JP6404747B2 - Design method of power transfer function in power leveling system and calculation method of storage battery capacity in power leveling system - Google Patents

Description

  The present invention relates to a system that mitigates output fluctuations of photovoltaic power generation by charge / discharge control of a storage battery.

  The feed-in tariff system for renewable energy has been put in place, and the introduction of solar power generation has increased rapidly. Solar power output fluctuates drastically due to weather effects. For this reason, when a large amount of photovoltaic power generation is introduced, it is regarded as a problem that the voltage and frequency of the distribution line system fluctuate due to the output fluctuation.

  As a countermeasure against this output fluctuation, a power leveling system that installs a storage battery system and relaxes (levels) the output fluctuation of solar power generation is known (see Patent Document 1).

Japanese Patent No. 4596695

  The function of the power leveling system is to level the output of the rapidly changing photovoltaic power generation and supply it to the system. In order to realize this function, a low-pass filter that smoothes the output of photovoltaic power generation may be configured and connected to the system.

  That is, configuring a power leveling system is the same as configuring a power filter. As the attenuation of the power filter is increased, leveling can be performed, but conversely, the storage battery capacity is increased. For this reason, in order to optimize the system, all that can be done is how to design the power transfer function of the power filter.

  Therefore, in the present invention, in order to optimize the storage capacity that occupies an important role in terms of performance and cost of the power leveling system, and a method for optimally designing the power transfer function of the power filter constituting the power leveling system. The calculation method of is presented.

  The invention according to claim 1 is a power leveling system as a power filter for leveling the output of solar power generation that varies rapidly by charge / discharge control of the power storage system and supplying the output to the distribution line system. A characteristic is that the required attenuation is determined from the maximum value of the output fluctuation and the allowable value of the fluctuation speed of the power supplied to the distribution system, and the cutoff frequency of the fluctuation suppression filter constituting the power filter is determined from the attenuation. Have.

  According to a second aspect of the present invention, there is provided a power leveling system as a power leveling system as a power leveling filter for leveling the output of photovoltaic power generation that fluctuates rapidly by charge / discharge control of the power storage system and supplying it to a distribution line system The storage capacity ratio corresponding to the cutoff frequency of the fluctuation suppression filter is calculated, and the minimum value (ideal value) of the storage battery capacity is determined by multiplying the storage capacity ratio by the total amount of power generation per day, and the charge / discharge efficiency, etc. It is characterized by determining the necessary storage capacity by taking into account.

  According to the first aspect of the present invention, the design of the power transfer function in the power leveling system that functions as a power filter can be easily realized.

  According to invention of Claim 2, the minimum storage battery capacity required in order to suppress the output fluctuation | variation of photovoltaic power generation to an allowable value or less can be calculated, and it is advantageous on system design.

It is a control structure of the power filter of this invention. It is a structure of the electric power leveling system of this invention. It is a control block diagram of the leveling controller of the present invention. It is a graph which shows the relationship between a cutoff frequency and electric power fluctuation attenuation amount. It is a graph which shows the relationship between a cutoff frequency and a storage amount ratio. It is a graph which shows the relationship between electric power fluctuation attenuation amount and a storage amount ratio.

Hereinafter, embodiments of the present invention will be described with reference to FIGS. FIG. 1 shows a control configuration of a power leveling system (power filter) A according to the present invention. That the output power P _in the solar power was smoothed by fluctuation suppression filter 1 becomes the target value P _o ^* of the power supplied to the grid. The difference between the target value and the output of the photovoltaic power generation is defined as an output power command value P _bs ^{* of the} storage battery system 2 including a storage battery and a storage battery power conditioner described later. The storage battery system 2 performs charge / discharge control of the power of the storage battery according to the command value.

In FIG. 1, P _out = P _in + P _bs and P _bs ^* = P _o ^* − P _in , P _o ^* = G _f P _in . Storage battery system 2 has P _bs = Since the output power P _bs is controlled to be P _bs ^* , P _out = P _in + P _bs ^* = P _in + G _f P _in − P _in = G _f P _in , and as a result, the transfer function G _f of the fluctuation suppression filter 1 = the transfer function G _{p of the} power filter (power leveling system A).

