REC operation is quite long, there is no problem in operation even if a relatively large value is used for the discharge control margin. Discharge efficiency is known to be the most efficient at an output of about 80%. Therefore, it is not absolutely necessary to predict the short-term power generation.

As described above, although the present invention has been described by limited embodiments and drawings, the present invention is not limited to the above embodiments, and various modifications and variations from these descriptions will be made by those skilled in the art to which the present invention pertains. This is possible.

Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the claims to be described later, but also by the claims and equivalents.

Claims (5)

delete The estimated excess power generation (Eo) and the control interval margin (Cb) are obtained based on the estimated power generation (Ef) based on the previous day power generation (Pf), and the output value (Ct) obtained for each control section using the control interval margin (Cb) ) REC (Renewable Energy Certificate) Energy management system that controls charging by distributing to the ESS from the start time to the expiration time.
The estimated power generation (Ef) is

ts: REC charging start time (10 o'clock)
te: REC charging expiration time (16:00)

The expected excess power generation (Eo) is

Ke: ESS installation capacity

The control section margin (Cb) is

Ks: Time to determine control section margin during REC charging allowable time

The output value (Ct) that can be obtained for each control section is:

Pr: PV output value According to claim 2,
The output value (Ct) that can be obtained for each control section is:
The energy management system, which is applied to the adjusted control interval margin (Cu) obtained in proportion to the size of the expected excess power generation (Eo).
The adjusted control interval margin (Cu) is

The output value (Ct) that can be obtained for each control section is:

Pr: PV output value According to claim 3,
The output value (Ct) that can be obtained for each control section is
The final correction control interval margin (Cv) obtained by applying additional correction values to the adjusted control interval margin (Cu) based on the softplus relationship function between the elapsed charging time and the ratio of the actual power generation to the expected generation amount is applied. , Energy management system.
The final correction control interval margin (Cv) is

The method according to any one of claims 2 to 4,
Energy management system for discharging and charging in the ESS from the start time of the REC charging to the expiration time according to the output value (Ct) that can be obtained for each control section, and controlling discharge according to the following equation.
The discharge value (Cd) is,

Kg: maximum output of solar power contract
Pfs: Early short-term predicted power generation (or actual power generation at the time of control)
Km: discharge control margin

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