JP2015115968A - Power storage system, power regulator, and method for controlling power storage system - Google Patents

Abstract

An object of the present invention is to extend the life and improve the reliability of a power storage system composed of a plurality of battery units connected in parallel. In a power storage system including a plurality of battery units connected in parallel to a common power system and a power regulator, an inverter and a sensor unit are connected to the battery unit, and the inverter is connected to the inverter. A control unit is connected, the inverter is arranged between the battery unit and the power system, and the sensor unit has a function of detecting the state of the battery unit and sending a signal related to the detected state of the battery unit to the power regulator. The power regulator controls charging / discharging of each battery unit so as to reduce the difference in deterioration state between the battery units. [Selection] Figure 1

Description

  The present invention relates to a power storage system, a power regulator, and a method for controlling the power storage system.

  In recent years, global attention has been focused on global warming prevention and carbon dioxide emission reduction. Renewable energy such as wind power generation and solar power generation has been introduced into power systems in large quantities and will play a major role in future power systems. It is predicted. However, since renewable energy depends on the weather, the output is unstable. Therefore, when a large amount of renewable energy is introduced, it is a problem to control frequency fluctuations and voltage fluctuations. In order to improve the stability and reliability of the power system, power storage systems are installed at different locations in the power network. An ancillary service (supplementary service) that controls the frequency or voltage within a specified range, or power smoothing, requires a highly responsive power storage system.

  Power storage systems are also used in hybrid vehicles that can reduce carbon dioxide emissions and fuel consumption compared to conventional vehicles. Various types of battery technologies have been developed for stationary and mobile applications. In order to maximize the benefit of using a power storage system, it is necessary to take into account the technical characteristics of each application in power control.

  In general, a power storage system includes one or a plurality of battery units and an inverter for converting a frequency. The battery unit has a configuration in which a plurality of string configurations in which a plurality of battery cells are connected in series are connected in parallel. The battery cell is mainly composed of three parts, a negative electrode, a positive electrode, and an electrolytic solution. In the process of charging and discharging the battery cell, electrons generated by the oxidation reaction move from the cathode to the anode. By repeating the charging / discharging cycle, a physical change occurs in the electrolytic solution and the electrode, and the period until the life of the battery cell is shortened due to irreversible deterioration, and the replacement time of the battery unit approaches.

  When a plurality of battery units are connected in parallel to the power system, the difference in deterioration state between the initial battery units is small. By repeating the charge / discharge cycle, a difference in the remaining amount of lifetime for each battery unit of the system occurs, and the difference in the deterioration state between the battery units increases.

  In order to avoid such a difference in deterioration state that impairs the reliability of the entire power storage system, it is desirable to apply a method for controlling the power charged / discharged for each battery unit.

  As disclosed in Patent Document 1, conventionally, power control is performed using a deterioration state in order to determine the amplitude of current for each battery unit. However, in Patent Document 1, it is assumed that the deterioration state of the battery is mainly caused by the amplitude of the current.

  In fact, battery manufacturers can select various materials for use in battery anodes, cathodes and electrolytes. In consideration of technical characteristics and cost, a plurality of materials and combinations of the materials to be used are conceivable. Therefore, the deterioration process varies depending on the material used. For some materials, the amplitude of the current is a major cause of degradation, but this is not the case for all materials. In some materials, the main cause of deterioration is the central charge state (hereinafter referred to as “central SOC”). Here, the center SOC is a value in which the state of charge is the center in the process of the charge / discharge cycle.

  The deterioration of the anode and the cathode is related to the expansion of the electrode material depending on the voltage, and there is a trade-off relationship between the expansion of the anode and the expansion of the negative electrode depending on the voltage value. Since the voltage is related to the state of charge, the central SOC affects the degradation process. Therefore, the lifetime of the battery cell is also affected.

  Patent Document 2 discloses a technique for controlling a power storage device of an electric vehicle so as to change a control center value SOCr (center SOC) in accordance with an estimated remaining capacity value.

International Publication No. 2012/032776 JP 2011-240863 A

  In a power storage system composed of a plurality of battery units connected in parallel, the difference in deterioration processes between different battery units increases as the number of charge / discharge cycles increases. Due to such a difference, the life of the entire power storage system is shortened and the reliability is lowered. The cause of the deterioration depends on the characteristics of the material constituting the battery cell of the battery unit. Depending on the material, the value of the central SOC is a major cause of degradation.