  FIG. 2 shows a configuration of a power leveling system A that is connected in parallel on the AC side to photovoltaic power generation according to the control configuration of FIG. The power leveling system A performs the power leveling control based on the storage battery 3, the sensors 4a to 4d such as transducers for measuring the output power of the solar power generation 7 and the storage battery 3, and the values therefrom, and the output current of the storage battery 3 The leveling controller 5 generates a command value, and a power conditioner (hereinafter referred to as a storage battery power converter) 6 that controls the output current of the storage battery 3 based on the generated command value and charges and discharges. The solar power generation 7 includes a solar battery 8 and a power conditioner (hereinafter referred to as a solar power converter) 9.

FIG. 3 is a control block diagram of the leveling controller 5. The leveling controller 5 has a function of the fluctuation suppression filter 1 and a function of performing feedback control of the output power P _bs of the storage battery power conditioner 6 in the storage battery system 2 including the storage battery 3 and the storage battery power conditioner 6.

The method for calculating the cutoff frequency of the power filter and the storage battery capacity is described below. The maximum absolute value of the fluctuation speed as an indicator of the intensity of output fluctuation | dP / Use dt | _max . After passing the power filter | dP / The power filter performance (degree of power leveling) is evaluated based on how small dt | _max is. When the power filter is determined by this evaluation, the storage battery capacity B _cap is determined according to the capacity of the photovoltaic power generation.

  First, an outline procedure for calculating the storage battery capacity will be shown, and then the details will be described. Hereinafter, the fluctuation speed of power and output is simply referred to as power fluctuation or output fluctuation. The general procedure for calculating the storage battery capacity is as follows.

(1) First, after passing through the power filter, | dP / Know how much dt | _max decays. | DP at input and output / The ratio of dt | _max is the power fluctuation attenuation amount G. Then, to understand the relationship between the power fluctuation attenuation G and the cutoff frequency f _c of the power filter. The above relationship is grasped for several types of filters, and the optimum filter is finally selected from them.

(2) Next, the fluctuation speed of the power supplied to the system | dP _out / dt | tolerance and photovoltaic power output fluctuation | dP _in / The required power fluctuation attenuation is determined from the ratio of dt | _max .

(3) and for each filter, obtain the cutoff frequency f _c which is required for obtaining the attenuation amount calculated above.

(4) Finally, when leveling is performed using each filter, a point (maximum charged amount) at which the amount of power stored in the storage battery 3 is maximized in one day is obtained. Then, the maximum value of this value is obtained throughout the year. The filter having the smallest maximum value is the optimum filter for the system, and the value is the minimum value B _o (ideal value) of the required storage battery capacity. For this B _o, charge and discharge efficiency and the battery and power conditioners, it takes into account the depth of discharge when using battery (ratio of the discharge amount to the battery capacity), the actual battery capacity B _cap required.

In carrying out the above procedure, first, as the procedure (1), the relationship between the cutoff frequency and the power fluctuation attenuation amount is grasped for several types of filters. Next, as the procedure of (4), the relationship between the cutoff frequency and the maximum charged amount is grasped in advance for each filter. Here, solar power generation equipment (100 kW and 10 kW), the case where these relations are grasped based on the output data (1 second sampling data) is explained.

First, examining the relationship between the cutoff frequency f _c and the power fluctuation attenuation amount G of the power filter. Specifically, by entering the P _in which the actual output data PV of interest based on the power filter to compute the output. From the results, the maximum fluctuation speed of the filter input | dP _in / dt | _max and maximum output speed | dP _out / A ratio G (amount of power fluctuation attenuation) of dt | _max is obtained. Then, several kinds of filters, determine to change the cut-off frequency f _c by power fluctuation attenuation G how changes.

  The power filters are primary, secondary, and tertiary Butterworth LPFs. The reason is that the output of photovoltaic power generation may change suddenly in a step shape, so that the point response characteristics are good and the design is easy.

First, from among the output data of the solar power of interest, variation is to choose a few days worth of data intense day, to calculate its output to input P _in accordance with the data to the power filter. Then, the power fluctuation attenuation amount is obtained from the result and graphed.

  There are various aspects of changes in the output of solar power generation. Therefore, it is necessary to use a graph when the power fluctuation attenuation amount is the smallest. FIG. 4 shows a graph in the case where the power fluctuation attenuation amount is minimized during the investigation.

Power filter by changing the cutoff frequency f _c of the result of obtaining the power fluctuation attenuation G, between the two approximately formula (1): G = Ten log ₁₀ (| dP _out / dt ｜ _max / | dP _in / dt | _max ) = a ₁ log ₁₀ ( f _c ) + b _I found that there is a relationship like ₁ .