  When the technique described in Patent Document 2 is used, since control is performed according to the estimated value, it is considered that there is room for improvement from the viewpoint of realizing accurate control.

  An object of the present invention is to prolong the life of a power storage system composed of a plurality of battery units connected in parallel and to improve reliability.

  The power storage system of the present invention includes a plurality of battery units connected in parallel to a common power system, and a power regulator. The battery unit is connected to an inverter and a sensor unit, and the inverter is controlled by an inverter. The inverter is arranged between the battery unit and the power system, and the sensor unit has a function of detecting the state of the battery unit and sending a signal related to the detected state of the battery unit to the power regulator. The power regulator controls charging / discharging of each battery unit so as to reduce a difference in deterioration state between the battery units.

  According to the present invention, since the variation of the deterioration state (SOH) between the battery units can be reduced, further deterioration of the deteriorated battery can be suppressed, thereby improving the life of the entire power storage system. It becomes possible.

It is a whole lineblock diagram showing an electrical storage system provided with a plurality of battery units connected in parallel to a common AC bus via a self-excited inverter, and a power regulator. It is a block diagram which shows the example of a self-excited inverter. It is a block diagram which shows the internal structure of a sensor unit. It is a graph which shows the example of a charging / discharging electric current pattern. It is a graph which shows the example of a SOC change pattern. It is a graph which shows the example of the relationship between center SOC and deterioration rate. It is a block diagram which shows the internal structure of a power regulator. It is a graph which shows the example of the relationship between a charge condition and the open circuit voltage of a battery unit.

  Hereinafter, preferred embodiments for carrying out the present invention will be described.

  FIG. 1 shows the overall configuration of a battery energy storage system.

  In this figure, the power storage system 100 includes a plurality of battery units 11-1 to 11 -N and a plurality of inverters 12-1 disposed between the respective battery units 11-1 to 11 -N and the power system 300. To 12-N, inverter control units 13-1 to 13-N for controlling the active power output from the respective inverters 12-1 to 12-N, and a power regulator 200 (power management system). Yes. Here, N corresponds to the number of battery units. The power storage system 100 includes a plurality of sensor units 400-1 to 400-N connected to the respective battery units 11-1 to 11-N. A power generation device 500 using solar power generation, wind power, hydraulic power, and the like are connected to the power system 300 and a load. The power system 300 is alternating current. Inverters 12-1 to 12 -N are connected in parallel to the AC bus of power system 300. Inverters 12-1 to 12-N are desirably self-excited inverters.

  Signals from the sensor units 400-1 to 400-N are sent to the power regulator 200. The power conditioner 200 can send a signal for controlling the inverters 12-1 to 12-N to the inverter control units 13-1 to 13-N. Further, the total power system monitoring unit 600 may be connected to the power regulator 200 and utilized for control. The total power system monitoring unit 600 mainly obtains information such as the power generation amount of the power generation apparatus 500, the power storage amount of the battery units 11-1 to 11-N, and the power consumption of the load connected to the power system 300. Accumulate and monitor.

  When the active power generated by the power generation device 500 exceeds the load, the power storage system 100 can store (charge) surplus active power. When the power generation device 500 cannot supply active power necessary for the load, the power storage system 100 can supply (discharge) insufficient active power so as to satisfy the power demand.

  The sensor units 400-1 to 400-N measure DC voltages and currents output from the battery units 11-1 to 11-N. The power conditioner 200 calculates the charged state and the deteriorated state of the plurality of battery units 11-1 to 11-N. In this calculation, the output voltage or output current of the battery units 11-1 to 11-N measured by the sensor units 400-1 to 400-N may be used. Moreover, the power regulator 200 controls the output power of the battery units 11-1 to 11-N.

  In order to control the charge / discharge power of the storage battery units 11-1 to 11-N, each of the inverters 12-1 to 12-N receives a control command transmitted from the inverter control units 13-1 to 13-N. The control commands transmitted by the inverter control units 13-1 to 13-N are based on waveform information received from the power regulator 200, respectively.

  FIG. 2 shows the configuration of the inverter. Here, the basic functions of the inverter will be described.

  In this figure, the inverter 12 includes semiconductor switches 120m, 120n, 120o, 120p, 120q, 120r and a harmonic filter 120. Here, insulated gate bipolar transistors (IGBTs) are used as the semiconductor switches 120m, 120n, 120o, 120p, 120q, and 120r. In addition, semiconductor switches other than IGBTs such as IGCT, MOSFET, GTO, etc. may be used.

  The battery unit is connected to terminals P and N, supplies DC power when the inverter 12 is discharged, and absorbs DC power when the inverter 12 is charged. The inverter 12 generates a desired AC voltage and current by the operation of a bridge circuit of semiconductor switches 120m, 120n, 120o, 120p, 120q, and 120r that performs high-frequency switching provided therein, and converts the DC power during discharge into AC. Convert to electricity. The gate signal supplied to the semiconductor switches 120m, 120n, 120o, 120p, 120q, and 120r at the time of conversion is supplied from one of the inverter control units 13-1 to 13-N. As a result, the semiconductor switches 120m, 120n, 120o, 120p, 120q, and 120r are controlled.

  Inverters 12-1 to 12-N shown in FIG. 1 each include a main circuit as shown in FIG.

  FIG. 3 shows the internal structure of the sensor unit (detector) of FIG.

  In this figure, the sensor unit 400 includes a current sensor 401, a voltage sensor 402, an SOC calculator 403 (charge state calculation unit), and an SOH calculator 404 (deterioration state calculation unit). The SOC of the storage battery is defined by the ratio of the possible discharge capacity to the rated capacity. This can be shown as the following formula (1). In addition, the following numerical formula (1), numerical formula (2) etc. are Eq. 1, Eq. Although they are represented as 2 etc., they respectively correspond to the same mathematical formula. The state of charge (SOC) is also referred to as “charging rate”.

Here, SOC (0) is the initial value, I is the current value of the storage battery unit 11 detected by the current sensor 401, and Ah _nominal is the rated capacity of the storage battery in units of ampere hours. The current I treats the charge direction as positive and the discharge direction as negative. The SOC calculator 403 includes a memory unit (storage unit) that stores the current and the SOC history calculated by the above equation (1).

SOH is an abbreviation for State of Health and quantitatively represents the “degraded state”. In other words, the SOH is a parameter expressed as a ratio based on a new article with respect to the degree of deterioration or deterioration of the quality of the electrode or active material of the storage battery. The decrease in quality is typified by an increase in internal resistance or a decrease in capacity of the storage battery. The instantaneous values of SOH _R related to internal resistance and SOH _Q related to capacitance are given by the following mathematical formulas (2) and (3), respectively.

Here, R _{int, new} is the internal resistance of the new battery, R _int (t) is the instantaneous value of the internal resistance, Q _new is the capacity of the new battery, and Q (t) is the instantaneous value of the capacity.

R _int (t) and Q (t) are calculated by the SOH calculator 404 based on the signals of the current sensor 401 and the voltage sensor 402. The SOH calculator 404 calculates SOH _R and SOH _Q using the above mathematical formulas (2) and (3). SOH _R increases with time, SOH _Q decreases, and SOH _R increases and / or SOH _Q decreases. Thus, the "deterioration state is bad", if the SOH _R is increased, and / or SOH _Q refers to the case that was reduced.

  The sensor units 400-1 to 400-N provided in each storage battery transmit SOC and SOH information to the power conditioner 200 through the transmission line to the power conditioner 200.

The deterioration process of the storage battery related to changes in internal resistance and capacity is affected by various factors such as current pattern, charge / discharge cycle, depth of discharge, central SOC, temperature, and the like. SOH _R and SOH _Q are expressed as weighted sums of these parameters. In particular, attention is focused on the central SOC as an element that contributes to battery deterioration of the battery units 11-1 to 11-N.

  The concept of the central SOC is shown below.

  FIG. 4A shows an example of a charge / discharge current pattern. FIG. 4B shows an example of the SOC change pattern. These are very simplified examples, but similar mathematical expressions can be applied to actual complex waveforms.

  FIG. 4B shows the SOC waveform in the case where the charge / discharge current pattern has a periodic waveform as shown in FIG. 4A.