By grasped a relationship between cutoff frequency f _c and the power fluctuation attenuation amount G of the power filter, it is possible to obtain the f _c of the filter for obtaining the required attenuation G.

Next, when the leveling is performed using each power filter, how much the maximum power storage amount _Qmax is calculated is calculated. Then, it is examined how the maximum charged amount Q _max changes by changing the cutoff frequency of the power filter.

From the control configuration of the power filter shown in FIG. 1, the storage battery 3 is _charged and discharged with the same power as the output power P _bs . The amount of power Q (t stored in the storage battery 3 ) Is the instantaneous power P (t ), The amount of stored electricity can be obtained by integrating the output power P _bs . This amount of electricity stored Q (t The maximum value of day of) is the maximum storage amount Q _max, the maximum value of Q _max through the year, the minimum value B _o of battery capacity required.

The maximum amount of electricity stored throughout the year is the day when there is a large amount of total power generation per day. For this reason, such a day is selected and the relationship between the cutoff frequency and the maximum charged amount is examined. However, since the value of the maximum power storage amount is directly dependent on the total power generation amount per day, Formula (2) normalized by the total power generation amount: power storage amount ratio C _b = Maximum storage amount / Consider the total amount of power generated per day.

  By normalizing with the total amount of power generated per day, the relationship between the cut-off frequency and the storage amount ratio can be applied to solar power generation with various capacities. This time, from the output data of the target photovoltaic power generation, we selected several days with a large daily total power generation amount, and calculated the storage amount ratio.

For each power filters, it shows the results of examining the relationship between varying the cut-off frequency f _c by the charged amount ratio C _b in FIG. The relationship is given by equation (3): log ₁₀ ( C _b ) = a ₂ log ₁₀ ( f _c ) + It can be approximated by a log-linear as b _2. Further, the slope a ₂ and the intercept b ₂ of the approximate line do not depend on the capacity of solar power generation or the day. This is thought to be due to the similar power generation pattern of the day with a large total daily power generation. Since the slope a _{2 of the} approximate line is approximately −1, it can be seen that f _c and C _b are in an inversely proportional relationship.

For each power filters can be derived a relationship of the relationship between the cutoff frequency f _c and the power fluctuation attenuation G, and the relationship between the storage amount ratio C _b and power fluctuation attenuation G and the storage amount ratio C _b.

Equation (1) and (3) result of deriving the power fluctuation attenuation G and the storage amount ratio C _b of the equation from the formula (4): log ₁₀ ( C _b ) = ( a ₂ / a ₁ ) ( G − b ₁ ) + b ₂ = ( a ₂ / a ₁ ) G − a ₂ b ₁ / a ₁ + b ₂ and its graph is shown in FIG.

The graph of FIG. 6, for the required power fluctuation attenuation G, the value of the charged amount ratio C _b is the smallest types of filters and C _b can be easily obtained.

The calculation procedure of the storage battery capacity is described below. Maximum output fluctuation of the target photovoltaic power generation | dP _in / dt | _max and the allowable value of the fluctuation speed of power supplied to the system | dP _r / From dt |, the required power fluctuation attenuation amount G _r is _expressed by Equation (5): G _r = Ten log ₁₀ (| dP _r / dt ｜ / ｜ dP _in / dt | _max ).

From the relationship between the cutoff frequency and power fluctuation attenuation as shown in FIG. 4, determine the cutoff frequency f _c of the filter necessary to obtain the required attenuation G _r.

A cut-off frequency as shown in FIG. 5 from the relationship of the charged amount ratio for each filter to determine the charged amount ratio C _b for the cutoff frequency f _c determined in the previous section. The storage battery capacity is minimized when _Cb is minimized. Therefore, C _b to select the filter having the smallest from among the relationship graph shown in FIG.

However, when the relationship between the power fluctuation attenuation amount and the storage amount ratio as shown in FIG. 6 can be derived, the storage amount ratio C _b is minimized with respect to the necessary power fluctuation attenuation amount G _r . Select a filter.

The maximum value W _max of the total power generation per day is obtained from the output data of solar power generation.

Battery capacity is calculated by multiplying the C _b and W _max obtained. However, this value is an ideal value when the charge / discharge efficiency of the storage battery 3 and the power conditioner 6 and the depth of discharge when using the storage battery 3 (the ratio of the discharge amount to the storage battery capacity) are assumed to be 100%. is not. For this reason, it is necessary to consider these efficiency and discharge depth.