  In this case, the SOC change with time has a periodic waveform as shown in the figure. In such a case, the center SOC is expressed by the following mathematical formula (4).

  FIG. 5 shows the relationship between the central SOC and the deterioration rate in a certain charge / discharge pattern.

The characteristics of a storage battery are usually shown by a charge / discharge cycle test. If the result is used, the tendency with respect to the center SOC can be clarified as in the deterioration curve 700 of FIG. Here, the degradation curve 700 takes a minimum value as indicated by SOC _{center, optimum} in the figure. The minimum value (optimum value) in the deterioration curve 700 is a value unique to the storage battery.

  Depending on the application, the charge / discharge cycle may not be fixed. In such a case, the central SOC is defined as in the following formula (5).

  Here, T represents the time from 0:00 to 24:00, and λ represents a weighting factor as an index representing the distortion between the current pattern of the cycle test and the actual current. The weighting factor λ (h) at time h is defined by the following mathematical formula (6).

Here, I _rated is a rated current of the battery unit, I _test is a data set representing a current waveform for 1 hour, and I is a data set representing an actual current waveform for 1 hour.

In general, for two data sets X = (x _i ) _{1 ≦ i ≦ N} and Y = (y _i ) _{1 ≦ i ≦ N} , the correlation coefficient between X and Y is defined as the following equation (7).

Here, the variances S _XX and S _YY of X and Y, and the covariance S _XY between X and Y are defined by the following formulas (8) to (10), respectively.

  FIG. 6 shows the internal configuration of the power regulator.

  In this figure, the power regulator 200 includes a command selection unit 201, and a power calculation unit 202 having a central SOC calculation unit 202-a and a compensation power optimization unit 202-b. The power regulator 200 calculates the power to be input / output by each battery unit using the output signal from the sensor unit.

The command selection unit 201 receives each SOH information of the power storage system 100 through the sensor units 400-1 to 400-N. The command selection unit 201 ranks the deterioration tendency for the SOH of each storage battery, and selects the highest SOH _R or lowest SOH _Q level in the equilibrium mode.

Here, in a situation where renewable energy occupies a large amount such as a remote island microgrid, the power demand per unit time is predicted on the previous day, and the power storage system 100 is operated all day. During operation, the power storage system 100 is operated so as to be so-called energy neutral in which the balance of charge and discharge becomes equal. Here, it is assumed to perform balancing mode for SOH _R level.

  Hereinafter, the charge / discharge command of each of the battery units 11-1 to 11-N will be described.

The power regulator 200 calculates the _total amount of power P _{total, ref} (t _k ) that the power storage system charges and discharges to and from the power system in order to control the balance between supply and demand for each unit time step t _k on the day before the working day. To do. At the end of the previous day, the sensor units 400-1 to 400-N calculate the SOC and SOH of the battery units 11-1 to 11-N. These values represented by SOC ₁ (0) to SOC _N (0) and SOH ₁ (0) to SOH _N (0) are transmitted to the power conditioner 200 through the transmission path. Command selection unit 201, ranking the value of SOH _R, to select the most deteriorated battery. Subscript k is, as representing a battery of up to SOH _R, unit k is the most upset of the unit to the original working days.

The power calculation unit 202 receives the initial SOC data of each of the battery units 11-1 to 11-N detected by the sensor units 400-1 to 400-N and the power demand P _{total, ref} (t _k ). The power charged and discharged from the battery j and P _j. Then, the reference value P _k (t _k ) given to each inverter in the unit time t _k is given by the following mathematical formulas (12) and (13).

The power calculation unit 202 of the power regulator 200 calculates ΔP (t _k ) that solves the optimization problem represented by the following formula (14) that minimizes the degradation of the most malfunctioning unit.

  This optimization problem satisfies the conditions represented by the following mathematical formulas (15) to (19).

Here, V _{battery unit, i} (t _k ) is a voltage, V _{OC, i} (t _k ) is an open circuit voltage, I _i (t _k ) is a current, SOC _i (t _k ) is a charging rate, and P _i (t _k ) _k) is the power of the storage battery unit 11-i at time step _{t k.} V _min and V _max are the minimum value and maximum value of the voltage of the battery unit 11, and SOC _{lim inf} and SOC _{lim sup} are the upper limit value and lower limit value of the SOC of the storage battery unit 11.

  The open circuit voltage of the storage battery unit is related to each SOC, as shown by the above formula (17).

FIG. 7 is a graph showing an example of the relationship between _VOC and SOC in the case of a lithium ion battery.

  With the power distribution method as described above, the most malfunctioning battery is prevented from being deteriorated, and the other storage batteries are operated to further deteriorate. As a result, the deterioration of the plurality of battery units can be promoted uniformly.

  11-1 to 11-N: battery unit, 12-1 to 12-N: inverter, 13-1 to 13-N: inverter control unit, 100: power storage system, 120: harmonic filter, 120m, 120n, 120o, 120p, 120q, 120r: Semiconductor switch, 200: Power regulator, 201: Command selection unit, 202: Power calculation unit, 202-a: Central SOC calculation unit, 202-b: Compensation power optimization unit, 300: Power system 400-1 to 400-N: sensor unit, 401: current sensor, 402: voltage sensor, 403: SOC calculator, 404: SOH calculator, 500: power generator, 600: total power system monitoring unit.

Claims (12)

A plurality of battery units connected in parallel to a common power system, and a power regulator,
An inverter and a sensor unit are connected to the battery unit,
An inverter control unit is connected to the inverter,
The inverter is disposed between the battery unit and the power system,
The sensor unit has a function of detecting a state of the battery unit and sending a signal related to the detected state to the power regulator;
The power regulator controls charging / discharging of each battery unit so as to reduce a difference in deterioration state between the battery units.   The power storage system according to claim 1, wherein the sensor unit includes a current sensor, a voltage sensor, a charge state calculation unit, and a deterioration state calculation unit.   The power storage system according to claim 2, wherein the power regulator includes a command selection unit that determines a battery unit having the worst deterioration state among the plurality of battery units, and a power calculation unit.   The power calculation unit is configured to determine each battery based on a prediction of power demand, the charge state and the deterioration state sent from the sensor unit, and the center charge state of the battery unit having the worst deterioration state. The power storage system according to claim 3, wherein the power output of the unit is determined. A plurality of battery units connected in parallel to a common power system;
An inverter and a sensor unit connected to the battery unit;
An apparatus for controlling charging / discharging of the battery unit in a power storage system including an inverter control unit connected to the inverter,
The inverter is disposed between the battery unit and the power system,
The sensor unit has a function of detecting the state of the battery unit and transmitting a signal related to the detected state.
A power regulator that generates a signal to be sent to the inverter control unit so as to reduce a difference in deterioration state between the battery units.   6. The power regulator according to claim 5, wherein the sensor unit includes a current sensor, a voltage sensor, a charge state calculation unit, and a deterioration state calculation unit.   The power regulator according to claim 6, comprising: a command selection unit that determines a battery unit having the worst deterioration state among the plurality of battery units; and a power calculation unit.   The power calculation unit is configured to determine each battery based on a prediction of power demand, the charge state and the deterioration state sent from the sensor unit, and the center charge state of the battery unit having the worst deterioration state. 8. The power regulator according to claim 7, wherein the power output of the unit is determined. A plurality of battery units connected in parallel to a common power system, a power regulator,
An inverter and a sensor unit connected to the battery unit;
An inverter control unit connected to the inverter, and a method for controlling charging / discharging of the battery unit in a power storage system comprising:
An inverter and a sensor unit are connected to the battery unit,
An inverter control unit is connected to the inverter,
The inverter is disposed between the battery unit and the power system,
In the sensor unit, the state of the battery unit is detected, and a signal relating to the detected state is sent to the power regulator,
A method for controlling a storage system, wherein the power regulator controls charging / discharging of each battery unit so as to reduce a difference in deterioration state between the battery units.   The method for controlling a power storage system according to claim 9, wherein the sensor unit detects a current and a voltage, and calculates a charged state and a deteriorated state.   The power storage device according to claim 10, wherein the power regulator determines a battery unit having the worst deterioration state among the plurality of battery units, and calculates electric power when charging / discharging the battery unit. How to control the system.   Based on the prediction of power demand, the charging state and the deterioration state sent from the sensor unit, and the central charging state of the battery unit having the worst deterioration state, the power output of each battery unit is determined. The method of controlling an electricity storage system according to claim 11.

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