When the power conversion efficiency of the storage battery power conditioner 6 is η _bpc , the amount of power charged in the storage battery 3 is η _bpc times (η _bpc B _o ) with respect to the ideal value B _o (= C _b W _max ).

Charging efficiency of storage battery 3 (= Discharge electric energy / When the charged electrical energy) and eta _b, dischargeable amount of power, with respect to charge power amount eta _bpc B _o, becomes eta _b doubled in battery 3, the eta _bpc times because further discharge from the storage battery power conditioner 6. Eventually, the amount of power that can be finally discharged is η _b η _bpc times (η _b η _bpc ² B _o ).

All of the daily solar power generated in the storage battery 3 is discharged to the grid within that day. Apparently, it means to charge the power up to B _o by solar power, it will discharge the same amount of power. However, since the amount of power that can be discharged is η _b η _bpc ² B _{o according} to the previous section, the loss (1 − η _b η _bpc ² ) B _o needs to be replenished in advance at night. The replenished power cannot be discharged 100%. As in the previous section, the amount of electric power that can be discharged with respect to the supplement is η _b η _bpc times. Therefore, the amount of power to be charged in advance is given by equation (6): (1 − η _b η _bpc ² ) B _o / (η _b η _bpc ) = ((η _b η _bpc ) ^-1 − η _bpc ) B _o .

Considering the maximum discharge depth K _dod when the storage battery 3 is used, the required capacity B _{cap of the} storage battery 3 is expressed by the equation (7): B _cap = (η _bpc B _o + ((η _b η _bpc ) ^-1 − η _bpc ) B _o ) / K _dod = B _o / (η _b η _bpc K _dod ) = C _b W _max / (η _b η _bpc K _dod )

Below, the calculation example which actually calculated | required the capacity | capacitance of the storage battery 3 is described. The target is a 100kW solar power generation facility. The maximum output fluctuation of the solar power generation | dP _in / dt | _max = 43 kW / s. 3% output fluctuation that can be followed by coal-fired power generator It shall be suppressed to less than / min. In other words, when the allowable value of the fluctuation speed of the power supplied to the system is 0.05 kW / s, the required power fluctuation attenuation amount can be calculated from Equation (5) as G _r = -29.3dB.

In this case, the power filter selects the Butterworth type second-order LPF from the relationship of FIG. When determining the cutoff frequency f _c of the power filter power fluctuation attenuation amount is -29.3dB from FIG. 4, 0.21 mHz.

From FIG. 6, the storage amount ratio C _b is calculated as 4.1. %.

Maximum value of solar power generation per day W _max = 650 When it is kWh, the maximum discharge depth of the storage battery 3 to be used is 80 %, Charging efficiency is 95 %, Efficiency of battery power conditioner 6 is 94 Assuming%, the required capacity of the storage battery 3 is B _cap = 37 kWh.

  As described above, according to the present invention, the cut-off frequency of the filter for obtaining the necessary power fluctuation attenuation amount can be obtained, and the system can be optimized.

  Moreover, the storage battery capacity according to the capacity of photovoltaic power generation can be calculated, which is advantageous in system design.

  The present invention is naturally applicable not only to the case of solar power generation but also to power leveling such as wind power generation.

  It can be used as an output fluctuation countermeasure for the distribution system.

DESCRIPTION OF SYMBOLS 1 Fluctuation suppression filter 2 Storage battery system 3 Storage battery 4a-4d Sensors, such as a transducer 5 Leveling controller 6 Storage battery power conditioner 7 Solar power generation 8 Solar battery 9 Solar power conditioner A Electric power leveling system

Claims (2)

  In a power leveling system as a power filter that leveles the output of photovoltaic power generation that fluctuates rapidly by charge / discharge control of the power storage system and supplies it to the distribution line system, the maximum value of output fluctuation of solar power generation and distribution Power transmission in a power leveling system, wherein a required attenuation amount is determined from an allowable value of a fluctuation speed of power supplied to a system, and a cutoff frequency of a fluctuation suppression filter constituting the power filter is determined from the attenuation amount. Function design method.   In the power leveling system as a power filter that leveles the output of photovoltaic power generation that fluctuates rapidly by charge / discharge control of the power storage system and supplies it to the distribution line system, the cutoff frequency of the fluctuation suppression filter constituting the power filter A method for calculating a storage battery capacity in an electric power leveling system, wherein a corresponding storage amount ratio is obtained, and a minimum value of the storage battery capacity is determined by multiplying the storage amount ratio by the total amount of power generated per day.

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